Estuarine Fish

Narragansett Bay is home to hundreds of species of estuarine fish and shellfish. Many of these species are migrants which spend only a portion of their lifecycle in the Bay. Others are residents, which may spawn in the Bay and spend a significant portion of their lifecycle here. The Bay’s fisheries have been an important cultural institution for centuries. In both Rhode Island and Massachusetts, recreational and commercial fisheries generate hundreds of millions of dollars annually. Narragansett Bay’s fish and shellfish are also the subject of some of the longest-running and most detailed environmental datasets related to Bay ecology, and therefore provide a window into long-term biological trends on Narragansett Bay.

Over the past 50 years, demersal, or bottom-dwelling fish, have declined in Narragansett Bay. Over the same time period, benthic invertebrates such as crabs and lobsters, as well as pelagic (mid-water) fish and squid have increased. Warming trends appear to be a primary cause of these changes; the Bay’s average sea-surface temperature at Fox Island has increased by about two degrees Celsius since 1959. A second, but important cause appears to be fishing pressure. As with any complex resource, there are undoubtedly many factors affecting Narragansett Bay’s fish populations, and different factors affecting different species.

Toxins in FishTissue

Heavy metals and other toxic compounds were formerly a major source of pollution to Narragansett Bay, as with other urbanized estuaries. Due to modern discharge regulations, improved wastewater pretreatment, and the decline of Northeastern manufacturing, these inputs have greatly decreased, but toxic substances can still be found in the muddy sediments of the rivers and upper Bay. Storm water and road runoff are now possibly the greatest sources of most toxics as well as bacteria to Narragansett Bay.

Substances of particular concern are toxic metals such as mercury and lead, and organic compounds such as DDT and Polychlorinated biphynyls (PCBs). The U.S. Environmental Protection Agency, through its National Coastal Assessment Program, analyzed fish tissue samples taken from Narragansett Bay and other northeastern estuaries for the presence of a variety of toxic substances, including hydrocarbons, PCBs, DDT and other pesticides, and 13 metals, including mercury and lead. Detailed information is available on EPA's Coastal Data Search Engine. Results were compared with “screening values” (SV) as an approximation of ecological risk. Most of the fish sampled are seasonal migrants, so some of the toxic compounds may come from sources outside of Narragansett Bay.

Results for Rhode Island found two chemicals in a number of fish samples violating the screening range levels: mercury (Hg) and PCBs. For total PCBs, the incidence of exceedance was more common. Both fell within a range comparable to other industrialized eastern coastal states from southern Maine to Virginia.

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