Date of Award

5-2014

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Yong Chen

Second Committee Member

James Wilson

Third Committee Member

Paul Anderson

Abstract

The Atlantic halibut (Hippoglossus hippoglossus) is a data-poor species in U.S. waters. Abundances remain low after a brief but intense commercial fishery in the mid-nineteenth century caused the population to decline precipitously. Low abundances pose challenges for the study of this species, resulting in many major gaps in the understanding of the life history, stock structure, and distribution of halibut in the Gulf of Maine. The research summarized in this report aimed to address specific data gaps relating to the growth rates and habitat preferences of halibut in the Gulf of Maine, both of which are necessary to understand in order to best manage human impacts on this species of concern.

Growth rates influence population abundance and biomass trends, both of which play an important role in fisheries stock assessment; however, because few data on young halibut are available, growth rates during the entire life cycle of halibut in the Gulf of Maine are poorly understood. This report presents evidence that back-calculations based on otolith measurements can provide accurate estimates of lengths at previous ages, thus filling a major data gap for young halibut. Back-calculated estimates suggest that female and male halibut have different growth rates, that growth rates are not sensitive to inter-annual environmental changes, and that halibut in the Gulf of Maine have different growth rates than those caught in on the nearby Scotian Shelf.

The habitat requirements and preferences of a species influence its abundance and distribution, as well as the ways in which humans interact with that species. The habitat requirements and preferences of Atlantic halibut in the Gulf of Maine are very poorly understood. This research sought to identify key environmental drivers of halibut distribution off the coast of Maine through statistical analysis of existing datasets. A generalized linear model (GLM) suggested that time of year, sediment type, distance to the nearest boundary between sediment types, temperature, depth, and moon phase have significant influences on halibut catches. Habitat suitability indices (HSIs) suggested that juvenile and adult halibut interact with the environment in different ways. Neither the GLM nor the HSIs were able to generate robust predictions of areas of highly suitable habitat for halibut off the coast of Maine.

Fishermen’s knowledge of halibut off the coast of Maine was also assessed as part of this research. Fishermen’s knowledge and statistical models provided different but complementary insights into halibut in the Gulf of Maine. The fishermen interviewed as part of this project shared a wealth of information regarding halibut distribution, abundance, and behavior. Some of the phenomena described by fishermen were not previously documented in the scientific literature.

The results summarized in this report suggest that it is not always necessary to collect additional biological samples in order to generate new and useful information. Back-calculations and fishermen’s knowledge are not commonly used in life history studies of marine fish species; however, this research demonstrates that both are useful techniques which can provide highly relevant information without requiring extensive and expensive data collection efforts.

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