Occurrence, Abundance, and Biology of the Blacknose Shark, Carcharhinus acronotus, in North Carolina

The biology of the blacknose shark, Carcharhinus acronotus, is presented for specimens captured by longlining off Shackleford Banks, North Carolina between 1973 and 1982. This entails comments on the number, seasonality, catch rate, color, age, growth, size, maturity, meristics, morphology, reproduction and parasites. C. acronotus frequents North Carolina coastal waters from May to October. Males dominate catches through July; females from August to early fall catches. Catches varied among years,and were probably afffected by seasonal water temperatures and salinity variations. Best longline catches occur on morning ebb tides and are depth specific at one depth rather than between depths. Catch per unit effort data indicate more blacknose sharks are caught/100 hooks in North Carolina than in Florida or the Gulf of Mexico; areas previously believed to harbor abundant populations of blacknose sharks. Vertebrae were aged following staining with a modified silver nitrate technique. A linear relationship was found between vertebral radius and shark fork length. Growth curves were constructed from back calculations developed from linear regression and von Bertalanffy equations. The largest male (1,640 mm TL) and female (1,540 mm TL) C. acronotus taken were larger than any previously reported. Near term embryos are about 510 mm TL. Smallest free living males were encountered at 556 mm FL (684 mm TL) and 715 mm FL (877 mm TL) for females. Von Bertalanffy plots predicted 1,640 mm TL males to be 9.6 yr old. Morphometric and meristic data are given for blacknose sharks 65 to 1,400 mm TL. Teeth and vertebral · counts were within ranges reported by others. Developing young 65 to 125 mm TL lack der· mal denticles. Specimens 200 mm TL or larger are completely covered with pedunculate three ridged denticles. C. acronotus was a new host for three of the five species of parasites found on adult specimens. Arguments are presented that indicate two breeding and pupping populations; one off North Carolina, the other off Florida and the Gulf of Mexico. A constant exchange of blacknose sharks seems to occur between these two populations and areas. The gestation period is believed to be only nine months. Carcharhinus acronotus, the blacknearshore species that is not abundant nose shark, characterized by a black (Dahlberg and Heard, 1969; Bearden, smudge at the tip of the snout, is one of 1965a, b; Clark and von Schmidt, 1965; the smaller members of the 25 to 32 Branstetter, 1981; Rivas and McClellan, spedes of Carcharhinus (Compagno, 1982) other than on the west coast of 1979; Garrick, 1982}. The species is Florida off Tampa (Springer and Woodbelieved to attain a total length of 1,370 burn, 1960), Englewood, Florida mm (Garrick, 1982). It occurs in the (Springer, 1938}, and off North Carolina. western Atlantic from North Carolina The biology of the blacknose shark southward throughout the Great and is relatively incomplete, even though Little Bahama Banks, Caribbean, west in various aspects of seasonality, size, the Gulf of Mexico to Louisiana, British catch per unit of effort, etc. are reported Guiana and along the South American for Florida and Gulf of Mexico specimens coast from Venezuela to off Rio de by Springer (1938), Clark and von Schmidt Janiero (Garrick, 1982). C. acronotus is a (1965), Dodrill (1977) and Branstetter 29 1 Schwartz: Occurrence, Abundance, and Biology of the Blacknose Shark, Carcha Published by The Aquila Digital Community, 1984