Evaluation pilote de l’abondance et de la répartition de l’orque

D1 - Diversité Biologique

D1.1 - Répartition des espèces D1.2 - Taille des populations D4.3 - Abondance/répartition des groupes trophiques/espèces clés

Message clé:

L’orque est une espèce longévive, se reproduisant lentement et un grand prédateur. Il existe plusieurs populations, mais les données sur leur abondance sont rares. On ne peut donc réaliser qu’une évaluation pilote. Les polluants organiques persistants accumulés par le biais du régime alimentaire ont des effets sur la vulnérabilité des orques, des niveaux élevés de polluants pouvant potentiellement affecter leur reproduction.

Contexte

L’objectif stratégique d’OSPAR, en ce qui concerne la biodiversité et les écosystèmes, est de stopper et prévenir une perte supplémentaire de la biodiversité, de protéger et de conserver les écosystèmes et de rétablir, lorsque cela est possible, les écosystèmes auxquels les activités de l'homme ont porté atteinte. Cette évaluation pilote se penche sur les modifications de l’abondance et de la répartition des populations d’orques dans l’Atlantique du Nord-est.

Certaines orques peuvent séjourner saisonnièrement dans des zones relativement petites, près du littoral. Ainsi, elles peuvent potentiellement être exposées à un niveau plus important d’activités humaines, étant donné leur proximité, que les populations présentes plus au large.

Bien que les orques soient très répandues, leur nombre n’est pas particulièrement élevé. La plupart des informations sur la structure de leurs populations proviennent des études d’identification photographique se focalisant sur des groupes particuliers présents dans les eaux côtières.

L’orque est une espèce longévive et un grand prédateur et elle est sensible aux changements de son environnement. Les modifications de son abondance et de sa répartition révèlent des informations importantes sur l’état des populations.

L’orque est vulnérable à l’accumulation des polluants organiques persistants par l’intermédiaire de la chaîne trophique, pression clé pour cette espèce. Les bruits sous-marins peuvent avoir des effets à long et court terme sur les cétacés (par exemple, perte auditive ou déplacement d’une zone) mais l’on ne sait pas dans quelle mesure l’orque est affectée.

Orque (Orcinus orca) (avec la permission de Christopher Michael)

Background (Extended)

Killer whales (Orcinus orca), are long-lived top predators, and are among the most iconic and recognisable of the cetacean species.

Killer whales are one of the most widely distributed of all cetacean species globally and occur throughout the North Atlantic. Killer whales are most numerous in Arctic Waters. In the remaining OSPAR Regions, killer whales are most commonly sighted along the coastal shelf edge west of the United Kingdom and Ireland, especially off Shetland and the Hebrides (United Kingdom) (Evans, 1988; Reid et al., 2003; Bolt et al., 2009; Foote et al., 2009; Beck et al., 2014). They are also seen near the Strait of Gibraltar, in Spain (Esteban et al., 2013). In these southern areas there are small, genetically distinct groups of killer whale.

Human Pressures

ICES (2015) reviewed and prioritised the key human pressures on killer whales in the OSPAR Maritime Area. The pressures listed in Table a represent those considered to have most relevance for killer whales (OSPAR, 2012; ICES, 2015). Pressures from human activities may affect killer whales directly or indirectly (such as by changing the food web structure and thus prey availability). For killer whales, the main pressures were identified as pollutants and military activities generating underwater noise (predominantly sonar but also including the potential of explosions occurring) (Table a).

Killer whales, along with other toothed whales, are top predators and so are vulnerable to bioaccumulation of pollutants. A recent study has shown that blubber samples from stranded killer whales within the Greater North Sea, Celtic Seas, and Bay of Biscay and Iberian Coast regions contain very high levels of polychlorinated biphenyls (PCBs) (Jepson et al., 2016). PCBs are known to cause pathological changes, and high levels of PCBs may be inhibiting reproduction and thus adversely affecting group size in small coastal cetaceans. PCB concentrations within the OSPAR Maritime Area are assessed in PCB Concentrations in Biota and PCB Concentrations in Sediment.

The pressures listed in Table a represent those considered to have most relevance for marine mammals. The risks associated with the identified pressures are classified as high, medium or low using the following criteria:

High: evidence or strong likelihood of negative population effects mediated through effects on individual mortality, health and / or reproduction;
Medium: evidence or strong likelihood of impact at individual level on survival, health or reproduction. Effect at population level is not clear; and
Low: potential negative impact on individuals but evidence is weak and / or occurrences are infrequent.

Table a: Pressure matrix for killer whales in the OSPAR Maritime Area
Pressure Category	Pressure	Risk
Pollution & Other Chemical Changes	Contaminants	High
Pollution & Other Chemical Changes	Nutrient enrichment	Low
Physical Loss	Habitat loss	Low
Physical Damage	Habitat degradation	Low
Other Physical Pressures	Litter (including microplastics and discarded fishing gear)	Low
Other Physical Pressures	Barrier to species movement (offshore windfarms, wave or tidal device arrays)	Low
Underwater Noise Changes	Military Sonar	Medium
	Seismic surveys	Low
	Pile-driving	Low
	Shipping	Low
Death by Injury or Collision	Death or injury by collision (with ships)	Low
Death by Injury or Collision	Death or injury by collision (with tidal devices)	Low
Biological Pressures	Introduction of microbial pathogens	Low
	Removal of target and non-target species (prey depletion)	Low
	Removal of non-target species (bycatch)	Low
	Disturbance (e.g. wildlife watching)	Low

Quality Status Report 2010

No comparable quantitative assessment of the distribution and abundance of killer whale was included in the OSPAR Quality Status Report (QSR) 2010. The report highlighted human pressures on marine mammals more generally, such as through bycatch, increased shipping and bioaccumulation of persistent hazardous substances.

The conservation status of killer whales has been assessed as unknown under the European Union Habitats Directive (Council Directive 92/43/EEC), Article 17 reporting in 2013 (EU, 2013).

Assessment Method

No assessment units (AUs) have been agreed for killer whale (Orcinus orca). However, there are distinctions between some groups based on photo-ID surveys, studies of well-known populations, genetic studies (biopsies and investigation of stranded animals) and on prey specialisation. Due to the lack of suitable data it is not possible to assess trends in abundance.

Résultats

Au sein de la zone maritime OSPAR, plusieurs milliers d’orques sont présentes dans les eaux Arctiques et les parties septentrionales de la mer du Nord au sens large, des mers Celtiques et de l’Atlantique au large. Il s’agit d’animaux mobiles qui se nourrissent essentiellement de poissons pélagiques se déplaçant en bancs, tels que le maquereau et le hareng. Certains se nourrissent également de phoques et d’oiseaux. Plus au sud, les orques sont très fréquemment observées près du détroit de Gibraltar et en bordure du plateau atlantique, en particulier à proximité du Royaume-Uni et de l’Irlande, notamment dans la mer du Nord septentrionale. Il se peut que l’abondance de ces orques plus méridionales ne dépasse pas 100 individus.

Un très petit groupe distinct (10 à 12 individus) est présent à proximité de l’ouest de l’Ecosse et du nord-ouest de l’Irlande. Les orques vivant près du détroit de Gibraltar résident saisonnièrement dans le golfe de Cadix (printemps) et le détroit de Gibraltar (été), suivant le thon rouge atlantique dont elles se nourrissent abondamment. On considère qu’elles sont génétiquement distinctes des autres populations d’orques.

Des charges élevées de polluants organiques persistants dans les individus causant des problèmes de santé et un échec de la reproduction pourraient avoir contribué au déclin du nombre et de la répartition des orques en particulier dans les zones industrielles.

L’état de la conservation de l’orque a été évalué par l’Agence européenne pour l’environnement, et considéré « favorable » du point de vue de la répartition. L’état de la conservation est considéré « inconnu » du point de vue de la population dans le cadre de la Directive habitats de l’Union européenne (Directive du Conseil 92/43/CEE).

Orque (Orcinus orca) (avec la permission de Robert Pitman NOAA)

Results (Extended)

There is no overall estimate for the size of the killer whale (Orcinus orca) population within the OSPAR Maritime Area. There is some information available for some localities.

The Strait of Gibraltar

The Strait of Gibraltar killer whales have been shown to be a genetically distinct population compared to those of the northern North Atlantic (Foote et al., 2011). The Strait of Gibraltar animals are seasonally resident in the Gulf of Cadiz (spring) and Strait of Gibraltar (summer) and comprise two types of killer whale: those that interact with the drop-line Atlantic bluefin tuna (Thunnus thynnus) fishery and those that do not (Esteban et al., 2016a). The population is estimated at 39 individuals using data collected between 1999 and 2011 (Esteban et al., 2016b). It comprises five pods, of which two interact directly with the tuna fishery through predating fish from drop-lines (Esteban et al., 2016a).

Survival parameters estimated for these animals have shown a difference, with adult survival rates being slightly higher in tuna fishing interacting pods (0.991, standard error (SE): 0.011) than non-interacting pods (0.901, SE: 0.050), suggesting access to the line-caught tuna improves the success of individuals by reducing energy requirements compared to active hunting, and providing access to larger prey items (Esteban et al., 2016b). As these two types of killer whale are not regularly seen intermixing, it is possible that this specialisation may lead to fragmentation of an already small population (Esteban et al., 2016a). Although calving rates are also higher for the interacting pods (0.22, SE: 0.02) than the non-interacting pods (0.02, SE: 0.01), calf survival is potentially lower. No calves survived in the interacting pods between 2005 and 2011, a period that coincided with a drop in tuna catches (Esteban et al., 2016b). Only one juvenile and one calf were observed among the non-interactive pods during the assessment period (1999–2011) (Esteban et al., 2016b).

Greater North Sea and Celtic Seas

In the Greater North Sea and Celtic Seas, killer whales are most commonly seen off Atlantic coasts and in the northern North Sea, while sightings are rare in the English Channel and in most of the North Sea (Reid et al., 2003). These killer whales have not been as extensively studied and little information is available on survival and breeding.

Greater North Sea, Celtic Seas and Wider Atlantic

Killer whales in the northern areas of the Greater North Sea, Celtic Seas and Wider Atlantic are known to form part of a wider population of animals inhabiting Arctic Waters (Foote et al., 2010, 2011; Samarra and Foote, 2015). There is no overall population estimate available, but in 2001 a survey found 15,041 (CV: 0.42) individuals in part of this area. Prey in this wide area mainly comprises pelagic shoaling fish, with some individuals also feeding on seals and birds at some times of the year (Luque et al., 2006; Foote et al., 2010, 2011; Samarra and Foote, 2015).

Celtic Seas

Within the Celtic Seas, photo identification studies have identified ten individuals regularly seen around the Hebrides and in Irish waters (Foote et al., 2010; Beck et al., 2014). This group is genetically distinctive. One of the killer whales of the Hebrides population died in 2016, and two adult males are nearing the expected life-span for the species, indicating that the population is likely to decline. No calves have been recorded with any of the individuals in this group while two adult females identified in 1992 have never calved (Foote et al., 2010; Beck et al., 2014).

Conclusion

Les orques de la zone maritime OSPAR se trouvent essentiellement dans les eaux Arctiques et les parties septentrionales de la mer du Nord, des mers Celtiques et de l’Atlantique au large. Plus au sud de plus petits groupes distincts sont présents dans les eaux côtières au large de l’ouest de l’Ecosse et du nord-ouest de l’Irlande et dans le détroit de Gibraltar.

On ne peut réaliser actuellement qu’une évaluation pilote, en l’absence de données.

L’orque est vulnérable aux effets de l’accumulation des polluants organiques persistants, des niveaux élevés de polluants pouvant potentiellement affecter leur reproduction. Les sonars militaires à moyenne fréquence peuvent également avoir des effets négatifs sur l’orque.

L’abondance et la répartition des orques pourraient être indicatrices des aspects spécifiques de l’état du milieu marin, tels que l’intégrité du réseau trophique et la charge de polluants.

Conclusion (Extended)

The number and distribution of killer whales (Orcinus orca) in the OSPAR Maritime Area is not known, partly due to the difficulty of surveying a rare species. In northern waters (Arctic Waters and the northern parts of the Greater North Sea, Celtic Seas and Wider Atlantic), killer whales range widely and feed on pelagic schooling fish such as mackerel (Scomber scombrus) and herring (Clupea harengus). In all waters, including those further south, killer whales occur in distinct groups of relatively few individuals in coastal waters. These whales feed on fish, with some individuals feeding on seals and birds at some times of the year. Two areas are known to hold these groups: west Scotland / north-west Ireland and south-west Iberia / Strait of Gibraltar. Some individuals in the Strait of Gibraltar population interact with a drop-line fishery for tuna. These have been shown to have higher adult survival rates and higher calving rates than those animals that do not interact, although calf survival may be lower. As these two sets of individuals are not regularly seen intermixing, it is possible that this specialisation can lead to the fragmentation of an already small population.

Killer whales, as long-lived top predators, are vulnerable to the effects of persistent organic pollutants, with high pollutant loads possibly inhibiting reproduction. Military activities using mid-frequency SONAR may negatively affect cetaceans, including killer whales.

Lacunes des connaissances

Les informations historiques sur l’abondance et la répartition de l’orque sont rares ou absentes. On ne peut entreprendre aucune évaluation de l’abondance, étant donné cette absence d’information et seule une évaluation pilote de la répartition est donc possible. On ne possède aucune estimation de la taille des populations d’orques au sein de la mer du Nord au sens large, des mers Celtiques, du golfe de Gascogne et de la côte ibérique.

Les activités humaines peuvent affecter l’orque. Les rapports entre les activités humaines (par exemple, perturbation, pollution, pêche, altération des habitats) et leurs impacts sur les populations d’orques devront donc faire l’objet d’études supplémentaires.

Knowledge Gaps (Extended)

Assessments for the groups of killer whales (Orcinus orca) in the OSPAR Maritime Area are not currently possible because trends in population size are unknown. Monitoring is required for at least ten years, with a minimum of four data points during that period, before an assessment is possible.

Information on historical distribution and, in particular, abundance is scarce or lacking. There are some published accounts, but much of the information is based on anecdotal accounts.

References

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