Spatio-temporal patterns in the abundance and population structure of a large temperate reef fish

Abstract

Density, size structure and sex distribution of the large temperate reef fish Cheilodactylus spectabilis were examined in 10 habitats on a rocky reef environment in northeastern New Zealand. Morphometric analysis of body form identified subtle features which enabled the sex of C. spectabilis to be identified readily in the field. Censuses of mapped areas and strip-transect counts were used to monitor the distribution patterns down a depth gradient at 2 localities over a 12 mo period (1985). Large differences in density, size and sex structure were found between habitats. Females and juveniles were found to inhabit the shallow sections of the reef, while males dominated the deeper regions. There was a strong trend toward increased mean fish size with depth. These trends in distribution, density and size were consistent over a wide range of time scales. Comparisons with surveys conducted in 1978 and 1988 showed the same patterns of distribution and population structure. Similar consistency was found on a between-month, between-day and within-day scale over a range of depths.