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



721 



- 50°N 



- 40"N 



30=N 



80= W 



70='W 



60°W 



50=W 



40"W 



Figure 1 



Locations of observed longline sets (1992-2002) recorded in the U.S. Pelagic 

 Observers Program database and analyzed in the present study. 



the event that a factor was found to be nonsignificant 

 (P>0.05), it was removed and a regression was rerun 

 until all highest order model terms were significant 

 (Hocking, 1976; Draper and Smith, 1981). We assumed 

 maturity (both sexes) occurred at 185 cm FL (Pratt, 

 1979). The average P DA and the ratio of immature-to- 

 mature individuals discarded in each 0.5-degree cell 

 were estimated and plotted in order to visually examine 

 the spatial distribution of these two variables. 



Table 1 



Regression coefficients and associated standard error 

 values (SE) for the estimation of proportion of blue shark 

 released alive IP DA ) in = 37), where fi corresponds to the 

 intercept, and fi, and /i, are coefficients associated with 

 blue shark fork length and set duration, respectively. 



Parameters 



Estimate 



SE 



P> If I 



ft 

 ft 

 ft 



0.967 



0.0021 



-0.0269 



0.0500 

 0.0002 

 0.0037 



<0.0001 

 <0.0001 

 <0.0001 



Results 



Data from 702 longline sets were used in analyses and 

 resulted in size and condition (i.e., live or dead) informa- 

 tion on 4290 individual blue shark. From these data, a 



total of 37 proportions (i.e., P DA values) were calculated shark size and set duration had significant effects on 



and used in regression analyses. P DA (r 2 =0.86, n=37, P<0.00001; Table 1). Plots of the 



Most of the sets targeted swordfish (39%) or sword- 

 fish and tuna (36%), or unspecified tuna species (14%). 

 Bigeye tuna and yellowfin tuna were the target of 8% 

 and 3% of the sets, respectively. About 88% of the sets 

 included in the analysis were characterized as "night 

 sets" and the remaining were "day sets." 



Overall, more blue shark were released alive (69%) 

 than dead. Shark sizes, water temperatures, and set 

 durations used in the multiple linear regression ranged 

 from 75 to 300 cm FL (median=175 cm), 8 to 29°C 

 (median=19°C), and 6 to 14 hours (median=12), respec- 

 tively. About 68% of all released animals measured less 

 than the size of sexual maturity (i.e., <185 cm FL). 



Multiple linear regression indicated that no interac- 

 tion terms were statistically significant and that only 



observed proportions and the predicted response surface 

 illustrate how the proportion of live releases increases 

 with shark size and decreases with duration of set (Fig. 



2, A and B). Whereas set duration has a moderate im- 

 pact on the largest size classes, the proportion of live 

 sharks <185 FL (i.e., immature stages) is consider- 

 ably reduced even at relatively short set durations. For 

 example, predicted P DA for the smallest sharks (i.e., 

 FL=75 cm) was 0.67 and 0.47 for set durations of 6 and 

 14 hours, respectively; for those animals measuring 250 

 cm FL, it was 0.94 and 0.80 for the same set durations. 

 Maps of mean P DA values and of the proportion of imma- 

 ture sharks caught indicated conspicuous differences off 

 the U.S. east coast versus over the Grand Banks (Fig. 



3, A and B). Specifically, the proportion of live releases 



