Climate Variability & Marine Fisheries

Impacts of Warming On Estuarine Dependent Marine Species on the Atlantic and Gulf Coasts

On the Atlantic coast of the U.S., there are many ocean species including shrimp, menhaden, flounder, sea trout, croaker, and red drum, that depend on bays or estuaries for part of their life cycle. Menhaden, while not popular as a food fish, are processed into fish meal, fish oil and fish solubles, and constituted 76% of the US production of fish meal in 1980. Atlantic Menhaden spawn all along the US Atlantic coast in different months at different locations. After 2 months in the ocean the larvae are carried into the bays and estuaries by ocean currents, and from there they move into the rivers for several months before migrating back to the ocean. Most mature by age 2 or 3 and can live to age 10; only older adults are found farther north. Menhaden are susceptible to changes in ocean currents that would disrupt the transport of larvae into the bays. Warmer temperatures would change adult migration patterns and spawning locations. Warmer temperatures in estuaries would be associated with lower disolved oxygen levels for larvae. Changes in sea level associated with global warming could increase nursery habitat in southern areas but likely flood nursery habitats in northern areas where spawning occurs in protected bays rather than on the shelf. Changes in the climate are likely to reduce the geographic distribution and abundance of this species. Menhaden are an important food fish for many larger fish such as striped bass (Morone saxatilis), bluefish (Pomatomus saltatrix), and bluefin tuna (Thunnus thynnus) and their reduced availability as forage fish would likely affect the populations of fish that prey on them.

Sea Level Relationship On Shrimp Production Click on image to enlarge

A more specific example may be considered for shrimp. Global warming scenarios call for increases in sea level. In the northern Gulf of Mexico, high rates of coastal submergence and associated increases in realized sea level provide an indication of how sea level rise may impact coastal ecosystems. As coastal marshes submerge and begin to degrade and convert to open water habitats, temporary beneficial conditions are established for fishery species (such as penaeid shrimps) that are dependent upon coastal marshes. A conceptual model shows the projected relationships between sea level rise, marsh loss, and shrimp production. Marsh submergence in the model increases inundation times and eventually causes habitat fragmentation and loss. Increased inundation and fragmentation increases access to the remaining marsh surface and stimulates shrimp production. Continued wetland loss, however, will outweigh these benefits and results in future declines in shrimp production.

[For more information on the impacts of warming, go to: http://www.epa.gov/globalwarming/impacts/fisheries/index.html]

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