Erik: Let’s talk about puffins when they are at sea. What is their life like?
Erpur: We have participated in a multicolony international collaborative program named SEATRACK, deploying geologgers on the Atlantic Puffin, together with ten other seabird species in order to map their winter distributions. Icelandic puffins have a triangular migration pattern, they head into the Labrador Sea in fall, stay there until the end of the year when they move south over the Atlantic ridge centering on the Charliecr-Gibbs fracture zone, and in spring, they head north.
The Charlie-Gibbs fracture zone in the Atlantic ridge is rich with prey in winter and is a mega hot spot for sharks, whales, as well as many seabird species of the North Atlantic It’s a fascinating place, with summer conditions in the middle of winter and undoubtedly the reason for the large size of many seabird populations in the North Atlantic.
Erik: And what about when they come back to Iceland?
Erpur: After a completely pelagic existence like other ‘true’ seabirds; they come back in the middle of April to meet up with their mate.
Puffins have monogamous relationships for life. We say that puffins have a pretty low ‘divorce rate’ – seven percent. For example, if the mate dies, or if they have breeding failure.
Between Iceland and Norway, there have been sharp declines, which is why Atlantic Puffins were put on the IUCN red list in 2015.
I am able to study puffins backwards in time, because we have data on the harvest records in the Westmans Islands going back to 1880. Eighty-percent of the puffin harvest is composed of three year classes that are 2, 3 and 4 years old. Since the effort has remained relatively constant, the harvest in any given year reflects how many were born 2-4 years before.
This gives us one of the longest and perhaps the most interesting time series of birds, as the data show that puffin chick production has a very strong correlation to sea temperature. When sea temperatures are warmer, fewer puffins are harvested, and vice versa.
We know that temperature is key, and temperature in the Atlantic follows a seventy year cycle termed the Atlantic Multidecadal Oscillation or AMO, characterized by 35 warm years, followed by 35 cold years A warm period started in Icelandic waters in 1996 with temperatures peaking in 2003. In Icelandic waters, the warming is greatly intensified by contemporal contraction of the Sub-Polar Gyre, a circular current system, which opens for great flow of warm and saline Atlantic seawater northwards.
In the process our waters warm by about one degree Celsius, in less than a decade the same warming as predicted by global warming for this century using the IPCC A1B1 “business as usual model!”
The polar currents coming from the north mix with the warmer waters and thus create three marine ecosystems. We have essentially a natural laboratory of extreme temperature variation gradient. That’s exactly where our study colonies are located.
Erik: The puffins are declining because their primary foodsource, the Silvery Sandeel, are in decline?
Erpur: The sandeel is one of the most commercially harvested fish in the North Sea, and is studied by a number of specialists. There are a number of exciting hypotheses for their decline and how this relates to seabird declines. One hypothesis is that the sandeel’s first winter survival is negatively related to temperature by increase in their Basal Metabolic Rate (BMR), leading to a premature depletion of their fat reserves, prior to the onset of their zooplankton food in spring. They die of starvation during these warmer years.
Another, complementary hypothesis is that in warm summers, the sandeel´s elevated BMR wastes energy, instead of building energy (fat) reserves and growth. We don’t always have warm and cold summers in conjunction. In 1948, for example, summers cooled during an otherwise cold winters AMO period, which allowed the sandeels to really strengthen, judged by the increase in Puffin harvest. In 1996, we started to see the reverse of this, and sandeel numbers declined very rapidly, much more than in the last warm period in the 1930´s. Oceanographers are modeling to see if global warming will buffer against the cooling of the AMO cycle, essentially terminating the cooling period.
If this warming trend continues, the puffin colonies here will be a shadow of their former past. In the north, the colonies would remain. We would have a northern coast with current numbers, and losing more than half of the rest of the populations. This IUCN red listing is really about this: If you would have been here in the 1980s, you would have seen so many birds! Now there is nothing like that! The puffins haven’t even socialized normally in the troubled colonies in the last decade. These social birds are known to spend a lot of time communicating with each other, they don’t have the time to hang around anymore. They need to put all their attention on acquiring food.
What is happening differently during this warm period now, I think, is that the algae blooms that normally occur in March and April, happen much later. The sandeel eggs are hatching about the same time as the algal bloom. The algae are grazed on by zooplankton, which is the prey of sandeels. If there is a delay in the bloom timing, we have what is termed a trophic mismatch. Basically the sandeel prey show up so late that they are already dead from starvation.
Puffin chicks have been fledging in September, rather than in late August. 2019 is however the sunniest year on record, creating a massive algae bloom that you can easily see from space. There is a huge amount of food in there. So there are a lot of variables out there.
Sandeel numbers are expected to increase when you have a good bloom year: early and intensive blooms benefit the the entire food pyramid.
We have satellite data since 1998 that shows that the blooms have been really late in the last decade or so, and one could expect that to increase with global warming: more evaporation and more clouds in our region, and consequently, less sun. That delays and reduces the blooms.