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- Title
The importance of small-scale turbulence in the feeding of herring larvae.
- Authors
Muelbert, José H.; Lewis, Marlon R.; Kelley, Dan E.
- Abstract
Herring larvae form a large, persistent and well-defined aggregate off southwest Nova Scotia coincident with a region of strong tidally generated turbulence. Our objective is to test the hypothesis that turbulent, tidally well-mixed regions constitute a preferential feeding environment for herring larvae, and are thus the proximate cause for the retention of larvae in these areas. Dimensional analysis, coupled with relevant biological parameters and field data, are used to derive two non-dimensional numbers from existing predator-prey encounter models, and to propose a third number which incorporates the minimum encounter rate required for larval maintenance. The results of this analysis show that when root-mean-square turbulent velocities are of the same order of magnitude as the prey velocities, they start to influence encounter rates significantly; and that when turbulent velocities are an order of magnitude greater than the predator velocities, they dominate the encounter process. At reported natural food concentrations, food items are on average one order of magnitude away from the larvae's reach. The importance of turbulence as a mechanism to bring fish larvae closer to their prey is revealed by the finding that in tidally well-mixed regions herring larvae would require one order of magnitude less food than their counterparts in the stratified regions. The model shows that the feeding environment on the adjacent stratified waters off southwest Nova Scotia is detrimental for herring larvae, and that high mortality would be expected if larvae had to overwinter in this region. Our analysis also shows that the growth pattern observed for autumn-spawned larvae is explained by the combination of the relevant physical and biological scales. The overall results of this analysis lend support to the hypothesis that turbulent, tidally well-mixed areas provide ideal feeding conditions for herring and may be the proximate cause for an retention.
- Publication
Journal of Plankton Research, 1994, Vol 16, Issue 8, p927
- ISSN
0142-7873
- Publication type
Article