AB 17:211-221 (2012)  -  DOI: https://doi.org/10.3354/ab00469

Environmental regulation of individual depth on a cod spawning ground

Justin J. Meager1,*, Jon Egil Skjæraasen1,2, Ørjan Karlsen2, Svein Løkkeborg2, Ian Mayer3, Kathrine Michalsen2, Trygve Nilsen4, Anders Fernö1,2

1Department of Biology, and 4Department of Mathematics, University of Bergen, 5020 Bergen, Norway
2Institute of Marine Research, 5817 Bergen, Norway
3Norwegian School of Veterinary Science, PO Box 8146, 0033 Oslo, Norway

ABSTRACT: Fine-scale characteristics of spawning grounds may provide the opportunity for cod Gadus morhua L. to regulate their external environment by adjusting their depth. Ultrasonic telemetry was used to study how the environment influenced the depth-related behaviour of individual wild and farmed cod on a spawning ground. Of the environmental predictors examined, temperature explained most variation in depth (best predictor in 16 of 21 fish). A decrease in surface-water temperature was accompanied by a pronounced reduction in daily maximum depth of nearly half the fish examined and movement to a shallower area of the spawning ground. Wind and light (after controlling for diel periodicity) had a comparably limited and variable influence on fish depth. Some of the vertical movements seemed to be associated with feeding rather than spawning activity; wild females with diel vertical migrations (DVMs) had poorer condition than wild females with no DVMs, and DVMs were absent in farmed females in better condition. Generally, there were no clear differences in responses to the environment between wild and farmed cod. The ability of cod to regulate their external environment by changing their depth was likely to have been limited by the location of the spawning shoal at the seafloor.


KEY WORDS: Broadcast spawners · Individual depth · Climate change · Mating systems


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Cite this article as: Meager JJ, Skjæraasen JE, Karlsen Ø, Løkkeborg S and others (2012) Environmental regulation of individual depth on a cod spawning ground. Aquat Biol 17:211-221. https://doi.org/10.3354/ab00469

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