Variable swimming speeds in individual Atlantic cod (Gadus morhua L.) determined by high-resolution acoustic tracking

Abstract

Although several studies have determined swimming speeds for Atlantic cod (Gadus morhua L.) using acoustic telemetry, none have reported high-resolution tracking (high sampling frequency) for individual fish in order to obtain more accurate estimates of swimming speeds and to quantify within- and between-individual variation. In this study, in situ swimming speed of acoustically tagged Atlantic cod were recorded with high resolution (position fixing every 17 s) throughout the diel cycle during summer in a fjord in northern Norway using a stationary positioning system. The frequency distributions of swimming speeds are presented for individual cod (~30–60 cm). The high-resolution tracking technique revealed higher swimming speeds than previously reported for cod. Swimming speeds below 1.0 body lengths (bl) s⁻¹ were most common (>70%), with only 4–7% of the recordings above the sustained swimming speed for this species. The observation that cod employed a blend of swimming speeds could reflect that searching for and capturing different prey types require a mix of swimming speeds.

Keywords:

• Gadus morhua
• high-resolution tracking
• swimming speed
• telemetry

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

We wish to thank Bente Ulvestad for assisting with the data analysis as well as the skipper of the research vessel F/V Fangst. This work was supported by the Norwegian Research Council. Financial support for P.D.W. was provided by the Bergen Exchange Fellowship and the Natural Sciences and Engineering Research Council of Canada.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark