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http://hdl.handle.net/11375/22473
Title: | Oxygen and Carbon Stable Isotope Analysis of the Otoliths of Atlantic Cod (Gadus Morhua L.) |
Authors: | Browne, David. R |
Advisor: | Schwarcz, H.P |
Department: | Geology |
Keywords: | oxygen, carbon stable isotope, otoliths, Gadus morhua |
Publication Date: | 1-May-1995 |
Abstract: | 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. |
URI: | http://hdl.handle.net/11375/22473 |
Appears in Collections: | Digitized Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Browne_David_R_1995May_Bachelors.pdf | 4.17 MB | Adobe PDF | View/Open |
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