Student Connection

This week, the NOAAS TOWNSEND CROMWELL is north of the Hawaiian Islands longlining for swordfish, tuna, and sharks. Longline fishing is so called because a thick fishing line several miles long with hundreds of baited hooks on it is used in an attempt to catch lots of fish at once. We are trying to catch and tag these fish to understand their migrations and behaviors.

Fish that are still very much alive are brought aboard and handled as gently as possible so that they survive the stressful tagging process. We are using three kinds of tags, conventional, archival and pop-up. The conventional tag is just a short spaghetti sized plastic tag that is poked through the skin and into muscle below the dorsal fin. This tag has a number code and a phone number to call if you catch the fish so that fishermen can report where the fish was caught. Archival tags have small computer chips in them that are connected to light, pressure, and temperature sensors. Archival tags are surgically inserted into the abdomen of the fish. If, or when, the fish is caught the tag is delivered to the laboratory and the data is retrieved and processed. Light data obtained from these tags is used to calculate the fish's position based on intensity and length of days using a sophisticated algorithm. Pop-up tags are a remarkable improvement on previous tagging technology. They are externally connected by a small wire that is run through the dorsal fin. The pop-up tagstays with the fish for a year or until it dies, collecting temperature, pressure, and light data. At a pre-set time (3 months to a year later), the tag harmlessly releases from the fish and the tag floats to the surface to transmit stored data to a satellite. If the fish dies and sinks, a mechanism reacts to the pressure and cuts the wire. The tag then floats to the surface and transmits its data to a satellite. All of this capability fits into an instrument the size of a banana.

Some fish don't survive the night on the hook. These fish are brought aboard
and their various organs, blood and stomach contents are sampled for further study. Two scientists on this trip are studying fish vision. They have the gruesome task of removing fish eyes and hooking electrical probes to the retinas and exposing them to various colors and intensities of light to measure the electrochemical response. They are particularly interested in the speed of the reaction to stimulus. This is important in deep water fish that live mostly in the dark.

Check back with us soon and we will let you know whether we are catching fish and show you pictures of tunas, sharks, swordfish and tags.
Other updates for this cruise:

April 6  April 12

Last Modified 4/5/01

http://atsea.nmfs.hawaii.edu/