ICES WKARGH2 REPORT 2016 Reports/Expert... · The Workshop for Age Reading of Greenland halibut...

ICES WKARGH2 REPORT 2016 SCICOM/ACOM STEERING GROUP ON INTEGRATED ECOSYSTEM OBSERVATION AND MONITORING

ICES CM 2016/SSGIEOM:16

REF. ACOM AND SCICOM

Report of the Workshop on age reading of Greenland halibut 2 (WKARGH2)

22-26 August 2016

Reykjavik, Iceland

International Council for the Exploration of the Sea Conseil International pour l’Exploration de la Mer

H. C. Andersens Boulevard 44–46 DK-1553 Copenhagen V Denmark Telephone (+45) 33 38 67 00 Telefax (+45) 33 93 42 15 www.ices.dk [email protected]

Recommended format for purposes of citation:

ICES. 2017. Report of the Workshop on age reading of Greenland halibut 2 (WKARGH2), 22-26 August 2016, Reykjavik, Iceland. ICES CM 2016/SSGIEOM:16. 40 pp.

For permission to reproduce material from this publication, please apply to the Gen-eral Secretary.

The document is a report of an Expert Group under the auspices of the International Council for the Exploration of the Sea and does not necessarily represent the views of the Council.

© 2017 International Council for the Exploration of the Sea

ICES WKARGH2 REPORT 2016 | i

Contents

Executive summary ................................................................................................................ 1

1 Opening of the meeting ................................................................................................ 2

2 Adoption of the agenda ................................................................................................ 3

3 Abstracts of presentations ............................................................................................ 4

3.1 Ole Thomas Albert – Review of Conclusions from 2011 WKARGH ............. 4 3.2 Rick Wastle – Taking some of the confusion out of the left otolith

thin-section method to estimate age for Greenland halibut ........................... 4 3.3 Margaret Treble – Greenland halibut age validation research at DFO

Central and Arctic Region ................................................................................... 5 3.4 Karen Dwyer – Greenland halibut: will we ever be able to age these

fish? ......................................................................................................................... 7

3.5 Ole Thomas Albert – The long and winding road to a new age reading method for Greenland halibut at IMR ................................................. 8

3.6 Ole Thomas Albert – Growth and annual zones in long-term ramblers ................................................................................................................. 8

3.7 Groa Petursdottir – Otolith exchange ................................................................ 9

3.8 Elvar Hallfredsson – Using fisheries/survey data and length-based GADGET model to assess the unassessable ...................................................... 9

3.9 Gudmundur Thordarson and Bjarki Thor Elvarsson – NWWG Greenland halibut - We need ageing ASAP for stock assessment ............... 11

3.10 Karen Dwyer – Comparison of growth rates .................................................. 12

3.11 Elvar Hallfredsson – Northeast Arctic (NEA) Greenland halibut growth .................................................................................................................. 12

3.12 Steve Campana – Using photoshop to enhance images ................................ 17

3.13 Karen Dwyer – Left vs. right sectioned otolith comparison ......................... 17

3.14 Steven E. Campana – Keynote – Use of data from problematic fish species .................................................................................................................. 18

3.15 Rasmus Nygaard – Tagging and OTC-marked Greenland halibut in Greenland ............................................................................................................ 18

4 Terms of Reference ...................................................................................................... 19

4.1 a) Review published and un-published (new) information on age estimations, otolith exchanges, workshops and validation .......................... 19 4.1.1 Information on age estimations ........................................................... 19 4.1.2 Otolith image exchange ........................................................................ 19 4.1.3 Workshops .............................................................................................. 22 4.1.4 Age validation ........................................................................................ 22

ii | ICES WKARGH2 REPORT 2016

4.2 b) Evaluate information on individual growth patterns in order to achieve a general consensus about the most probable levels of longevity and growth rates for the different stocks. ...................................... 23

4.3 c) Report on ageing protocols currently in use and their consistency with validation results. ...................................................................................... 24

4.4 d) Join international experts on growth, age estimation and assessment in order to progress toward a recommended procedure for future age determination of Greenland halibut. ...................................... 26

4.5 Based on results, conclusions and recommendations from this workshop design and initiate an international exchange of otoliths for age determination after the workshop....................................................... 26

4.6 e) Address the generic ToRs adopted for workshops on age calibration (see 'WGBIOP Guidelines for Workshops on Age Calibration') ......................................................................................................... 26

5 Conclusions .................................................................................................................. 27

6 Recommendations ....................................................................................................... 28

7 References ..................................................................................................................... 29

Annex 1: List of participants............................................................................................... 30

Annex 2: Agenda ................................................................................................................... 32

Annex 3: Recommendations ............................................................................................... 33

Annex 4: WKARGH2 ToRs ................................................................................................. 34

Annex 5: Photoshop Instructions for Image Enhancement .......................................... 36

ICES WKARGH2 REPORT 2016 | 1

Executive summary

The Workshop on Age Reading of Greenland halibut 2 (WKARGH2) met in Reykjavik, Iceland on 22–26 August 2016. This meeting was co-chaired by Karen Dwyer (Canada) and Groa Petursdottir (Iceland) and included 15 participants from four countries (Can-ada, Iceland, Greenland, and Norway). This meeting was convened to attempt to reach consensus on a method of age determination for Greenland halibut based on age vali-dation research, to complete an exchange between age readers based on two promising methods and to determine whether ages from one or both methods could be used for stock assessment. The two age estimation methods for Greenland halibut that were identified in the last WKARGH (2011), the frozen whole right otolith (viewed with transmitted light) and thin-sectioned left otolith (viewed with reflected light), were ex-amined for accuracy and precision. New information was presented at the meeting which confirmed the full or partial validation of both methods. Growth rates based on both methods were similar, although there was some data that indicated there may be regional differences. A comparison of methods using the WebGR for image exchange occurred prior to the meeting indicated some bias between these methods, and low precision, but generally these differences were felt to be acceptable. It was recom-mended that either method can be used to provide age estimates for assessments with the caveat that either an ageing error matrix (AEM) or a growth curve should be used to account for the uncertainty in the age estimation.

2 | ICES WKARGH2 REPORT 2016

1 Opening of the meeting

The Workshop for Age Reading of Greenland halibut (WKARGH) in 2011 concluded that there were two promising methods for estimating age of Greenland halibut; fresh frozen whole right otolith (viewed with transmitted light), and thin-sectioned left oto-lith (viewed with reflected light). Several publications provided age validation for each method (Albert et al., 2009; Treble et al., 2008) and information on precision (Gregg et al., 2006). However, both methods are challenging to apply and prone to misinterpre-tation. This meeting was held to review information published since 2011 (Dwyer et al., 2016; Albert, 2016), as well as unpublished information, that could help determine whether one or both methods can provide accurate enough age estimates for assess-ment purposes.


2 Adoption of the agenda

The agenda was presented and adopted in plenary (Annex 2). The work plan was agreed to by participants. Age validation studies and new work were presented first, followed by the results of the otolith image exchange. The assessment model GADGET used in assessments for the Northeast Arctic and West Nordic stocks were described. Growth studies were examined, and a comparison of age estimates from left and right thin-sections was presented. Finally, Steve Campana presented a keynote address on “Use of age data from problematic fish species” and a Photoshop primer on how to enhance images.


3 Abstracts of presentations

3.1 Ole Thomas Albert – Review of Conclusions from 2011 WKARGH

The meeting began with a presentation from Ole Thomas Albert reviewing the conclu-sions and recommendations of the 2011 workshop (WKARGH). A brief history of the problems with age estimation for Greenland halibut was documented, going back to the 1990s, with disagreement in ages between readers, labs, and countries. The WKARGH in 2011 focused on validation work, and the accuracy of ageing methods. It concluded that age validation work that had been done to date supported age esti-mates from the ‘new methods’ (ones that provided higher longevity and slower growth from ages than the traditional whole left otolith method), with the caveat that precision was still poor, more work should be done, and there might still be differences in age and growth between stocks and regions. Continued work on age validation as well as suggestions on how to deal with the ageing problem in the short term were recom-mended (ICES 2011).

3.2 Rick Wastle – Taking some of the confusion out of the left otolith thin-section method to estimate age for Greenland halibut

Refined otolith thin-sectioning techniques developed by Fisheries and Oceans Canada Fish Ageing Lab (DFO C&A) in Winnipeg were assessed for suitability when applied to Greenland halibut otoliths. Focus was placed on how the section plane was chosen for the left otoliths and a new technique for handling sections while making an age estimate (“reading” the section) (Figure 3.2.1). For this set of trials the centro-proximal protuberance (“dome”) on the left otolith was treated as if it was the entire otolith and the remaining material around it was ignored. That decision made Greenland halibut otoliths comparable to many of the other otoliths routinely handled in this lab - small otoliths from slow growing, long lived species. It has been shown that such otoliths require greater precision in selecting the section plane, and hitting that section plane while cutting. Therefore, the goal was to make one “good” thin-section per otolith, and that section would have one “good” side for an age estimate (the side closest to the nucleus). The “dome” (proximal side) has a short ridge at its peak, posterior to the sulcus, which presents two nearly parallel edges which can be used as a guide to go perpendicular to when choosing the section plane. The profile of the “dome” in ventral edge view is quite variable, ranging from narrow, high and bluntly pointed to rela-tively wide, low and flattened. Consequently, sectioning the “dome” at its thickest point (theoretically the ideal place) leads to significant variability of where the section is made with respect to the nucleus and that affects the quality of the sections pro-duced. By observing the gap between the peak of the “dome” (proximal) and the nu-cleus (distal) prior to sectioning, steps can be taken to “fine tune” where to section relative to the nucleus. Sections made were viewed in water, with reflected light and a black background.

Information was presented on the identification of the first annulus on these sections as well as interpretation of the otolith edge (last annulus). It was found that this atten-tion to detail when choosing the section plane did improve the quality (“readability”) of the otolith sections prepared. However, problem sections still occurred where the outer annuli were fairly easy to read but the inner annuli were blurry, weak, and diffi-cult to interpret. A technique developed for handling otolith sections while reading them for other species in the DFO C&A lab was successfully tested to help resolve these problem samples. Under the microscope, the proximal edge of the otolith section was


tipped up which helped focus the problem inner annuli, and then laid back down to finish the count of the outer annuli.

Information was also presented on the need for quality control procedures and a reader confidence index that is used in the DFO C&A lab for Greenland halibut age estimates.

Figure 3.2.1. Annotated image of a thin-sectioned left otolith “dome” (reflected light) from a 92 cm female Greenland halibut. Red ovals indicate presumed annuli (hyaline rings). Age estimated at 27+ years.

3.3 Margaret Treble – Greenland halibut age validation research at DFO Central and Arctic Region

Several mark and recapture age validation methods have been used over the last 20 years to assess longevity and age determination methods for Greenland halibut. The first was the injection of oxytetracycline (OTC) into longline caught fish in Cumberland Sound during 1998 to 2000 (Treble et al., 2008). Three recaptured fish ranged in size from 55 to 64 cm at time of marking and were recaptured at 1 year 11 months, 2 years 11 months, and 3 years 10 months postmarking. Among the left otoliths, the OTC mark was only visible on the surface of the one from the fish with the longest time post-marking. However, the expected 3 annuli could not be identified in the traditional age reading zone. Under increased magnification the mark could be observed on the ante-rior margin of the right whole otolith for 2 of the 3 samples. The mark was visible on the left otolith cross section for all three fish. There was inconsistency in the interpre-tation of annuli beyond the mark for both the surface of right otoliths and cross section of the left otoliths, depending on the reading axis chosen. This inconsistency could be due to uneven deposition of otolith material on particularly slow-growing otoliths.

During 2007 and 2009 a strontium chloride solution (SrCl) was used to mark Greenland halibut caught using a trawl modified with an aluminium box at the codend to protect the fish during capture and improve postmarking survival (Loewen et al. (in prep)). We examined otoliths from 7 recaptured fish using an electron microprobe to image backscatter electrons from the otolith surface to determine the location of the mark and assess the growth pattern observed beyond the mark. Fish were of medium size at time of marking (40–52 cm) and growth varied from about 1 to 3 cm/year, slower than ex-pected for this size of fish. Expected annuli were identified beyond the mark on whole right and left otoliths but interpretation differed by 1 or 2 years when compared to


whole otolith age estimates made prior to the embedding and polishing done to pre-pare for SrCl analysis. Expected annuli were consistently identified beyond the mark on left otolith cross sections when reading in the thick centro-proximal region (i.e. “dome”) (Figure 3.3.1). The increase in sample size of SrCl marked otoliths since WKARGH (ICES 2011) has helped to interpret growth and presumed annuli prior to the mark in the “dome” region but there are still challenges with clarity in some sec-tions and the occurrence of doubling of annuli patterns (“double lines”).

Carbon 14 (14C) deposited into ocean environments during nuclear bomb testing in the 1960s was taken up by fish and incorporated into their otoliths. This phenomenon leads to the development of techniques to assess 14C levels in otolith cores and the develop-ment of 14C chronologies, that allowed for the determination of fish longevity and age method validation (Kalish, 1993, Campana, 2001). Treble et al. (2008) examined bomb 14C in Greenland halibut caught in Davis Strait and the northern Labrador Sea (NAFO Divisions 0B, 2G, and 1C). A reference curve specific to Greenland halibut was devel-oped and otolith samples from adult fish (70–80 cm) were examined to validate age. Longevity for these samples was confirmed to range from 20 to 27 years. However, the left otolith section ages underestimated the 14C validated age by 1–15 years (average 6 years). The failure of the cross section method while unusual was not unprecedented and indicated that more work was necessary to improve this method before it could be accepted for use in Greenland halibut age determination.

During 2016, the thin-sectioned left otolith method was refined (see above summary by Rick Wastle). The 14C validated ages from our earlier research compare well with the growth curve resulting from 60 otoliths aged using this refined method (Figure 3.3.2). This observation combined with improved quality of the left cross sections has increased our confidence in the potential of this method for use in determining ages for Greenland halibut.

Figure 3.3.1. Annotated image of a transverse sectioned left otolith “dome” (reflected light) from a 40 cm male Greenland halibut (when tagged) that was injected with SrCl and recaptured 3.8 years later at 44 cm (red bar represents growth after the mark). Yellow ovals indicate presumed annuli formed during time at liberty. Extrapolating inwards, orange ovals indicate presumed earlier an-nuli. Age estimated at 11+ years.


Figure 3.3.2. Growth for bomb radiocarbon (14C) validated ages (Treble et al., 2008, dark squares) and ages estimated in the DFO C&A 2016 thin-sectioned left otolith trials for fish collected in Sub-area 0 (light circles).

3.4 Karen Dwyer – Greenland halibut: will we ever be able to age these fish?

Greenland halibut is a wide-ranging Pleuronectid species that supports several inter-national fisheries. Until recently, in the Northwest Atlantic, there had been only length frequency modes from DFO research vessel surveys used to corroborate ages in very young fish (up to age 4). Work published by Dwyer et al. (2016) was presented and included a comparison of age estimates between the traditional method of reading whole left otoliths and thin-sectioned left otoliths (using a mass production high-speed saw), which indicated a departure in the 1:1 line on an age bias plot at age 10. Thus, after age 9, bias is present between readings, with ages estimated from whole left oto-liths underestimating 40%, on average, the true age of Greenland halibut (however, the difference could be up to 18 years). For three fish, even thin-sections underestimated age. Thin-section ages indicate longevity of about 35 years and that Greenland halibut are slower growing and longer lived than ages indicated from the traditional whole otolith method. More recently, twenty samples were added to the bomb radiocarbon analysis to determine whether whole otoliths gave an accurate age for smaller fish. In general, most fish <70 cm were aged correctly using the whole otolith method although in one case, a fish that was 59 cm had the potential to be under-aged, even with the thin-sectioned otolith. A tagging experiment carried out in May 2013 used chemical injection (oxytetracycline) to mark otoliths for age validation. Two tagged and marked fish were returned. One fish that was tagged at 47 cm and at liberty for 1.8 years had an average growth rate during that time of 3.4 cm/year. The second fish tagged at 37 cm and at liberty 3.1 years had an average growth rate of 3.2 cm/year. Otoliths from both fish showed the correct number of annuli which corresponded to time at liberty in both whole and thin-sectioned otoliths. Overall it appears that whole otoliths are generally accurate for fish up to age 9, and beyond that thin-sections provide more accurate ages for the Northwest Atlantic stock of Greenland halibut.


3.5 Ole Thomas Albert – The long and winding road to a new age reading method for Greenland halibut at IMR

At the Institute of Marine Research (IMR), Norway, the process of establishing an im-proved age reading method for Greenland halibut started in 2004 after several years with repeated statements from the ICES Arctic Fisheries Working Group (AFWG) that there were some problems with the age data at that time. A new protocol for ageing of whole otoliths was made to ensure a high quality of samples and standardization of the interpretations. The protocol relies on fresh frozen whole right otoliths, imaging software, use of length measurements to define the first few zones, and use of the long-est growth axis of the right otoliths for older individuals. Age readers should be aware of frequent false zones during early years and of densely spaced annual zones in the outer “finger” regions of older otoliths.

To validate the new protocol, three OTC tagging surveys were conducted in the nursery areas north of Svalbard in September for the years 2006 to 2008. Nearly 25 000 juvenile Greenland halibut were tagged and a validation paper was published (Albert, 2016) based on 28 recaptured individuals that had been at large for 1–6 years and for which otoliths were provided in good condition. The results show that the established IMR protocol is likely accurate up to at least 50 cm and that mean annual growth is less than 2 cm for fish above 40 cm.

3.6 Ole Thomas Albert – Growth and annual zones in long-term ramblers

Provisional analyses from recent recaptures of fish that had been at large for up to 12 years were presented. The established pattern of length-at-age based on the IMR age-ing protocol is generally consistent with growth of tagged fish during time at large for fish up to 70 cm. New OTC recaptures of fish that have been at large for up to 10 years, show more or less the corresponding numbers of zones outside the fluorescent band (Figure 3.6.1). However, bias in age estimates for fish larger than 50 cm remains to be estimated. New recaptures of increasingly larger fish are still being made and formal validation of age at greater lengths should become feasible in coming years. The length-at-age pattern from these tagging studies in the NE Atlantic is below the corre-sponding pattern from the NW-Atlantic based on bomb radiocarbon validations (Dwyer et al., 2016). Since recent evidence show genetic structure of Greenland halibut between western and eastern sides of the North Atlantic (Westgård et al., 2016), this may be related to differential growth between populations.


Figure 3.6.1. Annotated image of a frozen whole right otolith (transmitted light) from a 43 cm male fish (when tagged) that was injected with OTC (yellow line marks the position of the fluorescent band under UV-light) and recaptured 7.7 years later at 49 cm. Yellow circles correspond to number of annuli (and number of years at liberty).

3.7 Groa Petursdottir – Otolith exchange

See Section 4.12 below

3.8 Elvar Hallfredsson – Using fisheries/survey data and length-based GADGET model to assess the unassessable

In an ICES benchmark process for Northeast Arctic (NEA) Greenland halibut that ended in spring 2015 (ICES 2015), a purely length based Globally Applicable Area Dis-aggregated General Ecosystem Toolbox (GADGET) model was approved to assess this stock. However, it was noted that the model would be considerably improved if accu-rate age data were available. Fisheries are divided into trawl and artisanal fleets, and four survey indices go into the assessment. The fisheries are mainly carried out by Rus-


sian and Norwegian fleets. Trawl, longline, and gillnets are the most usual gears ap-plied, and most lengths above the minimal legal size of 45 cm are targeted. None of the surveys cover the whole distribution of the stock, but together they cover the main areas of the stock distribution as defined by ICES. However, mark recapture and ge-netic analysis suggest that the population might extend further south and west than anticipated (Albert and Vollen, 2015; Westgård et al., 2016), and further research is needed to examine stock boundaries. Production models are not considered as a feasi-ble option for this stock for both biological (late entry to fisheries, significant sexual dimorphism and sporadic recruitment) and practical (lack of good catch-per-unit-ef-fort (cpue) series, especially after the 1992 partial moratorium) reasons. None of the available survey indices are singularly considered to reflect dynamics for the whole stock, and thus trend based assessment is not a good option. Aside from that, trend based assessment should be looked at as a last resort for a stock where managers wish to optimize exploitation. Clear modes in length distributions are observed, indicating recruitment pulses going through the stock (Figure 3.8.1). These signals allow the GADGET model to estimate growth for both sexes. Although there are assumptions in the assessment that can affect the growth estimate, it can be looked at as a growth es-timate that is independent of age readings.

Advice is now from an approved analytic assessment. Still, we have a first version of a model for a difficult stock and further work is needed on several issues, age reading being one of high importance. Length based assessment comes with a cost and lack of age information is one of the main data shortcomings for the stock. The developers of the assessment consider that the model would give a substantially better fit if accurate age information was included, leading to a considerable improvement in the assess-ment.


Figure 3.8.1. Length distributions for NEA Greenland halibut in the Norwegian Autumn Survey at the spawning areas along the slope from Lofoten islands to northwest of Svalbard. In the upper right corner of each panel survey abundance indices are shown in millions (Hallfredsson and Vol-len, 2015). Blue lines (fitted visually) suggest pulses of recruitment going through the years and may be indicative for growth.

3.9 Gudmundur Thordarson and Bjarki Thor Elvarsson – NWWG Greenland halibut - We need ageing ASAP for stock assessment

The ICES Northwest Working Group (NWWG) Greenland halibut stock is shared be-tween Greenland, Iceland and the Faroe Islands but the stock structure is uncertain as there is strong evidence of mixing with the Barents Sea stock. The advice for the NWWG Greenland halibut has been based on a stock production model in a Bayesian framework.

The model has been debated and has several shortcomings. In recent years a GADGET model has been run alongside the Surplus Production (SP) model but in its current state it is not usable for basing advice on. One of the advantages of the GADGET frame-work is that various types of data can be used and it does not need a continuous time-series. The main data gap in the GADGET model is the lack of age structured data. With the inclusion of ageing data better estimates of growth, recruitment and mortality will be obtained and the stability of the model will increase. Therefore, it is of para-mount importance that routine ageing of NWWG Greenland halibut be started as soon as possible.


3.10 Karen Dwyer – Comparison of growth rates

Length-at-age estimates from the thin-section otolith ageing method for Greenland hal-ibut in the Northwest Atlantic indicated a slowing of growth and plateau after age 10 for both males and females. Von Bertalanffy growth parameters indicated the follow-ing: for females, L∞=106 cm, K=0.09 and t0=-0.05 and for males, L∞=90 cm, K=0.09 and t0=-0.5. This suggests males grow at the same rate as females but do not reach the same size. These results differ substantially from von Bertalanffy estimates using the tradi-tional whole otolith age determination method where growth was linear with high es-timates of L∞ (Bowering and Nedreaas, 2001). A comparison of these parameters with stocks from other areas found that for the Alaskan and Arctic stocks, growth is both slower with a lower maximum length reached (Dwyer et al. 2016). Tagging estimates and bomb radiocarbon work from Treble et al. (2008) for the Arctic stock indicate that growth is about 1–2 cm/year for adult fish. Dwyer et al. (2016) concluded the growth rate for 50–70 cm fish was about 2.4 cm/year, and for >70 cm fish was 1.4 cm/year. Both studies concluded that growth was far slower than the 5 cm/year estimated from the traditional whole otolith method previously reported in Lear and Pitt (1975) and Bow-ering and Nedreaas (2001). Recently examined oxytetracycline (OTC) marked otoliths from two fish tagged and recaptured in the Northwest Atlantic had age estimates that indicate growth rates are faster (about 3.3 cm/year) for fish between 37 and 51 cm.

3.11 Elvar Hallfredsson – Northeast Arctic (NEA) Greenland halibut growth

Approximately 4500 Greenland halibut have been aged in Norway so far using the frozen whole right otolith method. These have been collected from two surveys; the Norwegian Slope Survey in autumn 2001 (otoliths were not frozen for this year), 2007, 2009, 2011, and 2013, and part of the Joint Norwegian Russian Ecosystem survey that covers the Greenland halibut juvenile area for years 2006, 2008, and 2011 (Figures 3.11.1 and 3.11.2). Growth curves derived from these age readings give realistic growth tra-jectories that align with age validations that are discussed in other chapters of this re-port, as well as growth curves for the stock as fitted by the length based GADGET assessment model (Figure 3.11.3, Table 3.11.1). In comparison the latter shows slightly slower growth for older ages, but the GADGET growth curves go through the origin (t0=0), and this will affect the shape of the curve for the older ages.


Figure 3.11.1. Length by age and sex for Greenland halibut as aged by the frozen whole right otolith method. The three uppermost panels are from the part of the Joint Norwegian Russian Ecosystem survey that covers the juvenile area in 2006, 2008, and 2011, while the lower panels are from the Norwegian Slope survey in autumn 2001 (note: dry otoliths), 2007, 2009, 2011, and 2013.

Figure 3.11.2. Length by age and sex for all Greenland halibut aged by the frozen whole right otolith method to present, collected at the juvenile areas (Ecosystem survey).


Figure 3.11.3. Growth curves for NEA Greenland halibut based on aging from surveys by the frozen whole right otolith method. Grey symbols are individual specimens. Also shown are growth curves for the stock as fitted by the length-based GADGET assessment model.

Table 3.11.1. Von Bertalanffy coefficients for growth of Greenland halibut aged using frozen whole right otoliths using all of the ages collected in Norway so far, fitted by the nls function in R, and compared to coefficients for growth as estimated from the length-based GADGET assessment for the NEA Greenland halibut stock.

Frozen whole right otolith

ageing method GADGET estimates

von Bertalanffy parameters

Male Female Male Female

Linf (cm) 71.2 106.6 56.1 72.1

K 0.10 0.05 0.14 0.10

t0 -1.9 -3.1 0 0

It can be expected that standard deviation in length by age increases with increasing age. Judged by simple plots (Figure 3.11.4) this seems to be true only for females when aged using the frozen whole right otolith method. This needs to be examined further.


Figure 3.11.4. Standard deviation for length by age in all Norwegian age readings derived up to 2015 using the frozen whole right otolith method.

Northeast Arctic (NEA) Greenland halibut collected in the juvenile/nursery areas show rather clear length modes that can be interpreted as age groups (Albert, 2003), and modes representing age up to around 4 years are apparent. Length distributions from the area were analysed with the R package MixDist (http://ms.mcmaster.ca/peter/mix/ mix.html) to fit gamma distributions to modes. This provided an age–length estimate for the youngest age groups that is independent of age readings (Figure 3.11.5).

http://ms.mcmaster.ca/peter/mix/%20mix.html

http://ms.mcmaster.ca/peter/mix/%20mix.html


Figure 3.11.5. Length distribution by year of juvenile NEA Greenland halibut from autumn surveys in the nursery areas (August-September) and gamma distributions fitted to modes (MixDist pacage in R) (from Hallfredsson and Vollen, 2015).

A preliminary analysis revealed that compared to the length mode analysis the aging by frozen whole right otolith method might slightly underestimate growth rate for the youngest fish (Figure 3.11.6). The GADGET model gave similar growth rates as the length mode analysis but estimates of length-at-age are lower for the young fish.


Figure 3.11.6. Three depictions of length (cm) at age: 1) Mu of length for gamma distributions by age for each year (coloured circles) and average of years (blue line) in mixed models analysis for NEA Greenland halibut from the juvenile surveys; 2) Average age using the frozen whole right otolith method (black diamond) with two times SE error bars (note: only one specimen at age 1) and von Bertalanffy growth curves (grey-black dashed line) based on all Norwegian ages up to 2015 (using frozen whole right otolith method); and 3) length-at-age as estimated by the GADGET model (yellow dashed lines) (see ICES IBPHALI 2015 benchmark report).

3.12 Steve Campana – Using photoshop to enhance images

A hands-on demonstration was carried out in order to show participants the value of using Adobe PhotoshopTM for enhancing images of otoliths, as described in Campana et al. (2016). Several images were taken and enhanced using a series of steps that im-prove the quality of an image and allows for annotation of the image. This can be used for training or quality control between labs. Images should be high resolution TIF for-mat (Annex 5).

3.13 Karen Dwyer – Left vs. right sectioned otolith comparison

One of the reasons the frozen whole right otolith method was chosen as a possible age determination method for Greenland halibut was because it has a longer growth axis compared to the whole left otolith (as indicated from OTC-marked otoliths). In cross section the left otolith differs from the right in that the left grows in two dimensions (i.e. in thickness as well as in diameter). The thin-sectioned left otolith was chosen as another possible method because the left otolith grows thicker in the centro-proximal region and this reading axis tends to have fewer checks and is easier to interpret than the thinner/flatter cross section of the right otolith.

Left and right otoliths from fifty (50) Greenland halibut from the Northwest Atlantic Fisheries Organization Divisions 3KL were collected to compare age determination methods. Forty of the otolith pairs were from multispecies surveys from fall 2014 and 10 were taken from the 2015 commercial fishery. Fish ranged in size from 10–92 cm. The whole left otolith was aged (in order to get traditional age estimates for compari-son) and then both the left and right otoliths were sectioned and aged to compare age


estimates from each. The traditional method of reading the whole left otolith was com-parable to thin-sectioned left otoliths up to age 9 after which bias increased with age. Ages derived from thin-sectioned right otoliths were generally younger than ages de-rived from the thin-sectioned left otoliths, but mainly at the oldest ages and bias in-creased with age. It appears that the right otolith sulcus is flattened comparatively, and annuli are difficult to see in this area.

3.14 Steven E. Campana – Keynote – Use of data from problematic fish spe-cies

Age data collected in support of a stock assessment is generally presented in the form of an age–length key, which is then scaled by the length frequency to prepare the catch-at-age matrix. However, species with considerable ageing uncertainty can produce sig-nificant bias in the assessment estimates of biomass and fishing mortality. The ageing precision of Greenland halibut (CV=13.5%) (see section 4.1.2 below) is poor compared to many other species (~5%). An ageing error matrix (AEM) is easily calculated from replicate age readings, and would allow most of the effects of ageing uncertainty to be removed from the stock assessment population model. AEMs are recommended for all age-structured assessments, but are particularly valuable with stocks showing high age uncertainty. Length-based assessments which are based on an accurate underlying growth model (with associated variance) are often used with species which are difficult to age annually; such growth/variance models are often preferred, since the same growth/variance model can be used every year until re-assessment of growth rate in-dicates an update to the growth model is required.

3.15 Rasmus Nygaard – Tagging and OTC-marked Greenland halibut in Greenland

Tagging experiments have shown that Greenland halibut in the fjords in West Green-land are highly stationary with seemingly little or rare migrations out of the fjords be-ing observed. The fjords are known for high concentrations of Greenland halibut and support a large fishery conducted from small boats, small vessels, and dog sledges during winter. Within the fjords, Greenland halibut are exclusively targeted using longlines and gillnets. This extensive but highly manual fishery means that tagged fish are likely to be found by fishers and hopefully returned frozen and whole. Therefore, the Fjords in Western Greenland and particularly the Nuuk area may act as a more suitable location for growth experiments than other areas of the North Atlantic. Tag-ging experiments with OTC injection of T-tagged Greenland halibut were undertaken by the GINR in the Upernavik area in 2014 and the Nuuk area in 2015. In total 407 Greenland halibut have been tagged and injected with OTC, in hopes some ageing will be done on these marked otoliths to produce a validated growth curve for these stocks. However, so far none of the tags returned have included whole frozen fish or otoliths. In an attempt to improve the data quality prior to release, the collected data has in-cluded total length (TL), fork length (FL), live weight and other notes besides the tag-ging number. In these experiments, FL (recorded in mm) should provide a more accurate measure of length/growth than TL (recorded in cm) due to the lower meas-urement uncertainty and the tail shape of Greenland halibut. Likewise, the different measures act as control of the length measurements and should decrease the error rate in the recorded length prior to release. No OTC tagging has occurred in 2016, but the experiments are expected to continue in future.


4 Terms of Reference

4.1 a) Review published and un-published (new) information on age esti-mations, otolith exchanges, workshops and validation

4.1.1 Information on age estimations

Two age estimation methods currently in use were reviewed:

1 ) Thin cross sections of left otoliths taken through the nucleus along the trans-verse axis and viewed with reflected light as used by DFO C&A and, for older fish, the Northwest Atlantic Fisheries Centre (DFO NWAFC). Age reading may be done in the thicker centro-proximal “dome” portion of the section near the sulcus and followed onto the “wings” if possible. See Treble et al. (2008) for description of the low-speed saw cutting method for individ-ual otoliths or Treble and Dwyer (2008) for description of high-speed mass production sectioning method.

2 ) Frozen whole right otolith method viewed with transmitted light using dig-ital images, as applied by the Institute of Marine Research (IMR), Norway and The Marine and Freshwater Research Institute (IMFR), Iceland. For de-tails on method refer to Albert et al. (2009).

Evidence was presented that indicated improvements could be made to the left otolith thin-section technique (see section 3.2 above). This involves using physical features of the “dome” to choose the section plane, as well as examining the ventral edge view profile of the “dome” to decide where to cut with respect to the nucleus. Also, a new viewing technique for thin-sections was presented to help reduce the confusion asso-ciated with the early (inner) annuli. These modifications to the method will hopefully improve the precision of the age readings.

4.1.2 Otolith image exchange

WebGR (an ICES online image exchange tool for calibration of age readers and meth-ods) was used prior to the WKARGH2 to compare the frozen whole right otolith and the thin-sectioned left otolith methods among designated labs.

Two hundred and fifty (250) otolith pairs were collected by Norway during their 2013 fall survey. Of these, one hundred pairs ranging in size from 35–80 cm were selected for this exchange. The whole right otolith from each pair was frozen, while the left otolith was embedded in epoxy resin and sectioned using a high speed mass-sectioning saw. Images were taken of each otolith preparation and entered into WebGR where participants could access and interpret them.

Participants (11 participants from 3 countries and 4 institutes) had varying levels of experience with each of the two methods. Usually a participant had some experience in one method or the other, but none had experience estimating age of Greenland hal-ibut using both methods (although 8 participants provided readings for both methods). Participants also indicated that precision might have been improved if they had been able to work with actual sections or/and better images.

Results showed low precision for both methods and some bias between methods:

1 ) Frozen whole right otolith method - When all age readers that read this method were compared, the precision, as measured by the coefficient of var-iation (CV) ranged from 8.9% to 19.4% with an average CV of 15.5%. When


only two age readers (who are more experienced using this method) were compared the CV was 8.9%.

2 ) Thin-sectioned left otolith method - When all age readers that read this method were compared, the CV ranged from 9.7% to 23.9% with an average CV of 17.5%. When only two age readers (who are more experienced using this method) were compared the CV was 11.7%.

3 ) Comparing both methods - When ages from the most experienced age read-ers are compared using their preferred method the CV was 15.3%.

Using data from all readers, the bias between these two methods was generally within 1–2 years until age 15 (however, sample size is very low beyond this age). A clear bias is evident, with whole right otolith ages greater than section left otolith ages for fish less than about 10 years of age, and greater section ages for fish above age 12 (Figure 12). Since this graph calculates the difference within each age-reader, it accounts for individual biases. However, most age-readers are experienced with only the frozen whole right otolith method or the thin-sectioned left otolith method, not both.

When only data from agers experienced in a particular method is compared the bias generally increased with age but remained within 1-2 years up to about age 15 (Figure 4.1.2.1). Ages estimated from the frozen whole right oto-lith method tended to be older at ages <8 and younger at ages >9 compared to the thin-section left otolith method (Figure 4.1.2.2).

Neither of these age bias plots indicates which ageing method is more correct; only age validation can provide that information.


Figure 4.1.2.1. Within-ager bias plot showing the difference between whole right otolith and section left otolith ages for each age, averaged across age-readers.

Figure 4.1.2.2. Age bias plot showing the difference between experienced readers of the frozen whole right otolith and thin-section left otolith methods.


For the frozen whole right otolith method, the Norwegian and Icelandic age labs plan to take images and adjust them in ADOBE Photoshop to estimate ages. It is recom-mended that these countries exchange images between labs with and without interpre-tation to improve precision in ageing Greenland halibut.

WebGR doesn’t allow the use of high resolution images (e.g. TIFF images using >10 bit resolution) and therefore it is suggested that Dropbox or a USB stick be used to ex-change images and that image analysis software such as Photoshop be used for the next exchange of Greenland halibut otolith images.

4.1.3 Workshops

There were no workshops outside this meeting on age estimation of Greenland halibut other than training between Norway and Iceland to learn the frozen whole right otolith method.

4.1.4 Age validation

Two papers published since WKARGH 2011 further validate both methods examined during this workshop (WKARGH2). Albert (2016) examined the frozen whole right otolith method, which documented new OTC-mark recaptured fish, increasing the sample size as well as the size range across which the method is valid. Dwyer et al. (2016) presented validation of the thin-sectioned left otolith method for the Northwest Atlantic stock using bomb radiocarbon analysis.

The meeting also reviewed additional, unpublished results, from OTC-mark recap-tured fish from the Northeast Atlantic that added further support for the frozen whole right otolith method. In addition, two OTC-mark recaptured fish from the Northwest Atlantic and strontium chloride-mark recaptured fish from the Arctic stock supported validation of the sectioned left otolith method. It is important to note that both of these ageing methods have been validated either partially or completely using high quality techniques.

Bomb radiocarbon analysis as a method of age validation confirms the maximum age of the fish (not just recent annuli) and is one of the most robust techniques for fish age validation (Campana, 2001). Chemical mark recapture is also a rigorous method of age validation but it does not validate the entire age range of the fish, as only the annuli that are laid down after the chemical mark are validated. Chemical mark recaptured fish are more valuable the longer they are at liberty. Samples have now been collected from fish at large for up to 10 years in Norwegian studies and tags are still being re-turned. As a result of the use of these robust validation methods, it is generally agreed that the thin-section left otolith method is, on average, accurate, especially for the old-est fish in the population. It is also true that ages estimated from the frozen whole right otolith method are accurate for fish up to at least 50 cm, and using the same method, age estimates were corroborated for fish up to 70 cm (from long-term tag recaptures, see next chapter and Figure 4.2.2).


4.2 b) Evaluate information on individual growth patterns in order to achieve a general consensus about the most probable levels of lon-gevity and growth rates for the different stocks.

Information on Greenland halibut growth rate was examined for each region. For DFO C&A and DFO NWAFC, thin-sectioned left otolith ages were similar to almost linear growth for the first 9 years then growth begins to slow and variation increases (Figure 4.2.1). Bomb radiocarbon validated ages are also included in the length-at-age plot and correspond well with ages derived by both labs using the sectioned left otolith method.

Growth for the NEA stocks using the frozen whole right otolith method was described in Section 3.11 above. Growth curves derived by the purely length based GADGET assessment model for this stock are independent of age readings, and show to be within similar range as growth curves based on available readings by the frozen whole right otolith method. Differences in growth rates were observed when comparing the growth from this region with the Canadian stocks (Figure 4.2.2). Growth rates began to diverge around age 10 (~65 cm). There is evidence of genetic structure in Greenland halibut (Westgård et al., 2016) and this may affect growth between populations. How-ever, further investigations are needed to determine whether the differences are related to stock dynamics or the age determination method.

Figure 4.2.1. Length-at-age for thin-sectioned left otoliths, from DFO C&A (green squares) and NWAFC (purple circles) as well as bomb radiocarbon validated ages for C&A (black triangles (Tre-ble et al., 2008) and NWAFC (blue diamonds (Dwyer et al., 2016).


Figure 4.2.2. Comparison of growth trajectories based on various age and growth estimates from the Northeast Arctic stock: 1) The yellow envelope include data from length mode analyses and tag recaptures from Albert et al. (2009); 2) Coloured circles show new recaptures of fish that were 25–33 cm (white) or 40–44 cm (green) at release; 3) Green arrows show overall growth during time at large for long-time ramblers; 4) Blue and red growth curves represent age readings of the same otoliths using the traditional whole left otolith and the frozen whole right otolith methods respec-tively (from Albert et al., 2009). For comparison, the blue envelope shows the thin-sectioned left otolith method from the Northwest Atlantic (data from Figure 4.2.1 (NAFC Section Ages)).

4.3 c) Report on ageing protocols currently in use and their consistency with validation results.

Modifications have been made to the sectioned left otolith protocol in use at the DFO- C&A lab (see Sections 3.2 and 4.1.1 above). Initial results indicate that these changes improve the clarity of annuli. Age estimates for fish of a given length generated using this revised protocol are comparable to bomb radiocarbon validated ages at similar lengths (for ages 15–35) (Figure 4.2.1) and validated ages for SrCl-marked otoliths (ages 9–13) (see Sections 3.3 and 4.14 above).

The DFO NWAFC section trials (Dwyer et al., 2016) produced age estimates for fish with length range of 9 to 110 cm (ages 0–33 years). From 57–108 cm, these age estimates correspond to the bomb radiocarbon validated ages (9–22 years) (Figure 4.2.1). The whole left otolith (traditional) method for age estimation currently used by the lab pro-duces younger ages beyond nine years (~65 cm) suggesting it is inaccurate for older fish (see Sections 3.4 and 4.1.4).

The frozen whole right otolith methodology used by Norway and Iceland has also been validated for fish up to 50 cm using OTC-marked recaptured fish and corroborated up to 70 cm with ages estimated by expert age readers using the same method. These are


also consistent with validated ages from the bomb radiocarbon analysis carried out on the Canadian stocks (Figure 4.2.2).

One way to verify a method for the youngest ages is to compare the size at age for the first few years to the first few length frequency modal sizes (Figures 3.11.5 and 3.11.6 in Section 3.11 above, as well as Figure 4.3.1 below). Differences in age estimates for young fish (<5 years) were observed when comparing ages derived from length fre-quency modes and from previous estimates in the literature (Dwyer et al., 2016) for the whole left otolith method and the left thin-section method. Previous work by Pitt and Lear (1979) for the Northwest Atlantic and by Bowering and Nedreaas (2011) provided length frequency modal values for the first strong modes in the Northwest Atlantic (both Labrador and Newfoundland) and for the Barents Sea. Estimates of length from the ageing methods were smaller at age than those from the length frequency modes. Growth at these young ages can be influenced by time of year the sample is taken and by regional differences in habitat conditions (Albert, 2003), and length modes can be composed of several age groups (Albert et al., 2009) therefore, while the use of length frequencies to verify an age determination method can be useful, it should be ap-proached with caution. We were unable to compare length at-age from the methods used in the exchange with the data in this figure because of low sample sizes at these ages. However, WKARGH2 recommends back-calculation of the lengths of Greenland halibut at ages 1–3 using both age determination methods (frozen whole right otolith and thin-sectioned left otolith) to see whether they correspond to early length fre-quency modes to corroborate age estimates of young fish for each method.

Age (years)

0 1 2 3 4 5

Leng

th (c

m)

0

10

20

30

40

50Left thin sections (Dwyer et al., 2016) Left whole otolith (Dwyer et al., 2016)LF Labrador Summer (Bowering Nedreaas 2001)LF Barents Sea Summer (Bowering Nedreaas 2001)LF Newfoundland fall (Bowering Nedreaas 2001)LF Labrador fall (Lear Pitt 1975)

Figure 4.3.1. Length-at-age for fish 5 years and younger as estimated from length frequency modes (from the North Atlantic (Bowering and Nedreaas, 2001)) and thin-sectioned left otoliths and left whole otoliths (Dwyer et al., 2016). Note that length-at-age estimated from length frequency modes are higher than those from age methods.


4.4 d) Join international experts on growth, age estimation and assess-ment in order to progress toward a recommended procedure for fu-ture age determination of Greenland halibut.

High quality age validation studies have been carried out on both preferred ageing methods for Greenland halibut using methods that have been peer-reviewed by ex-perts in the field. We are therefore equally confident in both methods, while cautioning that bias is still present and needs to be resolved. However, the magnitude of this bias is reduced compared to previous levels and the WKARGH2 recommends that current accuracy is sufficient for use in stock assessment while work to resolve the bias contin-ues.

From studies carried out in Canada by DFO NWAFC, the traditional method of age determination from surface reading of whole left otoliths provides similar ages as the thin-sectioned left otolith method for fish <10 years of age, therefore, a combination of methods (e.g. whole left otolith to age 9 and then thin-sectioned left otolith for 10+ fish) is likely an acceptable approach going forward.

Recognizing that there is still bias and low precision in these methods, WKARGH2 recommends the use of an ageing error matrix (AEM) or growth curve that incorpo-rates error when conducting stock assessments for Greenland halibut in the Northeast Atlantic, Northwest Atlantic and Arctic stocks. For stocks where age-based models are used in the assessment the accuracy of the catch-at-age matrix can be improved prior to input into the model through the use of an AEM.

4.5 Based on results, conclusions and recommendations from this work-shop design and initiate an international exchange of otoliths for age determination after the workshop.

WKARGH2 recommends an otolith exchange between labs that carry out the same method every second year and a workshop with all labs every five years.

WKARGH2 recommends the development of reference collections for different stocks (high quality digital >10 bit greyscale, resolution at least 2K, *tiff) and exchange images between labs for each method.

4.6 e) Address the generic ToRs adopted for workshops on age calibration (see 'WGBIOP Guidelines for Workshops on Age Calibration')

The relevant generic ToRs are addressed in the different presentations above, as well as in the conclusions and recommendations sections.


5 Conclusions

1 ) For the frozen whole right otolith method, new age validation results with older fish using chemical marking (OTC) and tagging by Norway confirmed previous validation results. This method has been validated using chemical marking up to 50 cm and corroborated for fish up to 70 cm using growth information from tag-recapture data.

2 ) For the thin-section method, new age validation results were presented us-ing chemical marking (SrCl and OTC) and bomb radiocarbon analyses by Canada, which confirmed previous validation results.

3 ) The otolith exchange that occurred prior to this meeting showed low preci-sion for both methods (11.7% section, 8.9% whole; 15.3% between methods for the most experienced reader(s) in each method) and some bias. For ex-perienced readers, the bias between the two methods generally increased with age but remained within 1–2 years until age 15. Ages estimated from the frozen whole right otolith method tended to be older at ages <8 and younger at ages >9 compared to the thin-section left otolith method. Further analysis should be carried out to determine whether the frozen whole right or thin-section left otolith method is more appropriate to young fish.

4 ) It may be that some combination of methods would be acceptable, if for ex-ample it can be shown that two methods give similar results up to a certain age then either method could be applied for that age range.

5 ) There may be differences in growth rates among regions that could be in-trinsic to the stock or due to the age methods applied, the specific cause re-mains to be determined.

6 ) GADGET models have been developed for the West Nordic and NEA stocks and it is recognized that inclusion of accurate age data would improve model output.

7 ) The growth curve for the NEA stock as estimated by a length-based GADGET assessment model provides a closer fit to the growth curve using ages estimated from the frozen whole right otolith method than by the whole left otolith (traditional) ageing method.

8 ) WKARGH2 concludes that current accuracy using age estimates from either method is sufficient for use in stock assessment while the bias issue is being resolved.

9 ) Recognizing some bias and low precision in these methods, the WKARGH2 concludes that an ageing error matrix or growth curve with error be pro-vided for use in future stock assessments.


6 Recommendations

1 ) While it is recognized that some ageing issues remain to be resolved, the WKARGH2 recommends that either the frozen whole right otolith or thin-section method can be used to provide age estimates for stock assessments.

2 ) Recognizing some bias and low precision in methods, the WKARGH2 rec-ommends that an ageing error matrix or growth curve with error be pro-vided for use in future stock assessments.

3 ) WKARGH2 recommends the back-calculation of the lengths-at-ages 1–3 from the otoliths using both age determination methods and to see how well they correspond to the length frequency modes to corroborate age estimates of young fish for each method.

4 ) Labs should establish reference collections for each stock using known age (based on validated samples) or consensus ages from exchanges. These ref-erence collections should be used as the single most important tool for en-suring accuracy and consistency between labs and across years.

5 ) WKARGH2 recommends regular inter-lab calibration exercises to improve precision (i.e. exchange of digital images between readers for each method and between methods).

6 ) The workshop recommends the use of high quality resolution images in-cluding some measurement device (micrometre) that can be manipulated by image analysis software for use in future exchanges (a *.tiff file, using >10 bit resolution where possible) and reference collections. The current ICES software for exchanging digital images (WebGr) provides insufficient image quality for reliable interpretation.

7 ) The workshop recommends the use of CV to measure precision, age bias plots to determine whether there is bias, and an ageing error matrix, as standard outputs in a calibration exercise.

8 ) WKARGH2 recommends that the otoliths from OTC recaptured fish (both Northeast and Northwest regions) should be aged using both methods.

9 ) WKARGH2 recommends that labs investigate time and resources to imple-ment and apply either method.

10 ) WKARGH2 recommends another workshop in 5 years.


7 References

Albert, O.T. 2003. Migration from nursery to spawning area in relation to growth and maturation of Greenland halibut (Reinhardtius hippoglossoides) in the Northeast Arctic. J. Northwest Atl. Fish. Sci., 31: 113-125 pp.

Albert, O. T., M. Kvalsund, T. Vollen and A. B. Salberg. 2009. Towards accurate age determina-tion of Greenland halibut. J. Northwest Atl. Fish. Sci., 40: 81-95.

Albert, O. T. and T. Vollen. 2015. A major nursery area around the Svalbard archipelago provides recruits for the stocks in both Greenland halibut management areas in the Northeast Atlan-tic. ICES Journal of Marine Science; 72: 872-879; doi:10.1093/icesjms/fsu191.

Albert, O. T. 2016. Growth and formation of annual zones in whole otoliths of Greenland halibut, a slow-growing deep-water fish. Mar. Freshwater Res., 67: 937-942, http://dx.doi.org/10.1071/MF15089.

Campana, S. E. 2001. Accuracy, precision and quality control in age determination, including a review of the use and abuse of age validation methods. J. Fish. Biol. 59 (2), 197-242.

Campana, S. E., Valentin, A. E., MacLellan, S. E., and Groot, J. B. 2016. Image-enhanced burnt otoliths, bomb radiocarbon and the growth dynamics of redfish (Sebastes mentella and S. fas-ciatus) off the eastern coast of Canada. Mar. Freshwater Res. 67: 925–936.

Dwyer, K. S., Treble, M. A. and Campana S. E. 2016. Age and growth of Greenland halibut (Rein-hardtius hippoglossoides) in the Northwest Atlantic: A changing perception based on bomb radiocarbon analyses. Fisheries Research 179: 342–350.

Gregg, J. L., Anderl, D. and Kimura, D. K. 2006. Improving the precision of otolith-based age estimates for Greenland halibut (Reinhardtius hippoglossoides) with preparation methods adapted for fragile sagittae. Fishery Bulletin 104: 643-648.

Hallfredsson, E. H. and T. Vollen. 2015. Juvenile index for Barents Sea Greenland halibut. WD 1 ICES IBPhali 2015.

ICES. 2011. Report of the Workshop on Age Reading of Greenland halibut (WKARGH), 14-17 February 2011, Vigo, Spain. ICES CM 2011/ACOM:41. 39 pp.

ICES. 2015. Report of the Inter Benchmark Process on Greenland halibut in ICES areas I and II (IBPHALI), August 2015, By correspondence. ICES CM 2015/ACOM:54. 41 pp.

Kalish, J. M. 1993. Pre- and post-bomb radiocarbon in fish otoliths. Earth Planet Science Letters 114: 549-554.

Lear, W. H. and T. K. Pitt. 1975. Otolith age validation of Greenland halibut (Reinhardtius hippo-glossoides). J. Fish. Res. Board Can. 32: 289-292.

Loewen, T. N., Treble, M. A., Wastle, R., Reist, J. D., Sidhu, R., Sünksen, K., Jørgensen O. A., and Holden, N. M. (in prep). Assessing strontium uptake and expulsion in Greenland halibut (Reinhardtius hippoglossoides) otoliths.

Treble, M. A., Campana, S. E., Wastle, R. J., Jones, C. M. and Boje, J. 2008. Growth analysis and age validation of a deepwater Arctic fish, the Greenland halibut (Reinhardtius hippoglos-soides). Can. J. Fish. Aquat. Sci. 65: 1047-1059.

Treble, M.A. and K. S. Dwyer. 2008. Age determination workshop. In: NAFO Scientific Council Studies (Ed. A. Thomson). Report number 41, pp. 1-90.

Westgård , J.-I., Saha, A., Kent, M., Hansen, H. H., Knutsen, H., Hauser, L., Cadrin, S., Albert, O. T., and Johansen, T., 2016. Genetic population structure in Greenland halibut (Reinhardtius hippoglossoides) and its relevance to fishery management. Can.J.Fish.Aquat.Sci. DOI: 10.1139/cjfas-2015-0430.


Annex 1: List of participants

Name Address E-mail

Karen Dwyer (chair) Northwest Atlantic Fisheries Center Fisheries and Oceans (DFO) Canada

[email protected]

Lindsay Blades Northwest Atlantic Fisheries Center Fisheries and Oceans (DFO) Canada

[email protected]

Margaret Treble Freshwater Institute Fisheries and Oceans (DFO) Canada

[email protected]

Rick Wastle Freshwater Institute Fisheries and Oceans (DFO) Canada

[email protected]

Steven E. Campana University of Iceland [email protected]

Ole Thomas Albert Institute of Marine Reseach (IMR) Norway

[email protected]

Elvar Hallfredsson Institute of Marine Reseach (IMR) Norway

[email protected]

Kjell Arne Gamst Institute of Marine Reseach (IMR) Norway

[email protected]

Lise Heggebakken Institute of Marine Reseach (IMR) Norway

[email protected]

Torfinn Larsen Institute of Marine Reseach (IMR) Norway

[email protected]

Rasmus Nygaard Greenland Institute of Natural Resources (GINR)

[email protected]

Asta Gudmundsdottir

Marine and Freshwater Institute (MFRI) Iceland

Asta,[email protected]

Gudmudur Thordarson


[email protected]

Audur S. Bjarnadottir


[email protected]

Gudrun Finnbogadottir


[email protected]

Groa Petursdottir (chair)


[email protected]

Gerdur Palsdottir Marine and Freshwater Institute (MFRI) Iceland

[email protected]


WKARGH2 Participants (L-R): Elvar Hallfredsson, Gudrun Finnbogadottir, Karen Dwyer, Torfinn Larsen, Groa Petursdottir, Lindsay Blades, Rick Wastle, Lise Heggebakken, Kjell Arne Gamst, Audur S. Bjarnadottir, Margaret Treble, Ole Thomas Albert, (missing, Steven E. Campana, Rasmus Nygaard, Asta Gudmundsdottir, Gerdur Palsdottir).


Annex 2: Agenda

WKARGH2 2016: Reykjavik, 22-26 AugustAGENDA (preliminary)

Day Time

Duration incl.

discuss. Presenter Title Comments10:30 Arrival, connection to network, etc

10:45 ChairsWelcome, Adoption of agenda, review Terms of Reference, work plan and distribution of responsibilities

11:00 ChairsIntroduction: The present unresolved situation and our expectations for progress during the meeting

11:15 Treble/Albert Review of conclusions from 2011 WKARGH 12:00 LUNCH

13:15 30 WastleWork by stock area: Central and Arctic/Greenland (0A and 0B/1A-F): Methods improvement Wastle

13:45 30 TrebleWork by stock area: Central and Arctic/Greenland (0A and 0B/1A-F): Update on validation progress Treble

14:15 30 DwyerWork by stock area: Northwest Atlantic (Newfoundland/Labrador) (SA2+3KLMNO): Update on validation progress

Dwyer

14:45 15 COFFEE

15:00 30 AlbertWork by stock area: Norway (AREAS?): Validation of annual zones in whole otoliths of young Greenland halibut Albert

15:30 30 AlbertWork by stock area: Norway (AREAS?): Growth and annual zones in long term ramblers

16:00 30 ThordarsonWork by stock area: Iceland (AREAS?): How ageing is used in the GADGET assessment model for Greenland Halibut Thordarson

16:30Other: (Gulf of St Lawrence, Spain & Portugal, Russia) & Discussion

16:30 Discussions: ToRs a) Review information on age estimates, otolith exchanges, workshops and age valication work done so far

17:00 ADJOURN

09:00 30 Chairs/PlenaryRe-cap of Day 1; carry-over of any presentations or discussion

09:30 30 Petursdottir Results of exchange between Norwegian method of whole otolith and thin-sectioned otolith (keep in mind level of experience and quality of pictures!)

10:00 Plenary Discussion

10:30 15 BREAK

10:45 15 DwyerGrowth analyses for various areas based on the methods used Tentative

11:00 15 Treble Quality control Tentative

11:15 60 Ageing Hands-on with examples of each methodThis can take more time

12:15 75 LUNCH13:30 30 Campana/Albert Photoshop: how to enhance images14:00 Hands-on working on examples?15:00 ADJOURN09:00 Chairs Re-cap previous day 09:30 60 Steve Campana Keynote: Use of age data from problematic fish species10:30 COFFEE

10:45 Chairs/PlenaryIntroduce discussion of key questions and items we need to address in the ToRs: also see the tab "List of questions"

12:00 LUNCH13:15 Chairs/Plenary Discussion & begin formulation of report15:00 COFFEE17:00 ADJOURN

Thur

sday

OUTING09:00 Chairs/Plenary Recap of discussions to this point 09:30 Finalize discussions and report12:00 CLOSURE

Mon

day

Tues

day

Wed

nesd

ayFr

iday


Annex 3: Recommendations

Recommendation Adressed to

1. The workshop recommends the use of high quality resolution images including some measurement device (micrometre) that can be manipulated by image analysis software for use in future exchanges (a *.tiff file, using >10 bit resolution where possible) and reference collections. The current ICES software for exchanging digital images (WebGr) provides insufficient image quality for reliable interpretation.

ICES


Annex 4: WKARGH2 ToRs

WKARGH – ICES_NAFO Workshop on Age Reading of Greenland Halibut (Rein-hardtius hippoglossoides)

2015/2/SSGIEOM08

A Workshop on Age Reading of Greenland Halibut (Reinhardtius hippoglossoides) (WKARGH2) chaired by Karen Dwyer, Canada, and Gróa Pétursdottír, Iceland, will be established and take place in Reykjavik, Iceland 22–26 August 2016 to:

a) Review information on age estimations, otolith exchanges, workshops and val-idation work done so far.

b) Evaluate all available information on individual growth patterns in order to achieve a general consensus about the most probable levels of longevity and growth rates for the different stocks.

c) Report on ageing protocols currently in use and their compliances with avail-able validation results.

d) Join international experts on growth, age estimation and assessment in order to progress towards a recommended procedure for future age determination of Greenland halibut.

e) Address the generic ToRs adopted for workshops on age calibration (see 'WGBIOP Guidelines for Workshops on Age Calibration')

WKARGH2 will report by 1 October 2016 for attention to ACOM and SCICOM.

Supporting information

Priority: Essential. Age determination is an essential feature in fish stock assessment to estimate the rates of mortalities and growth. Assessment of Greenland halibut stocks using age structured models has proved useful in establishing a diagnosis on stock status. However, the approach has several limitations and shortcomings such as stock structure, natural mortality and growth. Age data are provided by different countries and are estimated using different ageing criteria which have not always been validated. Therefore, a WK should be carried out in order to evaluate available information on otolith growth patterns, age determination issues and the current situation of age estimation of Greenland halibut which has been subject of concern of ICES AFWG and NWWG and make progress towards a solution.

Scientific justification:

The previous WKARGH (Vigo, 2011) concluded that the traditional ageing method for Greenland halibut severely underestimates age of fish older than age 5. The workshop demonstrated a common understanding of the underlying growth patterns of the species and evaluated two new age reading methods as promising but there was no common agreement as to which method is most accurate. Since then several institutions have continued tagging programs, ageing structure comparisons, and other work in order to validate seasonal zones in otoliths.

The workshop should be the forum to present and discuss the results of these investigations in relation to the previous findings.

For the purpose of inter-calibration between ageing labs an appropriate exchange programme, to be carried out after the meeting, will be planned and designed during the workshop.. This will include a set of otoliths images

http://www.ices.dk/reports/acfm/pgccdbs/PGCCDBSdocrepository.asp


collected partially from chemically tagged fish.

The aim of the workshop is to identify the state of art of age estimation of Greenland halibut after validation studies conducted so far.

Resource requirements:

The scientific institutions should make a concerted effort to compile the existing tagging material as well as sectioned otoliths (digital otolith images), that can be used as a reference collection.

Participants:: In view of its relevance to the ICES quality assurance , ICES NWWG and AFWG, and NAFO, the Workshop should try to include age readers and experts on fish growth and age determination working on Greenland Halibut

Secretariat facilities:

None

Financial: None

Linkages to advisory committee:

ACOM

Linkages to other committees or groups:

PGCCDBS, NWWG, AFWG, SSGEIOM, SCICOM and NAFO

Linkages to other organizations:


Annex 5: Photoshop Instructions for Image Enhancement

ADOBE PHOTOSHOP – COOKBOOK DIRECTIONS

To change an image from grayscale to colour, or colour to grayscale:

• Image-Mode-RGB Colour (or Grayscale)

To show Navigator window (to move around and zoom in on image):

• Window-Navigator

Image Enhancement

• Image-Adjustment-Levels o Move black arrow to right as much as possible, but not to point where

any point of otolith begins to disappear o Move white arrow to left until at right-most base of histogram, or until

part of otolith is becoming pure white o Move central arrow to point where image is pleasing to eye o OK

• Filter-Sharpen-Unsharp Mask o Leave Threshold at 0 o Move Radius to between 10-20; possibly higher if image is homogeneous o Move Amount to 100-200%, or until it suits taste

To add layer which can be annotated for training or quality control:

• Layer-New layer (if Layers window does not appear, Windows-Layers) • Ensure that layer is selected (will appear highlighted in layers window) • Select brush tool; change size with Windows-Brushes • To change brush colour, double-click on colour panels in left-hand menu

bar; note that a coloured brush cannot be used on a grayscale image, unless the image is first changed to RGB mode

• Use brush to mark growth bands; use Text tool (T) to add text to layer • To hide layer during testing, click on eye in layer window

ICES WKARGH2 REPORT 2016 Reports/Expert... · The Workshop for Age Reading of Greenland halibut...

Documents

Transcript of ICES WKARGH2 REPORT 2016 Reports/Expert... · The Workshop for Age Reading of Greenland halibut...