Key Points:

Changes in water temperature can affect the environments where fish, shellfish, and other marine species live. Certain fish species naturally migrate in response to seasonal temperature changes, moving northward or deeper—to cooler waters—in the summer and migrating back during the winter. As climate change causes the oceans to become warmer year-round, however, populations of some species adapt by shifting away from areas that have become too warm and toward areas that were previously cooler. Along U.S. coasts, this means a shift northward or to deeper waters that have a more suitable temperature. As smaller prey species shift their habitats, larger predator species may follow them.

About the Indicator:

This indicator tracks marine animal species based on their “center of biomass,” which is a point that represents the center of each species’ distribution by total biomass (or weight) in terms of their geographic location (i.e., latitude, longitude, and depth). If a fish population were to shift generally northward, the center of biomass would shift northward as well. Fish are especially mobile, and thus tend to shift their location more easily than species on land because they face fewer physical barriers. Also, many marine species, especially fish, do not have fixed nesting places or dwellings that might otherwise compel them to stay in one place.

Data for this indicator were collected by the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service (NOAA NMFS), who monitor marine species populations by conducting annual surveys in which they trawl the ocean at regular intervals along the coast. By recording what they catch at each location, scientists can calculate each species’ center of biomass. These data have been processed and made publicly available by Rutgers University at: https://oceanadapt.rutgers.edu.

This indicator focuses on two survey regions that have the most continuous and longest-running sampling: the Atlantic Ocean off the northeastern U.S. coast and the eastern Bering Sea off the coast of Alaska. The upper graphs show the average change in the center of biomass across 140 species in these regions. Tracking data from many species is useful, because if a change in behavior or distribution occurs across a large range of species, it is more likely the result of a more systematic or common cause. For consistency, these data are limited to species that were identified every year. The lower maps show these changes geographically for three species in each region. These species were chosen because they represent a variety of habitats and species types (a mixture of fish and shellfish) and because they tend to be fairly abundant. Some of these species support major fisheries that are presumed not to be heavily impacted by overfishing, reducing the chance that fishing is unduly influencing the observed trends. Additional detail related to this indicator can be found as part of the U.S. Environmental Protection Agency’s Marine Species Distribution indicator.

Key takeaways from this indicator follow:

- The average center of biomass for 140 marine fish and invertebrate species has shifted northward by about 20 miles and moved an average of 21 feet deeper between 1982 and 2018. - Economically important Atlantic species off the northeastern U.S. coast (American lobster, red hake, and black sea bass) have shifted northward by an average of 110 miles since the early 1970s. - In the Bering Sea, Alaska pollock, snow crab, and Pacific halibut have generally shifted away from the coast since the early 1980s and moved northward by an average of 19 miles.

Water temperature is not the only factor that can cause marine animal populations to shift. Interactions with other species, harvesting, ocean circulation patterns, habitat change, and species’ ability to disperse and adapt can also influence marine populations. As a result, species might have moved northward for reasons other than, or in addition to, changing sea temperatures.

Why It’s Important:

- Marine species are a particularly good indicator of warming oceans because they are sensitive to climate and because they have been studied and tracked for many years. - Marine fisheries and fishing communities are at high risk from climate-driven changes in the distribution, timing, and productivity of fishery-related species. - Fisheries management that incorporates climate knowledge can help reduce impacts, promote resilience, and increase the value of marine resources in the face of changing ocean conditions.