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



247 



reduction in the 1986-91 marlin bycatch could 

 have been attained with only a 1.1 to 2.8% re- 

 duction in the catch of target species, depend- 

 ing on the spatial resolution employed. This 

 would result by eliminating the effort in months 

 and areas where the reported billfish bycatch 

 exceeded the threshold percentage of billfish in 

 the combined catch indicated in Table 3. Simi- 

 larly, a 50% reduction in the 1986-91 marlin 

 bycatch would have been obtained by eliminat- 

 ing the effort in cells where the reported bill- 

 fish bycatch exceeded the table values with cor- 

 responding reductions of 16.4 to 20.7% in the 

 harvest of target species. A 95% reduction in the 

 1986-91 marlin bycatch would have been 

 achieved by eliminating all effort in cells that 

 reported catches of more than 0.73, 0.84, or 

 1.07% marlin for 1°, 2°, or 5° cells, and there 

 would have a concomitant reduction in target 

 species catch of 59.4, 63.1, or 66.5% respectively. 

 Obviously, the temporal and spatial distribu- 

 tion of the cells that would be eliminated with 

 the current method for any particular thresh- 

 old selected is of considerable interest. Figure 3 

 presents the distribution of cells by area and month 

 that correspond to a threshold selection that would 

 have eliminated 50% of the billfish bycatch from the 



o 



a 



T3 



m 

 <a 



CD 



Marlin percentage reduction 



Figure 2 



Percent reduction in target species and blue and white marlin 

 bycatch associated with the removal of effort in time-area cells 

 above the indicated threshold percentage of marlin in the catch 

 for cell sizes of 1°, 2°, and 5° of latitude and longitude. 



1986-91 U.S. pelagic-longline fishery as reported in 

 the log books. Areas where fishing effort was ex- 

 pended within 5° cells are stippled or diagonally 



