DIVE DRY WITH DR. BILL #774: DEVIL FISH
One of my least favorite fish in our waters is the bat ray (Myliobatis californica). Yes, most divers love them and are thrilled to spot them. Occasionally I enjoy them too. However, when they are feeding, especially in large numbers, they stir up the soft substrate just like beginning dive students and cause visibility to plummet. I detested them even more as they became suspect in the death of the only white abalone I've ever seen!
Yet one of my favorite fish is a relative of our bat ray. I'm talking about the manta ray (Manta birostris), also called the devilfish due to the cephalic fins projecting from the head. This ray is in the same family (Myliobatidae) as our bat ray, the eagle ray and others. Found in tropical to warm temperate waters with temperatures above 68° F, it is rarely seen in our offshore waters so I had to travel to Palau to get a good opportunity to film them. Yes, I know... I lead a tough life.
I chose to dive with Palau Dive Adventures (PDA) based on recommendations from friends. They certainly lived up to more than my expectations and it was a fantastic trip. I visited a little late in the manta season. We had very little luck at the manta cleaning station in German Channel. I did get some great shots of one that swam by up close and personal though.
PDA suggested a special trip to a secret spot over one of the weekends so I signed up. Despite strong currents that were somewhat of a challenge for this old geezer, we encountered about two dozen mantas. Why so many? The water was somewhat murky, indicating it was rich with plankton... and that's what these huge rays chow down on!
Yes, I said (er, wrote) huge... these fish get up to 23 feet in wingspan and up to 3,000 pounds in weight! They have a large head with a large mouth for taking in lots of plankton at a time. Unlike many rays the mouth is oriented forward rather than down as in bottom feeding species like the bat ray. Projections on either side of the mouth are the cephalic fins, which help funnel food into the mouth. Their pectoral fins are triangular in shape and very capable of propelling these majestic fish, while the dorsal fins are small and located near the base of the tail.
On the dorsal surface mantas are black or dark in color while the ventral side is light in color with spots located toward the rear. The spots are distinctive enough to allow recognition of individuals. Some mantas are all black in color. A coating of mucus on their skin protects them from infection. Not sure I'd take the same precautionary measures!
Supporting these massive bodies requires a lot of calories. Back when I was a svelte swimmer, I needed about 5,500 calories a day due to frequent and grueling morning and afternoon swim practices. Heck, mantas swim 24/7! They are said to eat about 13% of their body weight each week. That would be nearly 400 pounds of shrimp, krill and other plankton. I think Mom claimed I ate as much!
Thanks to Shark "Weak," many of you have seen the breaching great whites in the episode "Air Jaws." Mantas are also known to breach... and given their size they must create huge belly flops. They migrate over some distance to locate areas with rich plankton and may travel individually or in groups as large as 50. I think they must get a group rate.
You, my readers, have patiently awaited the prurient portion of this column. Yes, I'm talking about manta ray sex... "munching and mating" as I always say. Males are sexually mature at about 12-13 feet while the precocious females are ready in 8-10 years. Mating may occur at different times of the year in different parts of their range. The male follows behind his intended victim... er, mate... as she swims along. He attempts to grab her pectoral fin (usually the left one) in his mouth. Hmmm... I've never tried that strategy. Once her fin is securely captured, the male turns upside down and inserts his clasper into the female. The mating pair may be followed by several other males, apparently voyeurs.
The fertilized eggs remain inside the female and the developing embryo is nourished by the yolk. Once they hatch, the one to two young are retained inside the mother. Since they are not mammals, the manta possesses no placenta or umbilical cord. So how do they received food and oxygen? I was surprised to learn that the female produces secretions known as histotroph in her uterus. I learn something new every day! After about a year, the young manta is expelled and no longer cared for. If lucky, it may live 50 years. If not... an orca or large shark may have a BIG dinner.
© 2018 Dr. Bill Bushing. For the entire archived set of nearly 775 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Our local bat ray showing the downward facing mouth; manta ray close approach showing forward directed mouth; and mantas feeding in plankton rich water.
One of my least favorite fish in our waters is the bat ray (Myliobatis californica). Yes, most divers love them and are thrilled to spot them. Occasionally I enjoy them too. However, when they are feeding, especially in large numbers, they stir up the soft substrate just like beginning dive students and cause visibility to plummet. I detested them even more as they became suspect in the death of the only white abalone I've ever seen!
Yet one of my favorite fish is a relative of our bat ray. I'm talking about the manta ray (Manta birostris), also called the devilfish due to the cephalic fins projecting from the head. This ray is in the same family (Myliobatidae) as our bat ray, the eagle ray and others. Found in tropical to warm temperate waters with temperatures above 68° F, it is rarely seen in our offshore waters so I had to travel to Palau to get a good opportunity to film them. Yes, I know... I lead a tough life.
I chose to dive with Palau Dive Adventures (PDA) based on recommendations from friends. They certainly lived up to more than my expectations and it was a fantastic trip. I visited a little late in the manta season. We had very little luck at the manta cleaning station in German Channel. I did get some great shots of one that swam by up close and personal though.
PDA suggested a special trip to a secret spot over one of the weekends so I signed up. Despite strong currents that were somewhat of a challenge for this old geezer, we encountered about two dozen mantas. Why so many? The water was somewhat murky, indicating it was rich with plankton... and that's what these huge rays chow down on!
Yes, I said (er, wrote) huge... these fish get up to 23 feet in wingspan and up to 3,000 pounds in weight! They have a large head with a large mouth for taking in lots of plankton at a time. Unlike many rays the mouth is oriented forward rather than down as in bottom feeding species like the bat ray. Projections on either side of the mouth are the cephalic fins, which help funnel food into the mouth. Their pectoral fins are triangular in shape and very capable of propelling these majestic fish, while the dorsal fins are small and located near the base of the tail.
On the dorsal surface mantas are black or dark in color while the ventral side is light in color with spots located toward the rear. The spots are distinctive enough to allow recognition of individuals. Some mantas are all black in color. A coating of mucus on their skin protects them from infection. Not sure I'd take the same precautionary measures!
Supporting these massive bodies requires a lot of calories. Back when I was a svelte swimmer, I needed about 5,500 calories a day due to frequent and grueling morning and afternoon swim practices. Heck, mantas swim 24/7! They are said to eat about 13% of their body weight each week. That would be nearly 400 pounds of shrimp, krill and other plankton. I think Mom claimed I ate as much!
Thanks to Shark "Weak," many of you have seen the breaching great whites in the episode "Air Jaws." Mantas are also known to breach... and given their size they must create huge belly flops. They migrate over some distance to locate areas with rich plankton and may travel individually or in groups as large as 50. I think they must get a group rate.
You, my readers, have patiently awaited the prurient portion of this column. Yes, I'm talking about manta ray sex... "munching and mating" as I always say. Males are sexually mature at about 12-13 feet while the precocious females are ready in 8-10 years. Mating may occur at different times of the year in different parts of their range. The male follows behind his intended victim... er, mate... as she swims along. He attempts to grab her pectoral fin (usually the left one) in his mouth. Hmmm... I've never tried that strategy. Once her fin is securely captured, the male turns upside down and inserts his clasper into the female. The mating pair may be followed by several other males, apparently voyeurs.
The fertilized eggs remain inside the female and the developing embryo is nourished by the yolk. Once they hatch, the one to two young are retained inside the mother. Since they are not mammals, the manta possesses no placenta or umbilical cord. So how do they received food and oxygen? I was surprised to learn that the female produces secretions known as histotroph in her uterus. I learn something new every day! After about a year, the young manta is expelled and no longer cared for. If lucky, it may live 50 years. If not... an orca or large shark may have a BIG dinner.
© 2018 Dr. Bill Bushing. For the entire archived set of nearly 775 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Our local bat ray showing the downward facing mouth; manta ray close approach showing forward directed mouth; and mantas feeding in plankton rich water.
