Off the east coast of Abaco lies one of the longest barrier reefs in the world. Some authorities suggest it is the third longest, but the exact ranking of the top dozen coral barriers is a matter for considerable debate. None of the lists I have just checked agree, except that the Great Barrier Reef is the outright winner. I suspect that the problem lies in the loosely generalised description of ‘barrier reef’ and in variations of the appropriate criteria for determining length (it may also depend on who is doing the measuring, of course).
Melinda Rogers of Dive Abaco took this bright sunlit ‘Coralscape’ in the Fowl Cays National Park. It’s a place I have tentatively snorkelled around with great pleasure, despite being in the top dozen most useless swimmers in the world (my appalling underwater videos were disqualified from the rankings for being… rank).
Yellowtails are just one of several damselfish species in Bahamas waters. These small fish are conspicuous not just for the bright tails that give them their name. More striking if anything – especially if seen underwater in sunlight against the coral – are the electric blue spots visible in both adults and juveniles.
The body of adults is dark blue to brownish to almost black
The body of juveniles is blue
Yellowtails are a common and widespread variety of damselfish. They have a limited ability to change colour according to their surroundings, but with their bright tails and luminous blue flecks, it’s hard to see how they can look, to a predator, anything other than a tasty snack.
I have enjoyed seeing these little fish at Fowl Cay Marine Preserve, Abaco. The reef there makes for easy and rewarding snorkelling, with a wide variety of small and medium-size reef fishes to be seen. It’s an expedition I would definitely recommend to anyone wanting to see a healthy and active reef in a completely natural protected area.
I found that a video I took with a tiny camera was sadly of use only to myself. No one else would be able to make anything out due to the marked camera shake. Novices, huh? You are spared that: here’s a brief example of yellowtails swimming instead, showing the difference between juveniles and adults.
Credits: all photos, Melinda Riger / Grand Bahama Scuba; video from Desert Diving
Last summer, the big motion picture sensation for the bird world was, of course, Pixar’s ineffably adorable creation, Piper – the ultimate ‘Chick Flick’. This little ball of cartoon fluff was not, as some thought, based on a piping plover but on a sanderling – a type of sandpiper (clue in name). This 6 minute ‘short’ preceded the main event, the hugely popular Finding Dory. You can read all about the film Piper and the birding aspects of the film HERE.
Finding Dory is not about a fish of the dory species, of course. Voiced by Ellen DeGeneres, Dory is in fact a species of surgeonfish Paracanthurus, the familiar blue tang found on the reefs of the Bahamas. To see these fish in Abaco waters, Fowl Cays National Park is always a good bet.
Dory can be identified as a maturing juvenile: blue, with a yellow tail. In due course – in time for the sequel film – she will become blue all over, with perhaps the odd flash of yellow (see photos above).
In real life, a baby blue tang is in fact entirely yellow, except for blue rings around the eyes. In Pixarland, however, Dory is just an adorbs miniature version of her youthful self.
Blue Tang are lovely to watch as they cruise round the reefs, sometimes in large groups. Their colouring ranges from pale to dark blue. However, these are fish that are best looked at and not touched – their caudal spines are very sharp. When the fish feels in threatened, the spine is raised and can cause deep cuts, with a risk of infection.
Still from a crummy video taken at Fowl Cays some years back to illustrate a group of blue tang
Blue tangs are inedible, they apparently smell unpleasant, and they can cause ciguatera. However they are popular in the aquarium trade. This is a distinct downside of highly successful films such as Finding Nemo and Finding Dory. In defiance of the well-meant and broadly ecological message of both films, the trade in clown fish and to a lesser extent blue tang was boosted by their on-screen portrayal as adorbs creatures desirable for the entertainment of mankind… ‘Nuff said.
Credits: All excellent photos by Melinda Riger / Grand Bahama Scuba; one pathetically bad still from a low res video, me; cartoons purloined from an online aquarium somewhere or other
I have no idea if there is a collective noun for a large group of silversides. ‘Frenzy’ would cover it, but that is reminiscent of ‘feeding freezing’ which has a specialist meaning – and anyway, silversides are crazy even when they aren’t feeding. 24/7/12/365 as far as I can make out. I think ‘a panic of silversides’ might be the answer. They are just… all over the place at high speed. Sometimes swirling around pointlessly, other times moving in unison and suddenly all changing direction simultaneously, like a single creature made of tiny shards of silver.
There are quite a few silverside species around the world. The ones in the Bahamas are Atlantic silversides (Menidia menidia), also known in the north east of the United States as ‘spearing’. They seem to exist for two purposes. The main one is to be breakfast, lunch or dinner for larger fish, sea birds and shore birds. The other is for their usefulness in scientific research because of their sensitivity to environmental changes.
In one sense they are easy prey for predators. A determined fish will always manage a snack by swimming into the middle of a panic and (probably) simply by opening its mouth wide. On the other hand, their sheer numbers coupled with the speed and randomness of movement mean that a single may find a degree of safety in numbers. It’s hard for a predator to target any individual fish in the general melee and confusion. Silversides also favour seagrass beds, which give some shelter and protection – and a reasonably safe place to spawn. Or, as some of these photos show, they will hang around wrecks or squeeze into rocky spaces in the reef.
A panic of silversides apparently pouring like a waterfall down through a gap in the reef
WHAT DOES A STATIONARY ATLANTIC SILVERSIDE LOOK LIKE?
Some time ago we used to go to the reef at Fowl Cay Marine Preserve with Kay Politano, and I would snorkel with a small and very basic lo-res underwater camera. I was hampered by being a disgracefully feeble swimmer; by not having snorkelled for a length of time calculable in decades; and by being a complete novice at underwater photography. Despite these not inconsiderable disadvantages I managed to cobble together a few short movies on my computer (I was new to that too). Here’s one that nearly works, in that it gives an idea of what happens if you ‘swim with silversides’. I know you scuba guys all swim with sharks, but cut me some slack here please…
Photo Credits: Main photos Melinda Riger of Grand Bahama Scuba; Silverside Waterfall by Kay Politano; motionless silversides byFISHBASE.ORG. Music: Goldon Giltrap, ‘Fast Approaching’
The Blue Tang Acanthurus coeruleus is a species of Atlantic surgeonfish mostly found on coral reefs. They are known as surgeonfish because they can slice you with their sharp, spiny caudal fins. Adults are blue, ranging from a deep blue or even purplish to much paler blue.
Surprisingly, as juveniles, Blue Tang are bright yellow.
As they grow, they become blue, with the tail being the last part to lose the yellow.
Blue Tang are herbivores, cruising constantly round reefs feeding on algae. They also act as cleaners of other fish species, removing parasites. They themselves may be cleaned by gobies by visiting so-called ‘cleaning stations’. These piscine beauty parlours have a medicinal purpose as well, since cleaning helps to cure minor wounds.
These fish often move around reefs in large schools, as shown in the header image. Apart from having some value as an aquarium fish, they are not generally of use to humans. Their spiny caudal fins can cause a nasty wound. They have an unpleasant smell. Their flesh supposedly contains toxins, and they carrying a risk of the disease CIGUATERA. I can’t even find a recipe for them online – now, that is a bad sign, there are some people who will try anything. I guess best to boil them for an hour or two, drain the water, allow to cool, and throw away the fish.
FUN FACT In the Disney/Pixar film Finding Nemo, the character Dory (voiced by Ellen DeGeneres) is a blue tang.
BLUE TANG: THE MOVIE [RE-RELEASE]
“RECIPE Take one incompetent swimmer who hasn’t snorkelled in, oh, nearly 40 years. Place him over a coral reef for his first time ever. Add a small underwater camera totally alien to him. Immerse for 30 minutes in warm briny water. Lessons have been learnt for next time. Mainly, don’t keep waving the camera about; let the fish move round you rather than vice versa; and most important of all, remember to keep breathing or else…
Here is BLUE TANG: THE MOVIE (music by Adrian Legg), 45 secs of advanced camera-shake with some beautiful fish more or less in shot for most of the time. If you are prone to sea-sickness, do not enlarge the video. If you are allergic to poor photography… well, thanks for visiting.”
Credits: Good pictures, Melinda; bad pictures and execrable movie, not Melinda
The SOUTHERN STINGRAYDasyatis americana is a ‘whiptail stingray’ found in the Western Atlantic Ocean. Their habitat and personal habits – feeding and mating – are similar to those of the YELLOW STINGRAY. They live on the seabed, where they feed on small crustaceans, molluscs and fish. They expose their prey by flapping their ‘wings’ (= pectoral fins) to disturb the sand
You want to avoid treading on one of these if possible. Their tails have a serrated barb covered in venomous mucous, used for self-defence. These spines are not fatal to humans, but if you step on one it may be an experience in extreme pain to tell your grandchildren about.
Luckily they are likely to see you long before you notice them, and to swim away from your approach
IUCN LISTING: ‘DATA DEFICIENT’
Surprisingly, the ‘at risk’ status of the Southern Stingray is not known. However, as with other marine species that humans like to befriend in the wild for the perceived benefit of both parties, there are parts of the Caribbean where stingray swims involve rather more than merely swimming with and enjoying the rays in their own environment. There is organised hand-feeding with cut-up fish, even general fondling and cuddling, that can make these wild creatures seem ‘tame’. There is growing concern that such close dependent interactions with humans is not a good thing, at least for the stingrays.
A diver admiring a ray while keeping a respectful distance
If you watch out for them… they’ll keep an eye out for you
Credits: Melinda Riger of Grand Bahama Scuba; Wiki for thumbs / material; selected online trawlings
My incompetent first ever underwater video at Fowl Cay Marine Preserve, Abaco. I hadn’t snorkelled for X decades, and frankly had some breathing-and-swimming-simultaneously issues, let alone trying to hold a tiny camera steady. Still, here it is (with a proper diver’s video below)
Music credit on my vid to the fairly litigious Joe Satriani – see JS v Coldplay ‘If I could Fly’ / ‘Viva La Vida’ plagiarism case (settled, to no one’s great advantage). Hey, Joe, what you doin’ with that writ in your hand? For anyone the slightest bit interested in the alleged similarities, here is a mash-up reward for reading about stingrays. Or penalty.
Albert King, Lead Belly and Mike Bloomfield are prime examples of foremost bluesmen guitar-slingers who, in their own distinctive styles, favoured the key of… I’m sorry, what did you say? Oh yes, quite right. My misunderstanding. Apologies, I’ll take it from the top…
Deep blue sea. Deep blue fish. *Deep breath*. All better now. The fish below may all readily be found nosing around the coral reefs of the Bahamas in a leisurely manner. Mostly, they are feeding. Fowl Cay Marine Preserve, Abaco, is a great place for watching them. No need to have all the gear – a simple snorkel, mask and flippers, and an ability to float a bit, would be sufficient.
BLUE CHROMIS Chromis cyanea
These dazzling little blue fish will be one of the first you’ll meet (along with the omnipresent yellow and black striped sergeant majors, so friendly they will come right up to your mask). You can’t miss them. Though very small, their electric blue colouring cuts through the water even on the dullest of days up-top. They can reach 5 inches in length, but most that you see will be tiddlers. They are frequently seen in the company of larger fish.
BLUE PARROTFISH Scarus coeruleus
Parrotfish play a vital part in the ecology and health of the coral reef. They graze on algae, cleaning the coral and grinding the surface with their teeth. They take the nutrients and excrete the rest as… sand. This helps to form your beach! To find out more about their uses and habits, click PARROTFISH. You’ll find a great deal of interesting info about the species, conveniently compressed into factual bullet points.
BLUE TANG Acanthurus coeruleus
The blue tang is a type of surgeonfish, all-blue except for a yellow spot near the tail. The blueness can vary considerably, from very pale to dark. They tend to swim elegantly around in large groups.
Here are some images of schools of blue tang that I took with a cheapo underwater camera at Fowl Cay. They are a lovely sight as they drift slowly past alongside the reef. The top one also has a sergeant major (see above).
CREOLE WRASSE Clepticus parrae
This wrasse can grow up to a foot long, and may be found at considerable depths on deep-water reefs – 300 feet or more. They are active by day, and hide in rock clefts at night. This species is sociable, moving around in shoals. They develop yellow markings with age.
QUEEN TRIGGERFISH Balistes vetula
There are several species of triggerfish. The queen is capable of changing colour to match its surroundings, or (it is said) if subjected to stress. I think we have all been there. It is an aggressive and territorial fish, and its favourite prey is the sea urchin, a testament to its courage…
QUEEN ANGELFISH (JUVENILE)
I have featured this species before HERE, and strictly it as much yellow as blue. But the blue earns double points, surely, for its startling vividness. Anyway, I like the way it hangs casually upside down, and the bubbles in this photo.
Credits: Good photos – Melinda Riger of Grand Bahama Scuba; Poor photos – RH
From time to time I end a post with something musical. Just for fun (toxic concept). So here is a real “Slow Blues in C” from the fantastic guitarist Stefan Grossman off his eclectic ‘Yazoo Basin Boogie’ album. 22 quality tracks. Buy from Am*z*n – much cheaper than iT*nes.
I usually have 3 or 4 planned posts on the go. Some are quick to compose, some are not. Especially those requiring technical input from the technically unsound – downloading a video, changing the file format, editing and polishing, uploading to a compatible ‘carrier’ etc. I’ve been meaning to get round to making some fish and reef videos from footage of a trip with Kay Politano of Abaco Above & Below. Now I have…
If you are tolerant enough to at least start this one, which focusses on coral, can I restate the excuses? I swim like a panicking cat. I hadn’t snorkelled for a great many decades years until 2011. I was a stranger to underwater scenery, let alone photography. I wave my tiny camera around too excitedly, though not deliberately to inflict seasickness on hapless viewers… It is a bit less bad this time round, however. Luckily I can tell from my stats if anyone has bothered to click on the video below, and you can rely on me to trash the thing if I find a paltry (or non-existent) response. Best just to watch on the small screen, though.
With those dire warnings, here is the video. I would be very interested to ID all the corals that can be seen. There are the easy ones like sea fan, elkhorn, mustard hill, brain… but what’s that one over there? No, behind the waving one…? Comments / suggestions welcome. And if you don’t much care for coral, there are some pretty fish to look at…
Music Credit: Adrian Legg’s ‘Old Friends’, from ‘Guitar Bones’
ADDENDUM JAN 13 I am really grateful to Capt Rick Guest for taking the time to view the video, and the trouble to analyse the contents. He has very helpfully highlighted many points of interest in the film, both as to coral and as to fish, so I’ll post his commentary in full, with my thanks. Of both interest and concern are Rick’s remarks about the Elkhorn Coral. I had wondered about its bleached look. It’s dying…
At 0:36 a lavender Sea Fan…(Gorgonia ventalina).
At 0:52 Yellow “Leaf”,or “Letuce Coral”. Agaricia species growing around a living soft coral called a “Sea Rod”. Soft Corals have living polyps which feed on plankton just like the hard corals.
At 1:02 More Agaricia, and a small Brain Coral at bottom. Either a Diploria, or Colpophylia species.
At 1:10 A Sergent Major fish, (Abedefduf saxatilus). One of my favorite Taxanomic names! Behind is mostly dead, Elkhorn Coral. The white areas being indicative of “White Plague”. A disease responsible for Coral Whiting…..Death!
At 1:37 A Blue Tang swims over some “Mustard Coral”… Porites porites.
At 1:55 A chubby “Chub” swims by. Likes caves and caverns and edible, but not palatable.
At 2:33-38 Much coral bleaching damage here on these Elkhorn Corals.
At 2:40-48 A Thalassoma bifaciatum,or “Blue Headed Wrasse” is swimmin’ about. This guy used to be a lady,but he’s a product of Protandric Hermaphrodism! When there’s a paucity of males in the area, a yellow female will step up and become a male for the school.
At 3:29 Lower right: a fine example of Millepora complanata,”Fire Coral”. Fire Coral is more related to Man-O-War, and jellyfish than Corals.
This is the first short video from footage taken in June at Fowl Cay, 2000 acres of protected coral reef waters. This was the start of another great day out snorkelling and island-hopping with dive-diva Kay Politano ofABOVE & BELOW ABACOMarsh Harbour. In due course there will be more videos of fish and coral. There is very slight evidence that lessons have been learned since last year’s erratic novice snorkeler / underwater photographer efforts. Still a way to go of course. The production process has been hampered by a major format problem between my camera chip thingy and the Mac I now use. It told me the data was unrecognisable / corrupted / damaged etc, which was massively disappointing. Then I thought of <<techno-tip>> downloading to an old PC and transferring to the Mac on a memory stick. Problem solved.
This huge swirling mass of (tens of) thousands of small fish confronted me as I round one end of the reef. I’ve never seen anything like it before, except on TV. It was an astounding, dizzy-making spectacle. When I swam into the middle of the shoal, I expected to feel tickled all over – but despite the huge numbers of fish, their speed, and their sudden and apparently random direction changes, I wasn’t conscious of feeling them at all. I assume the commotion resulted from the presence of larger fish feeding on the small ones. Or possibly from my appearance…
Music credit: Gordon Giltrap (Hofner champion) ‘Fast Approaching’
A short time ago I posted in some detail about the poisonousLIONFISH. I included material about the rapid increase of this Pacific species in Caribbean and Floridian waters following accidental / deliberate releases in recent years. I also included videos from Grand Bahama scuba-expert FRED RIGER to balance the anti-lionfish orthodoxy, showing that the fish in fact do some good on the reefs. The post provoked a few comments, and had a surprising number of hits. Here is some further research courtesy of the excellent SEA MONSTERwhich adds a dimension to the debate and concludes with a very good point… Incidentally, in a recent morning snorkelling at Fowl Cay Marine Preserve, Abaco, I did not encounter a single one of these creatures (Mrs RH was unluckily stung by a jellyfish, though…). But I guess the Preserve is well policed against such intrusive species, which are otherwise found in large numbers in the area.
Why are lionfish populations exploding across the Caribbean?
Author: John Bruno on June 6, 2012
Lionfish are an exotic fish now found throughout the Greater Caribbean and eastern Atlantic that have become incredibly abundant on many reefs, especially in the Bahamas and off North Carolina. Lionfish are piscivores (fish that eat other fish) and were introduced from the Indo-Pacific by the aquarium trade in the late 1990s off Florida. Mostly likely, someone got tired of their fish and released them purposefully.
One hypothesis explaining their great success is the absence of natural enemies; predators, parasites and competitors. This is probably compounded by the fact that few Caribbean reefs have any predators left that could eat them (thanks to overfishing).
Another – and I think much more likely explanation – is because there is so much to eat in the Caribbean! Not because there are more fish, but because it is so much easier to catch them. Unlike fish in the Indo-Pacific, native Caribbean fishes do not appear to recognize lionfish as a potential threat. So the lionfish gobble them up, grow faster, make more babies, spread to new islands, etc.
Case in point: My lab group was working in Belize last week on the lionfish invasion. One of the things we were doing was collecting the otoliths and gonads from lionfish that we speared on a number of reefs to compare their fitness across the Caribbean (e.g., on reefs with and without native predators, etc). We also looked at stomach contents and many of them had parrotfishes in their tummies or still in their throats! The photo above is of the eggs from one lionfish we caught near Glovers Reef Atoll and the partial contents of it’s stomach (a juvenile striped parrotfish)!
Lionfish appear to be little more than machines that convert parrotfishes to baby lionfishes. Which is pretty much the purpose of all animals (consuming others and transforming them into your own genotype and species). But jeez, couldn’t those aquarium hobbyists have released a herbivore that could be converting macroalgae to fish biomass? That would have been much more useful.
EXPLORING THE CORAL REEF AT FOWL CAY MARINE PRESERVE, ABACO
First, a warning for anyone arriving new to this blog (hi! welcome) either on purpose or accidentally: I can’t swim very well, I hadn’t snorkelled for decades until last year, and I’d never before used a camera underwater.
That said, there is probably enough in this 2:40 min video to warrant a quick view. As with other videos from this expedition to Fowl Cay Marine Preserve (STINGRAY / BLUE TANG), best viewed small to avoid queasiness and disorientation. You can always Pause for a breather. There are some nice fish obligingly in view from time to time, and the coral is very diverse. And I’ll know what to do this year to get better results, besides trying harder with the swimming… (Music: East Wes by Eric Johnson, off Ah Via Musicom)
RECIPE: Take one incompetent swimmer who hasn’t snorkelled in, oh, nearly 40 years. Place him over a coral reef for his first time ever. Add a small underwater camera totally alien to him. Immerse for 30 minutes in warm briny water.
Lessons have been learnt for next time. Mainly, don’t keep waving the camera about; let the fish move round you rather than vice versa; and most important of all, remember to keep breathing or else…
Here for the first time on public release is BLUE TANG: THE MOVIE (music by Adrian Legg), 45 secs of advanced camera-shake with some beautiful fish more or less in shot for most of the time. If you are prone to sea-sickness, do not enlarge the video. If you are allergic to poor photography… well, thanks for visiting.
A while ago, I posted stills from a reef-snorkelling video – my first ever underwater video attempt, and indeed my first snorkel for about 40 yearsCLICK===>>>REEF FISH I started with a stingray, producing some rather… ok, very… modest results, but it was at least identifiable if you looked carefully and felt benign.
I’ve learned a few tricks since then. Here is the whole clip, still hopeless in most respects but there’s something quite cute about the creature. Mercifully it is only 37 seconds long. I reserve the right to delete this post when I realise no one has actually watched it! [LATER: Oh! I find a few hardy souls have done so. It’s a democratic vote for the ray to stay, as I see it]
[Belated credit to the fairly litigious Joe Satriani (see JS v Coldplay 2009) for borrowing the intro to one of his songs. It’s a non-commercial tribute, Joe]
Here are some more stills of reef fish taken from the video of our reef-snorkelling trip to Fowl Key with Abaco Above and Below. I’ll add the fish IDs gradually. The first batch are images of individual fish; the second batch is a sequence showing a queen parrot fish feeding on small fish (?gobies) – images that I’d expect David Attenborough to describe in his quiet and breathy way as “really quite extraordinary”, especially if he has seen the general standard of pics in this blog…
BLUEHEAD WRASSE (Thalassoma bifasciatum)
YELLOWTAIL DAMSELFISH (Microspathodon chrysurus)
YELLOWTAIL DAMSELFISH & Juvenile (I hadn’t noticed the baby yellowtail until I examined the video)
You will need: swimming kit; sweatshirt (it can be cold on the boat after snorkelling); stuff for Island Hopping later on, inc. camera, money etc; snorkel practice in the pool if you haven’t used one for (say) 20+ years – use the Club gear; Ian Took’s slim ‘Fishes of the Caribbean Reefs’. NB there is limited room on the boat, so you’ll need a bit of a nifty towel work to preserve modesty when changing…
Kay Politano of Abaco Above and Below in Marsh Harbour pencils in an unspecified number of places for a day’s island-hopping and reef-snorkelling while I find out how many non-fishing-that-day Delphi guests might be interested. Seven sign up, and one morning we all set off to Marsh Harbour. In Kay’s shop we try on our flippers, marvel at the scuba possibilities (a completely implausible proposition for most of us…), then we troop off to the marina and Kay’s reassuringly powerful and safe-looking catamaran. It takes 12 passengers; the other 5 are already aboard. We set off towards a threatening-looking weather front; rain later is a certainty…
Kay and rh at the controls
Passing by several Cays, we arrive at Fowl Cay Marine Preserve and drop anchor. We don our flippers, wrestle with our masks and snorkels, and in turn drop off the back of the boat (ok, stern, is it?) into warmish water, under thick grey cloud. My practice in the Delphi pool has paid off, and soon I am wheezing and gurgling my way towards the reef with my head (mostly) under water, a situation I generally avoid.
I am completely unprepared for what I find when I get to the reef. David Attenborough’s favourite production team has kindly arranged for a wide variety of bright fish, some electrically charged, to come up close and inspect me, an intruder in their world. I’ll spare you the colour-supp superlatives and graphic intensifiers – you’re probably blasé and have seen it all before – but I am totally gobsmacked, even with my mouthpiece in place. It’s all real! It’s even better than TV! And don’t get me started on the coral…
Blue Tang / Ocean Surgeonfish
While I gasp and bubble my way around, I keep a small waterproof video camera running (see GADGETS review). My swimming is feeble at the best of times, but somehow it all seems to be coming together – my flailing limbs, the laboured breathing, the reef, the fish and the footage. We circle round the reef – occasional pale figures appear in my lateral vision – for about 25 minutes, then return to the boat and the struggle to remove our flippers… Everyone is excited about what they have seen (some saw barracudas).Who cares that it’s started drizzling… we are wet already and it’s off to Lubbers Cay for lunch; see forthcoming Island-Hopping Post. And see MARINE LIFEpage for more reef fish photos taken on this expedition.
ADDITION April 2012 I notice there have been a few specific searches ‘what is the plural of Sergeant Major?’ Good question. The strict grammatically correct answer is, I suspect (as with the military rank), ‘sergeants major’ because it’s the sergeants who are plural and the ‘major’ is a qualifier to distinguish from other degrees of sergeant (were there sergeants minor, for example). It’s the same with courts martial – not ‘court martials’. BUT it sounds all wrong and pernickety. I reckon the whole fish is a sergeant major. If there are 2 or more, you’ve got some sergeant majors to play with.