STANDARDIZED AGE SPECIFIC CATCH RATES FOR ALBACORE, Thunnus alalunga, FROM THE SPANISH TROLL FISHERY IN THE NORTHEAST ATLANTIC,

SCRS/00/114 STANDARDIZED AGE SPECIFIC CATCH RATES FOR ALBACORE, Thunnus alalunga, FROM THE SPANISH TROLL FISHERY IN THE NORTHEAST ATLANTIC, 1981-1999. V. Ortiz de Zárate 1, J. Cramer 2 and M. Ortiz 2 SUMMARY Abundance indices by age group of albacore (Thunnus alalunga) caught by the Spanish troll fleet in the north east Atlantic were standardized using catch rate data from 4069 trips collected over the period 1981-1999. Standarized CPUE s for age groups 1 to 4 were estimated through the General Linear Modeling approach by applying the log-normal error distribution model. RÉSUMÉ Les CPUE par groupe d âge du germon (Thunnus alalunga) capturé par la flottille de ligneurs espagnols de surface sont standardisées à partir de 4.069 sorties répertoriées entre 1981 et 1999. Les indices d abondance relative pour les groupes d âge 1 à 4 ont été estimés au moyen de l approche du Modèle linéaire généralisé postulant une distribution log-normal d erreurs dans les modèles. RESUMEN Las CPUE por grupo de edad de atún blanco(thunnus alalunga) capturado por la flota de superficie española de cacea se han normalizado a partir de 4069 mareas recogidas para el período 1981-1999. Los índices de abundancia relativa para los grupos 1 a 4 años se estimaron por medio del procedimiento de Modelo Lineal Generalizado asumiendo una distribución log-normal de errores en los modelos. INTRODUCTION Data collected of nominal catch rates by age of individual trip from spanish surface commercial fleet have been used to develop relative abundance indices by age of young albacore from the North Atlantic stock (Mejuto and Garcia, 1997; Ortiz de Zárate and Cramer, 1999, Ortiz de Zárate et al. 2000). In the absence of other independent sources of information, the estimated catch rates derived by means of the General Linear Modeling approach was used as abundance indices to tune the VPA analysis of the north Atlantic stock. The SCRS has used standardized catch rates from the troll fishery as an index of abundance for juvenile albacore ages 2 and 3 of north Atlantic stock (Anonymous, 1997; Anonymous, 1999) 1 Instituto Español de Oceanografía Apdo. 240, Santander 39080, España 2 2 NMFS, Southeast Fisheries Science Center 75 Virginia Beach Drive, Miami, Florida 33149, U.S.A

The purpose of this paper is to update the relative catch rates indices by age for albacore surface troll fishery from 1981 to 1999. Standarized age-specific catch rates (ages 1 through 4) were estimated by means of the GLM approach assuming the log-normal error distribution model in the analysis. MATERIAL Information on trips from commercial trollers was recorded at landing ports through interviews of skippers. The following data was obtained for each trip: date of landing, number of fishing days, area of effort (5x5 degrees), catch in number, catch in weigth (kg), as well stratified length sampling to the nearest centimeter (FL= 35 120 cm range ) was carried out for catch commercial categories landed by single trips recorded. Age length keys (Santiago, 1999) obtained from length distribution analysis of north atlantic albacore stock catch by size for the period 1975-1997 done by means of Multifan length frequency analysis were used used to size the catch at age composition by trip for albacore age groups : 1, 2, 3 and 4. Age length key for 1997 was carried over 1999 catch at size distribution. METHOD The seasonal migration of inmature albacore to the northeast Atlantic waters and Bay of Biscay during summer months determines the performance of the fleets according to the species annual behaviour. In 1999 the distribution of catches for the troll fleet has remained in the traditional grounds (figure 1). Therefore the stratification of fishing areas used in the GLM analyses is the same as in previous analyses. Figure 2 shows the spatial divisions established for the model effect area specifications. The temporal strata month agreggation was done in order to have enough observations. As in previous analysis no changes were detected in the last two years when the following strata were chosen: May, June and July (T1), August and September (T3) and October and November (T2). The present analyses used the following factors: Year, Zone and Quarter to model age-specific cpue from 1 to 4 age groups for troll fleet. The final model set was: LOG (cpue) = µ+ Yi + Zk + Ql + ε ikl where µ= overall mean Y = effect year: 1981-1999 Z = effect zone: NW,NE,SW,SE in figure 2. Q = effect time, three artificially created quarters: T1, T2, T3. ε ikl = log-normal error distribution The fitting of the final model was conducted by GLM procedure of S-PLUS statistical software (Ver.4.5, release 2). RESULTS AND DISCUSSION Total number of data observations included in the analyses was 4,069 trips. Table 1 shows the distribution of observations by the classed predictor variables for the troll fleet. First years in the time series show very few number of observations for troll fleet specially for quarter T2 which corresponds to autumn months.

Examination of zero observations by age group is represented in table 2. As observed the percentage of null observations is less than 10 % for ages 1, 2 and 3 and over for age group 4 in the data set. Then log (cpue) was used to predict standardized least squares means by age only on the positive observations. Results of the analyses of variance for the four models fitted from 1 to 4 age group cpue s are included in table 3. All the effects explaining the dependent variable show significance tested by the analysis of variance as seen in the F-values obtained. The variance explained by the different models varies between 22.3% and 44.4% for the target groups 2 and 3 years old. The model which explains the most variability is the one fitted for age 2. The relative indices estimates by age, their standard error and 95 % confidence intervals are presented in table 4a for ages 1 and 2 and in table 4b for ages 3 and 4. Figures 3 and 4 show the plots of standardized residuals, predicted log cpue s and qq plots for the catch rates by age (1 to 4) estimated by the logcpue model with normal error distribution. Trends of relative indices of abundance obtained for ages 1, 2, 3, and 4 for the troll fleet are shown in figure 5. For the last year 1999, the age 2 group continues some decline that begun in 1996, as for age 3 after the decline in 1996 a slight upward trend is seen for this age group being very similar in the last 3 years. Age 1 is not a group size targeted by this fleet, however it could be interpreted as an indication of year recruitment strength.. Ages 2 and 3 are targetted by both fleets therefore could be more accurate indicators of relative abundance indices. Age 4 is very rare in troll catches and more present in baitboat catch, mainly in the autumn months in the Bay of Biscay fishing ground, although fluctuates on annually bases. There are some new predictor variables that could further be investigated such an environmental factors for which albacore seems to be specially sensitive and fleet structure that could be tested if explanatory variables are defined from available information to model troll cpue trends. REFERENCES ANONYMOUS, 1997. SCRS Detailed Report on Albacore. ICCAT, Col. Doc. Sci. vol XLVI(3). ANONYMOUS, 1999. SRCS Detailed Report on Albacore. ICCAT, Col. Doc. Scient. vol XLX (1). MEJUTO, J., B. GARCIA, 1997. Standardized age specific catch rates for albacore (Thunnus alalunga) from the spanish surface fleets in the northeast atlantic, years 1981-1995. ICCAT Coll. Vol. Sci. Pap. Vol. XLVI (3) pp: 131-137. ORTIZ DE ZARATE, V. and J. CRAMER 1999. Standardized age specific catch rates for albacore (Thunnus alalunga) from the spanish surface fishery in the northeast Atlantic, 1981-1997. ICCAT Coll. Vol. Sci. Pap. Vol. XLIX (4) pp: 151-161. ORTIZ DE ZARATE, V., M. ORTIZ and J. CRAMER, 2000. Updated standardized age specific catch rates for albacore (Thunnus alalunga) from the spanish surface in the northeast Atlantic, 1981-1998. ICCAT, Coll. Vol. Sci. Pap. Vol. LI, SCRS/99/115. SANTIAGO, J. 1999. North Atlantic albacore catch- at- age estimates for the period 1975-1997. ICCAT Coll. Vol. Sci. Pap. Vol. XLIX (4) pp: 182-187. S-PLUS. 1998. Professional edition for Windows. Copyright 1997. MathSoft, Inc.

Table 1. Observations (Nº trips) by year, area and quarter for TROLL fleet, 1981-1999. TROLL ZONE YEAR QUARTER 1 2 3 4 Total general 81 1 1 2 4 7 14 3 7 8 3 18 Total 81 8 10 4 10 32 82 1 18 4 4 14 40 3 31 11 1 43 Total 82 49 15 5 14 83 83 1 1 27 28 2 1 1 3 22 18 20 60 Total 83 24 18 47 89 84 1 12 3 24 39 3 10 4 30 44 Total 84 22 7 54 83 85 1 17 2 24 43 2 6 6 3 9 24 12 45 Total 85 15 41 2 36 94 86 1 1 1 33 12 47 2 10 6 16 3 26 8 2 22 58 Total 86 37 15 35 34 121 87 1 2 12 14 2 3 1 4 3 2 2 1 10 15 Total 87 5 3 3 22 33 88 1 6 3 29 15 53 2 14 10 24 3 40 26 7 30 103 Total 88 60 39 36 45 180 89 1 7 12 42 42 103 2 16 8 10 34 3 30 30 1 57 118 Total 89 53 50 43 109 255 90 1 2 11 64 56 133 2 28 24 52 3 17 60 4 67 148 Total 90 47 95 68 123 333 91 1 3 12 79 57 151 2 1 37 38 3 18 47 1 107 173 Total 91 22 96 80 164 362 92 1 5 36 53 54 148 2 22 2 24 3 40 43 2 47 132 Total 92 45 101 57 101 304 93 1 4 23 94 25 146 2 2 4 1 2 9 3 17 69 1 57 144 Total 93 23 96 96 84 299 94 1 102 2 104 2 5 1 6 3 70 16 1 30 117 Total 94 70 21 104 32 227 95 1 11 5 52 71 139 2 2 22 24 3 18 66 4 73 161 Total 95 31 93 56 144 324 96 1 20 36 62 30 148 2 2 18 2 22 3 31 44 1 23 99 Total 96 53 98 63 55 269 97 1 1 18 17 106 142 2 7 2 5 14 3 13 45 3 75 136 Total 97 21 65 20 186 292 98 1 15 37 55 50 157 2 1 1 3 46 57 37 140 Total 98 61 94 55 88 298 99 1 40 18 32 106 196 2 7 7 3 52 87 1 48 188 Total 99 92 112 33 154 391 Total general 738 1069 760 1502 4069

Table 2. Proportions of null observations by age from spanish TROLL fleet from 1981 to 1999. 1981-1999 TRO LL T o ta l T r ip s 4 0 6 9 % n u ll observation s A g e 1 3.5 A g e 2 2.4 A g e 3 3.3 A g e 4 3 1.2 Table 3. Analysis of variance ANOVA for the 4 CPUE s models estimates by age group. Troll fleet 1981-1999. Summary of fits GEAR AGE R 2 MSE F-STAT CV TR 1 O.346 1.2395 89.73 42.37 TR 2 0.444 1.1438 137.18 34.14 TR 3 0.223 0.9880 48.71 43.71 TR 4 0. 206 1.30307 31.35 42.93 Type III Sum of Squares for Model TR AGE1 Df Sum of Sq Mean Sq F Value Pr(F) YEAR 18 1569.993 87.2218 70.3682 0 ZONE 3 321.722 107.2406 86.5187 0 QUARTER 2 323.130 161.5649 130.3461 0 Residuals 3902 4836.556 1.2395 Type III Sum of Squares for Model TR AGE 2 Df Sum of Sq Mean Sq F Value Pr(F) YEAR 18 329.283 18.2935 15.9941 0 ZONE 3 1571.449 523.8165 457.9765 0 QUARTER 2 402.436 201.2181 175.9264 0 Residuals 3946 4513.288 1.1438 Type III Sum of Squares for Model TR AGE 3 Df Sum of Sq Mean Sq F Value Pr(F) YEAR 18 490.331 27.2406 27.5713 0 ZONE 3 336.573 112.1909 113.5530 0 QUARTER 2 61.833 30.9163 31.2916 3.297362e-014 Residuals 3911 3864.089 0.9880 Type III Sum of Squares for Model TR AGE 4 Df Sum of Sq Mean Sq F Value Pr(F) YEAR 18 562.026 31.22368 23.96168 0.0000000000 ZONE 3 27.173 9.05755 6.95094 0.0001170299 QUARTER 2 146.065 73.03232 56.04647 0.0000000000 Residuals 2775 3616.012 1.30307

Table 4.a. Estimated parameters, relative CPUE S and 95% confidence intervals for albacore age groups 1 and 2 for Spanish TROLL fleet, 1981-1999 Least Squares Means for LOG(CPUE1) TR fleet YEAR lsmean 1 st.error LCI CPUE1 UCI 81 3.3653 0.1986 36.44473 53.7881 79.3850 82 0.9412 0.1338 3.66455 4.7634 6.1916 83 0.1018 0.17 1.47455 2.0576 2.8713 84 2.5072 0.1257 17.82463 22.8044 29.1754 85 2.5233 0.1234 18.19577 23.1745 29.5155 86 2.6005 0.1031 20.45397 25.0345 30.6407 87 0.5439 0.2329 2.02824 3.2016 5.0538 88 2.8853 0.0852 28.16446 33.2832 39.3323 89 2.3325 0.0749 16.53450 19.1490 22.1770 90 2.5234 0.063 20.48459 23.1768 26.2229 91 3.4889 0.0615 53.95298 60.8647 68.6618 92 3.1208 0.0672 36.92323 42.1213 48.0511 93 3.1125 0.0687 36.51054 41.7731 47.7942 94 2.5596 0.0797 20.55576 24.0312 28.0943 95 3.5236 0.0656 55.41094 63.0138 71.6597 96 3.3302 0.0712 45.16855 51.9329 59.7103 97 3.9312 0.0701 82.56261 94.7226 108.6736 98 3.2998 0.0697 43.94509 50.3779 57.7524 99 3.2286 0.0632 41.44971 46.9157 53.1026 Least Squares Means for LOG(CPUE2) TR fleet YEAR lsmean 2 st.error LCI CPUE2 UCI 81 3.1295 0.1938 27.7028 40.5032 59.2182 82 3.4163 0.122 42.4812 53.9566 68.532 83 3.0736 0.1172 30.4403 38.3012 48.192 84 2.8938 0.121 25.2423 31.9982 40.5624 85 2.6414 0.1156 19.8203 24.8605 31.1825 86 3.0557 0.0994 30.9619 37.6217 45.714 87 3.1714 0.1873 29.2586 42.2363 60.9704 88 3.154 0.0819 35.3521 41.5078 48.7354 89 2.5537 0.0696 19.8691 22.7731 26.1016 90 3.0915 0.0608 34.6124 38.993 43.9279 91 3.4714 0.0593 50.7572 57.0131 64.0401 92 3.3205 0.0653 43.1375 49.0275 55.7217 93 3.1727 0.0662 37.1450 42.2913 48.1506 94 3.6204 0.075 57.1272 66.1736 76.6524 95 3.3784 0.0637 45.8525 51.95 58.8583 96 3.5455 0.0694 53.5897 61.3982 70.3445 97 3.0745 0.0684 33.5259 38.3357 43.8355 98 2.9673 0.0688 30.0942 34.4387 39.4104 99 2.7857 0.0623 25.4184 28.7196 32.4496

Table 4.b. Estimated parameters, relative CPUE S and 95% confidence intervals for albacore age groups 3 and 4 for Spanish TROLL fleet, 1981-1999. Least Squares Means for LOG(CPUE3) TR fleet YEAR lsmean 3 st.error LCI CPUE3 UCI 81 2.2175 0.1774 10.1985 15.0518 21.3105 82 2.9185 0.1133 23.3419 30.3409 37.8854 83 2.9587 0.1083 22.6350 31.5855 39.0548 84 2.6256 0.113 17.6940 22.6373 28.2496 85 2.28 0.1058 12.5803 16.0226 19.7147 86 2.6242 0.0919 18.4695 22.6056 27.0672 87 2.4946 0.1741 12.5801 19.8578 27.9337 88 2.6805 0.0755 20.2369 23.9148 27.729 89 2.3273 0.0639 14.5050 16.7986 19.04 90 2.0566 0.0563 11.3262 12.8148 14.3098 91 2.1419 0.0569 12.3710 13.9558 15.6024 92 2.3861 0.0611 15.6174 17.8160 20.0826 93 2.4386 0.0618 16.4109 18.7764 21.1942 94 2.0583 0.0701 10.9801 12.8366 14.7272 95 2.2096 0.0595 13.1316 14.9334 16.7805 96 1.238 0.0649 4.9158 5.6519 6.41861 97 1.8552 0.0639 9.1322 10.4772 11.8751 98 2.0893 0.0631 11.5500 13.2407 14.9839 99 2.1247 0.0587 12.1196 13.7179 15.3905 Least Squares Means for LOG(CPUE4) TR fleet YEAR lsmean 4 st.error LCI CPUE3 UCI 81-0.478 0.2311 0.7562 1.1895 1.8710 82-0.6303 0.1414 0.7742 1.02146 1.3477 83 0.0067 0.1386 1.4719 1.93138 2.5342 84-0.1715 0.1442 1.2182 1.61613 2.1440 85-0.5444 0.1398 0.8463 1.11308 1.4640 86-0.6013 0.109 0.8492 1.05152 1.3020 87-1.0339 0.2447 0.4223 0.68225 1.1021 88-0.2252 0.0944 1.2729 1.53163 1.8429 89-0.5491 0.0901 0.9285 1.10786 1.3218 90 0.1656 0.0686 1.9792 2.264 2.5898 91-1.2271 0.0818 0.4791 0.56239 0.6602 92-0.3921 0.0777 1.1131 1.2962 1.5094 93-0.7409 0.0819 0.7789 0.91451 1.0738 94-0.846 0.0866 0.6948 0.82327 0.9756 95-1.1457 0.0828 0.5187 0.61008 0.7176 96-1.3283 0.1141 0.4064 0.50826 0.6356 97-1.0594 0.094 0.5532 0.66507 0.7996 98-0.5356 0.0922 0.9373 1.12292 1.3453 99-0.0213 0.0855 1.5883 1.87805 2.2207

55º 50º 45º 40º 35º 30º 30º 25º 20º 15º 10º 5º 0º 5º 10º Figure 1. Locations of albacore operations for Troll fishery in 1999 55º 50º 45º NW SW NE SE 40º 35º 30º 30º 25º 20º 15º 10º 5º 0º 5º 10º Figure 2. Area divisions for East Atlantic albacore troll fishery used in the analysis.

Deviance Residuals -4 2004 3668 1443 Deviance Residuals -6-4 150 2209 3141-1 0 1 2 3 4 5 1 2 3 4 5 LGCPUE1 6 6 Pearson Residuals -4 LGCPUE2 6 Pearson Residuals -6-4 6-2 0 2 Quantiles of Standard Normal -2 0 2 Quantiles of Standard Normal A B Figure 3. A) Plots of residuals, the predicted logcpue age 1 and QQ plot for the predicted cpue age 1. Troll B) Plots of residuals, the predicted logcpue age 2 and QQ plot for the predicted cpue age 2. Troll

Deviance Residuals -4-2 0 2 Deviance Residuals 458 542 130 974 918 1794 0.5 1.0 1.5 2.0 2.5 3.0 3.5-1.5-1.0-0.5 0.0 0.5 LGCPUE3 Pearson Residuals -4-2 0 2 LGCPUE4 Pearson Residuals -2 0 2 Quantiles of Standard Normal -2 0 2 Quantiles of Standard Normal A B Figure 4. A) Plots of residuals, the predicted logcpue age 3 and QQ plot for the predicted cpue age 3. Troll B) Plots of residuals, the predicted logcpue age 4 and QQ plot for the predicted cpue age 4. Troll

ALB CPUE AGE 1 TROLL ALB CPUE AGE 3 TROLL Nº fish/fishing day 120 100 80 60 40 20 0 81 83 85 87 89 91 93 95 97 99 Nº fish/fishing day 50 40 30 20 10 0 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 YEARS A GE 1 CPUE 95% UCI 95% LCI YEARS AGE 3 CPUE 95% UCI 95% LCI ALB CPUE AGE 2 TROLL ALB CPUE AGE 4 TROLL 100 Nº fish/fishing day 80 60 40 20 0 81 83 85 87 89 91 YEARS 93 95 97 99 Nº fish/fishing day 3 2 1 0 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 YEARS A GE 2 CPUE 95% UCI 95% LCI AGE 4 CPUE 95% UCI 95% LCI Figure 5. Albacore standardized catch rates indices by age in number fish/day for TROLL fleet in the North Atlantic, years 1981-1999.