Movements of Atlantic Cod ( Gadus Morhua ) Within the Spring Thermocline in Trinity Bay, Newfoundland

• Published in: Journal of the Marine Biological Association of the United Kingdom
• Main Authors: Wroblewski, J.S., Goddard, Sally V., Smedbol, R. Kent, Bailey, Wade L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1995
• Subjects: Aquatic Science; atlantic cod; Gadus morhua; Newfoundland
• Online Access: http://dx.doi.org/10.1017/s0025315400018178; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0025315400018178

Using depth-telemetering, sonic tags orally inserted into the stomachs of Gadus morhua (Pisces: Gadiformes) found over-wintering in Trinity Bay, Newfoundland, the movements of individual fish were observed as surface waters warmed in early spring. Physiological measurements (antifreeze protein levels in the blood) indicate that many cold-adapted, bay cod change their thermal regime at this time. Fish acclimatized to subzero water temperatures enter the newly-formed thermocline and become available to a cod trap fishery. Most sonically-tagged fish resided in 0–1°C waters along the shoreline. Tracking data confirmed indications from declining antifreeze protein levels that cold-adapted cod, having moved into shallow waters in early spring, do not return to deeper, subzero-temperature waters for any appreciable time. At night some cod swam pelagically near the surface. Fish moved at times in the same direction as the tidal current, but ground speeds were several times greater than current velocities. Nocturnal pelagic swimming was also observed during the summer when temperatures within the thermocline exceeded 10°C.