Increasing sea temperature and growing mackerel numbers around Iceland are having a direct impact on the collapse of sand eel populations upon which birds like puffins and Arctic terns depend.
The low number of sand eels is causing another failed puffin nesting season, as previously reported.
According to Icelandic Marine Research Institute findings, the warming sea is directly related to the increase in mackerel, which is connected to the decrease in sand eels, which is in turn directly related to the collapse in sea bird breeding around Iceland. It is thought that mackerel are moving into Icelandic waters because the sea temperature continues to increase; while it is believed the sand eel stock is collapsing both because of the warmer water and also because of the influx of mackerel — two closely related, yet independent, factors.
Kristjan Lillendahl, marine research institute ornithologist, told RUV that when warmer waters cause the sand eels to spawn too early, there may not be enough suitable food around for the young, who then go on to starve. The opposite can also be true, whereby food supplies peak too early in the warmer waters and others (like mackerel) have already eaten the food by the time the young sand eels need it.
Meanwhile, it is reported that mackerel cause two problems for sand eels: firstly as competitors for the same food and secondly by eating the sand eels outright.
Lillendahl says that a single good year will not be enough to save the sand eels, which are eaten by other creatures in huge numbers. The species needs to have several good breeding seasons in a row in order to bounce back.
(Main page photo: Brad Houldcroft)