Coding Release Condition and Estimating Post-Release Mortality of Shark Bycatch in the Canadian Pelagic Longline Fishery

Bycatch in commercial fisheries is a major threat to many shark species. Until recently, there has not been a consistent approach to assess the condition of sharks upon release in Atlantic Canadian waters. In 2012, shark release condition codes were revised to ensure consistency between fisheries observers and researchers estimating post-release mortality from satellite tag data. By adding observed capture mortality and estimated post-release mortality, total fishing mortality can be estimated. Furthermore, these shark condition codes can be used to identify better fishing practices for handling and release of bycatch species. In the Canadian pelagic longline fishery, shark bycatch is well documented. Shark bycatch can account for greater than 30% of this fisheries’ catch by weight, of which blue sharks (Prionace glauca) account for more than 90%. Observer data from 2012 suggest 70% of released blue sharks will likely survive the capture process. However, observer data also indicated considerable variation in shark release condition and, therefore, post-release survival among vessels. Blue shark survival estimates ranged from 25-100% among vessels, with an individual observer reporting 65-100% survival onboard different vessels. Thus, there may be considerable scope for improving fishing, handling, and release practices with regards to shark bycatch.