Humpback whale calving range

In chapter 4 of this thesis I used photogrammetric methods to identify neonate calves in an area considered to be outside the recognised calving grounds of the BSD population. I combined these observations with behavioural data and population assessments and estimated that a minimum of ~20% of the expected number of calves in the BSD population were born near, or south of, North West Cape. As this location is situated 1000 km southwest of the recognised calving grounds of the BSD humpback whale population, my findings provided evidence that the calving grounds are more extensive than those currently recognised.

As animal populations recover from declines and their numbers increase, they may undergo range expansions or re-colonise areas that were previously inhabited. In the case of the BSD humpback whales, observations of large numbers of neonate calves off North West Cape during the commercial whaling era (Chittleborough, 1953) demonstrate that the humpback whales are now re-colonising calving areas they used before their population declined.

These areas being re-colonised are closer to the feeding grounds, potentially providing mothers and their calves with a reduction in the cost of travel. Although speculative, such reductions in energy expenditure would enable mothers to allocate more of their finite energy stores to offspring development, and calves to allocate more energy to growth rather than to locomotion. However, this benefit would be offset by other energetic costs, such as heat production in cooler waters (Rutishauser et al., 2004) or predation avoidance (Pitman et al., 2014) in higher latitudes. Also,

calving over widely dispersed areas, rather than localised areas with high density,

may offer reduced predation pressure from killer whales.

As calving areas expand, they may begin to overlap with areas of high anthropogenic activity. For humpback whales that prefer to migrate in shallow waters, these

expansions will typically take place along or near to coastlines. The preference to

breed in tropical waters between 21.1o_{C and 28.3}o_{C (Rasmussen et al., 2007) results}

in many breeding areas being located in areas of high human use. For example, humpback whale breeding and calving grounds around the world include popular tourist destinations such as the Hawaiian Islands (Alison and Louis, 2000), the Great Barrier Reef (Smith et al., 2012), and Ningaloo Reef (Irvine, 2016). Such overlap could potentially result in disruptions to migratory behaviour if calm and protected waters for mothers and calves are in conflict with areas of high human use. In the terrestrial environment, numerous long-distance migrations around the globe have been lost from the consequences of high human population in migratory corridors.

These include migrations of wildebeest (Connochaetes taurinus) in Namibia and

South Africa, bison (Bison bison) in Canada and U.S.A and elephants in Kenya

(Loxodonta africana) and India (Elephas maximus) (Berger, 2004). Long-distance migrants are particularly vulnerable to the effects of anthropogenic activity as they can be impacted at multiple locations, either singularly or cumulatively, along their migratory corridor (Berger, 2004, Moore, 2011).

In breeding grounds, baleen whale distribution is often segregated according to reproductive status. Males and non-reproductive females typically inhabit offshore waters, while maternal females and calves prefer shallow, protected waters around islands or in bays (Rice and Wolman, 1971, Ersts and Rosenbaum, 2003, Elwen and Best, 2004b, Rayment et al., 2015). Energetic benefits are conferred to mothers and calves in coastal waters through various mechanisms, including the minimisation of energy expenditure of calves in calm waters (Taber and Thomas, 1982), minimisation of predation pressure (Ford and Reeves, 2008, Pitman et al., 2014), and avoidance of

harassment by male conspecifics (Craig et al., 2014). However, coastal areas often experience high levels of human activity leading to potential overlap between critical habitat and anthropogenic disturbance. In Hawaiian breeding grounds for example, mother-calf groups have been found to avoid coastal areas with high levels of boat traffic, and use offshore waters instead (Cartwright et al., 2012). This exposes mothers and their calves to males actively seeking mating opportunities and results in a 30% increase in energy costs (Cartwright and Sullivan, 2009a).

For mammals, it has been suggested that behavioural modifications are potentially the most important tactic for minimising additional energy expenditure during reproduction (Gittleman and Thompson, 1988). Marine mammals use several

strategies to conserve energy. For example, lactating elephant seals minimise energy expenditure by sleeping for much of the lactation period and remaining very close to their birthing sites for the entire lactation period (Gittleman and Thompson, 1988). Humpback whales have a series of resting areas located along their migratory corridor (Bannister, 1994, Jenner et al., 2001), where mother-calf pairs spend long periods of time resting in shallow, protected waters on their migration to the feeding grounds. Resting in warm waters allows mothers to conserve energy for lactation and calves to use energy for growth rather than for travel or heat production in cooler waters.

Areas with high levels of anthropogenic activity may disrupt the balance between energy expenditure and energy conservation required by capital breeding marine mammals in their breeding grounds (Braithwaite et al., 2015). For example, animals may change their activity levels or behaviour when exposed to disturbance, such as increasing swimming speeds or exhibiting avoidance behaviours (Corkeron, 1995, Stamation et al., 2009), with mothers and calves being the most sensitive to anthropogenic disturbance (Stamation et al., 2009). Maternal females are

particularly vulnerable to the energetic consequences of disruptions as they must sustain both themselves and their suckling calves with their finite cache of energy

stores. Energy conservation strategies are important during the period of

simultaneous lactation and fasting as they maximise the energy available for transfer to offspring. This is particularly important during the early stages of development when the calves are small and totally dependent on their mother’s energy stores for nutrition (Lindström, 1999).

The results of this thesis highlight the need for monitoring the location and extent of calving areas as baleen whales recover from over-exploitation during the commercial whaling era last century. This is critical for identifying areas where potential conflicts with anthropogenic activity may occur, particularly in popular areas such as

coastlines or coral reefs.