Date of Award

Spring 2010

Project Type

Dissertation

Program or Major

Natural Resources and Earth System Science

Degree Name

Doctor of Philosophy

First Advisor

Andrew A Rosenberg

Abstract

In the marine environment, studies suggest that overfishing suppresses sustainability and resilience in fish populations. In the 1990s, the National Marine Fisheries Service (NMFS) implemented five large year-round fishery closures in the Gulf of Maine and Georges Bank. These closures are partially protected marine protected areas (MPAs) restricting commercial fishing with bottom-tending gears. To date, evaluation of their performance has focused on the productivity of individual species.

This research aims to understand if fish biodiversity changed after implementation of the five large fisheries closures. Here, a variety of datasets and statistical approaches are used.

Modern patterns constructed from NMFS bottom-trawl surveys (1971--2005) demonstrated that fish species richness increased in some areas, as species evenness declined. Fish species composition changed from demersal species to more abundant pelagic species inside and outside of the fisheries closures. Likely drivers of these changes included destruction of habitat by over fishing, and climate and fishery driven disturbance.

After constructing a historical baseline for the Western Gulf of Maine and Georges Bank, total genera detected by historical Fishhawk research trawl surveys in the late 19th century were 2 times greater than the number appearing in NMFS bottom-trawl surveys (1963-2007); however, in contrast, NMFS bottom-trawl surveys detected more fish genera. Guild composition was similar for both surveys with respect to demersal, but not pelagic species. These differences were explained by changes in survey sampling technology, fishing pressure, and ecosystem resilience.

Recent seasonal patterns of fish species richness from multiple fisheries-independent and dependent datasets showed that inshore areas (such as Massachusetts and Ipswich Bays), the transition between the Gulf of Maine and Georges Bank, and eastern Georges Bank exhibited high fish species richness. When data was available from observed commercial otter-trawl tows adjacent to or within closures, high richness areas occurred, regardless of season. Likely processes influencing species richness over the region and near the fishery closures consisted of seasonal prey availability, oceanographic conditions, and fishing pressure. High effort around fishery closure boundaries had important implications for the effective design of MPAs and future management of groundfish.

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