Capstone Title

A Review of the Distribution, Seasonal Occurrence and Demography of Selected Species of Large Coastal Sharks From the U.S. Coast and Gulf of Mexico

Defense Date

8-2003

Document Type

Capstone

Degree Name

M.S. Coastal Zone Management

First Advisor

Mahmood Shivji

Second Advisor

Andrew Rogerson

Abstract

Sharks are a diverse group of approximately 400 species. They belong to the class of fishes known as Chondrichthyes (sharks, rays, and chimaeras), subclass Elasmobranchii. Sharks are cartilaginous fish, possessing no true bone. Found throughout the world's oceans, they range in size from 25 cm in length (spined pygmy shark, Squaliolus laticaudus) to over 15m (whale shark, Rhincodon typus) (Compagno, 1984). Compared to the bony fishes (Osteichthyes), most sharks grow slowly, require many years to mature, have complex reproductive cycles, and produce relatively few offspring. The life-history characteristics of many elasmobranchs, such as late age of maturity and relatively slow growth rates, make them more susceptible to overfishing than most bony fishes. Adding to their complex life history strategies sharks are also migratory, with seasonal and/or diel movements related to food sources, reproductive cycles, temperature, photoperiod, and possibly other environmental factors (Castro, 1983). These characteristics, together with their low fecundity, result in low productivity for most species (Bonfil, 1994; Smith et al. 1998).

In order to manage sharks more effectively in fisheries the National Marine Fisheries Service (NMFS) separated 39 Atlantic sharks species into three species groups (large coastal, small coastal and pelagic sharks) in the first secretarial Fisheries Management Plan (NMFS, 1993).

This paper will focus on the large coastal shark group found off the east coast of the U.S. and Gulf of Mexico. Sharks in this group that will be reviewed are the bull, (Carcharhinus leucas); blacktip, (Carcharhinus limbatus); bignose, (Carcharhinus altimus); sandbar, (Carcharhinus plumbeus); lemon, (Negaprion brevirostris); dusky, (Carcharhinus obscurus); spinner (Carcharhinus brevipinna); tiger, (Galeocerdo cuvier); night shark ( Carcharhinus signa/us); silky, ( Carcharhinus falciform is); scalloped hammerhead, (Sphyrna lewini); smooth hammerhead (Sphyrna zygaena) and the great hammerhead, (Sphyrna mokarran). Several investigators have reported on the distribution, age and growth, and relative abundance of these species in the North Atlantic Ocean and the Gulf of Mexico (Branstetter et al. 1987; Berkeley and Campos, 1988; Kohler et al. 1994). In addition, data collected by commercial, scientific_ and recreational fishermen have been useful to migration and distribution studies of coastal and pelagic sharks in the north Atlantic (Klimley, 1987; Casey and Kohler, 1992; Quinn, 1994). These authors provided valuable information regarding individual species, however, a comprehensive review of the distribution, migration, demography, and relative abundance of these sharks in the western North Atlantic and Gulf of Mexico is lacking.

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