What Stresses Out a Fish?

The life of a modern fish is becoming increasingly stressful. The already challenging tasks of finding food, reproducing, and avoiding predation are getting more difficult with direct and indirect human activity.

Stress is a natural response shared by all living organisms to avoid unfavourable conditions. A short stressor causes an “acute” stress response that enables an organism to escape conditions such as predation. However, repeated or long-term stress becomes “chronic” and can cause permanent damage. The prolonged release of stress hormones and enzymes decreases growth, reduces reproductive potential, hampers cellular function, and increases susceptibility to disease.

One of the more obvious stressors fish experience in the Elk Valley is a thriving recreational fishing industry. While mortality is reduced by catch-and-release regulations, improper handling techniques or repeat catches can have significant adverse effects. Research shows keeping fish out of water and over-handling are the greatest causes of increased stress hormone release and post-release mortality. Keeping fish in the water, being ready to take a photo, wearing gloves, and decreasing playing time, all improve the chances of fish survival. To avoid repeat catches, consider limiting your day’s fishing effort to decrease chronic stress effects. 

More indirect impacts on fish stress are associated with land development. On a smaller scale, this includes human traffic and recreational water use. In creeks such as Coal Creek and Boivin Creek, a common activity is the construction of rock-dams or “weirs” to make pools to cool down in. Unfortunately, weirs can block fish movement and reduce flow speed which warms the water. While this may seem like a harmless activity, the Elk River Alliance discourages rock-dams to maintain a healthy fish habitat.

On a larger scale, major Elk Valley industries such as mining, forestry, and residential development have significant effects on fish. Mountaintop mining often results in the complete or partial burial of streams, reducing habitat and inter-habitat connectivity. In 2019, for example, the loss of Westslope cutthroat trout in Fording River was attributed primarily to stream channel alteration combined with harsh winter conditions. Additionally, leaching from waste-rock piles results in high concentrations of chemicals like selenium, which increases the chance of fish birth defects. At some monitoring sites, selenium levels are up to 337 times the aquatic quality guidelines and are 12-24 times higher in the Elk River mainstem compared to non-mine-impacted streams. 

Compared to mining, forestry impacts are under-researched in the Elk Valley. Studies from other watersheds show that tree removal directly adjacent to streams increases stream temperature by about 4C and decreases woody debris for fish habitat. Removal of trees on land above streams increases water sediment levels, alters nutrient concentrations, and increases snow-melt speeds. Residential development can have similar impacts to forestry with the additional contributions of stormwater runoff (i.e., fertiliser, car oils, litter, etc.). These local-level impacts will be exacerbated by higher stream temperatures, more frequent forest fires, and erratic flood/drought cycles that are expected with climate change.

It’s easy to throw up your arms and say, “What good are my actions when industry and climate change are such behemoths?” But fish don’t experience stressors one at a time; they experience the cumulative effects of all stressors in combination. If a fish can barely survive the impacts of climate change, tree-loss, invasive species, and pollution, the added incremental stressor of a warm rock-dam or lengthy line-time can be the final straw. Doing our part, however small, can make a life or death difference for a fish and its offspring.

A Westslope cutthroat trout unhooked underwater and briefly lifted out for a quick photo.  Photo by Chad Hughes, Elk River Alliance.