Biology of a resident cod (Gadus morhua) population in Gilbert Bay, Labrador

• Main Author: Morris, Corey John
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2000
• Subjects: Gilbert Bay; atlantic cod; Gadus morhua; North Atlantic
• Online Access: https://research.library.mun.ca/4212/; https://research.library.mun.ca/4212/1/Morris_CoreyJohn.pdf; https://research.library.mun.ca/4212/3/Morris_CoreyJohn.pdf

I studied the biology of a resident population of Atlantic cod (Gadus morhud) in Gilbert Bay (52° 35' N, 55° 52' W), Labrador. Gilbert Bay has an area of approximately 34 km2, and is generally less than 30 m deep. Water temperatures are sub-zero in winter but surface water warms rapidly after ice leaves the bay, usually in early May. Gilbert Bay cod spawned from mid-May to mid-June, 1999, and eggs hatched in about 24 days. A steep density gradient in the upper 5 m of the water column in The Shinneys, an arm of the bay where most data were collected, may be important in keeping eggs in the bay. Larvae and pelagic juveniles appeared to be more abundant in 1998 than in 1999. Cod ranging in size from 15 to 100 cm (2-15+years of age) were captured in shallow water (< 5m) throughout the summer. Tagging indicated that some Gilbert Bay cod move to the mouth of the bay during summer, but others were recaptured at the same location as tagged. Sexual maturity can be attained at 32 cm TL, and 4 years of age, but some females were not sexually mature at a length of 42 cm and age of 8 years. Gilbert Bay cod grow more slowly than adjacent offshore cod. Histological evidence indicates that some females may not spawn every year after reaching sexual maturity. Differences in life history characteristics of this population compared to other Atlantic cod within the North Atlantic Fisheries Organization (NAFO) divisions 2J 3K and 3L is further evidence of reproductive isolation. This resident population of Atlantic cod could be easily over exploited and should be managed separately from other northern cod.