DIVE DRY WITH DR. BILL #786: AFTER A WHILE, CROCODILE
Back in 2001 after I left the Conservancy, I decided I needed a vacation. I had only taken one in my years at the organization so I was due. I researched flight consolidators on the Internet and found one that offered a circle-the-Pacific trip and signed up. For a mere $1,600 I would visit Taiwan, Hong Kong, Thailand, Bali (later changed to Kuala Lumpur due to terrorist bombings), Australia (Darwin, Cairns and Sydney), New Zealand, Fiji, the Cook Islands and Tahiti over a period of about three months.
I didn't SCUBA dive in each country due either to a lack of suitable conditions (Hong Kong Harbor) or, in the case of New Zealand, a bad cold. However, I did enjoy diving in many of the other countries. However, this column is not about one of my dives on this trip. It is about the deadly salt water crocodiles near Darwin, Australia. Wouldn't have been prudent to dive there (although I did on the Great Barrier Reef).
When I got to my hostel in Darwin, I looked for activities to pursue other than in the water. The jumping crocs in the Adelaide River and Kakadu National Park seemed a good option to enjoy the Northwest Territories so I signed up for the excursion. It didn't disappoint. There are more salt water crocs in this part of the world than anywhere else. They are also known as the estuarine crocodile, Indo-Pacific crocodile, marine crocodile, sea crocodile or "saltie" by the locals. The species is known scientifically as Crocodylus porosus. They are found from eastern India to New Guinea, but are currently considered extinct in much of SE Asia and the Philippines.
They are the largest of all living reptiles. Males may reach 23 feet in length and weigh well over a ton, although most rarely grow longer than 20 feet. The more dainty ladies are smaller, only occasionally reaching half that size. Back when I lived in Florida as a youngster, I learned that crocs have a narrower head than the gators who "accompanied" me on my walk to school. However, this species has a broader head and jaw than other related species.
The salt water croc's genome (DNA) was sequenced back in 2007. Fortunately my DNA test on Ancestry.com shows we are not related. Its cousins appear to be other broad-snouted crocs like the mugger (C. palustris) in India and the Siamese (C. siamensis) crocs. Fossils of this species are known from as far back as 4.5 million years ago and biologists believe the species may be 6-12 million years. Of course individual crocs live a mere 70 years with a few hitting the century mark.
Although largely lethargic during the day, they are capable of swimming in fast bursts at 15-18 mph and could out sprint Mark Spitz (and definitely yours truly). However, over longer distances Mark may be able to take the gold against them. They prefer to feed at night and are not finicky eaters, often taking anything that crosses their path (including a few humans). Youngsters chow down on fish, frogs, insects and other aquatic invertebrates. Juvies add other amphibians, crustaceans, molluscs, birds, reptiles and small mammals. Unfortunately, despite many years of take for the crocodile skin trade, adult stomach content analysis was rarely performed and biologists are somewhat hesitant to approach them closely today!.
Yes, I know, you have all been waiting for the other "M" portion of this column. I've covered munching so it is time to deal with mating! This species mates during the warmer wet season in Australia. Generally females establish nests once a year although some do it twice a year and others every other year. Courtship occurs in the early fall and 40-60 and occasionally up to 90 eggs are laid during late fall and winter. Like other croc species, the gender of the hatchlings may depend on ambient temperature in an unusual relationship. From about 82 to 86° F they become females, from 86 to about 90° F the majority are male, but above that most are born male.
Both male and female guard the nesting area from egg predators like the goanna (Varanus giganteus) lizard although salt water crocs are better at defending against them than "freshies." Hatchlings and the young are subject to high mortality from a wide variety of predators with only 1% of the hatchlings reaching adulthood. Monitor lizards, predatory fish, wild boar, rats, birds, snakes and other crocs are among the culprits in The Mutual Eating Society..
While visiting Kakadu National Park, I did have an underwater close encounter with a fresh water crocodile (Crocodylus johnstoni) aqlso known as a "freshie." We had stopped at a waterfall to swim and cool off (after being warned there were about two dozen poisonous critters we might encounter on the walk to the water hole). Despite being more than twice as old as many of the other visitors in our group, I managed to swim against the current and get under the waterfall, beaten only by our tour guide. Then I body surfed to the other end and came face-to-face with a small (4 ft) croc. Fortunately they prefer fish, insects, spiders, turtles, small reptiles and water rats to humans!
© 2018 Dr. Bill Bushing. For the entire archived set of over 775 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Jumping salt water crocs in the Adelaide River near Darwin, Australia, and the goanna egg predator.
Back in 2001 after I left the Conservancy, I decided I needed a vacation. I had only taken one in my years at the organization so I was due. I researched flight consolidators on the Internet and found one that offered a circle-the-Pacific trip and signed up. For a mere $1,600 I would visit Taiwan, Hong Kong, Thailand, Bali (later changed to Kuala Lumpur due to terrorist bombings), Australia (Darwin, Cairns and Sydney), New Zealand, Fiji, the Cook Islands and Tahiti over a period of about three months.
I didn't SCUBA dive in each country due either to a lack of suitable conditions (Hong Kong Harbor) or, in the case of New Zealand, a bad cold. However, I did enjoy diving in many of the other countries. However, this column is not about one of my dives on this trip. It is about the deadly salt water crocodiles near Darwin, Australia. Wouldn't have been prudent to dive there (although I did on the Great Barrier Reef).
When I got to my hostel in Darwin, I looked for activities to pursue other than in the water. The jumping crocs in the Adelaide River and Kakadu National Park seemed a good option to enjoy the Northwest Territories so I signed up for the excursion. It didn't disappoint. There are more salt water crocs in this part of the world than anywhere else. They are also known as the estuarine crocodile, Indo-Pacific crocodile, marine crocodile, sea crocodile or "saltie" by the locals. The species is known scientifically as Crocodylus porosus. They are found from eastern India to New Guinea, but are currently considered extinct in much of SE Asia and the Philippines.
They are the largest of all living reptiles. Males may reach 23 feet in length and weigh well over a ton, although most rarely grow longer than 20 feet. The more dainty ladies are smaller, only occasionally reaching half that size. Back when I lived in Florida as a youngster, I learned that crocs have a narrower head than the gators who "accompanied" me on my walk to school. However, this species has a broader head and jaw than other related species.
The salt water croc's genome (DNA) was sequenced back in 2007. Fortunately my DNA test on Ancestry.com shows we are not related. Its cousins appear to be other broad-snouted crocs like the mugger (C. palustris) in India and the Siamese (C. siamensis) crocs. Fossils of this species are known from as far back as 4.5 million years ago and biologists believe the species may be 6-12 million years. Of course individual crocs live a mere 70 years with a few hitting the century mark.
Although largely lethargic during the day, they are capable of swimming in fast bursts at 15-18 mph and could out sprint Mark Spitz (and definitely yours truly). However, over longer distances Mark may be able to take the gold against them. They prefer to feed at night and are not finicky eaters, often taking anything that crosses their path (including a few humans). Youngsters chow down on fish, frogs, insects and other aquatic invertebrates. Juvies add other amphibians, crustaceans, molluscs, birds, reptiles and small mammals. Unfortunately, despite many years of take for the crocodile skin trade, adult stomach content analysis was rarely performed and biologists are somewhat hesitant to approach them closely today!.
Yes, I know, you have all been waiting for the other "M" portion of this column. I've covered munching so it is time to deal with mating! This species mates during the warmer wet season in Australia. Generally females establish nests once a year although some do it twice a year and others every other year. Courtship occurs in the early fall and 40-60 and occasionally up to 90 eggs are laid during late fall and winter. Like other croc species, the gender of the hatchlings may depend on ambient temperature in an unusual relationship. From about 82 to 86° F they become females, from 86 to about 90° F the majority are male, but above that most are born male.
Both male and female guard the nesting area from egg predators like the goanna (Varanus giganteus) lizard although salt water crocs are better at defending against them than "freshies." Hatchlings and the young are subject to high mortality from a wide variety of predators with only 1% of the hatchlings reaching adulthood. Monitor lizards, predatory fish, wild boar, rats, birds, snakes and other crocs are among the culprits in The Mutual Eating Society..
While visiting Kakadu National Park, I did have an underwater close encounter with a fresh water crocodile (Crocodylus johnstoni) aqlso known as a "freshie." We had stopped at a waterfall to swim and cool off (after being warned there were about two dozen poisonous critters we might encounter on the walk to the water hole). Despite being more than twice as old as many of the other visitors in our group, I managed to swim against the current and get under the waterfall, beaten only by our tour guide. Then I body surfed to the other end and came face-to-face with a small (4 ft) croc. Fortunately they prefer fish, insects, spiders, turtles, small reptiles and water rats to humans!
© 2018 Dr. Bill Bushing. For the entire archived set of over 775 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Jumping salt water crocs in the Adelaide River near Darwin, Australia, and the goanna egg predator.
