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USING A FISH INDEX TO ASSESS HABITAT QUALITY IN NARRAGANSETT BAY, RI: THE IMPORTANCE OF THE UPPER ESTUARY
Citation:
Meng, L, C. Orphanides, AND J. C. Powell. USING A FISH INDEX TO ASSESS HABITAT QUALITY IN NARRAGANSETT BAY, RI: THE IMPORTANCE OF THE UPPER ESTUARY. Presented at Estuarine Research Federation 16th Biennial Conference, Tampa, FL, November 4-8, 2001.
Description:
We developed an estuarine index of biotic integrity to assess habitat quality in Narragansett Bay, Rhode Island. Fish were collected with a 61 X 3.05 m beach seine monthly in July and August from 1988-1999 at 18 fixed stations. Stations were designated high or low quality depending on total nitrogen concentrations, low dissolved oxygen events, human disturbance, abundance of macroalgae, and presence of submerged aquatic vegetation. We used step-wise discriminant analysis on 13 candidate metrics to assess which ones were most important in distinguishing between high and low habitat categories. We then used discriminant analysis and canonical discriminant analysis with the resulting significant metrics. The six metrics that were able to discriminate between sites were number of estuarine spawner species, proportion of killifish, number of individuals, proportion of flounder, Shannon's diversity index, and proportion of benthic-associated species. The metrics distinguished between sites with an overall error rate of 22%. Surprisingly, when an index was calculated from the metrics, sites designated as low quality had the highest scores, whereas high quality sites had low scores. Degraded sites in the upper estuary may have scored higher due to availability of shallow-water refuge from predation, abundant food, and warmer water with less current.