192 



Fishery Bulletin 102(1) 



CD 



a. 



=0.10* 



•>•' 



y 



-0 1 ( I 2 



WP Distant coefficient 



m 

 o. 



/-0.65* 





-o I o o ii I ii 2 

 SP Yellowfin coefficient 



Q. 



,-=oo,s 





-ol I 0.2 



CP Bigeye coefficient 



r=0.15* 



o 



S 

 w 



0_ 



CL 



r=0. 12ns 



«*• 



-ii 1 0.0 I 2 



CP Bigeye coefficient 



r=0.79* 



3= 

 o 



S - 



• • 



-i' | 0.0 ii | (12 



CP Bigeye coefficient 



Figure 6 



Pair-wise comparison of soak time coefficients for species that were common to fisheries. The coefficients are from ran- 

 dom effects models where soak time is the only factor. The shading of each symbol represents the size of the standard 

 error of the estimate. V is the correlation coefficient of a linear regression of coefficients ( * indicates that the regres- 

 sion slope is significantly different from one at the 95% level, whereas "ns" indicates that the null hypothesis, that the 

 regression slope equals one, cannot be rejected). 



in the South Pacific bluefin tuna fishery — perhaps indicat- 

 ing that loss rates may be particularly high where blue 

 shark are abundant. 



Nevertheless, there are other plausible explanations for 

 the differences in soak-time effects between fisheries. The 

 movement of branchlines caused by wave action will cause 

 animals to fall off hooks, especially when branchlines are 

 near the sea surface. Rough seas are frequently experi- 

 enced in the North Pacific swordfish and South Pacific 

 bluefin tuna fisheries where the soak-time effects were 

 most pronounced. 



Another source of loss might be the breakage of longline 

 branchlines. The animal's teeth or rostrum might abrade 

 the branchline causing the branchline to fail and allow- 

 ing the animal to escape. In this regard it is noteworthy 

 that Central Pacific bigeye tuna longliners often use wire 

 for the end of branchlines or "leader" whereas North Pa- 

 cific wwordfish longliners use monofilament nylon leaders 

 (Ito 4 ). 



Mortality estimates 



The results of our study show that longline catch rates that 

 are not adjusted for the effects of soak time will under- 

 estimate the level of mortality of several species because 

 they are lost after being hooked. The soak time effect was 

 negative for albatrosses and other seabirds. This finding 

 agrees with field observations (e.g. Brothers, 1991) that 

 most seabirds are taken during longline deployment in 

 the brief period after the bait is cast from the vessel until 

 the bait sinks beyond the depth that seabirds can dive to. 

 Those observations indicate that counts of seabirds when 

 they are brought on board do not cover the total number 

 hooked because many fall off or are removed by scavengers 

 or are lost during the operation. 



1 It... K. 2002. Personal commun. National Marine Fisheries 

 Service (NOAA), 2570 Dole Street, Honolulu Hawaii 96822- 

 2396. 



