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Final Thermal Preferendum of Atlantic Cod: Effect of Food Ration
Author(s) -
Despatie SP.,
Castonguay M.,
Chabot D.,
Audet C.
Publication year - 2001
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(2001)130<0263:ftpoac>2.0.co;2
Subject(s) - gadus , atlantic cod , fish <actinopterygii> , zoology , fishery , significant difference , biology , analysis of variance , food science , mathematics , statistics
The spatial distribution of Atlantic cod Gadus morhua in the southern Gulf of St. Lawrence changed substantially between the 1970s and the 1980s. One proposed explanation for this phenomenon is that the fish were occupying different temperature zones as a result of changes in food availability brought about by changes in the species' abundance. To evaluate one key aspect of this hypothesis, we determined the final thermal preferendum of Atlantic cod in relation to food ration. After 6–15 weeks of conditioning to one of three predetermined rations, 72 fish 40–50 cm long were left to behaviorally thermoregulate three at a time in a horizontal thermal gradient for 45 h. Food ration produced significant differences among the condition indicators of the three groups. A small but significant difference (analysis of variance, P < 0.05) in final thermal preferendum was found between fish fed intermediate and low rations. Omission of the data from the first 3 weeks of the experiment, which showed signs of a ration × week interaction (indicating that the assumptions for analysis of variance without replication were not met), caused the difference between fish fed high and low rations to become significant as well (the thermal preferendum was 6.52°C with the high ration, 6.36°C with the intermediate ration, and 4.02°C with the low ration). These findings partly support the hypothesis of a food‐related change in the distribution of Atlantic cod in the southern Gulf of St. Lawrence because the fish in this study thermoregulated differently depending on food availability. Fish that had negative growth rates and that were in poor condition tended to select colder water. However, the absence of a significant difference between high and intermediate rations suggests that Atlantic cod need to be in poor condition before their temperature preference changes. The final thermal preferenda reported here are higher than the average temperatures experienced by fish in the wild during the test season but are substantially lower than the commonly accepted value for the species (13.5°C). This discrepancy may stem in part from differences among populations or ontogeny.