Mote begins first study of fishing-induced stress in Alaskan salmon sharks
Dr. Heather Marshall processes samples collected from salmon sharks off Alaska. Credit: Galen Lyon.
A Mote Marine Lab researcher and colleagues tagged four salmon sharks on July 31 off Alaska to conduct the first assessment of fishing-induced stress for this species.
Salmon sharks have been fished recreationally in Alaskan waters for more than a decade. Though no population assessments have been done for salmon sharks, they have faced increasing pressure from anglers who catch the daily limit of one salmon shark per person and release the rest. It is unknown how many salmon sharks survive the stress of capture and release.
“This is the first assessment of fishing induced stress response for this species and this fishery, as well as assessment of post-release mortality,” said Dr. Heather Marshall, a Postdoctoral Research Fellow at Mote in Sarasota, Florida. “With the data we collect, we will be better informed about the impacts of the fishery on individual sharks, and how this may impact local populations. We can use the data to help resource managers ensure sustainable fisheries.”
Marshall and colleagues, along with staff from Whittier Marine Charters, fitted four mature female salmon sharks with High Rate X-Tags, which are programmed to stay on the shark for 30 days and then detach, float to the surface and transmit their data to scientists via satellites. Data include depth and water temperature. Researchers analyze the depth data to infer whether a released shark has survived.
The researchers also took blood samples and body measurements for each shark. Marshall will examine the blood samples for chemical compounds that indicate stress.
While capture stress and mortality are challenging to document in sharks, Marshall’s work has helped reveal that some shark species are more susceptible to stress than others. For example, her 2015 peer-reviewed paper in Fisheries Research examined capture stress in dusky and sandbar sharks — prohibited species at risk for bycatch. Results showed that duskys were much likelier to die when caught and released from a longline than the hardier sandbars, and survival chances decreased for both species with more time fighting on the line.
The recent expedition to Alaska was supported in-part by the Christiane Howey Rising Scholar Award from Microwave Telemetry, which was awarded to Marshall for 2016 studies of salmon sharks and efforts to educate young people about sharks.
Marshall is a co-founder of The Gills Club, which holds free meetings to enhance science education — especially on sharks and related fishes — for girls ages 6-17. The Club began with the Atlantic White Shark Conservancy and expanded through partnership with Mote.
During the Alaska expedition, Marshall and fellow scientists Cindy Tribuzio of the National Oceanic and Atmospheric Administration and Rachael Cashman, a future Ph.D. student Marshall is advising, hosted a Gills Club meeting and shared their research and facts about shark biology with 18 girls on July 27 at Alaska SeaLife Center in Seward. The girls participated in a shark-tooth hunt and made shark-tooth necklaces as souvenirs.
