[1] Univ Tasmania, Inst Marine & Antarctic Studies, Sandy Bay, Tas 7005, Australia
[2] CSIRO Marine & Atmospher Res, Wealth Oceans Natl Flagship, Hobart, Tas 7001, Australia
[3] Dept Primary Ind Pk & Environm, Hobart, Tas 7001, Australia
[4] British Antarctic Survey, Nat Environm Res Council, Cambridge CB3 0ET, England