Use of Telemetry in Fisheries Management: Juvenile Sandbar Sharks in Delaware Bay

Abstract

Sandbar shark (Carcharhinus plumbeus) populations on the US east coast have undergone several decades of decline due to fishing pressure. One strategy for rebuilding stocks is improved survival of young sharks through enhancement of nursery areas. A key element for understanding the dynamics of shark nursery areas is increased knowledge about essential habitat for young sharks that occupy these nurseries. This study was conducted to quantify habitat use and movement patterns of juvenile sandbar sharks in Delaware Bay, which is a major east coast nursery for this species. Twenty five sandbar sharks were tracked for 2.5 to 75 h using ultrasonic telemetry. Although the sharks moved throughout the lower portion of the bay, and several sharks crossed the entire bay, individuals predominantly remained close to shore and in shallow water. The majority of sharks tracked showed movements that were heavily influenced by tidal currents, and sharks tracked on the New Jersey side of the bay had larger activity spaces, occupied deeper water, and ranged farther from shore than sharks tracked on the Delaware side. Management measures such as area/time closures would provide protection for a large number of sharks in a relatively small portion of Delaware Bay and may be improved if behavior of sharks is taken into consideration. For example, area closures on the Delaware side of the bay are likely to protect more individuals per unit area than an equal area on the New Jersey side. Our study demonstrates the utility of telemetry studies for providing information that will allow more precisely focused and effectively implemented fisheries management practices.