Estuarine Fish

NBEP — Thu, 30 Oct 2008 20:11:47 +0000

Like people who own summer houses on the shore, many of our fish and wildlife species are seasonal residents, traveling long distances to spend part of their lifecycle here. Some species have increased in recent years. Anecdotally, 2007 and 2008 saw more large menhaden in the Bay than any year in recent memory-and, as would be expected, abundant bluefish and striped bass were right behind them. Other important species such as river herring and winter flounder have declined precipitously. The causes of these kinds of fluctuations are only partially understood, but it is clear that large-scale ecosystem changes are driving at least some of the changes in Narragansett Bay’s estuarine fish communities.

Several recent studies by URI researchers have documented long-term changes in the Bay’s fish communities (Collie et al. 2008; Oviatt 2003). The studies found that once-dominant demersal (bottom-dwelling) species such as winter flounder and tautog have declined, while decapod crustaceans such as crabs and lobsters have increased. Concurrently, pelagic or mid-water fish species such as scup and striped bass have increased. Importantly, many of the demersal fish are resident species which spawn in Narragansett Bay, whereas the pelagic fish species tend toward southern migrants, which visit the Bay only in summer. Collie et al. also determined that the average size of fish has decreased over time.

The authors of both these studies suggest that the two main factors affecting Narragansett Bay’s fish communities are global warming and fishing pressure. In an earlier study, Taylor and Collie (2003) demonstrated that warmer temperatures can harm the reproduction of winter flounder by increasing predation by sand shrimp on juvenile flounder. The Collie et al. study also notes that warming-related changes in plankton dynamics may favor pelagic over benthic species. The study implies that, regardless of management measures such as fishing regulations, the Bay’s historic fish communities are unlikely to return; rather, the authors conclude that the Bay ecosystem is likely to continue its “shift toward a more warm-water or pelagic [fish] community resembling those of more southern estuaries such as Delaware Bay and Chesapeake Bay.”

[insert graphic here-demersal vs. pelagic spp.]

Pollution can also have negative impacts on fish species-residents as well as migrants-by affecting fish directly, harming their reproductive ability, and degrading the habitat upon which they depend. The “Estuarine Waters” section of this report describes how nutrient pollution causes low-oxygen conditions in Narragansett Bay which, in turn, kill fish and shellfish. Nitrogen pollution has also destroyed and degraded valuable fisheries habitat such as eelgrass, primarily in upper Narragansett Bay, in smaller coves along the edges of the Bay, and in salt ponds in the Bay and along the South Shore (see, e.g., Short 1996).

Historically, these areas were important spawning grounds for species such as winter flounder. The Brayton Point Power Station in Somerset, Mass. has contributed to the collapse of the winter flounder population in Mt. Hope Bay through direct (impingement and entrainment) and indirect (thermal pollution) impacts (Gibson 2002). Some of these impacts may be mitigated by the construction of new cooling towers slated to go on line in 2012 at a cost of $500 million. The 500-foot-tall towers are mandated by an agreement reached in December, 2007, between the operator of the plant and the U.S. Environmental Protection Agency (Welker 2008).

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