U.S. Atlantic and Gulf Migratory Pelagics Fishery
When accounting for the impacts of climate change, the U.S. Atlantic and Gulf of Mexico pelagic longline (PLL) fishery that target Highly Migratory Species (HMS) has key challenges to overcome in terms of economic viability and sustainability, which hinder resilience in the face of climate change. Fortunately, many of the solutions that can help build climate resilience will also address existing issues in the fishery. Many HMS have key attributes that provide ecological resilience, such as dietary flexibility and high mobility, though other characteristics (e.g., slow growth rate and late maturity) make some HMS incredibly vulnerable. A governance structure encompassing international and domestic domains and regulatory systems add complexity to the HMS fishery management, which can be inadequate and ineffective at the international level. Improved international management and cooperation to manage target stocks and bycatch more sustainably will improve overall population and ecosystem health. Domestically, the United States has adopted a strong legal mandates and several effective bycatch mitigation measures that promote sustainable fisheries, thus fostering resilience. The PLL fishery has a history of gear innovation, learning, and implementation of cutting-edge technologies (e.g., collection of real-time information through electronic technologies) that can help achieve more optimal fishing (higher rates of target species and less bycatch). However, the domestic fishery management is characterized by a top-down decision-making process, and some fishery regulations have not been co-developed with the industry. Every year, the PLL fishery registers a reduction in fishermen numbers, as many leave the fishery due to an inability to maintain profitability while complying with management measures and competing with import products that undercut prices. Given the difficult economic situation of many PLL fishermen, efforts to build resilience must be done collaboratively and inclusively with all affected fishing communities to ensure these measures are effective, practical, and achieve fishery sustainability goals.
This PLL fishery operates from ports stretching from New England, south along the Atlantic seaboard, into the Caribbean Sea (CS) and the Gulf of Mexico (GOM), targeting primarily North Atlantic swordfish, bigeye tuna, and yellowfin tuna. Secondary target species include mahi mahi (dolphinfish) and wahoo, and certain sharks that are retained and commercialized (e.g., shortfin mako sharks and common thresher sharks). Today, a U.S.-flagged fleet fishes for HMS in the Atlantic Ocean, CS, and the GOM, in the U.S. EEZ and beyond (NMFS, 2021). One of the major challenges in the PLL fishery is bycatch of marine life including sea turtles, sea birds, billfishes, marine mammals, and coastal and pelagic sharks (Garrison, 2007; Mandelman et al., 2008; Klaer, 2012; Stokes et al., 2012; NMFS, 2021). Gear adaptations in materials, lengths, and deployment methods can greatly affect the selectivity of longline fishing (Watson & Kerstetter, 2006; Gilman et al., 2020; Poisson et al., 2022).
Climate Impacts to HMS and the PLL Fishery
The effects of climate change on HMS will differ depending on the species, life stage, and the region. Projections indicate that many HMS will shift their ranges poleward, and some will experience changes to their abundances in equatorial areas (decreases for swordfish and increases for yellowfin and skipjack tuna) (Dueri et al., 2014; Muhling et al. 2015; Monllor-Hurtado et al., 2017; Erauskin-Extramiana et al., 2019; 2020). HMS are particularly sensitive to low oxygen levels (Brill, 1994; Bernal et al., 2009; 2012; Leung et al., 2019), and oxygen-depleted waters due to ocean warming will potentially make survival more difficult for many HMS after being released alive from fishing gear (Gallagher et al., 2014; Musyl et al., 2015; Dell’Apa et al., 2018). In some global coastal and marine regions oxygen-rich layers will become shallower, driving some species to the surface where they will become more vulnerable to fishing gear (Prince & Goodyear, 2006; Prince et al., 2010; Stramma et al., 2012; Vedor et al., 2021). In addition, the timing and location of spawning is projected to shift for Atlantic bluefin tuna in the northern GOM (Muhling et al., 2011), and certain populations of sharks (e.g., sandbar sharks) will likely lose important nursery habitat (Crear et al., 2019; 2020).
Key attributes (Mason et al., 2022) contributing to HMS ecological resilience include: 1) spatial flexibility due to wide adult mobility and environmental niche breadth and 2) behavioral and dietary flexibility. But other attributes may reduce ecological resilience, mainly evolutionary flexibility due to slow growth rate, late age of maturity, production of few offspring, and the fact that many HMS have specific thermal ranges and oxygen requirements. Also, several HMS have low population abundance due to overfishing and high bycatch levels contributing to reduced age structure in some HMS populations.
The current domestic governance structure of the PLL fishery result in a fishery system’s agency characterized by a top-down management process, which, at times, can be perceived by the fishing community as being less participatory and transparent, though recognizing elements of a strong management foundation resulting in higher levels of accountability as compared to other PLL fisheries. For many HMS populations, the resilience level conferred by governance attributes of the domestic regulatory system may be reduced by lower levels of compliance for the international management and the lack of responsive harvest strategies for target species and effective bycatch regulations for most of the non-target species (e.g., large pelagic sharks) across the Atlantic Ocean. Hence, the international fishery management process can be perceived as less responsive, accountable, transparent, and efficient and effective than the corresponding domestic governance structure. The fishery system is also characterized by a moderate flexibility due to a somewhat contentious HMS management with conflicting interests across stakeholder groups making policy change slow and less responsive, and HMS fishing mortality not being effectively integrated across scales and sectors. On the bright side, resilience to the governance system can be fostered by the presence of good opportunities for learning and experimentation through adaptive decision-making process and innovations in fishing technology and practices.
Resilience in the socioeconomic domain of the PLL fishery system is constrained by reduced wealth and reserves among the fishing community, coupled with the fact that this community is prone to low economic diversity because of high dependency on the specificity of the fishery, markets, and target species composition. Also, though some resilience mindset and social diversity are present in the fleet, groups don’t necessarily coordinate together. On the other hand, the high degree of flexibility due to high mobility through access to various fishing grounds and some presence of flexible and agile infrastructures that allow the fishery system to respond to unpredictable conditions and disruptions can help confer resilience in the face of climate change.
Climate change is already impacting HMS in the U.S. Atlantic and GOM and will continue to do so at an increasing rate. By continuing to build the resilience capacity of the existing management regimes and fishing communities, both nationally and internationally, the PLL fishery will be able to adapt to these impacts. Approaches that incentivize continued advancements in bycatch avoidance, while providing spatiotemporal flexibility in the fishery and facilitating adaptation to changing ocean conditions, could help to maximize the responsible and sustainable catch of target species and minimize bycatch of vulnerable species. Correspondingly, the international management of HMS needs the establishment of, and higher compliance to, sustainable harvest strategies for all target species and a more active and responsive management of bycatch species (e.g., reference points). Domestically, the transition to more adaptive, dynamic management approaches (e.g., deploying existing electronic technologies that can be used to develop real-time information systems to help fishermen optimize fishing) could enhance the fishery’s climate readiness, while improving conservation and economic outcomes. To be successful, these approaches will require effective collaboration between managers, fishing communities, industry, environmental organizations, technology providers, scientists, and others through cooperative research and throughout the policy-making process, both domestically and internationally. Ultimately, such a management scheme could result in a triple win by improving conservation, profitability, and resilience in the fishery.
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Photo: Longline fishing for yellowfin tuna. Credit: Animal Stock/Alamy