Dapp et al.: Immediate mortality of Prionace glauca and Galeocerdo cuvier caught by pelagic longlines 
33 
Regulatory period 
Figure 4 
The immediate mortality rates of blue sharks {Prionace glauca) caught in the U.S. Atlantic pelagic longline fishery by regu- 
latory period and geographic zone. Regulatory period refers to the period prior to the establishment of fin-to-carcass ratios 
(January 1992-February 1993), before the prohibition of the use of J-hooks (March 1993-August 2004), and during which 
the use of circle hooks was mandatory (August 2004-December 2008), denoted as prefinning, precircle hooks, and circle 
hooks only in the figure. The geographic zones are (A) Caribbean, (B) north central Atlantic, (C) South Atlantic Bight, (D) 
Florida east coast, (E) northeast coastal, (F) Sargasso Sea, (G) Mid-Atlantic Bight, (H) northeast distant (H), and (I) tuna 
north. Bars represent the mean immediate mortality, and error bars indicate 95% confidence intervals. 
This variable was examined in isolation because re- 
cords with multiple species had to be removed from 
the data set for the target catch analysis, resulting in 
a reduced data set. The reduced data sets, however, did 
not have the sample sizes necessary to examine all the 
geographic zones and regulatory periods. 
All statistical analyses were conducted with R® sta- 
tistical software, vers. 2.14.2 (R Core Team, 2012). 
® Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
Results 
Shark retention and total numbers reported before data 
screening 
There were 1,436,061 reported captures of sharks be- 
tween 1992 and 2008 in the USPL data set (Table 1). 
Blue sharks accounted for approximately 60% of the 
total catch (Table 1). Numbers reported for other spe- 
cies caught are available in Table 1. 
The percentage of animals retained varied consid- 
erably among species, with the blue shark having the 
lowest (1%; Table 1) and the porbeagle having the 
