The Swordfish: Deep ocean dweller

I sank to 80 feet and lined up on the fish as it began to turn away from me. I took a couple of frames. It seemed much bigger closer up, and the formidable bill or sword on the end of its face looked menacing. I kicked hard to get a closer shot, shooting as I went.
 

The fish accelerated away and then suddenly turned on me. I froze for a couple of seconds, and blew a huge burst of bubbles. I mean, what else could I do against a charging fish? It stopped, looked at me with its huge black eye, and turned away, racing up to the surface.  I have never been more scared in my life underwater and got back to the boat as quickly as possible.

I was shooting an episode of my TV series, “Portraits from the Deep,” and after another 90 minutes of hard work, the crew released the 300-pound swordfish. The underwater camera man, Ricky Westphal, and I swam down to 60 feet with the tired fish, marveling at its color changes, and the fluorescent purple hue of its back in contrast with the deep blue backdrop.

So much for my first underwater encounter with the enigmatic swordfish! Its reputation for aggressive behavior is well founded. From earliest history, there are stories of swordfish attacking boats and other marine animals for no apparent reason.

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Swordfish are found in the deep ocean around the Cayman Islands. Because deep water is very close to shore here, one would not have to go far to catch a swordfish. There have been several angling tournaments targeting swordfish here, which have had good results. One of the best spots to target swordfish is at a bank 30 miles to the east of Cayman Brac; a long run for anglers, but worth the effort when you get there, according to local swordfish experts.

Fishing for swordfish in the tropics is done in the daytime by drifting baits near the bottom in 1,200 to 2,000 feet of water, or fishing is conducted at night, drifting baits at 100 to 200 feet, when the fish rise close to the surface.

Swordfish or “broadbill swordfish” as they are sometimes called, are found in all tropical and temperate seas on the planet. They typically live at great depth in the open ocean, and feed upon a variety of small fish and squid. Their long bill, which is flat like a sword, has sharp edges and is used to slash at their prey, stunning or chopping it before consuming it.

Unlike its relatives, the marlins and sailfish, the lower jaw of the swordfish is not strong and has no teeth, so most of its prey consists of soft bodied animals.

There are several other anatomical differences: the dorsal, anal and pectoral fins are fixed, and there are no pelvic fins. There is a single large caudal keel either side of the peduncle (other billfish have two keels), and swordfish have no scales. Their shape and size is similar to other billfish, but they are an example of convergent evolution where two different families of fish have arrived at a similar result through the evolutionary process.

As with marlin, it has not been possible to keep a swordfish in captivity in an aquarium. This is the main reason I needed to dive with one, to see what they looked like underwater in their natural habitat.

In spending so much time at great depth, the swordfish does not compete with the other billfish. Its abyssal existence necessitates the large eyes, round muscular body, and an ability to rapidly change depth like no other bony fish.

Typically, the swordfish will rise close to the surface at night to feed, and descend again in the daytime. In the cooler oceans, they may spend time at the surface to warm their bodies after prolonged periods at depth.  At this time they are vulnerable to predators such as the mako shark. There are many eyewitness accounts of makos attacking swordfish from below, cutting off their tails to immobilize them and then chomping off their bills to neutralize any threat, before eating them at their leisure.

Swordfish spawn in the tropics, and those that live there may spawn all year round. The fish that live in temperate seas migrate to the tropics to spawn. Pairs form near the surface and fertilized eggs are planktonic, hatching in 48 hours, when the larvae grow rapidly.

After reaching a couple of inches, the prominent upper jaw becomes a distinctive bill. They grow very rapidly, like all ocean fish, with females reaching maturity in five years, and males earlier.

In the last 10 years, scientists have been able to attach mini computerized tags to swordfish to gather more information about their diurnal movements, use of the water column, and geographic migration. Results show this species will dive to 2,500 feet, and generally spend less than one percent of their time at the surface.

Swordfish have become the focus of several types of commercial fishing activity. Historically, large swordfish were harpooned from a boat as they basked at the surface. Adult fish were harvested using this method in temperate waters. 

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However, since the 1960s, popular demand for this fish led to high seas industrial exploitation through long lining. This led to the collapse of the species in the western Atlantic, and in the Mediterranean Sea, initiating conservation practices never before enacted for oceanic species. Large areas of ocean in the western Atlantic and the Gulf of Mexico were closed to long lining activity by U.S. fishery management organizations.

In the late 1990s, many prominent restaurants in the U.S. and Caribbean stopped serving swordfish in the “Give swordfish a break” initiative, to educate the public about their demise and reduce the demand for the species. In these areas the recovery has been well documented, but now commercial fishing interests are targeting the resource again.

Not only were the targeted species, swordfish and tuna, being over-exploited, but the by-catch of non-targeted species of billfish, sharks, turtles and manta rays was causing rapid declines in those populations.

One of the management issues with using indiscriminate fishing techniques is that there is by-catch. Techniques are constantly evolving and daytime deep lining for swords is very specific.

Many commercial fishermen are utilizing these directed techniques to capture swords and avoid any by-catch. Enjoy your swordfish steak knowing that it is from a well regulated fishery in the U.S. and here in Cayman, it was caught by a local fisherman fishing in a responsible manner.

It is our collective responsibility to conserve the marine environment and maintain the biodiversity of the planet.

Dive safely, fish responsibly.
Guy Harvey PhD.

 

 

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