SETTLEMENT INDEXES FOR BLUE-CRAB MEGALOPAE IN THE YORK-RIVER, VIRGINIA - TEMPORAL RELATIONSHIPS AND STATISTICAL EFFICIENCY

The efficacy of artificial settlement substrates in quantifying relati ve rates of settlement of blue crab, Callinectes sapidus, postlarvae ( megalopae) was examined. The technique has been widely used to assess settlement at local (Chesapeake Bay) and broad geographic scales (Atla ntic and Gulf Coasts). This analysis examined differences in settlemen t between two configurations of substrates and two depths of deploymen t, in relation to lunar day, month, year and hours of flood tide occur ring at night. Substrates were deployed daily for four years (1989-199 2) during the settlement season (July-November) in the York River, Vir ginia. Settlement did not differ between substrate configurations (fla t and cylindrical) deployed at the same location in the water column. Substrates deployed at the bottom of the water column had higher settl ement than substrates at the surface, except during the last lunar mon th sampled (approximately November), when settlement was higher at the surface. There was a semilunar periodicity in settlement with high se ttlement following the new and full moon phases. Settlement varied ann ually and with lunar month. Statistical efficiency was achieved with a minimum of three or four replicate substrates. Cylindrical artificial settlement substrates are efficient, reliable and capable of detectin g temporal patterns in settlement.