First find the whales, then you can save them
Killer whales, or orcas, can be found in just about every corner of the planet’s oceans, from the frigid poles to the much more comfortable Equator. One population of killer whales that plies the waters around the Iberian peninsula – which overlaps genetically with those spotted in the Canary Islands – has been designated by the IUCN as “critically endangered,” and the Spanish Ministry of Environment has labeled them as “vulnerable” in the Spanish Catalogue of Endangered Species.
In order to put together an effective conservation plan, it’s important to delineate the spatial distribution of these whales. And that’s not something that anybody has done yet, which is concerning, since the International Whaling Commission recommended that a specific conservation plan be implemented for these whales back in 2007. There was one study that described the summer range of killer whales in the central portion of the Strait of Gibraltar, and that’s it. Nothing on the Gulf of Cadiz, nothing on the Alboran Sea (a chunk of the Mediterranean juuuust past the Strait), and nothing on, well, the non-central portion of the Strait of Gibraltar.
Ruth Esteban, a researcher with an organization called CIRCE (Conservation Information and Research on Cetaceans) set out to collect that missing information, together with some colleagues. They combined a decade’s worth of data collected between 2002 and 2012 from research efforts, whale watching tours, and other opportunistic sightings both in spring and summer, with other environmental information to attempt to create a holistic picture for this group of killer whales, at least during the part of the year that they’re in those waters. In all, they rounded up 11,276 recorded cetacean sightings, 322 of which belonged to killer whales. Of those, 44 sightings were in the spring, and the rest were from the summer months.
They found that the killer whales preferred two areas in the spring: the eastern part of the Gulf of Cadiz in shallow Spanish and Moroccan waters and also off the southern coast of Portugal. In the summer, they spent most of their time in the western and central portions of the Strait of Gibraltar.
The contribution of this research to conservation actually goes beyond this particular population of whales. So often, conservation biologists have to contend with datasets that are, as Esteban puts it, “statistically difficult to deal with.” That could be, for example, due even to minor differences in sampling methods or surveying conditions. To get around that issue, the researchers were able to address the paucity of killer whale data by augmenting it with sightings of other cetaceans. The reasoning was that if killer whales were not detected but other whales were – in a particular place and at a particular time – then killer whales were indeed unlikely to be present. It’s called a “pseudo-absence,” and that sort of data could prove quite valuable to researchers working on establishing the spatial range of other species in other places as well. “Although the chosen approach is not ideal,” the researchers acknowledge, “in our opinion it is suitable due to the high amount of sightings of other cetacean species in the study area, and the non-availability of homogeneous effort.”
Thanks to such methods, the researchers wound up with some information that will likely prove critical to the conservation of these whales.
The Strait of Gibraltar and the Gulf of Cadiz, which forms the entry point where the Atlantic dumps into the Mediterranean, also happen to be prime spots for hunting Atlantic Bluefin tuna. In the spring, the tuna move from the open Atlantic, through the Strait, and into the Mediterranean Sea. But waiting at the gates are the orcas. And when the fish return to the open ocean from their spawning grounds, the orcas can easily pick them off once again. It’s therefore not surprising that the whales’ movements track with those of the tuna.
The researchers also discovered that the whales preferred certain water temperatures. This is again unsurprising, because those are the same temperatures that the tuna prefer. And in ten years, there were only four killer whale sightings in the Alboran Sea. The researchers suspect this is because the underwater topography there makes it difficult for them to hunt the tuna.
Together, the findings reveal the critical importance of the tuna migration for the viability of the killer whale population. And the Atlantic bluefin tuna are already overfished, making any further damage done to that population even further detrimental to the killer whales who depend on them. Armed with better information on their geographic range, the researchers advocate the creation of an exclusion zone where human activities that could disrupt the killer whales’ hunting – like whale watching, military exercises, or sport fishing – are prohibited. It would be particularly effective in the spring, and particularly in the eastern areas of the Gulf of Cadiz. Saving these whales will therefore require extensive international collaboration from Spain, Portugal, and Morocco. – Jason G. Goldman | 17 December 2014
Source: Ruth Esteban, Philippe Verborgh, Pauline Gauffier, Joan Giménez, Isabel Afán, Ana Cañadas, Pedro García, Jose Luis Murcia, Sara Magalhães, Ezequiel Andreu and Renaud de Stephanis (2014). Identifying key habitat and seasonal patterns of a critically endangered population of killer whales Journal of the Marine Biological Association of the United Kingdom, 94(6), pp 1317-1325.
Header image: shutterstock.com
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