Movement patterns of Atlantic cod in Gilbert Bay, Labrador: evidence for bay residency and spawning site fidelity

During three consecutive years of observation 23 Atlantic cod (Gadus morhua ) were tagged with ultrasonic transmitters as part of two experiments to de termine the movement patterns of adult cod in the genetically distinctive p opulation inhabiting Gilbert Bay, Labrador. Individual cod were relocated f or periods up to 15 months, indicating year-round residency within the bay despite unimpeded access to the open ocean. The tracking data show that ind ividual cod have a strong homing tendency. In experiment 1 displaced cod re turned (homed) to their place of capture in a small arm separated from the rest of the bay by a shallow sill while non-displaced fish remained at thei r capture site. In experiment 2 some cod remained within 2 km of their capt ure/release site, a spawning area, while others ranged widely in Gilbert Ba y before returning to this site. Whether an individual ranged widely or had more restricted movements was not related to size. Cod exhibited wider ran ging movements in the spring and early summer, following spawning, than in the late summer and early autumn. The return of Gilbert Bay cod to specific locations in the inner part of the have to overwinter and spawn is evidenc e of one mechanism that could have led to their genetic distinctiveness.