Seabird bycatch in New Zealand trawl and longline fisheries, 1998-2004

Abstract

Fisheries bycatch is a threatening process for populations of procellariiform seabirds, and is of particular importance for the conservation of albatross, an especially threatened group at a global scale. There is a high level ofendemism of albatross and petrels in New Zealand waters, and around one-third of the world's species of procellariiform seabirds breed in this area. Therefore, understanding the levels of mortality of these species in the New Zealand Exclusive Economic Zone is important for global conservation of the order. For New Zealand fisheries for the 1998-2004 fishing years, we estimated total seabird bycatch using data from scientific observers with model-based estimation procedures. Although sectors of the fishing activity were not evenly covered by observers, we were able to estimate seabird bycatch for large scale fisheries by vessel size (split at 28 m length), season, area and year. Approximately 5500 seabirds (credible interval between 2000 and 10 000) are estimated to be landed in New Zealand trawl and longline fisheries annually, as a result of interactions with fishing gear. Few data were available for the small vessels, thus estimates are highly uncertain. Mortalities are likely to be most common in trawl fisheries at approximately 2000-3000 seabirds annually, with the greatest contribution coming from large vessels. Around one half of these birds were albatross. For large surface longline vessels we estimated that fewer than 500 seabirds were killed annually during the main tuna fishing season. For large demersal vessels, seabird mortality was estimated to have decreased from around 1800 seabirds in 2001 to 600 seabirds in 2004. We report observed captures by species for each fishing method and area for the fishing years 1998-2004. Thirty-one species of Procellariiformes were identified during this period, over half of which are threatened species. For some species, such as White-chinned Petrel, Procellaria aequinoctialis and White-capped Albatross, 1halassarche steadi, several hundred individuals were caught. For 15 species, fewer than 10 individuals were identified. However, the unrepresentative deployment ofobserver coverage across fishery areas makes it difficult to interpret the conservation implications of species captures. A high proportion of the petrel species was observed caught primarily from areas surrounding their breeding sites while albatross were caught across breeding and non-breeding areas. Greatly improved observer sampling ratios, and studies of population status and trends, are needed to understand the conservation implications of the effects of New Zealand trawl and longline fishing mortalities on seabird populations.