Dive Dry with Dr. Bill

#238: It Starts at the Top

A recent event made this a very timely topic for my column. We were diving off the King Neptune at Blue Car Wreck. As usual, I went deep there to locate mating nudibranchs. Randy and Stacey Tucker, a couple diving with us, dropped right below the boat... and discovered the carcass of a soupfin shark being eaten by two sheep crabs. That night they sent me their pictures, and from them we surmised that the shark may have been speared or gaffed, cut deeply in the "neck" region, and left to die. Soupfin sharks were severely depleted earlier by fishers harvesting them for shark fin soup, and during World War II for the vitamin A in their livers. They are harmless if not provoked, and just beginning to make a comeback in our waters. I had to wonder why someone would kill such a beautiful, sleek (not slick) fish.

When I started diving Catalina waters back in the 60's, blue sharks were a common sight along our coast. I'd see them occasionally while diving, but frequently while operating the Toyon school's boat right along the coast. After "Jaws" was released, some of my students joined in the assault on our toothy friends by fishing for them and killing them. One even used to gut them and re-release the poor fish to swim off and die. Today, blue sharks are a rare sight... due in part to such activities, but more so to long-lining and gill netting. And it is not just in our waters. Sharks are rare in many of the regions I've dived around the world.

It is good to see SCUBA divers actively involved in the effort to stop the hideous practice of shark "finning" in which the fins are cut off and the shark dumped back to die a slow death. Last year, a group of divers including yours truly worked hard and successfully to get Disney to stop serving shark fin soup at their new theme park in Hong Kong. Once a meal fit for (and only available to) an Emperor's court, the increasing affluence of mainland Chinese has led to an ever increasing demand for shark fin soup.

Why would we, as divers who enter into their realm, want to see sharks? Let me outline a few reasons why the protection of sharks may be very important to the health of the world's marine ecosystems. Well, admittedly there are those that would prefer not to see them, when you've dived with numerous sharks in places like Tahiti, Fiji and Australia, or watched great whites from the "safety" of a shark cage off Guadalupe Island, they really are incredibly beautiful fish. Far more important is the fact that we are just beginning to realize the ecological impacts of removing these top predators from ecosystems around the world. When one major element in a food chain is removed, it often has consequences for the rest of the critters. That's the nature of the interdependency in natural ecosystems.

The beautiful coral reefs of the tropics are experiencing serious global impacts from warming waters, bleaching and algae growing over them. Recent studies have shown that the depletion of sharks, the top predator in many of these ecosystems, has allowed populations of groupers and large fish to increase. In turn, these fish may decimate populations of smaller fish such as surgeonfish that feed on the algae and keep the coral reefs free of it. Thus the removal of sharks has contributed to the diminished health of the coral reef ecosystems in these beautiful tropical ecosystems.

Another example involves the over-harvesting of sharks from some sandy bottom communities. With the sharks largely gone, the sting rays they feed on reproduce in larger numbers than if controlled by their main predator. The abundance of rays leads to serious declines in the scallop populations upon which they feed. Not only is the ecosystem impacted, but the economic viability of the scallop fishery is affected as well.

So you see, you just don't want to mess with the top of the food chain... and I'm not talking about the roof at Vons. It is often pointed out that sharks have far more to fear from the most dangerous species on the planet, than we have to fear from them. I may express a different opinion if a great white or tiger shark decides to sample a part of me in the future. However, the chance of that happening is less than dying from a falling coconut, or a vending machine, or from the sting of a bee. At least that's what the statistics tell us. I'll take those odds... but I don't think I'll buy a lottery ticket until the odds on winning there improve!

© 2007 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass" or "Common Fish and Invertebrates of the Sea of Cortez" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

Dead shark held in hands of diver; close-up showing wounds and neck cut with
sheep crab feeding on carcass (photo credit: Randy and Stacey Tucker)

This document maintained by Dr. Bill Bushing.
Material and images © 2007 Star Thrower Educational Multimedia