Recent Study Forecasts Impact of Marine Heatwaves on Apex Ocean Predators

In the vast expanse of the Pacific Ocean, on Midway Atoll, a tagged Laysan albatross takes flight. These tagged creatures are instrumental in aiding scientists in their quest to understand how various species react to shifting environmental conditions. The movement patterns of these tagged animals provide crucial data for estimating their responses to changes. The credit for this image goes to Scott Shaffer of San Jose State University.

Nowadays, the field of marine science has made significant strides in the ability to forecast the occurrence and characteristics of marine heat waves that have the potential to disrupt delicate marine ecosystems. However, the next frontier for scientists is predicting how these environmental shifts impact apex predators that inhabit these ecosystems.

In a recent publication in the journal Nature Communications, researchers have illuminated the diverse effects of marine heat waves on top predators like sharks, tuna, and marine mammals. These effects can result in the redistribution of species across international boundaries. To make these predictions, scientists harnessed the power of species distribution models that take into account variables such as temperature changes and other environmental factors.

Heather Welch, the lead author of this groundbreaking research and an affiliate researcher at NOAA Fisheries’ Southwest Fisheries Science Center, as well as a project scientist at U.C. Santa Cruz, articulated the research’s goal: “The goal is to provide forward-looking tools to help managers think ahead about how species could redistribute during heat waves and how they may need to proactively adjust regulations to account for these shifts. Predators often support important commercial fisheries, so it’s important to understand how they respond to changes in their surroundings.”

Marine heat waves have become a recurring phenomenon in the eastern Pacific Ocean off the West Coast over the past decade, with the most prominent event occurring between 2014 and 2016. There are indications that these heat waves may become more frequent and severe due to climate change. In response, NOAA Fisheries is actively pursuing the development of “climate-ready fisheries” by formulating management strategies that can adapt to evolving ecosystems and their inhabitants.

Adapting regulations to this shifting landscape of ocean life involves decisions related to open fishing seasons, catch quotas, and territorial boundaries that must adjust according to the changing distributions of species. This adaptive approach is especially crucial for species like tuna, which are targeted by fishing fleets, and for protecting endangered species like sea turtles.

Heather Welch posed a critical question: “How do we keep fishing sustainably and continue to protect important species in a world with a changing climate? We need to be prepared to change our approach as species move and shift. Fortunately, we can develop the tools to help do that in real time.”

The research delved into the effects of four significant marine heat waves in the northeastern Pacific Ocean on 14 different predator species, including sea lions, bluefin tuna, mako sharks, and albatrosses. The consequences for species distributions varied widely across heat waves and species. Some species faced the near disappearance of their habitat, while others saw their habitat nearly double in size.

The researchers’ ultimate objective was to establish an early-warning system capable of alerting managers to these changes before or as they occur. Elliott Hazen, a research ecologist at the Southwest Fisheries Science Center, emphasized the importance of proactive climate-ready management: “We are seeing large-scale changes in where and when predators go as a result of climate variability and change. Forecasting potential changes before they happen is critical for proactive climate-ready management.”

One striking finding of the research was the migration of great white sharks, with almost 40% of their habitat shifting from international waters into U.S. territorial waters during marine heat waves. This shift could impact other species that they prey upon. Additionally, the predicted habitat of commercially valuable species like albacore, bluefin, and yellowfin tuna shifted from Mexican waters to U.S. waters, accounting for between 10% and 31% of the predicted habitat. This shift was reflected in an unusual abundance of these tuna species reported by California’s commercial and recreational fishers in 2014 and 2015.

Heather Welch pointed out the significance of these changes, stating, “That gives an idea of the scale of the changes that management may have to adjust to in relatively short periods.”

In 2016, a marine heat wave along the California Coast led to an influx of humpback whales into coastal waters. These whales took advantage of the abundant anchovy population that had shifted and multiplied due to the unusual ocean conditions. Subsequently, the Dungeness crab season opened in the same waters, resulting in entanglements of humpback whales in the lines from crab traps. In response, the fishing fleet collaborated with fisheries managers to assess and adapt to the presence of whales off the coast before embarking on fishing trips, leading to a reduction in confirmed entanglements.

As part of this innovative research, scientists developed models capable of tracking ocean temperatures and other factors to offer real-time predictions of how top predators respond during marine heat waves. These predictions can be customized to suit the needs of fisheries and other ocean managers, providing an early warning system that alerts them to ecological shifts and guides proactive management strategies.

In summary, the study’s findings represent a significant leap forward in our understanding of how marine heat waves affect top ocean predators and how we can adapt our management practices to ensure the sustainability of both fisheries and ocean-based economies in a world with a changing climate. The research, authored by Heather Welch and her colleagues, was published in Nature Communications, and its implications are far-reaching.

Source: NOAA Headquarters

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