Image (above): The rocky habitat on lake shores is critical for fish breeding, and is the first thing to be stranded high and dry when drought strikes and lake levels drop. PC: Bernard Spragg via Flickr
Reference: Glassic, H.C. and J.W. Gaeta. 2019. Littoral habitat loss caused by multiyear drought and the response of an endemic fish species in a deep desert lake. Freshwater Biology 64:421-432. DOI 10.1111/fwb.13231
Fish need family-friendly housing
Like young couples who sacrifice their hip downtown apartments for peaceful, family-friendly suburban neighborhoods, many animals develop very specific real estate tastes when it’s time to breed.
Consider the sculpin. Sculpin are fish, but unlike the image of “fish” that just leapt to your mind, sculpin do not have the habit of swimming in open water. Instead, they rest their flat bellies on ocean, stream or lake bottoms where they balance on their front fins, something like a seal perched on its flippers. This bottom habitat is where they seek food and shelter, but when it’s time to breed not just any patch of lake bottom will do—sculpin eggs and offspring need a specific set of conditions to thrive.
Researchers Hayley Glassic and Jereme Gaeta from Utah State University asked what could happen to the sculpin of Bear Lake, Utah—a large lake in a region where water is scarce—when drought occurs, causing their prime breeding real estate to, quite literally, dry up. By monitoring lake water levels, the amount of suitable breeding habitat, and sculpin populations over time, Glassic and Gaeta have documented that drought is associated with lake shrinkage, breeding habitat loss, and the decline of the Bear Lake sculpin—a fish found nowhere else in the world.
Lakes shrink during drought, leaving fish breeding habitat high and dry
Bear Lake sculpin typically reside in the deeper, cooler parts of the lake, but when it’s time to start a family you might find them checking Zillow postings for rocky habitat near the shore. Expectant parents are on the market for protected spaces between small boulders in the shallow, warmer edge waters of the lake. The rocky habitat of the lake shore is special because it provides numerous shelters to hide vulnerable eggs from predators that rove open water at the lake’s center. But by definition this habitat is rare—the lake edge makes up a small fraction of the total lake area—and it is also first to go when drought strikes.
When lakes lose water they shrink like puddles drying in the sun, dropping lower and drawing down on the edges. Although droughts have always figured into the climate and hydrology of the North American southwest, the frequency and duration of droughts is expected to increase in this region. Scientists anticipate that future prolonged drought conditions will cause lakes to become shallower and smaller, leaving breeding habitats for fish like the Bear Lake sculpin stranded high and dry.
Even if sculpin beat the shrinking real estate market and manage to find the perfect home for their eggs, that doesn’t guarantee a happy ending for their family. Once hatched, juvenile fish remain near the shore because the complex, rocky environment shelters small invertebrates for them to feed on, and also offers them refuge from large predators. The authors believe that these immature sculpin could suffer the brunt of multiple stressors as lake edge habitats disappear—they project a steep decline (up to 85%) in juvenile sculpin numbers under future drought scenarios.
The plight of the Bear Lake sculpin is a grim reminder of a fate that has already met a related lake-dwelling species, the Utah Lake sculpin, which hasn’t been seen since severe drought and lake level declines in Utah Lake in the 1930s.
Facing an uncertain future due to drought and habitat loss
Even within Bear Lake, the effects of habitat loss could reverberate to other species. Sculpin are not the only fish to use the vanishing lake shore habitat, and sculpin themselves are an important food source for larger predatory fish in the lake that could suffer as their prey populations decline.
Glassic and Gaeta emphasize that despite a legacy of drought in the region, water resource planners aren’t able to assume that future drought conditions will echo those of the past –at the threshold of an unpredictable climate future planning for adaptation and resiliency is key to preventing habitat and species loss. One practical solution in discussion is to install breeding habitat structure on the lake shore—a possible way to rebuild housing for the fish if existing breeding habitat is decimated by drought. Confronting future climate uncertainty is a key challenge and opportunity for conserving freshwater biodiversity, including Bear Lake sculpin and the community of lake-dwelling neighbors who are linked to its fate.