Date of Award

Spring 2001

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

First Advisor

W Huntting Howell

Abstract

The ecological impacts of shrimp trawling on juveniles of selected benthic fish were studied in the southwestern Gulf of Maine. The fish community and selected environmental variables were sampled at two sites in summer and winter during 1998 and 1999. The community was composed of 24 species in 12 families. Site 1 was dominated by longhorn sculpin, Myoxocephalus octodecemspinosus , while American plaice, Hippoglossoides platessoides, was the dominant species in Site 2. Red hake, Urophycis chuss was abundant at both sites. There were also seasonal differences in the flux of fish at the two sites.

Correlation analysis showed the abundance of M. octodecemspinosus (Site 1) and H. platessoides (Site 2) to be predictable from environmental variables ordered into principal components (PC1--PC3) as predictors. These PCs represented a depth and sediment composite, a temperature and salinity composite, and an epibenthic macroinvertebrate composite, respectively. There was a strong overall correlation of the two species with PC2 (r c = 0.921). This was largely attributed to a significant correlation of the abundance of M. octodecemspinosus with this PC (F [1,4] = 21.703, p = 0.010).

American plaice (H. platessoides), silver hake ( Merluccius bilinearis), winter flounder (Pseudopleuronectes americanus), and Atlantic cod (Gadus morhua) were the four species selected for study. Only H. platessoides and M. bilinearis were caught in sufficient numbers to enable the correlation of their abundance with environmental variables ordered into PCs. The result was not significant ((RAdj.2 = 0.0; rc = 0.8545). Spatial and temporal differences in abundance of the two species tested with MANOVA were also not significant (F[2,4] = 2.7915, p = 0.1742; and F[2,4] = 4.9998, p = 0.0816, respectively).

The population structure of H. platessoides analyzed with length frequency analysis and scale-age determination revealed four age classes, Age 0+, 1+, 2+ and 3+, to be present in the study area. The diet of H. platessoides was also analyzed to understand potential impacts of trawling on its trophic ecology. Ampharetid polychaetes, other polychaetes, amphipods, bivalves and cyclopoid copepods were the dominant prey taxa. These taxa were also abundant in the environment.

A number of recommendations were proposed from these results on how such studies could increase our understanding of fishing gear impacts on benthic habitats, enabling appropriate management decisions to be made.

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