Date of Award

1999

Degree Type

Thesis

Degree Name

Master of Science in Oceanography

Specialization

Biological Oceanography

Department

Oceanography

First Advisor

Jennifer Specker

Abstract

The goosefish, Lophius americanus, is a commercially important fish species that is currently overfished. Little is known about the goosefish and the goal of this study was to provide a maturity schedule to assist fisheries managers in the development of an updated minimum catch size. My objectives were to describe gamete and gonad development by applying histochemical techniques to the analysis of gonadal tissue collected in several seasons from wild goosefish.

Gonadal tissue samples were collected during the winter, summer, and fall 1998 National Marine Fisheries Service (NMFS) survey cruises, and summer samples were also collected from the commercial fishery. Gonadal tissue samples were fixed in a buffered formalin solution, processed histologically, and stained with either hematoxylin and eosin as a general tissue stain, or osmium tetroxide to stain for lipids with eosin as a counterstain. Through microscopic examination of ovarian tissue, criteria were determined for maturity classification of oocytes. Seven stages of ovarian maturity were described using these criteria, and a maturity ogive was constructed to calculate lengthat- maturity estimates.

As of the passage of Amendment 9 to the Northeast Multispecies Fishery Management Plan in January of 1998, the north Atlantic goosefish population has been managed by northern and southern regions, each with its own minimum catch size. The current minimum catch size for the northern region is 43.2 cm, and for the southern region is 53.3 cm.

The minimum catch size is an essential fisheries management tool, and is typically determined using estimates such as the mean length-at-maturity for female fishes. The method used by NMFS to determine maturity is macroscopic examination of the gonad. Our current understanding of oocyte development in fishes indicates that these criteria can lead incorrectly to the assignment of immature females to the mature category, and the criteria used are also highly subjective. The most recent estimate of the L50 for female L. americanus is 44 cm (Almeida et al., 1995) and macroscopic examination was the method used. The results from this maturity study indicate that the L50 for females is 57 cm, which is an alarming result given the current minimum catch sizes of 43.2 cm and 53.3 cm. The information provided by histological examination of gonads very likely offers a more accurate picture of maturity than the traditional method of macroscopic examination and, since successful management is the goal, this new maturity information should be considered.

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