MEPS prepress abstract  -  DOI:

Fine-scale environmental effects on Cape hake survey catch rates in the Northern Benguela, using data from a trawl-mounted instrument package

Paulus Kainge*, Kai Wieland


ABSTRACT: Fine-scale effect of environmental variables associated with habitat distribution are investigated in this study for four size groups of the two Cape hakes, Merluccius capensis and Merluccius paradoxus, during the Namibian hake trawl survey of 2016, using Generalized Additive Models (GAMs) with a negative binominal error distribution. This was made possible by the collection of the oceanographic information with a trawl mounted instrument package concurrently with the catch data, for the first time in Namibia. Depth, geographical position, bottom oxygen and bottom temperature had the most pronounced effect on the catch rates of both hake species, whereas solar zenith angle representing diel effects and surface layer chlorophyll appeared to be less important. The explained deviance for the best models ranged from 71.4% for M. capensis to 92.7% for M. paradoxus between 43 and 57 cm, and differences in the response of the catch rates between the species and size groups were most pronounced for bottom depth and bottom oxygen. The results show the potential value of trawl-mounted instrumental packages in the collection of reliable environmental variables important in the study of environmental influence on abundance, catch rate or distribution, and in turn in the assessment and management of a resource.