Seasonality and temporal trends in counts of seabirds from pelagic tours off Kaikoura, New Zealand

Seabird populations frequently breed at remote locations, making it difficult to assess and monitor their populations. While the remoteness of seabird colonies may prevent regular ground counts of breeding pairs, consistently collected at-sea abundance data presents an alternative way of obtaining information on trends in seabird populations. Regular pelagic seabird trips carried out by ecotourism operators provide an opportunity to collect these at-sea data on seabird abundance.

In Kaikoura, New Zealand, the ecotourism operator Albatross Encounter conducts daily at-sea excursions for tourists. Albatross Encounter staff have systematically recorded seabirds encountered on each trip for over a decade. From their data collected over seven years between 2006 and 2012 off the coast of Kaikoura (2987 tours), we analysed the seasonality and temporal trend in the count data for each of 32 seabird species that were recorded on at least 10% of occasions. The pattern of seasonality was clear and consistent for all species, except for great albatrosses and coastal species. There was a significant decline in counts over time for five species, including little shag, wandering albatross, white-fronted tern, black-browed albatross, and Westland petrel. At the same time, there was an increase in counts of four species, including Buller’s shearwater, northern and southern royal albatrosses, and northern giant petrel. There was an overall mean of 16.7 species recorded per trip. The mean number of species recorded per trip declined over the study period, however, with one fewer species in 2012 than in 2006.

The observed changes in counts of seabirds may reflect either a real trend in population sizes, or a gradual change in at-sea distributions. As the count data were recorded at a single location, it was not possible to distinguish these causes. Conducting similar counts in other regions would allow a better understanding of the observed trends. Nevertheless, the present study highlights the value of seabird count data collected during seabird- watching trips, as they provide a unique opportunity to assess the temporal variation in the number of seabirds at sea.

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