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

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.