The Plight of the Mediterranean Monk Seal
The entire world watched as the Costa Concordia gradually sank beneath the waters of the Tuscan coast on January 13, 2012. The passengers were from a wide variety of countries, and as the 114,500-ton cruise ship slid ever lower into the water, the spirits of an entire globe of onlookers descended as well. With-at the time of this writing-17 people confirmed dead and 16 still unaccounted for, the sinking of the massive vessel has been a striking human tragedy, affecting thousands of people around the globe.
While the surviving passengers begin to recover, and as searches for the missing become more heavy-hearted, attention is shifting from the spectacle of a city-sized sea vessel being defeated by the ocean, to the dire consequences in store for the surrounding environment. According to the local Environment Minister, Corrado Clini, the cruise ship contains 2,380 metric tonnes (2,624 tons) of diesel fuel and oil–enough to fill a small oil tanker. It also carried additional tons of electronics, cleaning supplies, refrigerators and freezers, and other items made of material that can be highly toxic to plants and animals.
This situation would pose a serious environmental threat anywhere, but the massive vessel happened to go down near the acclaimed Tuscan Archipelago National Park. This park extends over seven islands—including the Isola del Giglio, where the Costa Concordia crashed—and is home to hundreds and hundreds of species of animals, as well as distinctive vegetation such as mountain chestnut trees, cypresses, olive groves, and other species that comprise the Mediterranean macchia habitat.
The Tuscan Archipelago also includes sites visited by one of the rarest marine mammals in the world: the Mediterranean monk seal (Monachus monachus). This species is listed as Critically Endangered by the International Union for the Conservation of Nature (IUCN)’s Red List of Threatened Species (Aguilar and Lowry 2008). There are thought to be only 350-450 Mediterranean monk seals left in the wild, including less than 250 mature adults.
If a population of 450 animals doesn’t sound too shabby, consider that a Broadway theater has 600 seats. All of the Mediterranean monk seals left in the world could attend the same showing of a play, and they would have almost half the theater to spare.
Unfortunately, you would never find all of the remaining Mediterranean monk seals in one place, Broadway play or otherwise. The problems incurred by having a small total population size are compounded by the fact that the remaining seals are scattered around the Mediterranean in tiny, isolated pockets. There are two main sites in which these seals can still be found:
- Cabo Blanco, a peninsula off the northwest coast of Africa, and
- A stretch of Greek/Turkish coast along the northern Aegean Sea.
A glance at a map shows that these two sites are at such a distance from one another as to effectively prevent any natural flow of individuals between the colonies. The only other places still home to these seals are small outposts of stragglers. Madeira, in the Desertas Islands, is home to about two dozen individuals, but outside of that, the IUCN reports that any other occupied sites are usually home to less than five seals. They are known to occur amongst the Tuscan Islands, but are not often sighted. After generations of aggressive persecution by humans, the seals appear to have adopted much more elusive habits than they historically displayed, and often den in caves only accessible from the sea.
The Mediterranean monk seal’s current distribution is a mere sprinkling of individuals, compared to the range that the species used to cover, throughout the Mediterranean Sea, Black Sea, and along the Atlantic coast of northwestern Africa. There is evidence that these tiny groups of seals are now suffering from low reproductive success due to high rates of inbreeding, a common problem faced by species that have undergone dramatic population decline or fragmentation.
The risks to fragmented populations go beyond genetic issues: the smaller the individual population of animals, the more likely they can be wiped out suddenly, which makes the survival of the species increasingly tenuous as populations shrink—an unfortunate positive feed-back loop of risk.
The danger posed by stochastic disasters is exemplified by the catastrophe on Cabo Blanco—home to what was, until the mid-1990s, the largest remaining Mediterranean monk seal colony. In 1996, the local seal population suddenly crashed from 317 seals to just 130. There has been controversy about the precise cause of the mass die-off, and the possible causes include a large local bloom of phytoplankton, which produce toxins that can be deadly for mammals, or a wave of deaths caused by a virus picked up from dolphins or domestic dogs.
The IUCN’s report on the risks facing the species hits directly on the issue now facing the Tuscan Islands:
Mediterranean monk seals are at an unknown but suspected high level of risk from oil tanker and other ship accidents, spills and groundings. Animals could be oiled or coated in fuels and lubricants, exposed to other toxic or environment-altering chemicals or products and experience disturbance at haulouts or coastal feeding areas.
The report also mentions a few previous oil spills in the region, and notes that effects on the seals were not documented, but the species is tough to monitor and the risks are real. In a population of so few individuals, even the loss of a dozen or so could be a major setback for the species.
The timing of the Costa Concordia crash is also unfortunate. Research has shown that pups born between September and January have a survival rate of just 29 percent, much lower than the 71percent survival rate of those born during the remainder of the year (Gazo et al. 2000). In other words, the ship went down at just the right time to wipe out a cohort of pups that were already extremely vulnerable.
The Mediterranean monk seal is hanging on by a thread, and makes for a good flagship species, but it is fortunate that the Tuscan Archipelago is not one of the main remaining colony sites. On the other hand, the seal is just one among hundreds of species that are vulnerable to toxic spills in this region. The Tuscan Archipelago is a critical stopover point for many rare birds during their annual migrations between Europe and Africa, and the waters around the island boast an array of corals and other flashy marine invertebrates, fish, and dolphins.
Hopefully, a method will be found to minimize the leakage of toxins from the Costa Concordia into the surrounding environment. One can only hope that the tragic event will bring much-needed attention to the biodiversity of the area, to the plight of the Mediterranean monk seal, and to the very real risks that random accidents—either natural or man-made—pose to endangered species, which are far too easily pushed over the thin line between persistence and extinction.
For more on the Mediterranean monk seal, see:
Gazo, M., Aparaicio, F., Layna, M. A., Layna, J. F., & Gonzáalez, L. M. (2000). Pup survival in a Mediterranean monk seal (Monachus monachus) colony at Cabo Blanco Peninsula (Western Sahara-Mauritania). Marine Mammal Science, 16(January), 158-168.