Date of Award

Spring 1992

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

First Advisor

W Hunting Howell

Abstract

A three part analysis of discarding of commercial fish species in the Gulf of Maine trawl fisheries was conducted from 1983 through 1992. Abstracts for each part of the dissertation are:

Part 1. The objectives of the research were to quantify commercial trawler discards of American plaice, witch flounder, yellowtail flounder, and winter flounder, and to examine variables that potentially influence discard rates. Data were obtained from 135 tows in 6 areas of the Gulf of Maine. Four different types of trawls were used. Mean discard percentages per tow, on a weight basis, were 25, 18, 13, and 5% for American plaice, witch flounder, yellowtail flounder, and winter flounder, respectively. Mean discard percentages were higher on a numerical basis, with 57, 27, 25, and 12% of the respective species discarded per tow. Both trawl type and area fished affected the discard percentages of American plaice and witch flounder. Stepwise multiple regression analyses indicated that six variables combined to explain 66.8% of the variation in discard percentage of American plaice, and that three variables combined to explain 31.2% of the variation in discard percentage of witch flounder.

Part 2. The objective of the research was to quantify discards of American plaice, witch flounder, yellowtail flounder, winter flounder, goosefish, silver hake, and cod in the Gulf of Maine shrimp fishery. Data were obtained from 50 tows made by commercial trawlers fishing in the southwestern Gulf of Maine. Mean discard percentages per tow, on a weight basis, were: 93% for silver hake, 87% for American plaice, 76% for witch flounder, 56% for cod, 41% for goosefish, 20% for yellowtail flounder, and 11% for winter flounder. Mean discard percentages per tow on a numerical basis were slightly higher. Discard percentage decreased with increasing depth for American plaice.

Part 3. Increased effort in the Northern shrimp fishery, in addition to documentation of the adverse effects of small mesh trawls on some finfish stocks, has prompted interest the development of more selective fishing gear. Studies of fish behavior during the trawling process using underwater video have provided information that has been extremely useful for the design of selective trawls. In this paper, fish behavior, trawl modifications, particularly those intended to separate finfish from shrimp, and regulations aimed at reducing finfish bycatch are discussed.

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