Adam et al ; Dynamics of Thunnus obesus and T albacares in Hawaii's pelagic fisheries 



225 



0.030 



0,025 



0.020 



0-015 



0.010 - 



0005 



0.000 



0.030 r 



0.025 



0.020 



0015 



0.010 



0.005 



0.000 



Bigeye Tuna 



Q 29-55 cm 

  56-70 cm 

 n> 71 cm 



M. 



m 



B3 



Cross Inshore Other 



Yellowfin Tuna 



Q 20-45 cm 

  46-55 cm 

 n> 56 cm 



JL 



B1 



82 



83 Cross Inshore Other 



Figure 5 



Estimates of fishing mortality (F) rate by size class and by site for bigeye and yel- 

 lowfin tuna. Error bars are one standard deviation from the mean value. 



suggests that fish associated with these structures con- 

 tribute substantially to the longline catch. Furthermore, 

 the longline fishery considered in our model is an open 

 compartment with no boundaries. Any recoveries outside 

 the bounded compartments will be considered as an emi- 

 grant from inshore and offshore fisheries' perspective. In 

 the likely scenario of higher underreporting of recoveries 

 from non-Hawaii-based fisheries, our estimate of transfer 

 rates from inshore and offshore sites to the longline fishery 

 will be lower. 



At first glance the higher transfer rates to the longline 

 fishery could be explained by the fact that these offshore 

 locations are contained within the geographical areas of 

 operation of the longline fishery. However, analysis of the 

 time-at-liberty offish released at Cross Seamount indicates 



that they first become vulnerable within the inshore FAD 

 areas before recruiting to the longline fishery. For instance, 

 bigeye tuna released at Cross Seamount were caught after 

 238 ±156 (median 254) days in the inshore fisheries but 

 in the longline fishery they were caught after 542 ±297 

 (median 509) days. For yellowfin tuna however, there was 

 little difference; 154 ±134 (median 88) days in the inshore 

 fisheries and 157 ±112 (median 89) days in the longline 

 fishery. These interspecific differences could be due in part 

 to the different vulnerability of the two species to the gears 

 used in the inshore and longline fisheries. Inshore fisheries 

 generally target surface swimming fish, thereby favoring 

 the exploitation of smaller-size yellowfin tuna, whereas the 

 longline gear targets deep swimming adults. Implicit in 

 these results are size-specific vulnerabilities in the inshore 



