Kangaroos and greenhouse gases: Response to Russell

Abstract

We used 50 kg as the average weight for kangaroos and not 19 kg as in table 2. This is an error in the table but not in our calculations. Published kangaroo weights range widely, perhaps because there is marked sexual and species dimorphism and because kangaroos, especially males, grow throughout most of their lives (Dawson 1995). In settling on a 50 kg average we referred to the following weight ranges for the larger, harvested species of kangaroos; for males 90–60 kg (Dawson 1995) and 78–28 kg (Wilson & Read 2003); and for females 40–23 kg (Dawson 1995), 27–16 kg (Wilson & Read 2003), and 23–19 kg (Kempton et al. 1976). Even if a 50-kg weight is high, overestimating it does not affect the conclusions. This is because the model manages the population during the transition to 2020 to take a high proportion of males, which will increase the average weight of harvested kangaroos and allow a greater proportion to be harvested. There is also scope for discussion about the size of sheep and cattle carcasses from the rangelands, the amount of meat they produce and its value. All are subject to environmental and market variation. Regardless, we stand by the estimate of an average 33 kg carcass from a 50-kg live kangaroo and the comparisons between cattle and kangaroos carcass weights as a proportion of live weight. We had decided that the personal communication of 19 kg average weight reported by Grigg (2002) was too low. Russell (1999) himself refers to kangaroo weights of 65 (male) and 25 (female) kg, giving an average of 45 kg. In concluding that 120 kangaroo carcasses equal one beef carcass, Russell (2008) asserts that the carcass yield of useable meat is higher for cattle than kangaroos. Our article does not discuss the relative boning-out percentages; however, studies on carcass composition and kangaroo anatomy reveal the opposite. Hopwood (1976) found that kangaroo carcasses yield approximately 79% muscle, which is higher than the 60–70% for beef quoted by Russell (2008). Hopwood et al. (1976) compared kangaroos and sheep and concluded that the “body composition of a kangaroo is a highly desirable one for a meat animal. Carcass fat is negligible and muscle mass is concentrated in the region of the loin, rump, and thigh increasing the percentage of high value muscle in the carcass.” Further, Russell (2008) refers to Kelly's (2005)“1.5 kg each of prime cuts;” this means that Russell discards all but the premium cuts from kangaroos; however, he does not do the same for cattle. He classifies all other kangaroo meat as “processed meat” whereas for cattle he uses the phrase “cuts or mince” to combine prime and processed meat from cattle. Russell (2008) notes that sheep numbers declined since 1990 but kangaroo numbers did not increase. However, he omits to refer to the rise in cattle. From 1990 to 2006, cattle have increased from 23.1 to 28.8 million (ABS 1992; 2008), while Australian sheep and lamb populations declined over that period from 170.3 to 92.7 million (ABS 1992; 2008). Using the same dry sheep equivalents (DSE) that were used in Wilson & Edwards (2008), the reduction of sheep creates 78 million DSE. The rise in cattle takes up 88% of this DSE and so accounts for much of the pasture made available from the decline in sheep. The decline in sheep numbers was a result of a reduction in the profitability of the wool industry. Many wool farmers adjusted by expanding other sectors such as cattle and cropping. So the decline in sheep numbers does not mean that pastures were made available to kangaroos. The expansion of other sectors may even have reduced kangaroo's access to pasture. Editor : Dr. Corey Bradshaw