How will climate change affect the biggest fish in the sea?
By Katie Westfall and Kristin Kleisner
Tunas, sharks, billfish and swordfish are wide-ranging species that can react quickly to environmental changes. Many within this group are top predators and can move across ocean basins and between shallow and deep waters in response to ocean conditions. For these reasons, some of these species can serve as ‘climate sentinels’ or animals that can offer important information about how climate change affects ocean processes and marine life. However, many of these species face a host of threats, including unsustainable fishing levels and climate change, making us wonder what the future holds for the sea’s larger fish.
To help shed light on this important subject, EDF and its collaborators produced the first comprehensive synthesis of the impacts of climate change on the main pelagic highly migratory species of the Northwest Atlantic Ocean and the Gulf of Mexico, based on more of 160 scientific studies. The report “Navigating Our Changing Oceans: An Assessment of Climate Change Impacts to Highly Migratory Species in the North Atlantic Ocean” explores the regional effects of climate change on dozens of species.
We have found that the consequences of climate change for these species depend on many factors. While there have been some common trends like some stocks moving towards the poles as the waters warm, responses to climate change largely depend on the species, its life stage, and the region. Different species will be affected in very different ways, and there is still uncertainty as to how many of these changes will occur.
Climate change is likely to make survival more difficult for many large pelagic sharks, even after being released alive from fishing gear. Warmer waters are less rich in oxygen, and large pelagic sharks are particularly sensitive to low oxygen levels due to their high metabolic rates. In some coastal and marine regions of the world, the oxygen-rich layers will become shallower, pulling some shark species closer to the surface where they will become more vulnerable to fishing gear. Some populations will also lose important habitat that serves as a nursery for young sharks to feed and grow.
The current situation is particularly dire for many shark species, with large oceanic sharks (and rays) experiencing a global decline of 71% in their abundance over the past half century and resulting in increasing extinction risks for almost all. the species. This decline is mainly due to excessive fishing pressure, often when sharks are caught accidentally (or unintentionally when targeting other species). Bycatch is one of the biggest threats to shark populations, and climate change is likely to amplify this threat to species survival in several ways.
So what can we do to protect the biggest fish in the sea? Although more research is needed to elucidate the complex and interconnected ways in which climate change affects the ocean and its main predators, it is clear from preliminary studies that highly migratory species need new, advanced strategies for their protection – and they do. need it quickly. While some efforts are underway, accelerated action in five key areas is urgently needed:
- Strengthen international cooperation and management. Due to their highly migratory nature and their ability to cross political borders, the successful management of many species depends on international coordination. Strong American leadership that prioritizes science-based precautionary approaches and builds cross-border coalitions to advance and ensure adherence to these strategies is essential in this context.
- Implement effective harvesting strategies for target species and set limits for bycatch species. A critical step in building climate resilience is to properly manage fundamental fisheries, including establishing harvest strategies and controlling bycatch of endangered and protected species. For stocks subject to targeted fishing, catch control rules that are prudent and responsive will be essential to manage fishing levels. Vulnerable shark species caught as bycatch need more stringent protections, including strict limits to provide incentives to avoid bycatch and accountability measures in fisheries that interact with them.
- Improve our scientific understanding of highly migratory species and climate impacts. Investments in science will be essential to effectively conserve these species in the face of climate uncertainties. Better data collection in national and international fisheries and more intensive monitoring of changes in stocks, ecosystems and the marine environment are needed to inform adaptive approaches. A better understanding of the complex relationships between species (including predator-prey dynamics) and oceanographic changes can aid in scenario planning, creation of early warning systems, and development of climate-resilient management approaches. .
- Switch to more adaptive and forward-looking forms of management at the national level. In the face of changing ocean conditions, we will need more adaptive and dynamic measures that encourage conservation and ingenuity. Advanced electronic technologies can enable real-time data collection and sharing to help fishermen locate optimal fishing areas and avoid areas where they are likely to encounter bycatch. In addition, monitoring of sentinel species can help guide ecosystem management and conservation efforts.
- Co-develop climate resilience solutions with fishing communities. Building socio-economic resilience will be essential for fishermen, fishing and seafood businesses and coastal communities. Fishing communities are no strangers to the need to adapt to change, whether to help protect an overfished species or to adapt to market fluctuations. Developing climate resilience solutions in collaboration with affected communities, especially with frontline and historically marginalized groups, better ensure that they are achievable and contribute to just and equitable outcomes.
The conservation of highly migratory species is a major global challenge that the international community must meet together. It is essential to recognize the essential role that these animals play in the ecosystem and potentially as sentinels of the oceanic climate. In the United States, collaboration between managers, fishermen, scientists and conservation groups can lead to innovative management approaches and fishing practices to effectively reduce bycatch. By leading by example and being a strong voice for conservation on the international stage, we can create successful models and momentum towards the long-term sustainability and resilience of fish stocks, the marine environment and communities. of fishermen.