Graduation Year

2020

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Ernst Peebles, Ph.D.

Committee Member

Steve Murawski, Ph.D.

Committee Member

Robert Weisberg, Ph.D.

Keywords

batch fecundity, histology, ocean circulation model, spawning, trajectories, West Florida Shelf

Abstract

Planktonic fish eggs can be reliably identified with DNA barcoding, and their distribution and abundance can be monitored. Passive drifting fish eggs can be advected by ocean currents and as a result, can either be locally retained or exported away from the West Florida Shelf (WFS). Investigating their retention or export helps in the interpretation of egg abundance trends and in understanding their distribution in long-term surveys. The present investigation was performed in two steps using a combination of biological and physical oceanographic methods. First, fish fecundity of three species (Red Snapper, Vermilion Snapper, and Sand Perch) was assessed, first, through hydrated egg counts leading to batch fecundity estimates, and second, through histological analysis of post-ovulatory follicles. Both approaches were used to find evidence of imminent or recent spawning and the results allowed the identification of spawning sites. In the second step, coordinates of the spawning and fish-egg collection sites were put into the West Florida Coastal Ocean Model (WFCOM). Trajectories of the drifting eggs were then simulated over two weeks at three depths (surface, mid-water, and bottom). The results indicated that there were two groups of trajectories: one nearshore group indicating retention and one offshore group resulting in long-distance dispersal and potential export. In addition, the nearshore stations were associated with higher fish-egg abundance. This study also found evidence of a relationship between retention and higher fish-egg abundance. This was hypothesized to be representative of increased spawning in those areas, increased drift convergence, or both processes acting together. Batch fecundity appeared to be higher nearshore, although no relationship between batch fecundity and retention was found. After fish eggs were identified to species via DNA barcoding, a community analysis using SIMPROF was performed and indicated the presence of a depth-related structure in the community. Fish eggs species were also categorized as pelagics or non-pelagics. No evidence of whether pelagic species are more likely to be exported was found. This study is a starting point for the creation of an index of egg abundance that will be fine-tuned over time with recurrent surveys. Ultimately, the index can be useful to fisheries management.

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