Date of Award

Spring 2010

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

First Advisor

W Huntting Howell

Abstract

The ocean sunfish, Mola mola, has a worldwide distribution and is a common resident of the NW Atlantic Ocean. Notable for its unusual anatomy and large size, the biology of the species is largely unknown. I examined the movement and behavior of M. mola using pop-up satellite archival tags (PSAT's). In addition, analysis of aerial survey data was conducted to determine the distribution of ocean sunfish (Family Molidae) in NW Atlantic shelf waters. Data was analyzed from twenty-five PSAT's deployed on M. mola in the northwest Atlantic between 2005 and 2008. Tags were attached from 7-242 days. Results indicate that M. mola in the NW Atlantic leave New England waters in the late summer and early fall and move south along the continental shelf break. Fish traveled as far south as the Bahamas and the Gulf of Mexico, and were strongly influenced by their proximity to the Gulf Stream. Results suggest that M. mola in the northwest Atlantic exhibit a seasonal migration pattern south driven by decreasing temperatures and the search for patchily distributed gelatinous prey. Fish spent over 80% of time in the top 200 meters of the water column. Max depth recorded by any fish was 844 m. Temperatures experienced by tagged fish ranged from 6 -- 30°C. Vertical behavior of M mola changed over temporal and seasonal scales. M. mola in northeast US waters in the summer months exhibited shallower swimming depths and more surface time than those that moved south in the winter and spring. This change in behavior is likely driven by temperature and thermocline depth, as fish adjusted their vertical behavior following a thermal gradient and/or searching for vertically migrating prey of the deep scattering layer (DSL). The shift in vertical behavior was especially apparent when fish entered the Gulf Stream. A diel pattern was observed in vertical behavior. Analysis of aerial survey data showed high numbers of animals in the northeast and mid-Atlantic in the summer and fall, and high numbers of animals in the southeast in the winter and spring, further demonstrating the seasonal migration of ocean sunfish along the eastern US shelf.

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