In my previous post I introduced the recent survey I attended around the Balearic Islands, Spain, in search of deep-sea sharks. In this post we will meet those shark species and learn a little more about them. Also, there are lots of pictures of these cute guys for your viewing pleasure!
The abundance of elasmobranchs around the Balearic islands was really quite staggering. This may, in part, be due to the highly variable substrates that also surround the islands, providing many a habitat for different species and life stages. However, don’t worry if you are planning a trip to the Med, as the majority of individuals caught were <60cm. The sharks in the Mediterranean are notoriously smaller than their Atlantic Ocean counterparts. These waters are often referred to as being oligotrophic, or low in nutrients, and subsequently the species of shark found here are usually smaller than those found in other oceans basins. With less nutrients available, species typically reach a maximum size much smaller here than their cousins in other ocean basins.
The 3 main species caught during this survey were Scylorhincus canicula (Lesser spotted dogfish), Galeus melastomus (Blackmouth catshark) and Etmopterus spinax (Velvey Belly Lantern shark). One individual of Squalus c.f. megalops (shortnose spurdog??) was also caught, but definitive identification could not be achieved using the resources on board. We will have to wait for the genetic work to come back with the answers on that guy.
My main personal objectives upon this survey were to collect samples of deep-water sharks and in particular a group of sharks called the Squaliformes (or dogfish). Although historically this survey has caught many species from this group, this trip would not be so fruitful. That is the nature of science though. They are undoubtedly there but I think this survey was just on the upper limit of their distribution. In the Med, typically, peak abundance of sharks occurs around 1000-1200 metres depth. The distribution of many of these deep-water dogfish has been recorded in less than 600m of water however. So you just never know! It just so happens on this leg of the trip we did not catch any. We went deep but not deep enough!
Most abundant in the shallower hauls was the lesser-spotted dogfish (Scylorhincus canicula). We recorded individuals from a whole range of sizes from small juveniles all the way through to large adults. They often occurred in very large numbers and were often dominated by one sex or the other. Females usually group together in rocks to hide from mature males. They feed mainly on crabs and fish that live on the seabed.
Almost as abundant but occurring at deeper depths was the blackmouth catshark (Galeus melastomus). This shark gets its name because of, you guessed it, the inside of its mouth is black. Its unique skin colouration is also fascinating and is most probably used for camouflage. Single sex hauls were less likely than the lesser-spotted dogfish, although this separation was sometimes observed. This shark also lives near the bottom and, like the lesser-spotted dogfish, eats mainly crabs and fish.
Of most interest to me was the deepest occurring of the sharks on this trip, the velvet belly lantern shark (Etmopterus spinax). Easily taking top spot as my new favourite shark ever, these remarkable little sharks are both very cute equally fascinating. Their shimmering skin is a decoration of purples, greens, silvers, blacks and blues. The black colouration on the belly of this shark is actually home to thousands of tiny glow in the dark cells, called photophores. When swimming in the middle of the water column, these cells will glow downwards thus hiding the sharks silhouette from the light penetrating from above. This type of bioluminescence is sometimes referred to as camouflage by counter-illumination. Other photophores have also been suggested to help distinguish gender in one another (via different glow in the dark genitals) and also warn predators of the two sharp spines on their back (like cautionary lightsabers).
The data collected from these lantern sharks will be invaluable in helping me better understand the distributions, movements and trophic roles of these mysterious sharks. They can be found in most waters of the Atlantic and Mediterranean so you can expect more coverage of this charismatic little fellow.
This survey was the first of a series of surveys I will be conducting around the Atlantic for my Ph.D thesis. I gained an invaluable array of skills and techniques that will be highly beneficial to my later work. I was also forced to develop my Spanish speaking language and although still terrible, mi espanol hablado esta mejorado (my Spanish speaking is improving). The whole experience was not only eye opening but highly inspirational. It gave me the opportunity to see creatures I had never seen before. It was hard work but it was doing what I am passionate about; working with sharks.
Thanks for reading. More #deepseadog information to follow.
Christopher Bird (@SharkDevocean)