The impact of climate fluctuation on food availability and reproductive performance of the planktivorous red-billed gull Larus novaehollandiae scopulinus.

1. Using 41 years of data, we examined annual variations in the reproductive performance of the red-billed gull at the Kaikoura Peninsula, New Zealand and related these to changes in climate, oceanography and the availability of the planktonic euphausiid Nyctiphanes australis, the bird's principal food. 2. In 1994 the population began to decline, and between 1983 and 2003 it was reduced by 51%. Adult non-breeders comprised an average of 32% of the population between 1983 and 1994, but following the decline they averaged only 18%. The age at recruitment changed markedly following the population decline: 27% of 2-year-old males bred for the first time prior to the decline, whereas the corresponding figure after the decline was 38%. The proportion of females commencing to breed as a 3-year-old was not significantly different before or after the decline. 3. An increase in the availability of euphausiids increased the likelihood of breeding and the recruitment of young individuals, caused earlier laying and resulted in an increase in the condition of adults, egg volume of gulls laying two egg clutches, clutch size and fledging success. 4. The relationship between food availability and the number of pairs that bred, laying date, clutch size and fledging success was significantly different prior to and after the population decline. The underlying cause appears to be a compensatory density-dependent mechanism that reduced interspecific competition for food. 5. The relative abundance of N. australis was correlated positively with the Southern Oscillation Index (SOI) and the frequency of occurrence of NE winds. The proportion of non-breeders and mean laying date were correlated negatively with the SOI, and mean egg volume of two egg clutches correlated positively with the SOI. 6. These results emphasize that availability of adult euphausiids is critical for red-billed gulls. We hypothesize that high primary productivity of inshore water near Kaikoura in winter, linked to a stable water column of coastal water and upwelling of additional dissolved inorganic nutrients, increases the availability of adult euphausiids to the red-billed gull as long as the coastal water is not replaced by offshore subtropical water intrusions of warmer, low-nutrient water.

Development of an ecologic marine classification in the new zealand region.

We describe here the development of an ecosystem classification designed to underpin the conservation management of marine environments in the New Zealand region. The classification was defined using multivariate classification using explicit environmental layers chosen for their role in driving spatial variation in biologic patterns: depth, mean annual solar radiation, winter sea surface temperature, annual amplitude of sea surface temperature, spatial gradient of sea surface temperature, summer sea surface temperature anomaly, mean wave-induced orbital velocity at the seabed, tidal current velocity, and seabed slope. All variables were derived as gridded data layers at a resolution of 1 km. Variables were selected by assessing their degree of correlation with biologic distributions using separate data sets for demersal fish, benthic invertebrates, and chlorophyll-a. We developed a tuning procedure based on the Mantel test to refine the classification's discrimination of variation in biologic character. This was achieved by increasing the weighting of variables that play a dominant role and/or by transforming variables where this increased their correlation with biologic differences. We assessed the classification's ability to discriminate biologic variation using analysis of similarity. This indicated that the discrimination of biologic differences generally increased with increasing classification detail and varied for different taxonomic groups. Advantages of using a numeric approach compared with geographic-based (regionalisation) approaches include better representation of spatial patterns of variation and the ability to apply the classification at widely varying levels of detail. We expect this classification to provide a useful framework for a range of management applications, including providing frameworks for environmental monitoring and reporting and identifying representative areas for conservation.