Document ID: chunk:federal_register_of_legislation:F2013L00289:body:0:p17
Version: federal_register_of_legislation:F2013L00289
Segment Type: other
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Character Range: 54473–57526

swimming16 and have thicker blubber (23–24 centimetres)94, with mature females slightly larger than males94. Right whales produce social sounds ranging in frequency from 50–600 hertz at sound levels ranging from 137–192 decibels. Modelling suggests they can hear frequencies in the range of 10 hertz to 22 kilohertz73, 74.

Reproduction
On average, southern right whales from both the south-eastern and south-western populations have a single calf every three years17, 79. Gestation is thought to be 12 months16, lactation lasts at least 7–8 months94 with weaning occurring within 12 months31. If mothers lose a calf, they may calve again the following year which results in a two year calving interval39. Longer intervals may be due to variability in environmental conditions: calving intervals and calf production on the Australian coast are likely to be influenced by large-scale climate variability, particularly increased sea temperature83. Southern right whales' low and slow reproductive rate has resulted in only a gradual recovery from whaling and affects the species' capacity to withstand impacts.

Southern right whale calving grounds are found at mid to lower latitudes and are occupied during the austral winter and early-mid spring. Mating has been observed within these areas33,79,104. Female southern right whales show calving site fidelity, generally returning to the same location to give birth and nurse offspring. This trait impacts on the whales' ability to respond to external threats, including their ability to tolerate and respond to habitat changes. Site fidelity limits their capacity to occupy new areas, even where suitable habitat is available and abundance is increasing. Site fidelity, combined with an average three-year calving interval, causes habitat occupation and coastal visitation to vary between years18, 84.

Reproductively mature females that calve in Australian waters are almost never recorded on the Australian coast between calving years17, 83, 33. The absence of these females in non-calving years suggests that conception occurs elsewhere. Although it is not known where conception takes place, surface-active groups apparently involved in mating have been observed in Australian coastal waters104. Reproductive maturity is reached at 6–9 years in the Australian population.

Foraging
The foraging ecology of southern right whales is poorly understood and observations of feeding whales are rare. As in the northern hemisphere70, 21, broad-scale foraging patterns are almost certainly determined by the location of oceanographic fronts and features that concentrate their planktonic food resources. Most feeding probably occurs when productivity is high – in the austral spring and summer. Feeding may also extend into autumn and occur opportunistically in winter nursery areas where suitable prey densities occur52. Satellite tagging and stable isotope analysis show right whales off South Africa feed both at, and south of, the Sub-Tropical Front in both Sub-Antarctic and Polar Frontal zones1, 29 and