FULL REPORT

Marine Mammals









Lead Author: 

Nicole Schumann 1

Co Authors: John. P. Y. Arnould 1, Nick Gales 2 and Robert Harcourt 3

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What is happening?

Substantial evidence that sea surface temperature influences foraging locations and reproductive success of marine mammals. However, studies on long-term effects of warming are rare, with only one study providing evidence that dugongs extend their range in warm years.

What is expected?

Warmer water temperatures are likely to have a profound influence on the distribution of marine mammals; the ranges of species currently associated with tropical and temperate waters are likely to expand southwards.

What we are doing about it?

The Australian Animal Tracking and Monitoring System (AATAMS) is using acoustic technology, satellite tags and biologgers to monitor coastal and oceanic movements of marine mammals. This will elucidate links between climate change in Australia’s coastal seas and the Southern Ocean, and responses of marine mammals.

Summary

Australian waters are home to 52 recognised marine mammal species. Of these, at least seven are listed as threatened, though insufficient information exists on a further 25 to determine conservation status. Foraging locations, foraging behaviour, distribution and reproductive success of several marine mammal species have been linked to climatic factors. Similarly, cetacean and dugong strandings, drowning of seal pups, habitat loss and exposure of coastal species to altered water conditions and disease have followed storms, floods and cyclones.

There is currently a very low to low level of confidence in the predicted effects of climate change on Australian marine mammals. This is due to a distinct lack of information on most species, with almost nothing known of the distributions, population sizes or ecologies of many species, particularly cetaceans. Therefore, the adaptive capacity of Australian marine mammals to climate change is poorly known, though some species, particularly those that occupy near-shore habitats, display high site fidelity and have fractured distributions, may be particularly vulnerable to impacts of climate change. However, there is some evidence that several species may modify their physiological responses to warming temperatures or alter their foraging locations, foraging behaviour or diet in response to shifts in prey availability and distribution. Changes in distribution are likely, as ranges of warm-water species expand to the south, and those of cold-water species contract, though how this will affect community structure and dynamics is unknown. Some species may also be limited by their inability to cross deep, oceanic waters, potentially resulting in extirpations in southern parts of their range. Finally, climatic changes may result in changes in reproductive success, a potential decline in the extent of suitable breeding and feeding habitat, greater exposure of coastal species to pathogens and pollutants, an increased incidence of cetacean and dugong strandings, and changes in habitat quality.

To develop our understanding of potential impacts of climate change on Australian marine mammals, research into population trends and critical habitats, as well as critical habitat dynamics (environmental and biological conditions, and how they change) used for breeding or feeding is required. Greater knowledge of energetics of focal species and the migration distances required to reach key feeding areas would also enable potential effects of climate change-induced shifts in prey abundance to be identified. In addition, our understanding of the cumulative effects of threatening processes, including climate change, on marine mammals is poor. Therefore, to increase the resilience of marine mammals to climate change, non-climatic threats also need to be addressed and, where possible, ameliorated. A key example of how this could be achieved is by strategic protection of critical habitats in Australia where this can be shown to achieve positive conservation outcomes.

Citation: Schumann, N. et al. (2012) Marine Mammals. In Marine Climate Change Impacts and Adaptation Report Card for Australia 2012 (Eds. E.S. Poloczanska, A.J. Hobday and A.J. Richardson) Retrieved from

[Date]

Contact Details: 
1 School of Life and Environmental Sciences, Deakin University, 221 Burwood Hwy, Burwood, VIC 3125, Australia, .(JavaScript must be enabled to view this email address).
2 Australian Antarctic Program, Australian Antarctic Division, 203 Channel Hwy, Kingston, TAS 7050, Australia
3 Graduate School of the Environment, Macquarie University, Sydney NSW 2109, Australia,

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Authors

John Arnould

Arnould

John Arnould has been studying marine mammals and seabirds and their impact on the marine ecosystem, in both temperate and polar regions, for over...
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Nicole Schumann

Schumann photo

Nicole is a vertebrate ecologist who has focused on marine mammals and seabirds, and their role in the marine ecosystem. She completed her...
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Rob Harcourt

Goulds-petrel-chick

Rob Harcourt, Professor of Marine Ecology at Macquarie University is the Facility Leader of the Australian Animal Tagging and Monitoring System, the...
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Nick Gales

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Scientific Review:

Marine mammals are apex predators that occupy all of the world’s oceans. Australia is recognised as a hotspot of marine mammal species richness (Pompa et al. 2011). There are currently 52 recognised marine mammal species around Australia’s coast, including its subantarctic islands, for at least some part of the year. Of these, 44 are cetaceans (whales, dolphins and porpoises: Bannister et al. 1996), six are pinnipeds (seals and sea lions), and one is a sirenian, represented by the dugong Dugong dugon. For some, Australian waters and its offshore islands represent key breeding or feeding habitat (e.g. Gill 2002, Kirkwood et al. 2005), while others occur as rare visitors or periodically haul out on Australian islands (Rounsevell and Eberhard 1980). For the vast majority of Australian marine mammals, however, there is little information on the nature and extent of their use of Australian waters.

According to the IUCN red list (IUCN 2011), at least seven species are considered threatened. Sei Balaenoptera borealis, blue B. musulus and fin whales B. phyysalus, and Australian sea lions Neophoca cinerea are listed as endangered, while sperm whales Physeter macrocephalus and dugongs are classified as vulnerable and Indo-Pacific humpback dolphins Sousa chinensis and Australian snubfin dolphins Orcaella heinsohni are listed as near threatened. However, due to insufficient data, the conservation status of 25 cetacean species is unknown.

The majority of research on Australian marine mammals has necessarily focused on readily accessible species such as seals, coastal dolphin species or whales which appear in seasonally predictable near-shore regions. This report focuses on marine mammal species that occur in waters around mainland Australia and its subantarctic islands (Macquarie, Heard and McDonald Islands), and aims to identify the observed and predicted responses of these to climate change.

Multiple stressors

Non-climatic stressors may act in synergy with climatic impacts to increase the vulnerability of marine mammals to environmental variability and change. However, there is a paucity of data on Australian marine mammals and consequently, the long-term, cumulative impacts of these on marine mammals are not well understood, though strategic amelioration of manageable stressors will increase the resilience of marine mammals to climate change.

Marine mammals are at risk of entanglement or as by-catch in fisheries operations. Australian fur seals Arctocephalus pusillus doriferus, for example, are known to forage from trawlers (Hamer and Goldsworthy 2006), placing them at risk of negative interactions. Australian sea lions and New Zealand fur seals A. forsteri from Kangaroo Island, South Australia, suffer high entanglement rates in marine debris, despite the recent development of government policies designed to reduce entanglement (Page et al. 2004). This frequently results in death of the entangled individual and may be impacting population recovery of Australian sea lions (Page et al. 2004, Goldsworthy and Page 2007). Cetaceans (Kemper et al. 2005) and dugongs (Heinsohn et al. 1976, Marsh et al. 1996) are also extremely vulnerable to entanglement in nets such as gill, shark, anti-predator and fishing nets.

The Southern Ocean ecosystem has been profoundly affected by human harvesting of marine mammals, possibly producing changes in ecosystem structure (Trathan et al. 2007). This has made it difficult to disentangle population responses to climate change from the effects of past exploitation in the region (Trathan et al. 2007). Harvesting of minke B. bonaerensis and fin whales continues under the guise of Japanese scientific whaling. The scarcity of accepted abundance estimates of minke whales makes it impossible to determine the impact of whaling on this species (Leaper and Miller 2011), though it is unlikely that the scale of take would result in measurable population consequences. Current levels of indigenous harvesting of Torres Strait and Cape York dugongs are believed to be unsustainable (Heinsohn et al. 2004, Grech and Marsh 2008).

Marine mammals are known to interact with vessels. Ship strikes cause injury and death to baleen whales (Leaper and Miller 2011) and other marine mammals (Lawler et al. 2007), while boats influence the feeding behaviour of dugongs. Individuals have been shown to cease feeding and move away in response to boats passing within 50 m (Hodgson and Marsh 2007).

Tourist activities may also impact marine mammals. Repeated exposure to boats in bottlenose dolphins in Port Stephens, south-eastern Australia, may prevent dolphins from maintaining large groups (Möller et al. 2002, Steckenreuter et al. 2011, 2012). An increase in vessel-based dolphin watching tours resulted in significant declines in bottlenose dolphins in Shark Bay, Western Australia, presumably due to more sensitive animals moving away from the area of disturbance (Bejder et al. 2006). Likewise, Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Jervis Bay, New South Wales, alter their behaviour to avoid boats (Lemon et al. 2006). Boat disturbance also influences resting and suckling behaviour in Australian fur seals, and causes many to flee into the water. However, this species is known to become habituated to boat-based ecotourism (Back 2010).

Coastal development poses a major threat to inshore dolphins and dugongs. Dredging near ports and at harbour entrances alters coastal habitats, potentially resulting in the degradation or complete removal of seagrass beds and mangrove systems (Bannister et al. 1996). Similarly, land clearing for urban, agricultural and industrial development threatens coastal wetlands and mangrove communities (Hale 1997). These retain sediment and nutrients, and when they are lost, urban discharge and agricultural runoff enter and degrade seagrass habitats (Hale 1997). These act as nursery grounds for fish prey (Bannister et al. 1996, Hale 1997) and provide a major food source for dugongs (Marsh et al. 1982). Thus, cumulative effects of the degradation and loss of coastal habitats may be considerable.

Contaminants from industrial, human and agricultural waste also produce increased inshore nutrient loads. These pose a particular threat to marine mammal species which occupy coastal regions near major contaminant sources, such as coastal industrial centres, through the bio-accumulation of contaminants within the trophic web (Bannister et al. 1996). Indeed, moderate to high levels of heavy metals and/or organochlorines have been recorded in several cetacean species, dugongs and Australian fur seals (Kemper et al. 1994). It is not known how marine mammals are affected by these pollutants but there is some evidence that they increase susceptibility to disease (Kemper et al. 1994). It is also suspected that African bottlenose dolphin Tursiops truncatus calves suffer significant mortality as a result of exposure to organochlorines (Cockcroft et al. 1989). In addition, entanglement in, and ingestion of, plastic debris is a significant problem, causing injury and death to marine mammals throughout the world (Derraik 2002).

Finally, acoustic pollution, including noise from vessels, industry and coastal developments and seismic activity for oil and gas exploration, may affect marine mammals, potentially causing them to abandon key habitats such as migration routes and breeding sites (Bannister et al. 1996). In the Southern Ocean, acoustic disturbance potentially disrupts swimming or feeding activities in whales which use sound for orientation, communication and to locate prey. While this typically occurs seasonally and along discrete shipping routes, data on impacts of noise pollution is lacking (Leaper and Miller 2011).


Observed Impacts:


Temperature

Cetaceans and dugongs

Marine mammals may be influenced by water temperature, through its effects on thermoregulation and biological productivity, as well as by ambient temperature, though it is not always clear which of these are the key influences or whether they operate in tandem. Some species may have a thermal tolerance limit that drives their distribution. For example, adult male bottlenose dolphins T. truncatus in Florida tended to occupy colder waters in summer than other age and sex classes of dolphins. Since adult males have greater difficulty dissipating heat than other dolphin age and sex classes, this tendency to exploit cooler waters is presumably a behavioural means of thermoregulation (Barbieri 2005). Likewise, ocean temperature influences the distribution of dugongs in Shark Bay, Western Australia, and there is evidence that ocean temperatures at the southern extremes of the range are marginal in winter (Marsh et al. 1994). This suggests that the southern distributional limit of dugongs is driven by ocean temperature.


However, the primary climatic influence on many marine mammals appears to be the link between ocean temperature, and food availability and distribution (Neuman 2001, Leaper et al. 2006). Accordingly, sea surface temperature (SST) is commonly used as a proxy for biological productivity (e.g., Bradshaw et al. 2004b). Many marine mammals select particular SST in which to forage. Dolphins at Ningaloo Reef in Western Australia were weakly associated with warmer waters (Sleeman et al. 2007). Similar preferences for warmer waters have been found in the Bay of Plenty, New Zealand, where common dolphins Delphinus delphis are found closer to shore with warmer SST during La Niña years. These dolphins also delayed their autumn movement offshore by approximately a month during greater than average SST, presumably due to shifts in prey distribution (Neuman 2001). Similarly, blue whales in South Australia occupied areas of warmer SST within feeding zones, though SST preferences vary across the species’ geographical range (Gill et al. 2011). They may also feed at depths where sub-surface temperature gradients concentrate biological productivity (Gill et al. 2011).


SST influences marine mammal distribution at a macro-scale. Although data on changes in cetacean distribution are lacking for Australian waters, evidence of distributional shifts in relation to SST has been recorded elsewhere in the world. Increasing SST in north-western Scotland, for example, appear to have led to changes in the cetacean community, with cold-water species declining and warm-water species increasing (MacLeod et al. 2005). The sole study documenting distributional shifts in a marine mammal in Australia was based on observations of dugongs sighted beyond the southern limit of their current accepted range along the coast of New South Wales during warm southerly water temperatures (Allen et al. 2004).


Sea surface temperature may also influence reproductive success, and a strong relationship has been recorded in the calving output of southern right whales and SST deviations, presumably driven by the availability of krill (Leaper et al. 2006). Whales from Argentina produced significantly fewer calves in years when SST was higher in the autumn of the previous year at South Georgia. In the Pacific Ocean, however, the opposite trend was observed and calf output increased with warmer SST anomalies six years earlier (Leaper et al. 2006).


In addition to water temperature, ambient air temperature impacts the distribution of some marine mammal species, particularly through its effects on sea ice extent in the Southern Ocean (Nicol et al. 2008). Several whale species, particularly blue and minke whales, are associated with sea ice in this region during the Austral winter (Nicol et al. 2008). However, over the past 50 years, warming in the Antarctic has resulted in a decrease in the frequency of winters with extensive sea-ice coverage (Loeb et al. 1997). The Antarctic pack ice influences krill abundance and recruitment (Loeb et al. 1997, Trathan et al. 2007, Nicol et al. 2008), and the decline in the frequency of extensive sea-ice has resulted in reduced krill availability (Loeb et al. 1997). Correspondingly, the range of blue whales in the Southern Ocean appears to have contracted to a narrow ring near the pack ice and continental shelf (Nicol et al. 2008).


Pinnipeds (seals and sea lions)

Several studies have documented an effect of warmer water temperatures on foraging areas, breeding success and survival. Southern elephant seals Mirounga leonina from Macquarie Island tended to forage in colder waters and areas with a rapid change in temperature, potentially associated with productive frontal zones (Bradshaw et al. 2004a). This species also responds to warmer SST by increasing diving depth in other parts of the Southern Ocean. Individuals on subantarctic Marion Island, for example, foraged at greater depths in warmer waters, presumably following the vertical distribution of prey, and spent less time at targeted dive depths in warmer water (McIntyre et al. 2011).


The influence of SST on marine mammals is also seen in their reproductive output. Goldsworthy et al. (2007a) reported an inverse relationship between fecundity of Antarctic fur seals A. gazella on Macquarie Island and SST. Fecundity (measured as the proportion of females that produced a pup) was lower when SST in foraging areas was higher 8 – 9 months before the onset of the breeding season, with each 1°C rise in SST resulting in a 10.6% reduction in fecundity. This may be associated with female condition preceding the placental phase of gestation, which determines whether the transition to placental gestation is successful. Likewise, higher SST over a three month period resulted in lower growth rates of pups (Goldsworthy et al. 2007a).


Climatic anomalies also influence the survival of marine mammals. Greater survival of first-year southern elephant seal pups on Macquarie Island has been linked to ENSO (El Niño Southern Oscillation) events and mass at weaning. This is probably related to a greater availability of prey associated with more abundant sea ice during cooler El Niño years, which enables females to better acquire and store resources for the pup. As a result, pups wean at a greater mass and are better equipped for longer foraging trips and deeper dives (McMahon and Burton 2005). Similarly, de Little et al. (2007) observed increased survival in first-year southern elephant seals when the mother’s pre-partum foraging trip occurred during El Niño conditions.


Susceptibility to disease in pinnipeds has previously been associated with greater temperatures in the northern hemisphere. For example, large-scale mortalities of European harbour seals (Phoca vitulina) due to phocine distemper virus (PDV) outbreaks followed higher temperatures, which promoted increased densities of seals on land and the length of time spent on shore. This produced ideal conditions for the spread of PDV (Lavigne and Schmitz 1990).


Fur seals forage in the ocean but breed, give birth and suckle pups on land, and the breeding season is in summer during the hottest time of the year. Increased ambient temperatures may, therefore, have important implications for fur seals during the breeding season. Gentry (1973) reported that New Zealand fur seal bulls whose territories did not include pools of water were forced to temporarily abandon their territories to access water. Similarly, in warmer temperatures, Australian fur seals enter water more frequently for thermoregulation (Willis 2008), whereas in conspecific South African fur seals A. pusillus pusillus in Namibia, heat stress is a significant cause of mortality in newborn pups (De Villiers and Roux 1992).


Extreme events (cyclones, storms and floods)


Cetaceans and dugongs

Cyclones, storms and floods impact marine mammals in a variety of ways. Floods alter water quality and potentially expose marine mammals to novel diseases and/or parasites, whereas cyclones and storms increase the risk of strandings and destroy habitat. During flood events, Indo-Pacific bottlenose dolphins move out of estuaries along the northern coast of New South Wales. These floods have resulted in lower salinity, pH and dissolved oxygen levels, increased turbidity and changes in water temperature in the estuaries. However, dolphins are mostly affected by changes to salinity and/or turbidity which may force prey fish out of the estuaries (Fury and Harrison 2011). Prolonged exposure to low salinity conditions has resulted in the deaths of Indo-Pacific bottlenose dolphins due to osmotic disruption when they have been trapped in reduced salinity environments by receding waters in low tides (Fury and Harrison 2011).


Floods have also been associated with increased risk of exposure to disease through increased freshwater runoff. Inshore species are particularly at risk. For example, Indo-Pacific humpback dolphins Sousa chinensis in coastal waters of the Townsville region were infected with toxoplasmosis (Toxoplasma gondii), a potentially fatal terrestrial parasitic disease, in a year of exceptional rainfall and floods. This may be due to runoff of flood water contaminated with cat faeces or litter carrying T. gondii oocytes (Bowater et al. 2003).


Storms appear to increase the risk of stranding in marine mammals. In the north-east Atlantic, rough seas were thought to contribute to mass strandings of short-finned pilot whales Globicephala macrorhynchus (González et al. 2000), whereas in New Zealand, dusky dolphins Lagenorhynchus obscurus have stranded after stormy conditions (Gaskin 1968). Mass strandings of a range of other cetaceans, including common dolphins, in Japan have been ascribed to dyspnea due to high wave conditions during storms (Honma et al. 1993). Other studies on cetacean strandings in New Zealand have shown some support for storms causing stranding but their results were inconclusive (Brabyn 1991). In Australian waters, at least 27 dugongs were stranded by a storm surge associated with a cyclone in the south-west Gulf of Carpentaria in the Northern Territory. Some dugongs, probably those foraging inshore, were washed up to 9 km inland (Marsh 1989).


Storms also influence habitat quality. In Hervey Bay, Queensland, cyclones and associated flooding have previously caused widespread decimation of seagrass beds upon which dugongs depend. This has resulted in severe crashes of dugong populations and vast numbers of dugongs emigrating from feeding areas (Preen and Marsh 1995). A dramatic increase in the number of dugongs captured in shark nets has also followed cyclones as individuals move greater distances in search for food (Heinsohn and Spain 1974). The low fecundity of dugongs means that recovery of dugong populations is slow (Preen and Marsh 1995), particularly with reduced reproductive output as a result of decreased food availability (Marsh and Kwan 2008).


Pinnipeds

Extreme events also influence seals on land through impacts of storms on pup survival. Storms and high swell are known to wash significant numbers of young Australian fur seal pups into the ocean where many drown (Pemberton and Kirkwood 1994, Arnould and Littnan 2000, Pemberton and Gales 2004).


Ocean currents, winds and circulation.


Cetaceans

Ocean currents and winds have a profound impact on marine mammals. In particular, upwelling systems influence patterns of distribution (Pompa et al. 2011). For example, several marine mammals aggregate in the Bonny Upwelling, a seasonally predictable area of upwelling during summer and autumn (Butler et al. 2002, Nieblas et al. 2009) along the coast of southern Australia between Cape Jaffa, South Australia and Portland, Victoria (Nieblas et al. 2009). This upwelling system is driven primarily by winds (Butler et al. 2002, Nieblas et al. 2009) and is a feeding area for blue whales (Gill 2002). However, a variety of other cetaceans have also been observed in this upwelling zone (Gill 2002, 2004). Similarly, Perth Canyon in Western Australia, also an area of upwelling, is known to be exploited by a range of cetaceans, including blue whales and Australian sea lions (McCauley et al. 2004, Rennie 2005).


Whereas strandings have been associated with short-term storm events, they also demonstrate a cyclic pattern in response to longer-term climatic perturbations (Evans et al. 2005). During years of persistent westerly and southerly winds associated with large-scale sea-level pressure gradients, more strandings of cetaceans, most commonly sperm whales, common dolphins, long-finned pilot whales Globicephala melas, bottlenose dolphins and pygmy right whales Caperea marginata, are known to occur in south-eastern Australia. This is probably due to the wind-driven transport of colder, nutrient-rich water to the southern coast of Australia or more frequent turnover of the water column along the coast, which results in higher coastal productivity. Thus, cetaceans follow their prey northward, resulting in an increased number of cetaceans in the region and, correspondingly, more stranding events (Evans et al. 2005).


Pinnipeds
Pinnipeds are also impacted by ocean currents and winds. The interaction of these influences reproductive output in Australian fur seals. Upwelling along the Bonney coast in summer and winter activity of the South Australian Current appear to positively influence Australian fur seal pup production (Gibbens and Arnould 2009). This also appears to be an important region for other pinnipeds, with the Bonney Upwelling used by New Zealand fur seals (Baylis et al. 2008a, 2008b) and Australian sea lions (Goldsworthy et al. 2007b).

Potential Impacts by the 2030s and 2100s: 


Potential impacts by 2030 (and/or 2100)


Temperature


Cetaceans

Air and water temperature can affect thermoregulation in marine mammals while biological productivity is influenced by water temperature. Projected warmer ocean temperatures are likely to impact marine mammals in a variety of ways, benefiting some species and adversely affecting others. Although species distributions may be influenced by thermal tolerances (Barbieri 2005), it is likely that marine mammals have some capacity to adapt. Bottlenose dolphins in Florida, for example, thermoregulate by seasonally altering the thermal conductance and amount of blubber they retain (Meagher et al. 2008), and by altering blood flow through their dorsal fins (Meagher et al. 2002, Meagher et al. 2008, Barbieri et al. 2010), pectoral flippers and tail flukes (Meagher et al. 2008). Therefore, it is possible that species will be able to alter their thermal tolerances to some extent in the face of climate change.


There is limited information on the distribution and habitat preferences of most marine mammal species and it is, therefore, difficult to predict the effects of climate change on marine mammal range in response to shifts in prey distribution with changing SST. Nonetheless, increasing water temperatures are likely to have a profound influence on the distribution of marine mammals (reviewed in Trathan et al. 2007 and MacLeod 2009). Species ranges in tropical and temperate waters are likely to expand southwards (Lawler et al. 2007, Trathan et al. 2007, Nicol et al. 2008, MacLeod 2009) while species whose ranges are bounded by warm- and cold-water limits are likely to shift to the south (MacLeod 2009). Such distribution changes may result in a loss of diversity in tropical cetacean communities, and an increase in diversity at higher latitudes (Whitehead et al. 2008). By contrast, cold water species are likely to experience southward range contractions and reductions in geographic extent (Lawler et al. 2007, MacLeod 2009). This may pose a serious problem for species restricted to shelf water regions and are unable to cross deep, oceanic waters. Thus, there may besignificant declines or local extinctions in southern areas bounded by deep waters (MacLeod et al. 2005). For some species, in particular southern right whales, it is possible that the migration southward of their southern limit will be greater than that of their northern limits. This may result in longer migrations between feeding and calving grounds (MacLeod 2009).


As species that were previously spatially segregated move into the same areas, community dynamics may change, potentially resulting in increased interspecific interactions (MacLeod et al. 2005, Nicol et al. 2008), competitive exclusion of species from a region (MacLeod et al. 2005), and the establishment of new predator-prey relationships. Although effects of these changes are difficult to predict given the paucity of information on habitat preferences of marine mammals (Nicol et al. 2008), such changes may produce a complete regime shift (Trathan et al. 2007). Distributional changes may also lead to the introduction of pathogens and viruses to previously unexposed populations (Simmonds and Eliot 2009) which may have important implications for survival rates.


Ambient temperatures are likely to have a significant impact on marine mammals, particularly through their effects on sea ice extent in Antarctica. Several cetaceans, such as blue and minke whales, feed near, or within, the Antarctic pack ice in the southern part of their range (Nicol et al. 2008). A decrease in the extent of sea ice with increased air temperatures is likely to have a detrimental impact on these species (Nicol et al. 2008). Blue and fin whales may be particularly vulnerable to changes in prey abundance since high costs of their lunge-feeding behaviour confines them to areas of dense aggregations of krill (Acevedo-Gutiérrez et al. 2002). However, some species show flexibility in their foraging behaviour or choice of prey. For example, blue whales may be able to migrate long distances to exploit new areas during poor conditions (Wiedenmann et al. 2011), and both blue and minke whales, considered Antarctic krill Euphausia superba specialists, also exploit other prey species in years when sea ice extent is low (Nicol et al. 2008), although alternative prey are not at sufficiently high abundances to support populations of these species. Nonetheless, projected temperature increases could influence the reproductive output of marine mammals (Trathan et al. 2007). Modelling of reductions in krill abundance in response to sea ice extent, for example, suggests that birth rates in blue whales may decline with reduced krill availability, slowing recovery of this species (Wiedenmann et al. 2011).


Climate change also has the potential to alter the breeding phenology of marine mammals (Trathan et al. 2007). Critical stages in the life history of animals, such as breeding and weaning, may be timed to match peak abundances of prey. Therefore, changes in conditions that influence prey distribution may result in a lack of temporal and/or spatial synchrony between predator and prey. Species that undertake long migrations between feeding and breeding areas may be particularly susceptible (Simmonds and Eliot 2009). Such mismatches could have important implications for reproductive output and survival.


Pinnipeds

Many species have a preference for particular SST associated with prey distribution, and how they respond to projected SST increases will depend on their capacity for altering their foraging behaviour or diet in response to shifts in prey distribution and availability. The diet of Antarctic fur seals on Heard Island (Green et al. 1997) and Australian fur seals, for example, varies seasonally and inter-annually (Hume et al. 2004, Kirkwood et al. 2008, Arnould et al. 2011), indicating that these species are able to alter their diet in response to prey availability. Similarly, there were strong seasonal differences in the diet of Antarctic fur seals on Heard Island


However, studies on Macquarie Island have shown a reduction in southern elephant seal pup survival during El Niño events (McMahon and Burton 2005) and in fecundity of Antarctic fur seals with warmer SST (Goldsworthy et al. 2007a), indicating warmer temperatures are likely to reduce reproductive success and recruitment of juvenile seals into the breeding population. Further, each 1°C rise in SST coincided with a 10.6% reduction in the proportion of Antarctic fur seal females that pupped on Macquarie Island (Goldsworthy et al. 2007a). Thus, predicted SST increases of up to 2°C within 30 years and 3°C within 100 years could result in a reduction of 21.2% and 31.8% in fecundity, respectively.


Increased air temperatures are also likely to impact pinnipeds. Southern elephant seals in the Antarctic are closely associated with the Antarctic pack ice (Biuw et al. 2010) and may, therefore, be adversely affected by a loss in sea ice extent with warmer air temperatures. However, elephant seals on Marion Island have demonstrated some plasticity in foraging behaviour, diving to greater depths in warmer temperatures following the distribution of prey. Nonetheless, this may incur greater physiological costs which could eventually influence survivorship (McIntyre et al. 2011).


The direct effect of warmer air temperatures on thermoregulation could have important ramifications for fur seals. While hauled out on land, warmer temperatures may result in greater energy expenditure to stay cool (Trathan et al. 2007). With more males temporarily leaving territories to enter water and increased movement of females between land and water in Australian and New Zealand fur seals (Gentry 1973, Willis 2008), there may bechanges in the mating systems of fur seals. However, the impact of such shifts on population viability is unknown. In Scotland, increased mobility of female grey seals Halichoerus grypus to enter water in response to drier conditions, resulted in reduced polygyny as a greater number of males had access to females (Twiss et al. 2007). More time spent in the water may also reduce maternal investment and expose fur seals to greater predation rates (Willis 2008), while warmer air temperatures may expose young pups to heat stress as reported in South African fur seals in Namibia (De Villiers and Roux 1992). Warmer air temperatures, particularly for large seal populations, may also increase susceptibility to disease, promoting more rapid spread of pathogens, as suggested for harbour seals in the northern hemisphere (Lavigne and Schmitz 1990).


Sea- level rise

Predicted sea level rises could have a deleterious effect on species that require coastal bays for breeding, such as humpback whales Megaptera novaeangliae, by reducing the amount of appropriate habitat available (Simmonds and Eliot 2009). A rise in sea level may also reduce the area of habitat that seals use to breed, nurse their pups and rest. Low-lying islands and rock outcrops, for example, are a feature of Australian fur seal (Kirkwood et al. 2005), New Zealand fur seal (Bradshaw et al. 1999, Arnould et al. 2000) and Australian sea lion (Dennis and Shaughnessy 1996), breeding habitat, and many low-lying Australian sea lion in South and Western Australia are likely to be at risk (Goldsworthy et al. 2000). Many colonies are also found in areas where the shoreline is limited by steep, hinterland slopes, with New Zealand fur seal and Australian sea lion colonies frequently abutting cliffs (Dennis and Shaughnessy 1996, Bradshaw et al. 1999). Therefore, sea-level rise could result in reduced, or insufficient, space for breeding. As a result, reproductive output could decline, potentially threatening the viability of these colonies.


Ocean acidification

There is evidence of ocean acidification in the Southern Ocean (Orr et al. 2005) and waters around Australia due to anthropogenic CO2 emissions (e.g., Wei et al. 2009). Although there are no direct links between ocean acidification and marine mammals, coral reefs (Anthony and Marshall 2009) and zooplankton, calcifying organisms such as pteropods are deleteriously affected by ocean acidification (Orr et al. 2005). Hatching success of Antarctic krill Euphausia superba is known to be inhibited in acidic conditions, though it is not known how predicted increases in ocean acidification will affect krill (Kawaguchi et al. 2011). Ocean acidification may also produce distributional shifts in calcifying organisms (Orr et al. 2005), range shifts and population declines in reef fish (Munday et al. 2009), and changes in the abundance of squid. These impacts may have flow-on effects through the trophic web, ultimately indirectly influencing Australian marine mammal predators (Lawler et al. 2007).


Extreme events (cyclones, storms and floods)


Cetaceans and dugongs

Projections of anthropogenic climate change suggest that the intensity of storms and cyclones will increase. Humpback whales in the West Indies (Whitehead and Moore 1982) and southern right whales in southern Australia (Pirzl 2008) prefer calmer waters for breeding, since rough water may be perilous to calves or force them to expend more energy (Whitehead and Moore 1982). Therefore, increased winds and intensity of extreme events predicted for Australia is likely to have a deleterious effect on the reproductive success of these species.


More intense cyclones, and associated rainfall and flooding, may also enhance transport of pathogens and pollutants into coastal waters (Lawler et al. 2007), potentially exposing marine mammals to these contaminants. Coastal species occupying bays and estuaries may be particularly vulnerable to these effects.


In addition, cyclones and storm surges are likely to increase the incidence of stranding marine mammals. As with contaminants, these may pose a particular threat to coastal, shallow-water species, such as some dolphin species and dugongs, since waters inhabited by these species make it impossible to escape physical disturbance by diving (Lawler et al. 2007).


Declines in the abundance and extent of seagrass can be expected under projected climatic changes, particularly in shallow waters, due to the scouring effects of storms (Connelly 2009). This is likely to adversely affect marine mammal species which are associated with seagrass habitats, such as snubfin dolphins in Cleveland Bay, Queensland (Parra 2006). In particular, dugongs are heavily dependent on seagrass beds (Marsh et al. 1982), and the impact of storms on seagrass meadows may, therefore, be detrimental to this species. However, storm-related disturbance may actually favour pioneer seagrass species, which are preferentially consumed by dugongs, thereby potentially counteracting seagrass loss. Nonetheless, if the intensity and/or frequency of cyclones increases and seagrass beds are unable to recover, dugong populations may be vulnerable (Lawler et al. 2007).


Pinnipeds

A significant source of mortality among Australian fur seal pups is the effect of storm surges on waves, which wash pups out to sea (Pemberton and Kirkwood 1994, Arnould and Littnan 2000, Pemberton and Gales 2004). Thus, projected increases in storm intensity may elevate mortality rates of seal pups, resulting in reduced reproductive output. This may also apply to other pinniped species on low-lying colonies.


Ocean currents, winds and circulation

Projected increases in wind strength with climate change may result in enhanced productivity in coastal areas of southern Australia. A concomitant increase in cetacean stranding events (Evans et al. 2005) may occur in this region as cetaceans move inshore to target prey in these productive areas.

Increased wind strength is also likely to benefit species that exploit upwelling areas. In southern Australia, greater winds may enhance upwelling activity leading to higher nutrient levels and greater phytoplankton productivity (Nieblas et al. 2009), with flow-on effects through the trophic web. This is likely to provide a more abundant food source for the cetaceans, fur seals and sea lions known to utilise upwelling zones, particularly along the Bonney Coast.

Pup production in Australian fur seals is influenced in part by upwelling in this region (Gibbens and Arnould 2009). Stronger winds could, therefore, benefit Australian fur seals by enhancing the influx of cooler, upwelled, productive water into Bass Strait. Indeed, Kirkwood et al. (2008) postulated that upwelling waters may bring fish prey of Australian fur seals to surface waters, which are then flushed into Bass Strait within foraging range of seals.

Confidence Assessments

Observed Impacts: 


Amount of Evidence (theory, observations, models)

Sea surface and air temperature: LIMITED – MEDIUM evidence
There is substantial evidence that SST influences foraging locations and reproductive parameters of marine mammals. However, data are lacking on potential effects of SST on distribution, with only one study providing some qualitative evidence that marine mammals (dugongs) may extend their range in years of warmer ocean temperatures (Allen et al. 2004) and a single study indicating range contractions (in blue whales) due to the indirect effects of greater air temperatures on sea ice extent (Nicol et al. 2008). Similarly, there are few studies on the effects of air temperature on fur seal behaviour and on the invasion of pathogens in pinniped populations, with information on the latter based on populations in the northern hemisphere.

Extreme events (cyclones, flood, storms): LIMITED – MEDIUM evidence

Several studies have provided data on the effects of cyclones, storms or floods on marine mammals. Changes to coastal water quality due to flooding is based on a single study (Fury and Harrison 2011), whereas toxoplasmosis in dolphins could not be conclusively attributed to flooding (Bowater et al. 2003). Similarly, information on the impact of storms and cyclones on cetacean strandings is largely anecdotal, with no definitive links and based mainly on observations outside of Australian waters. However, there is strong empirical evidence for the influence of extreme events on dugong strandings (Marsh 1989) and on seal pup mortality in storms (Pemberton and Kirkwood 1994, Arnould and Littnan 2000, Pemberton and Gales 2004).


Ocean currents, winds and circulation: LIMITED evidence
There is strong evidence of the importance of upwelling to a variety of marine mammal species. However, in Australia, this is based on few studies in two regions, and only one published study (Gibbens and Arnould 2009) reported on the effects of upwelling on reproductive parameters. A single study (Evans et al. 2005) has investigated links between wind-driven, nutrient-rich ocean currents on cetacean strandings.


Degree of Consensus (high level of statistical agreement, model confidence)
Sea surface and air temperature: MEDIUM consensus

There is medium consensus that SST and air temperature affects foraging locations, distribution and reproductive success of marine mammals, with many species adversely affected by warmer temperatures. However, there are regional differences; some studies have demonstrated a preference for warmer waters (dolphins in subtropical waters (Sleeman et al. 2007), and blue whales in temperate Australia (Gill et al. 2011)) and a single study suggested that increased water temperatures allow dugongs to expand their foraging ranges southwards (Allen et al. 2004). There are few studies on effects of air temperature on fur seals.

Extreme events (cyclones, flood, storms): MEDIUM consensus

There has been medium consensus among studies that investigated effects of extreme events on marine mammals. However, more studies on the effects of extreme events on marine mammal strandings using robust, scientific techniques are needed to determine the level of consensus with more confidence.


Ocean currents, winds and circulation: MEDIUM consensus
There is medium agreement among studies that marine mammals preferentially forage or are positively influenced by upwelling regions and frontal systems. However, information is scarce.

Confidence Level
An overall confidence rating for each climatic influence on marine mammals is provided in Table 1.


Table 1. Confidence assessments for observed impacts of climate change on Australian marine mammals.

Potential Impacts by the 2030s and 2100s: 


Confidence Assessment: Projected Impacts

Amount of Evidence (theory, observations, models)


Sea and air temperature: LIMITED
Evidence of associations of marine mammals with SST and on the ability for dolphins to thermoregulate in different SST is relatively robust. However, while some predictions are based on observed changes to foraging behaviour, most rely heavily on assumptions and do not focus specifically on Australian waters. In particular, whereas many predictions of changes in distribution are based on current ranges, information on distribution and key habitats used by marine mammals is scarce for all but a few resident, or temporally and spatially predictable, species in near-shore areas. Therefore, potential effects on community dynamics are based on few data. Evidence of effects of increased SST on reproductive output is based on a few studies only (McMahon and Burton 2005, Goldsworthy et al. 2007a) and information on heat stress in fur seal pups is based solely on an overseas study on conspecifics (De Villiers and Roux 1992). Potential for increased susceptibility of pinnipeds to disease is based on correlations in the northern hemisphere only. For other impacts, no direct, published evidence currently exists. In addition, the degree to which species will adapt to environmental change is unknown.

Sea level rise: LIMITED

Direct evidence does not yet exist.


Ocean acidification: LIMITED
No direct links between marine mammals and ocean acidification have been made.

Extreme events (cyclones, storms, floods): LIMITED

Information on preferences of humpback and southern right whales for calmer waters during breeding was provided by only two studies (Whitehead and Moore 1982, Pirzl 2008), and one of these was based on whales in the West Indies (Whitehead and Moore 1982). Similarly, a single study (Lawler et al. 2007) provided information on potential effects of floods on exposure of coastal species to pathogens and pollutants. Projected effects of storms on cetacean strandings are based on previous anecdotal observations only. By contrast, there is relatively strong evidence of effects of storms on dugongs based on previous records during extreme events and on drowning of seal pups with storms. However, data for most species are lacking.


Ocean currents, winds and circulation: LIMITED
Direct evidence is lacking, with information based on observations of species associations with upwelling areas.

Degree of Consensus (high level of statistical agreement, model confidence)

Sea and air temperature: LOW
There is some agreement in the type and direction of distributional shifts and high agreement among studies in the reproductive success of marine mammals with increased SST. However, information on future responses is based on few studies and is sparse for the majority of species. It is, therefore, difficult to assign a level of consensus.

Sea-level rise: LOW
Direct evidence does not yet exist.


Ocean acidification: LOW
There is no direct evidence of effects of ocean acidification on marine mammals.

Extreme events (cyclones, storms, floods): LOW – MEDIUM

There is high agreement between studies on the impacts of cyclones and storms on dugongs and several studies have commented on effects of storm surges on seal pup mortality. However, data are scant for most species.


Ocean currents, winds and circulation: LOW
There is reasonable agreement among studies that cetaceans and seals exploit upwelling areas. However, there is insufficient information on potential effects of increased upwelling due to greater winds to assign a level of consensus between studies.

Confidence Level

Table 2. Confidence assessments for projected impacts of climate change on Australian marine mammals.


Adaptation Responses

The various Australian marine mammal species are unlikely to be equally vulnerable to the effects of climate change. Cosmopolitan species that use multiple habitats and have diverse diets, such as some dolphin species, are likely to be more resilient to effects of climate change than species with fractured distributions that are restricted to near-shore waters and display high site fidelity (Lawler et al. 2007), such as Australian snubfin and Indo-Pacific humpback dolphins (Parra et al. 2006), and Australian sea lions (Gales et al. 1994, Campbell et al. 2008). The capacity of marine mammals to adapt to environmental change depends, in part, on their ability to alter their foraging behaviour and diet. Changes in prey distribution may not be important for baleen whales, which are able to travel large distances in search of prey (Nicol et al. 2008, Wiedenmann et al. 2011), and several species exploit different food resources according to availability (Hume et al. 2004, Nicol et al. 2008). Similarly, southern elephant seals in the Antarctic alter their dive patterns in response to warmer SST (Biuw et al. 2010) while the diet of Australian (Hume et al. 2004, Kirkwood et al. 2008, Arnould et al. 2011) and Antarctic fur seals (Green et al. 1997) varies among seasons and years, suggesting that they are able to alter their diet according to prey availability.

However, effects of climate changes on marine mammals do not act in isolation, and other threatening processes may elevate any adverse effects of climate change on marine mammals. Although our understanding of the cumulative effect of multiple threats, including climate change, is poor, strategic amelioration of manageable threats will almost certainly add resilience to species most vulnerable to climate change. However, the development and implementation of appropriate policies designed to protect and assist marine mammals to adapt to changing environmental conditions are hampered by a lack of knowledge. Therefore, information on trends in abundance, general ecology and conservation status is required for many marine mammals, particularly cetaceans. Key habitat also needs to be identified. This requires research into the locations, temporal use (both seasonal and daily) and physical characteristics of critical habitats used by marine mammals. Critical habitats are defined here, as those that are used for key life history events including breeding, giving birth, nursing young and migrating between feeding and breeding grounds, as well as important feeding areas.

Threats to marine mammals should be ranked and the most significant ones prioritised, focusing on manageable threats at the population level that lead directly to conservation gains. Critical habitats should be strategically managed for the protection of marine mammal populations, with an emphasis on maintaining high quality habitat. Protection could be achieved by managing levels of disturbance and by preserving key habitat elements, such as seagrass beds, coastal embayments, and pinniped colonies, and their surrounding waters.

This could be addressed in a number of ways, including:
• Developing fisheries legislation to regulate the scale and temporal occurrence of fisheries activities in key habitats.
• Establishing no-take zones in critical habitats where fishing activities and harvesting of marine mammals, including indigenous harvesting of dugongs, are prohibited. The latter could be managed under a voluntary suspension of hunting scheme.
• Establishing oil and gas legislation to control seismic activity, as well as legislation to manage other sources of noise, such as industry and port development (e.g., pile driving, dredging, blasting), in key areas.
• Developing policies for better sewage and waste disposal to reduce the influx of chemicals into coastal habitats.
• Developing improved land management practices to reduce chemical inputs into bays and estuaries.
• Establishing control programs for introduced species that may be vectors of novel diseases in coastal areas (e.g., feral cats, rodents).
• Protecting coastal ecosystems such as saltmarsh, wetland and mangrove systems to ensure that vital ecosystem processes are maintained to preserve water quality.
• Developing legislation to control the number of vessels that enter key habitats and their operation (e.g., speed, proximity to marine mammals)
• Establishing new, and expanding the extent of existing, marine protected areas around Australia that cover critical habitats for marine mammals

There is some scope for flexibility in the temporal designation of protected areas. It would be feasible, for example, to relax the protected status of areas of critical habitat during seasons when key marine mammals are absent. For example, fishing and vessel use are permitted in the Marine Mammal Protection Zone of the Great Australian Bight Marine Park between 1 November and 30 April (Natural Heritage Trust (Australia)/Director of National Parks 2005).

Current and planned research effort
The potential impact of increased storm surges and sea-level rise on Australian fur seal colonies is currently being modelled as part of a NARP (National Climate Change Adaptation Research Plan) program (Fisheries Research and Development Corporation). As part of this, research on available time series data investigating the relationships between foraging ecology and reproductive success of pinnipeds, and SST and ocean circulation is currently being undertaken.

The Fisheries Research and Development Corporation, and Department of Climate Change and Energy Efficiency, are currently investigating human adaptation response options to assist marine mammals vulnerable to climate change buffer climate change. This project aims to develop knowledge on effects of climate change on species, and develop adaptation options and monitoring guidelines in association with responsible management agencies.


Observations and Modelling

Observation Programmes

ClimateWatch (http://www.climatewatch.org.au), the national system for public recording of distribution of Australian species, has recently incorporated marine mammals (whales) to its scheme. This provides scope for the public to report their observations of whales in Australia. Such information will enable changes in the spatial and temporal distribution of species to be monitored, thereby improving our knowledge of effects of climate change on some whale species.

RedMap (http://www.redmap.org.au) is a similar, community-based initiative based in Tasmanian waters. This allows the public to log sightings of marine species and has already documented evidence of distribution changes in prey species of marine mammals.

The Integrated Marine Observing System (http://www.imos.org.au) includes the Australian Animal Tracking and Monitoring System (AATAMS), which is a sustained observing system designed to observe movements and foraging activity of higher predators in relation to oceanographic variables. AATAMS uses acoustic technology, satellite trackers and biologgers to monitor coastal and oceanic movements of marine animals including elephant seals and Weddell seals Leptonychotes weddellii in the Southern Ocean and sea lions in the Great Australian Bight. This information will be used to elucidate links between changes induced by climate change in Australia’s coastal seas and the Southern Ocean, and responses of higher predators including marine mammals.

Further Information

ClimateWatch (http://www.climatewatch.org.au) provides information on the effect of climate change on Australian species, including marine mammals. The public can register to record their observations.


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