Estimating the probability of different levels of recruitment for Cape hakes Merluccius capensis off Namibia, using environmental indices

This paper describes the use of multinomial logistic regression analysis to calculate the probability of strong, average or weak recruitment of Cape hake (Merluccius capensis). The model includes environmental indices, describing the extent of warm-water intrusion as well as the upwelling strength for different areas and periods over 2 years-from spawning until the fish are approximately 2 years of age. One of the warm-water indices as well as two of the upwelling indices have significant influences on the recruitment strength and these indices are included in the model. The rationale for using these indices is that if warm water is widespread during the spawning period (September-March) and the upwelling during the following May-September is reduced, the eggs spawned would be retained in favorable nursery areas which may result in potentially strong recruitment. If the up,welling during May-September of the following year produces sufficient food for the late juvenile hake, the chances of strong recruitment will be increased. The results indicate that the model accounts for 79% of the variance in recruitment. (C) 2002 Elsevier Science B.V. All rights reserved.