Hammerheads

Fishery interactions and space use of great and scalloped hammerheads, Sphyrna mokarran and S. lewini

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Overview

Adequate conservation and management of shark populations is becoming increasingly important on a global scale, with declines documented worldwide. Successful management of these species requires detailed information on their movement and distributions. Generating such information for large-bodied sharks is challenging, however, as they typically move over long distances, are logistically difficult to capture, and, as upper-trophic predators, are naturally low in abundance. The scalloped and great hammerhead sharks epitomize such challenges, they are target or by-catch species in a variety of fisheries. As a result, substantial population declines have occurred in many areas. In the U.S. Atlantic, both species are caught in commercial fisheries; however, due to their sensitivity to capture, such as high at-vessel mortality, reducing quotas or prohibiting landings will not decrease mortality. Thus, alternative methods for their management are urgently needed. Here, our team is working with scientists from Bimini Sharklab, NOAA, and Florida State University to analyze fishery capture data of hammerhead sharks in conjunction with tracking data on space and habitat use.

Conservation concern

Hammerhead sharks are increasingly recognized as species of conservation concern. The great hammerhead and scalloped hammerhead are both large-bodied, highly mobile, coastal-pelagic sharks with circumtropical distribution. Both species are target or by-catch species in a variety of fisheries throughout their range, and as a result, substantial population declines are suspected to have occurred in many areas. Globally, the International Union for the Conservation of Nature (IUCN) Red List categorizes both species as Endangered. In 2013, they were added to the Convention on International Trade in Endangered Species (CITES) Appendix II, and in 2015 the Convention on the Conservation of Migratory Species of Wild Animals (CMS) Appendix II. In addition to these listings, hammerheads were identified in 2017 as a priority group that would benefit the most from improved management.

 
 

 
 

Questions

  • What is the seasonal distribution and relative density of scalloped and great hammerhead sharks in the U.S. Atlantic?

  • Are time-area-closures a viable option for great and scalloped hammerheads to reduce spatiotemporal overlap between the Atlantic bottom longline fishery?