Cárdenas-González, E. (Enrique) de

Junquera, S. (Susana)

Motos, L. (Lorenzo)

English

Cárdenas-González, Enrique  de

Motos, Lorenzo

Junquera, Susana

Digital.CSIC

Expected Trends on teh 2J3KLMNO Greenland Halibut in Status Quo Conditions

Repositorio Institucional Digital del IEO

NOT TO BE CITED WITHOUT PRIOR REFERENCE TO THE AUTHOR(S) Northwest Atlantic Fisheries Organization Serial No. N3055 	 NAFO SCR Doc. 98/63 SCIENTIFIC COUNCIL MEETING - JUNE 1998 Expected Trends on the 2J3KLMNO Greenland Halibut in Status Quo Conditions by by E. de Cardenas, L. Motos 2 and S. Junquera 3 1 Inst. Espanol de Oceanografia , Av. De Brasil 31, Madrid, Spain. 2 AZTI, Avenida de Satrustegui 8, San Sebastian, Spain. 3 Inst. Espanol de Oceanografia , apdo 1552,Vigo, Spain 1.- Introduction The aim of this paper is to anticipate the trend in stock biomass, spawning stock biomass, and catches of the Greenland halibut stock in NAFO Divisions 2J3KLMNO in status quo conditions. In order to get estimates of the trends a simple model has been developed based on survey indices of numbers at age. 2.- Data Selectivity at age was derived from de Cardenas et al. (1995). Mean weight at age and age composition of the fall Canadian survey was obtained from Brodie et al. (1998). Maturity data at age was calculated as the average of the maturity ogive for NAFO Division 3M obtained by Junquera and Saborido-Rey (1995) for the years 1990 and 1994. These data are presented in table 1, 2 and 3. 3.- Method An abundance ratio between numbers-at-age a in 1996 and numbers at age a-1-1 in 1997 was calculated for each age presented in the Canadian fall survey (Brodie et al., 1998). Theoretically, these ratios should remained unchanged, without any assumption about natural mortality, or exploitation patterns, if the fleet composition keeps similar, as it is the case, and a status quo situation is maintained. So it can be used to project the number at age caught in a survey to the next year' survey. An index of the fishable stock for each survey can be obtained by using the selectivity of 130 mm mesh, which is transformed into a fishable biomass index by multiplying each resultant number at age by the corresponding weight-at-age. The ratio between catch and fishable biomass has to be constant in status quo situation. Therefore, once the 1997/1996 ratio is calculated, the catch for 1998 -and upcoming years in a similar manner- can be calculated as we has calculate the fishable biomass index for these years. At the same time, the mature portion of the fishable biomass index, i.e. a spawning biomass index, can be estimated by applying the maturity ogive to the biomass index at age. This can be used to monitor the expected evolution of the SSB level in the upcoming year. _2 This method is mainly dependent on the accuracy of the estimation of ratios, which are directly dependent on the precision of the number at age estimated by the surveys and in the 1997 survey which is used as base for the projection. To check the sensitivity of the output parameters to the accuracy of numbers at age estimated in the cruise, a resampling exercise was made. The numbers at age in the cruises were bootstrapped using Montecarlo replicates. The year effect and the age effect on number at age variability were computed separately. Normal errors with CV = 0.3 were used in both cases. Similarly, weights at age used to raise numbers to biomass and the selectivity pattern error were bootstrapped assuming a lognormal error with a s.e. of 0.2 for the weights. Finally, both the maturity ogive and the selectivity pattern were bootstrapped assuming normal errors after logit transformation for both parameters (cv=0.2). In order to compare the sensitivity of the assumed CV on the outputs, another exercise is presented with CV = 0.2 for either year or age effect on the error of numbers at age in the survey. 5.- Results Each Montecarlo replicate generates an estimate of Fishable Biomass index and corresponding Fishable Spawning Biomass index and catch estimate. 1000 replicates were made. Table 4 and 5 shows the point estimates and the results of the resampling exercise. For the estimated index and catches, mean, median, and several percentiles are shown. It is also shown the probability of the TAC being taken if a status quo fish mortality would be applied to the stock in 1998. The results are shown for the assumptions of cv = 0.3 and cv = 0.2 in either year effect and age effect of the errors of numbers at age in the surveys. Figure 1 shows the cumulative frequency distribution of expected catches in 1997 at status quo. Fig. 2 shows the same for the expected proportion of SSB increase. 6.- Reference Brodie, W.B., W.R. Bowering, D. Power and D. Orr, 1998. An assessment of the Greenland Halibut in NAFO Subarea 2 and Divisions 3KLMNO. NAFO SCR Doc. 98/47 Ser. No N3038: 7pp. De Cardenas, E., A. Avila de Melo, S. Iglesias and F. Saborido. 1995. Selectivity of 130 mm mesh size in deep sea bottom trawl fishery in NAFO Regulatory Area. NAFO SCR Doc. 95/47 Ser. No N2558: 7PP- Junquera, S. and F. Saborido-Rey, 1995. Temporal and spatial variation in length at maturity in 3LM and 3NO Greenland Halibut. NAFO SCR 95/9 N2538. 7pp. - 3 4 Table 1: Selectivity, mean weight and maturity at age vectors used in the analysis. Age Selectivity at age Mean Weight Maturity at age 1 2 0.00 0.00 0.00 0.00 3 0.13 0.126 0.01 4 0.26 0.222 0.02 5 0.41 0.383 0.03 6 0.58 0.581 0.05 7 0.90 0.909 0.08 8 1.00 1.264 0.18 9 1.00 1.85 0.32 10 1.00 2.427 0.48 11 1.00 3.104 0.62 12 1.00 3.996 0.74 13 1.00 5.141 0.82 14 1.00 5.943 0.89 15 1.00 6.658 0.92 Table 2: Numbers at age in the Canadian Fall surveys. Canadian Fall survey Years 1996 1997 41996 19546 1 793447 .222012 2 452542 486571 3 267483 398365 4 96586 192045 5 55611 89809 6 22305 40112 7 7422 17321 8 1920 5658 9 1141 1547 10  377 493 11 178 280 12 115 151 13 118 100 14 42 54 -4- Table 3: Abundance ratios for the different cohorts as observed in the 1996 and 1997 surveys. Ratio 1997/1996 1/0 5.29 2/1 0.61 3/2 0.88 4/3 0.72 5/4 0.93 6/5 0.72 7/6 0.78 8/7 0.76 9/8 0.81 10/9 0.43 11/10 0.74 12/11 0.85 13/12 0.87 14/13 0.46 Table 4: Point estimates of Stock numbers (at age) indices, Fishable biomass (at age and totals) indices, Spawning Stock Biomass indices, Catch, Catch/Fishable biomass ratio and expected change in these parameters in status quo conditions. Stock numbers Fishable Biomass Fishable SSB age 1997 1998 	1999 1997 1998 1999 1997 	. 1998 1999 0 1 19546 222012 103330 2 486571 136146 	63366 0 0 0 0 0 0 3 398365 428320 	119847 7438 7998 2238 89 96 27 4 192045 286014 	307521 10216 15215 16359 204 304 327 5 89809 178570 	265946 14198 28230 42044 469 932 1387 6 40112 64779 	128802 ' 	14345 23167 46064 717 1158 2303 7 17321 31149 	50304 13854 24915 40236 1108 1993 3219 8 5658 13204 	23746 7134 16649 29940 1270 2963 5329 9 1547 4559 	10639 2862 8433 19680 904 2665 6219 10 493 668 	1970 1197 1622 4781 572 775 2285 11 280 366 	496 869 1137 1541 540 706 957 12 151 238 	311 603 949 1241 446 701 917 13 100 131 	207 514 675 1062 423 556 874 14 54 46 	60 321 272 357 285 242 317 15 0 	0 0 0 0 Fishable biomass 73552 129261 205542 Proportion wrt 1997 1.00 1.76 2.79 SSB Biomass 7028 13092 24162 Proportion wrt 1997 1.00 1.86 3.44 Catch 19858 34899 55494 Catch/FB ratio 0.270 0.270 0.270 101.1,! 111111.1 	 - 0 3 ry 0 0 21  0 140 1- • 120 t • 00 g 80 • LE 60 40 r 20 0 1.0 . ... . 	o8 ... . _.t 0r - 06 . 	. 	. 0.3 	 00 200 	 t 0.9 160 ■ 140 - 120 - ff 100 - go 60: 	• 0.2 20 "7 0 0.6 0.3 ' 0.3 100 t 60 40 20 0.3 0.2 0101 2 r. 	:ter Clams of *wetted SSII Screw at statue quo 120 	 1.0 0.9 0.7 0.6 0.3 0.4 160 140 r - 	 : 	0.9 i 120 0.6 •- I " 1 It 100 4-- ..., i 0.6 1 so -, - - 	 - - 1 0.3 .. 0.2 0.3 40  20 . 0.1 i • 2222"2222 	:222 e 	00  Own *respected &SD I serene st steam dm Table 5: Results of the bootstrap (1000 replicates). CV denotes the coefficient of variation assumed for either the age effect or the = 0.3 on numbers at age in the surveys. CV = 0.3 CV = 0.2 Catch SSB increase Catch SSB Increase Average 39 446 2.44 37 811 2.18 sd 3.09 1.56 0.89 1.49 median 36 956 1.99 36 657 1.91 percentile 25 25 711 135 29 098 1.57 percentile 10 16 784 0.94 23 269 1.27 percentile 5 10 419 0.60 20 268 1.07 Prob<27000 0.28 0.19 Prob<1 0.13 0.03 Figure 1: Frequency distribution of the replicates of expected catch estimates. Left, cv = 0.3 on either year and age effect for survey numbers at age. Right, cv = 0.2. Figure 2: Frequency distribution of the replicates of the ratio of expected SSB increase catch from 1997 to 1998 in status quo conditions. Left, cv = 0.3 on either year and age effect for survey numbers at age. Right, cv = 0.2. 

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Expected Trends on teh 2J3KLMNO Greenland Halibut in Status Quo Conditions

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