Possible biological relationships of cod (Gadus morhua) with other important commercial
fishes are explored. Cod year-class variations are compared with variations of yellowtail
flounder and American plaice spawning biomass, mackerel age 1+ group abundance, and
redfish densities. The adult fish biomass of these species are considered as an index of their
egg and larval abundances. Possible competitive and predator-prey relationships between
the 0-age groups and young individuals of cod and these species are examined through
correlation analyses. No significant relationships between cod and redfish and yellowtail
flounder were found. It seems that mackerel is a predator on cod larvae. A positive high
correlation between spawning American plaice biomass and cod year-class strength was
found. High American plaice spawning biomass may promote high cod recruitment through
a predator-prey interaction. Alternatively, both species may respond similarly to an
environmental signal

Larrañeta, M.G. (Manuel Gómez)

Paz, X. (Xabier)

English

Repositorio Institucional Digital del IEO

J. Northw. Atl. Fish. Sci., Vol. 14: 129–134Cod Year-class Variations and Abundance of OtherCommercial Fish in NAFO Divisions 3NOJ. PazInstituto Español de Oceanografia, Centro Costero de VigoCabo Estay - Canido, Apartado 1.552, 36080, Vigo, Spainand M. G. LarrañetaInstituto de Investigaciones Marinas, Eduardo Cabello 6,36208 Vigo, SpainAbstractPossible biological relationships of cod (Gadus morhua)  with other important commer-cial fishes are explored.  Cod year-class variations are compared with variations of yellowtailflounder and American plaice spawning biomass, mackerel age 1+ group abundance, andredfish densities.  The adult fish biomass of these species are considered as an index of theiregg and larval abundances.  Possible competitive and predator-prey relationships betweenthe 0-age groups and young individuals of cod and these species are examined throughcorrelation analyses.  No significant relationships between cod and redfish and yellowtailflounder were found.  It seems that mackerel is a predator on cod larvae.  A positive highcorrelation between spawning American plaice biomass and cod year-class strength wasfound.  High American plaice spawning biomass may promote high cod recruitment througha predator-prey interaction.  Alternatively, both species may respond similarly to anenvironmental signal.IntroductionPhysical environmental factors, especially long-term changes, govern the biotic fluctuations of eco-systems, but how these fluctuations affect indi-vidual species is still not clear.  It can be expectedthat the immediate factors in the dynamics of aspecies are essentially biological through trophicinteractions, and that physical factors are second-ary.  Perhaps multispecies models have the defectof limiting themselves to trophic relationships, ig-noring the fact that these depend, at least in thelong-term, on physical environmental factors.In this context, cod (Gadus morhua) year-classvariations were compared with variations of adultbiomass of yellowtail flounder (Limanda ferruginea)and American plaice (Hippoglossoides plates-soides), mackerel (Scomber scombrus) age 1+group abundances, and redfish (Sebastes sp.) den-sities to examine potential biotic interactions atdifferent life history stages.  Adults of these spe-cies, except mackerel, are not considered to bepredators of eggs and larvae of cod.  The egg andlarval abundance of these is considered to be di-rectly related to their adult biomass.  However,there may be competition and predator-prey rela-tionships between the 0-age groups and youngindividuals of cod and American plaice, yellowtailflounder and redfish.  It was expected that the signof correlations will indicate the possible nature ofthose relationships.Materials and MethodsThe possibility of trophic relationships between0-age groups and juveniles of cod and other spe-cies was explored relating cod year-class size tothe biomass of other species, from 1 to 3 yearsbefore (negative lag) and after (positive lag) theyear of the cod year-class.  Using regression analy-sis, the relationships were explored for the codyear-class in relation to spawning biomass whichgave rise to it, and to the cod spawning biomasslagged from 1 to 3 years before or after.  The codyear-class size was measured at time of recruitmentaccording to a virtual population analysis in theusual practice, at three years of age (N3).   The codrecruitment (N3) and spawning biomass (B6+) data(Table 1) were taken from Baird and Bishop (MS1989). Correlations coefficients were calculated be-tween cod year-class variations and the fluctua-tions of other species:a) redfish densities,b) yellowtail flounder spawning biomass,c) mackerel biomass,d) American plaice spawning biomass.130 J. Northw. Atl. Fish. Sci., Vol. 14, 1992TABLE 1. Cod Div. 3NO:   recruitment (N3) and spawn-ing biomass (B6+).  (From Baird and  Bishop,MS 1989). Recruits BiomassYear-class (103) (´000 tons)    1956 5 368 –1957 5 309 –1958 8 214 –1959 10 776 8 8401960 7 825 7 2341961 11 238 8 9741962 16 252 8 0321963 20 999 8 7871964 18 324 11 2641965 10 050 12 0511966 12 785 10 4621967 8 032 9 3441968 8 442 8 2681969 6 211 8 0261970 3 502 8 1371971 3 654 8 8191972 2 283 7 8121973 2 714 7 6181974 4 536 5 3731975 4 258 1 9291976 1 807 1 2331977 2 078 1 6551978 2 921 1 9481979 2 306 2 6281980 3 549 5 7131981 5 079 8 8301982 4 716 9 1521983 952 10 0041984 1 000 9 5561985 3 300 10 3051986 – 11 0691987 – 10 9901988 – 9 120class, that is to say, three years before recruitment(N3).ResultsCorrelations between cod recruitment and itsspawning biomass are shown in Table 6.  The coef-ficients appeared to be slightly significant for 0 to+2 year lags.Correlation coefficients between cod year-classsize and redfish abundance are shown in Table 7,none were significant.  Also, none of the correlationcoefficients between cod recruitment and yellowtailflounder spawning biomass (Table 8) were signifi-cant.  On the other hand, correlation coefficientsbetween cod recruitment and mackerel abundance(Table 9) were negative and slightly significant for 0to –3 year lags, and between cod recruitment andAmerican plaice spawning biomass they were posi-tive and strongly significant (Table 10) with lagtimes of 0, +1, +2 and +3 years.  The two highestcorrelation coefficients for the relationship betweencod year-class size and American plaice spawningbiomass were for lags of 0 and +3 years.  Regres-sion analyses for these years are given in Fig. 1 andFig. 2, respectively, and the regression coefficientsfor these cases were the following:lag a b  0 –586.76  0.06624  3  –3352.1                0.13276The yellowtail flounder spawning biomass datawere obtained from the sequential population analy-sis using a short-term average partial recruitment(1982–86) and a terminal F of 0.9 reported by Brodieand Walsh (MS 1987).  The American plaice spawn-ing biomasses (B11+) were taken from Brodie (MS1988).  The redfish abundances were taken fromPower and Atkinson (MS 1987), where a multiplica-tive model was used to derive catch rates in NAFODiv. 3LN during 1959–86, and the values used werethe mean abundances calculated from three con-secutive years.  Finally, the mackerel biomasses(B1+) were taken from Anon. (1986) which referredto the Labrador-North Carolina area.  All these dataare shown in Tables 2–5.When a 0 year lag time was used, the year-classof recruitment related to the spawning biomass ofthe species in the same year as that of the cod year-TABLE  2. Yellowtail flounder Div. 3LNO: spawning stockbiomass (B6+).  (From tables 23 and 24 of Brodieand Walsh, MS 1987).Table  23 Table  24Year  (tons)  (tons)1968 25 926 25 9261969 40 372 40 3721970 50 199 50 1991971 48 747 48 7471972 33 846 33 8461973 24 049 24 0491974 21 034 21 0341975 18 159 18 1591976 19 152 19 1521977 18 809 18 8091978 21 776 21 7761979 17 413 17 4121980 26 322 26 3221981 20 350 20 3371982 16 838 16 6421983 30 565 28 8941984 53 811 47 4481985 63 087 50 5501986 39 536 23 722PAZ and  LARRAÑETA:  Cod Year-class Variations and Abundance of Other Fish in Div. 3NO 131TABLE  3. Redfish Div.  3LN:     average   catch  rate   ofthree years.     (From figure  3  of  Power andAtkinson,  MS 1987).Middle  year Catch rate1960 1.151961 1.211962 1.281963 1.251964 1.041965 1.111966 1.081967 1.061968 0.891969 0.901970 1.011971 1.041972 1.061973 1.151974 1.181975 1.131976 1.021977 0.921978 0.981979 1.111980 1.251981 1.331982 1.331983 1.25TABLE 4. Mackerel Labrador-North Carolina: populationbiomass (B1+).   (From  figure 19.1, Anon., 1986).BiomassYear  (´000 tons)1963 2751964 3111965 3231966 3711967 6231968 1 1981969 1 5331970 1 8561971 1 8681972 1 6531973 1 3891974 1 1261975 9701976 7191977 4911978 4671979 5031980 4671981 4791982 5991983 6951984 1,078TABLE  5. American plaice Div. 3LNO: spawning stockbiomass (B11+).   (From Brodie, MS 1988).BiomassYear  (´000 tons)1965 138 1971966 158 7561967 157 3251968 138 8371969 120 2381970 94 3781971 81 4031972 62 1291973 52 6191974 50 8891975 45 9061976 39 8641977 45 5151978 48 8181979 60 8461980 67 1251981 53 2781982 46 8521983 42 2941984 46 0901985 56 3571986 43 383A multiple regression was also calculated, where X1was the American plaice spawning biomass with a 0year lag, and X2 the American plaice biomass witha +3 year lag.  The resulting expression was Y = –1.4714 + 0.0392X1 + 0.0492X2, and the correlationcoefficient 0.911.DiscussionThe relationship between cod recruitment andits spawning biomass (Table 6) corresponds to thecomplex problem of the stock-recruitment question,which is not the object of this study.  These correla-tions were made to simply follow the same methodas in the case of the other species abundance.Nevertheless, the absence of negative correlationswith negative lags (cod spawning biomass beforethe year-class) indicated that cannibalism did notdetermine year-class size.  Koslow et al. (1987)have found that in NAFO Div. 3NO areas the highestcod recruitments are obtained from the lowest eggdensities.There was no significant relationship betweenredfish and yellowtail flounder abundances, andcod year-class size.  On the one hand, a negative132 J. Northw. Atl. Fish. Sci., Vol. 14, 1992TABLE  6. Correlations between cod year-class sizes (N3)  and cod spawningstock biomass.Lag –3 –2 –1 0 1 2 3n = 24 25 26 27 28 29 30r = 0.296 0.344 0.393 0.441 0.463 0.452 0.389p = 0.162 0.930 0.046 0.020 0.012 0.013 0.033TABLE  7. Correlations between cod year-class sizes (N3) and redfish catchrates.Lag –3 –2 –1 0 1 2 3n  = 23 24 24 24  24 24 24r   = 0.219 0.229 0.303 0.179 2 E-4 -0.199 -0.308p = 0.319 0.284 0.152 0.406 0.999 0.355 0.145TABLE  8. Correlations between cod year-class sizes (N3) and yellowtailflounder spawning stock biomass (B6+).Lag –3 –2 –1 0 1 2 3n = 15 16 17 18 19 20 20r = 0.099 0.120 0.028 0.115 –0.087 0.148 0.434p = 0.740 0.663 0.915 0.656 0.726 0.552 0.063TABLE  9. Correlations between cod year-class sizes (N3) and mackerelstock biomass.Lag –3 –2 –1 0 1 2 3n = 20 21 22 22 22 22 22r = –0.408 –0.444 –0.439 –0.421 –0.373 –0.246 –0.074p = 0.074 0.043 0.040 0.050 0.087 0.275 0.748TABLE  10. Correlations between cod year-class sizes (N3) and Americanplaice spawning stock biomass.Lag –3 –2 –1 0 1 2 3n = 18 19 20 21 22 22 22r = 0.470 0.693 0.774 0.876 0.830 0.863 0.940p = 0.480 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001et al. (1987), several authors have noted the influ-ence of mackerel abundance on Gadidae and her-ring recruitment in areas from Georges Bank to theGulf of Saint Lawrence, and these had been attrib-uted to predation by mackerel.  In contrast, Báezand Larrañeta (MS 1987) have found that silver hake(Merluccius bilinearis) year-class sizes on theScotian Shelf are positively correlated with mack-erel biomasses, suggesting predation on mackerel0-age group by silver hake 0-age group.correlation between mackerel and cod abundancesuggested that mackerel preyed on cod.  It isknown that adult mackerel prey on planktonic stagesof other fishes.  These correlations extended also to+1 and +2 year lags (Table 9), but predation bymackerel on 1 and 2 year age groups of cod seemedvery unlikely because of the large size of the prey.It is more reasonable to think that mackerel abun-dance will remain similar during the following 2years to that of the 0 lag year.  According to KoslowPAZ and  LARRAÑETA:  Cod Year-class Variations and Abundance of Other Fish in Div. 3NO 13320010050           100 150656667686970717273747576 777879808182 838485American plaice biomass ( 0 year lag)              Cod recruitsCod year-classesReduction = 55%20010050           100 150American plaice biomass (+3 year lag)Cod recruits62636465666768697071727374 757677787980818283Cod year-classesReduce 55%Fig. 1. Relationship between American plaice spawningbiomass (000 tons) with  a lag of 0 years from codyear-class and cod recruitment (Nx10-5).The most striking results were obtained with theAmerican plaice (Table 10).  The positive and highcorrelations suggest a great predation of 0-groupcod on American plaice spawn (eggs and larvae)and the resulting 0-group fish, which occur through-out the cod pre-recruitment period.  Significantcorrelations with lags of –1 and –2 years may bebecause American plaice spawning biomasses hada previous abundance similar to that correspondingto the year with a lag of 0 years.  It was previouslyshown (Larrañeta, 1986), that variations of Div. 3NOcod and American plaice year-class sizes are in-versely related, which is consistent with the presentresults.  In fact, if 0-group cod prey actively on 0-group American plaice, or both are strong competi-tors, they would exclude the simultaneous produc-tion of the highest year-classes possible for eachspecies.  Notwithstanding the very high significantlevels obtained in the statistical tests, we realizethat too many of the data points lie in the lower leftquadrant of Fig. 1 and 2, and for this reason it will beimportant to examine this relationship in a futureperiod when American plaice biomass again in-creases.Literature supports the view that American plaicecan be an important prey of cod during the 0-agegroup and pre-recruitment stages.  Marak (1960)studied the feeding habits of haddock and codpostlarvae (19–23 mm) on Georges Bank and foundthat 33% of the stomach contents were fish eggs.  InIceland waters Pälsson (1983) cited the predationof cod on American plaice.  Here the stomachcontent by weight in cod ranging from 15 to 19 and25 to 29 cm comprised 16 and 9%, respectively ofAmerican plaice.  Similarly, Daan (1973) cites thatthe food of cod 10–19 cm long in the North Seaconsisted of 85% of the Pleuronectidae; Limandalimanda is of the same family.  Hawkins (1985) alsoindicates that Pleuronectidae are food of young cod(13–43 cm).  These studies support the idea ofstrong predation by cod on 0-group American plaiceand also an active predation on the juveniles.The data available on cod and American plaicedistribution in Div. 3NO favour this idea.  The north-ern and southeastern slopes of the Grand Banksupport the largest American plaice concentrationin the Northwest Atlantic (Pitt, 1966).  According toWells et al. (MS 1988), cod and American plaicehave similar distributions on the Grand Bank, al-though cod does not tolerate temperatures lessthan –1°C that well.  Yellowtail flounder is distrib-uted in shallower zones and warmer waters, withtemperatures always above 1°C.  On the southernGrand Bank area, separation between Americanplaice pre-recruits and adults is not observed (Walsh,1982; Walsh and Brodie, MS 1988) as it is in Euro-pean waters, because the oceanographic condi-tions tend to retain the eggs and larvae near thespawning area (Nevinsky and Serebryakov, 1973).The metamorphosed juveniles (>20 mm) occupy thesame areas as the spawning adults.  Americanplaice larvae concentrate almost exclusively on thesoutheastern area of Grand Bank, in waters colderthan 1°C.  One other distinguishing characteristic ofyellowtail flounder is that they are distributed inwaters warmer than 1°C.   According to Kenneth etal. (1988), American plaice appear not to migratevertically during either the larval or pelagic juvenilephases, and are always col lected below thepycnocline at an average depth of about 30 m.  TheFig. 2. Relationship between American plaice spawningbiomass (000 tons) with   a lag of +3 years from codyear-class and cod recruitment (Nx10-5).134 J. Northw. Atl. Fish. Sci., Vol. 14, 1992poor dispersion of American plaice could make itmore vulnerable to predation.The correlation coefficient between Americanplaice spawning biomass and cod recruitment wasgreater for a lag of +3 years than for lags of +1 or +2years, and were even higher than for a lag of 0years.  We have interpreted the high correlationwhen there was a lag of 0 years, as a predation byindividuals of the cod 0-group on those of the Ameri-can plaice 0-group, but it seems unacceptable that3-year-old cod prey on American plaice 0-group.  Abetter hypothesis to explain the very high correla-tion with a lag of +3 years could be that adult cod isattracted by an abundant American plaice spawn-ing population, reducing cannibalism of adult codon 0–3 year age groups.  According to unpublisheddata of J. Paz, the cod of 4+ age-groups cannibal-ize the 1–3 year age groups.  In this case, prerecruitcod would have two critical periods: the first oneowing to feeding conditions, the second one owingto cannibalism.These considerations suggest that the pres-ence of a high American plaice spawning biomasspromotes high cod recruitment.  Alternatively, bothspecies may respond similarly to an environmentalsignal.  These analyses are exploratory and furtherresearch will be necessary to study the mecha-nisms underlying these correlations.AcknowledgementsWe are indebted to T. Wyatt for critically review-ing this manuscript.  The authors thank CarmenAlonso for helpful comments of the English text.ReferencesANON.  1986.  Status of the fishery resources off theNortheastern United States for 1986.  NOAA Tech.Mem., NMFS/NEC-43, 130 p.BÁEZ, M., and M. G. LARRAÑETA.  MS 1987.  Fisheryecology of silver hake in Divisions 4VWX.  NAFO SCRDoc., No. 11, Serial No. N1280, 19 p.BAIRD, J. W., and C. A. BISHOP.  MS  1989.  The assess-ment of the cod stock in NAFO Div. 3NO.  NAFO SCRDoc., No. 35, Serial No. N1611, 61 p.BRODIE, W. B.  MS 1988.  An assessment of the Americanplaice stock in Divisions  3LNO.  NAFO SCR Doc., No.37, Serial No. N1477, 51 p.BRODIE, W. B., and S. J. WALSH.  MS 1987.  An assess-ment of the yellowtail flounder stock in Div. 3LNO.NAFO SCR Doc., No. 44, Serial No. N1331, 24 p.DAAN, N.  1973.  A quantitative analysis of the food intakeof North Sea cod, Gadus morhua.  Neth.  J. Sea Res.,6(4): 479–517.HAWKINS, A. D., N. M. SOOFIANI, and G. W. SMITH.1985.  Growth and feeding of  juvenile cod.  ICES J.Cons.,  42(1): 11–32.KENNETH, T. F., J. E. CARSCADDEN, and W. C. LEGGETT.1988.  Comparative analysis of factors underlying ofcapelin and flatfish larvae on the southern GrandBanks.  ICES, Early life history Symposium, Paper No.107, 11 p. + 10 fig.KOSLOW, J. A., K. R. THOMPSON, and W. SILVERT.1987.  Recruitment to Northwest Atlantic cod (Gadusmorhua) and haddock (Melanogrammus aeglefinus)stocks: influence of stock size and climate.  Can. J.Fish. Aquat. Sci., 44: 26–39.LARRAÑETA, M. G.  1986.  Dynamics of yellowtail flounderand American plaice  populations in the Grand Bank.NAFO Sci. Coun. Studies, 10: 35–45.MARAK, R. R.  1960.  Food habits of larval cod, haddockand capelin in the Gulf  of Maine and Georges Bankarea. ICES J. Cons., 25(1): 147–157.NEVINSKY, M. M., and V. P. SEREBRYAKOV. 1973.  Ameri-can plaice, Hippoglossoides platessoides plates-soides Fabr., spawning in the Northwest Atlantic area.ICNAF Res. Bull., 10: 23–36.PÄLSSON, O. K.  1983.  The feeding habits of demersalfish species in Icelandic waters.  Rit  Fiskideild., vol.VII(1): 60 p.PITT, T. K.  1966.  Sexual maturity and spawning of theAmerican plaice, Hippoglossoides platessoides(Fabricius), from Newfoundland and Grand Bank ar-eas.  J. Fish. Res. Board Can., 23: 651–672.POWER, D., and D. B. ATKINSON.  MS 1987.  Redfish inNAFO Divisions 3LN.  NAFO SCR Doc., No. 58, SerialNo. N1347, 18 p.WALSH, S. J.  1982.  Distribution and abundance of pre-recruit and commercial-sized American plaice on theGrand Bank.  J. Northw. Atl. Fish. Sci., 3(2): 149–157.WALSH, S. J., and W. B. BRODIE.  MS 1988.  Americanplaice distribution on the Nose and Tail of the GrandBank.  NAFO SCR Doc., No. 28, Serial No. N1464, 12p.WELLS, R., W. B. BRODIE, C. A. BISHOP, and J. W.BAIRD.  MS 1988.  Distribution  and abundance ofthree fish species on the Grand Bank in relation todepth and temperature of the water.  NAFO SCRDoc., No. 94, Serial No. N1546,

Cod Year-class Variations and Abundance of Other Commercial Fish in NAFO Divisions 3NO

Paz, Xabier

Larrañeta, Manuel Gómez

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Cod Year-class Variations and Abundance of Other Commercial Fish in NAFO Divisions 3NO

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