Further analyses to separate pygmy blue whale catches by population
Branch, Monnahan, SÌŒirovic, Balcazar, Barlow, Cerchio, Double, Gavrilov, Gedamke, Hodge, Jenner et al.
There are widely recognized to be at least four clearly distinct populations of pygmy blue whales found respectively in the northern Indian Ocean (NIO, Sri Lanka to the central Indian Ocean), south-western Indian Ocean (SWIO, Madagascar to Kerguelen), south-eastern Indian Ocean (SEIO, Australia to Indonesia), and south-western Pacific Ocean (SWPO, New Zealand). This classification is based on catch locations and four song types associated with each pygmy blue whale population. A putative fifth song type has been proposed from recordings off Oman and north-western Madagascar and dubbed the Oman blue whale. Here we focus on the four well recognized blue whale populations, and use acoustic song location data to separate catches, providing population- specific catch time series for each populations. Scattered pygmy blue whale catches were taken at Durban (n = 4, SWIO); the west coast of Australia (n = 33, SEIO); east coast of Australia (n = 1, 1954, SWPO); in New Zealand and eastern Australia (n = 127, 1912-13, SWPO); and in pelagic expeditions off Kerguelen Island (n = 125, largely 1929/30), and in the southern Indian Ocean in 1934/35 (n = 13), 1935/36 (n = 1), 1937/38 (n = 1) and 1961/62 (n = 2). However, the vast majority of pygmy blue whale catches were caught by Japanese expeditions (n = 2578, nearly all in 1959/60â€“ 1963/64) in the southern Indian Ocean; and Soviet expeditions (n = 9299, nearly all in 1962/63â€“ 1971/72) that whaled in the northern and southern Indian Oceans and eastward into New Zealand waters. Here we define the region inhabited by pygmy blue whales, based on catch length frequencies, and then separate blue whale catches within this region among the four populations using song types, satellite tag data, and fetal lengths. Fetal lengths in Soviet catches demonstrate that blue whales off southern Somalia (south of 2Â°N) have similar conception dates to blue whales in the Southern Hemisphere, but those north of 9Â°N and off India (north of 4Â°N) have aseasonal or out-of-phase reproduction, suggesting that SWIO (or Oman) blue whales extend to 2Â°N, further north than previously assumed. A surface fitted to the locations of different blue whale songs was used to estimate the proportions of each population throughout the range of pygmy blue whales, and to split the pelagic catches by population. Estimated total catches for each of the four pygmy blue whale populations were 1796 (NIO), 7674 (SWIO), 2310 (SEIO), and 404 (SWPO), with 97.6% of the overall total of 12,184 coming during 1959/60 to 1971/72.