Adopting New Approaches to Reduce Risk of Injury and Mortality of Sand Tigers in Bottom Longline Surveys

Monday, September 9, 2013
Governor's Hall I (trade show) (Statehouse Convention Center)
Dewayne A. Fox , Department of Agriculture and Natural Resources, Delaware State University, Dover, DE
Bradley M. Wetherbee , Department of Biological Sciences, University of Rhode Island, Kingston, RI
Lori M. Brown , Agriculture and Natural Resources, Delaware State University, Dover, DE
Bottom longlines are commonly used to in commercial fisheries as well as research studies sample sharks and although much attention has been focused on longline configuration (e.g. baits, hook type/size, and soak time) little information is available on the potential injury of targeted species.  Sand tiger sharks (Carcharias taurus) although considered by many to be of poor food value, are highly sought after by the aquarium trade and are often encountered as bycatch in commercial fisheries.  Until recently, Delaware Bay served as the one of the primary collection sites for the global aquarium trade.  Due to concerns over population declines and lack of information required for proper management, the collection of sand tigers from Delaware Bay was effectively halted.   In 2007 we began using standard NOAA-NMFS longline gear to collect sand tigers in Delaware Bay.  An examination of our catch records suggested that the sand tigers’ feeding mechanism leads to high incidence of deep hooking (“gut hooking”) which is thought to cause injury and may impact post-release survival.  In 2012, in consultation with a charter captain, we examined the influence of blocker rigs on both encounter and deep hooking rates for 267 sand tigers landed during our survey.  The use of blocker rigs resulted in a nine fold decrease in the incidence of deep hooking rates.  Interestingly, males were twice as likely to be captured on the control hooks compared to females although this pattern was not documented in the blocker rigs.  Our results suggest that future surveys may want to employ blocker rigs as a conservation tool for shark sampling especially in areas where sand tigers are likely to be encountered.