Stable isotope analyses in otoliths of cod (Gadus morhua L., 1758): Implication for long-term environmental changes in the Canadian Atlantic

Stable isotopic analysis has been widely used in study of proxy materials with concentric layers, such as fossil shells, corals, and tree rings, and has recently begun to blossom in fish otoliths. This study describes some new developments of stable isotopic analyses in otoliths of cod (Gadus morhua) from the northeast Scotian Shelf, Nova Scotia, and demonstrates how powerful those analyses are in study of marine environmental changes.; It is known that the relationship between oxygen isotope {dollar}rm(deltasp{lcub}18{rcub}Osb{lcub}W{rcub}){dollar} and salinity is very useful in study of coastal settings, especially for study of the dynamic processes, water currents and possible sources of mixing, and the estimation of isotopic composition in paleo-oceans. In this study, I found that the best equation for describing this relationship in the 4Vs area is: {dollar}rmdeltasp{lcub}18{rcub}Osb{lcub}W{rcub}=0.524S{lcub}-{rcub}18.38.{dollar} I also found that this relationship varies vertically with water depth, especially at depths greater than 200 m.; Sagittal otoliths of cod were analyzed based on seasonal translucent (winter) and opaque (summer) aragonite zones, by a newly-established micromilling technique (DM 2800). The {dollar}deltasp{lcub}18{rcub}{dollar}O values range from 0 to +3.0{dollar}perthous,{dollar} with minor isotopic variations between seasons. However, there were significant differences in the growth of the first-year, indicating that juvenile cod are more active than adults at the early stage of their life history. Comparing opaque otolith zones of the 4-5 year group from different years of capture, the secular isotopic variation gradually increased by about 1{dollar}perthous{dollar} over the period of 1984-94, corresponding to a temperature decrease in the surrounding seawater of about 5{dollar}spcirc{dollar}C.; The life-long {dollar}deltasp{lcub}13{rcub}{dollar}C variation in otoliths of cod shows a consistent increase during the first 4 to 6 years, from the minimum values between {dollar}-{dollar}5 and {dollar}{lcub}-{rcub}2.5perthous{dollar} to a maximum near 0{dollar}perthous.{dollar} The early rise in {dollar}deltasp{lcub}13{rcub}{dollar}C is partly due to the fraction of metabolic HCO{dollar}sb3sp-{dollar} in the cod's blood, and partly due to a dietary shift or trophic effect. The maximum in {dollar}deltasp{lcub}13{rcub}{dollar}C is attained at an age (4-5 y) close to that of the age of maturity, and used to determine the age of sexual maturity of the 4Vs cod.; In this study, I also analyzed otoliths of known-history Norwegian cod from experiments. (Abstract shortened by UMI.)...