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

Abstract

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.

Age and growth estimates of the bull shark, Carcharhinus leucas, from the northern Gulf of Mexico

“…This overestimate has been noted for several carcharhinid sharks (Casey et al 1985, Parsons 198.5, Branstetter & McEachran 1986). The K value (0.076) was similar to values derived for Carcharhinus plumbeus (Casey et al 1985) and Sphyrna lewini (Branstetter 1987a), but was much lower than values estimated for the more rapidly growing C. acronotus (Schwartz 1983b), C. fafciformis (Branstetter 1987a), C. fimbatus, and C. brevipinna (Branstetter 1987~). Although Compagno (1984) listed the maximum length of C. leucas to be near 340 cm, only one specimen (316 cm: Sadowsky 1967) has been reported to exceed 300 cm (see Garrick 1982 for review).…”

Biological aspects of sharks caught off the Coast of Pernambuco, Northeast Brazil

“…) and in the Gulf of Mexico (Sulikowski et al, 2007). The progressive increase in embryos TL over the months suggests a 9 month gestation period, which is similar to that described by Hazin et al (2002) and Schwartz (1984), respectively, 8 and 9 months, and lower to values presented by Dodrill (1977) and Driggers et al (2004), which were between 11 and 12 months (both studies were carried out off Florida, USA). This divergence may be related to different temperature gradients in the study locations; it is possible that warmer waters at latitudes closer to the equator accelerate reproductive processes (fecundity, maturation, etc.)…”

“…The size at first sexual maturity found for females (around 105.0 cm TL) is smaller than that described by Branstetter (1981;113.0 cm TL), but larger than 96.4 cm described by Driggers et al (2004). The size at first maturity for males (here estimated at around 105.0 cm) was slightly smaller than that described by Schwartz (1984;110.0 cm TL), but closer to the 104.0 cm described by Hazin et al (2002) Hazin et al (2002 suggest that birth size for blacknose shark is approximately 45.0 cm TL. In the present study, 2 females were observed at term with mean embryo sizes of 50.0 cm and 63.2 cm TL, suggesting that the 45.0 cm birth size may have been underestimated.…”

Annotated checklist of the living sharks, batoids and chimaeras (Chondrichthyes) of the world, with a focus on biogeographical diversity

“…The skin of this specimen was preserved, but has apparently been lost (Compagno, 2001) , but specimens from much shallower water reported by Kerstetter & Taylor (2008) and Castro (2011) 853 (Bigelow & Schroeder, 1948) or 2200 mm cannot be assigned to concrete specimens. A specimen of 2400 mm reported by Fowler (1945) was not this species (Schwartz, 1984) 72 Lessa et al (1999) is much deeper than other references. Specimens from the NEA and SEA might belong to a distinct species based on molecular data so that one of the species currently placed in the synonymy of C. brachyurus might need to be resurrected (Naylor et al, 2012a) 855 (Garrick, 1982;White & Weigmann, 2014) 856 White, 2014, pers.…”