BWAS 2017: Rockall Trough Part Two - Cetaceans

Blue Whiting Acoustic Survey 2017 Week Two: Saturday 25^th to Friday 31^st March
by Sean O'Callaghan (IWDG Marine Mammal Observer)

The second week of BWAS marine mammal surveys got off to a blank start initially but the following day (Sunday) really signaled the start of a far more productive period.

Survey progress map for 31st March 2017 with thick lines show areas covered (c) Marine Institute

Not long after ascending into the crow’s nest to start the day's effort and while getting myself ready (equipping the necessary gear for the day along with applying some sun cream!) the seabird team began their observations from the bridge deck and spotted the first whales of the day which appeared initially 500m off the starboard bow, lazily surfacing, all the while moving closer to RV Celtic Explorer. Their slanted blows and boxed body shape gave them away as sperm whales and the three of them (one obviously large individual with two smaller individuals, probably juveniles) came within 100m of the vessel before diving under the bow. Moby Dick's relations up-close and personal, a great start to the day! 

Sperm whales (c) Niall T. Keogh

Sperm whales (c) Sean O'Callaghan

Sperm whale dive sequence (c) Sean O'Callaghan

An hour later, two tall blows were picked up out towards the horizon some 2.5km off the bow and when we reached the area both whales passed the vessel, decent views giving them away as fin whales on the move. The most elusive of the Sunday sightings was of an unidentified beaked whale picked up once by Aude through her binoculars while I was on a break. To round the day off we had a few common dolphins make an appearance off the port side showing no interest in the ship which has been the case for most of the survey. We had caught up with the fishing fleet on the northern side of the Porcupine Bank that day and had views of some of the large factory trawlers.

Maartje Theadora (c) Niall T. Keogh

The next batch of activity happened two days later along the shelf edge some 60km west off Mayo where more common dolphins were sighted in the morning while a group of long-finned pilot whales were recorded visually and acoustically simultaneously a kilometre and a half of the port side in the evening (really displaying how both survey methods can complement one another). While trying to get record shots of these pilot whales a distant blow from a large whale was inadvertently captured in their midst’s just as a group of offshore bottlenose dolphins powered past the starboard side to be picked up by those on watch in the bridge along with the seabird team who were up from dinner to see the pilot whales. Unfortunately these dolphins didn’t hang around and continued off in synchronised breaches which were the best that could be captured by the camera. Another day another species for the list!

Offshore bottlenose dolphins (c) Sean O'Callaghan

Wednesday was a day for housekeeping with heavy rain in the morning coupled with poor sea conditions which were unsuitable to watch or safely work in. Thursday was an unexpectedly interesting day, we had moved north into Scottish waters off the Hebrides with a species list standing at six but there was more transects to go yet. The weather had eased off and we were back on effort again. After turning onto a new transect at around 15:00, Aude started to hear a strange sounding whistle on the hydrophone, seemingly getting closer as time passed by. Continuing to watch from the crow's nest with the possibility of a new species in the area it didn’t take long to spot a large, grey, odd-shaped ship lingering on the horizon. We had heard that the survey tracklines might take us past a military exercise later in the day involving submarines, so with the navy-style appearance of the distant ship coupled with the consistency of the whistles being detected on the hydrophone, it became obvious that sonar was being used. About 30 minutes after the first ship was seen, another four appeared on the horizon to the east around the same time as the first marine mammal sighting of the day was made; a group of ten or so common dolphins moving west ahead of us at high speed! The sonar was detected for a further three hours, during which time another lone common was sighted but seemed unphased by the sound (in contrast to the previous sighting). Further sightings of common dolphins, two unidentified large whales and our first Minke whale of the survey capped off the day nicely as we continued north along the shelf edge and over shallow waters. 

Common dolphin (c) Niall T. Keogh

Navy vessels taking part in the 'Operation Joint Warrior' exercise (c) Sean O'Callaghan

Friday proved to be a fruitful day while over the deep Rockall Trough waters near the Anton Dohrn Seamount, with twenty long-finned pilot whales less than 200m off the port side just after conducting a fishing tow and before the day's watch effort began. This group of pilots engaged in some interesting behaviour such as 'spy-hopping'. Later on a lone Atlantic white-sided dolphin was seen to surface twice, giving tantalisingly brief views of the colourful side pattern but just not enough to put it down as a "definite" sighting for that species.

The day ended as the drizzle closed in from the east, with a lone large blow picked up from the crow’s nest some 3km away. Subsequent rain knocked the survey off effort for a while but as soon as it cleared we were met with the sight of a single fin whale lunging in front of the bow almost on cue in perfect sea conditions! It lunged a further three times as we steamed by, making for a nice end to the week despite heavier rain closing in!

Long-finned pilot whales 'logging' at the surface (c) Sean O'Callaghan

Long-finned pilot whale 'spy-hopping'! (c) Sean O'Callaghan

Lunge-feeding fin whale (c) Sean O'Callaghan

Fin whale lunge-feeding sequence (c) Sean O'Callaghan

Our man in the crow's nest... Sean wonders what species is next up for the marine mammal team! (c) Niall T. Keogh

COTF6 Day 2: Porcupine Bank Bonanza!

What a day! We awoke this morning with news from Enda and John (at the tail end of their hydrophone/acoustic monitoring night shift) that common dolphins were present around the R.V. Celtic Explorer throughout the night from about 02:30. The daytime observation teams were out on deck and in position, ready to go from 07:30 but were faced with a misty horizon, moderate sea state and some patches of rain for much of the day. Not ideal but we’ve been out in worse!

Steaming due West for the M6 weather buoy over the top end of the Porcupine Bank, crossing over a depth of 2,000m we came across a group of five Atlantic white-sided dolphins, a species limited to the deeper offshore waters within the Irish territory. In typical fashion for these dolphins, they didn’t approach the boat too close and headed off fairly quickly as we made our way along the transect line. Hopefully we’ll bump into more white-sides again over the coming days and secure some nice images as they are a species infrequently seen or photographed in Irish waters, at least in recent years.

About half an hour away from the M6 buoy, a whale blow appeared dead ahead up to 800m away. The frequent nature of the short, bushy blows coming from the same spot lead us to believe a sperm whale was the culprit and a view of the body during a break in the swell confirmed this. While concentrating on the sperm whale we were coming up on, a group of energetic and acrobatic, small sized dolphins suddenly started moving through our field of view with tremendous speed. Leaping clear out of the water like sleek, silver bullets it was instantly apparent that these were not your run of the mill common dolphins. A sub group breached not more than 100m from the bow and a solid view of the flanks complete with a thin, black, wavy line, confirmed that these were, as suspected, striped dolphins! In all three groups of 10-15 animals each barrelled North in front of us, clearing the water in an impressive, organised phalanx before re-entering with a forceful smack of the tail, sending a sizeable splash of water into the air. Striped dolphins are a real sub-tropical, oceanic species with sightings in Irish waters a relatively recent phenomenon, typically confined to late summer and autumn when surface water temperatures are at their highest. As such the window of opportunity for seeing them appears to be quite short and not surprisingly, these animals constituted a new species or only a second/third sighting for many present on deck at the time. Truly exciting stuff!

Striped Dolphins (c) Jason McGuirk

Striped Dolphins (c) Simon Berrow

Striped Dolphins (c) Hannah Keogh

Once maintenance works on the M6 buoy were completed in ever efficient fashion by the ship’s crew, we changed track and headed South East along the shelf edge, crossing over a changing water depth as we went over the slope, from 3,000m to 500m. Soon after a shout of ‘blow!’ went out and the on deck cetacean observation teams were treated to some nice, prolonged views of a feeding fin whale, the second largest animal on Earth. We came upon more fin whales later in the afternoon, this time a group of three animals actively feeding in close proximity with plenty of blows, side rolling and some shallow lunge feeding on offer at close range! Absolutely fantastic!

Fin Whale (c) Simon Berrow

Fin Whales (c) Simon Berrow

Fin Whale (c) Joanne O'Brien

Fin Whales (c) Hannah Keogh

Fin Whale lunge feeding/side rolling (c) Simon Berrow

Fin Whale lunge feeding/side rolling (c) Joanne O'Brien

The evening then drew to a close for the cetacean team with multiple sightings of common dolphins (some groups size of 40 animals) coming in to bow ride as we came over a water depth of 500m. The nocturnal acoustic team took over at 20:00 and soon after several detections of sperm whales were made really close to the ship, their position calculated as near as 200m! We were all able to gather in the dry lab and listen to their rhythmic clicks through the speakers, sounding almost like an electric fence pulse. Also best not forget to mention the sightings of two different ocean sunfish which we passed by at close range during the day! Bizarre fish altogether and always great to see.

Common Dolphin (c) William Hunt

Ocean Sunfish (c) Hannah Keogh

Sperm Whale clicks (c) Enda McKeogh

The seabird team had a day of quality over quantity, with just a trickle of fulmars, a handful of gannets and a small entourage of lesser black-backed gulls in attendance. Saying that a couple of excellent sightings early on made all the effort worthwhile (cetaceans aside!). A great shearwater came in for a look at us first thing before carrying on its way to the South. Not long after we approached a group of fulmars on the water with a Wilson’s storm-petrel bouncing around them which showed well at close range before travelling on to the West. Both of these species have undertaken a mammoth journey from their breeding grounds on sub-Antarctic islands to Irish waters in order to avail of rich feeding here in the late summer and autumn. Amazing to think the distance they have covered. Intrepid birds! A pomarine skua spotted by Simon, trundling by the ship late evening was the last addition to the seabird list for the day.

Great Shearwater (c) Niall Keogh

Wilson's Storm-petrel (c) Niall Keogh

Wilson's Storm-petrel (c) Niall Keogh

Wilson's Storm-petrel (c) Niall Keogh

The murky visibility, rain and moderate North East wind dropped some more migrating passerines (songbirds) onto the ship overnight with 10+ meadow pipits, 3 wheatears and a white wagtail doing the rounds of each deck throughout the day, some even ending up inside the dry lab! The inclement weather must have disorientated them whilst on migration to Iberia/West Africa and the R.V. Celtic Explorer looked like a good place to rest. A few individuals became very tame as they searched around the ship for scraps of food, but ignored all of the tasty morsels we left out for them! Hopefully clearer conditions in the morning will allow them to get their bearings and head off again on their merry way.

Wheatear (c) Jason McGuirk

White Wagtail (c) Niall Keogh

Meadow Pipit (c) Niall Keogh

Now we make our towards the Porcupine Bank SAC where we will retrieve a static acoustic monitoring device positioned there in May and will continue East across the Porcupine Seabight.