Relating oxygen levels in the Newfoundland offshore waters to the physiology of Atlantic cod (Gadus morhua)

Abstract

During the Northern Cod Science Program (NCSP), dissolved oxygen was measured routinely on oceanographic surveys on the Newfoundland Shelf from 1992 to 1994. A periodic regression was fitted to historical oxygen data to obtain a seasonal mean oxygen content, and divergences (anomalies) from the mean were examined. Anomalies were negative (below the photic zone) in the mid-1930s and 1960s and were lower in the early 1980s when data collection stopped until 1992. When data collection resumed in 1992 the anomalies were the lowest of the whole time series. Positive anomalies were found in the 1950s, early 1970s, and in 1993. Mean percent saturation values (% sO2) were also calculated for the Bonavista transect. In the historical mean for the Bonavista transect the minimum was 80% saturation. This minimum covered about 60% of the shelf from the shore outward. The levels of % sO2 for June, July, and September of 1992 were lower than the historical mean by about 10% sO2. In 1993 the levels were slightly higher than the mean. The lowest % sO2 found on the shelf in 1992 (65% sO2) is close to the published incipient lethal level of 60% sO2.