Mantis Shrimps

Funny thing about perception. When you don't expect something, you often don't see it. For me, one of the interests of diving is to discover creatures I didn't know before. I often poke into holes, turn over rocks to see what's crawling under them and generally become a nuisance to crawly critters under water...

A while back, I noticed a creature I hadn't seen before. It inhabited a perfectly round hole on the crumbly bottom at the foot of the cliff at the mouth of the lagoon. The hole was so perfectly round that I suspected the animal had carved it. It was about three to five centimeters diameter, and the animal occupied the opening completely. As I approached, it retreated inside the hole, but soon came back. Good. I like curious animals, they're fun to play with...

It took me quite a while to identify what I'd seen on the snorkeling outing that day, especially since the only part of that critter I'd seen was a pair of eyes, and the front of the head, or rather what I thought were eyes and head.

After much browsing of "Two Oceans", the excellent book by George and Margo Branch, and some searches on the Internet, I finally settled on a Mantis Shrimp.

The article on Wikipedia about Mantis Shimps, in particular, is very informative for a neophyte like me. A short extract about their eyesight might convince you to pay more attention to these creatures: 

The eyes of mantis shrimp may enable them to recognize different types of coral, prey species (which are often transparent or semi-transparent), or predators, such as barracuda, which have shimmering scales. Alternatively, the manner in which mantis shrimp hunt (very rapid movements of the claws) may require very accurate ranging information, which would require accurate depth perception.

The fact that those with the most advanced vision also are the species with the most colourful bodies suggests the evolution of colour vision has taken the same direction as the peacock's tail.

I have since visited the Mantis Shrimp very regularly at the mouth, Despite searching quite thoroughly, I haven't found another specimen. I have managed to coax it half-way out of its burrow, but not fully out. It has very interesting black and yellow patterns on its carapace and body, but I could not get a good picture because both my hands were occupied trying to make it come out of its hole.

Then, on a dive, I spotted a more colourful one:

Since then, I've been able to spot more and more on the dives.

The fact that they seem to stay in the same place most of the time makes it easy to find them again and again.

One more reason to dive in Bilene...

Dive safely, don't hold your breath!

Daniel                       :-)

<Added a few days later>... a video of one of the encounters. 

I think this is a Lysiosquillina maculata, the zebra mantis shrimp or striped mantis shrimp (see Wikipedia)

A lot more photos on my G+ albums.
A very interesting article in Practical Fishkeeping.

Lagoon dives

Diving has been very good lately. When we go outside the bay, we almost always see whales, and hear their song from the moment our ears are underwater and we've calmed enough to actually listen.
I don't know if there are more species, but I have positively identified Southern Right and Humpback whales last week, and quite a few are accompanied by calves.

For divers that have not been in the water for a long while and need to get back underwater gradually, and for divers that are enthusiastic about our artificial reef program, we organize lagoon dives.

I really like lagoon dives. First of all, there is the feeling of "being home". You might live in a nice area, be able to hike in a beautiful forest, but taking a short walk in your backyard does not take away from that beauty. Simply, what's in your backyard is different, and intimately known to you. You probably planted what's there to begin with, and looking at the birds visiting your bird-feeder from the comfort of your armchair is a different activity than going for a hike in the forest.

There are three spots in the lagoon where we go regularly, Legoland, The Graveyard and the Mouth.

We mostly go to the last one, the Mouth, for snorkeling sessions.
On the way, we often spot a flock of Flamingos.

The area covers the base of the rocky cliff, actually not "real" rocks, but ancient coral deposits, a length of about hundred by twenty meters, with barely more than three meters depth.
As you can see, it's well within the reach of beginner snorkelers.

The area is teeming with life. I have spotted Lion Fishes as small as a centimeter in length, among more mature ones of close to twenty centimeters.

There are also numerous eels, juvenile and mature.

Of course, it's not all about fish, there are also many crustaceans (Cleaner Shrimps, Hermit crabs), gastropods (Cowrie Shells, Nudibranch, Sea-Cucumber, Shaggy Sea-Hare) and of course all the flora.

A short distance away, we can observe Sea-horses, 

Pipefish and Razor Fish

Closer to the Water Sport Center, we have Legoland. So called because it consists of elements built with concrete blocs, used like one would use Lego blocks to build a playground.

The lagoon bottom is mostly flat sand, so any asperity will offer a refuge to fish and other creature from the fishermen, whose nets don't discriminate between edible and non-edible species, small or big individuals.

In my mind, the presence of so much fish life in the immediate proximity shows the artificial reef is beneficial to the fish population.

It's not uncommon to have a school of Kingfish circle around us on the way down.

At the bottom, we see quite a few resident Orangespotted Rockcod

Butterflyfish, Snappers, Parrotfish and many others I still haven't been able to identify.

The Graveyard is a different experience. Although the initial motivation in the construction of the reef was to provide a solid surface to which sea creatures would attach, the opportunity for having fun was too strong to resist. The shape of the concrete slabs evolved to resemble tombstones, and that's how the name of the reef was found. For a modest fee (about R100), you can inscribe your own tombstone (mother-in-law's names are popular, and so are the names of competing companies) and sink it yourself.

The rockcods like to hang at the foot of the tombstone.

The reef currently covers an area of over forty meters diameter, with dozens and dozens of tombstones. We also added a few "fish-houses" built with concrete blocks of the same model as Legoland. I have observed clouds of larvae in these fish-houses develop to juvenile fish.

This reef is a favorite destination for night dives, adding to the spookiness of the experience...

So when the tide table doesn't allow us to go out of the mouth, diving inside the lagoon can be an enriching experience.

Stay tuned for more diving news, don't hold your breath,

Daniel     ;-)

Looking for Marine Scientists...

After many discussions with local people and visitors, I've come to the conclusion that the best course of action to improve the survival chances of the seahorses in the area is to get the specie we have here (Hippocampus Camelopardalis) on the CITES list of endangered species.
The way to do that is to have a study published by scientists that shows the decrease in population.
So I'm appealing all that read this blog and their friends, who would like to come to Bilene to study the seahorse population?

This is a job that would be most appealing to someone doing honors, a masters or a phD thesis. Speak around you, let's make things happen...

What to do about the disappearing Seahorses?

One of the elements that drew me to Bilene (Mozambique) is the sight of Seahorses.

More of my photos of Seahorses here

Just over three weeks ago, we had a wonderful time looking at dozens and dozens of Seahorses. The next day, I really struggled to find one. I was hoping that the late time of day made it difficult to see them on that afternoon,  but a long swim on Sunday morning confirmed my fears: most of the Seahorses have been fished out. This was further confirmed by some people from our group talking to local fishermen, who were holding handfuls of the dead creatures. This sad occurrence has been on my mind since then, and I'm reaching out to start a discussion and request ideas for a solution.

Wikipedia asserts that over 20 million Seahorses are used every year for medicinal purposes.

While it would be easy to demonize the Chinese people for eating animals we find cute, and dismiss the local fishermen as stupid for trying to earn a living, I believe the roots of the problem lie deeper.

I came across a similar problem in South Africa almost thirty years ago. Perlemoen , the local name of Abalone, was being poached in increasing numbers, mostly because of an increasing demand on the Far East markets, ease of international communication and transport, and increasing standards of living.
Nowadays, despite drastic legislation and big efforts at policing the situation, the poaching still continues and the number of shells found in the wild have plummeted.

I believe the seahorses we have in the Bilene lagoon are Giraffe seahorse . There is some confusion in the endangered status of this species, as the IUCN Red List shows there is no public data available to make a judgement about it. Meantime, Fish Base says " International trade is monitored through a licensing system (CITES II, since 5.15.04) and a minimum size of 10 cm applies."
Very few of the specimen we came across were as big as that, and since this is Africa, there is very little enforcement of the catch size.


The high population resilience characteristic is supported by "minimum population doubling time less than 15 months", but that is little comfort if more than half the population is fished out every year, and more importantly, before the specimen reach sexual maturity.


Therefore, the question I am asking is how best can we address this problem for the long term ?
Should we just shrug, be happy with the memories and photos and accept the unavoidable disappearance of these cute fish?
Should we keep the information about where the seahorses are a secret, and hope the local fishermen don't come across their habitat by chance?
Should we request that the authorities invest more resources into control and repression?


What are your thoughts on the matter? Please use the comments to discuss this issue, suggest possible solutions, or describe schemes that have worked elsewhere.

Stay tuned for more diving news, don't hold your breath,

Daniel     ;-)