• heterospecific foraging
• Hauraki Gulf
• foraging plasticity
• feeding efficiency
• Bryde's whales
• hierarchical clustering
• ARIMA models
• MSFAs

Multi-species feeding associations are temporary communities of animals exploiting the same or co-occurrent resources and influence the foraging efficiency of the species involved. MSFAs are common in the Hauraki Gulf and Bryde’s whales (Balaenoptera edeni) are habitual members feeding on both fish and zooplankton.
This study aimed to identify types of MSFAs and examine their frequencies over time, to detect trends in MSFA diversity and in Bryde’s whale participation and to reveal changes in Bryde’s whale prey preference.
Foraging events were observed from the MV Dolphin Explorer of Auckland Whale and Dolphin Safari from 2011 to 2020. and clustered hierarchically using Ward’s method. Influential groups for between-cluster differences were identified by SIMPER analysis. Temporal patterns in cluster frequencies, MSFA diversity, Bryde’s whale foraging in MSFAs and Bryde’s whale zooplankton feeding were examined by ARIMA modelling.
Three types of MSFAs were identified. Bryde’s whales, petrels and common dolphins had the highest contribution to between-cluster differences. Cluster frequencies varied significantly over time. Stable MSFA diversity suggested an extant diversity optimum. Bryde’s whale association rate showed no long-term trend, whereas their reliance on zooplankton varied seasonally and increased over time.
Bryde’s whales play variable roles in MSFAs depending on the species associated. The shifts in prey preference underpin their foraging plasticity but also the need to study fish stocks and zooplankton response to environmental changes. Heterospecific foraging impacts the fitness of marine predators, so safeguarding key predator and prey species is essential to assure marine ecosystem functioning.