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Saptial and Temporal in Stable Carbon and Oxygen Isotope Ratios of Juvenile Winter Flounder Otoliths From Selected Nursery Areas
Citation:
PRUELL, R. J., B. K. TAPLIN, AND J. D. Karr. Saptial and Temporal in Stable Carbon and Oxygen Isotope Ratios of Juvenile Winter Flounder Otoliths From Selected Nursery Areas. Presented at 4th International Symposium on Fish Otolith Research, Monterey, CA, August 23 - 28, 2009.
Impact/Purpose:
The purpose of this research is to develop tools that can be used to identify the important nursery areas for winter flounder in Southern New England. Stable isotope ratios in fish otoliths were used for this technique.
Description:
Winter flounder (Pseudopleuronectes americanus) populations have supported large commercial and recreational fisheries along the coast of New England. In recent years, however, the population of this important species has declined precipitously in some areas, especially Narragansett Bay. Winter flounder spawn in late winter in nearshore areas and juvenile fish reside in shallow-water habitats along the coastline during their first summer. Once young-of–the-year flounder undergo metamorphosis and settle they remain in close proximity to that site until fall. Adult fish move offshore during the late winter and spring then return to their natal estuaries during the fall and winter to spawn. The present study was designed to determine if stable carbon (13C) and oxygen (18O) isotope ratios in otoliths could be used to differentiate the locations and habitat types that serve as important nursery areas for winter flounder along the Rhode Island, USA coastline. Locations included the upper, mid and lower bay portions of Narragansett Bay, three coastal salt ponds and Narrow River, an estuarine river system. Juvenile winter flounder (45 – 65 mm) were collected yearly over a three-year period from 18 nursery locations along the coast. Sampling locations were selected to include a wide range of physical characteristics (salinity, temperature) and important habitat types (unvegetated, macroalgae and eelgrass). Sagittal otoliths from the flounder were analysed for13C and 18O using continuous flow isotope ratio mass spectrometry. Results from these analyses show significant differences in 13C and 18O among location types. Mean 18O values in the juvenile flounder otoliths ranged from -4.8 ± 0.4 to -0.8 ± 0.1 ‰ and mean 13C ranged from -3.9 ± 0.7 to -0.4 ± 0.3 ‰ among nursery areas. Isotope ratio trends were observed along salinity gradients in Narragansett Bay and Narrow River and significant positive correlations (2002: r = 0.93; 2003: r = 0.80; 2004: r = 0.97) were found between 18O and salinity. Results from the first two years were strongly correlated but the third year data were somewhat different. This indicates that it is important to obtain results for each yearly cohort in order to investigate recruitment to the offshore fishery from various nursery areas.