Sixty-eight yellowfin tuna, Thunnus albacares, (60-135 cm fork length) were caught and released with implanted archival tags offshore off Baja California, Mexico, during October 2002 and October 2003. Thirty-six fish (53%) were recaptured and the data were downloaded from all 36 recovered tags. Time at liberty ranged from 9 to 1,161 days, and the data were analyzed for the 20 fish that were at liberty for 154 or more days. The accuracy in the position estimates, derived from light-level longitude data and sea-surface temperatures (SSTs) based latitude, is about 0.41° in longitude and 0.82° in latitude, in this region. The movement paths, derived from position estimates, for the 20 yellowfin indicated that 19 (95%) remained within 1,445 km of their release locations. The estimated mean velocity along movement paths was 77 km/day. The southern and northern seasonal movement paths observed for yellowfin off Baja California are influenced by the seasonal movements of the 18°C SST isotherm. Cyclical movements to and from suitable spawning habitat (≥24°C SST) was observed only for mature fish. For the 12 fish that demonstrated site fidelity, the mean 95 and 50% utilization distributions were 258,730 km2 and 41,260 km2, respectively. Evaluations of the timed depth records resulted in discrimination of four distinct behaviors. When exhibiting type-1 diving behavior (78.1% of all days at liberty) the fish remained at depths less than 50 m at night and did not dive to depths greater than about 100 m during the day. Type-2 diving behavior (21.2% of all days at liberty) was characterized by ten or more dives in excess of 150 m during the day. Type-2 diving behavior is apparently a foraging strategy for fish targeting prey organisms of the deep-scattering layer during the day, following nighttime foraging within the mixed layer on the same prey. Yellowfin tuna exhibited occasional deep-diving behavior, and some dives exceeded 1,000 m, where ambient temperatures were less than 5°C. Surface-oriented behavior, defined as the time fish remained at depths less than 10 m for more than 10 min, were evaluated. The mean number and duration of surface-oriented events per day for all fish was 14.3 and 28.5 min, respectively. Habitat utilization of yellowfin, presented as monthly composite horizontal and vertical distributions, indicates confined geographical distributions, apparently resulting from an affinity to an area of high prey availability. The vertical distributions indicate greater daytime depths in relation to a seasonally deeper mixed layer and a greater proportion of daytime at shallower depths in relation to a seasonally shallower mixed layer.

Movements, behavior, and habitat utilization of yellowfin tuna ( Thunnus albacares ) in the northeastern Pacific Ocean, ascertained through archival tag data

Movements, behavior, and habitat utilization of yellowfin tuna (Thunnus albacares) in the Pacific Ocean off Baja California, Mexico, determined from archival tag data analyses, including unscented Kalman filtering

Fishery management decisions are commonly guided by stock assessment models that aggregate outputs across the spatial domain of the species. With refined understanding of spatial population structures, scientists have begun to address how spatiotemporal mismatches among the scale of ecological processes, data collection programs, and stock assessment methods (or assumptions) influence the reliability, and ultimately, appropriateness of regional fishery management (e.g., assigning regional quotas). Development and evaluation of spatial modeling techniques to improve fisheries assessment and management have increased rapidly in recent years. We overview the historical context of spatial models in fisheries science, highlight recent advances in spatial modeling, and discuss how spatial models have been incorporated into the management process. Despite limited examples where spatial assessment models are used as the basis for management advice, continued investment in fine-scale data collection and associated...

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Space Oddity: the Mission for Spatial Integration

Pertinent data and literature are examined to determine the effects of the environment on the spatial distribution of skipjack tuna, Katsuwonus pelamis, in both the Atlantic and Pacific Oceans. Environment/skipjack distribution relationships derived from this information are applied to longterm annual mean distributions of dissolved oxygen and thermal structure for the Atlantic Ocean between lot. 40"N and 40% The depth of skipjack habitat is mapped. Within the defined habitat areas, high vulnerability of skipjack tuna to surface gear is inferred and areally compared with the long-term catch of the FIS (French, Ivory Coast, and Senegalese) fleet to confirm the validity of this approach. This technique is then used to hypothesize areas of vulnerability of skipjack to surface gear outside the range of the FIS fleet effort in the western Atlantic. Finally, the effects of surface winds on fishing operations are discussed and those areas where wind speed may hamper operations are outlined for the Atlantic Ocean between lot. 30"N and 30"s. environmental indicators to infer habitat limits of skipjack tuna appears preferable to habitat forecasts based on skipjack tuna forage or migration patterns because of the limited data available to assess these factors. In contrast, a comparatively large amount of physical oceanographic data is available for comparison with catch statistics since oceanographic observations are routinely made for other purposes. Physiological experiments on captive skipjack tuna from the Pacific have been carried out to ascertain habitat preference as functions of several environmental indicators (Dizon, 1977; Dizon et al., 1977, 1978). No attempt has been made to integrate existing environment/ habitat relationships and data .with Atlantic catch data to define those areas where skipjack tuna should be available to surface gear. This paper attempts to do this and, in doing so, to develop working hypotheses for identifying areas of potential skipjack tuna concentration as an aid to exploiting and managing the resource. R . H . Evans is with the Southwest Fisheries Center, National Marine Fisheries Service, NOAA. La Jolla. C A 92038; D. R . McLain is with the Pacific Environmental Group, National Marine Fisheries Service, N O M , Monterey, C A 93940; and R. A. Bauer is with Compass Systems, Inc., San Diego, CA 92109.

Atlantic Skipjack Tuna: Influences of Mean Environmental Conditions on Their Vulnerability to Surface Fishing Gear

Tunas, a very large and charismatic food fish with a wide distributional
range, are valuable both in domestic and foreign markets and hence, play a
vital role in the economies of many countries especially oceanic Islands. The
oceanic waters adjoining the Asia-Pacific region contribute the bulk of the
global tuna production. Although they constitute less than 5% of the world
commercial catch by weight, they contribute much by dollar value (US $ 5.3
billion). Research and development efforts on tuna resources all over the world
have contributed to a rapid growth of literature. The present bibliography is
prepared to incorporate all the available publications including electronic
references on this commercially important group, so that a large spectrum of
researchers in this area would be benefited.

Bibliography on Tunas

ENGLISH: Totals of 59,547 tagged yellowfin and 90,412 tagged skipjack were released during 1952-1964 throughout the range of the fishery in the eastern Pacific Ocean during that period. Most of the fish were released from commercial baitboats, either on regular fishing trips or on chartered trips to catch fish for tagging. There we re 8,397 yellowfin and 4,381 skipjack returned from these releases. There appear to be two main groups of yellowfin in the eastern Pacific Ocean. There is considerable intermingling among the fish of the two groups, however. The fish of the northern group (west coast
of Baja California, Gulf of California, and Revillagigedo Islands) first appear in the Revillagigedo Islands in about April, and migrate north along the Baja California coast during the spring and summer and south along that coast during the fall. Recruits to the southern group (Tres Marias Islands to northern Chile) appear at many points or continuously along most of the coast. The fish which first appear in the northern Panama Bight in April migrate rapidly northwest to Central America and Mexico and south to the Gulf of Guayaquil. There also appear to be two main groups of skipjack in the eastern Pacific Ocean. The fish of the northern group (west coast of Baja California, Gulf of California, and Revillagigedo Islands ) perform about the same migration as do the yellowfin of the same area, but most of the skipjack apparently then migrate to the central Pacific Ocean during the fall and/or winter. Recruits to the southern group (Central America to northern Chile) appear mostly in or near the Panama Bight. The fish which first appear in the northern Panama Bight in April migrate rapidly northwest to Central America and south to the Gulf of Guayaquil. The proportions which migrate in these directions vary considerably from year to year, this perhaps being dependent on differences in the sea-surface temperatures. SPANISH: Durante el periodo de 1952-1964 se libero a traves de todos los limites de distribucion de la pesqueria en el Oceano Pacifico oriental un total de 59,547 aleta amarilla y 90,412 barriletes marcados. La mayoria de los peces fueron liberados de barcos de carnada comerciales, o en viajes regulares de pesca o en viajes en los que se fletaron los barcos para capturar atunes y marcarlos. De estas liberaciones se recapturaron 8,397 aleta amarilla y 4,381 barriletes. Parece que haya dos grupos principales de aleta amarilla en el Oceano Pacifico oriental. Sin embargo, existe una entremezcla considerable entre los peces de los dos grupos. Los peces del grupo septentrional (costa occidental de Baja California, Golfo de California y Islas Revillagigedo) aparecen primero en las Islas Revillagigedo alrededor de abril, y durante la primavera y el verano se desplazan al norte a lo largo de la costa de Baja California y durante el otono al sur a lo largo de la costa. Los reclutas del grupo meridional (Islas Tres Marias hasta el norte de Chile) aparecen en muchas partes o continuamente a lo largo de la mayoria de la costa. Los peces que aparecen primero en la region septentrional del Panama Bight en abril se desplazan
rapidamente al noroeste a la America Central y Mexico y al sur al Golfo de Guayaquil. Parece tambien que existen dos grupos principales de barrilete en el Oceano Pacifico oriental. Los peces del gr upo septentrional (costa occidental de Baja California, Golfo de California e Islas Revillagigedo )
realizan casi la misma migracion que el atun aleta amarilla de la misma area, pero aparentemente la mayor parte del barrilete se desplaza luego al Oceano Pacifico central durante el otono y/o en el invierno. Los reclutas al grupo meridional (America Central al norte de Chile) aparecen en su mayoria en el Panama Bight o cerca a este lugar. Los peces que aparecen primero en la region septentrional del Panama Bight en abril se desplazan rapidamente al noroeste a la America Central y al sur al Golfo de Guayaquil. Las proporciones que se desplazan en estas direcciones varian considerablemente de ano a ano; tal vez esto depende en las diferencias de temperatura de la superficie del mar.

(PDF contains 227 pages.)

William H. Bayliff

Papers

Migrations of yellowfin and skipjack tuna in the Eastern Pacific Ocean as determined by tagging experiments, 1952-1964