DIVE DRY WITH DR. BILL #877: THE SILENT WORLD?
Some of our younger divers may not realize that Jacques-Yves Cousteau's first major film was called "The Silent World." Sadly a number of them don't even know who JYC was. I had a screening of the film for our local Catalina divers a year ago and wish I could resume having screening parties up at the house as we did pre-COVID. Wouldn't be prudent today.
Despite the title of the film, those of us who dive know that our oceans are not really a silent world. There are many sounds that we hear as we dive ranging from the snap, pop and crackle of Rice Krispies... er, pistol shrimp... to the melodious tunes of our large cetaceans. Fortunately we are free of the aircraft noise and sirens of the topside world, although we do get engine noise from the boats that venture close to our dive park boundaries (or even enter it!).
Back when the dive park was open for night diving, I would often hear noises as I approached the Suejac end of the park. I quickly learned that they were the grunts of black croakers (Cheilotrema saturnum) and filmed a few of them both in small cavelets and out in the open. Another site where I've seen them in numbers during daylight is the Empire Landing Quarry (aka Crane Point) and the adjacent Sea Fan Grotto.
This species is found from Pt. Conception to southern Baja California and the Gulf of California. They tend to prefer shallower water down to about 50 feet, although they have been recorded at depths below 300 feet.
As the name suggests, they are dark in color. The species name saturnum means dusky in Latin, a language I avoided in high school preferring German which was said to be the language of science. Hmmm. Haven't seen many German scientific names (but, of course they do exist... in German-speaking countries!). The ones I've filmed are generally grey to black in color although Dr. Milton Love says they may be brown, purplish, bluish or coppery. Some exhibit a pale bar in the mid-body and light blotches on the back at night or when in caves.
Young black croakers look little like their parents and were once thought to be a separate species. Although they school early on, they move into small cavelets and crevices. At this point they tend to be solitary. The adults may be observed individually or in small groups. I have noted more "schooling" behavior in the ones I've filmed at the Quarry as they often swam out in the open even during daylight.
Black croakers chow down on crabs and shrimp (yummy) as well as amphipods and isopod crustaceans. Add some worms and smaller fish to complete their diet. Hmmm... I think I prefer pizza with pineapple, Italian sausage and Canadian bacon which I'll order tonight from Antonio's Pizzeria. Males and females grow at about the same rate and may live as long as 21 years (but most barely make it into their teens).
Dr. Love cites a report by Eigenmann back in 1892 that San Diego Bay was very noisy with the sound of these croakers. Jacques-Yves should have consulted Milton prior to filming "The Silent World!" I know his son Jean-Michel Cousteau did as I worked with both of them on early Cousteau Project Ocean Search programs here on Catalina Island in the 70s.
© 2020 Dr. Bill Bushing. For the entire archived set of over 875 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Solitary black croaker in dive park; one with bar and light patch on back and a school of them at the quarry.
Some of our younger divers may not realize that Jacques-Yves Cousteau's first major film was called "The Silent World." Sadly a number of them don't even know who JYC was. I had a screening of the film for our local Catalina divers a year ago and wish I could resume having screening parties up at the house as we did pre-COVID. Wouldn't be prudent today.
Despite the title of the film, those of us who dive know that our oceans are not really a silent world. There are many sounds that we hear as we dive ranging from the snap, pop and crackle of Rice Krispies... er, pistol shrimp... to the melodious tunes of our large cetaceans. Fortunately we are free of the aircraft noise and sirens of the topside world, although we do get engine noise from the boats that venture close to our dive park boundaries (or even enter it!).
Back when the dive park was open for night diving, I would often hear noises as I approached the Suejac end of the park. I quickly learned that they were the grunts of black croakers (Cheilotrema saturnum) and filmed a few of them both in small cavelets and out in the open. Another site where I've seen them in numbers during daylight is the Empire Landing Quarry (aka Crane Point) and the adjacent Sea Fan Grotto.
This species is found from Pt. Conception to southern Baja California and the Gulf of California. They tend to prefer shallower water down to about 50 feet, although they have been recorded at depths below 300 feet.
As the name suggests, they are dark in color. The species name saturnum means dusky in Latin, a language I avoided in high school preferring German which was said to be the language of science. Hmmm. Haven't seen many German scientific names (but, of course they do exist... in German-speaking countries!). The ones I've filmed are generally grey to black in color although Dr. Milton Love says they may be brown, purplish, bluish or coppery. Some exhibit a pale bar in the mid-body and light blotches on the back at night or when in caves.
Young black croakers look little like their parents and were once thought to be a separate species. Although they school early on, they move into small cavelets and crevices. At this point they tend to be solitary. The adults may be observed individually or in small groups. I have noted more "schooling" behavior in the ones I've filmed at the Quarry as they often swam out in the open even during daylight.
Black croakers chow down on crabs and shrimp (yummy) as well as amphipods and isopod crustaceans. Add some worms and smaller fish to complete their diet. Hmmm... I think I prefer pizza with pineapple, Italian sausage and Canadian bacon which I'll order tonight from Antonio's Pizzeria. Males and females grow at about the same rate and may live as long as 21 years (but most barely make it into their teens).
Dr. Love cites a report by Eigenmann back in 1892 that San Diego Bay was very noisy with the sound of these croakers. Jacques-Yves should have consulted Milton prior to filming "The Silent World!" I know his son Jean-Michel Cousteau did as I worked with both of them on early Cousteau Project Ocean Search programs here on Catalina Island in the 70s.
© 2020 Dr. Bill Bushing. For the entire archived set of over 875 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Solitary black croaker in dive park; one with bar and light patch on back and a school of them at the quarry.
