Scale-dependent variations in the precision of larval fish abundance estimates: a study of Sebastes sp. on Flemish Cap

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Abstract
We test the assumptions of synopticity over a 6-d sampling period and homogeneity within a 40 times 40 km stratum by investigating the effect of sampling scale, or station spacing, on the precision (i.e., variance) of abundance estimates of larval redfish (Sebastes sp.). We contrast the results obtained for larval redfish with observations of scale-dependent variability in temperature, salinity, chlorophyll, and zooplankton, which have been shown to be interrelated in other systems. In contrast with previous studies, our results show that the patterns of variance in temperature, salinity, chlorophyll, and zooplankton are not scale dependent. Although the assumption of synopticity cannot be rejected, our results show that the variance in abundance of larval redfish is scale dependent and that it is much greater than the variances of the other variables considered. The contrasting pattern may be due to differences in the relative importance of physical and biological processes during the very early life history of marine fish. We suggest that sampling programs must be preceded by pilot studies designed to determine the effort required to obtain the most precise estimates of abundance given the limitations caused by the underlying sampling variability and the influence of physical processes.

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