Using winter flounder growth rates to assess habitat quality in Rhode Island's coastal lagoons

Abstract

We used growth rates of juvenile winter flounder Pseudopleuronectes americanus, to assess habitat quality in 3 of Rhode Island's coastal salt ponds that had differing levels of nutrients and human development. In each pond, 1 m2 cages were placed in vegetated and unvegetated habitats and growth rates of individually marked fish were measured in three 10 to 15 d experiments from 4 June to 7 July 1997. Water temperature, salinity, dissolved oxygen, and benthic food were also measured. Stable isotopes of C and N were measured in experimental and wild fish. Growth rates were 0.06 to 0.76 mm d-1 and decreased through the experiments. Growth rates of wild fish (0.19 mm d-1 in Point Judith Pond and 0.21 in Ninigret Pond) were similar to the average of the 2nd and 3rd experiments (0.24 mm d-1). Growth rates were the same in vegetated and unvegetated sites. They were also the same in Point Judith and Ninigret ponds but lower in Green Hill Pond. An ANCOVA suggested that Green Hill's lower rates were caused by its higher temperatures, particularly during the 3rd experiment. Benthic food was similar in the different ponds, different habitat types, and in cores taken inside and outside cages. Categories of food consumed by fish were not affected by the presence of vegetation in a cage, although food consumed did differ from pond to pond. Amphipods were the preferred food in all ponds; fish consumed proportionately more amphipods and fewer polychaetes in Ninigret Pond than in the other ponds. Values of δ15N in the fish varied with the degree of development in the watershed but not with total nitrogen in the water column. The results of this study indicate that growth rates of fish can be used as indicators of habitat quality.