Feeding conditions of Arcto-Norwegian cod larvae compared to the Rothschild-Osborn theory on small-scale turbulence and plankton contact rates. [HELP 29]

Feeding conditions of Arcto-Norwegian cod larvae compared to the Rothschild-Osborn theory on small-scale turbulence and plankton contact rates. [HELP 29]

1989

Data on first feeding Arcto-norwegim cod larvae in Lofoten, northernNorway, sampled during the period 1974 - 1984, are examined to verifythe theory on the influence of small-scale turbulence on the contactrate between predator and prey (Rothschild and Osborn, 1988). The numberof prey per cod larval gut are compared to the concentration ofprey, Galanus finmarchicus nauplii, and to data on wind speed andstatic stability of the upper layer. The data indicate that the contact rateincreases by a factor of 2,8, when the average wind speedincreases from 2 m s-1 to 6 m s - 1 . Independent data on cod larvalcruising speed, the velocity and concentration of prey organisms,inserted into the model of Rothsehild and Osborn (1988) show a comparableaverage increase in contact rate of 2,2 times for the sameincrease in wind speed. The data indicate that the turbulent velocityhas a greater contribution to contact rate than the Larval swimmingspeed, when wind speed exceeds 4 m s-1 . The larval period of Arctonorwegiancod is an important period for the formation of the yearclass. Larval stages are confined to the mixed layer, and thereforethe variable contact rate induced by wind mixing aust be an importantregulatory mechanism for the formation of year class strength.

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