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1 December 2009 Experimental Trials on the Nursery Culture, Overwintering, and Field Grow-Out of Hatchery-Reared Northern Quahogs (Hard Clams), Mercenaria mercenaria (L.), in Eastern Maine
Brian F. Beal, George Protopopescu, Katy Yeatts, Joseph Porada
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The easternmost commercial population of hard clams, Mercenaria mercenaria, in Maine was discovered recently near the low intertidal in Goose Cove, in the town of Trenton (Hancock County). A fast- and slow-growing morph was identified that reaches commercial size (50.8 mm shell length) in 4 y and 5 y, respectively. Fast-growing individuals were selected as broodstock, and conditioned to spawn at the Downeast Institute. The fate and growth of cultured juveniles was followed for 5 mo beginning in July 2006 at 4 stocking densities (2,500–10,000 animals/1.1 m2 floating, nylon window screen-lined tray; n = 20) at a coldwater field nursery approximately 60 km east of Trenton, in the town of Beals, ME (Washington County). Survival was nearly 100%, and growth was density dependent, with animals attaining a final mean shell length ±95% confidence interval of 8.4 = 0.13 mm and 7.6 ± 0.218 mm in the lowest and highest density treatments, respectively. In November 2006, cultured seed was separated into 2 sizes (large, 8.7 ± 0.2 mm; small, 5.1 = 0.2 mm) and overwintered in window-screen bags (0.2 m2) at densities ranging from 0.6–1.6 kg (large) and 0.5–1 kg (small), representing approximate densities ranging from 3,360–15,510 individuals per bag. Bags were placed on horizontal shelves within modified lobster traps (overwintering containers) that were added to a 35,000-L tank receiving ambient seawater for 177 days until May 2007. Seawater temperatures during this interval ranged from -1-10°C. Survival rates exceeded 99%, and no negative effects resulting from stocking density were observed. Hatchery seed was transplanted in May 2007 to the lower intertidal at Goose Cove and a second intertidal location approximately 30 km east of Beals at Duck Brook Flat, in the town of Cutler, and the fate and growth of these juveniles was followed for 6–7 mo. Survival was independent of planting densities (330–1320 individuals/m2), and predator netting did not enhance survival compared with controls without netting. Growth was seasonal, with the greatest incremental shell increases occurring between early July and late September. Growth rates varied between planting locations, with clams adding approximately 10 mm shell length at Goose Cove between May and December (initial shell length, 8.2 mm; final shell length, 17.9 mm) and approximately 5 mm shell length at Duck Brook Flat between June and November (initial shell length, 9.3 mm; final shell length, 14.3 mm). Hard clam farming in eastern Maine may help to diversify a wild shellfish industry that is currently in decline for most species except lobsters; however, additional efforts are needed to explore alternative grow-out sites and methods to enhance growth rates.

Brian F. Beal, George Protopopescu, Katy Yeatts, and Joseph Porada "Experimental Trials on the Nursery Culture, Overwintering, and Field Grow-Out of Hatchery-Reared Northern Quahogs (Hard Clams), Mercenaria mercenaria (L.), in Eastern Maine," Journal of Shellfish Research 28(4), 763-776, (1 December 2009).
Published: 1 December 2009

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