Goodyear: Analysis of time-area closures to minimize billfish bycatch 



251 



48.6% from 1° to 5° cells compared with the predicted 

 levels of 50%. The mean reductions for targeted spe- 

 cies were slightly greater than the predicted values. 

 The observed mean values were 18.6, 20.1, and 

 22.8%, compared with the predicted values of 16.4, 

 19.6, and 20.7% for the 1°, 2° and 5° cells, respec- 

 tively. As with billfish combined, the larger 5° grid 

 produced results that were closest to the values pre- 

 dicted from the 1986-91 data set and showed the 

 least year-to-year variability in the percent reduc- 

 tion of marlin catches. Overall, the result for marlin 

 at the 5° resolution was in remarkable agreement 

 with the values predicted from the evaluation of the 

 1986-91 data. 



Discussion 



This study was intended to consider pelagic longlines 

 only. However, bottom-longline and pelagic-longline 

 sets could not always be clearly distinguished in the 

 database used for the analysis. Consequently, some 

 of the effort and catch included in the analyses were 

 likely from bottom-longline sets. Some additional 

 refinement of the analyses might have been possible 

 with additional attention to eliminating bottom- 

 longline data. However, the total of the bottom- 

 longline sets is thought to be only about 10% of the 

 longline sets in the database (Cramer-), and all iden- 

 tified bottom-longline sets were eliminated from the 



^ Cramer, J. 1996. Sustainable Fisheries Division, Southeast 

 Fisheries Science Center, 75 Virginia Beach Drive, Miami. FL 

 33149. 



analysis. Consequently, it is not likely that a com- 

 plete elimination of the bottom-longline sets would 

 have had an important effect on the basic pattern 

 seen in the results of this study. 



The International Commission for the Conserva- 

 tion of Atlantic Tunas (ICCAT) CPUE data files (task 

 ii) indicate that billfish often accounted for 15% or 

 more of the Japanese longline catch in the Gulf of 

 Mexico and Caribbean before about 1977. However, 

 the total harvest of billfish by the pelagic-longline 

 fishery documented in the 1986-95 U.S. logbooks was 

 never large in comparison with other species in their 

 reported catch, and most were discarded even before 

 the prohibition on harvest was promulgated by the 

 U.S. Atlantic Billfish Plan. According to logbook 

 records only 16.26% of the billfish caught during the 

 period 1986-89 were retained. This figure dropped 

 to 4.82%) for the period 1992-95. Observer data for 

 pelagic-longline trips indicate that the actual bycatch 

 rates for billfish in this fishery are much higher than 

 is currently being reported in logbooks ( Cramer M. 

 This phenomenon perhaps exists because billfish are 

 not economically important components of the har- 

 vest, a phenomenon that was intensified by the U.S. 

 Atlantic Billfish Plan which prohibited commercial 

 harvest of billfishes after 1988. If so, it is likely that 

 billfish were under-reported in the logbook data for 

 the 1986-91 period used in the present analysis. The 

 magnitude of the reporting rate is unknown for the 

 1986-91 period. However, unreported rates would not 

 pose a problem for the analysis presented here if they 

 were randomly distributed in time and space. This 

 question could possibly be addressed in future analy- 

 ses by using observer data from U.S. domestic pe- 



