Searching for Deep-sea Sharks in Scotland: Part One

Part One: Introduction

Studying some of the worlds deepest living sharks is a challenge. When diving down to 1800m is not an option, as research scientists, we must bring the sharks up to us. My latest trip to Scotland was to do just that and lucky for me, it would be an epic shark filled trip.

Research was conducted on board R.V Scotia.

The research expedition took place in a region called the Rockall Trough, located about 100km off the west of Scotland. Our fishing efforts were concentrated on the continental slope of this region, a sloping area of the sea floor that connects the shallow shelf seas 250m to the deep plains of the Rockall Basin 2000+m (See map).

The Rockall Trough is a deep trough that runs along the west coast of Scotland and Ireland.

This abnormally massive haul weighed in at about 25 tonnes….all of which needed to be sorted through and recorded.

Whilst the primary objectives of the research cruise were to record the faunal diversity and abundances in the these waters, I was on board to collect shark samples as part of my Ph.D research at Ocean and Earth Sciences at the University of Southampton.

As well as amazing diversity below the waves, our boat was accompanied by various bird species looking for a free meal

Big nets were towed behind the boat, for about an hour, at depths from 500m – 2000m. By carrying out fishing tows at different depths, we are able to observe how fish populations varied across different depths. Our catch would then be brought on board and passed onto the scientists to be sorted and recorded. Once all fish had been weighed, measured and returned to the ocean, I would then begin to collect the samples that I needed for my research.

A typical catch from the deep-sea. Lots of roundnose grenadier along with other bizarre species. Can you spot the shark?

In addition to information on the length, weight and sex of the shark, I collected a small piece of tissue from them. This would then be placed in the freezer and upon our return, transported back to Southampton where I could run chemical analysis on them. The chemical tests I run on this tissue will allow me to understand aspects on both the diets and movements of these sharks.

Various species of deep-sea catshark, Apristurus spp., caught at 1500m. Subtle differences between species can make it very difficult to distinguish them from one another.

At 500m we would catch mainly velvet belly lantern sharks and blackmouth catsharks but as we started moving deeper down, the diversity and size of the sharks just seemed to grow and grow. Longnose velvet dogfish would begin to take over and different species of catshark would begin appearing. Larger shark species such as leafscale gulper sharks and fat portuguese dogfish were common in catches but only in very low numbers, 1 or 2 at a time.

Portuguese dogfish, Centroscymnus coelolepis, are one of the largest species of deep-sea shark in this region. We often found fish, squid and even whale meat in the stomachs of these guys

Chimaeras, sharks’ cartilaginous cousins, were also abundant and we found a variety of different species depending on the fishing depth. These ranged from the tiny large-eyed rabbitfish to the huge pale ghost shark, more on these at a later date.

The large-eyed rabbitfish, Hydrolagus mirabilis, was one of the smallest species of chimaera in the region…..and who said deep-sea creatures can’t be cute.

Whilst I was astonished by the huge diversity of sharks that occurred in this relatively small area, the diversity of fish was equally amazing. Most catches were dominated by a couple of fish species, mainly Roundnose grenadiers or Agazzi smootheads, but there was a remarkable range of other utterly bizarre looking fish. Each haul yielded something different, something that made it memorable.

The roundness grenadier, Coryphaenoides rupestris, is one of the most common species of fish found in these waters. These wonderful looking fish are targeted by French deep-water fisheries and their populations have been historically hammered.

I will be producing more articles over the next coming weeks, looking at the different fish and shark species in more detail. Additionally we caught two extremely rare species of shark that this survey had not seen before and infact very few people have ever seen in these waters. More on this in the next few articles, so follow me on Twitter (@SharkDevocean) or on Instagram (@sharkdevocean) to keep up-to-date.

Christopher Bird