Patterns of abundance and population size structure of herbivorous fishes at the subtropical Kermadec Islands and in mainland New Zealand

Abstract

Patterns of abundance and population size structure for nominally herbivorous fishes were investigated at the subtropical Kermadec Islands in 1992 using both tape transect and timed-count techniques. Timed counts were subsequently used to sample six localities in mainland New Zealand, including coastal offshore islands. Herbivorous fishes of all genera were most abundant in shallow water. Kermadec Islands had slightly greater species richness of herbivorous fishes than north-eastern mainland New Zealand and abundances in timed-transects also showed a clear decline from north to south, with the southern localities having extremely low abundances. Offshore island groups in north-eastern New Zealand had assemblages that were dominated by one pomacentrid, and size-frequency distributions that were dominated by one adult size class of that species, whereas size-frequency distributions at mainland New Zealand and Kermadec Islands locations were platykurtic. At Leigh, herbivorous fishes were observed throughout the depth range sampled (0-15 m) but were much more common in shallow macroalgal-dominated habitats. There were suggestive patterns of increasing size and decreasing abundance with increasing latitudes.