Microhabitat Use and Vertical Habitat Partitioning of Juvenile Atlantic (Gadus morhua) and Greenland (Gadus ogac) Cod in Coastal Newfoundland

D Craig Knickle,George A Rose

doi:10.2174/1874401x20140416001

Abstract

Twenty co-occurring juvenile gadids (10 Gadus ogac and 10 Gadus morhua) were surgically implanted with ultrasonic transmitters with depth sensors and continuously monitored for up to 23 days in the summers of 2009 and 2010 to test fine-scale habitat use and vertical distribution overlap in coastal Newfoundland (>18700 positional fixes). A habitat map with 8 substrate and 3 slope classes (low (<5°), moderate (5-10°), and high (>10°)) was generated from acoustic data and coincident video data using seabed mapping software (QTC). Fish locations were integrated with a habitat map to assess and quantify habitat preference. Both species avoided fine gravel/sand substrates with little vegetation and selected for large particle (cobble and boulder) substrates with moderate or dense vegetation, and spent the majority of time in < 10 m of water. Nevertheless, species differences in habitat use were evident. G. ogac typically remained in close proximity to the seafloor whereas G. morhua was often distributed more pelagically and showed greater variation in vertical distribution. Habitat use and vertical distribution patterns were consistent across the diel period. Our results suggest that despite high overlap in habitat use, G. morhua and G. ogac often segregate vertically in the water column, which may reduce competitive interference. We suggest that these patterns are related to differences in diet.

Highlights

Divergent habitat selection is a common attribute of closely related species that may reduce competition and promote coexistence [1,2,3,4]
Mean (± SE) fish length did not differ between years (ANOVAs, p > 0.05), telemetry data for both years were pooled by species
Results from the present study suggest that juvenile G. ogac and G. morhua in coastal Newfoundland occupied the same habitats and were distributed at similar depths of < 10 m

Summary

Introduction

Divergent habitat selection is a common attribute of closely related species that may reduce competition and promote coexistence [1,2,3,4]. Atlantic cod (Gadus morhua) and Greenland cod (Gadus ogac) are two congeneric species of gadids that co-occur as juveniles in coastal areas of Newfoundland and Labrador and more northern areas to Greenland [5, 6]. It has been suggested that competition for resources between the two species is likely [7], few studies on their interactions exist. Recent studies suggest that sympatry of these species is facilitated primarily through partitioning of food resources, with G. morhua pursuing more pelagic prey [8] and to a lesser extent by differences in activity patterns [9]. Microhabitat partitioning could be an enabler of sympatry but has not been studied in these species. Competition for habitat can negatively impact fitness components such as growth and survival by forcing individuals to use habitats that offer less protection from predators or poorer foraging opportunities [10]

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