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NOAA Technical Memorandum NMFS-AFSC-73

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Suitability of Dry Bay, southeastern Alaska, as rearing habitat for juvenile salmon

Abstract

Dry Bay is located at the terminus of the Alsek River, a large glacial river originating in Canada and flowing to the Gulf of Alaska. The Alsek River was historically a major producer of chinook salmon (Oncorhynchus tshawytscha) in southeastern Alaska, but the stock is currently depressed even after decades of rebuilding efforts. We studied physical characteristics and juvenile salmon utilization of Dry Bay to determine whether rearing conditions in Dry Bay may limit production.

Dry Bay provided poor rearing habitat for juvenile salmon. The water was mostly cold (<5°C) and turbid throughout summer. Little salt water intruded into Dry Bay from the Gulf of Alaska; at high tide it is a shallow, 80-km2 freshwater lagoon, and at low tide the impounded water flows out at 80-180 cm/s. Strong currents and sand substrate result in habitat instability and absence of large organic debris. The few juvenile salmon captured were in low-current refuges near the mouth. Neither zooplankton nor benthic prey were abundant in Dry Bay. The diets of juvenile chinook, coho (O. kisutch), and sockeye salmon (O. nerka) were similar, presumably because all three species occupied the same low-current refuges.

Dry Bay has undergone substantial geomorphological changes since the early 1900s due to heavy glacial silt deposition and the rising of the land mass following glacial recession. These changes may have reduced suitable rearing habitat and increased predator pressure on juvenile salmon.


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