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Climate Change

Many observed changes in river herring biology related to environmental conditions have been noted, but few detailed analyses are available to distinguish climate change from climate variability. Impacts from global climate change induced by human activities are likely to become more apparent in future years (Intergovernmental Panel on Climate Change (IPCC)). Climate also varies naturally on the inter-annual scale: one winter is mild and the next is harsh. Furthermore, there is natural climate variability at the scale of decades: El Niño Southern Oscillation (ENSO) represents multi-year variability in the surface temperature of the tropical eastern Pacific Ocean. ENSO variability has global effects; for example, it causes changes in rainfall patterns across parts of North America, Africa, and the Indian subcontinent. Other forms of inter-annual and decadal natural climate variability include the Pacific Decadal Oscillation, the North Pacific Gyre Oscillation, and the North Atlantic Oscillation, each with known basin-scale effects on weather, pelagic food webs, and fisheries. All of these forms of natural variability in the Earth’s climate system act simultaneously and in association with ongoing climate change, which is defined as a long-term change in the climate system (>50 years). Impacts of climate change on river herring have been investigated in marine habitats and freshwater habitats. For example, a change to the amount of preferred marine habitat and a potential northward shift in marine distribution is expected as a result of climate change.  Also, environmental conditions may effect juvenile recruitment of river herring in freshwater.  A fisheries climate vulnerability assessment has found river herring to be very highly vulnerable to climate change.

The river herring Technical Expert Working Group (TEWG) Climate Change Subgroup has considered issues related to the above specific to the impacts of climate change and climate variability on river herring rangewide (including in freshwater). Additional information on these discussions, including identified research needs to inform the topic and ongoing efforts can be found at: