| Summary: | Diversity within populations not recognized or represented in management may lead to reductions in productivity and population collapse. Physically distinct ecotypes of Atlantic cod Gadus morhua coexist in close proximity, but their importance to population structure remains unclear. A first step to assessing that importance is identifying how these ecotypes use available habitat and how limited they are to particular habitat types. Since tracking fish movements over prolonged periods of time is impossible through direct observation, we employed remote acoustic telemetry to identify fish location at fine temporal scales over a period of 5 months at nearshore (<5km from shore) and offshore (100km from shore) shallow rocky habitats. Cod caught within each telemetry array were classified as red or olive ecotypes based on color (red-to-green ratio) and shape (box-truss analysis), implanted with acoustic transmitters, then returned to the water and tracked remotely. We predicted that red cod would be resident within shallow, rocky habitat, while olive cod would be less discriminating in their habitat choices and far more mobile. We employed a combination of statistical approaches to identify differences in ecotype behaviors including: residency in shallow rocky habitats via time spent within arrays (Poisson regression) and probability of presence in arrays over time (binomial regression); and spatial behaviors within shallow habitats via depth preferences within the offshore array (AR(1) mixed effects model). Red cod were more mobile than expected, but mostly restricted to shallow habitats <40m in depth. This depth limitation persisted despite active spawning occurring in adjacent deeper habitats.
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