The killer whales — or Orcas as they are often known — that live off of the Iberian peninsula (Gulf of Cadiz, the Strait of Gibraltar and the Alboran Sea) are increasingly isolated and in a precarious position, according to researchers from Spain and Portugal.
The killer whale populations in the region can now have their locations each year identified with far greater precision than in the past, owing to the new work.
Previous work over the last ten years compiling a database of sighting (11,200 of them) had allowed for the creation of models that showed that the orcas were closely linked with the distribution of what is apparently their main prey in the region, red tuna. This older work also deter engined that these populations are much more limited in numbers than was previously thought. The new work built on this.
“We have created two generalized models: the presence model (sightings of orcas) and the pseudo-absence model (sightings of other cetaceans), with the information gathered from the 11,276 sightings between 2002 and 2012,” stated Ruth Esteban, the main author of the new study and a researcher for Conservation, Information and Research on Cetaceans (CIRCE).
The researchers devised a new model utilizing data from spring — when red tuna enter into the Mediterranean Sea –and an other model utilizing data from summer (when red tuna leave for the Atlantic Ocean).
The findings make it clear that the presence of orcas is linked closely to the distribution of the red tuna during their migration. “This limits their distribution to the Gulf of Cadiz in spring and the Strait of Gibraltar in summer,” Esteban stated.
In addition, Esteban noted that “any reduction in the abundance of tuna could endanger this population of orcas.” Simple observation, but worth noting.
The press release provides more:
She considers it important to demarcate an exclusive marine area where human activity, such as whale watching, military exercises or recreational fishing, does not interrupt their predation techniques.
According to the predictions of the model generated using 278 orca sightings and 7,206 of other cetaceans, it has been forecast that in summer there will be a large number of orcas in the most westerly part of the centre of the Strait of Gibraltar.
The 44 sightings of orcas from research vessels, whale watching companies and opportunist observations and the 3,746 sightings of other cetaceans have shown that the orcas remain in two specific areas in spring: in the most easterly area of the Gulf of Cadiz -in shallow waters around Spain and Morocco-, and in southern Portugal, in particular close to Faro.
In the Alboran Sea, only four orca sightings have been registered in ten years. Scientists have therefore not been able to identify any important habitat area with the models used in the other areas.
“During autumn and winter, orcas have barely been observed in the most regularly populated areas. It is possible that this group of marine mammals travels in waters close to the migration route of the tuna,” the researchers concluded.
The new findings were published in the Journal of the Marine Biological Association of the United Kingdom.
Image Credit: CIRCLE