Hawaii's pelagic fisheries

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

Abundance and Availability

Background

The primary concern in Hawaii's pelagic fisheries today is whether fishing effort should be limited to protect the local abundance or availability of fish (Pooley, 1990; Boggs(3), In press; Skillman et al., 1993). Increased catches by Hawaii's pelagic fisheries over the last two decades could hypothetically have reduced the abundance of local stocks, if such stocks exist. It is more likely that Hawaii's fisheries exploit locally available fractions of Pacific-wide stocks (Wetherall and Yong(16); Skillman and Kamer(4); Boggs, In press). In the latter case immigration may limit yields and excessive fishing effort might result in reduced CPUE (Sathiendrakumar and Tisdell, 1987; Boggs(3), In press). In either case, excessive local fishing pressure should be evidenced by corresponding declines in local CPUE.

Several studies suggest that local fishing pressure can reduce local CPUE for wide-ranging pelagic species (Wetherall and Yong(16), Squire and Au, 1990; Boggs(3), In press; Skillman and Kamer(4)). Many of these studies also found that the relative abundance (CPUE) of fish over a wider geographic area could statistically account for much of the variation in local CPUE. Relative abundance estimated as CPUE is confounded with catchability, so that widespread environmental effects on catchability, as well as true changes in stock-wide abundance, could explain the statistical relationships between Pacific-wide CPUE and local CPUE.

The following examination of Hawaii CPUE time series extending from the early years of each fishery to the present was undertaken to show whether or not the expansion of Hawaii's pelagic fisheries over the last two decades, 1970-91, corresponded with declines in local CPUE. Major declines in local CPUE were often found to predate local fisheries expansion and corresponded with declines in the CPUE of more widespread fisheries. Over the last few decades the time series indicated much interannual variation and little net change in CPUE.

Calculation of Hawaii CPUE

Longline CPUE was calculated from a combination of data sources including published literature, HDAR data summaries, and NMFS market sample estimates. Troll and handline CPUE was calculated solely from HDAR data summaries because these data identify troll and handline gears (NMFS estimates do not). HDAR summaries do not differ substantially (in total) from NMFS estimates for combined troll and handline (Pooley, 1993b). All available summary statistics (HDAR and NMFS) were used in the present study, but no new analyses of raw data were conducted.

To calculate CPUE in the early longline fishery (e.g., Fig. 4A), Hawaii longline data on two size-classes of vessels for 1948-56 (Shomura, 1959) were combined, and catch was converted from number of fish to weight. The results were similar to 1948-52 CPUE data published by Otsu (1954). The CPUE based on combined data differed little from the data for large vessels (Shomura, 1959), and although vessel size is important, it was ignored in the present study because data summaries by vessel size for subsequent years were not available.