Timing and rate of seasonal zone formation in southern North Sea cod Gadus morhua otoliths was studied. Samples were taken from two time periods, representing low and high temperature regimes. Opaque zones were laid down between January and June, in contrast with the pattern described in other published studies. Translucent zone formation started earlier in the warmer period, corresponding to peak annual sea surface temperatures, and a period of slow body growth and low metabolic activity. Translucent zone formation, however, continued once temperatures decreased and growth rate increased. It is hypothesized that translucent zone formation is triggered at a threshold of metabolic stress, and that the combined energetic requirements of reproduction, growth and migration may maintain translucent zone formation even if feeding conditions improve. Higher temperatures had a significant negative effect on the rate of translucent zone deposition, but caused a slight increase in opaque zone formation rate. The findings of this study indicate that historical otolith collections could provide key inputs into future phenological studies to improve the understanding of climate change impacts and the dynamics of otolith structure.

Item Type:	Refereed Article
Keywords:	Atlantic cod, Gadus morhua, North Sea, otolith, phenology
Research Division:	Agricultural, Veterinary and Food Sciences
Research Group:	Fisheries sciences
Research Field:	Fisheries management
Objective Division:	Environmental Management
Objective Group:	Terrestrial systems and management
Objective Field:	Assessment and management of terrestrial ecosystems
UTAS Author:	Tidd, AN (Dr Alexander Tidd)
ID Code:	116256
Year Published:	2007
Web of Science® Times Cited:	36
Deposited By:	Fisheries and Aquaculture
Deposited On:	2017-05-04
Last Modified:	2017-12-01
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