The purpose of this study was to apply oxygen and carbon stable isotope microsampling
techniques to the seasonal banding of the otoliths of the Atlantic cod, Gadus morhu~ in order
to determine their potential use in reconstructing the environmental conditions experienced by
cod. A reconstruction of the changes in environmental temperature is seen as particularly
applicable to the determination of cod migration routes based on the known temperature profile
of the North Atlantic. Transverse thin sections of six otoliths from cod taken off the coast of
Atlantic Canada were prepared using standard methods. Material was sampled from each semiannual
band of the otoliths and run on a Finnigan MAT 251 ratio mass spectrometer to determine
0180 and 013C.
The results for 0180 indicated that the otoliths had an approximate initial value of either
1.4%o or l.O%o for sample material taken from the nucleus. The 0180 signal was characterized
by oscillating values in which sample material from hyaline bands corresponded predominantly
with the troughs and sample material from the opaque bands corresponded with the peaks. The
average range of 0180 was found to be 0.87%o corresponding to a temperature range of 3.6°C
which was within the expected 3 to 4 °C seasonal average temperature shift experienced by cod.
Seasonal cycling was apparent in three of the otoliths, with semi-annual values alternating
between high opaque bands and low hyaline bands.
It was concluded that seasonal temperature changes due to migration from offshore to
inshore waters are recorded in the 0180 signal and that future sampling should attempt to resolve
several samples within each seasonal band in order to resolve the migratory changes in temperature on an sub-annual basis. It is also suggested that experiments be carried out to
determine the species specific 0180 versus temperature relationship for cod to make accurate
interpretation of the data possible.
The o13C signal was found to be characterized by an increasing logarithmic trend in o13C.
The 013C signal was observed to increase over the first three years of growth and to level off at
age 4 and fluctuate at a value close to O%o. The otoliths of cod were found to contain a high
proportion of inorganic carbon with a minimum 013C value of -4.53%o and a maximum of 0.23%o.
It was suggested that the initial increase in 013C was a product of a combination of factors
affecting metabolic rate and therefore, indirectly, the amount of metabolically derived carbon
circulating in the blood. It was concluded that further research into the growth and development
of cod was necessary in order to reach a comprehensive understanding of the biological processes
responsible for the observed trends in 013C.
0180 was plotted against 013C for samples from growth bands of age four or greater and
found to have a positive correlation with a slope of 0.269 (S.E. 0.049) and an r-squared of 0.537,
P < 0.0001 when the results for otolith 176 were excluded due an anomalous trend in that data
set. Two hypotheses were suggested to account for the observed positive correlation, a
metabolic/temperature effect, and a depth/temperature effect.
It was concluded that, with further research into the controlling factors behind the
fluctuations in 013C, the 013C signal may provide a second source of information with regards to
changes in habitat and environmental characteristics over the life time of the cod. It is suggested
that a study be carried out to determine the amount of metabolic carbon incorporated into the
otolith in order to clarify the observed trends. / Thesis / Candidate in Philosophy
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22473 |
| Date | 01 May 1995 |
| Creators | Browne, David. R |
| Contributors | Schwarcz, H.P, Geology |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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