Author Archives: cl20

Revision of Design Based Estimates…

Download the revised SCANS-III report on estimates of abundance here: SCANS-III_design-based_estimates_


**The SCANS-III Design Based Estimates report (Hammond et al., 2017) has been revised following the discovery of some analytical errors. The information in the revised report (SCANS-III_design-based_estimates_final_report_revised_June_2021)  supersedes the original report and should be used in place of the original. **


The SCANS-III Surveys

In July and August 2016, three ships and seven aircraft surveyed an area of 1.8 million square kilometres from the strait of Gibraltar in the south to Vestfjorden, Norway in the north over 6 weeks. Teams of observers searched along 60,000 km of transect line, recording thousands of groups of cetaceans from 19 different species. The survey (SCANS-III) is the third in a series that began in 1994 (SCANS) and continued in 2005 (SCANS-II).

SCANS-III survey area and achieved tracklines. Blue areas were surveyed by vessel, pink areas by air. Image (C)SCANS-III

SCANS-II survey area and achieved tracklines. Blue areas were surveyed by vessel, pink areas by air. Image (C)SCANS-III

SCANS survey area and achieved tracklines. Blue areas were surveyed by vessel, pink areas by air. Image (C)SCANS-III

The data were collected using sampling methods designed to allow correction for animals missed on the transect line, without which estimates of abundance would be negatively biased. This was achieved using two semi-independent teams of observers on the ships and using the “circle-back” aerial survey method, in which the aircraft flies a loop to re-survey the same piece of transect.

Aerial observer searching from a bubble window on the SCANS-III survey

The new estimates of abundance will be integral to cetacean assessments undertaken for the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR) quality status report and for the EU Marine Strategy Framework Directive assessments of Good Environmental Status.

The results also enable the impact of bycatch and other anthropogenic pressures on cetacean populations to be determined, fulfilling a suite of needs under the EU Habitats Directive and the UNEP Agreement on the Conservation of Small Cetaceans in the Baltic, North east Atlantic, Irish and North Seas (ASCOBANS).

The most abundant species were harbour porpoise (467,000), common dolphins (473,000) and striped dolphins (441,000), with a further 184,000 either common or striped dolphins.  Numbers of other species of dolphins estimated to be present were 33,000 bottlenose dolphins, 36,000 white-beaked dolphins and 16,000 white-sided dolphins.

Deep-diving whales that feed primarily on squid in offshore waters were estimated to be 29,000 pilot whales, 17,000 sperm whales and 8,000 beaked whales of several different species. Of the filter-feeding baleen whales, 15,000 minke whales and 27,000 fin whales were estimated to be present.

The results indicate that the shift seen in harbour porpoise distribution in the North Sea from the northwest in 1994 to the south in 2005 was maintained in 2016, with the highest densities found in the southwestern North Sea, and north and east of Denmark.

Harbour porpoise density (animals per square km) per SCANS-III survey block. (C) SCANS-III

Further updates to follow: Watch out for results of the distribution and habitat use modelling, coming later this summer.

For harbour porpoise, white-beaked dolphin and minke whale in the North Sea, the series of abundance estimates show no evidence of any change over the 22 years covered by the surveys.

For the other species in the region, at least one more survey will be needed in the future before the conservation status can be assessed.

Resources available for download:

SCANS-III revised report on estimates of abundance: SCANS-III_design-based_estimates_final_report_revised_June_2021

Survey block shapefilesShapefiles

Coarse scale density maps for harbour porpoise, bottlenose dolphin, white-beaked dolphin, common dolphin, striped dolphin, minke whale, pilot whale and fin whale: Species density maps


UK Vessel – Over and Out…

UK survey run-down

By Claire Lacey (Cruise Leader)

Team Skoven

Team Skoven

The more avid readers amongst you will have noticed that updates from the UK vessel have been coming in fits and starts- our apologies for this – our internet connection has been having problems so we’ve had to save them all up to post at the end. That means, you’ve guessed it as you are reading this one online, that we have now reached the end of our 6 week survey cruise.

It has been an interesting  trip; we started in the cold northern waters to the north and west of the Hebrides, and worked our way south, conducting our final few weeks in the (comparatively) warm climate of the Bay of Biscay.  This geographic range has yielded a good range of species seen over the course of the survey too – from the harbour porpoise, which rarely exceeds 1.8m in length- to what was probably the trip highlight for many people on board – the blue whale – which can exceed 25m in length in the northern hemisphere.

Harbour porpoise (C) Marijke de Boer

Harbour porpoise (C) Marijke de Boer

Blue whale (c) Marijke de Boer

Blue whale (c) Marijke de Boer

Prior to the appearance of the blue whale on our very last survey day, the accolade of “trip highlight” had been awarded to a fin whale. We’ve seen many of these whales in both the northern and southern parts of the survey- but nothing really prepares you for the sight of a 20m long animal leaping from the water.  As well as being  a spectacular sight on its own- this also provided a view of the amazing colouration of these animals, which is often not visible from the surface.

Fin whale breach (C) Marijke de Boer

Fin whale breach (C) Marijke de Boer

In case you were wondering – they make quite a splash

Fin whale splash (C) Marijke de Boer

Fin whale splash (C) Marijke de Boer

The more usual view of a fin whale…

Fin whale (C) Marijke de Boer

Fin whale (C) Marijke de Boer

A trip “special mention” should probably also go to the humpback whales we saw. They weren’t really expected to make much of an appearance during our survey, but they were a welcome sight nonetheless.

Lobtailing humpback whale (C) Paul French

Lobtailing humpback whale (C) Paul French

It has been interesting to note the change in dolphin species observed as we worked our way south. To begin with, we were seeing mainly white-sided dolphins, occasionally mixed in with a few oceanic bottlenose dolphins as well. The white-sided dolphins are quite shy of the boat, and despite having a large number of keen photographers on board, we have no photos of these to share with you!

As we worked our way south, we start to see common dolphins. This species is notorious for bowriding and come charging in to the vessel. They didn’t seem to like the Skoven very much though – perhaps our hull was the wrong shape to create the pressure wave required for bowriding to work properly?

Common dolphins (c) Darren Craig

Common dolphins (c) Darren Craig

As we headed further south still, we started seeing striped dolphins as well as the common dolphins. Less keen on the ship, these dolphins are either very easy to spot, or very difficult, depending on their activity. When travelling they stay very low in the water and you don’t get much of a view at all- until that is they start to leap. When they have a mind to be, they are incredibly acrobatic, and produce a display you just can’t miss.

Striped dolphin (C) Marijke De Boer

Striped dolphin (C) Marijke De Boer

Our final sighting of the trip came as we were cruising along the south coast of England, heading back in to harbour. The survey had finished, but the people standing on deck to enjoy the evening view (and make use of the phone signal) were treated to a good view of white-beaked dolphins which came in to check out the boat. They seemed to be of a similar opinion to the common dolphins however, as they didn’t stick around long.

White-beaked dolphins (C) Marijke de Boer

White-beaked dolphins (C) Marijke de Boer

Enormous thanks to the fantastic team aboard the good ship Skoven – it was hard work, but worth it. Now we just need to get on with the data analysis…

UK Vessel – deep divers edition…

The deep divers

by Becci Jewell

The northern transect lines of SCANS-III zig-zag between the edge of the continental shelf and the deep waters beyond and many of our sightings have been of the deep diving cetacean species that inhabit these waters. Deep diving species are often difficult to detect because of the long periods of time they spend foraging at depth. Beaked whales in particular can be elusive, with their long dives and cryptic surfacing behaviour. Despite this, beaked whales and sperm whales were seen multiple times during the survey, as were numerous groups of long-finned pilot whales.

Long-finned pilot whales (C) Darren Craig

Long-finned pilot whales (C) Darren Craig

Beaked whales are incredibly difficult to detect both visually and acoustically and very little is known of many of the 22 species of beaked whale. One of the better known species, Cuvier’s beaked whales, have been recorded diving to a depth of 2,992m during a dive that lasted for 137.5 minutes – the longest and deepest mammalian dive ever recorded. Sowerby’s beaked whales, a species found exclusively in the North Atlantic, were seen in the northern block of the survey and Cuvier’s beaked whales were seen in both the northern and southern blocks.

Cuvier's beaked whale (c) Paul French

Cuvier’s beaked whale (c) Paul French

Sowerby's beaked whale (C) Paul French

Sowerby’s beaked whale (C) Paul French

Sperm whales, the second deepest diving species of cetacean, often associate with the bathymetric features such as the continental shelf, sea mounts and submarine canyons where upwelling water brings nutrients from the depths, driving primary productivity. This productivity attracts the squid and fish that sperm whales feed on, at times diving for over an hour to forage at depths of more than 1,000m. Using a hydrophone array towed behind the M/V Skoven in the northern block, we detected the broadband echolocation clicks of sperm whales foraging in the depths as well as seeing them logging at the surface between dives. Our busiest sperm whale encounter was of at least 10 individuals at the surface in little over an hour.

Sperm whales (C) Paul French

Sperm whales (C) Paul French

Long-finned pilot whales were one of the most frequently sighted species in the northern block and were also seen in French waters in the southern survey block. Despite undertaking dives to depths of over 900m, this species is much easier to detect than the more stealthy beaked whales. With their broad black dorsal fins and conspicuous surfacing behaviour we often spotted groups of pilot whales well ahead of the vessel and could track them as we passed.

Long-finned pilot whale breaching (C) Marijke De Boer

Long-finned pilot whale breaching (C) Marijke De Boer

The data recorded during sightings of these deep diving species will allow new estimates of abundance to be calculated and will shed light on the current distribution and status of their populations in the northeast Atlantic.

UK vessel – Shearwater Bingo

Bingo! full house on shearwaters

By Mark Tasker

For the first half of this cruise (north and west of Britain and Ireland), we were lucky enough to have Mark Lewis and Paul French as our on-board bird observers.  Since they stepped ashore, we have only been able watch birds informally.  The Bay of Biscay has lower densities of all species except perhaps European storm-petrel than the north-west approaches, but its bird fauna is different.  This is perhaps best demonstrated by the differing set of shearwater species. We have seen all six species that are reasonably feasible in NW European waters – a full house!

North of Ireland and west of Scotland, wee saw many Manx shearwaters – their main breeding colony here is on Rum in the Inner Hebrides, but there are smaller colonies also, such as St Kilda. We know that most of the birds from these colonies remain to forage reasonably close to home, but some may be seen out in the Atlantic.

(C) Mark Tasker

Manx shearwaters (C) Mark Tasker

Many shearwaters migrate between the hemispheres during the year; so it is for the second species seen predominantly in the northern sector. Sooty shearwaters breed in the South Atlantic on, for example, the Falkland Islands. It seems that their migration route take them northwards in the west Atlantic, before crossing to the east and making their way southwards.  We found most of these birds on the Rockall Bank, perhaps freshly arrived from their transatlantic crossing.

(C) Paul French

Sooty shearwater (left) with Northern fulmar. (C) Paul French

Our southern survey section was far offshore in the Bay of Biscay, venturing inwards towards France and the UK.  The second long distance migrant shearwater visiting the northern hemisphere in its non-breeding season was seen soon after we left Cork. Great Shearwaters breed in the Tristan da Cunha archipelago but tend not to venture as far north as sooty shearwaters, perhaps reflecting the warmer waters of their breeding sites compared to the sub-Antarctic home of the sooties.

(C) Mark Tasker

Great shearwater (C) Mark Tasker

The final three shearwaters all breed in less remote locations. Cory’s shearwater breeds in Madeira, the Azores and the Canary Islands and is the commonest seabird in the offshore Bay of Biscay at this time of year, its long languid flying posture with wings held slightly bowed downwards was always a welcome sight – groups of them can signal the presence of (apparently) feeding common dolphins.

Cory's shearwater (C) Marijke De Boer

Cory’s shearwater (C) Marijke De Boer

Balearic shearwaters breed (surprise!) on the Balearic islands in the Mediterranean but venture out into the Atlantic in the non-breeding period. There they occur in highest numbers on the inshore parts of the Bay of Biscay off France, with relatively few venturing northwards to waters off SW England. The species is classified as Critically Endangered (due mostly to pressures on or near their breeding colonies) so it was a pleasure to see three of these birds – they look like a browner and smudgy version of Manx shearwater on the southernmost legs of the survey.

The final shearwater seen was a Baroli shearwater – this smaller bird breeds also on the Azores, Madeira and Canary Islands but visits western Iberia particularly. The Bay of Biscay is at the northern edge of its range. The one bird seen took off from the water on small rounded wings rather like some of the auks at a position almost as far west as the survey went in international waters. We saw another in the northern part of France’s offshore waters.