Date of Award

2022

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Gardiner, Jayne

Area of Concentration

Marine Biology

Abstract

Seasonal temperature change has been shown to be a key driver of migration for many species. Increasing ocean temperatures have been observed to cause shifts in the range and timing of migratory movements in marine animals, including sharks. For harvested species, these behavioral changes could have significant implications for fisheries management. The blacktip shark (Carcharhinus limbatus) is one of the Gulf of Mexico’s most recreationally and commercially important species. Terra Ceia Bay, FL, is a nursery for blacktip sharks that has been extensively studied. In the late 1990s through early 2000s, young-of-the-year sharks were found to reside in the bay for the first 6 months of life, depart in October to November following water temperature drops of at least 1.5°C over two days, and return beginning in April. The goal of this study was to examine the current timing of immigration/emigration of blacktip sharks from this nursery and any potential cues associated with them. Departure and return dates of acoustically tagged juvenile blacktip sharks (n=25 sharks, tagged from 2016-2021; n =40 departures; n=16 returns) from/to Terra Ceia Bay, Sarasota Bay, and Manatee River were determined using a directionally-gated array of acoustic receivers. Mixed-effects models were used to examine the effects of absolute water temperature, change in water temperature, day length, and day of year on the timing of immigration and emigration. Results indicate a significant shift over the last two decades towards both later departures and earlier returns from/to this nursery. This study determined that the best predictor for emigration from / migration to this nursery are absolute temperature and day length, respectively. Significant differences were present between study animals based upon both age and sex.

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