Publication Abstract

Phenology and North Sea cod (Gadus morhua) otoliths: has climate change affected annulus formation?

G.M. Pilling, R.S. Millner, M.W. Easey, D. Maxwell and A. Tidd

The timing and rate of southern North Sea cod (Gadus morhua) otolith marginal increment deposition from two time periods representing low and high temperatures was studied. Opaque zones formed during the period January to June, in contrast with published studies. Translucent zone formation started once temperatures had increased to similar levels in the two time periods, onset being earlier in the warmer time period This corresponded with the highest monthly temperatures in the southern North Sea, and was also a period of decreased growth rate and low metabolic activity. However, translucent zone formation continued once temperatures had decreased and growth increased. If formation of this zone were linked to a threshold for metabolic stress, the combined requirements of reproduction, growth and migration may maintain translucent zone formation despite improving conditions. General linear models indicated that higher temperatures had a significant negative effect on the rate of translucent zone formation. Opaque zone formation was slightly faster at higher temperatures, although this may have been the result of year effects. Changes due to temperature and environment have potential impacts on the accuracy and precision of age determination under future climate scenarios. Historical otolith collections could provide key inputs into future phenological studies to further improve our understanding of both climate change and otolith structure dynamics.

Reference:

G.M. Pilling, R.S. Millner, M.W. Easey, D. Maxwell and A. Tidd (2007) Phenology and North Sea cod (Gadus morhua): has climate change affected otolith annulus formation and growth? Journal of Fish Biology, 70(2): 584-599