Common dolphins, once abundant in the Mediterranean, are no longer so common in this region.
Photo - Chris Johnson
December 10, 2004
Common Dolphins - Not So Common in the Mediterranean
This is Genevieve Johnson speaking to you from the Odyssey at the conclusion of five months of research in the Mediterranean Sea.
Over the past several months, one species of dolphin eluded us - the common dolphin (Delphinus delphis). Traditionally one of the most abundant cetacean
species in the Mediterranean basin, it appears that the common dolphin is no longer so common in this region.
The common dolphin is a small distinctive species with a wide global distribution. At present, two distinct forms are recognized - the long-beaked and the short
beaked common dolphin, although only the short-beaked type is found in the Mediterranean.
Probably numbering in the low millions, the common dolphin is the most numerous dolphin in offshore warm temperate waters in the Atlantic and Pacific oceans. By contrast, the short-beaked common dolphin in the Mediterranean Sea was listed as 'endangered' in 2003 in the International Union for the Conservation of Nature (IUCN) Red List of Threatened Animals. This implies a 50% decline in abundance over the last three generations. Of greatest concern
is the fact that the causes of the decline may not have ceased, may not be understood or may not be reversible.
Until the late 1960's, Common dolphins were widespread in both the pelagic and inshore waters of the Mediterranean Sea. However, their comparatively recent and
rapid decline is the subject of scientific controversy and political indifference. For example, common dolphins were sighted regularly in the Northern
Adriatic Sea until the 1970's, yet for unknown reasons they are almost entirely absent today. Unfortunately, research on this species is limited with
no systematic effort to assess abundance and distribution. Although still relatively abundant in the western most area of the Mediterranean including
the Alborian Sea, relic groups are occasionally sighted around the Maltese Islands, parts of the Aegean, Ionian and the southeast Tyrrhenian Seas.
Today, this species is thought to be rare in, or completely absent from most areas of the Mediterranean where data is available, while no data exists for the eastern Mediterranean.
On our final research leg in the Mediterranean in the Alborian Sea, we finally encountered this species with five sightings in two days.
As soon as we sighted the animals, it was obvious these were common dolphins. The common dolphin is a slender, evenly proportioned animal with an elaborate
hourglass pattern of white, gray, black and yellow on their sides. They usually live in schools of about 30 but often gather in the hundreds or thousands.
The Odyssey crew regularly encountered this species in enormous numbers in the Eastern Tropical Pacific, they were always eager to bow ride and were very
active at the surface. In the Mediterranean, we only encountered common dolphins in small groups, usually no more than 8-10 animals. They were conspicuously
wary of the boat and only rode the bow for short periods.
It is suggested that several factors may be contributing to the decline of this species in the Mediterranean, including prey depletion caused by overfishing,
habitat degradation from human activity, the accumulation of persistent organic pollutants (POPs), bycatch in fishing gear such as industrial trawls, gillnets and
illegal driftnets, and perhaps even climate change. The individual and combined effects of these factors are poorly understood and as a result, few conservation
measures are currently implemented.
Common dolphins ride the bow of the Odyssey.
Photo - Chris Johnson
It there is to be any hope of preserving the common dolphin throughout much of its historic range in the Mediterranean Sea, governments, scientific researchers and non-government organizations (NGOs) must act now. The fate of the remaining animals is dependent upon the adoption of a coordinated framework between governments and the implementation of precautionary conservation and management measures.
What can you do to help the common dolphin in the Mediterranean Sea? Most important, as a consumer, is to select you seafood wisely. Some fishing practices are depleting fish stocks and are causing small cetaceans, like the common dolphin, to become entangled in their gear. Also, it is important to support NGOs trying to work with governments to create conservation-based policies for the species.
Log written by Genevieve Johnson.