Using a remote drift underwater video (DUV) to examine dredge impacts on demersal fishes and benthic habitat complexity in Foveaux Strait, Southern New Zealand

Abstract

Foveaux Strait is a shallow body of water at the southern tip of New Zealand. It supports nationally significant dredge oyster Ostrea chilensis and blue cod Parapercis colias fisheries. Fish counts and benthic habitat descriptions from drift underwater video (DUV) transects conducted in two seasons over an area of recovering biogenic reef and an adjacent recently dredged area are presented. Over all, seven demersal fish species (5.10 per 100 m 2, 75% P. colias) were recorded on the recovering area surveyed, whereas only three species (0.47 per 100 m 2, 91% spiky dogfish Squalus acanthias) were recorded on the recently dredged area. There were few seasonal differences except for S. acanthias. Descriptions of benthic habitat derived from video stills showed topographic complexity was greater on the recovering area; general epifauna cover, sponge cover and macro-algal cover were also greater on the recovering area, but with seasonal interactions. In contrast, the numbers of tunicates and ophiuroids were higher on the dredged area. Sponge cover (absent from the dredged area) was also correlated with the abundance of leather jackets Parika scaber and scarlet wrasse Pseudolabrus miles as well as all color phases of P. colias. Topographic complexity, general epifauna cover, and macro-algae cover were also positively correlated with the abundance of adult P. colias and P. scaber. The drifting video methodology was able to estimate densities of demersal fish and make broad-brush measures of benthic habitat capable of demonstrating the importance of benthic habitat complexity to demersal fish in Foveaux Strait. The potential mitigation of reduced benthic habitat complexity from oyster fishing is then discussed.