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.
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).
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.
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.
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.
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.
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.
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.
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.