Return to Estuary

This estuary along San Gregorio Creek provides critical habitat for salmonids as they enter the ocean then return to freshwater streams.

Estuaries play a vital role in the life cycle of salmonids by providing a location for outmigrating smolts and returning adults to adjust to the differences in salinity between freshwater streams and the ocean. Returning salmonids navigate to their home estuary by using receptors that detect changes in the earth’s magnetic field, navigating by the stars, and using ocean currents (Atlantic Salmon Trust 2004). Once the fish are closer, they rely on smelling familiar substances, like pheromones, in the water. When the returning adults arrive, the brackish waters of estuaries provide conditions in which they can undergo the physiological changes necessary to survive in fresh water.

Once in an estuary, salmonids must physiologically adjust to less salt in the water. To maintain water balance when in the ocean, salmonids take in a lot of water and excrete salt through their gills and in urine, but in fresh water, they minimize drinking, take salt in through the gills, and produce large amounts of dilute urine (Uy 2004). In an estuary, salt concentrations change along a gradient from the ocean to the stream mouth, allowing salmonids to gradually adjust. Increased pollutant concentrations, temperature, and salinity can interfere with physiological adjustments once salmonids reach an estuary (Stark 2000).

References

Atlantic Salmon Trust. 2004. Atlantic Salmon Facts - Salmon Biology [Web page] [cited 2004]. View on-line source .

Stark, M. 2000. Salmon cycle: The estuary plays a crucial role for the Northwest's trademark fish. The Daily Astorian. View on-line source .

Uy, A. 2004. "Biology 170, Animal Diversity: Morphological Adaptations of Vertebrates." San Francisco State University. Class Lecture. View on-line document .

General Reference

Oregon Coast Aquarium. 2003. Anadromous Fishes: Pacific Salmon [Web page] [cited 2004]. View on-line source .

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