32 
Fishery Bulletin 115(1) 
Geographic zone 
Figure 3 
The effect of analyzed factors: A) sea surface temperature, (B) regulatory period, (C) geographic zone, 
and (D) target catch (swordfish or tunas), on the immediate mortality of discarded tiger shark (Galeo- 
cerdo cuvier) in the U.S. Atlantic pelagic longline fishery. Regulatory period refers to the period before 
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 (Au- 
gust 2004-December 2008), denoted as prefinning, precircle hooks, and circle hooks only in the figure. 
Bars represent the mean immediate mortality, and error bars indicate 95% confidence intervals. The 
geographic zones are Caribbean (CAR), Florida east coast (FEC), Gulf of Mexico (GOM), Mid-Atlantic 
Bight (MAB), north central Atlantic (NCA), northeast coastal (NEC), South Atlantic Bight (SAB), and 
Sargasso Sea (SAR). 
December 2008) was characterized by a new manda- 
tory use of circle hooks for U.S. pelagic longline ves- 
sels (NMFS^). Although this rule was implemented to 
reduce bycatch mortality of species of turtles (NMFS^), 
circle hooks are less likely than traditionally used J- 
hooks to be swallowed by some species of shark. The 
use of these hooks, therefore, reduces occurrences of 
internal injuries and immediate mortality rates in 
some species (Kerstetter and Graves, 2006; Campana 
et al., 2009; Serafy et al., 2012; Gilman et al., 2016; 
but see Yokota et al., 2006). 
In accordance with the methods of Serafy et al. 
(2012), we considered only specific regulatory periods 
in our analysis. There were other measures enacted 
that were required for the use of longlines in com- 
mercial fisheries during the period examined, but they 
were not incorporated into models because they were 
unlikely to have had a substantial effect on the im- 
mediate mortality of sharks. A few examples of regula- 
tory measures enacted include the fishery management 
plan for Atlantic tunas, swordfish, and sharks (which 
was enacted in 1999 to prohibit the retention of sev- 
eral species of sharks and reduce commercial coastal 
quotas for sharks; these regulations did not affect our 
analysis because we examined discarded animals and 
species only) and time or area closures (e.g., the closing 
of the NED zone in 2002; NMFS^). 
To determine how target catch influenced immediate 
mortality, the following generalized linear models with 
a logit link function were used: 
Immediate mortality = Target. (3) 
Target = target catch and was defined as catch of tu- 
nas, swordfish, or sharks. 
