Date of Award
2024
Degree Type
Thesis
Degree Name
Master of Science in Biological and Environmental Sciences (MSBES)
Department
Biological Sciences
First Advisor
Bradley Wetherbee
Abstract
The shortfin mako shark (Isurus oxyrinchus) is common in both recreational and commercial fisheries. Makos have life history characteristics that make them vulnerable to overexploitation, which combined with data gaps and management challenges has led to makos being overfished and experiencing overfishing in the Western North Atlantic (WNA). Effective management of makos is hindered by limited information on their ecology, including their movements, behaviors, as well as interactions with fisheries. I leveraged a long-term satellite telemetry database of 67 individual makos to investigate their seasonal movement patterns and to describe a suite of movement metrics that together constitute behavioral syndromes for makos in the neritic and oceanic provinces. Satellite telemetry data revealed seasonal movements characterized by contraction towards the US East coast continental shelf in summer and fall followed by an offshore and southern expansion to during winter and spring. Distinct behavioral states were observed for makos in the neritic and oceanic provinces. In neritic waters, sharks exhibited more tortuous movements, reported more frequently, and moved over smaller ranges. In the oceanic regions, makos traveled greater distances and covered wider ranges.
I also integrated data from four fisheries monitoring programs in combination with the satellite telemetry data to evaluate catch, composition, temporal trends, spatial patterns, and movements of makos. Datasets included information on location, date, size, and sex for 19,243 fishery dependent capture records between 1962 and 2017; and 19,143 fishery independent satellite telemetry detections from 67 individuals from 2013 - 2023. The Pelagic Observer Program (POP) was the most comprehensive fishery dependent source for understanding catch, composition, temporal and seasonal distributional patterns of mako sharks. Catch of makos was relatively consistent, as were temporal trends for the sex ratio, size distributions and proportion of mature sharks captured. Seasonal distributions inferred from fishery dependent observations varied but heavily reflected seasonal shifts in fishing locations. Satellite telemetry data indicated that the seasonal distribution and movement patterns of makos independent of fisheries differed considerably from fishery-dependent observations. Demographic information from fishery dependent sources suggested mature males were common, whereas nearly all females were immature. Fishery dependent sources had a large number of undetermined sexes and sizes of individuals.
Understanding the biology of makos and effectively managing their populations is challenging. Given their highly mobile nature and frequent interactions with fisheries, managing mako populations will require innovative and collaborative solutions. This study demonstrates the usefulness of including multiple sources of data to investigate interactions with fisheries that provide inferences of population structure, behaviors, and movements. Integrating this information into management strategies will result in better informed stock assessments, and management of their population.
Recommended Citation
Kresge, Colby D., "INVESTIGATING THE MOVEMENTS, BEHAVIORS, AND INTERACTIONS WITH FISHERIES OF THE ENDANGERED SHORTFIN MAKO SHARK IN THE WESTERN NORTH ATLANTIC OCEAN" (2024). Open Access Master's Theses. Paper 2484.
https://digitalcommons.uri.edu/theses/2484