356 
Fishery Bulletin 109(4) 
8 Jan 
8 Feb 
9 Mar 
9 Apr 
Temperature (°C) 
5 10 15 20 25 30 
0 
100 
200 
300 
400 
Hourly depth, 5 Dec 2002-3 May 2003 
Shortfin mako (ID 38572) 
30 Dec 2002 •• 
Hourly depth (120 hrs) 
Temperature (°C) 
4 Jan 2003 
Q. - 
-10 £ io 'Ft 
£ D Day 
5 I 
Shortfin mako 
Isurus oxyrunchus (n= 2) 
Cl> 
Q 
7 
T 
T 
7 7 
E 
7 
Night 
20% 10% 0% 10% 20% 
■£ 200 
Day 
Night 
15:00 10:00 23:00 03:00 07:00 11:00 
Time of day (HST) 
10% 0% 10% 20% 
Percent of time (%) 
Figure 7 
Shortfin mako ( Isurus oxyrinchus ) depth and thermal ranges as identified by pop-up satellite archival tags (PSATs). 
(A) Representative vertical movements. (B) Temperature-depth profiles obtained from the aggregated data from all 
sharks. (C) Expanded section from panel A with horizontal black bars representing nighttime. (D) Percentage of 
time spent in individual temperature strata (±standard deviation, SD) for daytime and nighttime diving activities 
(all tags). (E) Average hourly depth (±SD) readings calculated for all samples (all tags). (F) Percentage of time 
spent in individual depth strata (±SD) for daytime and nighttime diving activities (all tags). 
et al. 2006; Campana et al., 2009a; Musyl et al., 2009) 
captured and released from longline gear. Similar find- 
ings have been reported for istiophorid billfish, which 
showed significantly lower at-vessel mortality (Diaz, 
2008; Serafy et al., 2008) and postrelease mortality 
(Horodysky and Graves, 2005) with the use of circle 
hooks over J-hooks. Campana et al. (2009a; 2009b) did 
not mention the hook type used on blue shark that ul- 
timately died when released from commercial longline 
gear. However, we argue that given their observed rates 
of at-vessel mortality, it is likely that this factor, along 
with handling and time spent hooked, were important 
factors to explain their rates of postrelease mortality 
(Musyl et al., 2009). 
The amount of time spent on the hook shows a posi- 
tive relationship with mortality for a variety of pelagic 
species, presumably because the captured animal expe- 
riences increased stress over time and is more vulner- 
able to predation (Boggs, 1992; Erickson and Berkeley, 
2008; Carruthers et al., 2009). Many authors suggest- 
ed that shorter soak times could significantly reduce 
bycatch mortality (Diaz and Serafy, 2005; Erickson 
and Berkeley, 2008; Carruthers et al., 2009). Without 
the benefit of hook timers (Boggs, 1992; Erickson and 
Berkeley, 2008) however, it would be challenging to 
test the correlation between time spent on the line and 
mortality. Our samples probably consisted of both ma- 
ture and immature sharks, but we could not determine 
any significant trends between mortality and size as 
reported in Diaz and Serafy (2005). 
Lastly, we also observed species-specific differences 
in the at-vessel mortality rates which other authors 
