Population Dynamics of Bigeye and Yellowfin tuna in Hawai‘i’s Fishery1

Around the Hawaiian Islands, a variety of small and medium-scale fisheries target bigeye (Thunnus obsesus) and yellowfin tuna (T. albacares) associated with offshore seamounts and weather monitoring buoys, an inshore network of fish aggregating devices (FADs), and natural aggregation sites (Itano and Holland, 2000). These fisheries, conducted from longline, troll and handline, and to a lesser extent from pole-and-line vessels, provide an important source of revenue for the state (Boggs and Ito, 1993; Ito and Machado, 1999). The small-gear fleet (essentially the trolling and handline vessels) supports recreational and subsistence fisheries for both residents and the tourist industry (Pooley, 1993; Hamilton and Huffman, 1997). An important sector within Hawai‘i’s small-scale commercial fisheries is the offshore handline fishery, which targets mixedspecies aggregations found in association with NOAA offshore weather monitoring buoys and seamounts (Itano and Holland, 2000). Most of the catch and effort in this fishery, which currently lands roughly 500 t per year, concentrates on the Cross Seamount and takes mostly juvenile and sub-adult yellowfin and bigeye tunas. Concerns have been raised as to whether the fishery intercepts too many juveniles that might otherwise recruit to inshore fisheries or to the offshore longline fishery (Holland et al., 1999). There is also concern among handline fisherman exploiting the Seamount that further increases in fishing effort could over-exploit offshore tuna resources, and/or reduce the economic viability of their fishery. Moreover, yellowfin and bigeye around Hawai‘i are part of the wider Pacific Ocean stock that is being exploited by various coastal and high-seas fisheries (Hampton and Fournier 2001b; Hampton and Fournier, 2001a). Therefore, the overall health of the Pacific-wide stock is important for the viability of local fisheries. In these concerns, the Cross Seamount fishery exemplifies resource allocation and sustainability issues that are increasingly frequent in all oceans.