Predicting commercial catches of red cod for the next season
Science Centres: Fisheries
A special feature of the red cod fishery is that several years of good catches are followed by a similar period of poor catches. These fluctuations, which are thought to be due to variable recruitment, fast growth, high mortality, and the small number of year classes, create challenges for management under the Quota Management System.
Observed and predicted commercial catch for RCO 3 up until 2001-02 fishing year. (click to enlarge)
The major variable in the red cod fishery is probably recruitment, and a key to successful management could lie in the ability to predict abundance in the next fishing year. In a study funded by the Ministry of Fisheries, we have been examining whether variations in red cod recruitment are related to variations in their environment.
A statistical model was developed that relates commercial catch in RCO 3 (east coast South Island) and RCO 7 (west coast South Island) to environmental variables. Sea surface temperature was found to be the best predictor of catch variability, followed by southwest and northeast air-flow patterns. The model indicates that higher catches are associated with low water temperatures about 14 months before the start of the fishing year, which implies that juvenile fish – about 1 year old – are the most sensitive to environmental conditions.
We have used this model to provide predictions of RCO 3 catch to the fishing industry for the 2001–02 fishing year. The commercial RCO 3 catch to May 2002 (2191 t) was 86% of the predicted catch of 2564 t. We expect that by the end of the 2001–02 fishing year on 30 September 2002 our prediction may be even more accurate. Given that catches of red cod can vary by six-fold or more, our predictions of comparatively low catch in 2001–02 have proved to be correct.
The fishing industry has used this information to better manage their fleet and processing operations, and to make more informed marketing decisions. We anticipate that there will be an ongoing demand for predictions of red cod abundance by the fishing industry.