Residency and depth movements of a coastal group of Atlantic cod (Gadus morhua L.) |
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Authors: | Francis C Neat Peter J Wright Alain F Zuur Iain M Gibb Fiona M Gibb David Tulett David A Righton Robert J Turner |
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Institution: | (1) Marine Laboratory, Fisheries Research Services, 375 Victoria Road, 101, AB11 9DB Aberdeen, UK;(2) Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, NR33 0HT Lowestoft, UK |
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Abstract: | Atlantic cod stocks are subdivided into geographically and biologically discrete populations; some being locally resident,
others migratory. The reasons for the variation in migration pattern and the consequences it may have for population structuring
is poorly understood. We studied a group of cod from the coastal waters of the Shetland Isles in the northern North Sea. During
the spawning season, electronic tags that record depth and temperature over time were implanted into 133 individuals and the
fish released within a few kilometres of where they were captured. Thirty-nine cod have been recaptured up to 608 days later,
throughout the year and, in all but two cases, within 15 km of their release site. Geolocation methods based on temperature
and bathymetry also suggested that the cod had a limited home range, remaining resident year-round in coastal waters. The
cod were deeper during the winter and moved to shallower water in late spring and summer. They showed diel, fortnightly and
monthly cycles in depth movement that varied much within and between individuals over the season. Residency and the individual
variability in vertical movement may reflect a combination of locally complex depth strata, variable seabed substrate and
the wide range of seasonally available prey resources. |
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