Hp. Schwarcz et al., STABLE CARBON-ISOTOPE VARIATIONS IN OTOLITHS OF ATLANTIC COD (GADUS-MORHUA), Canadian journal of fisheries and aquatic sciences, 55(8), 1998, pp. 1798-1806
Stable carbon isotope ratios (delta(13)C) were measured in annual laye
rs of otoliths of Atlantic cod (Gadus morhua)from the northeastern Sco
tian Shelf, Atlantic Canada. Layers deposited during the first 4-6 yea
rs of otolith growth increased in delta(13)C from minimum values betwe
en -5 parts per thousand and -2.5 parts per thousand to a maximum near
0 parts per thousand. This pattern of increase was independent of the
years in which the fish was collected. Layers formed after reaching t
he maximum delta(13)C value displayed decreasing or nearly constant is
otopic ratios. Early rise in delta(13)C may be a combined result of (i
) decrease in the fraction of metabolic oxidized carbon in the fishes'
blood as they mature, relative to the proportion of seawater-derived
carbon, and (ii) dietary shift to higher trophic-level foods with high
er delta(13)C values. Age of maximum in delta(13)C may be indicative o
f age of maturity of cod. The maximum delta(13)C value attained by oto
liths decreased steadily between 1983 and 1993, while cod stocks in At
lantic Canada were declining. Drop in age of attainment of maximum del
ta(13)C between 1984 and 1985 coincides with changes in population dyn
amics of the 4Vs stock. This decrease. as well as the post maximum dec
rease in delta(13)C values of the mature cod otoliths may represent mo
vement of the fish to deeper waters of the shelf, where delta(13)C of
dissolved inorganic carbon is lower.