Technical Report
 

Controlled rearing of dungeness crab larvae and the influence of environmental conditions on their survival : completion report, November 16, 1965 to June 30, 1971

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  • It is possible that the large fluctuations In annual Dungeness crab landings are caused by displacement of crab larvae by currents. We studied the effects of various environmental factors on crab larvae survival and behavior. Tests were conducted on cultured zoeae and megalopae and on wild megalopae. Our studies showed that the highest survival (93.3%) of crab larvae through the fifth zoeal stage occurred when they were reared in a closed environment. Newly hatched San Francisco brine shrimp, when fed at concentrations of five per ml of rearing water, were the most satisfactory food source. Optimum larvae densities appeared to be five zoeae per 200 ml of rearing water. All cultured crab megalopae were significantly smaller than those larvae collected from Yaquina Bay. Diet concentration appeared to affect size. Temperature-salinity tests showed that optimum ranges to rear crab larvae are 10.0 to 13.9 C and 25 to 30 0/00, respectively. We were unsuccessful in rearing Tanner crab larvae through the first zoeal stage using handling and rearing techniques developed for Dungeness crab larvae. Post larval Dungeness crabs exhibited a preference for a sand substrate over a gravel substrate and rejected plexiglass and mud bottoms. Crab larvae displayed variable responses to different light Intensities. Generally, the cultured larvae displayed a positive phototactic behavior to low light intensities and a negative response to high light intensities. Cultured Dungeness crab larvae displayed a passive response to current; whereas wild megalopae swam actively in the current chamber. A swimming capability of 62.7 mm per second was observed for the wild megalopae. Although the wild megalopae exhibited a slight positive rheotaxis, there is no evidence that the larvae at sea would display this response. In considering the speed and direction of the ocean currents adjacent to the Pacific coast, it is reasonable to expect larvae to be transported at the mercy of the currents.
  • Closing report, November 16, 1965 to June 30, 1971.
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  • U. S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Commercial Fisheries Research and Development Act, Subprojoct 1-5-R, Subproject 1-66-R-1, Contract No. 14-17-0001-2325
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  • File scanned at 300 ppi (Monochrome) using Capture Perfect 3.0.82 on a Canon DR-9080C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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