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Jill Studholme
Writing on the marine environment and scuba diving
Writing on the marine environment and scuba diving

Jill's posts

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Florida sharks worth more alive than dead, says study
A week after Florida senators watered down a shark finning bill, research from Oceana finds that shark-related dives in Florida generated more than $221 million in revenue and fuelled over 3700 jobs in 2016. This compares to the total U.S. shark fin export market of just $1.03 million.

While shark finning is illegal in U.S. waters, shark fins – including imports from countries that allow finning – continue to be bought and sold throughout the U.S.

The demand for shark fins is one of the greatest threats facing shark populations around the world. Fins from as many as 73 million sharks end up in the global market every year.

Many shark populations have declined by more than 90 percent in recent decades due to overfishing.

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Good to know - researchers find humans can interact with reef sharks without affecting the behaviour of the shark in the long term, and that well-regulated shark diving tourism can be accomplished without undermining conservation goals.

Bradley D, Papastamatiou YP, Caselle JE (2017) No persistent behavioural effects of SCUBA diving on reef sharks. Mar Ecol Prog Ser 567:173-184.


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Gozo's Azure Window, loved by divers as part of the Inland Sea to the Azure Window dive, has collapsed into the sea.
More at

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Gozo's Azure Window, loved by divers as part of the Inland Sea to the Azure Window dive, has collapsed into the sea.
More at


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Happy International Women's Day
"It’s Never Too Late To Be What You Might Have Been"
George Elliot

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200th issue of SCUBA News (ISSN 1476-8011) Now Up
I've been editing SCUBA News for over 16 years and we've just sent our 200th issue.

We sent our first newsletter in the year 2000. It was before any social media, before Wikipedia.

The newsletter has changed in that time. The first issues were all text: no pictures whatsoever. We still, though, aim to provide useful information for divers who like to travel the world and care about the marine environment.

And if you are, or have been, one of our subscribers - THANK YOU! We couldn't have kept going without your articles, emails, suggestions and photos.

You can read the 200th issue at - it contains a feature on award winning underwater photographs such as the one below.
Other issues, including the first one, are archived at


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Which sunscreens are safe for sea life?
It’s a minefield trying to buy a sunscreen which doesn’t harm the sea life. Even those trumpeting their green credentials are not always free from harmful chemicals and components. You have to read the label very carefully. So what are the nasties of which scuba divers and snorkellers should be wary?

Nano-particles are minute chemical substances, which are about 100,000 times smaller than the diameter of a human hair.

Titanium dioxide and zinc oxide nanoparticles are often used in sunscreens. They allow clear sunscreen which can be sprayed on. However, they produce significant amounts of hydrogen peroxide, a strong oxidizing agent that generates high levels of stress on reef-building corals and marine phytoplankton. They have also been shown to make sea urchin embryos more vulnerable to toxins.

A study by Dr Craig Downs published last year showed Oxybenzone (also known as Benzophenone-2 or BP-2) increased the rate of coral bleaching. Additionally, the chemical damages the coral’s dna, affecting their reproduction. If that wasn’t enough other effects are to make juvenile corals become grossly deformed and encase themselves with their own skeletons.

Octinoxate, Butylparaben, 4-Methylbenzylidene Camphor
Another study, this time by Roberto Danovaro et al, named butylparaben, octinoxate and 4-methylbenzylidene camphor as being harmful to reefs.

How Much of a Problem is it?
According to NOAA (National Oceanic and Atmospheric Administration) 4,000 to 6,000 tons of sunscreen enters reef areas annually. This does not spread out rapidly or evenly over the entire ocean, but concentrates on popular tourist sites. It is estimated that 90% of snorkellers and scuba divers are concentrated on 10% of the world’s reefs.

So which sunscreens can you use?
Look for ones without the ingredients mentioned above. Zinc oxide and Titanium dioxide are good as long as they are not in nano-format. A quick guide is whether the sunscreen is clear or not. If it is clear, or in a spray, it probably contains nano-particles.

If the ingredients state “uncoated” zinc oxide then these are larger particles (non-nano) and safe.

Photo credit: Tim Nicholson

Original research at
Downs, C.A., Kramarsky-Winter, E., Segal, R. et al. Arch Environ Contam Toxicol (2016) 70: 265. doi:10.1007/s00244-015-0227-7

Danovaro, Roberto; Bongiorni, Lucia; Corinaldesi, Cinzia; Giovannelli, Donato; Damiani, Elisabetta; et al. Environmental Health Perspectives; Research Triangle Park116.4 (Apr 2008): 441-7.

Sunscreens as a Source of Hydrogen Peroxide Production in Coastal Waters
David Sánchez-Quiles and Antonio Tovar-Sánchez
Environmental Science & Technology 2014 48 (16), 9037-9042
DOI: 10.1021/es5020696


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I was drawn to this by the nudibranch connection - but I love the hyperbolic crochet 
The nudibranch sea slug embodies hyperbolic geometry, taking a form that, over hundreds of years, many great mathematical minds tried to prove impossible. Indeed the world is full of unconscious things ‘performing’ fiendishly complex mathematics. How can we make sense of this, and what impact can it have on the way that humans ‘do’ maths?

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Some great winning photos in the Ocean Art contest 2016

Photo credits and details at
11 Photos - View album

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When I posted this on my own page I got loads of comments about how the research was a waste of money. Obviously I disagree, just because it isn't apparent how research benefits people doesn't mean it's wasted. What do you think?
White Sharks Don't Mistake Surfers for Seals
It’s commonly said that sharks, especially great white sharks, Carcharodon carcharias, mistake surfers for seals when looking at them from below and thus bite them by mistake.

Researchers from Florida and Vienna, though, have found that this is not the case.

They discovered that the majority of damage to surfers and their boards is at best moderate in nature and does not reflect the level of damage needed to immobilise or stun a seal. Not only that, but the sharks biting surf boards tend to be smaller than those that bite seals.

The working basis of the mistaken identity theory is the silhouette similarity between a seal and surfer when looked at from directly below. However, the average depth among the examined cases was was only around 4m, so the shark is not coming directly from below but at a shallow angle.


The original research is at
Erich Ritter and Alexandra Quester, “Do White Shark Bites on Surfers Reflect Their Attack Strategies on Pinnipeds?,” Journal of Marine Biology, vol. 2016, Article ID 9539010, 7 pages, 2016. doi:10.1155/2016/9539010
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