The Spanish skate fishery in NAFO Regulatory Area is performed from August to November in a quite
restricted area of Div. 3N at depths between 51 and 100 m. Fishing effort, unstandardized catch rates, length
composition, sexual maturity, by-catch, discards and sex-ratios are presented in this paper.
The length range of thorny skate in the catches is mainly between 30 and 85 cm, with a mode of 50-51 cm. Both
sexes appeared equally represented in the catches. The main by-catch in this fishery is American plaice and
yellowtail flounder. A large proportion of mature males are observed

Junquera, S. (Susana)

Río-Iglesias, J.L. (José Luis) del

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Repositorio Institucional Digital del IEO

NOT TO BE CITED WITHOUT PRIOR  REFERENCE TO THE AUTHOR(S)    Northwest Atlantic Fisheries Organization  Serial No.  N4408   NAFO SCR Doc. 01/31   SCIENTIFIC COUNCIL MEETING – JUNE 2001  Spanish Skate (Raja radiata Donovan, 1808) Fishery in the Grand Bank (NAFO Division 3N): 1997-2000.   by  J. L. del Río and S. Junquera  Instituto Español de Oceanografía, Vigo, Spain   ABSTRACT  The Spanish skate fishery in NAFO Regulatory Area is performed from August to November in a quite restricted area of Div. 3N at depths between 51 and 100 m. Fishing effort, unstandardized catch rates, length composition, sexual maturity, by-catch, discards and sex-ratios are presented in this paper.  The length range of thorny skate in the catches is mainly between 30 and 85 cm, with a mode of 50-51 cm. Both sexes appeared equally represented in the catches. The main by-catch in this fishery is American plaice and yellowtail flounder. A large proportion of mature males are observed.   INTRODUCTION  As a result of the increase in fishing effort towards non-regulated species added to the decline in the traditional groundfish resources in the area of the Grand Bank, in recent years the catches of non-traditional resources in NAFO area have been increasingly important (Durán et al., 1997; Junquera and Paz, 1998).  Thorny skate distribute widely on the Grand Bank region, though it is most highly aggregated on the Southern part (Simon and Frank, 1996). The pattern of aggregation observed shows seasonal differences in distribution, with a period of concentration mainly in fall in shallow waters on the southern Grand Bank (del Río and Junquera, 2000; Kulka and Mowbray, 1998).    The skate fishery in the Grand Bank and the Scotian Shelf within Canadian waters is regulated since 1994, through quota control (Simon and Frank, 1996), but the fishery in the Regulatory Area is currently unregulated. Since 1996, part of Spanish fleet formerly targeting exclusively on Greenland halibut, started to undertake occasionally the skate fishery on the southern Grand Bank Regulatory Area in shallow waters. The estimated catches of thorny skate by the Spanish fleet in NAFO Div. 3N in 1999 were 4 700 tons (Junquera et al., 2000) and increased to about 10 700 tons in 2000.   In 1997-2000 biological sampling on three of the trawlers targeting skate have been performed by Spanish national scientific observers. Besides, data on fishing effort provided by NAFO observers are analysed to obtain further evidences on the seasonality of this resource.   MATERIAL AND METHODS  Two sources of information have been used in this study:   2(I) Three scientific observers from the Spanish sampling program have been on board three trawlers involved in the skate fishery in Div. 3N in the second half of the year (September and October in 1997; August to December in 2000). Those observers provided data on fishing activity and carried out biological sampling of this species. Skates were sexed, weighed to the nearest 10 g and measured to total length (LT), taken as the distance between the tip of snout to terminal point of the caudal fin, to the lower centimetre. Sexual maturity was assessed macroscopically.  (II)  Data from the NAFO observers (100% coverage of the fleet) have been used to obtain the proportion of fishing effort directed to this species. Those observers report on hours fishing, hauls position, catches, discards and mesh size, in a year round haul basis.  The fishing time targeting skate is identified as the vessels change to a trawl with a codend mesh size of about 220 mm, instead of the usual 130 mm used when targeting for others species.   Results and Discussion  Fishing effort and CPUE   In Table 1 the monthly distribution of the Spanish fleet effort targeting skate in Div.3N by depth, as reported by the NAFO observers is presented. The majority of these hauls (98.7%) were realised in Div. 3N and the presence in Div. 3O is only occasional. The results show that the 65% of fishing effort is performed at depths between 51 and 100 m.   The unstandardized catch rates (kg/hour fishing) by depth strata in 1997 and 2000 appear in Table 2. The highest catch rates occurred at depths less than 100 m.  In 2000 the best catch rates were 1079.3 Kg/hour obtained in August at depths less than 50 m.         The present results confirm the previous evidences regarding the seasonality of the fishing effort distribution in this fishery obtained in 1997, 1998 and 1999 (del Río and Junquera, 2000). The pattern of the fleet activity indicate that this species form seasonal dense concentrations from August to November in shallow waters, between 51 to 100 m, in a quite restricted area in Div. 3N.   By-catches and discards.  The main by-catch species in the skate fishery are presented in Fig. 1.  In 1997 and 2000 the main by-catches are American plaice and yellowtail flounder and secondarily cod and juvenile Greenland halibut. The discarded proportions (%) of those by-catches are shown in Fig. 2.   Biological information  Table 3 and Figure 3 shows the length composition (0/00) by sex of thorny skate Spanish trawl catches in Div. 3N in 1997 and 2000. The length range is mainly between 30 and 85 cm and is approximately similar in the two years analysed. Modal length coincides in males and females in 48-49 cm in 1997. In 2000 the modal length is 50-51 cm and 46-47 cm for males and females respectively. Length classes between 42-59 cm are dominant in the catches (61.9%).  Figure 4 present the sex ratio in 1997-2000. Both sexes appeared equally represented in the catches. A total of 1977 and 8704 skates have been sampled in 1997 and 2000 respectively.  Female ratio is 52% in year 1997 and 51% in year 2000. Female proportions at length are shown in Fig. 5. In the first length-classes (24-40 cm), females are more abundant than males. Between 40-72 cm sex ratio fluctuates around 50%. In larger length-classes (72-94 cm), females proportion decreased very fast  (72 cm 50% and 78 cm 25%) and at length-classes over 88 cm the 100% are males.  A total of 2 629 males ranging from 21 cm total length to 95 cm total length and 2 284 females from 28 cm total length to 88 cm total length were examined from August to December 2000 (Table 4).  A 70% of the males and 47% of the females sampled were mature (adults). Similar proportions have been observed in previous years (Junquera and Paz, 1998; del Río and Junquera, 2000). Thus in the autumn concentrations the proportion of mature males is  3consistently higher than that of females, and besides, the majority of males were ripe whereas females were at earlier maturity stages. It could mean that the fishing activity is probably targeting on a mating concentration.   Length-weight relationship for males and females in year 2000 are illustrated in Fig. 6. The relationship between LT (cm) and weight (g) was assumed to be adequately expresses by the exponential function. Relationship for males is W(g) = 0.0169*LT(cm)2.8698  and for females W(g) = 0.0141*LT(cm)2.9165. Differences between sexes are not significant. The sexes combined relationship is W(g) = 0.0158*LT(cm)2.8878.  Acknowledgements  This study was made with the financial support of the European Commission (DG XIV, Study 98-048) and the Spanish Fisheries Administration.  References  del Río, J. L., and S. Junquera.  2000.  Seasonality and reproductive parameters of the thorny skate (Raja radiata Donovan, 1808) in NAFO Div. 3N. NAFO SCR Doc. 00/18. 8 pp.    Durán, P., X. Paz, and L. Ramilo. 1997. By-catch in the Spanish Greenland Halibut Fishery (NAFO Divisions 3LMNO): 1991-1994. NAFO Sci. Coun. Studies, 30: 1-20.  Junquera, S., and S. Iglesias.  1992. Spanish Fishery of Greenland Halibut (Reinhardtius hippoglossoides) in 1990-91. NAFO Sci. Coun. Studies, 28: 14 pp.  Junquera, S., and X. Paz.  1998. Non-traditional resources: Skate fishery and survey results in Division 3NO. NAFO SCR Doc. 98/26. 6pp.  Junquera, S., A. Vázquez, H. Murúa, E. Román, and J. L. del Río.  2000.  Spanish Research Report for 1999. NAFO SCS Doc. 00/20, Serial Nº 4245. 14 pp.  Kulka D. W., and F. K. Mowbray.  1998. The Status of Thorny skate (Raja radiata), a non-traditional species in NAFO Divisions 3L, 3N, 3O and Subdivisions 3Ps. DFO Res. Doc. 98/131, 70 pp.  Simon, J. E., and K. T. Frank.  1996.  Assessment of the Division 4VsW skate fishery. DFO Res. Doc. 96/105, 51 pp.  Table 1.- Fishing effort (%) in hours in the Spanish skate fishery in Div. 3N,  2000.  Div. 3N DEPTH (meters) JAN. FEB. MAR. APRIL MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC. TOTAL 0 -  50   (0) (1) (8) (11) (6) (3) (0) (30) 0 0 0 0 0 17 33 485 646 364 196 11 175251 - 100   (1) (5) (7) (10) (16) (24) (1) (65) 0 0 0 0 0 80 314 426 590 919 1397 30 3756101 - 150   (0) (0) (0) (1) (0) (0)  (2) 0 0 0 0 0 10 13 10 69 10 8 0 120151 - 200   (0) (1) (1)   (2) 0 0 0 0 0 0 23 0 63 31 0 0 117201 - 250   (0)    (0) 0 0 0 0 0 0 0 0 21 0 0 0 21TOTAL   (2) (7) (16) (24) (23) (28) (1) (100) 0 0 0 0 0 107 383 921 1389 1324 1601 41 5766  4Table 2.- CPUE (kg/h) by month in the skate fishery in Div. 3N, 1997 and 2000.  1997 DEPTH (meters) AUG. SEPT. OCT. NOV. DEC. TOTAL 0-  50 - 355,7 576,2 - - 527,3 51- 100 - 508,5 582,1 - - 541,9 101- 150 - 3,3 - - - 6,7 151- 200 - 22,3 1,9 - - 15,4 201-250 - - - - - - TOTAL - 457,4 573,9 - - 519,1  2000 DEPTH (meters) AUG. SEPT. OCT. NOV. DEC. TOTAL 0-  50 1079,3 592,4 - 640,2 937,5 801,9 51- 100 768,9 729,9 897,1 663,8 275,3 686,9 101- 150 - - - 13,9 11,4 10,9 151- 200 - 485,9 - - - 489,1 201-250 - 234,7 - - - 663,5 TOTAL 995,9 626,3 897,1 628,4 298,8 690,6     5 Table 3.- Thorny skate length composition (0/00) by sex in the Spanish commercial catches in Div. 3N: 1997-2000.        LENGTH 1997  2000 (cm) MALES FEMALES TOTAL  MALES FEMALES TOTAL 24 - 25 0 1 1  0 0 0 26 - 27 1 2 1  3 3 3 28 - 29 0 5 3  18 5 11 30 - 31 5 6 6  16 16 16 32 - 33 6 13 10  20 18 19 34 - 35 11 23 18  19 28 23 36 - 37 31 25 28  16 31 23 38 - 39 63 57 60  28 29 28 40 - 41 69 78 74  34 43 38 42 - 43 65 82 74  41 59 50 44 - 45 76 66 71  68 79 73 46 - 47 70 85 78  75 82 79 48 - 49 88 90 89  86 74 80 50 - 51 57 66 62  87 74 80 52 - 53 60 67 63  70 71 70 54 - 55 57 74 66  65 66 65 56 - 57 53 38 45  61 50 55 58 - 59 44 42 43  46 46 46 60 - 61 32 35 34  37 40 38 62 - 63 24 35 30  28 32 31 64 - 65 31 20 25  26 35 30 66 - 67 26 31 28  21 28 25 68 - 69 22 13 17  22 24 24 70 - 71 19 11 15  19 22 21 72 - 73 16 9 12  15 18 16 74 - 75 15 10 12  19 10 15 76 - 77 13 6 9  16 8 12 78 - 79 13 6 9  15 6 10 80 - 81 14 0 7  9 2 6 82 - 83 12 2 7  8 0 4 84 - 85 5 1 2  5 0 2 86 - 87 1 0 0  2 0 2 88 - 89 0 0 0  1 0 1 90 - 91 3 0 2  2 0 0 Total 1000 1000 1000   1000 1000 1000 Fish measured 936 1041 1977  4325 4379 8704 Nº samples 12  56 Sample weight (kg) 3150  13612 Depth range (m) 40-250   40-250  6 Table 4.- Number of adult and immature individuals by length in 2000.         MALES  FEMALES Length (cm) Immature Mature Total %  Immature Mature Total % <25 1 0 1 0  - - - - 26 - 27 1 0 1 0  - - - - 28 - 29 2 0 2 0  2 0 2 0 30 - 31 1 0 1 0  3 0 3 0 32 - 33 6 0 6 0  4 0 4 0 34 - 35 14 0 14 0  15 0 15 0 36 - 37 23 0 23 0  28 0 28 0 38 - 39 54 0 54 0  43 0 43 0 40 - 41 70 1 71 1  78 3 81 4 42 - 43 97 6 103 6  106 2 108 2 44 - 45 131 12 143 8  152 4 156 3 46 - 47 139 42 181 23  196 8 204 4 48 - 49 131 99 230 43  181 20 201 10 50 - 51 72 166 238 70  127 38 165 23 52 - 53 33 171 204 84  123 52 175 30 54 - 55 17 148 165 90  87 67 154 44 56 - 57 3 156 159 98  34 92 126 73 58 - 59 0 103 103 100  17 93 110 85 60 - 61 0 118 118 100  7 82 89 92 62 - 63 1 88 89 99  3 93 96 97 64 - 65 0 85 85 100  3 86 89 97 66 - 67 0 75 75 100  0 68 68 100 68 - 69 0 70 70 100  0 91 91 100 70 - 71 0 73 73 100  0 80 80 100 72 - 73 0 80 80 100  0 67 67 100 74 - 75 0 81 81 100  0 55 55 100 76 - 77 0 64 64 100  0 24 24 100 78 - 79 0 48 48 100  0 28 28 100 80 - 81 0 55 55 100  0 12 12 100 82 - 83 0 35 35 100  0 5 5 100 84 - 85 0 26 26 100  0 4 4 100 86 - 87 0 17 17 100  - - - - 88 - 89 0 7 7 100  0 1 1 100 >90 0 7 7 100  - - - - TOTAL 796 1833 2629 70  1209 1075 2284 47  7  Thorny skate64%American plaice14%Greenland halibut 1%Cod3%Yellowtail flounder18%1997     Thorny skate41%Roughhead grenadier2%Greenland halibut 7%American plaice31%Cod4%Yellowtail flounder15%2000   Fig. 1.- By-catch species in the skate fishery in Div. 3N, 1997 and 2000.    8020406080Greenlandhalibut YellowtailflounderCod ThornyskateAmericanplaice%19972000  Fig. 2.  Proportion discarded of the by-catches species in the skate fishery in Div. 3N, 1997 and 2000.   1997010203040506020 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95Total length (cm)0/00MalesFemales 2000010203040506020 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95Total length (cm)0/00MalesFemales  Fig. 3.-  Length composition (0/00) by sex of the thorny skate in the Spanish commercial catches  (NAFO Div. 3N): 1997 and 2000.    9  00,250,50,7511997 2000Years% individualsFemalesMalesN = 10681  Fig. 4.- Thorny skate sex-ratio (%) by year.    00,250,50,75124 29 34 39 44 49 54 59 64 69 74 79 84 89 94Total length (cm)Females proportion  Fig. 5.- Female ratio by length in 1997 and 2000 (NAFO Div. 3N).           10MALESW = 0,0169*LT2,8698R2 = 0,9601000200030004000500060007000800020 30 40 50 60 70 80 90 100LT (cm)Weight (g) FEMALESW = 0,0141*LT2,9165R2 = 0,9601000200030004000500060007000800020 30 40 50 60 70 80 90 100LT (cm)Weight (g)    Fig. 6.-  Thorny skate length-weight relationship in the Grand Bank by sex, 2000. Males: N=2630, LTmin=21, LTmax=95, Wmin=130, Wmax=7540. Females: N=2285, LTmin=28, LTmax=88, Wmin=310, Wmax=6790.          

Spanish Skate (Raja radiata Donovan, 1808) Fishery in the Grand Bank (NAFO Division 3N): 1997-2000.

Río-Iglesias, José Luis  del

Junquera, Susana

Digital.CSIC

http://www.repositorio.ieo.es/e-ieo/bitstream/10508/736/1/scr01-031.pdf

Spanish Skate (Raja radiata Donovan, 1808) Fishery in the Grand Bank (NAFO Division 3N): 1997-2000.

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