The Importance of Scale to Predator‐Prey Spatial Correlations: An Example of Atlantic Fishes

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Abstract
The signs and strengths of spatial correlations between densities of predators and their prey were scale dependent both in simulations and when calculated from acoustic transects across nearshore distributions of Atlantic cod (Gadus morhua), and its prey, capelin (Mallotus villosus). Spectral analyses of 1985 and 1986 transects indicated that spatial correlation (coherence) varied relative to: (1) the occupation of thermal refuge areas by capelin (sea temperatures <—0.5° or >8.5°C), (2) the aggregation dimensions of each species, and (3) the activity level of the predator. When capelin did not occupy thermal refuges, cod and capelin densities were coherent across a wide range of scales (2—30 km). At large scales (>4—10 km) densities were in phase (positively correlated), but at scales less than aggregation dimensions (3.5 km), densities were out of phase (negatively correlated). At the smallest scales measured (2—3 km), densities exhibited maximum negative correlation in both years. When capelin were aggregated within thermal refuges, predator—prey densities were coherent (in phase) only at scales larger than those of the refuges. When actually feeding, cod achieved coherent, in—phase distributions with capelin at scales as small as 3.5 m.

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