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BOWEN, W.D., P. CARTER, M. HAMMILL, 2011. Estimated Grey seal diets near Sable Island derived from fecal samples : 1991 to 2010 ; Estimation des régimes alimentaires des phoques gris près de lîle de Sable daprès les échantillons de fèces : 1991 à 2010. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/024, 13 p .
Fecal samples collected seasonally at Sable Island were used to estimate the species composition of the diet of grey seals during the period 1991-1998 and in winter, 2010. Sand lance dominated the diet in all seasons and years. Sand lance was recovered in an average of 77.6 % (CV 20.7 %) of scats indicating that most individuals in the population consumed this species. Both the occurrence (30.9 %) and percentage of the diet (wet weight) comprising Atlantic cod were highly variable, with CVs of 53 % and 104 %, respectively, among seasons and years. Number correction factors were applied to attempt to reduce the bias associated with complete digestion of otoliths. Percentage of cod in the diet varied from 0 to 21.7 %, but showed no trend over time or significant differences among seasons. Cod averaged 7.1 % (7.4 SD) of the diet.
HAMMILL, M.O., G.B. STENSON, F. PROUST, P. CARTER, D. McKINNON, 2007. Feeding by grey seals in the Gulf of St. Lawrence and around Newfoundland. Pages 135-152 in T. Haug, M. Hammill & D. Olafsdottir (ed.). Grey seals in the North Atlantic and the Baltic. North Atlantic Marine Mammal Commission (NAMMCO Sci. Pub., 6) .
Diet composition of grey seals in the Gulf of St. Lawrence (Gulf) and around the coast of Newfoundland, Canada, was examined using identification of otoliths recovered from digestive tracts. Prey were recovered from 632 animals. Twenty-nine different prey taxa were identified. Grey seals sampled in the northern Gulf of St. Lawrence fed mainly on capelin, mackerel, wolffish and lumpfish during the spring, but consumed more cod, sandlance and winter flounder during late summer. Overall, the southern Gulf diet was more diverse, with sandlance, Atlantic cod, cunner, white hake and Atlantic herring dominating the diet. Capelin and winter flounder were the dominant prey in grey seals sampled from the east coast of Newfoundland, while Atlantic cod, flatfish and capelin were the most important prey from the south coast. Animals consumed prey with an average length of 20.4 cm (Range 4.2-99.2 cm). Capelin were the shortest prey (Mean = 13.9 cm, SE = 0.08, N = 1126), while wolffish were the longest with the largest fish having an estimated length of 99.2 cm (Mean = 59.4, SE = 2.8, N = 63). In the early 1990s most cod fisheries in Atlantic Canada were closed because of the collapse of the stocks. Since then they have shown limited sign of recovery. Diet samples from the west coast of Newfoundland indicate a decline in the contribution of cod to the diet from the pre-collapse to the postcollapse period, while samples from the southern Gulf indicate little change in the contribution of cod.©2007 North Atlantic Marine Mammal Commission
HAMMILL, M.O., V. LESAGE, P. CARTER, 2005. What do harp seals eat? Comparing diet composition from different compartments of the digestive tract with diets estimated from stableisotope ratios. Can. J. Zool., 83: 1365-1372 .
This study compared diet reconstructed from different compartments of the digestive tract of harp seals (Pagophilus groenlandicus (Erxleben, 1777) with the diet estimated using stable carbon and stable nitrogen isotope ratios in mixing models. Diet composition in 18 feeding harp seals (mean age = 2.4 years, SD = 1.8 years, range = 0-6 years) was determined using traditional methods of hard-part identification and reconstruction, and stable carbon and stable nitrogen isotope ratios. Diet composition consisted of 68.8 % (SD = 8.7 %) and 69.6 % (SD = 11.6 %) by mass of invertebrates or 65.0 % (SD = 8.8 %) and 66.5 % (SD = 11.8 %) by energy of invertebrates for the stomach and small-intestine compartments, respectively. Reconstructed diets using material recovered from the large-intestine contents suggested a diet of 43.1 % (SD = 12.2 %) and 38.0 % (SD = 11.9 %) invertebrates using mass and energy, respectively. Stable carbon and stable nitrogen isotope ratios determined for the same individual harp seals suggested a diet consisting of approximately 66.1 % (SD = 117.4) invertebrates, indicating that diet reconstructions based on hard parts from stomachs are likely to be more representative than reconstructions from large-intestine contents. In species that feed on a combination of vertebrates and invertebrates, the use of faecal material to reconstruct diet composition will likely underestimate the importance of invertebrates in the diet.©2005 National Research Council Canada
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