P-02-01-001
Otolith analysis for determination of feral versus escapee Atlantic salmon

The exotic introduction of Atlantic salmon to BC is one of the most contentious issues facing the aquaculture industry in BC. To have any hope of understanding the impact of this introduction, there must be a method for determining which fish are feral and which are escapees. Since 1998, feral juvenile Atlantic salmon have been counted in three rivers on Vancouver Island. As of yet, there is no evidence of a naturally produced Atlantic salmon surviving in the wild to maturity and spawning; however an absence of evidence does not necessarily constitute evidence of absence. We must be able to detect and distinguish these fish with virtually 100% accuracy. Therefore, it becomes necessary to have a practical and scientifically defensible method of determining the origin of Atlantic salmon effectively and efficiently for all age classes.
Incremental otolith growth occurs through differential deposition of calcium carbonate and protein over a 24-hour period. The width and spacing of the daily growth increments are affected by the environmental factors facing the fish, including temperature and feeding. It is also known that the pattern of microstructure formation remains constant over the life span of the fish, therefore allowing the origin of an adult salmon to be determined based on the microstructure patterns formed throughout its life history. Hatchery-reared fish have a more regular pattern of post-feeding daily growth increments, uniform in width and contrast. This is due to the constant and abundant food supply and regulated environment of the hatchery fish. Wild Chinook salmon exhibit a great deal of variation in the width and contrast of the daily growth increments following the first feeding check.
Otoliths will be removed from three sample groups of Atlantic salmon: farmed, wild, and recaptured fish of unknown origin. The daily growth increments and patterns of growth of the three sample groups will then be compared under a compound microscope. An experimental trial of Otolith Microstructural Analysis (OMA) in 2000, helped to develop of a checklist of features for wild vs. escapee determination. This study will test the accuracy of that checklist by using a double blind experiment.

Project Start Date: September 1, 2003

Project Completion Date: May 31, 2004

For further information please contact: DFO project leader: Andrew Thomson (E-mail: ThomsonAn@pac.dfo.gc.ca) or Regional ACRDP Coordinator: Ruth Withler (E-mail: WithlerR@pac.dfo-mpo.gc.ca).