Date of Award

5-2006

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Bio-Resources

Advisor

William R. Congleton

Second Committee Member

Brian F. Beal

Third Committee Member

Maine at Machias

Abstract

Clam landings have dramatically decreased in Eastern Maine since 1982. Densities of 0-year M. arenaria recruits were sampled at twelve sites within two Maine counties, Washington County (Downeast) and Cumberland County (Southwest). Five core samples were haphazardly taken at the low and high tidal marks at each site over three years (1996-1999). Washington County had significantly fewer M. arenaria recruits than Cumberland County during years one and three (P < 0.001). Year two was also significantly different at a slightly higher confidence level (a = 0.10). There was a site by tidal height interaction where more recruits were found in the low tidal area in Cumberland County than in the high tidal area. Washington County saw no difference between tidal heights. To determine whether this recruitment difference was due to lack of M. arenaria larvae in near-shore waters or post-settlement mortality, vertically arranged spat bags filled with monofilament were placed in Mason Bay (Eastern Maine) and the Scarborough River (Southern Maine), for five months during the summer of 1998 (May-October). The spat bags were replaced monthly and contents sieved through a 750 pm screen. The Scarborough River showed significantly higher densities of M. arenaria per spat bag during the mid summer months (P < 0.001). Monthly tidal flat samples were simultaneously taken along with the spat bags. Collector pots filled with mason sand were placed on the local tidal flats corresponding with the deployment and replacement of the spat bags. There was significantly higher tidal flat recruitment during the months of July, September and October. The Washington site did not show any difference in recruit throughout the entire five months (June, July, August, September, October). This evidence suggests Eastern Maine's lack of M. arenaria recruits is due to reduced densities of larvae in near-shore waters rather than post-settlement mortality or location rejection. This research can aid the conservation efforts of clam management committees. Since poor recruitment in Eastern Maine appears to be due to lower densities of M. arenaria larvae in the near-shore waters it would make sense to seed the flats with hatchery seed instead of trying to protect the flats with netting or constructing obstacles on the flats to promote settlement.

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