The distribution of cod (Gadus morhua) in relation to temperature and oxygen level in the Gulf of St. Lawrence

Abstract

Bottom temperature and oxygen level were measured in the northern Gulf of St. Lawrence during a ground‐fish trawl survey held in August and September 1991. Cumulative relative frequencies of temperature and oxygen level and cumulative relative frequencies of temperature x cod and oxygen X cod were computed with consideration of the random stratified sampling scheme. A total of 84‐3% of temperature x cod frequency cumulated from 2oC to 4oC, but only 25% of the frequency of temperature alone cumulated from 2oC to 4oC. At an oxygen level of 3.4 mg/1, only 2.6% of the oxygen X cod frequency had cumulated, while 24.3% of the cumulative frequency of oxygen alone was already observed at the same oxygen level. A comparison of the cumulative relative frequencies of temperature and of temperature X cod indicates that cod choose intermediate temperatures in the available range. A comparison of the cumulative relative frequencies of oxygen and of oxygen x cod indicate that cod avoid water with an oxygen level below 3.4 mg/1. This oxygen level is known to cause physiological stress in captivity. Data from the stations with oxygen levels ± 3.4 mg/1 were ignored, and the cumulative relative frequency of temperature was recomputed. As a result, the avoidance of cold water by cod was emphasized: 23% of the cumulative frequency of temperature alone was below 2oC, and 47.8% was above 4oC, in contrast to 17.2% and 57.5%, respectively, prior to removal of data from hypoxic stations.

Effect of acute and chronic hypoxia on the swimming performance, metabolic capacity and cardiac function of Atlantic cod (Gadus morhua)

“…Further, this species has traditionally inhabited areas, such as the Baltic Sea (Gerlach, 1988) and the Gulf of St Lawrence (GSL) (D'Amours, 1993;Kiceniuk and Colbourne, 1997;Gilbert et al, 2005), where they are now likely to encounter environmental oxygen levels that may strongly affect their distribution, growth and reproduction, at least during part of their life history. For example, GSL cod are sensitive to hypoxia (D'Amours, 1993), completely avoid regions of water oxygen partial pressures (Pw O2 ) below a threshold of ~6.6kPa (Kiceniuk and Colbourne, 1997), and there are thus areas in the GSL that are below the threshold for survival (Plante et al, 1998;Gilbert et al, 2005).…”

Conservation physiology for applied management of marine fish: an overview with perspectives on the role and value of telemetry

“…Hypoxia is a common phenomenon in a range of sea areas such as the Baltic Sea and the Gulf of St Lawrence [68], as well as large parts of the eastern Tropical Pacific (ETP) and eastern Tropical Atlantic (ETA) at depths below about 100 m [33]. The oxygen-minimum zones in the tropical Pacific and Atlantic are among the largest areas of naturally occurring hypoxia in the world oceans and are predicted to expand with climate change [33].…”

Associations between Atlantic cod (Gadus morhua) and hydrographic variables: implications for the management of the 4VsW cod stock

“…Recent studies have shown that a number of groundfish species exhibit strong and repeatable associations for a particular range of depths, temperatures, or salinities, or some combination thereof (Scott, 1982;Smith et al, 1991;Sinclair, 1992;D'Amours, 1993;Page et al, 1994;Perry and Smith, 1994;Swain and Kramer, 1995). There is also ample evidence that the amount of bottom water that exhibits these seemingly preferred characteristics or the amount of bottom water of this type being sampled can fluctuate over time and may therefore affect the availability or catchability of the species being surveyed by the trawl (Smith et al, 1991;Page et al, 1994;.…”