Dive Dry with Dr. Bill

#621: Silver Streaks That Go Bump in the Night

Well, the New Year is here and my mind would normally be turning toward warm, tropical waters with beautiful coral reefs, colorful fish and bikinis. However, it is awfully difficult for my mind to make that transition when our water temperatures are in the 60s at depth and I'm still wearing a thin 3/2mm wetsuit (thanks to my bountiful layer of bioprene). At this point the only trips on the agenda for 2015 are Palau in March, the Egyptian Red Sea in August (Egypt in August???) and the Galapagos in October.

To get my mind jump-started (wish I could do that to my golf cart some days), I'll just have to return to those thrilling days of yesterday... well just six months ago actually when I went down to the Dutch Antilles, three islands just off the coast of Venezuela. I only dove Bonaire and Aruba but spent a little time on Curacao waiting for my frequently delayed flight on Insult Air (er, I mean Insel Air).

During my time on Bonaire I stayed at Bruce Bowker's Carib Inn. Being an old geezer, I loved having their dive boat take me to distant dive sites rather than having to stumble over the coral beaches and through the surf. However, each night I shore dove the house reef to film and was rewarded with some nice footage. Time to share some more of that with my readers!

I was filming over the reef and felt something go bump in the night... when it ran right into me. Could it be a nocturnal predator distantly related to Jaws? After a few more bumps, I realized that my wetsuit had not developed any new holes (there were already plenty to go around) and realized it was just a group of tarpon (Megalops atlanticus) using my bright video lights to feed with.

Now I had encountered tarpon on ocean dives and kayak excursions on the rivers down in Belize about 10 years ago so I knew that although these fish can get pretty big (4-8 ft long and up to 355 lbs), they are essentially harmless. Rather than being "man eaters," they settle for much smaller prey (heck, only whales are bigger than the good doctor... and it's a close call on that).

There are actually two species of tarpon, the Atlantic tarpon I encountered, and the Indo-Pacific tarpon (Megalops cyprinoides). The Atlantic tarpon is found from Virginia to Brazil, the Gulf of Mexico and the Caribbean as well as from Senegal to South Angola on the west African coast. The Indo-Pacific version is observed along the eastern coast of Africa, Southeast Asia, Japan, Tahiti and Australia. They are found in both marine and freshwater habitats, and are able to tolerate low salinity and varying pH. However, they do not tolerate cool water and swift changes in temperature may create die-offs.

One interesting fact about tarpon that I was unaware of is that they can also survive in waters of low dissolved oxygen content. They can do this because of an interesting adaptation of their swim bladders. As any angler worth their salt (and biologist as well) knows, the swim bladder is usually used for buoyancy control. The tarpon's does that but it is also modified for breathing air! They can rise to the water's surface and take a gulp of air that allows them to achieve a burst of speed. Apparently these fish must be able to breathe air at the surface or they may die. I wonder if that makes them semi-amphibious?

Tarpon are distinctive. Their long, slender bodies are covered with silvery scales that are very reflective. At night they look like silver streaks in my video lights. The genus name Megalops is Greek for large eye, and theirs helps them hunt at night. Their lateral line is very distinct. One of the physical features that intrigues me the most are their mouths with the prominent lower jaw.

On these night dives the adults were feeding on small fish caught in my video lights. I was concerned that I might highlight some of the butter hamlets that were spawning over the reef each night, but fortunately their mating was not cut short due to the tarpon's munching. Tarpon are nocturnal feeders that hunt in midwater and swallow their prey whole (gulp). Some sources state they also feed during the day. Their larvae do not actively feed but absorb nutrients from the surrounding water. Sometimes I think that is how I ingest all the unnecessary calories. Older youngsters feed on zooplankton, insects, small fish and later add crustaceans such as crab or shrimp. Their silvery color makes the young vulnerable to predation by birds while the adults may be taken by sharks, porpoises and reptiles such as 'gators and crocs!

Tarpon apparently like a little privacy when mating and seek out isolated, offshore locations for their romantic trysts. They are sexually mature when they reach about 30-50 inches. Spawning takes place in late spring and early summer (you know, when a male Homo sapiens' mind turns to... butter). Females produce prodigious numbers of eggs, reportedly as many as 12 million at a time.. Male tarpon may live up to 30 years while the ladies can reach a ripe old age of more than 50 years. I'm guessing there may be some cougars among them!

Tarpon are considered one of the great game fish because they will put up quite a fight. Since most consider their flesh undesirable and full of bones, they are usually not kept by anglers. I'm always concerned when I think of "sport" fishing. Often the fish that are caught and then released are weakened by the fight and may have significant build-up of lactic acid in their muscle tissues and be weak, thus potentially succumbing to a predator. Of course I have nothing against the legal take of fish for food... heck, my dinner plate often has such a meal (but even my plate... and stomach... are not big enough for a tarpon).

© 2015 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Tarpon darting in front of my camera; tarpon snapping its jaws to feed and
one chasing a butter hamlet near the bottom.

This document maintained by Dr. Bill Bushing.
Material and images © 2014 Star Thrower Educational Multimedia