New research co-authored by a Griffith University researcher into the lifespans of baleen whales has yielded boom-or-bust results for two well-known species, with one species’ age estimates almost doubling from what was previously thought and the other drastically reduced due to human-driven impacts.
The international research team have given new lifespan estimates to southern right whales and North Atlantic right whales, both of which are baleen (filter feeding) whales whose previous documented ages were, it turns out, estimated low. Centuries of whaling had killed off old whales, leading to an inaccurate picture of how long these whales could live.
The study, led by Dr Greg Breed from the University of Alaska Fairbanks, with Dr Els Vermeulen of the University of Pretoria and Dr Peter Corkeron from Griffith University, used ongoing 40+-year mark-recapture databases from the thriving southern right whale (SRW) and highly endangered North Atlantic right whale (NARW).
The team found the median lifespan for SRW was 73.4 years, with 10% of individuals surviving past 131.8 years.
NARW lifespans were likely shortened due to human impacts, with a median lifespan of just 22.3 years, and 10% of individuals living past 47.2 years.
The researchers said using the context of extreme longevity recently documented in another whale species, all balaenid and perhaps most great whales had an “unrecognised potential for great longevity that has been masked by the demographic disruptions of industrial whaling”.
Dr Peter Corkeron, an Adjunct Senior Research Fellow at Griffith’s , said this unrecognised longevity had considerable implications for basic biology and conservation of whales.
“Received wisdom is that the longest that right whales live is into their 70s,” Dr Corkeron said.
“This work shows that they can live to about twice that – models estimate that 10% of them live to over 130, and the tail of the best-fit model stretches out to past 150.
“A major reason why scientists haven’t realised how old whales can be is because whaling killed all the old ones long before we could start trying to understand this, and it seems that there may have been, or perhaps still is, an unwillingness to believe that whales could live that long.”
Dr Peter Corkeron
“We have better ways of modelling whales’ ages, combined with populations of whales that are recovering after industrial whaling, so we have far more information to assess how long these whales could live.”
Dr Corkeron and the team also reanalysed the lifespans of female North Atlantic right whales, which he said painted a “very different story” – models estimated that few of these whales now survived past 50 years.
The median longevity for NARW was estimated as being in the early 20s. This means that the lifespan of half all female NARW is about one-third that of half of southern right whales.
“This is down to human-caused deaths – entanglements in fishing gear and being hit by vessels,” Dr Corkeron said.
“North Atlantic right whales used to start calving at 9-10 years and had a calf every 3-4 years. Now most females who start calving do so in their mid-teens, and their calving interval is about 7 years.
“So, females could just produce enough calves to replace themselves when things were going well for North Atlantic right whales.
“Putting these two findings together underlines when we get the biology wrong, it’s harder to get management right.
“In some ways, it’s a tale of how one conservation disaster – whaling – has contributed to our failure to solve another conservation disaster – North Atlantic right whales’ current plight.”
The study was led by the University of Alaska Fairbanks with the University of Pretoria and Griffith University.