Quantifying Uncertainty in Estimates of Atlantic Cod (Gadus morhua) Consumption by Harp Seals (Pagophilus groenlandicus)

No abstracts are to be cited without prior reference to the author.

The decline in many groundfish stocks in Atlantic Canada has raised concerns about the role of seals in the Northwest Atlantic ecosystem. Estimates of consumption by predators are one piece of information that is required in order to determine the impact predators are having on the recovery of cod stocks. The objective of this paper is to describe the model used to estimate prey consumption by harp seals and to assess the sensitivity of estimate to model parameters. Consumption of Atlantic cod by harp seals in the northern Gulf of St Lawrence (NAFO zone 4RS3Pn) was estimated for the period 1985-2003. Estimates were obtained by combining information on harp seal abundance, energy requirements, diet composition and the distribution of animals. Consumption of Atlantic cod in 2003 was estimated to be in the order of 27,000 (SD = 6,800) tonnes. Current estimates differ from earlier studies by attempting to incorporate variability in population estimates, energy requirements, seal distribution, and diet composition. Sensitivity analysis indicated that the model was most sensitive to changes in population size, the parameters required to estimate energy requirements (ME, AF, body mass), the proportion of seals that enter the Gulf and the length of winter residency. Assumptions about the proportion of animals that remain throughout the year in the Arctic or southern waters had little impact on the estimates of cod consumption.