. The Canadian field-naturalist. / -A/ V\,.. A/- I STAGE 4 ,/\/. Figure 7. Seasonal mean daily abundance of Blueback Herring eggs in different stages of development and larvae in the drift. Mean daily water temperatures recorded at the sampling site are shown for the study period. both freshwater and marine nurseries. He reported that fish of 34-47 mm could tolerate 28 °/oo salinity. McKenzie (1964) observed that smelt larvae were carried back and forth with the tide and that during the day larvae were on the bottom and at night near the surface. The present study shows that younger stages suc
. The Canadian field-naturalist. / -A/ V\,.. A/- I STAGE 4 ,/\/. Figure 7. Seasonal mean daily abundance of Blueback Herring eggs in different stages of development and larvae in the drift. Mean daily water temperatures recorded at the sampling site are shown for the study period. both freshwater and marine nurseries. He reported that fish of 34-47 mm could tolerate 28 °/oo salinity. McKenzie (1964) observed that smelt larvae were carried back and forth with the tide and that during the day larvae were on the bottom and at night near the surface. The present study shows that younger stages such as eggs and protolarvae can tolerate salinities as high as 22 *^/oo and that estuaries of Prince Edward Island are important nursery areas for these stages. Further investigations are needed to determine more precisely the salinity tolerance and mortality level of eggs at different stages of development and of newly hatched larvae in saline conditions. Euryhaline tolerance of egg and larvae of smelt and Blueback Herring permits these species to utilize both freshwater and the saline environment of Prince Edward Island estuaries for early development. Successful growth and development in both environments may provide better survival, growth of the young and larger populations. Alterations in the circulation of estuaries due to causeway construction or the addition of pollutants can markedly alter the success of these early stages and affect the fishery. This was observed in the West River in late August 1984 when a combination of high water temperatures, excessive eutrophication, and poor circulation in the estuary caused the water in the nursery area to become depleted of oxygen and a large mortality of juveniles occurred. The effect of such a kill on the total population of smelt and Blueback Herring has not been documented, but future causeway construction should consider the impoundment effect on such important nursery areas. Acknowledgments We wish to thank Ms. Joy Mores
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