FAO Fisheries and Aquaculture Technical Paper No. 568

Bycatch and non-tuna catch in the tropical tuna purse seine fisheries of the world


Martin Hall and Marlon Roman
Inter-American Tropical Tuna Commission
La Jolla, United States of America

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Food and Agriculture Organization of the United Nations


This report provides a review of our knowledge of the bycatches, defined as discarded dead, from the tropical tuna purse seine fisheries of the world. The major fishing grounds involved (eastern and western Pacific, eastern Atlantic, and western Indian Oceans) share the gear, the ways of fishing, and the structure of the pelagic communities. Because of that, the species taken in association with tuna schools tend to be the same in all regions. After describing the gear and fishing operations, it discusses the reasons why bycatches happen, and explores the options to mitigate them. The types of sets used to capture tunas and the detection methods used to locate the schools are a major factor to determine which are the catches and the bycatches. The main bycatches are tunas, sharks and rays, pelagic bony fishes, billfishes, and sea turtles. The total discards amount to one to five percent of the total tonnage captured, and tunas of the species targeted amount to over 90–95 percent of those bycatches. The silky shark is the most common shark species by far, followed by the oceanic whitetip sharks. Marlins and sailfishes are also taken but in reduced numbers. Olive ridley sea turtles are the most common turtle captured, but the majority of them are released alive and unharmed. Rainbow runners, mahi-mahis, wahoos and amberjack yellowtail are the major pelagic bony fishes taken with the tunas. They are being retained in increasing numbers for utilization. Besides discussing problems of estimation, the report presents most of the ideas proposed or in different stages of testing, to mitigate those bycatches, including ways to avoid the captures, or to release the individuals from the net or from the deck. Finally, the known or potential ecological impacts of the rapidly increasing fishery on fish aggregating devices (FADs) are reviewed, emphasizing some of the uncertainties that still prevail.

Hall, M.; Roman, M. 2013.
Bycatch and non-tuna catch in the tropical tuna purse seine fisheries of the world.
FAO Fisheries and Aquaculture Technical Paper No. 568. Rome, FAO. 249 pp.

Table of Contents

Preparation of this document
Abbreviations and acronyms


1. Introduction
2. Definitions and framework
3. Purse seining


4. From log fishing to fishing on fish aggregating devices
5. Conditions during the capture process that may cause mortality


6. Distribution of effort by set type
7. Sources of information on bycatch in the tuna purse seine fisheries
8. Estimating bycatch
9. Species taken in association with tropical tunas


10. Tunas
11. Billfishes


12. Shark and rays


13. Large pelagic bony fishes (other than tunas)
14. Sea turtles
15. Marine mammals
16. Impacts of the development of the FAD fishery on fishing operations
17. Final conclusions


Appendix 1


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