Dusky dolphin (Lagenorhynchus obscurus) feeding tactics and multi-species associations

In this study, monthly changes in dusky dolphin (Lagenorhynchus obscurus) feeding tactics and multi-species associations in Admiralty Bay and Current Basin, New Zealand were described from August to November 2005 and from May through August 2006. Concurrent changes in dusky dolphin abundance, prey characteristics, and locations of feeding bouts were examined. Data were collected during systematic surveys and focal follows of dolphin groups. During 335 dolphin feeding bouts (52 observed underwater), data were recorded on number of associated fur seal (Arctocephalus forsteri), seabirds, and sharks; dolphin behaviour; prey ball parameters; and locations. Dolphin feeding tactics, multi-species associations, and locations of feeding bouts were different from May through July than from August to November. From May through July, dolphins fed on mobile prey at depth; from August to November, they herded small schools of fish (including pilchard Sardinops neopilchardus) to the surface. Primarily shearwaters (Puffinus spp.) fed with dolphins from May through July; shearwaters, gannet (Morus serrator), gulls (Larus spp.), and fur seal frequently fed with dolphins from August to November. These intra-annual differences suggest that changes in prey species or behaviour influence dolphin feeding tactics, and influence which species benefit from feeding with dolphins.