Predation on myctophids by the squid Moroteuthis ingens around Macquarie and Heard Islands: stomach contents and fatty acid analyses

The diet of the sub-Antarctic onychoteuthid squid Moroteuthis ingens was as sessed using stomach contents analyses and fatty acids as dietary tracers. The contents of 54 stomachs (50 from squid collected near Macquarie Island and 4 from squid collected near Heard Island) were examined visually, and p rey remains were identified to species level where possible. Myctophid fish were the most common prey item in the stomach contents of M, ingens and we re identified in 59 % of stomachs. In total, teleost fish remains were foun d in 96 % of stomachs. The lipid class and fatty acid profiles of the diges tive gland and mantle tissue were analysed for 5 to 6 squid from each area, in addition to 4 stomach fluid samples taken from Heard Island animals. Ma ntle tissue was low in lipid, and contained high concentrations of phosphol ipids and polyunsaturated fatty acids. Digestive gland tissue had a high li pid content, with a mean value of 26.8 +/- 12.9 % wet mass in Macquarie Isl and squid and 41.7 +/- 8.5 % wet mass in Heard Island squid, and was rich i n triacylglycerol (TAG) and monounsaturated fatty acids (MUFA). Stomach flu id generally contained high concentrations of TAG, although 1 sample was hi gh in wax eater. Stomach fluid was also characterised by high MUFA concentr ations. The digestive gland of M, ingens grouped with the fatty acid profil e of stomach fluid and some myctophid species in cluster analysis and multi dimensional scaling, and appears to be a source of fatty acid dietary trace rs. Thus the fatty acid profile of the digestive gland supports findings fr om stomach contents analyses that myctophids, particularly TAG-rich species , are an important prey group of M, ingens at Macquarie and Heard Islands. This combination of techniques has a potential to increase our knowledge of the feeding ecology of squids in the Southern Ocean.