34 
Fishery Bulletin 1 15(1) 
Table 1 
The numbers (and percentages) of sharks retained, discarded alive, and discarded dead on longline 
sets reported in the U.S. pelagic longline logbook data set from 1992 through 2008. Numbers re- 
ported are total numbers before data screening. An asterisk (*) indicates species for which numbers 
reported are likely to be accurate. Numbers recorded for species other than blue sharks (Prionace 
glauca), tiger sharks {Galeocerdo cuvier), oceanic whitetip sharks (Carcharhinus longimanus), and 
porbeagle {Lamna nasus) should be interpreted with caution because it was likely that these species 
were consistently misidentified. 
Species 
Number 
Retained 
Discarded alive 
Discarded dead 
Blue shark* 
863,153 
9362 (1%) 
702,955 (81%) 
150,836 (17%) 
Sandbar shark 
167,887 
157,261 (94%) 
7973 (5%) 
2653 (2%) 
Blacktip shark 
91,723 
77,033 (84%) 
9669 (11%) 
5021 (5%) 
Shortfin mako 
66,750 
51,710 (77%) 
10,696 (16%) 
4344 (7%) 
Dusky shark 
53,561 
30,934 (58%) 
16,376 (31%) 
6251(12%) 
Silky shark 
42,647 
18,236 (43%) 
14,472 (34%) 
9939 (23%) 
Tiger shark* 
33,063 
4975 (15%) 
26,737 (81%) 
1351 (4%) 
Hammerhead (unidentified) 
23,238 
10,024 (43%) 
8050 (35%) 
5164 (22%) 
Bigeye thresher 
13,227 
3675 (28%) 
7255 (55%) 
2297 (17%) 
Scalloped hammerhead 
13,062 
5629 (43%) 
4097 (31%) 
3336 (25%) 
Spinner shark 
11,439 
9340 (82%) 
1560 (14%) 
539 (5%) 
Night shark 
11,082 
3084 (28%) 
4432 (40%) 
3566 (32%) 
Oceanic whitetip shark* 
10,847 
2422 (22%) 
7254 (67%) 
1171 (11%) 
Smooth hammerhead 
9922 
4433 (45%) 
3646 (37%) 
1843 (19%) 
Porbeagle* 
8113 
3980 (49%) 
3312 (41%) 
821 (11%) 
Longfin mako 
7367 
2523 (34%) 
3887 (53%) 
957 (13%) 
Thresher (unidentified) 
5248 
2313 (44%) 
2197 (42%) 
738 (14%) 
Bignose shark 
2288 
992 (43%) 
940 (41%) 
356 (16%) 
White shark 
1435 
488 (34%) 
879 (61%) 
68 (5%) 
All recorded sharks 
1,436,061 
398,415 (28%) 
836,395 (58%) 
201,251 (14%) 
highest (49%; Table 1) rates of retention of the 4 spe- 
cies deemed to be accurately reported. When animals 
retained were included in our analyses, the porbeagle 
was the species least likely (41%) to be released alive 
by fishermen among the 4 species deemed to be accu- 
rately reported (Table 1). In contrast, tiger and blue 
sharks were the most likely species examined (both 
81%; Table 1) to survive initial capture by the U.S. pe- 
lagic longline fleet. 
Quantitative comparisons of mortality rates with rates 
from other published sources 
The rates of immediate mortality reported for com- 
monly discarded species, specifically the blue shark 
(1% retained after data screening completed) and the 
tiger shark (3% retained after data screening com- 
pleted), in the USPL data set were similar to rates 
of immediate mortality reported for these species in 
other data sources. Rates of immediate mortality for 
the tiger shark were 3%, 3%, and 3% in the POP 
data set, in the USPL data set, and for the mean of 
5 studies of immediate mortality, respectively (Table 
2). For the blue shark, rates of immediate mortality 
were 15%, 18%, and 19% in the POP data set, in the 
USPL data set, and for the mean of 11 studies of im- 
mediate mortality, respectively (Table 2). In contrast. 
rates of immediate mortality for occasionally retained 
species (i.e., oceanic whitetip sharks and porbeagles) 
deviated considerably from the rates in the POP data 
set (Table 2). 
Immediate mortality analysis 
Because rates of immediate mortality for blue and ti- 
ger sharks were comparable with estimates from other 
sources (Table 2), factors affecting mortality of these 
species were assessed. All factors tested had a statisti- 
cally significant effect on immediate mortality of blue 
sharks (Table 3; Fig. 2). Similar factors affected im- 
mediate mortality of tiger sharks, including regulatory 
period, geographic zone, and target catch (Table 3, Fig. 
3). Both models explained only a small percentage of 
the deviance within the data set: 1.6% for blue sharks 
and 4.5% for tiger sharks (Table 3). 
In both species, rates of immediate mortality during 
examined regulatory periods were significantly differ- 
ent. Before March 1993, 7.2% (95% confidence interval 
[Cl]: 5.7% to 9.0%) of tiger sharks were discarded dead; 
however, from March 1993 through August 2004, only 
2.8% (95% Cl: 2.4% to 3.1%) were discarded dead (Fig. 
3). The percentage of discards of tiger sharks that were 
dead did not differ significantly between periods from 
March 1993 through August 2004 and periods after Au- 
