Diving with British Marine Life: The John Dory

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Part 1 of a new series by our latest blogger Georgie Bull…

A few years ago, I attended a work experience placement at the London Aquarium. During a school session, the staff members gave the children a group of 20 photo cards and asked them to choose which ones they thought showed native species. The cards pictured the likes of corkwing wrasse, orca, basking sharks, cod, whiting, mackerel, and vibrant nudibranchs. Of these, colourful species were seldom selected. At the end of the activity, it was revealed that all the cards showed permanent or seasonal UK residents, which was met with shock from both the pupils and staff.

From this experience, and many more like it, I’ve come to realise just how underappreciated British marine life is.

Over the next six blogs, I will explore just a handful of the charismatic species encountered in the South West of England. I aim to introduce each species, describing my encounters with them before highlighting any relevant literature. There is still so much we don’t know about the species living on our doorstep.


In the build up to my first night dive at Chesil Cove last year, sighting reports circulated that john dory (Zeus faber) were seemingly everywhere. This species had been on my ‘to see’ list for quite some time so any likelihood of seeing one filled me with excitement. Halfway through the dive I noticed a faint, but frantic undulation centred around what looked like a large grumpy dinner plate. It was indeed a john dory. This individual was so full of expression that I found it hard not to fixate myself for the duration of the dive! This was the start of what became a frequent occurrence throughout the season.

Profile

As well as their false eyespot, elongate fins, and disc like body, john dory demonstrate distinctive behaviour in the water. Their movement is relatively slow, though their soft anal and dorsal fins (positioned behind their spined counterparts) move frantically to alter their position in the water. While small, their mouth is capable of rapid extension to draw in prey, and they’ll manoeuvre their bodies into all sorts of strange positions in the water to do so.

Zeus faber are often associated with warm water, but their distribution conflicts this idea, with their Northern range extending as far as Norway!

John dory are categorised as data deficient by the IUCN. The IUCN ranks species based on their population trends, and they are particularly famous for their ‘Red List’ which categorises endangered species. Sometimes insufficient information is available, and the organism is regarded as data deficient. As this is the case for the john dory, questions arise about how their population is coping with its value to the fishing industry.

Literature

It’s true that anglers and divers value john dory, but scientists have been finding out more about the species in recent years. One of their most distinctive features is the false eyespot. These spots are found in a variety of organisms from butterflies to lizards and are thought to divert predator attacks to less essential parts of the body (e.g. the tail) which may offer increased chance of escape. The role of eyespots in nature is understudied, but lab experiments in 2011 and 2013 showed that predators were inclined to attack eyespots spots more so than other areas of the body. This provided evidence in favour of eyespots acting as attack diversions.

On a different note, sound in the marine environment is receiving increased attention recently. Iconic footage captured by the BBC for Blue Planet 2 of reef noise, or hot topics like noise pollution from boat traffic are taking centre stage. But sound in the marine environment is used by individuals to communicate in a variety of different ways. John dory create sounds with sonic muscles that surround their swim bladder. Until 2018, this sound had only been recorded in air. A study recorded the species using baited remote underwater video (BRUV) footage and found that individuals would make the sound when predators were near. This caused predators to flee, suggesting the sound could serve as a territorial defence mechanism. As with all species, there are still many aspects to the life of john dory that we are only just beginning to understand.

References:


Hear more from Georgie here: https://georgiebullphotography.home.blog/

Georgie Bull

Georgie Bull

Georgie is a Marine Biology and Coastal Ecology student at Plymouth University and an active diver in the South West of England. This year she will be completing the HSE Scuba qualification with the University in the hope that scuba will become part of her future career. She is particularly interested in native species and has a soft spot for elasmobranchs and molluscs.

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