Chapter Objectives

  1. Review briefly the primary tuna species caught in the tropical tuna purse seine fishery.
  2. Learn to distinguish small yellowfin from small bigeye tuna.
  3. Practice tuna species identification on non-ideal specimens.

Once details on a vessel’s identifying information and fishing operations have been recorded by the observer, attention can be turned to recording the results of the catch. During tropical tuna purse seine fishing, the species that makes up the bulk of the catch depends on a number of things, such as the type of set, the area, the time of the year, etc. Generally, skipjack tuna is targeted on FAD sets and free school sets, while yellowfin is targeted in free school sets or in association with dolphin schools (in the eastern Pacific Ocean). Bigeye and yellowfin, usually of small sizes, are often caught in association with skipjack in FAD sets.

Observers are charged with recording both a set’s catch amount and its species composition. This is almost always challenging, given the speed and scope of work during the brailing and sorting process. While working experience is the best means of developing quick and accurate species ID skills, at the end of this chapter are some images that illustrate typical non-ideal and “spill” samples to help observers learn. Additional information on sampling strategies is covered in a later chapter.