Hawaii's pelagic fisheries

Marine Fisheries Review, Spring, 1993 by Christofer H. Boggs, Rusell Y. Ito

Introduction

Hawaii's pelagic fisheries are small in comparison with other Pacific pelagic fisheries (NMFS, 1991), but they are the largest fisheries in the State (Pooley, 1993b), and much larger than other U.S. island-based fisheries in the western Pacific (Hamm et al. (1)). Stocks of tuna, billfish, and other tropical pelagic species supply most of the fish consumed by Hawaii residents and support popular recreational fisheries.

In recent years (1987-91) the composition and magnitude of Hawaii's commercial pelagic fisheries have changed. The longline fishery greatly expanded and the troll, handline, and pole-and- line fisheries declined (Ito(2)). The expansion of the longline fishery was consistent with fishery development plans that viewed pelagic fish resources as underexploited (State of Hawaii Division of Aquatic Resources (HDAR) 1985). Pelagic fish resources available to Hawaii fisheries may be capable of sustaining even greater yields. However, the decline of the troll and handline fisheries has raised concerns regarding the continued availability of pelagic species and local overfishing (Boggs(3), Ito(2)). Pelagic fish availability is synonymous with local abundance, here defined as the amount of fish present within the range of the local fishery. Overall abundance refers to population size, which is greater than local abundance unless the entire population resides within range of the local fishery. The stock structure of large pelagic species is unclear, but a common assumption is that pelagic populations extend over much wider areas than are covered by Hawaii's fisheries (Skillman, 1989a, 1989b; Suzuki, 1989, In press; Miyabe, In press).

Availability probably depends on overall abundance, but the availability of fish to Hawaii's pelagic fisheries is also highly seasonal (Shomura, 1959; Yoshida, 1974; Skillman and Kamer(4)), suggesting that highly mobile pelagic fish change their distribution in response to environmental conditions (Seckel, 1972; Mendelssohn and Roy, 1986), or to enter different areas for reproduction. Availability may also be confounded with catchability, defined as the vulnerability of fish to being caught by a given type of fishing gear. Catchability is also influenced by environmental conditions (Sharp, 1978; Hanamoto, 1987).

The limited mobility of most island fishermen causes yield to be poor when availability is low. Intense local fishing effort is not likely to cause a decline in overall abundance unless there are discrete stocks residing in, or periodically returning to, island waters. Otherwise, the fishing mortality caused by Hawaii fisheries is minor compared with overall fishing mortality caused by larger Pacific fisheries. Thus, local fishing pressure is unlikely to cause a significant reduction in overall abundance.

Even though locally exploited pelagic stocks may be wide-ranging, and relatively invulnerable to local fishing pressure, catch per unit effort (CPUE) in local fisheries may decline if local fishing effort is so intense that most fish entering the local area are soon caught. It is hypothesized (Sathiendrakumar and Tisdell, 1987; Boggs, In press) that if fish availability depends on immigration, increases in local fishing effort result in an asymptotic yield, beyond which further increases in local effort do not increase the catch, and local CPUE declines. The possible impact of local fishing effort on the CPUE and profitability of Hawaii's pelagic fisheries is currently an issue of great concern to Hawaii's fishery managers (Boggs(3), In press).

This paper describes Hawaii's longline, troll, and handline fisheries for pelagic species, trends in landings and CPUE over time, and problems with the data used to monitor these fisheries. Changes in the apparent relative availability of fish (local CPUE) are reviewed in relation to local fishery expansion and overall abundance (Pacific-wide CPUE). Current attempts at managing for optimum yield and the outlook for these fisheries are described. The Hawaii skipjack tuna fishery is covered in a separate paper (Boggs and Kikkawa, 1993).

Synopsis of the Fisheries

The fishing methods, target species, vessel sizes, yields, and operational areas of Hawaii's domestic pelagic fisheries are diverse. The commercial sectors are largely composed of the pole-and-line and longline fisheries utilizing large (>12m) vessels. The small-vessel troll and handline fisheries include poorly differentiated commercial, recreational, and subsistence components. The pole-and-line fishery targets skipjack tuna, Katsuwonus pelamis, and lands about 1,000 metric tons (t), (2.2 million lb) annually for sale to the local market (Boggs and Kikkawa, 1993). The longline fishery targets broadbill swordfish, Xiphias gladius; and bigeye tuna, Thunnus obesus, and now lands about 9,000 t (20 million lb, including all species) much of which is exported. The commercial, recreational, and subsistence troll and handline fleets primarily target yellowfin tuna, T. albacares; mahimahi, Coryphaena hippurus; and blue marlin, Makaira mazara; annual commercial landings (all species) now average about 2,300 t (5.2 million lb). No valid estimates exist for current recreational or subsistence landings (Pooley, 1993a).