This deep sea shark pales in comparison – for an unknown reason

Gajić, A. A., de Loose, E., Martin, A. G., Neuman, E., & Karalić, E. (2024). First description of leucism in the deep‐sea angular rough shark (Oxynotus centrina) and the first documented pigment disorder in family Oxynotidae Gill, 1912. Journal of Fish Biology.

An accidental bycatch from a trawler became a puzzling surprise to both fisherman and scientist alike. A ghostly pale individual was brought up from the waters of Albania in March this year – a deep sea angular rough shark that looked remarkably different from its relatives. This discovery led to a scientific investigation into the reason for this individual’s distinct colorating – or lack thereof.

Many animals, like sharks, have color patterns that are genetically determined by the regulation of pigment-containing cells called chromatophores. Certain cells, however, can be affected by pigment disorders and create a deviation from the common coloration. One such disorder called leucism leads to a partial absence of pigment, leaving pale patches on certain areas of an animal. This was hypothesized to be the cause of this shark’s abnormally pale skin. Instead of the average typical black-brown or dark gray, this deep sea angular rough shark sported a wash of pale gray, save for a few dashes of white spread unevenly across its tail, dorsal fins and trunk.

A study was conducted on the bycatch, which was caught due to commercial fishery activity in the area. The morphology and colorations of the abnormal shark were compared to a common one using specific identification keys and criteria. The shark’s overall health was examined as well as any hormonal changes or environmental factors that could have potentially affected its pigmentation. It was determined that this shark had been in good physical health at the time of its unfortunate capture. This may be an indication of the endangered species’ survival; the presence of such distinct color anomalies may not impair its ability to live in the darkness of deep waters.

It’s an extremely rare occurrence among elasmobranchs, the cartilaginous fish known as sharks and rays. In fact it’s the only documented case of the pigment disorder in any rough shark species, which only makes the discovery more intriguing. The exact reason for this color pattern is still unknown, but scientists surmise it could have been brought on by anthropogenic factors or low population density since the angular rough shark species is critically endangered. The diversity in the gene pool could be decreasing due to inbreeding, potentially leading to more abnormalities in their coloration.

There is still much more work to be done to fully understand these rare deep sea creatures, which is why studies like these can offer glimpses into their survival. Understanding a species is the first step in the journey to protect it, but learning without damaging it is just as important. The bycatch of endangered or at risk species in commercial fishing is a severely unfortunate event, and its occurrence should not be regarded lightly. There is a great need for more appropriate regulation surrounding the action and its consequences. While the presence of the deep sea angular rough shark provides some knowledge, there are mysteries that remain with the rest of those lurking in the depths of the ocean.

Piper Evans

I’m a California native with a lifelong curiosity for all things related to the ocean. I got my bachelors in Marine Biology from the University of California Santa Cruz, and I’m currently pursuing a masters degree in Animal Science at the University of Idaho where my main focus of study is fish nutrition in aquaculture. My favorite subject to study outside of school is the deep sea. I enjoy learning about new mind boggling species, the latest discoveries of the deep, and the history of deep sea pioneers, research and technology. If I’m not studying the mysteries of the ocean, I’m probably roller skating or watching scary movies.