Marine Invertebrate Resources Annual Report 1972-973
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Marine Invertebrate Resources Annual Report 1972-973

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  • Sea Grant Program:
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    Our laboratory monitored spat-fall for the fifth consecutive year. The data indicated that natural recruitment in the Bay beds was highest (0-​3651/collector) in 1972 for the past five years. Set in the rivers was low (0-​121/collector). The spatfall occurred unusually late (September). High temperatures in early summer before oysters were conditioned to spawn may have delayed spat-fall. A study of long-line oyster techniques showed that oyster spat can be caught on the natural rocks and moved to other locations for growth. Growth rates indicate commercial size can be obtained in two years. The hard clam in Indian River and Rehoboth Bay has become one of Delaware's most valuable shellfish resources. Planting experiments involving protective aggregate indicate that juvenile clams can be planted on a commercial basis. Sediment preference experiments show that clams can discern between silt and sand sediments. However, finer selection be tween sand sized particles is not evident. The blue crab data for Indian River Bay show comparable population levels to past years. However, there has been an absence of juveniles that may become evident in decreased populations in future years. Size frequency data indicate a negative population trend Trap and tag studies in Delaware Bay have produced conservative population estimates. Tagging has shown that the majority of the crabs in the Port Mahon area do not migrate great distances. A lobster creel census by the Marine Advisory Service indicates the importance of this fishery and the need for further investigation by the State and University.
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