Seal Diets and Declines: Competition Reshapes Marine Food Webs
A 24-year study of harbour and grey seals in Scotland provides a rare long-term view of how interspecific competition and prey availability drive population dynamics. Researchers analyzed dietary niches using hard parts found in seal faeces, finding high dietary overlap between the species. In the Moray Firth, where harbour seal numbers have declined, their diet shifted from a narrow, energy-rich focus on sandeels and clupeids to a broader, less optimal mix of gadids and flatfish as their population fell. Meanwhile, the stable and increasing grey seal population maintained a consistently narrow, sandeel-dominated diet. In southeast Scotland, where both species’ diets showed less change, sandeel availability decreased over time. The findings suggest grey seals outcompeted harbour seals for key prey in one region, while broader ecosystem changes in prey availability likely hindered recovery in another.
Why it might matter to you: This research offers a concrete, data-driven case study of how competition theory plays out in real-world marine ecosystems, directly relevant to understanding trophic interactions and population declines. For your work in ecological modeling and conservation biology, it underscores the critical importance of long-term dietary datasets for untangling the complex drivers of species success and failure. The methodology for standardizing disparate historical datasets could also inform your own approaches to analyzing ecological time series.
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