Understanding Thermal Sensitivity and Resilience to Improve Fisheries Management

Aquatic connectivity restoration projects in Maine opened up an additional 30 miles of habitat for the endangered Atlantic salmon, Eastern brook trout, and other native species. (Credit: US Fish and Wildlife Service - Recovery Act Team via Flickr CC BY 2.0)

Thermal sensitivity and resilience shape how fish move through an ecosystem and survive. Thermal sensitivity refers to a species’ sensitivity to changes in temperature. Some species are more sensitive than others. Generally, every species has a range of temperatures that they are able to tolerate, and the smaller this range, the more sensitive it is.

Species with high thermal sensitivity are more likely to show signs of thermal stress and migrate out of areas that are experiencing spikes or drops in temperature outside of their hospitable range.

Such migration behaviors, as well as the loss of fish through thermal stress, can endanger fisheries as population distribution and density change. Understanding species’ response to thermal stress is a key part of fisheries management.

Responses to Thermal Stress

Depending on the thermal sensitivity and resilience of species, each species responds differently, with some diving deeper or migrating to cooler waters to beat the heat.

Spikes or drops in water temperature can be driven by natural or unnatural environmental factors. For example, a dam upstream of a cold-water fishery can decrease the flow of fresh, cool water, leading to increases in temperature below the dam. Because dams create barriers to movement upstream, fish may be forced to migrate to cooler waters downstream, changing distributions.

Climate change has also led to air and, therefore, water temperature increases, which have made habitats that were formerly hospitable for cold-water species unsuitable. While cold-water fish are often the focus of thermal sensitivity and resilience research, warm-water fish can also be impacted by temperature changes like marine cold spells.

Understanding Thermal Sensitivity in Two Fish in a Temperate River

A 2024 study published in Aquatic Sciences documented the responses of two riverine species to summer water temperatures. Spatial habitat use and body temperature observations were completed for individual European barbel (Barbus barbus) and common bream (Abramis brama).

According to the study, barbel have a thermal optima of up to 26 °C and an upper lethal temperature of 36 °C, and bream have a thermal optima of 10 to 24 °C. At the conclusion of the study, neither species showed short-term behavioral thermoregulation, meaning that the fish stayed in place even when temperatures exceeded their thermal optima range.

This suggests that preservation of temperatures and ensuring access to cold-water refugia (or warm-water for species that prefer higher temperatures) for fish when temperatures shift.

Conclusion

Understanding the thermal sensitivity and resilience of key species is critical to conservation and fisheries management. Under a continuously changing climate regime, thermally sensitive species are expected to experience thermal stress, leading to population declines and changing distributions.