Lost leviathans: Hunting the world's missing whales
Posted: 02-09-2010

Lost leviathans: Hunting the world's missing whales

09 February 2010 by Fred Pearce
Magazine issue 2746. NewScientist

THEY are enigmatic sea monsters - rare, magnificent beasts patrolling the ocean depths. Yet old chronicles tell of populations of whales hundreds of times greater than today. Such tales have long been dismissed as exaggerations, but could they be true? Have humans killed such a staggering number of whales?

New genetic techniques for analysing whale populations, alongside a growing archive of fresh historical analysis, suggest so. Taken together, they indicate that we have got our ideas about marine ecology completely upside down: whales may once have been the dominant species in the world's oceans.

This is not simply an academic question. It matters now more than ever before. Whale numbers have been recovering slowly since the end of large-scale hunting in 1986, but this global moratorium is only temporary. The International Whaling Commission, the club of mostly former whaling nations which maintains the ban, has rules that say it can reconsider hunting a given whale species if its population climbs back to more than 54 per cent of its pre-hunting levels. Right now, according to IWC estimates, Atlantic humpbacks and Pacific minkes may have recovered sufficiently to put them back in whalers' sights. But, crucially, such decisions rest on the veracity of the IWC's estimates of historical whale populations - 54 per cent of what, exactly? If the old salts' tales of whale abundance are true, it is way too early to be dusting off those harpoons.

Human pressure on whale stocks "was much earlier, much larger and much more significant than previously thought", environmental historian Poul Holm of the University of Dublin, Ireland, told a meeting of the Census on Marine Life (CML) project in 2009.

Most estimates of how many whales were present in the oceans before hunting began come from population modellers, many of them working for the IWC. These estimates are mostly based on combining the size of current populations with numbers caught in the past, as recorded in the logbooks of whalers. There are other ways to calculate historical whale numbers, though.

So far, genetic evidence has received the most attention, in particular the publication of a controversial study in 2003 by Stephen Palumbi and Joe Roman of Stanford University's Hopkins Marine Station. This study's high numbers appeared to blow IWC historical estimates out of the water, particularly for humpback whales (Science, vol 301, p 508).

The pair had investigated whales for signs of genetic variation. Geneticists claim to be able to use this to estimate the size of the population in the past since large populations tend to accumulate diversity through random DNA mutations and breeding, while small populations lose it through inbreeding. The results were dramatic.

Resume the hunt

The IWC believed that before large-scale whaling began, the North Atlantic was home to about 20,000 humpback whales. With a current population of about 10,000 and rising, this meant that under the 54-per-cent rule hunting could soon resume. But Roman and Palumbi estimated the pre-exploitation population was more than 20 times as great, at 240,000. Globally, they suggested, there may have once been 1.5 million humpbacks, rather than the 100,000 estimated by the IWC.

Unsurprisingly, Palumbi got a hostile reception when he presented these figures to the IWC in 2004, and the numbers remain controversial. One leading expert, on condition of anonymity, told New Scientist that the estimates were "ridiculous" and privately accused Palumbi of being "more interested in getting papers into Nature and Science than in getting it right".

There are problems with the analysis. It assumes that the particular whale population under scrutiny never bred with others. Critics point out that the now-distinct humpback populations of the North and South Atlantic may well have once done just that. It could be that Roman and Palumbi have inadvertently estimated the entire Atlantic humpback population, or even the global population rather than that in just the North Atlantic.

Palumbi and Roman are not alone, however. Charles Scott Baker, a conservation geneticist at Oregon State University in Newport, has used DNA analysis to investigate minke whales. IWC estimates put their number today near their historical levels of around 600,000 globally. But Scott Baker reckons that as recently as 300 years ago there were probably close to 1.5 million of them. That suggests its recovery is still at an early stage.

Can these conflicting numbers be reconciled? Historical abundance is estimated using a combination of the current population and the total historical catch. The problem is that nobody can be sure how many whales were taken in the past. Some estimate that the total catch for the 20th century was about 4 million. But official whaling records are incomplete, especially post-war logs.

The most dramatic revelations have come from the archives of the former Soviet Union, which carried out massive illegal harvesting of whales - especially in the 1950s and 1960s - while sending false logbook records to the IWC. Memoirs of Russian whaling inspectors published in the past two years reveal that from 1959 to 1961, Soviet whaling fleets killed 25,000 humpback whales in the Southern Ocean, while reporting a catch of just 2710. This continued well into the 1970s according to new revelations at an IWC conference in 2009 by one of the original whistle-blowers, Yuri Mikhalev of the South Ukrainian Pedagogical University in Odessa, Ukraine.

Earlier records, where they exist, may be more reliable. Tim Smith, who heads the World Whaling History project, says that "the keepers of logbooks [in the 19th century] had no incentive and little latitude to under-report catches". Even so, there may still be huge gaps in the data used by today's modellers. British whaling records were often dramatically incomplete, for example. Jennifer Jackson of Oregon State University in Newport has studied right whales off New Zealand, which were heavily hunted in both the 19th and 20th centuries. She discovered that British whalers took an estimated 10,000 whales in the South Pacific that had simply not been included in previous catch estimates.

But even after such data gaps are accounted for, the numbers still cannot be reconciled. So what else may have been going on?

Roman points out that whalers' logbooks, even if scrupulously kept, only report some of the killings. For one thing, many whales are killed but never landed. Population modellers have traditionally added a few percentage points to allow for this, but many believe that only a minority of the whales attacked by vessels were killed, landed and logged - a large number escaped their hunters to die later from harpoon injuries. Others died in fishing nets, were struck by ships or used as target practice by naval vessels, says Roman.

A large number of whales escaped the hunters to die later from harpoon injuries
Ancient hunters

There is also growing evidence of massive damage to whale populations inflicted by humans long before the industrial era of explosive harpoons and factory ships. Some 70,000 records of whale catches and sightings assembled by the History of Marine Animal Populations project, part of the CML, suggest the impact of pre-industrialised hunting on whale stocks was much greater than previously assumed.

Basque and Japanese fishermen were catching right whales 1000 years ago. And for centuries, many other island and coastal communities have harvested the creatures. Whaling was the first global industry, says marine biologist Callum Roberts of York University in the UK. Whalers were hunting deep in Arctic waters long before explorers showed up. When Darwin reached the Galapagos Islands in 1835, they were already overrun with American vessels pursuing sperm whales.

According to Robert Allen of the University of Oxford, it now appears that many whale populations in the northern hemisphere were ravaged in the 17th and 18th centuries by whalers employing hand-held harpoons and sheer manpower. Back then, whales were essentially "floating oil wells", providing oil for candles, street lamps and machinery, as well as ingredients for perfumes, plus bones for everything from corsets to fishing rods.

Whales were 'floating oil wells', providing oil for candles, street lamps and machinery
The downfall of the Arctic bowhead whale is the best documented. Thousands of Dutch whaling ships headed into the Arctic in the 17th and 18th centuries to catch bowheads off Spitsbergen, until the population collapsed. Whaling then moved to the waters off Greenland where a frenzied hunt soon wiped out what had been the biggest whaling ground in the world. Today there are only about 1000 bowheads swimming west of Greenland - and none at all between Greenland and Spitsbergen, says Allen.

The emerging history of pre-industrial whaling, and what it suggests about past whale numbers, raises some important questions. Not just about the wisdom of a return to commercial whaling, but also about ocean life in general. Jeremy Jackson of the Scripps Institution of Oceanography in San Diego says the hunting of whales has fundamentally reorganised ocean ecosystems. Today, ocean biomass is dominated by small creatures. But he says this "trophic pyramid", with only a tiny tip of large creatures, may not be natural. Before we intervened, he says, the pyramid was probably the other way up, with large beasts dominating the biomass.

Keeping these big beasts fed would be possible if the turnover of their smaller prey species was fast enough to ensure that fresh food was constantly being produced. And rather than devouring an ecosystem, a greater number of whales might help feed it: when a whale dies, its carcass sinks to the seabed where it could feed a local population of scavenging species for up to 80 years. Peter Karieva, chief scientist at conservation charity The Nature Conservancy in Seattle, Washington, says there is evidence that the decline of sperm whales in the tropical Pacific has moved the entire ecosystem towards domination by species like squid. We don't know what was lost with the whales - or what else might reappear if their numbers soared.

All this new research is putting the scientific credibility of the IWC under increasingly scrutiny. Some hope that the issues might be resolved at the IWC's annual meeting in Agadir, Morocco, in June this year. Don't hold your breath: "The discrepancies are unlikely to be resolved in the scientific committee of the IWC," says IWC scientist Sidney Holt.

Until now, says Jeremy Jackson, the widespread anecdotal evidence of huge numbers of whales and other large animals on the planet has been systematically downgraded by scientists simply because it cannot be proved. He calls the process "scary, unbridled anti-historical determinism". The result, he says, is that "we deny the once-great existence of anything we killed more than a century ago".

The new ecological perspective on the past abundance of whales is, like Palumbi's work, controversial. Nevertheless, the ever-growing body of historical evidence is siding with the DNA. It suggests that even the most "recovered" of today's whale populations are mere ghostly reminders of their former dominance.

The whale's past may be shrouded in mist, but one thing's for sure - their future is in our hands.
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