Overfished and Understudied: The Critical Conservation Threat of Cetacean Bycatch in Indian Ocean Tuna Gillnet Fisheries

Abstract

Bycatch, or the incidental capture of non-target species in fisheries, is widely recognized as the leading cause of mortality for marine mammals. Despite decades of effort across scientific, policy, and diplomatic fields, information on cetacean bycatch is limited in many fisheries, and policy responses are slow and ineffective. This is particularly the case in the Indian Ocean, where data are scattered, highly uncertain, and incomplete, but the limited available information suggests that bycatch rates in drift gillnets targeting tuna may be very high and likely unsustainable for some cetacean species. Nevertheless, the best available information estimates that over 4 million cetaceans were killed in Indian Ocean driftnet fisheries from 1950-2018. Drift gillnets, widely recognized as the fishing gear causing highest cetacean mortality, are historically the dominant gear type used by tuna fisheries in this region – a situation unique to the Indian Ocean region. In 1992, the United Nations banned the use of large-scale pelagic driftnets (e.g., over 2.5 kilometers in length) on the high seas largely because of their threats to marine megafauna (UNGA Resolution 46/215). Three decades later, however, drift gillnets remain one of the primary fishing gears in the Indian Ocean, accounting for approximately 30 percent of tuna catches in this ocean – including large-scale and smaller-scale drift gillnets and fishing vessels. Most drift gillnet fleets in the Indian Ocean are comprised of small vessels for which accurate data are lacking, and the management of the fishing effort has proven to be challenging. This contrasts with purse seine and pelagic longline fleets operating in this region – the predominant gear types for distant water fishing fleets in the IOTC – for which fleet classification, fishing effort, and target catches are better documented and, in some cases, subject to more reporting requirements under the IOTC. In some ways, bycatch is just as much a diplomatic and policy challenge as a scientific one. The multilateral management body charged with regulating tuna fisheries and bycatch in the Indian Ocean region, the Indian Ocean Tuna Commission (IOTC), is riddled with complicated politics and socioeconomic differences amongst its 29 Member States that impede sustainable fisheries management. For some Members, war-torn histories and competing economic priorities have prevented nations from addressing fisheries issues, with nations of vastly different capacity and interests in the region trying to cooperate on their own national interests in the multilateral context. The IOTC adopts decisions based on consensus, but consensus on management measures can be difficult to reach. When it is, some nations later issue formal objections to these measures, thereby eroding progress at the multilateral level. The IOTC passed a binding measure to reduce cetacean bycatch in 2013 (13/04) – later revised in 2023 (23/06) to include additional gear types – but efficacy of this measure in reducing bycatch is not well documented. In addition to the multilateral lens to address bycatch, the U.S. promulgated a regulation pursuant to its Marine Mammal Protection Act that established a recent, unprecedented unilateral approach to managing marine mammal bycatch in 2016. This regulation affects numerous fishing nations, including 26 IOTC Members, and issues the possibility that the U.S. could block seafood imports if a nation does not implement conservation measures that are comparable to those required in U.S. fisheries. This new policy, the Marine Mammal Protection Act Import Provisions Rule, holds unprecedented conservation potential for marine mammals but also creates the potential for a considerable socioeconomic burden, particularly for countries with limited capacity in the Indian Ocean region. This dissertation relies upon a multidisciplinary approach to advance the limited body of knowledge on cetacean bycatch in Indian Ocean gillnet fisheries from a multidisciplinary approach. The dissertation begins from a global perspective, then proceeds to a regional perspective, and, finally, concludes with a more narrowly-focused country perspective. The first chapter details the global landscape of policy efforts within 15 Regional Fisheries Management Organizations (RFMOs), including the IOTC, to address cetacean bycatch, and highlight the efforts in addressing bycatch at this multi-national level. RFMOs manage many, but not all, of the geographic footprint of fisheries, and this chapter is the first to review RFMO performance in specifically addressing cetacean bycatch. Building on this information, the second chapter focuses on the Indian Ocean, describing the extent of known information on cetacean bycatch to-date, particularly in the Arabian Sea where gillnet fishing effort is highest. The third chapter then examines the potential effect of the recent, unilateral regulatory approach to bycatch management, the U.S. MMPA Import Provisions as another policy tool to reduce bycatch, particularly in the top six gillnet fishing nations in the Indian Ocean: India, Indonesia, Iran, Oman, Pakistan, and Sri Lanka. The fourth chapter then focuses on one of the top driftnet nations in the Indian Ocean, Pakistan, using satellite imagery, machine learning, and interviews to better understand the size of its gillnet fleets, and test the efficacy of developing such methods for data-poor fisheries. Collectively, these chapters shed light on an area that experiences the world’s highest cetacean bycatch today – but which has received far less political and scientific attention than other fisheries. There is an urgent conservation need to address bycatch in Indian Ocean fisheries, as data gaps contribute to inaction. This dissertation leverages recent efforts by the international community (e.g., implementation of the MMPA Import Provisions and the IOTC-International Whaling Commission Bycatch Mitigation Initiative) to address cetacean bycatch in the Indian Ocean and to address some of these knowledge gaps. This work culminates in recommendations to IOTC stakeholders and global managers about increasing capacity, monitoring, and management of cetacean bycatch in the Indian Ocean region.