Dive Dry with Dr. Bill

#434: Sharks on the "Run"

"Regular" readers of this column are familiar with my stories of "the way things were" "back in the old days" (well, dating back to the late 60s for me in Catalina waters). Other readers should perhaps try All-Bran. I'm referring to the days when one could count the sharks swimming in our waters as we motored to our next dive site or fishing hole. Blues were abundant, as they should be in a healthy marine ecosystem.

That's all changed, of course. Today it is a rarity to see a blue shark (Prionace glauca) anywhere near our shores. You have to go pretty far off shore and chum to bring in just a few of them. By-catch from long liners, drift and and gill netters undoubtedly took many of them, but the State banned these unhealthy fishing practices years ago. So why haven't we seen a major recovery of that species since the bans?

Most shark species are slow to reproduce, maturing later in life and producing smaller litters. In some species of live-bearing sharks, the young exhibit extreme prejudice in their sibling rivalry... with the stronger ones eating the weaker ones prior to birth. Sure glad my sisters loved their big brother! Certainly this is one reason, but thanks to shark tagging and tracking programs, we are learning some interesting new facts about their lifestyles that may also impact recovery.

Studies of shark movements based on tagging and then tracking the sharks over time have opened our eyes to some unexpected discoveries. Six years ago I was privileged to be invited on a great white shark tagging expedition to Guadalupe Island 150 miles off Baja California, Mexico. Dr. Michael Domeier, then of the Pfleger Institute of Environmental Research (PIER), used lances to embed radio tags into the shark's back. Later, when the sharks were near the surface, they transmitted data indicating the route they were traveling.

Through this and other tracking efforts, scientists discovered that great white sharks travel much longer distances than expected. Some of the great whites took off for a gathering place out in the Pacific near Hawaii. Given our chilly waters, can you really blame them? Others undertook trips from South Africa to Australia... and back. These findings opened up a new understanding of the great white's behavior, life history and ecological relationships.

About 10 years ago, a blue shark tagged off Monterey on the California coast was recaptured by fishermen near Japan. While this may set a Guinness distance record for that species, a number of other tagged blue sharks were found in the mid-Pacific. To be fair, Steve Crooke of CDF&G does not believe blue sharks migrate (or that their numbers have been greatly reduced in our waters. Hmmm). The important implication if migration does occur is that blue sharks, largely an open water (pelagic) species, may also visit far off (and far out?) places. If so, what happens to them elsewhere in the Pacific... or possibly throughout their worldwide distribution in temperate and tropical waters... may affect their populations here off southern California.

Compared to many other sharks, blues are fairly prolific. However, if truly migratory, when they are fished or caught as by-catch in other fisheries such as swordfish, thresher or mako shark throughout the Pacific; the impacts may be felt even on our local populations. Fishing in other geographical regions where the sharks breed and pup before returning to our coast may be of great importance to a shark population's recovery.

Sean Van Sommeran, director of the Pelagic Shark Research Foundation which tagged the world traveling blue, noted that a few years ago the shark fins he saw in Asian markets in northern California were largely from pelagic species like the blue and great white. Lately he has observed an increasing percentage come from reef and coastal sharks such as black tips. To the good doctor (yours truly), this suggests that pelagic stocks have declined making it less economic to harvest them than those concentrated in near shore waters.

I have written of the significant ecological effects resulting from the depletion of sharks in marine ecosystems ranging from our temperate waters to the coral reefs of the tropics. Some 70 million sharks are believed to be caught each year for shark fin soup. The practice of "finning," cutting the fins off live sharks and then dumping their still "living" bodies back into the ocean, was banned in US waters through the passage of the Shark Conservation Act late last year. It continues in the waters elsewhere throughout their geographic distribution, thus potentially affecting the populations we see here.

However, the sale and trade of shark fins is still legal. In California there is a bill in the House (AB376) that will ban this if passed in both chambers and signed by the governor. It was co-sponsored by an Asian-American legislator, but opposed by another Asian representative. I have tremendous respect for the cultures of Asia, but I do not feel any tradition gives a country, or a culture, the right to devastate fish or wildlife stocks that are international in scope. This includes not only sharks (largely by China), but also whales and dolphins by Japan and some European countries. Of course we all need to recognize our own country as complicit in these and other activities harmful to the marine environment. Very few cultures can claim the moral high ground. If you agree about the ban on shark finning, please contact your state representatives.

© 2011 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. 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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Blue shark on close approach to me and another videographer; SCUBA Luv's Tim Mitchell
hand feeding a blue and "NO" on shark fin soup.

This document maintained by Dr. Bill Bushing.
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