Near Anacapa Island, the sea was rich with birds, bait balls, sea lions and common dolphins today. The fishing was much better here than near Catalina Island yesterday. Our total catch: 9 mako sharks, 3 blue sharks and one of those amazing open-ocean (aka pelagic) stingrays. Two of the blue sharks were quite large at lengths of more than 63 inches (160 centimeters) long, from the tip of their noses to the fork in their tail. (If you stood them on their tails, they'd be taller than the average American woman.) We again collected the pelagic ray and will bring it to the USC Marine Institute on Catalina in a few days.

Although we didn't deploy any satellite tags today, we did tag and release all the sharks for our ongoing studies on their age and growth. It's impossible to tell how old a shark is by looking at it, except to say that it's a juvenile or an adult. That's a problem, especially when it comes to managing shark fisheries. You can imagine that the lifetime productivity of a species that does not become sexual maturity until it's 20 years old, and then perhaps only lives to the age of 30, may be far less than for a species that matures at the age of 10 and lives for 30 years, especially if they both produce the same number of offspring each year. If we can learn this, then it can help fishery managers make decisions that promote sustainable fishing.

So....how do we tell how old a shark is? It's sort of like counting the rings on a tree....except that we don't know how many rings a shark adds to its vertebrae every year. So, we use an injection of oxytetracycline (OTC), a chemical that will be absorbed by the calcifying tissue over the next week, to place a mark on the edges of the vertebrae of the sharks. The vertebrae of shark grow in diameter as they age and the calcifying tissue forms rings, kind of like rings in a tree. We don't know exactly how many rings are formed during each year, however. The band of OTC can be visualized as a fluorescent ring in the vertebrae that identifies the time of the injection.

Here's the catch (pardon the pun). The shark has to be caught for us to figure it out. (That happens, actually -- fishermen are pretty good at helping us out, because they want to know these answers, too.) So, if the shark is recaptured and the vertebrae returned to us, we can count the rings in their vertebrae that have formed since the time we injected the shark. That way we can determine how many rings represent each year's growth. Once we have determined how many rings are formed in each vertebra every year, we can then go back and determine the age of any other sharks for which we have vertebral samples. In order to understand the productivity of these species, it is important to understand how fast they grow, how long they live, and at what age they become sexually mature.

The pictures today show how we handle the sharks in the tagging cradle and the types of tags we insert. These were taken 2 days ago when we were fishing in "baby blue country". The first picture, taken by Jason Larese, shows a small blue shark being restrained in the cradle and the researchers are preparing to place a tag in the dorsal fin. The second picture, taken by Carl Safina, shows a close up of the tags once they are inserted. The yellow and white tags in the fin have instructions written in English and Spanish on collecting and sending the vertebrae back to us in the event that the shark is recaptured. The thin yellow tag inserted in the shark's back is a second type of tag we use to mark these sharks so that in the event that one or the other tag is lost, anyone who catches the shark will still know to report the recovery information to us. -- ABOARD THE R/V DAVID STARR JORDAN, Near Anacalpa Island.