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50 Yellowfin Tagged To Study The Eastern Pacific Ocean Stock Eastern Pacific Ocean, March 25, 13

Understanding the behavior of tunas is integral to so many aspects of improved practices and management. In the Eastern Pacific Ocean Kurt Schaefer and Dan Fuller, scientists with the Inter-American Tropical Tuna Commission (IATTC), recently returned after spending two weeks aboard the San Diego based 92-foot US-flag long-range sport fishing vessel Royal Star. They traveled with 19 anglers, on a regularly scheduled fishing trip to Clipperton Island.

Clipperton Island is a coral atoll west of Costa Rica and carries the flag of France

According to Schaefer, “The trip was successful as 50 yellowfin, ranging from 73-142 cm fork length (FL), were landed aboard the vessel, measured, tagged, and released.”

The pair used two types of tags – Lotek Wireless LAT 2810 archival tags (ATs) and Hallprint plastic dart tags (PDTs), which were surgically implanted in each of the 50 yellowfin released.

“Tagging experiments on yellowfin tuna utilizing plastic dart tags (PDTs) in the eastern Pacific Ocean (EPO) since the 1950’s appear to indicate that movements of tagged fish at liberty for more than 30 days tend to be restricted to less than 1,000 nautical miles of their release positions,” Schaefer said. “However, tagging studies utilizing PDTs have limitations for studies of spatial dynamics of fish, because it only provides information about the release and recapture positions, and recaptures are highly dependent on spatial and temporal variability in fishing effort, fish behavior, and gear selectivity.”

“Electronic archival (data storage) tags (ATs) with light-sensors, have been successfully used to estimate positions and reconstruct most probable tracks, for many marine epipelagic species, based primarily on daily records of ambient light and sea-surface temperatures. Current-generation ATs are capable of autonomous sampling of high-resolution data for multiple years, providing opportunities to evaluate the influence of seasonal and inter-annual environmental variability and ontogenetic changes in movement patterns, behavior, and habitat utilization. ATs can vastly improve our understanding of the large-scale movements, stock structure, behavior, and habitat utilizations, essential for improving stock assessments. Furthermore, utilizing state-space models, with sea-surface temperature (SST) measurements integrated, for analyses of AT geolocation data sets, can provide improved estimates of geographic positions, most probable tracks, and movement parameters. The movement parameters can subsequently be incorporated into population movement models. A recent tagging experiment in which large numbers of yellowfin were released with implanted ATs, for several consecutive years off Baja California, Mexico, demonstrated restricted movements, quantified movement parameters, and elucidated behavior patterns and habitat utilization.”

Schaefer added that, “Considering the restricted movements, and limited mixing of yellowfin throughout the EPO, the development of a spatially-structured stock assessment model with movements appears to be warranted. However, in order to develop a scientifically valid spatially-structured assessment model with movement for yellowfin in the EPO, it is necessary to better understand yellowfin stock structure, obtain estimates of movement parameters, and life history characteristics, from several spatial strata. This can be achieved, but requires large-scale multi-year tagging studies utilizing ATs, conducted throughout the region of the EPO inhabited by yellowfin and exploited by commercial fishing vessels.”