graphical representation of all data. Tags currently on the market weigh 25 g in air, have up to one megabyte of memory, can retain data for 20 years, and have a lifetime of four to five years. The tags cost approximately $1,000 each. Development teams are concentrating on reducing the size of the package, increasing the memory, and reducing the cost. An additional area of experimentation is in the attachment methodologies. The requirement for long-term attachment necessitates development of attachment methods that can hold the package in place for years. Methods for mounting the tags will vary widely, depending on the species being examined.
Archival tags typically contain a data logger board with a microcontroller, a mass data store with up to one megabyte of memory, and an analog sensor board. The tags vary between development teams but range from having one to seven sensors. This flexibility is designed to allow the user to be able to tailor the tag to the different requirements for studies on a given species. Tags are coated in an epoxy resin to keep the weight of the unit as low as possible. Programming and data retrieval are done with PC-based software. Communication is via a serial RS232 infrared optical link in both the English and Australian tags (the most advanced available).
The Australians have recently put archival tags on bluefin tuna. Use of the tag followed an extensive conventional and acoustic tagging effort that provided data suggesting that archival tagging would be successful. From 1990 to 1993, over 27,000 southern bluefin tuna were tagged with conventional techniques. To date, over 900 have been returned via Australian and Japanese fisheries. Acoustic tagging efforts have provided approximately 16 days of depth and temperature preference data from 11 individual bluefin tuna. The success of handling the fish in both programs with positive results (returns and survival upon acoustic tag and release) led to a recent experiment with archival tagging on one-and two-year-old bluefin tuna. Archival tags have been placed in numerous bluefin tuna over the past year. The tags are inserted invasively with the light sensor trailing outside the fish. To date, three tags have been returned with several months of data. Implementation of this program with successful attachment and recovery bodes well for the use of this technology on the northern bluefin tuna in the Atlantic Ocean. The conventional tag and release program in the Atlantic Ocean provides encouraging numbers which indicate that archival tagging would be successful in the Atlantic Ocean. The recovery of just a few tags would exponentially increase our knowledge of where these fish go, and a major effort in this area should be encouraged. Problems that need to be solved before archival tags are put on bluefin tuna in the Atlantic Ocean are the following:
In what geographic location would we see the highest recovery of tags? This is vital to making sure the experiment works (i.e., survival with the tag is ongoing).
Where and how should a tag be attached to a fish that has enormous