Speed Presentation 2024 Australian Marine Sciences Association Annual Meeting combined with NZMSS

Associations between seabirds and zooplankton across the Sub-Tropical Frontal Zone off Otago, New Zealand (#658)

Daragh K Brown 1 , Nicholas Winterle Daudt 1 , Evelyn Armstrong 1 , Kim L Currie 1 2 , William J Rayment 1
  1. University of Otago, Dunedin, OTAGO, New Zealand
  2. National Institute of Water and Atmospheric Research, Auckland, New Zealand

The distribution of pelagic seabirds is often driven by oceanographic features which concentrate their prey, but the relationship remains poorly understood. As a persistent localised oceanographic feature, the Southland Front off Otago, New Zealand, provides an opportunity to study these predator-prey interactions. While aboard six voyages of the Munida Transect Time Series, seabirds (via strip-transect surveys) and zooplankton (via surface tows) were concurrently sampled at nine points along the 60-km transect between October 2022 –and March 2024. Preliminary model-based multivariate abundance analysis suggests seabird distribution is primarily influenced by season and distance from shore, followed by water mass. Generalised linear mixed models indicate crustacean zooplankton, as well as distance from shore, to be a significant factor in the abundance of sooty shearwaters (Ardenna grisea), a zooplanktivorous species. Zooplankton community structure and hydrological affinities were investigated using model-based ordination. In contrast to previous studies, which used oblique and vertical tows, surface zooplankton showed no discernible water mass groupings. No environmental drivers of zooplankton distribution were significant either, potentially suggesting that the surface and deep zooplankton communities are structured differently. Greater understanding of seabird-prey dynamics in a region of high seabird diversity will improve management and offshore protection of a vulnerable group