MEPS 131:11-16 (1996)  -  doi:10.3354/meps131011

Effects of turbidity, light level and prey concentration on feeding of juvenile weakfish Cynoscion regalis

Grecay PA, Targett TE

Highly turbid and dimly lit mid-Atlantic estuaries, such as Delaware Bay (USA), are important nursery areas of juvenile weakfish Cynoscion regalis where mysid shrimp Neomysis americana dominate their diet. Laboratory experiments were conducted to determine the effect of light, turbidity, and prey concentration on feeding by juvenile weakfish on mysid shrimp. Juveniles were fed 48 mysids daily at turbidities ranging from 0.95 to 11 nephelometric turbidity units (NTU) and light levels ranging from dark to 0.70 x 1014 quanta s-1 cm-2. At all turbidities, they consumed virtually all prey in light as low as 0.01 x 1014 quanta s-1 cm-2. However, complete darkness (<0.01 x 1014 quanta s-1 cm-2) reduced feeding regardless of turbidity. Darkness reduced foraging efficiency to a similar degree among prey concentrations ranging from 0.5 to 4 times typical field densities, suggesting that feeding in the dark depends on prey concentration and is likely to depend on a less efficient, non-visual encounter rate. Therefore, under dark conditions adequate feeding may occur only when prey concentration is sufficiently high or when adequately dense patches of prey are encountered with sufficient frequency. Juvenile weakfish appear well-adapted for feeding under the highly turbid and frequently dark conditions of their estuarine nursery areas. Patterns of turbidity/light levels in conjunction with patterns of prey density are likely to control mysid availability to juvenile weakfish and influence patterns of feeding, growth, and survival.

Turbidity . Light . Fish . Feeding efficiency . Estuaries

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