Possible Reasons for an Extraordinary Species Diversity
Fabian Ritter, M.E.E.R. e.V., Berlin, Germany. E-mail: firstname.lastname@example.org
To date, 26 cetacean species are known to inhabit or visit the waters of the Canary Islands, making the archipelago an important area for cetacean observation. From 1 September 1995 to 31 January 2000, sighting data were collected during regular whale watching trips. Additional cetacean sightings were communicated by whale watching skippers for the period from 1994 until 1999.
In total, 21 species could be identified, comprising three mysticete families and three odontocete families of the cetacean order. The bottlenose dolphin (375 sightings/32%) is the most frequent cetacean off La Gomera, followed by the short-finned pilot whale (171/15%) and the Atlantic spotted dolphin (164/15%). Three more species were also seen year round: the rough-toothed dolphin, the striped dolphin and the dense beaked whale.
There was a distinct peak in the seasonal abundance of cetaceans with March, April and May being the months with the most sightings. A seasonal variation of group size was found in the Atlantic spotted dolphin and again there was a peak in springtime. Also, the number of species encountered per month was highest during April (12 species).
Thus, the waters off La Gomera seem to concentrate large numbers of cetaceans – especially during springtime – both on the species level and the total number of animals. Possible reasons for this concentration, such as special oceanographic conditions can be identified: e.g. upwelling filaments, eddies, island mass effect, etc., all of them eventually leading to a high density of cetacean prey species.
As we are not aware of any other small-scale area with such a variety of cetacean species, the non-profit association M.E.E.R. proposes to apply a protection status to the waters off La Gomera, so as to avoid adverse developments like the excessive expansion of whale watching activities or negative impacts through the rapidly growing mass tourism.