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Stable isotope tracers can be valuable tools for interpreting the way an ecosystem has functioned over time. Both modern and archaeological swordfish rostra spanning 4,200 years were collected from the Gulf of Maine and other parts of the western North Atlantic for 15N and 13C analysis to understand shifts in swordfish populations and reconstruct their diets through time. In addition, several selected whole rostra were subsectioned and analyzed for bulk carbon and nitrogen isotope analysis in order to evaluate the isotopic variability that can occur along the length of a rostrum.
Preliminary results show notable variability of both δ13C and δ15N along individual rostra, particularly between the outer edge and inner chamber regions. This variability may be due to differences in nutrient exchange throughout the internal bone structure, and may reflect natural changes in the diet of the swordfish throughout its life as the rostrum grows. The δ15N of the archaeological rostrum collagen is relatively constant between 4.2 ka BP and 3.5 ka BP, and then becomes about 1‰ depleted in modern samples. These data may reflect (1) a decrease in trophic level of the swordfish, (2) a change in nutrients at the base of the food web, or (3) a fundamental shift in swordfish populations. Swordfish used to be an important resource to human cultures in the nearshore region of the Gulf of Maine; thus, the study of the dietary habits provides useful information on changes in their ecology as well as human exploitation.
Morrison, Rachel C., "Isotopic Reconstructions of Swordfish Diets in the Gulf of Maine" (2013). Standard Theses. 9.
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