Guest Post by Jit
The following was a recent comment posted at my Birdageddon article. It is reproduced here in full, since it serves as a worthy article in its own right.
The story goes like this. Puffins are stubby little cute things. They eat tiny fish called sand eels. The eels are declining owing to climate change. Climate is changing because human civilisation is emitting more CO2 than the Earth can handle. Because of this, we’re really worried about the puffins and we have to change our ways.
Of course you would not be surprised to find that there is more to this than meets the eye. It is probably true that should sand eels decline for any reason, then puffins will suffer. (Puffins do not always major on sand eels, and this varies by location and time of the year.) The puffin is an iconic bird. It’s one of three on the cover of my copy of Peterson (the other two are a hoopoe and a lapwing).
The first question I suppose is, are sand eels threatened by climate change? JNCC thinks so, & they are not alone. [Note: puffins are also said to be at threat from increased storminess; a “wreck” a few years back was blamed on climate change. Nevertheless, there is a long history of wrecks; but I can’t definitively say that climate change won’t cause more storminess.]
In another thread, Vinnie Burgoo mentioned a paper by Wanless in 2004. (For someone I presume is not an ecologist to pluck a memory of this paper out of the ether is impressive.) My memory of Wanless et al 2004 is that it made quite a stir at the time, and that I didn’t believe the results (my memory may be faulty; I certainly didn’t believe the results). Wanless et al measured the lengths of innumerable sand eels at a sand bank call Wee Bankie off the Firth of Forth (relevant to foraging by the Isle of May puffin colony). They had data from ’73 to ’02, and over that time the average length of a sand eel had declined by 20%. In terms of mass and therefore nutritive quality for a chick, this decline was larger.
A fishery started in the area in 1990 and persisted until 2000, when it was curtailed over fears for the puffins. But according to Wanless et al, this was not the cause of the decline, which was more likely due to environmental factors. To give them credit, Wanless et al did not pin the blame directly on warmer water, as has been done since. Indeed they mentioned that sand eels might shrink if the water was too warm or too cold.
Simply increasing temperature could not by itself shrink the sand eels. Fish are dependent on the temperature of the water for activity and metabolic levels. If the water gets a little warmer, sand eels grow faster, not slower… so long as there is enough prey to go around.
So now we have to rewind to Fromentin & Planque 1996 where it was noted that one of the key prey items of the sand eel is affected by the North Atlantic Oscillation. This beast is a planktonic copepod called Calanus. There are two very similar species in the North Sea (I think there is a third species found further north). Calanus finmarchicus is more abundant when the NAO is in its negative phase, and Calanus helgolandicus is more abundant when the NAO is positive. When the NAO is positive, there are more westerlies. The surface of the sea is more mixed. The spring plankton bloom is delayed. This favours helgolandicus because its reproductive timing is later. This may also explain why helgolandicus is less nutritious prey for sand eel larvae.
So the picture is now: carbon dioxide goes up. NAO trends positive. Plankton bloom delayed. Less nutritious species of zooplankton dominates the community. Sand eel larvae perform less well. Young sand eels settling into the sand are smaller, and don’t catch up. Puffins have to catch more sand eels to feed their chicks. We’re still worried about the puffins.
What happened next? To their eternal credit, Wanless and colleagues kept collecting data on sand eel lengths. And after a couple more years of continued shrinkage, the trend reversed and the eels started to grow again (although average sizes are not yet back to 1970s levels).
I was not inclined to believe the NAO story. There was another rather obvious potential driver of sand eel shrinkage: fishing. The North Sea sand eel fishery has risen from nothing in the 1950s to levels of up to a million tonnes in some recent years. Such a cull does not just affect population size. It also exerts selection pressure: the biggest predator is now the net. Thus if an eel waits too long to reproduce, or until it has reached a certain size, there is now a better chance that it will never reproduce at all – it’ll be in someone’s fish cake. And while the local fishery lasted only from 1990 to 2000, a species with planktonic larvae has its genes “sieved” over a much larger area. Fishing pushes reproduction to happen earlier at smaller sizes. And as you might expect, fishing at this scale has also reduced the spawning biomass of sand eels. This happens a lot with fisheries. Fish stocks are treated as infinite, since most (bony) fish have very small eggs and lots of them. Then at some point recruitment falls.
What is normal? We hear a lot of doom and gloom about puffins. And compared to the pristine world before human civilisation, they are obviously less common. But you don’t have to go back too far to find times when they were less common than now. The Isle of May was mentioned above. In the first half of the twentieth century it had a handful of breeding puffins. That number is now about 40,000 “apparently occupied burrows.” They were helped by a cull of 30,000 gulls in the 1970s (it couldn’t happen now). But my own suspicion is that the initial growth was helped by immigrants from down south. At the time grey seals, because of new protection from hunting, were thriving in the Farne Islands. Low lying puffin nests were crumbling. The soil was eroding. Those refugee puffins may have made their homes at the Isle of May.
In historical times St Kildans, as well as using puffins to flavour their porridge, exported the feathers of tens of thousands of the poor blighters to form decorations for women’s hats. On Lundy (“puffin” in Norse) Island, rats saw to the demise of a colony, as they did on Ailsa Craig after a shipwreck (both colonies probably >100,000 pairs).
I find it interesting that we are inclined to blame the terror of the day for all our ills. So soon we forget the carnage of the past. And conservation flips from saving animals and plants in the places they live to trying to save everything at once by cutting carbon dioxide emissions.
At least, unlike for kittiwakes, I don’t expect wind farms to harm this particular species of bird.