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.
The structure of the yolk syncytial-endoderm complex of the preimplantation yolk sac of the shark is examined by light- and transmission electron microscopy. The yolk syncytium is bounded by a membrane that is anchored to the plasmalemma of adjacent endoderm cells by desmosomes. Enlarged nuclei, rough endoplasmic reticulum, Golgi complexes, mitochondria, and other cellular organelles populate the syncytium. Microtubules and filamentous elements are also observed free in the syncytium. Yolk is present as pleomorphic droplets, the profiles of which are generally spherical but may be vesicular, especially at the periphery of large yolk droplets. Occasionally, large yolk droplets have a paracrystalline configuration. Small yolk droplets are modulated through the Golgi complex of the yolk syncytium, and it is suggested that acid hydrolases are added there. Small yolk droplets released from the maturing face of the Golgi complex are sequestered in membrane-limited packets. The membrane of the packets fuses with the membrane enveloping the yolk syncytium and the yolk droplets are released into the yolk syncytial-endoderm interspace. Subsequently, the yolk droplets are endocytosed by the endoderm. Yolk droplets disperse and fuse to form the large irregular yolk inclusions of the endoderm. Yolk metabolites are transported out of the endoderm through the yolk sac endothelium. The yolk sac endoderm thus mediates the transfer of metabolites from the yolk mass to the extraembryonic circulation.
Colcemid-treated blood sampling methods permitted conventional cytogenetic
studies of elasmobranch karyotypes. Representatives were karyotyped from the
superorders: Galeomorphii (4 orders), Squalomorphii (3 orders),
Squatinomorphii (1 genus), and Batoidea (4 or 5 orders). The 36 elasmobranch
species karyotyped by this method, together with 20 species using colchine,
represent ~4.3% of living chondrichthyans. DNA content exhibited the
greatest variability. Chromosome arm numbers, centromere numbers and DNA
content data for 47 species indicated the direction of karyotypic change
during evolution within the elasmobranchs. Thus arm number has been the most
conservative genomic parameter in elasmobranch evolution. A fusion model
(rather than fission or modal models) best explained the data obtained for the
galeomorphs and batoids studied and explains karyotypic change in other
superorders.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.