Fisheries Pêchesand Oceans et Océans

Central and ArcticDFO Science

Stock Status Report D5-61 (2001)

March 2001

Rat River Dolly Varden

BackgroundChar west of the Mackenzie River were originallythought to represent a distinct form (western Arctic-Bering Sea) of Arctic char (Salvelinus alpinus)(McPhail 1961, McCart 1980). Re-evaluation oftaxonomic identity using morphological and geneticcriteria confirmed that the char found in highgradient rivers west of the Mackenzie River are infact Dolly Varden (Salvelinus malma) (Reist et al.1997). Arctic char typically occur in river systems tothe east of the Mackenzie River drainage (e.g.,Hornaday River, Kuujjua River).

The Rat River, located 90 km south-west of Inuvik,NT, flows east from headwaters in the RichardsonMountains, and drains into the Husky Channel of theMackenzie River (Fig. 1). The northern form of DollyVarden, described by Reist et al. (1997), inhabit thissystem. Spawning and over-wintering areas for theDolly Varden are located in spring-fed reaches ofFish Creek, a tributary of the upper Rat River.

The Gwich’in word for Dolly Varden is “Dhik’ii”(GRRB 1997), while the Inuvialuit word is“qalukpik” (Lowe 1984). The common name "char"is still used locally and in community-baseddocuments such as the "Rat River Char FishingPlan" (Aklavik RRC et al. 2000) and the community-based "Rat River Char Monitoring" study.

This stock was assessed in support of the Rat RiverChar Fishing Plan (Aklavik RRC et al. 2000), whichwas prepared with the assistance of the Departmentof Fisheries and Oceans (DFO), the Gwich’inRenewable Resource Board (GRRB), and theFisheries Joint Management Committee (FJMC).

Summary• Anadromous Dolly Varden, known

locally as “char”, inhabit the Rat Riverand its tributaries.

• Rat River Dolly Varden represent one ofsix known populations of the northernform of Dolly Varden in Canada.

• The Dolly Varden that inhabit thissystem are genetically distinct and showa higher degree of genetic diversity thanpopulations in neighbouring systems.

• Harvesters from two adjacent land claimgroups, the Gwich'in and the Inuvialuit,harvest Dolly Varden from the Rat Riverstock.

• Communities of Aklavik and FortMcPherson developed and implementedtheir "Rat River Char Fishing Plan" in1995.

• The Plan currently recommends that thetotal take of Dolly Varden in the food

Joe

Firth

Babbage

Shingle

Point

Blow

Big

Fish

Rat

Stony

River

River

River

River

Ck

Fish

Inuvik

Aklavik

Ft. McPherson

Creek

River

Ck

Vittrekwa

Rive

r

Mackenzie

Peel

River

River

MackenzieBay

Beaufort Sea

Alas

kaYu

kon

NorthwestTerritories

YukonNorth

SlopeRichardson

Mountains

N

Inuvialuit Settlement Region Gwich’inSettlement

Area

Fig. 1. The lower Mackenzie River and tributaries,including the Rat River.

Road

Trail

Caribou

River

River

Rive

r

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fishery not exceed 2000 fish per year,and specifies the number of nets whichmay be used per household, their sizeand depth restrictions.

• Compliance with the Plan has beenimproving over the past years, with thecommunity harvest during 1999 and2000 being in full compliance with therecommendations of the Plan.

• The fishery has been monitored througha community-based sampling programsince 1989. This program was expandedfrom one site to five sites in 1995 andcontinues to the present day.

• The average annual harvest between1990-1999 is equivalent to 13.0% of the1998 stock size estimate, and 17.7% ofthe 1996 estimate.

• There has been no decline in the size ofthe Rat River Dolly Varden stock, asestimated over the last decade.

• During the monitoring program from1989-2000, CPUE (catch-per-unit-effort), length- and age-frequencydistributions, sex and maturity ratios ofRat River Dolly Varden have remainedrelatively unchanged.

• The stock appears to be stable and in noimmediate danger under the currentharvest strategy. The outlook for thestock is favourable, given careful annualmonitoring of harvest, periodicindependent experimental estimation ofthe size and composition of the stock,and continued compliance with thecommunity-based fishing Plan.

Species BiologyDolly Varden are closely related to theArctic char, lake trout (Salvelinusnamaycush) and brook trout (Salvelinusfontinalis). Externally, Dolly Varden can bedistinguished from anadromous Arctic charbecause they have a more fusiform bodyshape, pupil-sized light spots on the bodywith blue halos (as opposed to trout and

salmon which usually have black spots orspeckles), and generally, a less-forked tailfin. The sea-run form of Dolly Varden aresilvery with an olive-green to brown colouron the dorsal surface.

In the Canadian Arctic, Dolly Varden occurin several rivers to the west of theMackenzie River, including the YukonNorth Slope during the summer months.The Vittrekwa River (upper Peel Riverdrainage), Big Fish River, Babbage River,Firth River and the Rat River all supportseparate genetic stocks of this species (Fig.1).

Many Dolly Varden stocks exhibit both ananadromous (sea-run) and a residual, non-migratory (solely freshwater) form (McCart1980). The former is the most commonlyobserved. They reside in their headwaterstreams for approximately three years,before making their first migration to theBeaufort Sea to feed in summer. Theyreturn in the fall to the freshwater riverineenvironment for over-wintering. At thisstage they are approximately 120 mm inlength, and are called smolts.

They continue to make summer and fallmigrations to and from the sea for theremainder of their lives. Spawning in theRat River drainage occurs in the Fish Creektributary from mid-August through to earlyOctober.

The residual form is comprised almostexclusively of males, which reside in theheadwater streams for their entire lives.Although the residual form is common inthe neighbouring Dolly Varden systems,they have yet to be observed in the RatRiver or it’s tributaries (J. Reist, S.Sandstrom, pers. comm.). They mature at asmaller size and younger age than their sea-run counterparts, and “sneak” into the reddsto spawn with the anadromous pairs.

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Sea-run males and females from NorthSlope populations begin to mature at age 4and 450 mm and 355 mm respectively,although most mature at an age of 5-6 years,after having spent two or three summersfeeding at sea.

Upon reaching maturity, they appear tospawn every second year, although there isevidence that a proportion (e.g., 25% in1998) of them are capable of spawning inconsecutive years (L. Harwood, unpubl.data). This is likely variable from year toyear depending on individual condition,prevailing environmental conditions and theage of the fish (Dutil 1986), and is similar tothe situtation found with Arctic char. FewRat River Dolly Varden live past eight yearsof age, and most do not spawn every year.Similar to Atlantic salmon (Salmo salar), aproportion of the Dolly Varden live tospawn a second time and a small numbermay live long enough to spawn more thantwice.

The Dolly Varden is an opportunisticpredator in nearshore lagoon and coastalmarine waters, feeding mainly on smallfishes and benthic organisms. Communityfishermen from Aklavik and FortMcPherson found that aquatic insectremains were the most common food itemsin the stomachs of fish caught returningfrom sea (J. Carmichael, pers. comm.).During the upstream migration, and duringthe spawning and over-wintering period,sea-run Dolly Varden feed very little (S.Sandstrom, pers. comm.).

Description of Habitat

The Rat River straddles the Yukon-Northwest Territories border, and flowsfrom headwaters in the RichardsonMountains along a 130 km (80 miles)course, entering the Husky Channel of theMackenzie River 35 km (22 miles) north-west of Fort McPherson, NT. Trees are

confined to the valleys and lower slopes, andthe rest of the basin area is covered bytundra vegetation. The bedrock is mainlysandstone, with some limestone in thenorthern sections. A headwater tributary,Fish Creek, has many deep pools and is fedby one or more perennial groundwatersprings. Water temperatures at the springdischarge sites are in the 4-5 °C range.

The limiting factor for Dolly Varden in theWestern Arctic is thought to be theavailability of accessible spawning andover-wintering habitat. The high gradientrivers in this area freeze completely to thebottom over much of their length. Theexception to this is where groundwatersprings discharge, producing sections of thestream that do not freeze to the bottom inwinter. This in turn provides over-winteringand spawning habitat (known locally as“fish holes”) for the Dolly Varden.Downstream of the discharge area, a largefield of layered ice (aufeis) forms as thewater becomes cooler, dissipates and finallyfreezes. During the summer months, mostor all of the ice field melts, revealingshallow flows through a braided, gravelplain which is used by the current year non-spawners in fall before ascending to theover-wintering site (Sandstrom et al. 2001).

Spawning and over-wintering sites arerelatively well known and recent studieshave documented that the physicalcharacteristics of similar “fish holes” changeover time as sodium, water and silt levelsfluctuate (Clark et al. 2001).

Specific rearing areas for juvenile DollyVarden are unknown but, based onknowledge from other similar systems, aremost likely located in the spring-fedchannels and within the braided area of FishCreek. They may also make use of habitatin upper reaches of the Rat River mainstem.Any juveniles that disperse downstream ofthe spring-fed areas must return to them to

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over-winter. It may be possible that deeperpools along the main river course couldoffer over-wintering opportunities, but thishas not been documented.

The Rat River basin is utilized eitherpermanently or seasonally by at least 13other species of fish (Jessop et al. 1973). Atthe spawning and over-wintering site, themost common species next to Dolly Vardenis the Arctic grayling (Thymallus arcticus).The slimy sculpin (Cottus cognatus) is alsoprevalent.

In the lower reaches of the Rat River, broadwhitefish (Coregonus nasus), roundwhitefish (Prosopium cylindraceum),northern pike (Esox lucius), burbot (Lotalota), longnose sucker (Catostomuscatostomus), inconnu (Stenodus leucichthys)and Arctic cisco (Coregonus autumnalis) arefound during spring, summer and fall.

Burbot and northern pike likely contribute tothe natural mortality of sea-run DollyVarden in the lower reaches of the Rat Riverand in the Mackenzie River channels andestuary. Predation by sculpins likelycontributes to mortality of eggs andjuveniles at the nursery and rearing areas inFish Creek. The presence of fresh seal scarsand lamprey wounds on returning sea-runmigrants indicate that both these predatorsalso contribute to mortality of sea-runindividuals. In addition, wolves, grizzlybears, mink and golden eagles have beenobserved to feed on all life history stages ofDolly Varden at the spawning and over-wintering site (S. Sandstrom, pers. comm.).

The FisheryDuring the summer months, Rat River DollyVarden are caught along the Beaufort Seacoast, mainly at whaling and fishing campslocated along the Yukon coast and atShingle Point (Fig. 1). Tagging programshave shown that the coastal fisheries harvest

Dolly Varden from a mixture of stocks,including those from the Babbage, Firth, BigFish, and Rat rivers (Fig. 1). The VittrekwaRiver stock and some Alaskan stocks mayalso represent a small proportion of theDolly Varden harvested at these locations.

Once the Rat River Dolly Varden begin theirreturn migration from the sea, usuallybetween late August and mid-September,they encounter fishermen’s nets at a numberof locations along the way (Fig. 2). Thesubsistence harvest usually takes place for 3-4 weeks each year. Floating monofilamentgillnets, with mesh sizes of 102 mm (4") and114 mm (4½”), usually 25 m in length and30 meshes deep, are currently the mostcommonly used. Smaller mesh nets (e.g.,89mm or 3½”) were used prior to 1998along with the 102 mm and 114 mm nets,but their use has largely been discontinuedsince the community fishing Plan was putinto place (Aklavik RRC et al. 2000).

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There is apparently no fishing for DollyVarden at the over-wintering site in FishCreek, a tributary of the Rat River, at thepresent time. This practice apparently hasnot taken place since the mid-1980s (J.Francis, J. Carmichael, pers. comm.).

Table 1. Estimated harvest of Rat River DollyVarden, 1972-2000.

Year Number of Fish

Inuv. at 50% Gwich’in Unspec. Total AK 1,4 Inuv. at 2,3 origin5,6 est. SP1,4

1972 6500 6500 1973 2600 2600 1975 2100 2100 1980 1545 1545 1986 50 1050 1100 1987 125 3000 3125 1988 74 1607 1681 1989 132 53 1814 19991990 60 107 884 1051 1991 20 3 353 376 1992 250 9 775 1034 1993 381 60 968 1409 1994 842 17 1296 2155 1995 377 32 1115 1524 1996 547 403 1970 2920 1997 643 62 2688 3393 1998 255 386 3119 3760 1999 225 125 1561 1911 2000 8 0 1485 1493

AK= Aklavik; SP = Shingle Point; Inuv= Inuvialuit1 Inuvialuit Harvest Study, unpublished data, for all years listedexcept 19992 Inuvialuit Harvest Study, unpublished data, for the years 1986-19943 Gwich'in Harvest Study (MacDonald 1998a,b) and Rat RiverMonitoring Study (Harwood 2001) for 1995-20004 DFO Fish Harvest Study (S. Stephenson, unpubl. data) for 19995 DFO files, R. Peet, G. Low, unpublished data6 Thought to include commercial harvests in 1972,1973 and 1975

Total annual harvests of Dolly Varden wereestimated by summing 50% of the Inuvialuitcatch at Shingle Point, the total caught in thePeel Channel at Aklavik by both Inuvialuitand Gwich’in fishers, and the totals caughtat Husky Channel, Big Eddy, the mouth ofthe Rat River and at Destruction City (Fig.2, Table 1). An unknown but probablysmall proportion of this harvest likely

includes Dolly Varden from the VittrekwaRiver and other Peel River tributaries (S.Stephenson, pers. comm.).

The average harvest of Rat River DollyVarden was 3733 Dolly Varden per year forthe three years of available data for the1970’s, 1890 for five years of data for the1980’s, and 1953 for ten years of data forthe 1990’s. Fishermen concur that harvestlevels in the 1970’s were higher than atpresent (J. Francis, J. Carmichael, pers.comms; GRRB 1997).

A small proportion of the subsistenceharvest was sold commercially in 1972 and1973. A commercial fishery with a quota of900 kg was closed in 1985.

Resource User PerspectiveThe Gwich’in and Inuvialuit have longdepended on the Rat River Dolly Varden forwinter sustenance. These fish, called Dhik’iiby the Gwich’in (GRRB 1997) and qalukpikby the Inuvialuit (Lowe 1984), continue tobe an important element of diet, traditionand culture to the present day. There arepresently an estimated 190 head-of-household Gwich’in harvesters in Aklavikand Fort McPherson combined (B. Arey,pers. comm.) and of these, an average of 18(9.4%) report regular annual harvests of RatRiver Dolly Varden.

Forty years ago the majority of familiesfrom Fort McPherson went to the Rat Riverto fish (GRRB 1997). GRRB (1997:163)states:

“Char are important to people becausethey are considered a delicacy and atype of food that local people cannot getvery often. Everybody likes the charbecause it is rich and tasty. In the olddays, people would never joke about thechar, or any other fish or animalbecause their survival depended onhaving a good relationship with them”.

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“Long ago a medicine man used to liveup the Rat River, near the Fish Hole.Even after he died, when in the fallfamilies went to that place, parents toldtheir children not to run around and bequiet because it was a sacred place”.

Concerns of the harvesters about the statusof the stock led to the development of acommunity-based fishing Plan, which hasnow been in place for six years (AklavikRRC et al. 2000).

The goals of the Plan are to:• maintain a healthy stock of char (Dolly

Varden) in the Rat River system,• maintain and manage the Rat River

fishery for the continued use andenjoyment by the residents of Aklavikand Fort McPherson, and

• encourage co-operation among all users.

The Plan currently recommends that thetotal take of Dolly Varden in the foodfishery not exceed 2000 per year, andspecifies the number of nets that may befished, their size and depth restrictions.Compliance with the Plan has beenimproving in recent years, with fishing inthe 1999 and 2000 seasons being in fullcompliance with the recommendations ofthe Plan.

Resource StatusStock Delineation

For Dolly Varden in North America, twosubspecies are formally recognised: thesouthern taxon, Salvelinus malma lordi, andthe northern taxon, S. m. malma (Behnke1980). It is the northern subspecies that ispresent in the ISR and the Gwich’inSettlement Area. The two subspecies differsignificantly with respect to their biology,productivity and related aspects of biologyrelevant to fishery management. Giventhese differences, the general transfer of

understanding from the southern taxon,which is well studied, to the northern taxon,which is not, is problematic and must beconducted carefully if at all (Reist 2001).

The populations of the northern form ofDolly Varden that occur in Arctic Canada(Firth River, Joe Creek, Babbage River, BigFish River, Rat River and Vittrekwa River)represent the only known populations of thisdistinct taxon in Canada. Thus, these fish areof interest as a unique part of the Canadianfish fauna (Reist 2001).

There appear to be at least six populations ofthe northern form of Dolly Varden inCanada. Studies using both morphology andgenetic methods have confirmed thediscreteness of fish from four river systems(Firth, Babbage, Big Fish and Rat). Dataalso indicate that fish from Joe Creek, atributary of the Firth River, may be distinctfrom those that spawn in the Firth River(Reist 1989). Additional geneticinformation (i.e., sequence variation inmitochondrial DNA) confirms that thesepopulations are all different from each other(J. Reist, unpubl. data) but mix along thecoast during summer feeding andmigrations.

Preliminary analysis of stock structure usingotolith microchemistry for Firth River, JoeCreek and Babbage River confirms thestructuring of Dolly Varden populations asdetermined by other methods (Babaluk et al.1998; J. Babaluk unpubl. data).

Recapture of tagged fish support the geneticand microchemistry results, indicating thatNorth Slope Dolly Varden stocks arediscrete and show a high degree of fidelityto their natal spawning streams and over-wintering sites. Floy tags applied to DollyVarden at the Rat River have only beenrecaptured approaching, or within, the RatRiver system.

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Dolly Varden tagged at the over-winteringsite on the Big Fish River and at the FirthRiver have never been recaptured at, orapproaching, the Rat River. Tagged fishfrom each of these sites have been caughtduring the summer coastal fishery at ShinglePoint demonstrating that stocks do mix inthe nearshore coastal environment.However, only small numbers of DollyVarden tagged at the Rat River have beenrecaptured at the Shingle Point coastalfisheries (L. Harwood, unpubl. data).

Structuring within the Rat River Stock

Field observations in Fish Creek suggest thatDolly Varden of the Rat River may consistof two (or more) different spawning groups,although it is not known at this time if thesegroups represent genetic stocks. Spawningand spent sea-run Dolly Varden have beencaptured in Fish Creek in mid-August (S.Sandstrom, unpubl. data). A second groupof Dolly Varden was observed spawning ina separate area of Fish Creek in mid-September (L. Harwood; S. Sandstrom,unpubl. data). Fishermen’s observations oftwo or more pulses in the fishery (B.Mitchell, J. Carmichael, pers. comm.) alsosuggest there may be more than one groupof Dolly Varden using the basin.

Preliminary genetic results also support this.Among anadromous Dolly Varden from theRat, Babbage, Firth and Big Fish rivers, andJoe Creek, genetic diversity was highest inthe Rat River samples (J. Reist, unpubl.data). These results also suggest that hiddenstructuring may be present in the Rat Riverstock(s), and is consistent with thesuggestion of two or more temporallydifferent spawning groups. Two distincttemporal groups of sea-run spawners, asummer and fall group, have beendocumented in some Alaskan systems(DeCicco 1989).

Stock Size

Several attempts have been made to estimatethe number of sea-run Dolly Varden in theRat River (Table 2). The first was in 1983and involved a weir constructed upstream ofDestruction City. An attempt was made toenumerate all migrants returning from thesea (Gillman and Sparling 1985). The weirwas operational from August 8-30, 1983,during which time a total of 1312 upstreammigrants were counted. Of this number,57% were spawners. High water levelsforced the removal of the weir while the runwas in progress, and a complete count wasnot obtained.

Table 2. Mark-capture estimates of the size of theRat River Dolly Varden stock(s)

Year Est 95% CI Method no lower upper

19891 100003 Schaefer19891 11191 8532 15020 Petersen19962 9679 8194 11158 Petersen19982 14919 11265 18573 Petersen1 Stephenson and Lemieux (1990)2 L. Harwood, S. Sandstrom, unpublished data3 adjusted upwards by 1000 to account for fish takenin fisheryCI=confidence interval

In 1989, a mark-recapture estimate wasconducted in the Destruction City area,using a hoop net to catch migrants returningfrom the sea, and the subsistence fishery atDestruction City as the recapture site(Stephenson and Lemieux 1990). APetersen estimate was done one month laterat the spawning and over-wintering site,using the tags put on downstream thatsummer and electro-shocking to recapturethe fish (Table 2).

Petersen estimates were also conducted in1996 and 1998 (Table 2). These involvedcapturing Dolly Varden at the over-wintering site using seine nets and markingwith individually coded floy tags (n=355 in1995; n=402 in 1997), and the subsistencefishery the following year as the recapture

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mechanism (S. Sandstrom, L. Harwood,unpubl. data). The component of the harvestwhich would not have been vulnerable totagging the previous fall was excluded fromthe calculations, and adjustments were madefor tag loss and newly recruited fish.

Stock trend

Stock size estimates described above,although few in number, indicate no majorchange in the size of the stock in recentyears. The 1998 estimate of stock size washigher than the 1989 and 1996 estimates,and this may represent an increase in thenumber of Dolly Varden using the system.Further mark-recapture studies arewarranted to confirm the apparent trend.

Harvesters have observed an increase in thesize of individual fish in recent years, andfelt this was consistent with estimates ofstock size which appear to be stable orpossibly even increasing in number (J.Carmicheal, pers. comm.).

The CPUE (catch-per-unit-effort) in the1995-2000 subsistence fishery remainedrelatively consistent with two exceptions(Table 3). The mean CPUE for 1998 wasnearly twice the average for the 1995-2000period, while at the other extreme the 2000value was less than half the average for thisperiod. It is believed these results arecorrelated with the timing of the runs inthose particular years (Fig. 3). The runoccurred three weeks earlier than usual in1998, and three weeks later than usual in2000. This in turn was thought to be relatedto the timing of break-up of the river ice,which was earlier than usual in 1998 andlater than usual in 2000, and may explain thedifferences in CPUE and the timing ofmigration in those years (Harwood 2001).

Biological assessment surveys of DollyVarden at the spawning and over-winteringsite in Fish Creek in the fall of 1995 and

Table 3. Summary of sex, maturity and CPUEfrom the Rat River Dolly Varden subsistencefishery, 1989-2000

Year % % Mean No. of silvers males CPUE* fishers

1989 51.4 23.5 nd nd1990 71.9 37.9 nd nd1991 91.1 42.9 nd nd1992 nd nd nd nd1993 98.4 36.5 nd nd1994 93.5 30.3 nd nd1995 83.5 35.3 21.0 151996 68.7 33.1 30.6 141997 90.9 36.1 45.2 191998 83.9 40.6 74.0 181999 41.6 39.5 39.4 232000 68.8 37.8 18.6 19

Mean 76.7 35.8 38.1 18

nd = no data*CPUE = no. of Dolly Varden/100 m net/24 hours

1997 revealed that the mean size ofindividual fish did not change significantlyduring the intervening period for malespawners (Harwood 2001), female spawnersor current year non-spawners (Fig. 4).

Subsistence harvest levels between the 1995and 1997 studies were 1.5-1.7 times higher(n=2920, 1996; n=3393, 1997) than theaverage for the decade (n= 1953). The factthat size distribution of the fish between thetwo surveys remained relatively constantlends support to the conclusion that theharvest is sustainable.

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Sampling of the Dolly Varden harvests atDestruction City (1986-1994), and at four orfive monitoring sites including DestructionCity (1995-2000) (Fig. 2), provides a long-term record of size, sex, age and conditionof Dolly Varden taken in the fishery(Harwood 2001). Current year non-spawners predominate the catch. Resultsfrom the harvest monitoring suggest thestock is stable, as a wide range of sizeclasses were taken in the fishery each yearand this did not appear to vary over time(Fig. 5; Harwood 2001). These results areconsistent with the available historical dataas well (Sparling and Stewart 1986).

One noticeable change in the distribution ofsize classes was the absence of smolts(approximately 320 mm fork length) in theharvest after 1998. This is likely due to theincrease in mesh sizes used by thefishermen, associated with implementationof the Fishing Plan. An accurate estimate ofthe relative abundance of this component ofthe stock is important in interpreting trendsand forecasting what will be available to thefishery the following year.

The average sizes of the male and femaleDolly Varden taken in the fishery variedamong years but there were no obvioustrends toward increasing or decreasing

length over time, up to and including 1998.In 1999 and 2000 the average length of bothmales and females was significantly greaterthan in the other 11 years examined(Harwood 2001). The apparent shift towardlarger fish in 1999 and 2000 (Fig. 5) is likelythe result of increased growth followingoptimal feeding opportunities in 1998.

Tagged Dolly Varden also showed highgrowth rates in 1998. Mean annual growthof 450-600 mm individuals, tagged in fall1997, and recaptured in August 1998, was75.9 mm (n=9). In contrast, the growth rateof 450-600 mm individuals tagged in fall1995 and recaptured in late summer 1996averaged 31.2 mm (n=32).

Silvers were caught more often thanspawners in the fishery, and femalesoutnumbered males (Table 3). Theproportion of silver Dolly Varden caught inthe fishery has averaged 76.7% between1989 and 2000. The sex ratio of the catchhas remained similar throughout themonitoring program. On average, 35.8%were males. This same bias toward femaleshas been apparent in earlier studies at the

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Rat River (Jessop et al. 1973, Gillman andSparling 1985, Stephenson and Lemieux1990).

There were no apparent shifts in the agestructure of the Dolly Varden taken in thesubsistence fishery. The average age ofmale and female Dolly Varden variedamong years of the monitoring study, butthere were no consistent trends towardincreasing or decreasing mean age over time(Harwood 2001). Between 1995 and 2000,and as far back as 1986 (Sparling andStewart 1986; Harwood 2001), the age-frequency distributions show a consistentand continued representation of the olderage classes and no detectable changes in theshape of the distributions (Fig. 6).

While there was a decrease in the modal ageclass of one year between 1999 and 2000,this is likely due to a larger than averageyear class being recruited to the fisherybecause of unusually high growth rates in1998. This will be monitored further in2001 and beyond.

The instantaneous mortality rate (Z),calculated from the catch curve for DollyVarden from the neighbouring (notharvested) Babbage River stock, was 0.28(Sandstrom et al. 1997) for 1990-1992. Incontrast, instantaneous mortality rates for

the Rat River were higher, reflecting thecombination of natural and fishing mortalityat this system. Instantaneous mortality rates,calculated from the catch curves, were 0.57in 1986 and 0.94 in 1989. Rates were evenhigher during the 1990's (Harwood 2001),with the most recent being 1.50 in 2000.

The condition of the Dolly Varden caught inthe fishery was calculated using theequation: K = weight (g) x 105 /length (mm)3

(Anderson and Gutreuter 1983). Conditionwas significantly different among years withboth male and female Dolly Varden havingsignificantly higher K values in 1998 than inany of the other years examined (Harwood2001; Fig. 7). In spring of 1998, regional iceconditions were light and ice break-up wasearlier than usual. This appears to haveresulted in particularly favourable or extendedfeeding conditions in the ocean that summer.

In summary, a number of differentindicators suggest that the Rat River DollyVarden stock is stable and sustaining thepresent harvest level. Additional samplingof the juvenile sea-run components (smolts)would contribute further to ourunderstanding of trends in the status of thestock.

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Sustainable Harvesting Rate

The average annual harvest between 1990-1999 is equivalent to 13.0% of the 1998estimate and 17.7% of the 1996 estimate.The present rate of harvest is probably lowerthan in the 1970's when the stock went intodecline. Current indicators suggest that thepresent harvest is sustainable. There is nofishing at the spawning and over-winteringsite at Fish Creek, a practice that furtherconserves the stock.

Sources of UncertaintyCPUE may be indicative of changes inrelative stock size, but at the same time isgreatly influenced by changes inrecruitment, migration patterns, localenvironmental conditions and/or changes infishing practices. For these reasons, CPUEdata must be interpreted with caution, and incombination with other lines of evidence.

Research and management initiatives to datehave assumed that there is one stock ofDolly Varden in the Rat River. However,genetic and observational data suggest theremay be more than one stock using thesystem. It has not yet been determined ifearly and late spawners are geneticallydistinct. Further, if there are other stockspresent that are non-anadromous, theirpresence could bias information collected inthe river.

Dolly Varden of the Vittrekwa River exhibitanadromy and thus likely migrate past thesites at which the Rat River Dolly Vardenare fished (Fig. 1). The question remainsas to the size of the Vittrekwa stock and it'scontribution, if any, to the fishery. TheVittrekwa stock appears to be small, incomparison to the Rat River stock. Adult,juvenile and young-of-the-year DollyVarden have been captured in the Vittrekwaduring fall surveys, indicating spawning

does take place within the basin (S.Stephenson, unpubl. data).

Fort McPherson residents also report thepresence of Dolly Varden in the Road andTrail rivers, upstream of the Vittrekwa River(Fig. 1). Limited available information onthese stocks suggests that, depending on thedegree of anadromy, individuals from thesestocks may be harvested during theirmigrations past Aklavik and along HuskyChannel. If the Vittrekwa and other stockscontribute substantially to the Dolly Vardenfisheries in the Mackenzie River delta, thenestimates of the harvest from the Rat Riverstock are probably high.

The proportion (50%) of the catch at ShinglePoint which is assigned to the Rat Riverstock is likely an overestimate, given therelatively few Rat River tag returns in theShingle Point fishery. This overestimate isnot likely to be consequential in terms ofestimating the size of the harvest, however,as 50% of the harvest at Shingle Point issmall, averaging only 120 per year (1990-1999, Table 1).

Biological data collected from fish harvestedprior to establishment of the expanded andstandardized monitoring program in 1995,are useful but must be interpreted withcaution. Only one site was studied, incontrast to five sites in 1995-2000, and themonitor did not receive detailed instructionon assessing sex and maturity of the catch.

Harvest data from the 1970’s may beincomplete, as sources and accuracy couldnot be evaluated.

OutlookThe outlook for the stock appears to befavourable, given further careful monitoringof the fishery and the harvest; periodicestimation of stock size; and compliancewith the community-based and self-imposed

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fishing restrictions. The timing of the runand condition of the fish vary considerablybetween years, and are closely tied to theenvironment.

Management Considerations

The Rat River Char Fishing Plan 2000(Aklavik RRC et al. 2000) is the mostimportant and specific managementinitiative in place at the present time for RatRiver Dolly Varden and was endorsed bythe RAP meeting participants. The RatRiver Char Working Group consists of fivefishers from each of the Aklavik RRC, theFort McPherson RRC and the Aklavik HTC,two representatives from DFO, one memberfrom the FJMC and one from the GRRB.The Group meets annually to update andratify the fishing Plan for the year.

The upper reaches of the Rat River, whichinclude the critical spawning and over-wintering sites for the Dolly Varden stock,are within the boundaries of the privatelands of the Gwich’in established under theGwich’in Final Agreement (Gwich’in andINAC 1992). The Gwich’in LandAdministration is responsible foradministration of these private lands.

The lower Mackenzie River and coastalwaters used by Rat River Dolly Varden arelocated within the Inuvialuit SettlementRegion (ISR; Fig. 1). The EnvironmentalImpact Screening Committee and theEnvironmental Impact Review Board,established under the Inuvialuit FinalAgreement (1984), are responsible forscreening and review of any developmentactivity on crown lands within the ISR thatmay have detrimental effects on theresources or their habitat.

Management of this fishery is complicatedby not knowing the relative contribution of

other stocks upstream of the Rat River (e.g.,Vittrekwa, Road and Trail rivers).

Other ConsiderationsInfectious pancreatic necrosis virus isendemic in the Dolly Varden of the RatRiver (Souter et al. 1984, 1986). This is adisease that only affects fish. Mortality ofyoung fish is high and survivors can becomelifelong carriers. The virus can betransferred from fish to fish by infectedindividuals excreting the virus into thewater, and also through the eggs and spermof infected adults to their offspring. Oncethe virus is present in a water system in thewild, eradication is impossible. Theprevention of the introduction of diseased orcarrier fish into non-infected watershedsremains the best control method for this andother fish pathogens. Periodic assessment ofdiseases in wild fish stocks, such as the RatRiver Dolly Varden, is important to considerin the future (O. Nielsen, pers. comm.).

Other potential impacts such ascontaminants and parasite loads on thesefish have never been studied. Arcticlamprey and seals may be a significantsource of mortality for juvenile sea-runDolly Varden (primarily smolts) (S.Sandstrom, pers. comm.).

Habitat alteration and/or degradation of thespawning and over-wintering sites on FishCreek are the major threats faced by thisstock of Dolly Varden. Any developmentactivity (e.g., roads, right-of-ways) whichwould diminish the integrity or physicalcharacteristics (water level, oxygen level,silt loads, temperature, pH) of the spawningand over-wintering area, could pose a threatto developing embryos, rearing juvenilesand/or spawning and over-wintering adultsfound in these areas. The integrity of thewatershed must be maintained.

Central and Arctic Rat River Dolly Varden

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More pervasive threats, such as climatechange and/or increased incident ultravioletradiation resulting from ozone depletion,may affect the fish and their habitat, but thedetails of this are not understood at thepresent time.

For more Information:

Contact: Lois HarwoodDepartment of Fisheries andOceansBox 1871Inuvik, NT CanadaX0E 0T0

Tel: 867-777-7505Fax: 867-777-7501E-Mail:harwoodl@dfo-mpo.gc.ca

References

Aklavik RRC, Fort McPherson RRC andAklavik HTC. 2000. Rat River CharFishing Plan. Available: Departmentof Fisheries and Oceans, Box 1871,Inuvik, NT Canada, X0E 0T0.

Anderson, R.O. and S.J. Gutreuter. 1983.Length, weight and associated structuralindices. Pp 283-300. In: FisheriesTechniques, Nielsen, L.A. and D. L.Johnson, eds. American FisheriesSociety, Bethesda, Maryland.

Babaluk, J.A., J.D. Reist, V.A. Sahanatien,N.M. Halden, J.L. Campbell and W.J.Teesdale. 1998. Preliminary results ofstock discrimination of chars in IvvavikNational Park, Yukon Territory,Canada, using microchemistry of otolithstrontium. Pp. 992-998, In Munro,N.W.P; Willison, J.H.M. [eds.] 1998.Linking Protected Areas with WorkingLandscapes Conserving Biodiversity,proceedings of the third international

conference on science and managementof protected areas, 12-16 May 1997.Wolfville, Canada: SAMPAA.

Behnke, R.J. 1980. A systematic review ofthe genus Salvelinus. Pp. 441-481, InE.K. Balon (ed.), Chars, Salmonidfishes of the genus Salvelinus, Dr. W.Junk, The Hague.

Clark, I.D., B. Lauriol, L. Harwood and M.Marschner. 2001. Groundwatercontributions to discharge in apermafrost setting, Big Fish River,N.W.T., Canada. Arctic, Antarctic andAlpine Research, vol. 33, No. 1, pp.62-69.

DeCicco, A. 1989. Movements and spawningof adult Dolly Varden charr (S. malma)in Chukchi Sea drainages ofnorthwestern Alaska: evidence forsummer and fall spawning populations.Physiol. Ecol. Japan. Spec. Vol. 1: 229-238.

Dutil, J. D. 1986. Energetic constraints andspawning interval in the anadromousArctic char (Salvelinus alpinus). Copeia4: 945-955.

Gillman, D.V. and P.D. Sparling. 1985.Biological data on Arctic char,Salvelinus alpinus (L.)., from the RatRiver, Northwest Territories, 1983.Canadian Data Report Fisheries andAquatic Sciences 535: iv + 15p.

Gwich’in and INAC. 1992. Gwich’inComprehensive Land ClaimAgreement. Gwich’in Tribal Counciland Indian and Northern AffairsCanada. Vol. I and II.

GRRB (1997). Gwich’in words about theland. Prepared by the Gwich’inRenewable Resources Board (GRRB),

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Box 2240, Inuvik, NT Canada X0E0T0. 212p.

Harwood, L. A. 2001. Status ofanadromous Dolly Varden (Salvelinusmalma) of the Rat River, NorthwestTerritories, as assessed throughcommunity-based sampling of thesubsistence fishery, August-September1989-2000. Canadian StockAssessment Secretariat ResearchDocument 2001/090. Department ofFisheries and Oceans Canada, Ottawa,Canada.

IFA (Inuvialuit Final Agreement). 1984.The Inuvialuit Final Agreement,Department of Indian and NorthernAffairs, Ottawa, Ontario Canada.

Inuvialuit Harvest Study. 1999.Unpublished annual reports of theInuvialuit Harvest Study, 1986-1998.Prepared by Joint Secretariat, Box 2120,Inuvik, NT Canada. X0E 0T0.

Jessop, C.S., T.R. Porter, M. Blouw, and R.Sopuck. 1973. Fish resources of theMackenzie River Valley: an intensivestudy of the fish resources of twomainstream tributaries. Canada TaskForce on Northern Oil Development,Environmental-Social ProgramNorthern Pipelines. 198 p.

Lowe, R. 1984. Uummarmiut Uqalungihamumikhitchirutingit. Basicuummarmiut Eskimo Dictionary.Prepared by Committee for OriginalPeoples Entitlement, Inuvik, NT,Canada, X0E 0T0. 262p.

MacDonald, I. 1998a. Gwich’in HarvestStudy Data Report, August 1995-December 1996. Prepared by theGwich’in Renewable Resources Board,

Box 2240, Inuvik, NT Canada X0E0T0.

MacDonald, I. 1998b. Gwich’in HarvestStudy Data Report, 1997. Prepared bythe Gwich’in Renewable ResourcesBoard, Box 2240, Inuvik, NT CanadaX0E 0T0.

McCart, P. J. 1980. A review of thesystematics and ecology of Arctic char,Salvelinus alpinus, in the westernArctic. Canadian Technical Report ofFisheries and Aquatic Sciences 935:vii+89p.

McPhail, J.D. 1961. A systematic study ofthe Salvelinus alpinus complex in NorthAmerica. Journal of Fisheries ResearchBoard of Canada 18:793-816.

Reist, J. D. 1989. Genetic structuring ofallopatric populations and sympatric lifehistory types of char, Savelinusalpinus/malma, in the western Arctic,Canada. p 405-420. In Kawanabe, H.,F. Yamazaki and D.L.G. Noakes, eds,Biology of chars and masu salmon:proceedings of the InternationalSymposium on chars and Masu Salmon.Physiol. Ecol. Japan, Spec. Vol. 1.

Reist, J.D. 2001. Taxanomic issues, lifehistory and stock discrimination - RatRiver Dolly Varden. Canadian StockAssessment Secretariat ResearchDocument 2001/091. Department ofFisheries and Oceans Canada, Ottawa,Canada.

Reist, J.D., J.D. Johnson and T.J. Carmichael.1997. Variation and specific identity ofchar from northwestern Arctic Canadaand Alaska. American Fisheries SocietySymposium 19: 250-261.

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Sandstrom, S.J., P.J. Lemieux, and J.D.Reist. 1997. Enumeration andbiological data from the upstreammigration of Dolly Varden char(Salvelinus malma) (W.) from theBabbage River, Yukon North Slope,1990 to 1992. Canadian Data Reportof Fisheries and Aquatic Science 1018:iv + 132.

Sandstrom, S.J., C.B. Chetkiewicz and L. A.Harwood. 2001. Overwintering habitatof juvenile Dolly Varden char(Salvelinus malma) in the Rat River,NT, as determined by radio telemetry.Canadian Stock Assessment SecretariatResearch Document 2001/092.Department of Fisheries and OceansCanada, Ottawa, Canada.

Souter, B.W., A.G. Dwilow, K. Knight, T.Yamamoto. 1984. Infectiouspancreatic necrosis virus: isolation forasymptomatic wild arctic char(Salvelinus alpinus L.). Journal ofWildlife Diseases 20(4): 338-339.

Souter, B.W., A.G. Dwilow, K. Knight andT. Yamamoto. 1986. Infectionspancreatic necrosis virus in adult Arcticchar, Salvelinus alpinus (L.), in rivers inthe Mackenzie Delta region and YukonTerritory. Canadian Technical ReportFisheries and Aquatic Sciences: 1414:iv + 11p.

Sparling, P.J. and D.B. Stewart. 1986.Data from the monitoring ofdomestic/commercial fisheries forArctic char in the Big Fish River andRat River areas, Northwest Territories,1986. Fisheries Joint ManagementCommittee Report No. 86-002. 28 p.Available: FJMC, Box 2120, Inuvik,NT, Canada. Prepared by ArcticBiological Consultants, Pinawa, MB.

Stephenson, T. and P. J. Lemieux. 1990.Status of the Rat River char population,1989. Fisheries Joint ManagementCommittee (FJMC) Report No. 89-008.62 p. Available: FJMC, Box 2120,Inuvik, NT, Canada. Prepared byDepartment of Fisheries and Oceans,Box 1871, Inuvik, NT Canada.

Personal Communications

Arey, B., GRRB, Inuvik, NTBabaluk, J., DFO, Winnipeg, MB.Carmichael, J., Aklavik, NT.Francis, J., Fort McPherson, NT.Harwood, L., DFO, Inuvik, NT.Mitchell, B., Aklavik, NT.Nielsen, O., DFO, Winnipeg, MB.Reist, J., DFO, Winnipeg, MB.Sandstrom, S., Bracebridge, ON.Stephenson, S., DFO, Inuvik, NT.

This report is available:Freshwater Institutec/o Larry DueckCentral and Arctic Region501 University CrescentWinnipeg, Manitoba R3T 2N6Tel: (204) 983-7795Fax: (204) 984-2403dueckl@dfo-mpo.gc.cawww.dfo-mpo.gc.ca/csas

ISSN 1480-4913 (for English series)ISSN 1480-4921 (for French series)

La version française est disponible àl’adresse ci-dessus.

Correct citation for this publication

DFO, 2001. Rat River Dolly Varden. DFOScience Stock Status Report D5-61(2001).