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A sea scallop (Placopecten magellanicus) population study on the effects of a fishery closure in Lunenburg county N.S., Canada

Brocken, F. (1998) A sea scallop (Placopecten magellanicus) population study on the effects of a fishery closure in Lunenburg county N.S., Canada. Master's Thesis / Essay, Biology.

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Abstract

From November 1995 until January 1998, Bayport and Second Peninsula (Lunenburg county, N.S., Canada) were closed for all forms of sea scallop fishing. Except for a small stock assessment in Second Peninsula in 1997, no extensive research on the population has been done since the closure. This report presents the results of a study on the effects of a fishery closure on the sea scallop (Placopecten magellanicus) population and community in Lunenburg county, N.S., Canada. In June and August, 1998 scallops were sampled at several sites in three areas off Lunenburg county. Lunenburg and three sites at Second Peninsula were open for scallop fishing, the other samples at Second Peninsula and those at Bayport were in closed areas. Shell height, meat, gonad and soft tissue weight were recorded. A subsample of the meat was used for RNA/DNA ratio analysis to determine the nutritional state of the scallops. At each sample site the presence of filterfeeders, potential predators, depth and bottom type were also recorded. The sea scallop density and the percentage of clappers were not significantly different in the open and closed areas. The closed areas Bayport and Second Peninsula have proven to be better growth environments than Lunenburg because the % yield in these areas was significantly higher. These better growth conditions combined with reduced fishing mortality on spawners, are probably the reasons why recruitment is taking place in Bayport and Lunenburg. Due to this recruitment in the closed areas, significant effects of the fishing status of the areas were found on meat weight, gonad weight, soft tissue weight and shell height. For Bayport evidence was found for at least one minor spawning in May. No indication of spawning at the time of sampling was found for Second Peninsula and Lunenburg. The regression models of meat weight, gonad weight, % yield and GSI against shell height showed great variability among dives at the same area. This made comparison of areas with the same fishing status and with different status difficult or impossible with our sample sizes. Therefore no conclusion from these data can be drawn about the effect of the closure on the sea scallop population. Although not significantly, bottom type does seem to have an effect on scallops. Bottoms with gravel showed higher densities than all other bottom groups found in this study. The main potential predators found were Cancer irroratus, Homarus americanus and Asterias forbesi. Although not significant, RNA/DNA ratios correlated positively with lower % clappers. The low ratios found, reflect poor food conditions combined with summer months and spawning state. Based on data on meat count and percentage of animals over 100 mm of this study, the SFA29 Inshore Scallop Advisory Committee increased the restriction of the minimum shell height from 100 mm to 110 mm for both open and closed areas, thereby protecting more large animals to provide future recruitment.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:45
Last Modified: 15 Feb 2018 07:45
URI: http://fse.studenttheses.ub.rug.nl/id/eprint/9460

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