Counts of seabirds around commercial fishing vessels within New Zealand waters

Citation

Richard, Y., Abraham, E. R., & Filippi, D. (2011). Counts of seabirds around commercial fishing vessels within New Zealand waters. (Unpublished report held by the Department of Conservation, Wellington.). Retrieved from http://files.dragonfly.co.nz/publications/pdf/Richardetal_2011_counts.pdf

Summary

There are over 80 species of seabird breeding in New Zealand waters, but for many species their at-sea distribution remains largely unknown. This report presents a summary of seabird data in the New Zealand region, based on seabird counts made by fisheries observers on-board commercial fishing vessels between January 2004 and June 2009. During the 5.5-year period, there were 13 114 observations of seabirds around fishing vessels in New Zealand waters, from 442 fishing trips and 10 333 fishing events, resulting in 66 543 seabird counts.

The seabird counts were made in trawl, bottom-longline, surface-longline, set-net, and purse-seine fisheries, with the majority of observations in trawl fisheries. The spatial distribution of seabird counts observations corresponded with fishing effort, with observations in trawl fisheries widely distributed throughout continental shelf waters in New Zealand’s Exclusive Economic Zone. Seabird count observations on bottom-longline vessels were concentrated on the Chatham Rise and in the Hauraki Gulf, and observations on surface-longline vessels were made in northeast and southwest New Zealand. For set-net and purse-seine fisheries, seabird count observations were in inshore waters, although the purse-seine fishery was represented by relatively few observations, which were restricted to northern North Island waters.

Seabird counts were made of sub-species, species, or species groups, depending on the level of identification. The recorded seabirds encompassed a wide range of species and species groups, from coastal taxa such as penguins, shags, gulls and terns to oceanic taxa such as albatrosses, petrels, and shearwaters. The most frequently recorded taxa were Cape petrels Daption capense, present in over 8000 observations, followed by New Zealand white-capped albatross Thalassarche cauta steadi and the species group giant petrels (Macronectes spp.), which were present in over 5000 observations. Southern Buller’s albatross Thalassarche bulleri bulleri, the species group black-browed albatross (Thalassarche melanophris and Thalassarche impavida), white-chinned petrel Procellaria aequinoctialis, Salvin’s albatross Thalassarche salvini, sooty shearwater Puffinus griseus, and great albatrosses (family Diomedeidae) were present in at least 3000 observations each. Other species and species groups were present considerably less often, being recorded during fewer than 200 observations.

The two most frequently recorded seabird species were also the most abundant, with Cape petrels and New Zealand white-capped albatross recorded at mean abundances of 63 and 33 individuals, respectively. Salvin’s albatross were also common, reported at an average of 22 individuals in the observer counts. The species and species groups white-chinned petrel, sooty shearwater, southern Buller’s albatross, albatrosses, and great albatrosses (Diomedea spp.) were each recorded with average abundances of at least 10 individuals per observation. All other species and species groups had low abundances, with an average of less than one individual recorded per observation. Recorded seabird counts were generally higher within a distance of 100-m from fishing vessels than at distances further away.

Seabird abundance around fishing vessels varied in relation to fishing method, with seabirds observed at considerably higher abundances around trawl vessels than in any other fishing method. The two seabird groups that consistently dominated abundance data across fisheries were albatrosses and petrels, although the albatrosses grouping was scarce or absent in set-net and purse-seine fisheries. In contrast, gulls and terns were only observed around set-net vessels. The observed abundance patterns are likely related to differences in the inshore-offshore distribution of the different seabird types and fisheries involved.

Regarding the spatial distribution of different seabird groups throughout New Zealand waters, small albatrosses (or mollymawks) Thalassarche spp. were the most dominant genus in seabird observations around fishing vessels, featuring frequently in inshore and offshore waters, including on Chatham Rise, north of Auckland Islands, and on New Zealand’s west coast. Shearwaters Puffinus spp. dominated observations in northeastern North Island, i.e., Hauraki Gulf, while Procellaria petrels were the dominant genus in observations from northern New Zealand, and in some records southeast of South Island and in subantarctic waters. Frequent records of giant petrels Macronectes spp. and great albatrosses Diomedea spp. were localised in southern waters and northwestern North Island, respectively, with prions Pachyptila spp. only dominating count data on the southern North Island west coast. Sea gull species within the genus Larus were only dominant in inshore records, interspersed across different North and South Island locations.

In view of the scarcity of information, observer records provide a valuable source of data regarding the distribution and abundance of seabirds in New Zealand waters. There are, however, limitations to these data, including different levels of observer skill and experience in the identification of seabird species, particularly for birds at a distance from the vessel and when similar-looking species are present. This limitation is partly alleviated through the use of species groupings and generic codes, but the identification of species at a lower taxonomic level also represents a loss of information. However, as these data are collected from fishing vessels, they are ideally suited for assessing the overlap between seabird species and fisheries. They account for both the distribution of the birds and how attracted they are to the fishing vessels, providing a measure of the interaction rate between seabirds and fisheries. This information is a key input to seabird risk assessments, and it is expected that these data will help to determine the risk that New Zealand fisheries pose to seabird populations.