From an area of the north Atlantic where we know very little to an area where we know substantially more, orca researcher Andy Foote brings us up to date with what's going on for the orca in the north-east Atlantic.
Killer whales in the Northeast Atlantic are, or have been subject to several threats during the past century. These threats fall in to two categories: ‘deterministic’ or direct threats that cause increased mortalities, and stochastic or random effects that typically result from small population sizes. The deterministic effects include takes by the whaling and live capture industry. The number of recorded catches of killer whales total 2,472 across the NE Atlantic, dating back to 1920. Catches of killer whales by Norwegian whalers were recorded from 1938 until 1981 when this species was no longer targeted, and totalled 2,435 for this period. Small numbers (51) were taken by the live-capture fishery from Icelandic waters and by opportunistic drive fisheries in the Faroes (64 animals recorded 1960-1983). The US navy targeted killer whales in Icelandic coastal waters during October 1956, following interactions with fishing activity, but the number of animals taken is unknown. The killer whale is now protected in these areas and has not been hunted for meat or for live capture for aquariums in these waters for 25 years. A less acute threat comes from contaminant levels, which have been found to rival those of the belugas in the St Lawrence Seaway as some of the highest on the world. The effect of such high contaminants is typically to reduce calf survival, especially the first born, reduce adult male survival and increase susceptibility to disease.
The impact of these deterministic threats is to some extent related to the size of the population, as larger populations are more robust and able to recover from periods of exploitation. This would appear to be the case with the populations or communities that follow the large prey stocks of pelagic fish such as the Norwegian and Icelandic stock of Atlantic herring. Smaller populations can be less resilient to these deterministic threats and this can in turn lead to stochastic effects having an influence on the long-term viability of the population. For example, a collaborative effort between the Hebridean Whale and Dolphin Trust and myself has found that a small community of less than ten whales regularly sighted off the west coast of Scotland and Ireland are made up of four adult males and five adult females. This is an unusually high proportion of males, and probably results from the small size of this community in which events that are subject to a degree of chance, e.g. whether a female gives birth to male or female offspring, are more likely to become skewed and have a greater impact than in large populations. Stochastic genetic effects known as ‘drift’ are also higher in small populations, and this can lead to reduced genetic diversity which can be harmful in the long-term. This small ‘west coast’ community of killer whales have not been photo-identified with a calf since 1992, indicating that the skew in demography may be affecting birth rate. This community belong to an ecotype, which we believe specialises in preying on minke whales and other dolphins. This ecotype may therefore be subject to higher contaminant levels which become more concentrated up the food chain, and may have been subject to greater exploitation by Norwegian whalers who were primarily targeting minke whales but would take killer whales opportunistically on the minke whale hunting grounds. Other groups belonging to this ecotype have only been sighted in much more Northerly waters. If the west coast community are isolated from these other groups then they will probably not survive for many more generations.
A long-term photo-identification study by the conservation and research organization CIRCE has identified another at-risk community in the Strait of Gibraltar. This community is subject to several threats, which include negative interactions with the local tuna fishery that have led to the death of at least one killer whale. The main prey of this community is the blue fin tuna which is also severely depleted and may be restricting population growth. The work of CIRCE has led to this community being provisionally listed as a threatened population by the IUCN, and a recent upgrade in their conservation status by the Spanish Government leading to greater protection. The research effort led by CIRCE of which I am an affiliated member has in addition to the long-term photo-id, also included the collection of skin samples for diet and genetic analysis which will help identify if the Strait of Gibraltar community are a demographically independent population, or if these pods belong to a more widespread population.
This multi-disciplinary approach by CIRCE, which has bought together a range of specialised researchers to address key study questions and then work on a synthesis that brings all the findings together is a great example of the current collaborative nature of research on killer whales in the North Atlantic. This collaboration and communication means that the research findings are feeding directly back to the Spanish and Scottish governments and via our collaborators at the Marine Research Institute, Reykjavik and Institute of Marine Research, Bergen feeding back to the Icelandic and Norwegian governments and therefore influencing policy. There is therefore plenty to be optimistic about for the future of killer whales in the Northeast Atlantic.