In this paper yellowtail length at maturity estimates based data collected in the spring Spanish surveys in the
Regulatory Area of Divisions 3NO are presented. Female length at 50 % maturity decreased from 35 cm in 1995 to
23 cm in 1998. In males, this parameter decreased from 23 cm in 1995 to 19 cm in 1998. The differences in L50
estimates in females were significant between 1997 and the previous years , and between 1998 and both 1996 and 1995,
and were not significant between 1997 and 1998. In males, differences were significant between all the years, except
between 1997 and 1998. The covariance analysis between the linearized maturity curves were highly significant in both
sexes

Durán-Muñoz, P. (Pablo)

Junquera, S. (Susana)

Álvarez-Pérez, M.S. (María Soledad)

English

Repositorio Institucional Digital del IEO

 NOT TO CITED WITHOUT PRIORREFERENCE TO THE AUTHOR(S)Northwest Atlantic Fisheries OrganizationSerial No. N4065 NAFO SCR Doc. 99/16SCIENTIFIC COUNCIL MEETING – JUNE 1999Yellowtail Flounder Length at Maturity in the Grand Bank (1995-98).byP. Durán,  S. Junquera and M. S. AlvarezInstituto Español de Oceanografía, Apdo. 1552, Vigo, SpainABSTRACTIn this paper yellowtail length at maturity estimates based data collected in the spring Spanish surveys in theRegulatory Area of Divisions 3NO are presented. Female length at  50 %  maturity decreased from  35 cm in 1995 to23 cm in 1998.  In males, this parameter decr ased  from 23 cm in 1995 to 19 cm in 1998.  The differences in L50estimates in females were significant between 1997 and the previous years , and between 1998 and both 1996 and 1995,and were not significant between 1997 and 1998. In males, differences were significant between all the years, exceptbetween 1997 and 1998.  The covariance analysis between the linearized maturity curves were highly significant in bothsexes.KEYWORDS: Yellowtail flounder,  maturity curves, length at maturity, males and females.INTRODUCTIONThe yellowtail flounder is an spring-early summer spawner species (Zamarro 1988).  In past this stock had anorthern distribution limit in commercial concentrations off Newfoundland coast, but at present it is concentrated onthe Grand Bank, mainly in the southern part, where the juvenile and the adult components overlap in theirdistribution (Walsh 1992, Brodie et al. 1998).  There was a fishing moratoria for this stock from 1994 to 1997, andfor 1998 the Scientific Council recommended  reopening a limited fishery,   stating also that this fishery should becarefully monitored and sampled.Morgan and Walsh (1977) presented estimates of  length and age at maturity for yellowtail flounder inDivisions 3 LNO from 1975 to 1995, based on the Canadian spring survey.  They observed  a declined in maleslength at maturity, but no decline was evident in females.  Durán et al. (1998)  pr sented estimates of the length atmaturity based on the Spanish spring survey in the Regulatory Area, where the decline was observed in both sexes.Variations in length  at maturity can be caused by several factors:  growth variability, geographic distribution and stockabundance.  Besides random natural variability can occur, though under stable population conditions this should be small(Walsh and Morgan 1998).In this paper  additional data from the spring  Spanish survey in Divisions 3NO on this subject is examined, inorder to determine the consistency of the declining trends observed in previous years.2MATERIAL AND METHODSYellowtail maturity data used in this study have been collected during the Spanish spring surveys conducted inthe Regulatory Area in Div. 3NO from 1995 to 1998 (Paz et al. 1996 and 1997; Durán et al.  1998).  The geographicdistribution of the yellowtail samples  analysed in the successive surveys appear in Fig. 1,  and the length ranges andnumbers in Table 1.  Fish were classified as mature or i mature  by visual examination of the gonads. A simplefour-point scale was used to do it, where the first stage is designed as immature and all the others (maturing,spawning and post-spawning) as matures. The proportion of mature  males and female by size were adjusted to a logistic equation as described by Ashton(1972) :where $P  is the predicted mature proportion,a and b  the coefficients estimated of the logistic equation and L the length.The size at maturity can be estimated as the minus ratio of the coefficients (- a /b) by substituting $P = 0.5 in the aboveequation. To evaluate the differences in size at maturity between years, the variance of those parameters every year wascalculated from  the variances and covariance of the maturity curve coefficients  (Ashton, 1972):Assuming that L50 estimates are normally distributed, then the Z statistic can be computed as:where a and b are the logistic regression coefficients and V1 and V2  the L50  variances of every year compared. Zvalues can be used to test the null hypothesis of parameters equality  (Gund rson, 1977).  The  linear transformationof  the maturity curves are also compared using a covariance analyses to evaluate between years  differences  in thecurve slopes and  the influence of the length distributions on the  length at maturity estimates.All the statistical analysis have been performed using the Statistica  package (StatSoft. Inc., 1995).RESULTS AND DISCUSSIONThe length range is approximately similar in the three years analysed (table 1),  but since 1997 the proportion ofthe  smaller length classes increased in the samples. This is r flecting a parallel decrease of the yellowtail lengthscaught in the survey (Paz et al. 1997).$Peea bLa bL= +++1and the logit transformation:ln$$PPa bL1-= +V LbV aabV baba b( ) ( ) ( ) cov( , )50 2221 2= + -éëêùûúZababV V=+-11221 23The maturity curves for females and males are shown in Fig. 2, and the parameters of the fitted curves  in Table 2.Female length at  50 %  maturity  slightly decreased from 1995 (35 cm) to 1996 (34 cm), but a pronounced decrease isobserved in 1997 (24 cm), maintained in 1998 (23 cm) .  In males L50 ra ges from 23 cm in 1995 to 27 cm in 1996, andthen decrease to 21 cm in 1997 and 19 cm in 1998.  The differences in L50 estimates in females were significant between1997 and the previous years (1996 and 1995), and between 1998 and both 1996 and 1995, and were not significantbetween 1997 and 1998 (table 3). In males, differences were significant between all the years, except between 1997 and1998 (table 3).The covariance analyses of the maturity curves  (Table 4) indicate that the slopes and intercepts are significantlydifferent between years in both sexes. Thus,  the mature proportions at length are different in the years analysed, not onlydue to a difference in the length distributions involved. Also the rate of increase of the mature proportions with length isdifferent.Decreases in both age and length at maturity in coincidence with decreases in  stock abundance has been observedin recent years in several shelf species from this same area (Stearns et al. 1984; Morgan et al. 1993; Saborido andJunquera 1998).  However it is difficult to assert that such could be the case of th   y llowtail lounder, as the stockseems to be at present in a better situation than it was in the past (Anon. 1997 ).   From Morgan  and Walsh (1997)results, including a much longer time series (1975 – 95), few trends were evident , though a decline in males L50 sinc1984 occurred from 30 cm to 25 cm at the end of their time series. The L50 e timates in the only  coincident  year withthe present study (1995) are approximately similar in both sexes, but in contrast , Morgan and Walsh (1997) found amore pronounced decreasing trend on males L50 whil  we found it in females.The present study are based in a series of  surveys which cover only partially the yellowtail flounder distributionrange, namely the part of the stock in the Regulatory Area.  The length at maturity results obtained in 1997 are consistentwith the 1998 estimates, and can be reflecting a change in the species distribution pattern. In 1997 and 1998   mai lysmall fish appeared  in the survey area  (Paz et al. 1997, Durán et al. 1998) and  they were largely more concentrated thanin previous surveys. Thus mature small fish, likely first spawners, became more available to the surveys in 1997-1998just  because of a change in their distribution, or those small adults became more abundant because they belong to a largeyear class.REFERENCESAnon. (1997).-  Report of Scientific Council NAFO SCS Document,Ashton, W. D. (1972).- The logit transformation with special reference to its uses in bioassay. Hafner PublishingCo., Inc., New York, 88 pp.Brodie, W. B., S. J. Walsh, D. B. Atkinson (1998).- The effect of stock abundance on range contraction of yellowtailflounder (Pleuronectes ferruginea) on the Grand Bank of Newfoundland in the Northwest  Atlantic from 1975 –1995. J Sea Res. 39: 139 – 152.Durán, P. , X. Paz and E. Cárdenas (1988).- Results from the 98 Spanish bottom trawl survey in the NAFORegulatory Area  for Divisions 3NO. NAFO SCR Doc. 98/48.Gunderson, D. R. (1977).- Population Biology of Pacific Ocean Perch, Sebastes alutu , stocks in the Washington-Queen Charlotte sound region, and their response to fishing. Fishery Bulletin, 75 (2): 369-403.Morgan, M. J. , Bishop, C. A., Baird,  J. W.  (1993).- Temporal and spatial variation in age and length at maturity in2J3KL cod.  NAFO SCR Doc. 93/57.Morgan, M. J. and S. J. Walsh (1977).- Observations on maturation, recruitment and spawning stock biomass inyellowtail flounder on the Grand Bank. NAFO SCR Doc. 97/71.Paz, X., P. Durán and E. de Cárdenas (1996).- Preliminary results from the 1996 Spanish bottom trawl survey in theNAFO Regulatory Area for Divisions 3NO. NAFO SCR Doc. 96/49.4      (1997).- Preliminary results from the 1997 Spanish bottom trawl survey in the NAFO Regulatory Area forDivisions 3NO. NAFO SCR Doc. 97/25.Saborido - Rey,  F. and S. Junquera (1998) Histological assessment of variation in the sexual maturity of cod (Gadusmorhua L.) at the Flemish Cap (north-west Atlantic). ICES J. Mar. Sci., 55: 515 - 521.StatSoft  Inc. (1995).-  STATISTICA for Windows [Computer program manual]. Tulsa, OK.Stearns, S. C., and Crandall, R. E. (1984).- Plasticity for age and size at sexual maturity: A life-history response tounavoidable stress. In: Fish Reproduction. Strategies and Tactics. Edited by G. W. Potts and R.J. Wootton.Academisc Press, London. pp. 13-33.Walsh, S. J. (1992).- Factors influencing distribution of juvenile yellowtail flounder (Limanda ferruginea) on theGrand Bank off Newfoundland. Neth. J. Sea Res. 29: 193 – 203.Walsh, S. J. and M. J. Morgan (1998).- Factors in maturation of yellowtail flounder (Pleuronectes ferruginea) on theGrand bank. NAFO SCR Doc. 98/105.Zamarro, J.  (1988).- Spawning process of the yellowtail flounder (Limanda ferruginea ). NAFO SCR Doc. 88/33: 1-11.5Table 1.-  Numbers of yellowtail flounder sampled by  length, sex and year in  thespring Spanish survey in Div. 3NO.FEMALES MALESLENGTH 1995 1996 1997 1998 1995 1996 1997 1998>14 2 6 2 1 214-16 12 18 9 8 16 12 417-19 37 42 42 51 8 55 38 5020-22 22 61 87 90 14 82 85 7923-25 28 103 100 82 26 53 91 7526-28 20 48 118 53 22 64 109 7029-31 34 55 150 69 34 74 80 8432-34 66 71 112 68 33 60 66 5635-37 46 123 121 59 33 20 60 4538-40 39 119 116 74 17 9 34 3841-43 24 51 91 79 3 1 10 1944-46 12 42 23 41 4 547-49 5 14 4 11 150-52 3 2 153-55 5 1total 348 736 986 692 198 436 591 527Table 2.-   Parameters of the  yellowtail flounder females (F) and males (M) maturity curve in Div. 3NO (1995 –98).  ‘a’ and ‘b’ = coefficients of the adjusted logistic curve;  St. Error = standard error of the estimates; L50  =length at 50 % maturity; Var. exp.= variance explained by the model; N = numbers sampled.FEMALES1995 1996 1997 1998a b a b a b a bEstimate -12.98 0.37 -15.65 0.46 -13.08 0.55 -10.98 0.48St. error 1.50 0.04 1.34 0.03 0.85 0.03 1.34 0.06L50 35 cm 34 cm 24 cm 23 cmVar. exp. 54 % 62 % 64 % 62 %N 348 736 986 692MALESa b a b a b a bEstimate -6.65 0.29 14.06 0.50 -12.45 0.59 -9.63 0.51St. error 1.41 0.06 1.27 0.04 1.46 0.07 1.38 0.02L50 23 cm 27 cm 21 cm 19 cmVar. exp. 35 % 64 % 50 % 40 %N 198 436 591 5276Table 3.- Z values of the comparative analysis of the yellowtail flounder length at maturity betweenyears.  * significance (p<0.05); ** significance (p<0.01); otherwise not significant.Z - FEM. 1996 1997 19981995 0.55 5.18** 14.1**1996 8.53** 16.8**1997 0.65Z – MALES 1996 1997 19981995 2.99** 2.15* 1.78*1996 4.36* 5.26**1997 0.41Table 4.  Covariance analysis between years (1995 – 98) of the mature proportions at length (effect)in 3NO yellowtail flounder.F E M A L E SSS df MS F P - levelEffect 26.16 44 0.59 16.46 0.0000Error 3.09 122 0.04M A L E SSS df MS F P - levelEffect 17.12 38 0.45 12.84 0.0000Error 2.07 93 0.037Fig 1.- Yellowtail flounder sampling area in the Spanish spring bottom trawl surveys inDiv. 3NO (1995-1998).8M A L E S F E M A L E SFig. 2.- Yellowtail flounder maturity curves by sexes in Div. 3NO (1995-98).199702040608010011 14 17 20 23 26 29 32 35 38 41 44 47Length%199602040608010011 14 17 20 23 26 29 32 35 38 41 44 47Length%199602040608010013 16 19 22 25 28 31 34 37 40 43 46 49Length%199502040608010013 16 19 22 25 28 31 34 37 40 43 46 49Length%199702040608010013 16 19 22 25 28 31 34 37 40 43 46 49Length%199502040608010011 14 17 20 23 26 29 32 35 38 41 44 47Length%199802040608010011 14 17 20 23 26 29 32 35 38 41 44 47Length%199802040608010013 16 19 22 25 28 31 34 37 40 43 46 49Length%

Yellowtail Flounder Length at Maturity in the Grand Bank (1995-98)

Durán-Muñoz, Pablo

Junquera, Susana

Álvarez-Pérez, María Soledad

Digital.CSIC

P. Durán

S. Junquera

M. S. Alvarez

CiteSeerX

Yellowtail Flounder Length at Maturity in the Grand Bank (1995-98). by

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Yellowtail Flounder Length at Maturity in the Grand Bank (1995-98)

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