Impact of chronic hypoxia on food ingestion, growth and condition of Atlantic cod, Gadus morhua
Bibliographic record
Abstract
The Gulf of St Lawrence is an enclosed sea located in Eastern Canada. It is characterised by the presence year-round of a layer of cold water (temperature < 0 °C and average salinity = 32.4) (Lauzier & Trites, 1958; Gilbert & Pettigrew, 1997). In winter, the water column is a two-layer system (Koutitonsky & Bugden, 1991). The permanent cold layer mixes with surface waters via storm events and density changes of surface waters caused by cold winter air temperatures. As a result, water is below 0°C from the surface down to circa 100 m. Starting in April, the water column becomes a three-layer system, with a cold intermediate layer (CIL), due to the increasing temperature and lowering salinity of surface waters (Koutitonsky & Bugden, 1991) (Gilbert & Pettigrew, 1997). In summer, the CIL is found from circa 50 to 100 m. Both surface waters and the CIL are rich in oxygen. Waters deeper than the CIL are warmer: temperature is circa 2°C below the CIL, around 125 m, and increases with depth up to about 250 m, where it typically reaches 4 to 6°C, and remains relatively stable at greater depths (Bugden, 1991). Deep waters do not mix with the CIL or surface waters. This prevents them from getting replenished in oxygen. Furthermore, deep waters flow upstream. A variable mix of waters from the Atlantic and the Labrador Current enters the Laurentian channel, with oxygen levels varying between 60 and 70% saturation (Bugden, 1991; Gilbert & Pettigrew, 1997). As these waters progress toward the head of the Laurentian channel, they get progressively more depleted in oxygen, and levels of 20–30% saturation are typical of the western end of the Gulf of St Lawrence and of the estuary (Figure 1). <br> The Gulf of St Lawrence can be divided into a southern and a northern part, each occupied by one distinct cod stock in summer. The southern part, which is located south of the Laurentian channel, consists mainly of a relatively shallow bank bathed by the CIL and characterised by high levels of dissolved oxygen. The northern part includes the Laurentian channel and other deep waters troughs (Figure 1). In winter, cod from this stock are found along the eastern slope of the Esquiman channel, and the northern slope of the Laurentian channel along the southern coast of Newfoundland, in relatively warm waters that are also hypoxic (50–60% saturation). In spring, cod disperse into the northern Gulf and even the estuary, either in cold shallow waters or warm hypoxic waters, for the period of peak feeding activity. In late autumn cod older than 2 year-old return to deep waters in the Esquiman and Laurentian Channels. <br> The cod stock of the northern Gulf of St Lawrence inhabits cold waters (Brander, 1995; Campana et al., 1995), is poorly productive (Dutil et al., 1999) and slow growing (Chouinard & Fréchet, 1994). Our objective was to investigate whether hypoxia reduces growth production of the stock. In this paper we review three laboratory experiments that aimed to determine the lethal threshold of hypoxia for cod, and the impact of hypoxia on cod growth. Finally, these results are incorporated into a simple model to estimate the possible impact of hypoxia on biomass growth of the fish from this stock.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.079 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".