Blaming whales for declining penguin populations?

Some of my colleagues are going to accuse me of going off on one with this, and for it being 'too scientific', but I am peeved at an article I read this morning and needed to get some comments off my chest. It's in the vein of my last entry on the way science is presented, so you could say that it's at least following a theme.

Headlines can be deceptive and misleading and I have to take issue with the National Geographic’s headline -  ‘Penguin Numbers Plummeting—Whales Partly to Blame?

The article states that ‘Penguin populations have plunged by as much as 50 percent during the past three decades in the West Antarctic Peninsula and Scotia Sea, scientists report.’ The article goes onto say that the report the article is based on, in Proceedings of the National Academy of Sciences states that ‘The problem appears to be a shortage of krill, the seabirds' primary fare, caused by rising regional air temperatures and rebounding populations of hungry whales.’ But hold your horses. It seems that penguins only started eating krill when the ecosystem was changed by human impacts.

It appears that the seabirds abandoned their 38,000-year diet of fish in favour of krill, shrimp-like crustaceans that are a major component in the diets of fur seals and baleen whales only when the krill became available because whaling and sealing wiped out huge numbers of marine mammals.

When discussing whales the original paper references ‘Reilly, S., Hedley, S.L., Borberg, J., Hewitt, R., Thiele, D., Watkins, J., Naganobu, M. 2004. Biomass and energy transfer to baleen whales in the South Atlantic sector of the Southern Ocean. Deep Sea Research II 51, 1397-1409’  which states that the amount of krill consumed by whales estimated from a 2000 Antarctic survey amounted to some ‘4–6% of the estimated krill biomass in the region (and probably less than this percentage of the total annual krill production).’

The Reilly et al. paper does not appear to set out to blame whales for low krill population numbers but indeed, seems to say that any future krill fishery should be managed so as to allow for recovery of whales, - it states in the abstract that, ‘the depleted numbers of baleen whales resulting from past or current whaling activities should be taken into account when setting quotas for the commercial exploitation of krill if there is to be a recovery to pre-exploitation biomass levels of baleen whales’

An earlier article in National Geographic (2007) supports the theory that Antarctic sealing and whaling led to a krill population explosion, and that the penguins apparently took advantage of the surplus. But now the krill has seen a decline in the last 30 years, but a corresponding increased percentage of fish are not appearing in the penguins diet

The report does later on note that, ‘fish stocks have also been heavily fished out by Russian trawlers’ and so denying the penguins their food of choice. The report also notes that krill fishing is increasing. The earlier 2007 National Geographic story fully acknowledges that overfishing is a negative impactor. In this report researchers are noted to say, ‘"And now with krill on a decline and fish harvested out in a lot of areas … that's a concern…. What do [the penguins] have left to switch to? They don't really have any options left…. In addition, fishers are now actively taking krill, which are used as feed in fish farms. This "will further cause problems,"’ One other note of concern is that the Academy of Sciences paper reports that, ‘In addition, the Marine Stewardship Council’s recent certification of one company’s krill fishing as being sustainable* and the introduction of new products (e.g., Omega-3 krill oil, a popular dietary supplement) suggest that the [krill] fishery may be poised to expand further in the near future.'

Reading the original paper in in Proceedings of the National Academy of Sciences we see that it states that, ‘The West Antarctic Peninsula (WAP) and adjacent Scotia Sea support abundant wildlife populations, many of which were nearly extirpated by humans. This region is also among the fastest- warming areas on the planet, with 5–6 °C increases in mean winter air temperatures and associated decreases in winter sea-ice cover. These biological and physical perturbations have affected the ecosystem profoundly.’

The abstract concludes that, ‘Linking trends in penguin abundance with trends in krill biomass explains why populations of Adélie and chinstrap penguins increased after competitors (fur seals, baleen whales, and some fishes) were nearly extirpated in the 19th to mid-20th centuries and currently are decreasing in response to climate change.'

So whilst the Academy of Sciences paper tests the hypothesis that the reduction of whaling is removing fewer whales from the Antarctic ecosystem and they are eating more krill, the significant conclusion is that the major impact on the penguins is ... yes you guessed it...climate change.

I suggest we should all be wary of extracting the comments from papers, in this case about whales being ‘partly to blame?’, and therefore giving overdue inference to just one element of a complex issue. There are enough people willing to abuse the science without respected journals helping them with juicy spin.