Using otoliths as natural tags to study stock structure and connectivity of Atlantic cod (gadus morhua) in Newfoundland and Labrador waters

D'Avignon, Genevieve (2013) Using otoliths as natural tags to study stock structure and connectivity of Atlantic cod (gadus morhua) in Newfoundland and Labrador waters. Masters thesis, Memorial University of Newfoundland.

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Abstract

Atlantic cod (Gadus morhua) stock structure and dynamics are complex and remain a challenge to effective management. Otoliths have the ability to record the elemental signatures of a cod's environment. My research investigated the use of otolith chemistry to identify cod stocks within Newfoundland and Labrador waters, and to track cod movements and connectivity within and between stocks. Laser ablation inductively coupled mass spectrometer A-ICP-MS analyses provided precise and accurate measures for magnesium, mangnanesen, strontium, and barium concentrations. At large spatial scale, otolith elemental signatures and mean growth rate offish were used to segregate cod into four spawning areas with 66-89% accuracy when the two closely related inshore sites were pooled. Elemental variations in the otoliths of cod in Newfoundland waters are associated with environmental and geographical conditions that enabled reassigning 89% of cod to their correct area at small spatial scale and the discrimination of inshore vs. offshore fish within the 3Ps stock complex. This study demonstrated that otolith chemistry shows great potential to identify the origin of cod and reconstruct inshore-offshore migrations, both important elements in managing fisheries.

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