Ward et al.: The effect of soak time on pelagic longlme catches 



193 



2" 4(1 <M 80 100 



SP Bluefin 



20 -40 no 80 100 



SP Yellowfin 



• Oiltish 



Escolar 



"... 1 % « 



Other seabirds 



=0.32ns 



Escnlai 



: •: • 



Skipjack 



f": 



=0.54 



20 40 60 80 100 



20 40 60 80 100 



Proportion alive (%) 



Figure 7 



Soak-time coefficients plotted against the proportion of each species reported to be alive 

 when brought on board. Not included are species where less than ten individuals for the 

 fishery had a record of life status. The coefficients are from random effects models where 

 soak time is the only factor. The shading of each symbol represents the size of the standard 

 error of the estimate. The proportion alive is assumed to be measured without error. V is 

 the correlation coefficient of a linear regression of coefficients (* indicates that the regres- 

 sion slope is significantly different from zero at the 95<7c level i. 



Seabirds provide a unique case for estimating loss rates 

 because they are only caught when the longline is deployed 

 (Brothers. 1991). Within minutes of the branchline being 

 deployed, the capture rate ( a in Eq. 4 ) falls to zero whereas 

 the loss rate /3 might be constant or it might vary. There- 

 fore, the probability of a seabird being on a hook when the 

 branchline is retrieved is 



n\T) 



-0T 



(6) 



We estimated a soak-time coefficient of -0.0302 (CI 

 ±0.0462) for albatrosses in the South Pacific bluefin tuna 



fishery. Substituting 0.0302 for ft in Equation 6 and 10.4 

 hours for T ( the average soak time of hooks deployed by 

 the longliners), we estimated that 27% of albatrosses are 

 lost after being hooked but before the branchlines are 

 retrieved. The loss rate is about 12% for petrels 1/3=0.0123) 

 and 45% for other seabirds (0=0.0582). It is about 26% for 

 other seabirds in the South Pacific yellowfin tuna fishery 

 (j6=0.0307, T=10.0 hours). 



For fishes and sharks, we do not know how the probabil- 

 ity of capture, or capture rate, or loss rate varies during 

 a longline operation. However, hook-timer experiments 



