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3.0 SOFT-SHELL CLAMS AND MARINE WORMS
3.1 INTRODUCTION
Soft-shell clams (Mya arenaria; bivalve mollusk), bloodworms (Glycera dibranchiata; polychaete) and sandworms (Nereis virens; polychaete) were identified among the most valuable commercially-fished species landed in Waldo and Hancock counties in the early 1980s (USDOT and MDOT 1987) and continue to be harvested (Section 7.0). The landings (by weight) of bloodworms were higher in 1991 and 1992 than in 1983 and 1984; sand worm landings were similar among these years (Section 7.0). Soft-shell clam harvest has declined dramatically, even between 1983 and 1984. Because NMFS consolidates landings statistics over two counties, encompassing more than 1000 miles (1600 kin) of shoreline, identification of specific harvesting locations is not possible. However, the western shoreline of Sears Island was demonstrated to support soft-shell clams (Bertrand and Birge 1979); bloodworms have been harvested commercially from the tidal flats of Long Cove (Gilfillan et al. 1977).
As with other marine species, abundances of soft-shell clams, bloodworms and sandworms may vary substantially from year to year (e.g., NAI 1991) and a single-year survey of standing crop may not identify all potentially productive habitat within an area. Therefore, a qualitative survey of the intertidal zone of the northwestern shoreline of Sears Island was conducted in 1992 to evaluate whether any areas not previously identified as productive for these species currently exist in the project area. A survey conducted in 1978 along the entire western shoreline of Sears Island (Bertrand and Birge 1979) divided the shoreline into 23 zones, of which zones 10-14 were located within the boundaries of the cargo terminal proposed in the EIS (USDOT and MDOT 1987). Because zone 14 exhibited a high standing crop (94 bushels of clams per acre), MDOT constructed a 2.5-acre (1.0-ha) clam flat in Stockton Harbor near Kidder Point to compensate for anticipated impacts from construction of the cargo terminal on soft-shell clams. Two flats (totalling 1.3 acres, or 0.5 ha) were constructed in Stockton Harbor along the causeway to compensate for loss of clam habitat due to causeway fill. Current status of these areas is provided in Section 3.4 (Discussion).
Earlier sampling in soft substrate along Sears Island intertidal shoreline for benthic species other than soft-shell clams was limited. Bloodworms and sandworms were not identified from the intertidal zone (CMP 1982c) but may have occurred there.
3.2 METHODS
A qualitative survey of the intertidal area along the western shoreline of Sears Island, within the same boundaries established for the eelgrass survey, was conducted on September 1, 1992. Participants included biologists from NMFS, USEPA and NAI. The purpose of the preliminary survey was to determine whether there were areas that appeared to support high standing crop of soft-shell clams or commercial worm species that had not previously been identified, and to assess the potential quality of the habitat based on substrate conditions.
Biologists fanned out across the intertidal zone from approximately mean high water (MHW) to mean low water (MLW). Because distribution of benthic communities and individual species is often closely related to substrate (sediment or surface) conditions, NAI’s observations on these characteristics were recorded. Knowledge of substrate conditions can be used to predict the types of benthic communities that could exist at a site in the absence of biological data. These visual criteria could result in underrepresenting gravel and overrepresenting sand compared to standard grain size analytical techniques. Observations were based on these criteria:
• silt - no granular feel, sink when walking
• sand - granular feel or appearance
• gravel - >3 mm; individual particles could be handled
• cobble - larger than 4 cm in diameter
• boulder - >25 cm in one dimension.
Mud flats, identified on a separate field visit, were defined as consisting of sediments of equal to or more than 50% silt by visual observation, more inclusive than Brown’s (1993) definition of at least 75% mud (silt and/or clay) in her “classification of Marine and Estuarine Habitats in Maine” prepared for Marine Natural Areas Program, were designated as potential mudflats.
Biologists occasionally excavated sediments with clam forks (approximate dimensions: 20 cm x 30 cm x 30 cm deep) to make observations on infauna, particularly soft-shell clams and worms. Sampling locations were loosely selected based on the judgement of the individual biologists who were instructed to examine different substrates and areas with signs of biological activity (e.g. siphon holes, worm castings). Therefore, no estimates of standing crop were made.
The biologists discussed their observations immediately after concluding the preliminary investigation to evaluate whether quantitative sampling was warranted. The general consensus was that current standing crops of the species of interest appeared to be low, and, therefore, quantitative sampling would be unlikely to elicit a different understanding of soft-shell clam or baitworm habitat than the 1978 survey or current substrate maps would provide.