Cetaceans of the Celtic Sea_Part 3

31st Oct 2018

IWDG Science Officer Seán O'Callaghan reports from RV Celtic Explorer after the third and final week of the annual Celtic Sea Herring Acoustic Fisheries Survey. This is the 15th consecutive year the IWDG have conducted a cetacean survey using this research platform which estimates the biomass of herring for stock assessments. It is one of the longest datasets collected in Ireland to explore predator-prey relationships, explore changes in distribution and abundance and assess predator requirements to input into fishery models. 

Cetaceans of the Celtic Sea, week three of surveying: Monday 22nd – Sunday 28th

Our last week at sea started off on a northern approach to Waterford in ideal but cool conditions. Breakfast was spent trawling through a few online articles marking the return of Boomerang the humpback whale or more formally HBIRL3 but without a location or date of the supposed sighting, Cork or Waterford were the two most likely locations where he had turned up.

We started the days watch just before turning west on an inter-transect near Tramore. Our first sighting was a fleeting one, four small skittish brownish shapes rolled at the surface moving towards the morning glare their overall size and non-distinct dorsal fin ear marked them as harbour porpoise but then they were gone, minutes later Andrea spotted a far larger animal lingering around the portside glare, a fin whale which turned out to be closest whale we had to shore for the trip.

Turning south again as the Celtic Sea began to take command of our field of view with the mainland just starting to haze away we picked up distant blows, some tall further out but one lower and bushy a little bit closer in. We focused on the lone whale without binoculars for a while and then its head protruded clearly vertical from the water momentarily followed by raised fluke upon descent.... a humpback! And then the Explorer turned around to go fishing so we went off effort but tried to keep an eye on the whales.

 

Fin whales and Humpback #IRL3. Photos Andrea Fariñas

When we went back on track after the haul we instantly picked up the humpback initially within 300 m of the vessel while we were preparing the laptop to resume effort so a hastily start was made and then the big camera telephoto lens was brought out to capture then distant images of the animals dorsal fin and dorsal surface of the tail fluke on one observed dive. A nearby lunging fin whale was seen as a bit of "distraction" while obtaining these images! Despite the distance between the vessel and the whale it was very apparent that it had a visible white scar on both sides of the dorsal fin like Boomerang and his identity was later confirmed by IWDG Sightings Officer Pádraig Whooley so it was quite a coincidence that we were reading about that particular humpback whale out of the 92 individuals currently in the Irish catalogue.

Heading south away from shore we lost the large whales so it was just the occasional dolphin or tuna seen from then on which was the case for the remainder of the fisheries survey as we snaked our way west into Cork despite the great sea conditions and sometimes numbing northerly wind.

The survey had finished up by Thursday outside Cork Harbour (where we still had not connected with the resident group) so as the dark started to kick in we steamed to Dunmanus Bay for a day of calibrations before heading back north to Galway on Saturday.

Saturday's sea state was far too poor for any productive watches since any present cetaceans would likely be lost amongst a rising swell and streaked white caps. However the rugged landscapes of the Beara, Iveragh and Dingle peninsula's marking Ireland's southwest corner were well worth being up in the bridge while we bounced about in a strong head on wind.

   Skelligs Photo: Sean O'Callaghan

Shortly before passing the Skellig's, Sophia Wassermann, a PhD student from NUI Galway spotted a wispy vertical spray rise above the sea on the portside, when they blew again we were ready and tried to take images to confirm the species while being knocked around. Two whales were present close in but just one was positively identified as being a fin whale, a species rarely seen in the region. Common dolphins were in attendance but the whales were lost just as quickly as they appeared. Continuing on north passing the peninsula's, the first fall of snow gave away the areas highest points and while midway across Dingle Bay, the highest of them all, Carrauntoohil stuck up like a frozen shard.

  Celtic Explorer. Photo Nick Massett

A few more common dolphins were seen approaching the Blaskets but the hauled out dark shapes of the Great Blasket’s grey seals were the last marine mammals observed since we were then sieged by the swell slamming the Dingle peninsula's exposed northwest side. We arrived in Galway Bay early Sunday morning and a few hours later we were land bound again.

It was a great few weeks with nice sightings and great people throughout.

Cetaceans of the Celtic Sea, week two of surveying: Monday 15th – Sunday 21st

Week two started uneventfully as we moved on to Wexford, passing Hook Head with no sightings on Monday despite the reasonable weather conditions, but we reconnected with the large whales on Tuesday with distant blows in the morning followed by a confirmed fin whale later in the day. We were treated to numerous common dolphin sightings along with feeding blue fin tuna before the day was out. There was a noticeable change in marine traffic south of Tuskar rock with Rosslare’s supersized ferries appearing on the horizon along with chemical tankers and numerous beam trawlers, so it didn’t feel like we out on our own quite as much.

 

Breaching blue fin tuna and bow riding common dolphins

With Carnsore Point to the north of us on Wednesday morning and with the first leg starting to wind down before our port stop back in Cork for a crew change, we headed south once again where we were swarmed by common dolphins that seemed to be magnetically drawn to the bow before heading off on their way. Some Bluefin tuna also made an appearance but disappeared just as quickly as they zoomed into sight. In the evening the last line transect was completed and the Explorer steamed for Cork.

Waking up the following morning we were clearly entering Cork Harbour, with its tree lined hills towering above passing vessels in view outside my port side cabin. The first winter chill was felt outside while the River Lee steamed despite the clear blue sky and unabated sunshine offered from above. With the crew swapped over for leg 2, the Explorer pushed off from the pier, turned clockwise and set off out to sea.

 Fin whales on the fishing grounds. 

Andrea Fariñas Bermejo, a MSc student from the Galway-Mayo Institute of Technology joined us on this changeover to assist with the MMO work, so we ran through the daily workload and did a dummy run visual survey leaving Cork harbour to see if we could locate the harbour's small resident group of bottlenose dolphins, but as we cleared Roches Point and motored eastwards it was clear that the dolphins weren’t going to materialise.

   

Lunge feeding fin whales with common dolphins

Fabulous sea conditions greeted us early Friday morning with a mercury sea state and amber sun. It didn’t take long to spot our first common dolphins, while another mammal, a bat species, was spotted by the surveys newest birding addition Sally O’Meara. A string of common dolphins were seen as we headed initially south and then north in the morning with the occasional tuna making characteristically brief appearances. The morning was grey to the point where it was almost tricky to distinguish the skyline from the horizon, but anything that broke the surface was very obvious, so when the first fin whale appeared 2 km off the bow, its blow wasn’t that obvious but its long profile and dorsal fins were. Over the course of the rest of the day we picked up more fin whales where some individuals were feeding but the stand out moment of the day was when an adult fin whale accompanied by an immature and another individual began feeding within 300 m of the vessel. The day ended with an unexpected but welcome sighting of 11 bottlenose dolphins including one new born calf who kept their distance while the sunset, not a bad first day for Andrea.

 

Saturday was very much a day for the tuna who outnumbered the few common dolphin sightings, although the rolling back reactionary dive of a seal (potentially a grey) just by the bow before we finished up was an offshore surprise. On the ship front, the 113 mt ZEELAND factory trawler past us in the morning and an offshore resupply vessel was also seen in the distance. Our luck changed on Sunday with a chilling 18 knot westerly wind hitting us straight on the nose as we passed Hook Head for the last time. The accompanying frothed sea’s made the day's observational effort trickier than the two previous days, but not impossible. Unfortunately, all that was on offer were two brief tuna sightings, despite the evenings improved weather.

With good weather forecast, we’ll be aiming to locate the large whales once again for our final week at sea.

 

Cetaceans of the Celtic Sea, week one of surveying 8th – 14th October 2018

This year’s Celtic Sea Herring Acoustic Survey began with a rolling start as wind has been a defining factor of our first week at sea. The survey will do sweeps of the South coast's inshore and offshore herring grounds from Cork to Wexford and back again over a three week period by the Marine Institute R.V. Celtic Explorer to determine the current status of herring stocks, which will inform management decisions for next year’s fishing season.  I’m aboard to record marine mammal observations along the way.

A 04:00 am departure from Galway’s Docks on Monday the 8th October had to be scrapped due to strong westerly winds that risked scraping the Explorer against the docks lock gates, so a day time departure at 4.30 pm was opted for instead. Once out in the open it didn’t take long to hit the swell churned up by the overnight strong winds, so a retreat to the bunk for the evening was made, as the vessel negotiated a lumpy North Atlantic.

Surveying started ahead of schedule to accommodate storm Callum and the Fastnet Rock signalled the start of observational effort on Wednesday 10th Oct. Not too long after settling into the rhythm of the crows nest, four bulky but shiny shapes shot over a breaking wave heading towards the bow, at first they seemed to be a couple of dolphins heading for the bow but the second time they surfaced I was ready for them. With an oval shaped body and vertical caudal fin, they turned out to be bluefin tuna, and then they were gone. A couple of common dolphins on the bow later on closed out the first grey day of surveying.

Day two was equally grey with plenty of white caps but surveying began nonetheless. A trickle of common dolphins showed in the morning, all were coming from the east but heading west.  As we steamed into the afternoon, the trickle of dolphins soon became a conveyor belt, with two melanistic individuals in attendance, one of which could have passed for a striped dolphin if it wasn’t for a faint inkling of its diagnostic hourglass pattern (see image). One final big group of dolphins finished off the days sightings and once we passed the Old Head of Kinsale we headed for the shelter of the River Lee in Cork City to wait out Storm Callum.

 

Friday 12th Oct.: the swell was too big for safely walking around Celtic Explorer, let alone for any surveying, so the day was spent trying to avoid the ever present threat of sea sickness that was back on the agenda.

We picked up more dolphins and tuna on Saturday 13th but Sunday 14th Oct. has been the standout day so far with fantastic sea conditions, a crisp chill in the air and large whales, lots of them! The morning watch began like usual, with the computer happily recording our position, I set up shop and scanned near and far thinking about what it would have felt like for “goon” (blow) to have been called out on one of the Norwegian whaling steamers operating out of Mayo a century ago after a few fruitless days at sea. Sure enough, a puff of white shot up from the sea in the near distance, its second appearance confirmed it was no illusion and so we were heading towards our first fin whale of the trip. The bird surveyors (Dr Heidi Acampora and Conall Hamill) had just also wanted to see whales and they weren't disappointed.

More blows were sighted off the starboard side as we headed inshore, including two pairings each with an accompanying smaller blow. With fish about, the fisheries team went trawling, so with all the activity I stayed on to see if anything else was about; it paid off; as two fin whales surfaced 200 m off the bow and starboard side just as the coastguard Helicopter Rescue 117 came over to attempt a few excercises. Common dolphins and blue fin tuna were picked up as we headed north but it was offshore yet again where we connected with the whales, this time a lone minke followed by an adult and immature fin whale pair that crossed within 400 m of the bow, well southwest of Hook Head. It was a great way to round off the first week of surveying.

Seán O'Callaghan

IWDG Science Officer

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