University Events

Description: The School for Marine Science and Technology
Department of Fisheries Oceanography
PhD Dissertation Defense

"Movements and Habitat Selection of Basking Sharks, Cetorhinus maximus Gunnerus, in the Western North Atlantic Ocean"


By
Toby Hayward Curtis

Advisor
Steve Cadrin

Committee
Gregory Skomal
Diego Bernal
Geoffrey Cowles


Tuesday, January 16, 2018
10:00 am

SMAST East, Room 101-102
836 S. Rodney French Blvd., New Bedford, MA


Abstract
The basking shark (Cetorhinus maximus, Gunnerus 1765) is the second largest extant fish species. It is a passive filter-feeder, well-documented to occur in productive temperate coastal seas with seasonally abundant zooplankton prey. Basking sharks have supported sporadic directed fisheries in the North Atlantic and elsewhere, but their populations were quickly depleted when exposed to significant fishing mortality. Given the basking shark's population status, and numerous gaps in our understanding of key biological parameters and ecological relationships, more research is necessary to help improve conservation and fisheries management. The goal of this study was to better quantify basking shark movements, habitat use and selection, and fisheries susceptibility using a combination of fishery-independent data sources. Satellite-linked Smart Position or Temperature Transmitting (SPOT) tags (N=10) and archived sightings data (N=144) were used to examine meso-scale movements and habitat selection with respect to numerous abiotic and biotic environmental factors during summer and fall months off the northeastern U.S. Pop-up Satellite Archival Tags (PSATs; N=57) were used to better quantify large-scale seasonal movements, fisheries susceptibility, and conservation status throughout the western North Atlantic. The results revealed that summer and fall presence and movements off the northeastern U.S. were associated with areas of high primary productivity, shallow bottom depths (<100 m), and high abundance of copepods including Centropages hamatus, Centropages typicus, and Calanus finmarchicus. There did not appear to be consistent selection for any particular zooplankton taxa, supporting the hypothesis that basking sharks are non-selective foragers in regions with high total zooplankton abundance. PSAT tracks revealed large-scale movements of basking sharks to the southeastern U.S., Sargasso Sea, Caribbean Sea, and as far as Brazil during winter and spring. These sharks passed through the territorial seas of at least 18 nations in which basking sharks have variable legal protection status. However, the tracked sharks cumulatively spent approximately 2/3 of their time adjacent to the U.S. and Canadian coasts where they are well-protected and fisheries bycatch is monitored. Collectively, the data presented in this dissertation will inform fisheries management and improve the ability to assess potential anthropogenic impacts on basking sharks in the western Atlantic. Furthermore, the results enhance our understanding of basking shark population structure and spatial ecology, setting the stage for additional investigations to further enhance their conservation.

For additional information, please contact Christine Fox at cfox@umassd.edu.