The importance of the physical conditions, such as temperature and salinity, and the feeding conditions experienced by maturing salmon in the high seas, is one of the least studied aspects of salmon life history. In large part this is due to the difficulty and cost of collecting fish and measuring environmental conditions in the remote and inhospitable north Pacific where the salmon mature before their returning to their natal streams to spawn
The north Pacific has undergone large scale and long term changes in atmospheric and ocean conditions, controlled by the long term cycling between warm and cool phases of the Pacific Decadal Oscillation, and shorter term oscillations between El Niño and La Niña phases of the El Niño Southern Oscillation. The resultant shifts in physical conditions in the north Pacific significantly affect the abundance, composition and distribution of zooplankton (including krill and copepods) and micronekton (small pelagic fish and squid), the primary prey of salmon. There is growing evidence that these changes in prey availability, as well as inter-specific competition, are a significant factor in salmon production.
The High Seas Food Webs Program collects returning adult fish, from both the pre and post spawn period. From each specimen collected we collect sample of scale, muscle and otoliths. These samples are returned to the lab where we measure the tissue stable isotope ratios as proxies for high seas conditions experienced by maturing salmon.
Through stock and species specific monitoring of tissue stable isotope values we aim to improve understanding of the role of high seas conditions in population fluctuations of BC salmon.
Photos by Billie Johnson
Variation in the carbon (δ13C) and nitrogen (δ15N) isotope ratios, and the elemental ratios of carbon and nitrogen (C:N), in the muscle tissue of returning Rivers Inlet sockeye salmon.