Compensatory Growth of the Sandbar Shark in the Western North Atlantic Including the Gulf of Mexico

J G Romine,R A Johnson,J A Musick

doi:10.1080/19425120.2013.793631

Abstract

AbstractThe number of Sandbar Sharks Carcharhinus plumbeus in the western North Atlantic Ocean has experienced a drastic decline since the early 1980s, reaching a minimum during the early 1990s. Catch rates in the early 1990s were a mere 25% of those during the 1980s. According to several fishery‐independent surveys, the low point in Sandbar Shark abundance followed a period of high exploitation. Growth models fit to age–length data collected from 1980 to 1983 and from 2001 to 2004 were compared to investigate potential changes in parameter estimates that might reveal compensatory responses in the Sandbar Shark population. Statistical differences were found between the model parameters for the two time periods, but the differences in growth rates were minimal. The parameters from the three‐parameter von Bertalanffy growth model for female sharks during the 1980–1983 and 2000–2004 time periods were as follows: L∞ = 188.4 and 178.3 cm FL; k = 0.084 and 0.106; and t 0 = −4.097 and −3.41. For males the growth parameters were as follows: L∞ = 164.63 and 173.66 cm; k = 0.11 and 0.11; and t 0 = −3.62 and −3.33. The estimated age at 50% maturity for female Sandbar Sharks changed from 15 years to 12.49 years between the two time periods.Received December 21, 2012; accepted March 28, 2013

Highlights

The Sandbar Shark Carcharhinus plumbeus is a common large coastal shark that inhabits temperate and subtropical waters worldwide and attains lengths greater than 2 m (Compagno 1984)
One stock is found from Cape Cod south to the northern Yucatan peninsula and throughout the Gulf of Mexico; the other is found from Trinidad to Brazil (Springer 1960; Kohler et al 1998)
Genetic studies conducted on specimens from Virginia waters and the Gulf of Mexico further support the existence of a single stock that utilizes the area of Cape Cod to the northern Yucatan peninsula (Heist et al 1995)

Summary

Introduction

The Sandbar Shark Carcharhinus plumbeus is a common large coastal shark that inhabits temperate and subtropical waters worldwide and attains lengths greater than 2 m (Compagno 1984). Due to the advanced development of the pups, a long gestation period of approximately 9–12 months is required (Springer 1960; Clark and von Schmidt 1965; Lawler 1976; Baremore and Hale 2012) Maturity in both males and females has been estimated to occur between 12 and 30 years of age Subject editor: William Driggers, National Marine Fisheries Service, Pascagoula, Mississippi. Casey et al (1985) provided a more comprehensive study of the age and growth of Sandbar Sharks in the WNA that had a large sample size (n = 475), but they too produced unrealistic asymptotic length estimates (303 cm FL) that resulted in very low growth coefficients (k = 0.04 and 0.05 for females and males, respectively). Age-at-maturity estimates for Sandbar Sharks in the WNA have ranged from 12 to 30 years since 1985, with the most recent estimates being those estimated by Baremore and Hale (2012)

Methods

Results

Conclusion