Language selection

Search

Research Document - 2001/011

Approaches and methods for the scientific evaluation of bird and mammal predation on salmon in the Northwest Atlantic.

By D.K. Cairns

Abstract

Decreases in numbers of Atlantic salmon returning to North American rivers have prompted interest in methodologies to determine if seabird and marine mammal predation has contributed to this decline. Predation rates on salmon by seals and seabirds (other than gannets) in the Northwest Atlantic are too low to be reliably measured. However, predators could remove a substantial proportion of salmon biomass even if salmon are very rare in their diets, because the biomass of salmon in the sea is very small. Several approaches are proposed to clarify the relation between salmon and their predators. 1) Marine-phase salmon have very high growth and high mortality rates in comparison with other pelagic fishes that occupy the same habitat. The basis of this highly risk-prone life history needs to be examined, including behavioural thermoregulation for growth promotion, temperature effects on ability to avoid predation, and use of schooling as an anti-predator strategy. 2) Examination of predator scars on returning salmon, use of chemical tracers to detect salmon predation, and improved reporting of salmon remains in conventional diet analysis may shed light on salmon interactions with their predators. 3) Exploitation rates of salmon by gannets on the high seas and by birds and seals in estuaries should be measured. 4) The effect of predation on salmon populations, and the consequences to salmon of changes in predator numbers, should be examined through food-web and trophic models. A broadly-based approach encompassing these diverse methodologies is recommended because predator-salmon relations in the sea are complex and are difficult to study directly.

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.

Date modified: