Distribution of seabirds in coastal waters off Otago, New Zealand

Abstract

The occurrence, abundance, and distribution of seabirds was studied in a physically dynamic region off the coast of Otago, New Zealand. Eleven line‐transect surveys were conducted in late summer and autumn of 1994–96, when surface swarms of “krill”, Nyctiphanes australis, were present in the study area. Twenty species of seabird were recorded. The abundance and occurrence of species varied between sitting and flying counts. The most numerous species were sooty shearwaters (Puffinus griseus), red‐billed gulls (Larus novaehollandiae), black‐billed gulls (L. bulleri), and black‐backed gulls (L. dominicanus). Most species were recorded throughout the study area, and different species were commonly observed together. Spatial similarity matrices revealed strongest association between red‐ and black‐billed gulls and black‐backed gulls. The small (kilometre) scale distribution of seabirds varied between surveys, between transects, and between repeated runs of the same transect 1–3 h apart. Correlations between seabird abundance, salinity gradient, and krill density were weak. Counts of seabirds were highly positively skewed. This skewness, together with spatial and temporal variability in the distribution of flocks, would make abundance estimation at sea difficult.