Riddle in the Wind

Since permanent research bases were established on the islands of Crozet and Kerguelen in the 1950s, ornithologists have been able to observe population variations in several species of seabirds that have adapted to life in the stormy Southern Indian Ocean. From immense wandering albatrosses to tiny gentoo penguins, from petrels to sheathbills, each species is closely monitored. With varying degrees of success, scientists are trying to explain the changes that have been observed… and are investigating to determine a cluster of lethal causes that lead to “excess mortality”.

Fur seals and elephant seals are mammals that live in the stormy seas of the Southern Ocean and haul out on the scattered volcanic islands in order to give birth. This behavior has allowed scientists to conduct annual population studies for more than half a century. They have noted strange fluctuations: fur seal populations grow steadily by almost 20% from one year to the next, yet elephant seal populations declined rapidly until the late 1990s, before rebounding strongly. It is difficult to correlate these changes with those of the ocean’s top predators, orcas. From one island to another, their feeding habits have adapted so that they feed on elephant seals in one place and fur seals in another.