Tagging Salmon Sharks, February 2003

Working with new satellite tagging technology and a new TOPP species has yielded impressive results for scientists and students from Stanford University's Hopkins Marine Station.

During a short expedition in the Gulf of Alaska last summer, Dr. Barbara Block and a few graduate students attached a new type of satellite tag - a Smart Position and Temperature Transmission 2 tag (SPOT2) - to the dorsal fins of a handful of salmon sharks. Not only are the tags working better than expected, the data reveal interesting behavior.

"We went up to Alaska and put the tags on the sharks - having no idea how well they would work - and every shark that we’ve tagged is sending back data," Block said.

Block and the graduate students usually work with pop-off satellite tags, which remain attached to an animal as they collect and store data. At a pre-programmed date, the tag detaches itself, floats to the surface and begins transmitting data via satellite back to the laboratory.

A SPOT2 tag is unique because although it also stores data, it transmits those data automatically each time the tag is out of water, i.e. when a salmon shark's dorsal fin with the tag attached breaks the surface. This access to “near-real-time” data is a rare treat for scientists who usually have to wait months or years to learn where their tagged subjects went.

"What we're doing with the salmon shark experiment is - for the very first time - directly sending information from the dorsal fin of a shark up to a satellite," Block said. "The tag gives us a position every day on where the sharks are, and in some cases the temperature of the water they're swimming through. We've been really impressed with how well it's working."

Biologists are analyzing the SPOT2 tag's effectiveness as part of assuring that TOPP uses the best equipment available.

"What TOPP is about is figuring out which technologies work best on any particular animal," Block said. "The SPOT tag has the advantage of giving us a much more exact position than the pop-up satellite tag, so we’re trying to combine the two technologies."

Block said that data collected so far shows individual sharks traveling in different - and sometimes unexpected - directions. Some moved west along the outer chain of Alaskan islands, while others traveled far south, to the Central California coast. Some were tracked patrolling some of the major salmon streams of British Columbia and Washington.

Salmon sharks are the northernmost member of the family lamnidae, which also includes the great white, mako and porbeagle sharks. This species is of interest to TOPP because it's a top predator that is capable of surviving in the sometimes near-freezing waters found in the northern part of the program's range.

"Our interest is how does a big predacious shark actually use these cold Alaskan waters? It's very unusual to have a big, active shark up in this region," Block said. "What we do know about this shark is that it's feeding on the salmon. What we want to know is where does it go, and what is the relationship between this big shark and the salmon?" -- Diane Richards