Abstract.- A substantial long- 

 line fishery has recently developed in 

 the Gulf of Mexico. Tuna are believed 

 to aggregate in regions of sea-sur- 

 face temperature change (frontal 

 zones), and this behavior may sig- 

 nificantly bias the catch and effort 

 statistics critical for managing the 

 fishery. We report the results of an 

 effort to relate the sea-surface ther- 

 mal structure evident in satellite 

 imagery to yellowfin tuna Thunnus 

 albacares catch and effort, with the 

 goal of providing fishery managers 

 an assessment of how the yellowfin 

 tuna catch-per-unit-of-effort (CPUE) 

 is affected by the presence/absence 

 of temperature variability. We exam- 

 ined over 6000 longline set records 

 and 109 satellite sea-surface temper- 

 ature (SST) images, and compared 

 the CPUE with sea-surface tempera- 

 ture statistics computed from image 

 data in the corresponding area of the 

 longline set. We found no discernable 

 relationship between image SST 

 statistics and CPUE, and conclude 

 that catch statistics in the north- 

 western Gulf of Mexico are not 

 biased by yellowfin tuna aggregating 

 in regions of SST variability. 



Satellite observed Sea-surface 

 Temperatures and Yellowfin Tuna 

 Catch and Effort in the 

 Gulf of Mexico 



James H. Power 



Coastal Fisheries Institute, Center for Wetland Resources 

 Louisiana State University. Baton Rouge. Louisiana 70803 



L. Nelson May Jr. 



Coastal Fisheries Institute. Center for Wetland Resources 



Louisiana State University. Baton Rouge. Louisiana 70803 



Present address: Southeast Fisheries Center, National Marine Fisheries Service, NOAA 



Bldg. 1 103. Room 218, John C Stennis Space Center 



Stennis Space Center. Mississippi 39529 



Manuscript accepted 25 February 1991. 

 Fishery Bulletin, U.S. 89:429-439 (1991). 



Satellite sensors that detect ocean 

 color or temperature have repeated- 

 ly confirmed that the ocean environ- 

 ment is highly structured, with the 

 juxtaposition of different water 

 masses forming frontal zones where 

 important parameters such as salin- 

 ity, temperature, and nutrient con- 

 centration can change rapidly over 

 short horizontal distances. In turn, 

 phytoplankton, zooplankton, and 

 nekton abundances may also change 

 significantly in these regions, either 

 in response to favorable nutrient/ 

 food conditions or by accumulating in 

 converging currents. Because the 

 surface water mass boundaries are 

 sometimes discernable in satellite im- 

 agery, the locations of associated 

 phytoplankton, zooplankton, and 

 pelagic fish assemblages can some- 

 times be determined from such im- 

 agery (Thomas and Emery 1988, 

 Klimley and Butler 1988). 



Large and commercially important 

 pelagic fishes, such as tuna, are 

 thought to respond to increased food 

 concentrations or other favorable 

 conditions by aggregating in these 

 frontal regions (Alverson 1961, 

 Beardsley 1969, Laurs et al. 1984, 

 Maul et al. 1984, Fiedler and Bernard 

 1987, Klimley and Butler 1988). Fish- 



ermen have long believed that fishing 

 near thermal or color fronts would 

 increase fishing success, and some- 

 times refer to presumably favorable 

 waters as "tuna water" (Alverson 

 1961). The fisherman's ability to 

 locate such frontal zones is usually 

 limited by the field of coverage avail- 

 able from his vessels for sampling 

 temperature (or color) or that of a 

 spotter pilot's ability to detect color 

 boundaries. Because satellite sensors 

 can now detect ocean temperature or 

 color over large geographic areas, 

 pilot projects to use satellite imagery 

 as a fisheries aid have been under- 

 taken on both the east and west U.S. 

 coasts (Breaker 1981, Montgomery 

 1981, Wittenberg-Fay 1986, Cornil- 

 lon 1986). 



Efforts to provide sea-surface tem- 

 perature (SST) charts as fisheries 

 aids have been accompanied by scien- 

 tific investigations to evaluate the 

 possible relationships between SST, 

 ocean color, and fishing success. 

 Laurs et al. (1984) used thermal and 

 ocean color imagery from the Coastal 

 Zone Color Scanner to relate alba- 

 core Thunnus alalunga catch to 

 oceanographic features in the eastern 

 Pacific, and concluded that albacore 

 catch was clearly associated with 



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