With summer in full swing, millions of Americans are fishing in the nation’s streams, lakes, and coastal waters. However, many of these waterways are heating up, spelling trouble for fish and the nation’s $46 billion dollar recreational fishing industry.

Warming waters can push fish out of their optimum temperature ranges—forcing them to migrate if there’s room, or else struggle or even die. The graphics below depict these temperature ranges for three popular game fish (trout, bass, and salmon), but the concept applies to other species.

Stream temperatures are rising at 65% of the continental U.S. gauges with sufficient data since 1990. While many factors influence stream temperatures, from water source and depth to agriculture and dams, rising air temperatures can play a key role. Warming streams impact fish by intensifying some algae blooms and allowing viruses to affect more species. Inland fish are also moving north, altering predator-prey interactions and changing the timing of migrations and spawning.

Meanwhile, every Great Lake has warmed at least 1.5°F since 1995 (when data became available for all lakes), led by Lake Ontario at 2.2°F. In addition to the above impacts, warmer water has increased the size and feeding rates of the parasitic sea lamprey, which can latch onto and devastate large Great Lakes fish.

 

In addition, all surface waters off the contiguous U.S. coast have warmed since 1901. The North Atlantic has recorded the most warming (up to 3°F near Maine), followed by the West Coast (1-2°F), Gulf of Mexico (0.5-2°F), and South Atlantic (0.1-0.4°F). Since 93% of the additional heat in the climate system goes into the oceans, this trend will continue as the climate warms. Saltwater fish and fishing industries could be profoundly changed—from costly ‘Red Tide’ algae blooms to projected migrations. According to the National Academy of Sciences, the total mass of sea animals could drop by 5% for every 1.8°F of ocean warming.

To minimize economic and ecological losses, organizations must take a localized approach. NOAA has developed regional action plans, while state governments in New York and Montana have restricted or even suspended freshwater fishing when water temperatures are too high. As our waterways warm, these bodies are gearing up for a major sea change.

METHODOLOGY

  • Annual average sea surface temperatures from 1901-2018 were analyzed using the NOAA Extended Reconstructed Sea Surface Temperature (ERSST) V5 dataset.

  • Great Lakes temperature data is from NOAA’s Great Lakes Environmental Research Laboratory. Climate Central calculated the average annual surface water temperature for each lake since 1995.

  • Only 40 of 500+ stream gauges analyzed had consistent, long-term temperature data, missing no more than 10% of the days each year since 1990. The average water temperature was then estimated for spring and summer (March - August) at the remaining gauges.

  • Temperature changes were estimated using a linear regression through each dataset’s period.

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