High-Seas Driftnet Fisheries of Japan, Korea and Taiwan in the North Pacific Ocean

During 1990 and 1991, scientific observers from Japan, Canada and the U.S. were deployed on selected fishing trips (a sample of all trips) by high-seas squid driftnet vessels of Japan in the North Pacific Ocean. During the same years, under U.S.-Korea and U.S.-Taiwan bilateral agreements, similar joint observer programs in the North Pacific were executed on Korean high-seas squid driftnet vessels and on Taiwanese driftnet vessels targeting either squid or tuna/billfish (large-mesh operations). In addition, under a U.S.-Japan bilateral agreement, observers of the two nations were deployed during a single season of Japan's large-mesh driftnet fishery in the North Pacific targeting tuna/billfish, the season straddling 1990 and 1991. In each case, observers documented details of the daily operations following agreed data collection procedures and guidelines. At the end of each fishing season, observer data records were shared and edited jointly by scientific staff of participating partner nations. Just prior to the onset of the 1991-1992 Japan large-mesh driftnet season, a United Nations-mediated international agreement to end high-seas driftnet fishing by 31 December 1992 was reached. Plans to launch a second season of scientific observations in Japan's large-mesh driftnet fishery were canceled. High-seas driftnet fleets continued to operate in the North Pacific through 1992 but without scientific observers.

A typical deployed driftnet consisted of many discrete net sections strung together. Each section was made up of a varying number of net panels (tans), usually about 50-m in length. On each day of monitoring, observers recorded data from a subset of deployed net sections, usually selected at random. In most sampled sections, observers recorded the numbers of squid, fish and other animals decked as gear was retrieved aboard the vessel, by species; to maximize accuracy of decked-animal counts, fish and squid dropping out of the gear during retrieval were generally ignored. In some operations, a couple of selected sections were designated to specifically assess fish dropout rates. In these cases, observers counted the numbers of fish decked and the number of fish dropping out during net retrieval, by species. During dropout monitoring on squid vessels, observers typically suspended observations of squid to maximize accuracy of fish counts. For all monitored net sections observers recorded the number and length of tans deployed and the mesh size of the gear. Ancillary biological data and specimens were sometimes collected on decked animals following agreed procedures. Observers collected data from most fishing operations during the trip, allowing for one day per week for rest and data processing/editing.

In most operations, driftnet sections were set and retrieved on the same day. However, in a small number of cases, retrieval of some net sections was delayed by a day or more (so-called "Tomi Ami" operations). Further, in most operations all sections of gear were set with the top of the net at the sea surface, but in a few cases a subset of experimental sections were deployed with the top of the net 1 or 2 meters below the surface. Accordingly, section-level data from monitored driftnet operations can be classified by retrieval type ("Type") and deployment depth ("Depth").