Yellowtail Rockfish, Sebastes flavidus,Length and Age Composition OffCalifornia, Oregon, and Washington in 1977

JL C'ijkl

Pikl)=1

-PiJ 3 LL L L C'ijkl

)=1 k=1 1=1

MICHAEL E. FRAIDENBURG

Introduction

Yellowtail rockfish, Sebastes flav­idus, is a significant component of theshelf rockfish complex living on thePacific coast continental shelf. Al­though living in depths of 0-300fathoms (0-550 m) (Hart, 1973), thisspecies is most abundant in the 50- 100fathom (91-183 m) depth zone (Alver­son et aI., 1964; Gunderson and Sam­ple, 1980) where it is associated withcanary roclefi sh, S. pinniger , and silver­gray rockfish, S. brevispinis. Thespecies range extends from San Diego,Calif., to Kodiak fsland, Alaska (Hart,1973), but its center of abundance isfrom Oregon to British Columbia (Al­verson et aI., 1964; Westrheim, 1970).Landings in this region by NorthAmerican trawlers have ranged fromapproximately 1,600 to 5,000 t annu­ally (Fraidenburg et aI., 1977).

In the 1977 survey of rockfishes, yel­lowtail rockfish were most abundant offnorthern Oregon and Washington and97.2 percent of the biomass present wasat depths less than 100 fathoms (183m). Because yellowtail rockfish are an

Michael E. Fraidenburg is with the WashingtonState Department of Fisheries, 115 General Ad­ministration Bldg., Olympia, WA 98504.

ABSTRACT-Yellowtail rockfish, Sebas­tes flavidus, length and age samples from a1977 survey of rockfishes off California,Oregon, and Washington were analyzed toproduce length and age composition datafor the area from lat. 35°30' to 48°30'.N.There was evidence ofa north to south clineofdecreasing size and age. Length composi­tion data showed strong single modes formales and many modes over a broader size

54

abundant and commercially importantspecies in the rockfish survey area, itwas designated as a target species forcollection of length and age composi­tion data. To date, the only publisheddata on length or age composition of thestocks or from the fishery in this areaare in Alverson et al. (1964).

Methods

Weighted length compositions wereobtained by first calculating the numberof fish caught per kilometer by size andsex (C :jkl):

Sijkl . CijC'ijkl = --"'--"---"---

3 L

L L Sijklk=1 1=1

where C. = total number of fishIJcaught, s = number of fish sampled, i= stratum, j = station, k = sex (I =

male, 2 = female, and 3 = unsexed), l= length group, L = number of lengthgroups, and km = kilometers towed.

These C 'ijkl val ues were thensummed over all hauls in a stratumand expaJ.1ded to the total estimated pop­ulation (P) to obtain the estimated pop­ulation size for each size and sex group(Pik/):

range for females. Age composition datashowed two prominenr modes ar 8-10 and/3-/4 years old. No major differences in rheage-length relationship were noted betweenareas using data from rhe survey and datafrom market samples from Washington'strawl fishery. Data for all areas werepooled to fit a common growth curve for rhenorthern California ro Queen CharlotteSound, British Columbia, region.

where J = number of stations for whichlength frequency data are available.

These length data were then used toexamine the need for geographic andbathymetric stratification.

Otoliths were aged by the Washing­ton Department of Fisheries usingaging criteria developed by Kimuraet al. (1979). Age compositions werecalculated in each stratum bydecomposing the weighted length fre­quencies into age compositions utiliz­ing an age-length key developed fromthe age samples collected during thesurvey.

Results

A total of 2,288 length measure­ments and 1,321 usable otolith readingswere available from the survey. Lengthsamples were collected from lat. 35°30'to 48°30'N and age samples from lat.40°26' to 400 30'N (Fig. 1).

For each sex, length compositionswere examined by a variety of geo­graphic areas and by depth as indicatorsfor data stratification. No substantialdifferences in length composition wereobserved by depth, but differencesamong areas were present. Based onthis analysis, all depths were com­bined, and fi ve separate geographicareas (Fig. I) were selected as strata(areas) for presenting length and agecomposition results.

Length compositions (Fig. 2)showed strong modes in all areas.Males showed particularly strongsingle modes and a cline of generallydecreasing mean length and increasingproportion of fish less than 45 cm fromnorth to south. Females had a largermean size than males in each area and,rather than strong single modes, hadmany modes over a broader size range.A cline similar to that observed formales was not evident. A cline may

Marine Fisheries Review

35" 30' N---------,

FEMALE

I· 49.4n' 98

L' 44.9n' 313

;

15

1w 10 L • 43.5

.5 0'106 M• 0 O~IO--''''~lJ~.,--C9J;c,:-;''';:-;;;70~'''-'''~'OO

LEN G T H (CMI

MALE

n:I_~~:~i: ~:I a:LO a: 10.~ w~ Q. 5 Q. 5

~ 0 O,!--;-;~-=-:;;'L-,;:-~;;:-;;;:-;;;~o 10 00 :IJ o()L CJN fe T ~ (8]) !:ll 100 0 10 00 :IJ o()L CJN ff T~ (~) ':I) 100

WASHINGTON

OREGON

CALIFORNIA

L ~ 320

A "'" 257

L = 321A-O

L - 384A-O

40" 26' N-----{

46° 44' N L = 775

45" 50' N A - 658

4]0 30' N----\

La!. 48° 30' N----~

Figure 2.-Size composition of yellowtail rockfish by area and sex.

AGE

fEl1ALES

60

.• OJOJ

. .ffi OJ

I!I. 47"30'-48°30'N(!) 45° 50' - 46°44' Nl!J 40 0 26'-45°49'N

• ~ ffi I!lI!l

III

eOJ

OJ I!l

40 @I

SO MALES

3OS'------:,'='0---------:''='5-------:20

50

50

40

Figure 3.-Mean length at age foryellowtail rockfish by area and sex.

3OS~-----;'';;"0 -----:''''''5-------:20

age-length key by sex for decomposinglength frequencies into age com­positions.

Coastwide age compositions (Fig. 4)show two prominent modes at 8-LO and13-14 years. For males there is a clineof increasing importance of the 8- tolO-year-old fish from north to southcorresponding to the cline observed inlength composition data. A demarca­tion line is evident at lat. 40050'Nwhere 13- to 14-year-old males weremost important to the north and 8- to9-year-olds most important to the south.For females, a cl ine or demarcation lineis not evident, and excepting the areafrom lat. 46°44 I to 47~9'N, 8- to LO­year-old fish were most importantcoastwide.

Growth was estimated by combiningrockfish survey data with market sam­pling data from Washington's trawlfishery for yellowtail rockfish. The de­tails of this analysis are being describedby Fraidenburg (in prep.). From thisanalysis, homogeneous growth was ob­served in the northern California toQueen Charlotte Sound, British Co­lumbia, region. A total of 4,211 age­length observations were available for

Figure I.-Areas chosen foranalysisof length and age composition of yel­lowtail rockfish. L = number oflength observations in an area and A= number of otolith readings avail­able in an area.

exist, but low female sample sizes inthis study may have obscured such atrend. More data would be desirable forboth sexes and future studies of size andage composition should be designed toexamine north-south clines in more de­tail. Sex ratios varied from 74 percentto 56 percent male, with no obviouslatitudinal trend (Fig. 2).

The sex ratio data may suggest that aportion of older females were not avail­able to the survey. The lack of excep­tionally large fish (Fig. 2) may alsosuggest this because the record size isreported to be about 66 cm (Hart,1973).

Prior to construction of the age­length key used for calculating agecompositions, mean length at age datafrom three areas (lat. 40°26' to 45°49',45°50' to 46°44', and 4r30 ' to48°30 'N) were examined for geograph­ic differences. These data (Fig. 3) didnot show any important differences thatwere consistent among areas, so thedata were pooled to produce a single

March-April 1980 55

"-,,.-"0

55

50

] .5

1·0~

35 0 ~

30

Figure 5.-Yellowtail rockfish meanlength at age and calculated growthcurves by sex. Survey and marketsampling data combined.

Kimura, D. K., R. R. Mandapat, and S. L. Ox­ford. 1979. Method, validity, and variability inthe age determination of yellowtail rockfish(Sesbastes j1avidus), using otoliths. J. Fish.Res. Board Can. 36:377-383.

Phillips, 1. B. 1964. Life history studies on tenspecies of rockfish (genus Sebastodes). Calif.Dep. Fish Game, Fish Bull. 126,70 p.

Six, L. D., and H. F. Horton, 1977, Analysis ofage detennination methods for yellowtailrockfish, canary rockfish, and black rockfishoff Oregon, Fish. Bull., U.S. 75:405-414.

Westrheim, S, J. 1970. Survey of rockfishes,especially Pacific ocean perch, in the northeastPacific Ocean, 1963-66. 1. Fish. Res. BoardCan. 27: 1781-1809.

____, and W. R. Harling, 1975. Age­length relationships for 26 scorpaenids in thenortheast Pacific Ocean. Environ. Can., Fish.Mar. Serv., Tech. Rep. 565, 12 p.

to 15 20AGE (years)

Table 1.-Mean and calculated lork length at age loryellowtail rockfish, and least squares estimates 01 vonBertatanffy growth parameters.

Male Female

Cal· Cal-cu- cu·

Age Mean n lated Mean n lated

5 34.38 13 32.45 32.86 22 31.946 34.95 19 35.58 34.69 26 35.497 37.35 65 38.12 37.34 53 38.508 40.26 198 40.18 41.48 128 41.079 41.83 193 41.85 43.59 160 43.24

10 43.11 167 43.20 45.37 128 45.0911 44.43 198 44.31 46.47 117 46.6612 45.29 278 45.20 47.63 128 48.0013 46.06 366 4592 49.31 203 49.1314 46.43 350 46.51 50.12 230 50.1015 46.98 278 46.99 50.51 150 509216 47.22 219 47.38 51.76 102 51.6117 47.59 153 47.69 52.73 44 52.2018 48.00 114 47.94 54.16 19 52.7019 48.35 40 48.15 52.20 10 53.1320 48.42 19 48.32 53.00 5 53.4921 49.12 8 48.45 50.50 222 47.67 6 48.57

Lx to Lx k to

Est. 49.04 0209 -0.185 55.54 0.163 -0.250SD 0.27 0.012 0386 092 0.016 0.549

25

Literature Cited

Alverson, D. L., A. T. Proter, and L. L. Ronholt.1964, A study of demersal fishes and fisheriesof the northeastern Pacific Ocean. H.R. Mac­Millan Lectures in Fisheries,lnst. Fish" Univ.Brit. Columbia, Vancouver, 190 p.

Dixon, W. J. 1976. Biomedical computer pro­grams. Univ. Calif. Press, Los Angeles, 738 p.

Fraidenburg, M., J. E. Smith, W. H, Barss, andT. Jow, 1977, Minimum estimates of the allnalion removals, North American trawl speciescomposition and CPU E for' 'other rockfish" inthe northeastern Pacific Ocean. Wash, Dep.Fish., Tech. Rep. 34,31 p.

Gunderson, D. R., and T. M. Sample. 1980.Distribution and abundance of rockfish offWashington, Oregon, and California during1977. Mar. Fish. Rev. 42(3-4):2-16.

Hart, J. L. 1973. Pacific fishes of Canada. Fish.Res. Board Can., Bull 180,740 p.

(1977), however, was observed to fit apower function better than a von Ber­talanffy and this observation was attrib­uted to a lack of young fish in thesamples, It is also possible this couldhave resulted from low sample size ingeneral and/or a tendency to under-ageold fish,

2525

>-- 20 >-- 20 >-- 20

iii 15 iii 15 iii 15u u uffi 10 ffi 10 ffi 10CL

5CL

5CL

5

04;---"'--'--'7,10~LLJ--!l--f6--Lt"-"" 047-'~--'--7*-,--LL--'-7;!-,,~---":, 04;---"'--'--'+.10~LLJ--!1--f6-=-;o;2'2

AGE (YR) AGE (YR)

25[ 25 251

~20 rrr~~20 >--20~g~~ rl I g~~ g~~CL 5 £ CL 5 CL 5

04 10 16 22 °4~..L.L-'+.t-'-.LL-'+.o!==----;;22 04 10 16 22AGE (YR) AGE (YR)

~;~ ~~~ g~~L'_ffi 10 ffi 10 ffi 10CL5 CL 5 CL5

04~..L.L-'--!o(--,-LU-+,f~"-;o;, 04 22 04 10 16 22

AGE (YR) AGE (YR) AGE (YR)

Figure 4,-Age composition of yellowtail rockfish by area and sex,

'Daniel K. Kimura, Fisheries Biometrician,Washington State Department of Fisheries, M-IFisheries Center, University of Washington,Seattle, WA 98195, pers. commun.

growth studies, Kimura l has describeda procedure and provided an examplefor calculating von Bertalanffy growthparameters using the general purposenonlinear least squares computer pro­gram BMD 07R available in Dixon(1976), This approach was used here toestimate the growth parameters for yel­lowtail rockfish from the data in Table Iand Figure 5, Only mean length at agedata based on fi ve or more observationswere used for these calculations,

A comparison of the results obtainedfrom these data with those of previousworkers is presented in Fraidenburg (inprep,), The parameters presented herecompared well with von Bertalanffy es­timates by other authors (Westrheimand Harling, 1975 and Phillips, 1964),Growth reported by Six and Horton

56 Marine Fisheries Review