Highly migratory species (HMS) are fish stocks that often have trans-oceanic movements and life cycles. Tunas, billfishes, swordfish, and sharks are taxa which comprise HMS. Historically, pelagic shark population dynamics and biology have been difficult to study given their migratory nature and open-ocean habitat. Displaying large-scale migration patterns and crossing international management boundaries, pelagic sharks are susceptible to many international fisheries at various life stages. Pelagic sharks are slow-growing, late-maturing, long-lived, and produce few offspring, resulting in slower and much more reduced population recruitment than most marine species. These life history characteristics make pelagic sharks vulnerable to overexploitation by global commercial and recreational fisheries and elevate concerns of their long-term survival.
While it is widely accepted that pelagic sharks are K-selected species and at-risk to overfishing throughout various life stages, domestic and international fishery managers have yet to develop effective methodologies for managing pelagic sharks. Most shark species are classified as fully fished, overexploited, already depleted, or commercially extinct. Others are poorly researched and their stock status is classified as uncertain and unknown. Despite there are no current directed pelagic shark fisheries in most parts of the world, demand for shark products (e.g., shark fins) and landings continue to increase and more countries are now reporting shark landings than at any other time. In fact, even without estimating or understanding the virgin (i.e., before commercial fishing) population, most scientific population assessments demonstrate that pelagic shark populations over the last three to four decades have declined to levels that are alarming. Compelling scientific evidence suggests that there are a number of sharks that are in danger of extinction. Some species of pelagic sharks, such as porbeagle (Lamna nasus) and shortfin mako (Isurus oxyrinchus) sharks are already listed under the international trade regulatory regime of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Given these dramatic population declines, new scientific evidence also suggests that the loss of apex predators throughout the world’s oceans has even changed trophic dynamics in certain geographical areas which is having striking impacts on unique marine ecosystems such as coral reefs.
In the past, pelagic sharks have received little attention by domestic and international fishery managers considering their lower economic value in comparison to other HMS. Along with the lack of life history information, pelagic shark population modeling has been limited by small data sets, inaccurate dependent fisheries information, and the lack of independent fishery data. Today, many positive advances have been made in pelagic shark research, domestic management plans, and the implementation of various international agreements for shark conservation and management; however, additional domestic and international protection is imperative for the survival, recovery, and conservation of pelagic sharks. In addition, even with the improvement of pelagic shark life history information, better commercial fisheries data, and the development and application of advanced population assessment techniques; assessment models are problematic. Among various topics, this book reviews and discusses some of the limitations for the use of population models in pelagic shark management. This book reviews the current scientific information and finds that there are some new statistical, biological, and practical approaches to understanding the effects of fishing on pelagic shark populations. Moreover, new shark avoidance measures show promise for reducing shark bycatch in commercial fisheries. Discussions and recommendations are included for most of these new conservation and management approaches which might be hopeful for improving global pelagic shark populations. Overall, this book demonstrates that even with conservative management and the use of advanced population models, most pelagic sharks can not be sustainably exploited for very long, if at all. Unlike any other previous shark book, this book was specifically intended for the use by domestic and international pelagic shark fishery managers. The book highlights a historical perspective on shark conservation, but the focus of the book is on the importance of improving current modeling applications and management approaches. Overall, the book provides a review of the past, present, and the future needs of pelagic shark conservation and management.