SYNTHESIZING ELASMOBRANCH POST-RELEASE MORTALITY (PRM) AND DETERMINING PRM RATES FOR SANDBARS (CARCHARHINUS PLUMBEUS) AND SAND TIGERS (CARCHARIAS TAURUS) IN DELAWARE’S RECREATIONAL SHARK FISHERY

Abstract

This thesis examines mortality rates of sharks, using both a literature review and field sampling. Chondrichthyan fishes are widely recognized as being particularly susceptible to overexploitation due to their life history characteristics, making accurate assessments of fishing mortality even more imperative to maintaining healthy populations. Unfortunately, at-vessel mortality (AVM) and post-release mortality (PRM) rates are available for very few species across gear types, hindering management efforts. Fisheries management must often apply surrogate mortality rates from different species and/or gear types. However, mortality rates can be highly variable among species, within species, and across gear types. As a result, using proxy values may lead to biased catch estimates, negatively impacting the accuracy of stock assessments and the resultant sustainability of these fisheries. In Chapter 1, to assist future management efforts, we synthesized all available literature regarding AVM and PRM for chondrichthyans (n = 108 publications). We used these data to characterize mortality rates for various gear types (e.g., trawl, longline, gillnet, purse seine, and recreational rod-and-reel) by taxonomy (orders and families). We also calculated an index variable that describes the current state of our knowledge to better inform future studies on the prioritization of research efforts. Then, in Chapter 2, we determined PRM in Sandbar (Carcharhinus plumbeus) and Sand Tiger Sharks (Carcharias taurus) in Delaware Bay’s recreational shark fishery using an integrative approach that combined biologging with stress physiology. Sharks were caught and tagged with accelerometer data loggers (ADLs) and pop-off satellite archival tags (PSATs) to quantify immediate (< seven days) and delayed (30+ days) mortality events, respectively, following capture and release. We also quantified stress physiology to investigate blood parameters as indicators of stress and predictors of mortality events. Our literature analysis demonstrates a clear lack of knowledge of mortality rates across taxonomic groups and gear types, highlighting a need for additional research on chondrichthyan AVM and PRM. Future directions should focus on enhancing collaborative international research efforts, developing innovative bycatch reduction technologies, and implementing comprehensive management strategies informed by robust and accessible scientific data. Our field sampling found that Sandbar and Sand Tiger Sharks are hardy species with comparatively low PRM rates and stress physiology. However, management must consider that Delaware Bay is a habitat area of particular concern (HAPC) for both Sandbar and Sand Tigers. Moving forward, scientists need to continue to collaborate with anglers to determine and develop evidence-based best practice guidelines and appropriate regulations with the goal of population restoration and conservation.