Ocean’s ‘breathability’ for anchovies being used to track impacts of climate change

A research team that includes SCCWRP has found that populations of Northern Anchovy fish rise and fall in predictable ways in response to how “breathable” the ocean water is for them – a finding that has enabled scientists to use this keystone prey species to begin tracking the impacts of climate change on West Coast ecosystems.

The research finding, published in May by the journal Science Advances, showed that the southern part of anchovies’ range in the Southern California Bight could become uninhabitable by 2100 as a result of reduced availability of dissolved oxygen. Global climate change is reducing oxygen availability by triggering ocean warming and by altering seawater chemistry.

During the anchovy study, researchers showed that there is a strong correlation between the “breathability” of the ocean water and the abundances of Northern Anchovy found in a particular area. The water’s “breathability” was calculated using a recently developed, anchovy-specific metabolic index that’s designed to measure the temperature-dependent availability of dissolved oxygen in relation to the species’ oxygen needs.

The anchovy work is part of an ongoing, four-year study to develop a similar, species-specific metabolic index for each of 13 commercially and ecologically important California Current species, then apply the indices to explore how their habitats will be squeezed by reduced oxygen availability.

The study is a collaboration of the University of Washington, University of California, Los Angeles and SCCWRP.

The study has validated the use of the metabolic index – which was originally developed in 2015 – to explain historic data on the population cycles of the Northern Anchovy.

In building the “breathability” index, researchers combined observations with ocean models to fill gaps in field data.

They showed that the suitability of aerobic habitat of ambient ocean waters changes over time and corresponds with when anchovy populations rise and fall, and when they move deeper or closer to shore.

Researchers are continuing to probe how much natural climate cycles vs. climate change are affecting population abundances of the Northern Anchovy. Their goal is to improve understanding of the role of global climate change in driving habitat compression vs. the role of local, land-based nutrient discharges and carbon emissions.