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



Table 4.-Zooplankters and other organisms from stomachs of 124 chum salmon fry (length, 32 to 51 mm) collected in daylight and 20 

 (length, 35 to 43 mm) collected at night in Traitors Cove, 1964-66, and percentage relative importance by volume. 



indicates less than 0.5% 



Feeding Behavior in Relation to Water 

 Currents 



Our visual observations of individual chum and 

 pink salmon fry in shore-oriented schools indicat- 

 ed that their feeding varied with the speed of the 

 water currents. At velocities of to 10.7 cm/s, a fry 

 would typically swim a darting course as much as 

 three times its body length to capture a food item. 

 At higher velocities, 10.8 to 19.8 cm/s, schools of 

 fry sometimes held position relative to the shore or 

 bottom while facing the current, and an individual 

 would typically deviate up, down, or to the sides no 

 more than one-third of its body length to capture 

 oncoming food. At still higher velocities, 19.9 to 

 24.4 cm/s, fry in schools often held a constant 

 position relative to shore or bottom but did not 

 feed. Fry that appeared to be in visual contact 

 with the shore or bottom avoided currents above 

 24.4 cm/s unless frightened. 



Effect of Daylight on Feeding 



The cessation of feeding at night by pink salm- 

 on fry was confirmed by the two feeding 

 experiments we conducted in the aquarium. In the 

 first experiment, feeding rate was directly related 



to light intensity. During a 78-min period when 

 light intensity ranged from 65 to 170 footcandles 

 (three tests), the average consumption was 2.2 to 

 3.1 zooplankters per minute per fry (Figure 2). At 

 light intensities of 2 footcandles or less, the 

 average feeding rate was only 0.5 zooplankter per 

 minute per fry (three tests). In the second 

 experiment, performed entirely in darkness, little 

 feeding took place. One fry had eaten 48 plankters 

 (less than 0.2 plankter per minute), and the 

 remaining 13 had eaten 13 plankters (0 to 0.001 

 plankter per minute). These observations agree 

 with laboratory experiments of Hoar (1942) in 

 which young salmon fed little during darkness. 



Z Q 



!i; o 

 5 u o.s 



016 0.032 06S HO 260 O.SOO 



16 11 65 130 260 



FOOT CANDLES 



Figure 2. -Effect of darkness on feeding rate of pink salmon fry 

 confined in an aquarium. Each dot represents a single test of 

 feeding rate. 



851 



