DIVE DRY WITH DR. BILL #746: BAT RAY MUNCHING
There is one critter in the ocean I'm not overly fond of. No, it isn't due to ugly looks or a poor disposition. It is because when they enter relatively shallow water (say recreational diving depths), they often ruin my dives. Late spring and summer is the time I usually see them there. Okay, they are kind of fun to film... until they start munching!
I'm talking about the bat ray (Myliobatis californica), a member of the eagle ray family. This week I'll focus on their munching behavior and next week on their... er.... ah... reproductive behavior. Remember that Dr. Bill is all about Munching and Mating in the Macrocystis or giant kelp forests. Munching is critical so the individuals in a species can grow and survive... to perform the ultimate function of any species, mating, which ensures the species itself will survive.
So why do I react so negatively to bat rays? They use their rather enlarged cephalic (head) region to hammer away at soft substrate trying to unearth tasty morsels. In doing so they stir up major clouds of sand and silt. Often times the only way you can locate these battering rams is by the thick sediment clouds they "kick" up.
Once out at Long Point the visibility dropped to a few feet as a massive cloud of dust was carried by the current toward me. At first I wasn't sure what caused it, and slowly swam over in its direction. Then I began seeing about two dozen bat ray tails sticking up above the cloud. Another time I was diving off Descanso Beach to conduct monitoring studies required by the State for the Sea Trek permit. The vis was horrible and I was just 2-3 ft off the bottom as unseen bat rays took off beneath me. I was a little concerned I might get Steve Irwinized!
Bat rays which behave themselves and "fly" in midwater or glide through our kelp forests are tolerable. However when these excited excavators land on the bottom, they begin digging large pits. They do so by flapping their "wings" (pectoral fins) and ramming their heads down into the soft bottom. As they dig, they encounter animals living within the substrate (called infauna). Delectable munchables may include Chaetopterus tube worms, clams, crabs, snails, sea cucumbers and even fish. In turn they may fall victim to various species of shark, including the great white.
Dr. Milton Love wrote that these depressions may be 2-3 ft wide, but I have seen ones in the 5-6 ft range. Now you get a dozen or more bat rays feeding in the same general area, and once the dust settles the bottom may look like a World War I battlefield due to the pits. If the bat ray has been successful there may also be dozens of worm tubes scattered about. Now I think Chaetopterus worms are pretty cool so although this is the "mutual eating society" at work, I am saddened by the chondrichthyian carnivore's carnage.
A while back I discovered another reason to detest bat rays. A few years earlier CDS instructor Ruth Harris discovered a single white abalone (Haliotis sorenseni) in the dive park. We carefully monitored it since this species is endangered. Then in April, 2016, Ruth discovered its shell crushed and no sign of the snail. She thought it might have been poached. However I spoke with former ab diver Randy Brannock who told me bat rays will hammer abalone to break their shells and eat them. I noticed Dr. Love also mentioned them preying on abalone on rocky reefs. Grrr. Now I despise them even more!
© 2017 Dr. Bill Bushing. For the entire archived set of over 700 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Bat ray coming at you and after landing on the bottom; hammering the bottom digging a feeding pit to chow down and minor dust cloud created by feeding.
There is one critter in the ocean I'm not overly fond of. No, it isn't due to ugly looks or a poor disposition. It is because when they enter relatively shallow water (say recreational diving depths), they often ruin my dives. Late spring and summer is the time I usually see them there. Okay, they are kind of fun to film... until they start munching!
I'm talking about the bat ray (Myliobatis californica), a member of the eagle ray family. This week I'll focus on their munching behavior and next week on their... er.... ah... reproductive behavior. Remember that Dr. Bill is all about Munching and Mating in the Macrocystis or giant kelp forests. Munching is critical so the individuals in a species can grow and survive... to perform the ultimate function of any species, mating, which ensures the species itself will survive.
So why do I react so negatively to bat rays? They use their rather enlarged cephalic (head) region to hammer away at soft substrate trying to unearth tasty morsels. In doing so they stir up major clouds of sand and silt. Often times the only way you can locate these battering rams is by the thick sediment clouds they "kick" up.
Once out at Long Point the visibility dropped to a few feet as a massive cloud of dust was carried by the current toward me. At first I wasn't sure what caused it, and slowly swam over in its direction. Then I began seeing about two dozen bat ray tails sticking up above the cloud. Another time I was diving off Descanso Beach to conduct monitoring studies required by the State for the Sea Trek permit. The vis was horrible and I was just 2-3 ft off the bottom as unseen bat rays took off beneath me. I was a little concerned I might get Steve Irwinized!
Bat rays which behave themselves and "fly" in midwater or glide through our kelp forests are tolerable. However when these excited excavators land on the bottom, they begin digging large pits. They do so by flapping their "wings" (pectoral fins) and ramming their heads down into the soft bottom. As they dig, they encounter animals living within the substrate (called infauna). Delectable munchables may include Chaetopterus tube worms, clams, crabs, snails, sea cucumbers and even fish. In turn they may fall victim to various species of shark, including the great white.
Dr. Milton Love wrote that these depressions may be 2-3 ft wide, but I have seen ones in the 5-6 ft range. Now you get a dozen or more bat rays feeding in the same general area, and once the dust settles the bottom may look like a World War I battlefield due to the pits. If the bat ray has been successful there may also be dozens of worm tubes scattered about. Now I think Chaetopterus worms are pretty cool so although this is the "mutual eating society" at work, I am saddened by the chondrichthyian carnivore's carnage.
A while back I discovered another reason to detest bat rays. A few years earlier CDS instructor Ruth Harris discovered a single white abalone (Haliotis sorenseni) in the dive park. We carefully monitored it since this species is endangered. Then in April, 2016, Ruth discovered its shell crushed and no sign of the snail. She thought it might have been poached. However I spoke with former ab diver Randy Brannock who told me bat rays will hammer abalone to break their shells and eat them. I noticed Dr. Love also mentioned them preying on abalone on rocky reefs. Grrr. Now I despise them even more!
© 2017 Dr. Bill Bushing. For the entire archived set of over 700 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Bat ray coming at you and after landing on the bottom; hammering the bottom digging a feeding pit to chow down and minor dust cloud created by feeding.
