Mitigating bycatch and depredation of marine mammals in longline fisheries

ICES Journal of Marine Science ICES Journal of Marine Science (2015), 72(5), 1576– 1586. doi:10.1093/icesjms/fsv092 Introduction to the Themed Section: ‘Marine Mammal Bycatch and Depredation’ Introduction Mitigating bycatch and depredation of marine mammals in longline fisheries 1 John H. Prescott Marine Laboratory, New England Aquarium, Central Wharf, Boston, MA 02110, USA Biology Department, Boston University, Boston, MA, USA 3 Sea Mammal Research Unit, University of St Andrews, St Andrews, UK 4 Department of Environmental Conservation, University of Massachusetts, Amherst, MA, USA 5 Office of International Affairs, NOAA Fisheries, Silver Spring, MD, USA 2 *Corresponding author: tel: +1 617 226 2137; e-mail: Werner, T. B., Northridge, S., Press, K. M., and Young, N. Mitigating bycatch and depredation of marine mammals in longline fisheries. – ICES Journal of Marine Science, 72: 1576 – 1586. Received 23 April 2015; revised 28 April 2015; accepted 28 April 2015. Demersal and pelagic longline fisheries involve frequent and geographically widespread interactions with many individuals, populations, and species of marine mammals. Animals sometimes suffer mortality and serious injury following these interactions, attracted mainly to longlines as a source of food. This depredating behaviour can have serious consequences for fishermen, especially when they lose valuable catch and face other associated operational and regulatory challenges. Using input from a group of international experts in the science, fishing industry, and government sectors, we produced a list of methods for mitigating depredation and bycatch of marine mammals in longline fisheries, collectively assessed their potential as a solution, and determined priorities for further research. The intention of this review is to help synthesize our current understanding about potential solutions, to provide an introduction to the articles that appear in this themed set of the ICES Journal of Marine Science, and to help fishermen, fisheries managers, and research scientists advance solutions to this global problem. Keywords: bycatch, depredation, longlines, marine mammals. Background Longlines are a prevalent form of commercial hook and line gear. They consist of a mainline with attached branchlines containing baited hooks to catch target fish. Mainlines usually extend many kilometres from the fishing vessel that deploys them. Longlines can be distinguished between those that target demersal fish and those targeting pelagic ones. Between 1950 and 2000, longline fisheries produced an estimated annual average of 10% of all recorded fishing catches worldwide by weight, the fifth most of all gear types (Watson et al., 2006). The species catch composition on average consists of the largest (by length) and highest trophic level fishes, such as tuna and swordfish, compared with those caught by other gear. As with all types of fishing, longlines produce considerable bycatch, including many species of endangered megafauna such as sea turtles, elasmobranch fishes, seabirds, and marine mammals (Lewison et al., 2004). Often, bycatch is the principal threat to the recovery of these species and populations (Lewison et al., 2004; Read et al., 2006; Žydelis et al., 2009). For marine mammals, longline bycatch is a threat to several species and populations including false killer whales (Pseudorca crassidens) in the insular Hawaiian Islands, and Risso’s dolphin (Grampus griseus) and pilot whales (Globicephala spp.) in the Northwest Atlantic. However, relative to other fishing gear such as gillnets, considered the most immediate threat to the survival and recovery of many marine mammal species and populations (Reeves et al., 2013), longline fishing generally does not pose as much of a threat, although many individuals suffer mortality and serious injury as a result of the interactions (Gilman et al., 2006; Garrison, 2007). Moral and ethical issues notwithstanding, fishers are mostly concerned by the loss of valuable target catch and # International Council for the Exploration of the Sea 2015. All rights reserved. For Permissions, please email: Timothy B. Werner 1,2*, Simon Northridge 3, Kate McClellan Press 4, and Nina Young 5 1577 Mitigating bycatch and depredation of marine mammals operations, with an emphasis on odontocetes. A four-day workshop was held on the campus of the Woods Hole Oceanographic Institution from 22 to 25 October 2013, with 24 participants representing government, marine scientific institutions, and fishers from the United States, South America, Europe, and Australia (Table 2). The workshop featured presentations giving fishing industry perspectives and collaborative research programmes undertaken in different parts of the world to mitigate marine mammal bycatch and depredation. Many of these presentations are included in this themed article set of the ICES Journal of Marine Science. The studies in this themed article set The articles published herein are important contributions to understanding the dynamics of marine mammal –longline interactions as well as potential solutions. They include studies from two of the most important long-term collaborations between scientists, fishers, and fisheries managers to address marine mammal depredation in demersal longline fisheries from the Crozet Islands (Guinet et al., 2015) and the Gulf of Alaska (Straley et al., 2015). Although in both fisheries (targeting Patagonian toothfish and sablefish, respectively), neither paper identifies one or more definitive long-term solutions, they highlight the progress towards finding them, and provide convincing arguments that the most promising and sustainable ones will emerge through collaboration between science and industry. Only through these close collaborations is it possible to fully understand how fishing practices contribute to the problem as well as potentially solve it, a process that is the focus of studies by Tixier et al. (2015a) and Thode et al. (2015). The overriding motivation of collaborative research is for reducing depredation to reduce economic losses, and less borne out of urgency for population recovery of an endangered species or ethical concerns. More recent regional studies come from the southwest Atlantic, involving both demersal and pelagic longline fisheries (Passadore et al., 2015a, b). They examine physical oceanographic, environmental, and fishing operation variables (e.g. season, temperature, fishing depth, etc.) under which interactions occur, as a means to identify strategies for avoiding or reducing fishing and marine mammal conflicts. The remaining articles evaluate four potential bycatch deterrents, including devices that have not undergone rigorous scientific testing. These include acoustic harassment devices (Tixier et al., 2015b) and passive acoustic devices (O’Connell et al., 2015), which for years have sometimes been used by fishers to deter marine mammal interactions, despite a lack o (...truncated)