As global warming wreaks havoc on the oceans, marine ecosystems are increasingly under threat, writes Samantha Trenoweth.
It is late-June in Byron Bay, and unseasonably warm. From the lighthouse, tourists watch humpback whales swim north on their annual migration. One of the giants crests and rolls, and blows a fountain of sparkling vapour skywards. On the rocky precipice, the onlookers gasp, but none of them notices whether the whales are passing by earlier or later than they did last year, or whether they’ve returned from their Antarctic feeding grounds replete or undernourished.
Climate Change is no longer a nebulous future threat. It has become a present day reality and, while a great deal of discussion has taken place about the role of the oceans in regulating the earth’s climate, not enough research has yet been done into the impacts of climate change on marine ecosystems and their inhabitants, including marine mammals.
Studies by teams of scientists at the University of St Andrews in Scotland and at Murdoch University in Western Australia have added to the global body of work indicating that cetaceans may already be experiencing significant effects.
The Saint Andrews team, which worked in conjunction with the Mingan Island Cetacean Study in Canada, observed the migration patterns of humpback whales over a period of 27 years, between 1984 and 2010. The study found that, as the ocean water warmed, the whales arrived at their feeding grounds, on average, one day earlier each year. So, over the length of the study, the whale migration shifted its timing by a month.
Dr Christian Ramp, one of the study’s authors, is concerned that it may not be possible for the whales to adapt to changing ocean temperatures indefinitely.
“The continuing rise in ocean temperatures,” he explains, “could eventually cause problems for long-distance migrating humpback whales in terms of timing their arrival in the feeding grounds with the occurrence of their main prey… The sheer pace of the adaptations by baleen whales leads to questions such as how much further can they push it?”
Dr Nahiid Stephens, a veterinary pathologist from Murdoch University, agrees that climate change, warming oceans and changing currents, among other issues, are going to have an enormous effect on migration patterns.
“Most species of whales, dolphins and porpoises have temperature-linked home ranges,” she explains. “So we’re likely to see significant impacts, such as loss of habitat, changes in prey availability and increased competition, as different species expand or alter their range. This could have a detrimental effect on nutrition and reproductive success.”
“Catastrophic weather events are predicted to increase in frequency and severity as a result of climate change.”—Dr Nahiid Stephens, Murdoch University
Dr Stephens and colleagues, including Dr Carly Holyoake, also from Murdoch, and Douglas Coughran, from the Department of National Parks and Wildlife, WA, have also been observing humpback whales. Following an unprecedented number of whale strandings, back in 2008 they began looking into whale health and causes of mortality.
“Just to paint the picture,” Dr Stephens begins, “between 1989 and 2007, the mean number of humpback whale strandings on the WA coast was between two and three animals per year. Then, in 2008, we had 13 strandings; in 2009 we had 46; in 2010 we had 16. These anomalous spikes led to our investigation in 2011, during which there were
The researchers noticed a few interesting features that were common to many of the strandings. Firstly, the majority of these whales did not die as a result of common human impact activities, like line entanglements and ship strikes.
Secondly, says Dr Stephens, “in 2011 the 17 strandings comprised 14 calves and three juveniles. We saw a lot more neonates than we had in previous years and most of these animals were less than 48 hours old.”
Finally, these animals were not where they should have been. “All the strandings occurred at least 1000 kms south of the whales’ known breeding ground. The humpbacks we were studying head south by October to spend their summers in Antarctica, where they feed on krill, and then they migrate north by May, towards the Kimberley breeding grounds, where they calve. So we were seeing these whales way too far south with their babies.”
A number of theories were proposed as to why the neonatal whales were so far from their breeding ground and why the young calves died.
“Could it be,” Dr Stephens asks, “that we were seeing calving occurring in unsuitable areas, outside known breeding grounds, because of changed environmental conditions? Were the mothers in a malnourished state and therefore giving birth to malnourished, non-viable calves? We managed to post-mortem three of the stranded neonates and two of them were found to be in an extremely malnourished state.”
Do these whale strandings confirm Dr Ramp’s fears that, as krill populations are affected by sea ice melt and migration patterns shift with changing ocean currents and temperatures, whales may not be able to adapt indefinitely?
Dr Stephens cautions against jumping to conclusions and admits that her team’s report “raised a lot more questions than answers”. There are questions to be asked about coastal species, like dugongs and river dolphins, too.
“Catastrophic weather events are predicted to increase in frequency and severity as a result of climate change, so we’re likely to see a higher risk for coastal species strandings,” she suggests. “Floods, cyclones and heavy rainfall can kill seagrass beds, on which dugongs rely. We could lose a lot of topsoil around estuarine and coastal areas and therefore see higher concentrations of heavy metals and organic compounds in waterways and in the food chain. These could have damaging effects on things like immune function and reproductive success.”
What is needed now, Drs Ramp and Stephens agree, is a global, inter-disciplinary effort to further study the impacts of climate change on marine mammals. Ramp is calling for studies to investigate the effects of climate change on population dynamics and health. Stephens suggests a ‘One Health’ approach.
“Climate change is a wicked problem and it will require a concerted team effort to understand and rectify it,” she says. “It’s a good example of a problem best tackled with a ‘One Health’ approach, recognising the connections between human health, animal health and the environment. Veterinarians have a significant role to play, and we can’t work in isolation any more.”
Aside from active research, she suggests that vets could join citizen science programs, like Coastal Walkabout and Dolphin Watch in WA, where their training and observation would be invaluable. She also recommends volunteering to help with marine mammal stranding responses. The rescue organisation, ORRCA, trains volunteers at various experience levels.
“Finally,” Dr Stephens adds, “vets are members of the public. We can contact our local MPs and remind them of the importance of taking effective action to address climate change. Vets are charged with protecting animal health and welfare, preventing and relieving animal suffering and the promotion of public health. Climate change may have a negative impact on all those things and, I believe, veterinarians have an important role to play.”