Spatial pattern and patchiness during ontogeny: post-settled Gadus morhua from coastal Newfoundland

Abstract

We tested the hypothesis that patchiness increases after settlement to the bottom in a marine broadcast spawner, the Atlantic cod Gadus morhua . Patchiness P=1+1/k was estimated from the dispersion parameter k of the negative binomial distribution. Estimates were based on length frequency distributions of fish from 18–330 mm that were seined from shallow nursery areas (<10 m depth) during autumn. Patchiness was highest for small cod (<24 mm) in the process of settling to benthic or epibenthic habitats. Settling cod were only collected from coastal sites located in deep fjords where adults overwinter and spawn. Patchiness was lowest for fish newly settled to benthic habitats (c. 50 mm SL) and increased thereafter with length to 200 mm SL. Our analyses suggest that patchiness in G. morhua > 200 mm depends on a shifting balance between establishment of home ranges (tending to reduce patchiness) and schooling behaviour (tending to increase patchiness). Patchiness generally increased for G. morhua between 25–200 mm SL when examined at different spatial (major bays along the northeast coast of Newfoundland) and temporal (years) scales suggesting processes responsible for these patterns may be consistent among the bays and years examined. Our results show that more is learned about the distribution of fish by examining the zeroth, first, and second moments (presence/absence, mean abundance and patchiness) than by examining only one measure. We hypothesize that patchiness continues to increase for larger juvenile and adult G. morhua that were not examined in this study. We propose that patchiness may then decrease for the very largest cod, “mother fish” that may not undergo extensive annual spawning migrations.

Author notes

Present address: Department of Biology, University of New Brunswick, PO Box 5050, Saint John, New Brunswick, Canada E2L 4L5; e-mail: