Strait of Gibraltar and Gulf of Cadiz IMMA
Area Size
4 538 km2
Qualifying Species and Criteria
Killer whale – Orcinus orca
Criterion A; B (1); C (1, 2); D (1)
Marine Mammal Diversity
Criterion D (2)
Tursiops truncatus, Stenella coeruleoalba, Globicephala melas, Delphinus delphis, Grampus griseus, Physeter macrocephalus,
Balaenoptera physalus
Download fact sheet Diversity
Summary
The Strait of Gibraltar, with the adjacent Gulf of Cadiz, is the only area with a regular presence of killer whales (Orcinus orca) in the Mediterranean Sea. During spring and summer this area provides essential feeding and nursing habitat for the small seasonal resident population of killer whales, which is genetically and ecologically distinct from killer whales in the Atlantic Ocean. The Strait of Gibraltar subpopulation of killer whales is considered Vulnerable in the Spanish National Catalogue of Endangered Species but may be considered Endangered based upon other monitoring studies.
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
The Gulf of Cadiz and Strait of Gibraltar subpopulation of killer whales is considered Critically Endangered in IUCN’s Red List and Vulnerable in the Spanish National Catalogue of Endangered Species (Royal Decree 139/2011). The vulnerability of this subpopulation has been demonstrated in the published peer-reviewed literature, based on its small size, isolation from other Atlantic populations, limited fecundity and low survival of offsprings, and dependency to a depleted main prey, the Bluefin tuna. On May 17th 2017, the Spanish Ministry of Environment issued the Conservation Plan for Iberian killer whales (Order APM/427/2017), identifying critical killer whale habitat in Spanish waters and the necessity to protect it.
Criterion B: Distribution and Abundance
Sub-criterion B1: Small and Resident Populations
This area is seasonally used by a population of 39 killer whales in spring and summer. The same individuals have been re-sighted annually from 1999 to 2016. They belong to 5 social pods, stable over the study period. This is the only area with regular presence of killer whales in the Mediterranean Sea. Annual dedicated vessel surveys were performed from 1999 to 2016, including field observations and photo-identification. Photo-identification allowed the identification of 45 individuals, with an abundance count of 39 individuals in 2011, belonging to 5 stable social pods. Genetic analysis as well as ecological indicators of stable isotopes and contaminant levels have shown that these individuals are isolated from other Atlantic Ocean killer whales.
Criterion C: Key Life Cycle Activities
Sub-criterion C1: Reproductive Areas
There is a seasonal presence in spring and summer of killer whales observed from 1999 to 2016. Newborn, calves and juvenile have been observed almost every year. The area is also a feeding ground, providing the nutritional requirements for whales to produce offspring and nurse them.
Sub-criterion C2: Feeding Areas
The area has been identified to be a seasonal feeding ground in spring and summer of killer whales due to the concentration of their main prey Bluefin tuna. This takes place as the tuna migration towards (in spring) and from (in summer) the Mediterranean Sea through the Strait of Gibraltar. Whales have been observed annually feeding on Bluefin tuna, using two foraging strategies. The first strategy happens in spring and summer and consists in a “chase-exhaustion” technique where the whales actively chase the tuna until the its exhaustion. The second strategy happens only in summer and consists in depredating the tuna caught by the drop line Spanish and Moroccan fisheries. Only some of the social groups have exhibited this second strategy. Following the decrease in drop-line fishery catches, no calves have been reported to survive.
The population growth rate was positive at 4% for interacting individuals, and no growth was observed for non-interacting individuals. These differences in demographic parameters could be explained by access to larger tuna through depredation. Consequently, whales would need more tuna to cover their daily energy requirements while actively hunting, suggesting an effect of artificial food provisioning on their survival and reproductive output.
Criterion D: Special Attributes
Sub-criterion D1: Distinctiveness
The area in the only place in the Mediterranean Sea with a regular presence of killer whales. Genetic analysis as well as ecological indicators (stable isotopes and contaminant levels) have shown that these individuals are isolated from other Atlantic Ocean killer whales. The population is considered Vulnerable in the Spanish Catalogue of Endangered Species.
Sub-criterion D2: Diversity
The eastern part of the area in the Strait of Gibraltar is regularly inhabited by six other cetacean species including pilot whales, resident common bottlenose dolphins, common dolphins, striped dolphins, sperm whales, and a migratory corridor for fin whales. The western part in the Gulf of Cadiz has also a known presence of common bottlenose dolphin, common dolphin, and Risso’s dolphin.
Supporting Information
Barón, E., Giménez, J., Verborgh, P. et al. 2015. Bioaccumulation and biomagnification of classical flame retardants, related halogenated natural compounds and alternative flame retardants in three delphinids from Southern European waters. Environmental Pollution, 293:107-115. doi 10.1016/j.envpol.2015.03.041
Carpinelli, E., Gauffier, P., Verborgh, P. et al. 2011. Assessing sperm whale (Physeter macrocephalus) movements within the Mediterranean Sea through photo-identification. Aquatic Conserv: Mar. Freshw. Ecosyst., 24: 23–30. doi: 10.1002/aqc.2446
Chico Portillo, C., Giménez, J., Torres, S. et al. 2011. Survival rate, abundance and residency of bottlenose dolphins (Tursiops truncatus) in the Strait of Gibraltar. 25th Ann. Meeting European Cetacean Society, Cadiz, Spain, March 2011.
De Stephanis, R., Cornulier, T., Verborgh, P. et al. 2008. Summer spatial distribution of cetaceans in the Strait of Gibraltar in relation to the oceanographic context. Marine Ecology Progress Series,353, 275-288
De Stephanis, R., Giménez, J., Esteban, R. et al. 2014. Mobbing-like behavior by pilot whales towards killer whales: a response to resource competition or perceived predation risk? Acta Ethologica. doi: 10.1007/s10211-014-0189-1
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Esteban, R., Verborgh, P., Gauffier, P. 2016c. Using a multi-disciplinary approach to identify a critically endangered killer whale management unit. Ecological Indicators 66, 291-300
Esteban, R., Verborgh, P., Gauffier, P. 2016d. Conservation Status of Killer Whales, Orcinus Orca, in the Strait of Gibraltar. In: G. Notarbartolo di Sciara, M. Podestà, B.E. Curry (Editors), Mediterranean marine mammal ecology and conservation. Advances in Marine Biology 75:141-172. http://dx.doi.org/10.1016/bs.amb.2016.07.001
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