Dietary Composition And Sources Of Variability In Emerging Offshore Grey Seal Colonies In The Northwest Atlantic

Project Context and Objectives
This dataset was created as part of a project aimed at improving our understanding of the foraging ecology of the grey seal (Halichoerus grypus) in the Northwest Atlantic. The substantial growth of this population over recent decades as well as the emergence of offshore colonies in the archipelago of the Magdalen Islands has raised concerns regarding their interactions with commercially important fish species in these newly dominant colonies. This data was used in the rendering of the scientific article by Irani et al. (2026) found it the cited literature attached. The article aims to characterize the diet of grey seals in these emerging offshore colonies of the Magdalen Islands and compare them to coastal colonies in the southern Gulf, in order to support ecosystem-based fisheries management and inform discussions related to human–wildlife conflicts.

Methodology and Data Collection
As part of scientific and commercial harvesting activities, between 2015 and 2023, 496 grey seals were sampled across three regions of the southern Gulf of St. Lawrence - the Magdalen Islands, Miramichi Bay, and the Northumberland Strait - during the fall, and during the summer in the Magdalen Islands. The analysis of hard parts, more specifically the shape and size of otoliths – bone structures that form the internal ear of fish, resistant to digestion – that were extracted from the digestive tracts (stomach and intestines), enabled the identification of the different taxonomic groups that contributed to the grey seal diet. Additional metadata includes information on seal age and sex, determined using teeth and reproductive organs. For the detailed methodology, please refer to the scientific article by Irani et al. (2026) in the cited literature attached.

Description of the Dataset
The dataset is comprised of four parts:

1. Species-specific multipliers used to adjust count data in intestine samples for the underrepresentation, due to digestion, of prey having smaller size or fragile otoliths (Numerical_Correction_Factors.csv),
2. The taxonomic groups of prey and their counts, after adjusting for digestion, within each of the 431 grey seal digestive tracts that contained fish otoliths (Fish_Count.csv).
3. Measurements from a subset of well-preserved otoliths used to estimate the mass of each prey consumed (Otolith_Length.csv), and
4. Metadata associated with each sampled grey seal: region, year and season of harvest, and information on seal sex and age (Seal_metadata.csv).
   A .RData version of these files is also available for use with the R scripts provided on the first author's GitHub page. Please refer to the cited literature attached.

Organization: Fisheries and Oceans Canada | Pêches et Océans Canada

Last modified: 2026-05-20T17:12:22.655210