Stomach contents of long-finned pilot whales, Globicephala melas mass-stranded in Tasmania

Abstract

New data are reported from analyses of stomach contents from 114 long-finned pilot whales mass-stranded at four locations around Tasmania, Australia from 1992-2006. Identifiable prey remains were recovered from 84 (74%) individuals, with 30 (26%) individuals (17 females and 13 males) having empty stomachs. Prey remains comprised 966 identifiable lower beaks and 1244 upper beaks, belonging to 17 families (26 species) of cephalopods. Ommastrephidae spp. were the most important cephalopod prey accounting for 16.9% by number and 45.6% by reconstructed mass. Lycoteuthis lorigera was the next most important, followed by Ancistrocheirus lesueurii. Multivariate statistics identified significant differences in diet among the four stranding locations. Long-finned pilot whales foraging off Southern Australia appear to be targeting a diverse assemblage of prey (≥10 species dominated by cephalopods). This is compared to other similar studies from New Zealand and some locations in the Northern Hemisphere, where the diet has been reported to be primarily restricted to ≤3 species dominated by cephalopods. This study emphasises the importance of cephalopods as primary prey for Southern long-finned pilot whales and other marine vertebrates, and has increased our understanding of long-finned pilot whale diet in Southern Ocean waters.

Fig 1. Location of LFPW mass-strandings around Tasmania from 1992 to 2006.

The size of the location icon is representative of the number of individuals that stranded at that location (see Table 1): 24 individuals stranded at Bicheno (26/09/92), 41 at Maria Island (29/11/04), 161 at Marion Bay (25/10/05) and 27 at Ocean Beach (01/12/2006). At total of 24, 19, 49 and 22 stomach samples were available from these sites respectively.

Fig 2

(A) Percent numerical abundance (%Num) and (B) percent reconstructed prey mass (%BM) of cephalopod genera found in the diet of LFPWs stranded along the Tasmanian coastline from 1992 to 2006. Species where the %Num and %BM were <1% are not included.

Fig 3. Percent reconstructed prey mass (%BM) of cephalopod families found in the diet of LFPWs stranded along the Tasmanian coastline from the four stranding locations.

Species where the %BM are <1% are not included.

Fig 4

(A) Frequency histograms of the lower rostral lengths (LRLs) of the three most important squid species in the diet of LFPWs stranded in Tasmanian waters: Ommastrephidae spp., Lycoteuthis lorigera and Ancistrocheirus lesueurii, for all four stranding locations combined. Shaded areas show the young beaks with undarkened wings (unknown LRL for L. lorigera). (B) Average LRL (±SD) of the three most important squid species in the diet of LFPWs stranded in Tasmanian waters, separated by stranding location.

Fig 5. The pruned classification tree which splits prey items consumed by LFPWs stranded in four locations.