RELATIVE ABUNDANCE AND REPRODUCTIVE CHARACTERISTICS OF SHARKS IN SOUTHEASTERN NORTH CAROLINA COASTAL WATERS

摘要

We conducted a two-year gillnet survey of the relative abundance, species diversity, and reproductive condition of sharks from southeastern North Carolina coastal waters. Sixteen shark species were recorded of which Rhizoprionodon terraenovae (Richardson, 1836) was the most common, representing >80% of the total catch in both years. Large coastal species such as Carcharhinus limbatus (Mueller and Henle, 1839) and Carcharhinus plumbeus (Nardo, 1827) were caught infrequently, representing 1% of the total catch. Juvenile, or sub-adult size classes in the total catch were dominated by Carcharhinus brevipinna (Mueller and Henle, 1839), Carcharhinus obscurus (LeSueur, 1818), C. plumbeus, and Carcharias taurus Rafinesque, 1810. Sub-adult, or adult size classes in the total catch were dominated by Sphyrna tiburo (Linnaeus, 1758), C. limbatus, Carcharhinus isodon (Muller and Henle, 1839), and Carcharhinus acmnotus (Poey, 1860). The smallest mature specimen of R. terraenovae, C. limbatus (female) and C. isodon were smaller than previously documented minimum sizes at maturity. Based on the association of gravid females present in catches with neonates, or small juveniles of the same species, southeastern North Carolina was identified as a primary and/or secondary nursery ground for R. terraenovae, C. brevipinna, C. acronotus and C. obscurus during the months of investigation. Our data also suggest that C. limbatus and Sphyrna lewini (Griffith and Smith, 1834) use southeastern North Carolina as a nursery ground, although more infrequently. Similarly, C. plumbeus uses southeastern North Carolina as an over-wintering ground and neonates are reported infrequently. Almost 100% mature female R. terraenovae and S. tiburo were gravid; most were caught from August-October. Embryos of S. tiburo, based on growth rate extrapolation, were at documented parturition size by September.