The reason this is done is to compare the performance and retention qualities of each type of tag which ultimately determines which tag is more effective.
Retention is the ability of a tag to stay in a fish over a period of time.
The two types of tags curretnly used are The Billfish Foundation's tage whose anchor is constructed of hydroscopic nylon and the National Marine Fisheries Service tag whose anchor is constructed of stainless steel. The tag anchor is the part of the tag that stays in the fish. This helps scientists answer biological questions on billfish movements, migrations, age and growth and stock structure. This information also provides insight into fishery management questions concerning billfish as well as other spieces. Once a fish is tagged, the matching tagging report card is filled out and sent to The Billfish Foundation and that information is kept in their database.