Growth of juvenile salmon when they first enter the ocean is critical to recruitment due to size-selective mortality. Determining how conditions during the early marine period effect salmon growth and development depends on accurate estimates of the length of time that individual fish spend in different habitats. Otoliths, fish “ear stones”, are calcium carbonate structure that grow through the accretion of daily rings. The elemental composition of the otolith reflects that of the water in which the fish lives, and changes are recorded in the otolith rings when fish encounter new conditions.
We use laser ablation inductively coupled with a plasma mass spectrometer (ICPMS) to determine the point at which otolith Strontium:Barium ratios shift from low to high values, indicating that a fish has moved from fresh water to salt water. In this way the marine entry point of an individual fish can be identified, and subsequent daily otolith ring accumulation used to determine marine residence time. Applying this methodology we are investigating juvenile sockeye salmon migration dynamics in Rivers Inlet, Central Coast BC, specifically focusing on the role of environmental conditions and prey hotspots in determining migration / growth rates.
Analysis of salmon otolith Strontium:Barium ratios using ablation inductively coupled with a plasma mass spectrometer (ICPMS).