Differentiating trophic niches of salmonids in Lake Ontario using three isotopes

Session: Exploring Predator-Prey Relationships and Feeding Ecology in the Great Lakes (3)

Sarah Larocque, University of Windsor, GLIER, [email protected]
Timothy Johnson, Ontario MNRF, Glenora Fisheries Station, [email protected]
Aaron Fisk, University of Windsor, [email protected]

Abstract

Diet studies of Great Lake salmonids have generally revealed a high consumption of alewife (Alosa pseudoharengus), yet there is evidence that some salmonids feed on round goby (Neogobius melanostomus) and/or increase diet variability as alewife populations decline (e.g., in Lake Huron). Diet analyses with stable isotopes allows us to assess longer-term diet without the bias of a snapshot stomach sample. Generally, ?¹³C and ?¹⁵N can determine habitat/carbon sources of prey and trophic position, respectively. However, prey species can exhibit similar ?¹³C and ?¹⁵N making it difficult to decipher what is being consumed without verifying with stomach samples. A third isotope, ?³⁴S, is proving useful to further distinguish the feeding ecology and trophic niches of freshwater fish. Using these three isotopes, we collected muscle and fin tissue of salmonids (five species; n = 377) and a comprehensive collection of prey species from Lake Ontario in 2018 to take a more in-depth examination of salmonid diets and trophic niches. We also assessed the impact of lipid extraction methods on ?³⁴S and whether fin and muscle exhibit similar isotopic signatures. Lastly, we compare our results to a 2013 Lake Ontario isotope study to determine if salmonid diets are changing with different prey availability.