The changing climate has detrimental effects on many polar species, especially in the Arctic, which warms twice as fast as the rest of the planet. Numerous studies have shown that traits like reproduction are negatively impacted. However, a long term study conducted by researchers of the University of Washington has found that one of Alaska’s most abundant freshwater fish species is altering its breeding patterns in response to climate change. This could impact the ecology of northern lakes, which already acutely feel the effects of a changing climate.

Three-spine sticklebacks are one of the most fish species in Alaska’s freshwater lakes. They are used often for environmental research studies due to their life history and their reliance on clean water. Picture: Jason Ching
Three-spine sticklebacks are one of the most fish species in Alaska’s freshwater lakes. They are used often for environmental research studies due to their life history and their reliance on clean water. Picture: Jason Ching

While several papers have speculated that conditions brought on by a warming climate may allow animals to breed more often in a single year, this has only been empirically shown in insects. This study is the first to document multiple breeding cycles for fish in a single season due to climate change, said lead author Rachel Hovel, a postdoctoral researcher in the UW’s School of Aquatic and Fishery Sciences. “The exciting thing about this paper is that it shows, for the first time, the emergence of multiple breeding in a vertebrate as a response to climate change,” Hovel said. “Climate change literature features many predictions and vulnerability assessments, but we don’t have many opportunities to actually observe species’ responses over time, as this is very data-intensive. Our ability to detect multiple breeding in fish is attributed to our comprehensive and high-quality long-term dataset.”

Three-spine sticklebacks are rather small and agile and hard to catch by hand. For the study, fish were collected by nets in the course of another study on sockeye salmon. Picture: Jason Ching
Three-spine sticklebacks are rather small and agile and hard to catch by hand. For the study, fish were collected by nets in the course of another study on sockeye salmon. Picture: Jason Ching

The data was collected from 1963 until 2015 in Lake Aleknagik in southwest Alaska. The research program has for decades recorded the abundance of juvenile sockeye salmon and other fish that live in the region’s freshwater lakes. For 52 years, fish were captured in nets along the lakeshore at 10 different sites every seven days between June and September. All fish were identified and measured. Originally, the program was aimed at studying sockeye salmon. As sticklebacks are one of the most abundant fish species in Alaskan lakes, the findings could be relevant throughout the entire region. “Alaska is warming about twice as rapidly as most of the rest of the planet,” she said. “These fish are adapted to survive in relatively cold environments with limited productive seasons. The responses to rapid warming that we see in lakes, like early spring ice breakup, are releasing some of these constraints.”

This lake is one of several lakes in the southwest corner of Alaska. It is 32 km long and 26 km wide and via its tributary Wood River and Nushagak River, it flows into Bristol Bay and Beriing Sea. Picture: Alex Smith
This lake is one of several lakes in the southwest corner of Alaska. It is 32 km long and 26 km wide and via its tributary Wood River and Nushagak River, it flows into Bristol Bay and Beriing Sea. Picture: Alex Smith

By using size data as well as environmental data, researchers found that three-spine stickleback spawned earlier in years when ice breakup occurred earlier, and in some years, the fish produced more than one brood. Given the short summers in Alaska, most stickleback have time and stamina for only one brood, but increasingly they are rearing two broods a summer as climate change ushers in earlier springs. These factors could have wider ecological effects, as three-spine stickleback are a dominant fish species in many northern lakes. This is particularly true for sticklebacks’ primary competitor in many coastal lakes in Alaska: juvenile sockeye salmon. The two species share the same habitats in lakes and generally eat the same things. “If stickleback are increasing in abundance because of their modified reproduction strategy, this can have ecosystem implications for the productivity of species we commercially care about, like sockeye salmon,” Hovel said. Researchers don’t yet know if breeding more often and earlier in life is beneficial for three-spine stickleback, but it does appear that over the long term, the fish will likely increase their abundance. “We don’t know exactly what this means for demographics of this species,” Hovel explained. “It could also mean that fish are living shorter lives because there’s a higher physiological cost to breeding more than once. In the lower-latitude extent of their range, fish mature earlier and die earlier.”

Three-spine sticklebacks build a nest into soft muddy grounds. These nests are guarded by the male to make sure eggs are safe and oxygenated. Picture: Jason Ching
Three-spine sticklebacks build a nest into soft muddy grounds. These nests are guarded by the male to make sure eggs are safe and oxygenated. Picture: Jason Ching

Source: Michelle Ma, University of Washington