Coastal fish dynamics across scales: roles of warming and restoration, and interactions with fisheries

Hardison, Sean, Environmental Sciences - Graduate School of Arts and Sciences, University of Virginia
Castorani, Max, AS-Environmental Sciences (ENVS), University of Virginia

Coastal fish population dynamics are highly variable in time and space, and in the Mid-Atlantic Bight (MAB) region of the U.S. Northeast Continental Shelf, many species migrate seasonally and ontogenically between the coastal zone and offshore shelf habitats. The seasonal timing of migrations and spawning, the survivorship of larvae and juveniles, the locations of inshore habitats that fishes move into, and the presence and quality of nursery habitats like seagrasses impact the abundances and species diversities of inshore fish communities and have implications for the small-scale commercial fisheries that depend on them. In Chapter 1 of this dissertation, I explored how ocean warming on the continental shelf due to climate change has impacted the abundances of fishes in inshore habitats across the MAB. I found that, on the spatial scale of the MAB, the population responses of fishes to warming were weakly mediated by life history characteristics, but that smaller-bodied, faster-lived species whose populations responded positively to warming tended to be warm-adapted, while populations of larger-bodied, slower-lived species responding negatively were cool-adapted. In Chapter 2, I evaluated how seasonal species asynchrony—the temporal offset in the population dynamics of species biomasses—related to seasonal asynchrony in the harvests of those species, and how harvest asynchrony contributed to the stability of small-scale commercial fisheries operating in the Chesapeake Bay (USA).

I showed that harvest asynchrony and stability were associated with both social and ecological dynamics, including fisher behaviors in response to management restrictions and changes in effort, and to the availability and variability of targeted species populations that contributed to species asynchrony. In Chapter 3, I studied the impacts of seagrass restoration on the abundance and diversity of juvenile coastal fishes. I showed that fish communities within restored meadows were more abundant and diverse compared to nearby unvegetated habitats, further bolstering the case that seagrass restoration is a worthy endeavor. Together, this body of work provides novel insights into the impacts of continental shelf warming on inshore fish populations in the MAB, the consequences of population variability on small-scale commercial fisheries, and how seagrass restoration can enhance the function of inshore ecosystems.

PHD (Doctor of Philosophy)
fish, fisheries, stability, synchrony, community ecology, restoration, coastal habitats, zostera marina, seagrass, climate change
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