INTER-AMERICAN TROPICAL TUNA COMMISSION - ComisiÃƒÂ³n ...

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116Some marine mammals are adversely affected by reduced food availability during El Niño events, especially in coastal ecosystems.Examples that have been documented include dolphins, pinnipeds, and Bryde’s whales off Peru, and pinnipeds around the GalapagosIslands. Large whales are able to move in response to changes in prey productivity and distribution.2.6. Sea turtlesSea turtles are caught on longlines when they take the bait on hooks, are snagged accidentally by hooks, or are entangled in the lines.Estimates of incidental mortality of turtles due to longline and gillnet fishing are few. At the 4th meeting of the IATTC WorkingGroup on Bycatch in January 2004, it was reported that 166 leatherback (Dermochelys coriacea) and 6,000 other turtle species,mostly olive Ridley (Lepidochelys olivacea), were incidentally caught by Japan’s longline fishery in the EPO during 2000, and that,of these, 25 and 3,000, respectively, were dead. At the 6th meeting of the Working Group in February 2007, it was reported that theSpanish longline fleet targeting swordfish in the EPO averaged 65 interactions and 8 mortalities per million hooks during 1990-2005. The mortality rates due to longlining in the EPO are likely to be similar for other fleets targeting bigeye tuna, and possiblygreater for those that set their lines at shallower depths for albacore and swordfish. About 23 million of the 200 million hooks seteach year in the EPO by distant-water longline vessels target swordfish with shallow longlines.In addition, there is a sizeable fleet of artisanal longline vessels that fish for tunas, billfishes, sharks, and dorado (Coryphaena spp.)in the EPO. Since 2005, staff members of the IATTC and some other organizations, together with the governments of several coastalLatin American nations, have been engaged in a program to reduce the hooking rates and mortalities of sea turtles in these fisheries.Additional information on this program can be found in Section 8.2.Sea turtles are occasionally caught in purse seines in the EPO tuna fishery. Most interactions occur when the turtles associate withfloating objects, and are captured when the object is encircled. In other cases, nets set around unassociated schools of tunas orschools associated with dolphins may capture sea turtles that happen to be at those locations. The olive Ridley turtle is, by far, thespecies of sea turtle taken most often by purse seiners. It is followed by green sea turtles (Chelonia mydas), and, very occasionally,by loggerhead (Caretta caretta) and hawksbill (Eretmochelys imbricata) turtles. Only one mortality of a leatherback turtle has beenrecorded during the 10 years that IATTC observers have been recording this information. Some of the turtles are unidentified becausethey were too far from the vessel or it was too dark for the observer to identify them. Sea turtles, at times, become entangled inthe webbing under fish-aggregating devices (FADs) and drown. In some cases, they are entangled by the fishing gear and may beinjured or killed. Preliminary estimates of the mortalities (in numbers) of turtles caused by large purse-seine vessels during 2008 areas follows:Set typeOBJ NOA DELTotalOlive Ridley 1 0 0 1Eastern Pacific green 0 0 0 0Loggerhead 0 0 0 0Hawksbill 0 0 0 0Leatherback 0 0 0 0Unidentified 1 0 0 1Total 2 0 0 2The mortalities of sea turtles due to purse seining for tunas are probably less than those due to other types of human activity, whichinclude exploitation of eggs and adults, beach development, pollution, entanglement in and ingestion of marine debris, and impactsof other fisheries.The populations of olive Ridley, green, and loggerhead turtles are designated as endangered, and those of hawksbill and leatherbackturtles as critically endangered, by the International Union for the Conservation of Nature.2.7. Sharks and other large fishesSharks and other large fishes are taken by both purse-seine and longline vessels. Silky sharks (Carcharhinus falciformis) are themost commonly-caught species of shark in the purse-seine fishery, followed by oceanic whitetip sharks (C. longimanus). Thelongline fisheries also take significant quantities of silky sharks, and a Pacific-wide analysis of longline and purse-seine fishing isnecessary to estimate the impact of fishing on the stock(s). Preliminary estimates of indices of relative abundance of silky sharks,based on data for purse-seine sets on floating objects, show a decreasing trend during 1994-2006; the trends in unstandardized by-
catch per set are similar for the other two types of purse-seine sets (standardized trends are not yet available). The unstandardizedaverage bycatches per set of oceanic whitetip sharks also show decreasing trends for all three set types during the same period. It isnot known whether these decreasing trends are due to incidental capture by the fisheries, changes in the environment (perhaps associatedwith the 1997-1998 El Niño event), or other factors. The decreasing trends do not appear to be due to changes in the densityof floating objects.Scientists at the University of Washington are conducting an analysis of the temporal frequency of areas of high bycatches of silkysharks in purse-seine sets on floating objects, which will be useful for determining the effectiveness of area-time closures as a meansof reducing shark bycatch. Results show that both model predictions and observed data tend to indicate that these bycatches occurmost frequently north of 4°N and west of 100-105°W. However, due to large tuna catches south of 5°N, the greatest reduction inbycatch from sets on floating objects with the least loss of tuna catch would be achieved north of approximately 6°N.A sampling project has been initiated by scientists of the IATTC and the NMFS to collect and archive tissue samples for sharks,rays, and other large fishes for future genetics analysis. Data from the archived samples will be used in studies of large-scalestock structure of these taxa in the EPO, information that is vital for stock assessments and is generally lacking throughout thePacific Ocean.A stock assessment for blue sharks (Prionace glauca) in the North Pacific Ocean has been conducted by scientists of the NMFS andthe NRIFSF. Preliminary results provided a range of plausible values for MSY of 1.8 to nearly 4 times the 2001 catch of blue sharkper year.Preliminary estimates of the discards (in metric tons) of sharks and other large fishes in the EPO during 2008, other than those discussedabove, by large purse-seine vessels are as follows. Complete data are not available for small purse-seine, longline, and othertypes of vessels.117Set typeOBJ NOA DEL TotalSharks 611 55 41 707Rays (Mobulidae and Dasyatidae) 4 33 11 48Dorado (Coryphaena spp.) 1,143 21 2 1,166Wahoo (Acanthocybium solandri) 242 1
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COVER PHOTOGRAPH BY WAYNE PERRYMANF
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3FISHERY STATUS REPORT 7TUNAS AND B
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5INFORME DE LA SITUACIÓN DE LA PES
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7A. THE FISHERY FOR TUNAS AND BILLF
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10fisheries, and have been reported
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12line vessels.The estimated size c
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14Figure 2. Carrying capacity, in c
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16FIGURE A-2a. Average annual distr
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18.FIGURE A-4. Distributions of the
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20FIGURE A-6a. Estimated size compo
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26FIGURE A-9. Estimated catches of
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28FIGURE A-11. Estimated size compo
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30TABLE A-2a. Estimated retained ca
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32TABLE A-2a. (continued)TABLA A-2a
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34TABLE A-2b. (continued)TABLA A-2b
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36TABLE A-3a. Catches of yellowfin
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381TABLE A-3c. Catches of skipjack
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40TABLE A-3e. Annual catches of big
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42TABLE A-4b. Preliminary estimates
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44TABLE A-6a. Annual retained catch
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46TABLE A-7. Estimated numbers of s
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48TABLE A-8. Types of floating obje
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50TABLE A-10. Numbers and well volu
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52TABLE A-11b. Estimates of the num
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54A. LA PESQUERÍA DE ATUNES Y PECE
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56En la Tabla A-2a se presentan las
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581.3. Composición por tamaño de
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601.5. Descargas de atunes y bonito
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62bodega en el mar (VEM), en miles
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64when the true dynamics includes a
Page 68 and 69: 66FIGURE B-2. Estimated recruitment
Page 70 and 71: 68FIGURE B-4. Spawning biomass traj
Page 72 and 73: 70FIGURE B-6. Catches of yellowfin
Page 74 and 75: 72FIGURE B-8. Phase plot of the tim
Page 76 and 77: 74TABLE B-1. Estimates of the MSY o
Page 78 and 79: 76Es importante señalar que la cur
Page 80 and 81: 78FIGURE C-1. Total catches (retain
Page 82 and 83: 80C. ATÚN BARRILETESe ha usado un
Page 84 and 85: 82fishing mortality are expected to
Page 86 and 87: 84FIGURE D-3. Average annual fishin
Page 88 and 89: 86FIGURE D-5. Trajectory of the spa
Page 90 and 91: 88FIGURE D-7. Catches for 1975-2008
Page 92 and 93: 90FIGURE D-9. Phase plot of the tim
Page 94 and 95: 92D. ATÚN PATUDOEn la presente eva
Page 96 and 97: 946. Los resultados son más pesimi
Page 98 and 99: 96FIGURE E-1. Retained catches of P
Page 100 and 101: 98F. ALBACORE TUNAThere are two sto
Page 102 and 103: 100300 000250 000200 000t150 000100
Page 104 and 105: 102fue aproximadamente 0.75, nivel
Page 106 and 107: 104FIGURE G-1. Retained catches of
Page 108 and 109: 106H. BLUE MARLINThe best knowledge
Page 110 and 111: 108H. MARLÍN AZULLa mejor informac
Page 112 and 113: 110FIGURE I-1. Retained catches of
Page 114 and 115: 112J. ECOSYSTEM CONSIDERATIONS1. In
Page 116 and 117: 114have been identified (by presenc
Page 120 and 121: 118tors of stress, and removing liv
Page 122 and 123: 120Knowledge of the trophic ecology
Page 124 and 125: 1226. AGGREGATE INDICATORSRecogniti
Page 126 and 127: 124b. The incidental mortalities of
Page 128 and 129: 126FIGURE J-1. Simplified food-web
Page 130 and 131: 128FIGURE J-4. Trophic level estima
Page 132 and 133: 130cual no es incluida en los anál
Page 134 and 135: 132Especie y poblaciónMortalidad i
Page 136 and 137: 1342.7. Tiburones y otros peces gra
Page 138 and 139: 136condición de la población del
Page 140 and 141: 1387‰ con respecto a la línea de
Page 142 and 143: 140entre índices de asociación de
Page 144 and 145: 142b. En junio de 2003, la CIAT ado
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