Seasonal distribution and historic trends in abundance of white sharks, Carcharodon carcharias, in the western North Atlantic Ocean.

Tobey H Curtis,Harold L Pratt,John J Hoey,Camilla T Mccandless,John K Carlson,George H Burgess,Lisa J Natanson,Gregory B Skomal,Nancy E Kohler,A Peter Klimley

doi:10.1371/journal.pone.0099240

Abstract

Despite recent advances in field research on white sharks (Carcharodon carcharias) in several regions around the world, opportunistic capture and sighting records remain the primary source of information on this species in the northwest Atlantic Ocean (NWA). Previous studies using limited datasets have suggested a precipitous decline in the abundance of white sharks from this region, but considerable uncertainty in these studies warrants additional investigation. This study builds upon previously published data combined with recent unpublished records and presents a synthesis of 649 confirmed white shark records from the NWA compiled over a 210-year period (1800-2010), resulting in the largest white shark dataset yet compiled from this region. These comprehensive records were used to update our understanding of their seasonal distribution, relative abundance trends, habitat use, and fisheries interactions. All life stages were present in continental shelf waters year-round, but median latitude of white shark occurrence varied seasonally. White sharks primarily occurred between Massachusetts and New Jersey during summer and off Florida during winter, with broad distribution along the coast during spring and fall. The majority of fishing gear interactions occurred with rod and reel, longline, and gillnet gears. Historic abundance trends from multiple sources support a significant decline in white shark abundance in the 1970s and 1980s, but there have been apparent increases in abundance since the 1990s when a variety of conservation measures were implemented. Though the white shark's inherent vulnerability to exploitation warrants continued protections, our results suggest a more optimistic outlook for the recovery of this iconic predator in the Atlantic.

Highlights

The white shark Carcharodon carcharias is one of the largest, most widespread ocean predators distributed in sub-polar to tropical seas of both hemispheres [1]
Only Baum et al [15] and McPherson and Myers [16] have attempted any quantitative assessment of the status of the white shark population in the northwest Atlantic Ocean (NWA)
Using sparse sightings data (N = 31) from Atlantic Canada, McPherson and Myers [16] estimated a 3-950 fold decrease in white shark population size between 1926 and 1988. Due to studies such as these, evidence of population declines in other regions around the world (e.g., [18,19]), and their iconic and charismatic nature, white sharks have been afforded some of the highest level of protection of any elasmobranch

Summary

Introduction

The white shark Carcharodon carcharias is one of the largest, most widespread ocean predators distributed in sub-polar to tropical seas of both hemispheres [1]. Using sparse sightings data (N = 31) from Atlantic Canada, McPherson and Myers [16] estimated a 3-950 fold decrease in white shark population size between 1926 and 1988 Due to studies such as these, evidence of population declines in other regions around the world (e.g., [18,19]), and their iconic and charismatic nature, white sharks have been afforded some of the highest level of protection of any elasmobranch. In the NWA, The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has recommended that white sharks be listed as ‘‘Endangered,’’ and they have been listed as a prohibited species (i.e., no commercial or recreational harvest) in US waters since 1997 [21] Due to these conservation concerns, and the high uncertainty associated with previous studies [15,16], there is a need to better understand the historic and current status of white sharks in the NWA, incorporating as much reliable data as possible

Methods

Results

Conclusion