NOTE Diaz and Serafy: Factors affecting the number of Pnonoce glauca available for live release in fisheries 



723 



50°N 



70" W 



60" W 



50"W 



40°W 



40"N 



50"N 



70"W 



60°W 



40 : N 



50"W 



40"W 



50"N - 



40 N 



70 W 



60"W 



50"W 



40"W 



U |m 0.4-0 6 



HI 0.0-0.2 |] 0.6-0.8 



H 7 ?] 0.2-0 4  0.8-1.0 



50N 



40°N 



70 : W 



60°W 



50 ,: -W 



40"W 



Figure 3 



(Ai Average proportion of blue shark released alive and (B) average proportion 

 of immature blue shark released in pelagic longline sets. Proportions were 

 estimated for 0.5-degree cells where at least one longline set was deployed in 

 the period 1992-2002. 



Ward et al. (2004) modeled the effect of set duration 

 on pelagic longline catches and found that blue shark 

 catch rates increased with set duration. According to 

 our results, the increase in set durations also leads to 

 increases in the number retrieved dead. In concept, a 

 possible management measure to achieve reductions 

 in blue shark mortality may include shortening long- 

 line set durations. However, a regulation of this nature 

 would be difficult to implement (let alone enforce) be- 



cause swordfish catch rates are also lowered when set 

 durations are shortened (Ward et al., 2004) and there- 

 fore result in negative economic impacts that would 

 likely be unacceptable to the industry. 



Results of this analysis also have implications for 

 blue shark stock assessment. Stock assessments based 

 on longline fisheries data often use a hook selectivity 

 function of a logistic form, whereby hook retention is 

 100% for fish larger than a certain size. In the particu- 



