SOUTHERN STINGRAYS: BAHAMAS REEF FISH (41)

January 9, 2018 by Rolling Harbour

SOUTHERN STINGRAYS: BAHAMAS REEF FISH (41)

Anyone who has scuba-dived or snorkelled around the bright coral reefs of the Bahamas, or hunted bonefish out on the Abaco Marls will have come across Southern Stingrays Dasyatis americana. And there are certain places (eg Manjack Cay) where you can actually feed them – and not come to any harm…

FEED THEM? AREN’T THESE GUYS LETHALLY DANGEROUS CREATURES?

The name that always comes to mind in connection with stingrays is poor Steve Irwin, the charismatic Australian wildlife expert who was tragically ‘stung’ over his heart as he swam close over a ray while filming underwater. But this was, it would appear, a dreadful combination of circumstances with a terrible outcome.

The ray’s stinger is in fact an erectile venomous barbed spine near the base of the tail and not on the end of it (as one might expect). But these creatures are not out to harm you – though of course when you are in their environment you should accord them the respect that they merit.

If you are walking / wading in the water, avoid the risk of accidentally treading on a ray. Best to shuffle your feet forward in the sand; if there’s a half-concealed ray feeding or resting on the bottom nearby, it will swim away peacefully. I took the photo below while bonefishing on the Marls; the ray directly ahead slowly makes off as the skiff drifts closer. The next one is of a ray with its young – completely aware of us as we glide past to one side, but not especially bothered.

If you are swimming, snorkelling or diving, don’t get too close – especially by swimming directly over a ray (apparently Steve Irwin’s mistake, so that he was struck right in the chest by the stinger when the ray reacted).

Enough of the potential dangers. The southern stingray is a magnificent creature, as Melinda’s wonderful photographs show. She spends half her life underwater and I’m not aware that she has had a problem with a ray.

Like many larger sea creatures, stingrays need help with their personal care – the removal of parasites, dead skin and so forth. And so they make use of the services offered by small fish like gobies, wrasses and shrimps at a CLEANING STATION. Here are 2 photos of rays doing just that. You can see the tiny fish by the reef, going about their work. There’s a mutual benefit in this symbiotic relationship, in which it is understood that the cleaners are unharmed. Indeed, they will often enter the mouths and gills of a fish to clean… including the teeth. So there’s dental hygiene on offer too…

RELATED POSTS

YELLOW STINGRAY

GRACE WITH ATTITUDE

TAKEN TO THE CLEANERS

Photo Credits: Melinda Riger / Grand Bahama Scuba, except for the feeding photo (cheers, Samantha Regan), the ‘specimen’ from Tomas Willems (Wiki) and my two noted above

MANGROVE DIE-BACK IN THE ABACO MARLS: THE FACTS

September 1, 2015 by Rolling Harbour

MANGROVE DIE-BACK IN THE ABACO MARLS: THE FACTS

For some time now, there has been understandable concern about the increasing evidence of mangrove die-back in the Abaco Marls and elsewhere in Abaco waters. Scientific investigations are ongoing and you will find some of the survey results so far on the excellent Abaco Scientist interactive map HERE. You’ll find other relevant and authoritative mangrove material if you check out the BLOG menu of the website.
Abaco - The Marls

The ‘200 sq. miles’ in my map is debatable, depending what one includes. Other estimates are of 300 or even 400 sq. miles. Whichever, the Marls cover a massive area of mangroves, islets, flats, channels and wonderfully diverse wildlife. A large proportion of the many species – fish, birds, turtles etc – depend on the complex ecology of the mangroves for food, shelter and breeding. Depletion of the mangroves from whatever cause will have a direct effect on the creatures of the Marls.

Ryann Rossi, a PhD student with North Carolina State University, has been researching the worrying phenomenon of mangrove die-back in the Marls this summer. She has written an interesting and informative account (conveniently in the RH ‘Facts about…’ style) that was published in Abaco Scientist last week. The blue links will take you to the ABSCI site for further information on each topic. I’m grateful to Ryann and ABSCI for permission to use the material.

Five Things to Know About the Mangrove Die-back in The Marls (at this point, anyway)

1. This die-back appears to be the result of multiple stressors acting together. Think of it in the sense of our own body – when our immune system is down, we are often more susceptible to getting sick. The same thing is likely happening to the mangroves.

2. It appears as though a fungal disease may be taking advantage of already stressed mangroves and causing die-back. We did preliminary surveys across Abaco and found fungal lesions nearly everywhere. However, the fungus was present in different densities in different areas. In the die-back area nearly all the leaves remaining on trees have lesions. We think that this pathogen capitalized on the mangroves being weakened by other stressors such as hurricanes, which cause extensive leaf drop, change in the movement of water, change in sedimentation and erosion.

3. We are still working on identifying the pathogen associated with the lesions we’ve found. We are confident that it is a fungus and are currently growing fungal cultures in the lab to examine defining morphological characteristics in addition to using DNA sequencing to identify the culprit.

4. We have documented the presence of the Robust Bush Cricket (Tafalisca eleuthera) in the die-back areas as well as other areas with high densities of lesions. These crickets are documented to consume Red and White mangrove leaves. As such, we were concerned about their potential role in die-back. We set out a caging experiment to exclude the crickets from certain dwarf Red mangrove trees to see just how much grazing they may be doing in the die-back area. This experiment is ongoing.

5. The take home: there is likely more than one causal agent of the die-back in The Marls. Many factors govern mangrove productivity and functioning: nutrient availability, salinity, sedimentation rate, herbivory, and disease are just a few of the factors that contribute to overall mangrove function making it very difficult to pin point which factors may be driving the die-off. On the bright side, we are confident that we have a lead on the causes and we are working hard in the field and laboratory to fully understand what is going on in The Marls.

By Ryann Rossi|August 26th, 2015|Disease, fungus, Insects, Mangroves and Creeks, The Marls

All pics below taken while fishing on the Marls except Melinda’s shark (I’ve never got a good one)

Hawksbill Turtle, Abaco Marls (Keith Salvesen)

Reddish Egret (White Morph), Abaco Marls

Southern Stingray, Abaco Marls (Keith Salvesen 4)

FRIENDS OF THE ENVIRONMENT has also included an article on die-back by Ryann in its latest Newsletter:

Mangrove Die Off on Abaco by Ryann Rossi, NCSU

This summer Stephanie Archer and I continued research efforts focused on determining the cause of the mangrove die-off in The Marls (work funded by the National Science Foundation). Our efforts were predominantly focused on the fungal pathogen we found associated with the die-off site. We created a small citizen science and outreach project to document the presence or absence of the pathogen across Abaco. This project consisted of short surveys and leaf collections. In total, 92 areas were surveyed including locations from Abaco and San Salvador. We also took this outreach project to the annual Bahamas Reef Environment Education Foundation (BREEF) teacher training conference. There we disseminated survey packets to teachers from islands throughout The Bahamas who will help us collect more data on the presence (or absence) of this pathogen on other Islands.

3 men on a skiff, Abaco Marls (Keith Salvesen : Rolling Harbour)

Three men on a skiff – Abaco Marls

On Abaco, we constructed an experiment to investigate the role of grazing and the presence of fungal lesions on Red mangroves. We simulated grazing using crafting scissors to cut small sections on 600 leaves in 4 different mangrove creeks. We observed the leaves for 28 days to determine if cutting leaves predisposed leaves to fungal infection. At these sites we also trapped for insects to gain an idea of what kind of grazers may be chewing on the leaves. We also did a series of disease incidence surveys that will be routinely monitored for disease progress over the next 2 years. These surveys will allow us to systematically track the progress of the disease. In addition to our field work, we spent many hours in the laboratory isolating fungi from leaves to grow in culture. These cultures were brought back to North Carolina State University and will be sequenced in order to help us identify the fungal pathogen responsible for making the lesions on the mangrove leaves.

Credits: Source material Ryann Rossi; Abaco Scientist; all photos © Keith Salvesen @ Rolling Harbour except those by Ryann / ABSCI in the main article and Melinda Riger’s cool shark

GRACE WITH ATTITUDE: SOUTHERN STINGRAYS IN THE BAHAMAS

April 27, 2015 by Rolling Harbour

GRACE WITH ATTITUDE: SOUTHERN STINGRAYS IN THE BAHAMAS

Southern Stingrays are often seen in Abaco waters. In the bay of Rolling Harbour at Delphi, we sometimes watch them admiringly from the balcony or beach as they lazily cruise along the shoreline in the turquoise water. If someone is in the water, they will make a leisurely detour round them – unfrightened in their own element, but unthreatening and disinclined to investigate human intrusion. Diving with them is a wonderful experience (though I have never got very close). Melinda Riger – a scuba expert with great camera skills – takes the most beautiful photos of the stingrays she encounters. Here are a few that I haven’t yet featured. Notice the little striped CLEANING GOBIES going about their business.

Southern Stingrays are often encountered when one is bonefishing in the low waters of the Marls. I took the photos below while we were fishing in a channel between areas of mangrove. As the skiff was poled very slowly forward, I saw the stingray coming straight towards us. I wondered how it would react. Very elegantly, was the answer. It turned effortlessly and unperturbed to one side, then resumed its original course leaving a clump of mangrove between it and the skiff.

RELATED POSTS

SOUTHERN STINGRAYS

RAYS OF SUNSHINE

YELLOW STINGRAYS

Credits: Melinda Riger, Grand Bahama Scuba; RH

RAYS OF SUNSHINE ON THE ABACO MARLS

March 25, 2014 by Rolling Harbour

RAYS OF SUNSHINE ON THE ABACO MARLS

The Marls of Abaco are prime bonefishing grounds, a vast area of labyrinthine mangrove swamps, sandy islets, channels and shallow flats on the west side of the main island. The fish are wily and powerful, the fly hooks are barbless, and each one caught, retained, boated and swiftly released is a prize. There’s plenty of other wildlife to be seen. Heron and egrets, ospreys, belted kingfishers, wading birds and many other bird species make the Marls their home. In the water, there are snappers, jacks, barracuda, and sharks of various kinds and sizes. These latter range from small black tip, lemon and hammerhead sharks to more substantial contenders, with the occasional massive bull shark to add a frisson for those on a suddenly fragile-seeming skiff…

There are also rays. I have posted before about the SOUTHERN STINGRAY and the YELLOW STINGRAY. Out on the Marls I have mainly seen Southerns as they move serenely and unhurriedly through the warm shallow water. A couple of weeks ago, we were out with the rods when we had a completely new Ray experience. I’m not overly given to anthropomorphism and getting too emotional about encounters, but we all found this one quite moving – even our very experienced guide.

Gliding to our right side, a pair of stingrays slowed as they neared the skiff

The adult paused very close to us, allowing the little ray to catch up

Lifting a wing slightly the adult let the juvenile creep under, while keeping a beady eye on us

The large ray was missing the tip of its tail, presumably from some adverse encounter

The creatures examined us carefully for 2 or 3 minutes, before separating

Then they slowly drifted away across the sand…

According to our guide, this gently protective behaviour is not uncommon. They may well have been completely unrelated, the large ray tolerating the smaller one accompanying it through the waters and offering a kindly wing in the presence of danger or suspicious objects like us.

Photo Credits: Mrs RH (I was too entranced at the sharp end, with a bird’s eye view, to get a camera out)