BAILEY ET AL.; ZOOPLANKTON ABUNDANCE AND FEEDING HABITS OF FRY 



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INDtX MAP 



Figure 1. -Traitors Cove estuary, Revillagigedo Island, Alaska, 1963-65 (from McLain 1968), showing locations of plankton sampling 



stations. 



for fry in relation to water temperature? How 

 many fry can the estuary support based on es- 

 timates of abundance of food organisms and 

 grazing rates? 



Traitors Cove is about 50 km nortli of Ketchikan, 

 Alaska. Several tributaries used by pink and chum 

 salmon enter Traitors Cove, the major one being 

 Traitors River, which has about 55,000 m^ of 

 spawning grounds. The dominant feature of the 

 estuary is a narrow constriction with a sill, 1 or 2 m 

 below mean low water, which divides the estuary 

 into two basins. The inner bay is about 5.9 km long 

 and 0.7 km wide and has a maximum depth of 46 m. 

 The outer bay is about 6.5 km long and 1.3 km wide 

 and has a maximum depth of 130 m. The tidal 

 range of about 7 m and the constricted flow at 

 the sill create exceptionally strong currents and a 

 reversing tidal falls throughout the year. The tur- 

 bulence and surface currents affect distribution 

 and movement of fry for at least 0.5 km on both 

 sides of the constriction. We measured surface 

 temperatures of 5° to 13 °C in the estuary when fry 

 were present. Some aspects of the oceanography 



of Traitors Cove have been described by McLain 

 (1968). 



Pink and chum salmon fry from the tributary 

 streams enter the estuary from mid-April to late 

 June. Schools with thousands of fry are typically 

 present until late June. 



METHODS 



To determine if juvenile salmon feed while still 

 in Traitors River, we compared the contents of the 

 entire digestive tracts of individuals excavated 

 from redds with those trapped in nets while 

 migrating downstream at night. All specimens 

 were preserved whole in 10% Formalin solution.- 

 The contents of the digestive tract were later 

 removed in the laboratory and examined under a 

 stereoscopic microscope. To determine the kinds 

 and numbers of food organisms eaten in the es- 

 tuary, we compared stomach contents of fry 

 samples collected in the estuary in 1964, 1965, and 



-Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA." 



847 



