The lobster and shrimp fisheries in Hawaii – Fisheries of Hawaii and U.S.-associated Pacific Islands
Jeffrey J. Polovina
The Lobster Fishery
The commercial lobster fishery in Hawaii is a trap fishery which harvests several lobster species in the Northwestern Hawaiian Islands (NWHI)–an isolated range of islands, islets, banks, and reefs extending 1,500 n.mi. northwest, from Nihoa Island to Kure Atoll (Fig. 1). The fishery targets two species: the endemic spiny lobster Panulirus marginatus (Quoy and Gaimard, 1825) and the common slipper lobster Scyllarides squammosus (Milne-Edwards, 1837) (Fig. 2,3). Two other species–the ridgeback slipper lobster S. haanii (de Haan, 1841) (Morin and MacDonald, 1984) and the Chinese slipper lobster Parribacus antarcticus (Lund, 1793)–are caught incidentally in low abundance.
Lobster concentrations in the NWHI were documented by research cruises in 1976, and commercial trapping began in 1977 (Uchida and Tagami, 1984). Since 1983, the lobster fleet has ranged from 9 to 16 vessels (15 to 35 m long), each averaging 3 trips per year. A typical vessels sets about 800 traps per day and remains at sea almost 2 months per trip. The NWHI lobster fishery is Hawaii’s most valuable demersal fishery; in recent years, annual landings have averaged about 600 metric tons (t) (I million lobsters), valued at about $6 million U.S. ex-vessel (Fig. 4). Since 1988, about 80% of the landings have been spiny lobster (Polovina(1)).
A commercial shellfish trap made by Fathoms Plus2 iS used by all the fishermen. This is a dome-shaped, single-chambered trap made of molded black polyethylene which measures 980 x 770 x 295 mm, with a mesh size of 45 x 45 mm (inside dimensions). Each trap has two entrance cones located on opposite sides. Each trap also has two escape vent panels each consisting of four 67 mm diameter circular vents located on opposite sides to facilitate the escapement of sublegal lobsters (lobsters under minimum legal harvest size). The traps are typically baited with chopped mackerel (Scomber sp.) and fished in strings of several hundred traps per string most frequently set in depths from 20 to 70 m.
Synopsis of the Fishery
The historical landings from the lobster fishery exhibit a classical trend of a developing fishery with a period of low catches at the beginning of the fishery (1977-83) followed by a rapid increase in landings as more vessels entered the fishery and markets were developed (1984-86) and most recently a decline in landings as the population is reduced by overfishing (1987-91) (Fig. 4). In the early years of the fishery (1977-84) and since 1988, landings have been about 80% spiny and 20% slipper lobsters. However, for a three-year period from 1985 to 1987 the fishery targeted and largely depleted a previously lightly exploited population of slipper lobsters.
Stock assessment has used the annual catch of spiny and slipper lobsters and trapping effort data from the commercial logbooks since 1983 (Table 1).
[TABULAR DATA 1 OMITTED] Both spiny and slipper lobsters may be caught in the same trap but fishermen can alter the proportion of each species by selecting the trapping area and depth. Logbooks record only the number of traps hauled and do not specify when effort targets spiny or slipper lobster. Since 1983 when logbook reporting was in effect, the combined catch per unit effort (CPUE) for legal slipper and spiny lobsters has declined from 2.75 to 0.56 lobster per trap-haul (Fig. 4).
Stock assessment of the lobster resource is hindered by the relatively short catch and effort time series and our inability to age lobsters. A dynamic production model, fit to the combined spiny and slipper lobster catch and effort data for the entire NWHI, estimates an equilibrium production curve with a maximum sustainable yield of 900,000 lobsters/year from a fishing effort of 740,000 trap-hauls, resulting in a CPUE of 1.22 lobsters/trap-haul ([Polovina.sup.1]). A CPUE time-series model estimates the annual instantaneous natural mortality (M) at 0.7/year and catchability (q) at 1.0 x [10.sup.-6] ([Polovina.sup.1]). Thus the 1990 fishing effort of 1.2 million trap-hauls corresponds to a fishing mortality (F) of 1.2/year or 1.7 times M. Based on the minimum harvest sizes and this level of fishing mortality, the spawning stock biomass per recruit is estimated at 40% of the level in the absence of fishing.
Both the level of fishing mortality relative to natural mortality and the relative spawning biomass suggest that fishing effort alone was not sufficient to cause the decline in CPUE observed in 1990 and 1991. Current research suggests this decline is the result of poor recruitment (due to oceanographic conditions) at some banks which resulted in a concentration of fishing effort at the remaining banks where recruitment was strong.
After the initial research cruises documented lobster concentrations in the NWHI in 1976, research focused on the biology of the spiny lobster Panulirus marginatus. Tagging studies at Kure Atoll and French Frigate Shoals estimated a von Bertalanffy growth curve for growth (in carapace length) to have a parameter K of 0.3/ year with an asymptotic carapace length of 13.2 cm, a mean natural mortality estimate of 0.37/year, and estimates for the ages at the onset of sexual maturity of 2.7 and 1.7 years for males and females, respectively (MacDonald, 1984). Trapping surveys mapped the spatial distribution of P. marginatus in the NWHI and indicated that the highest catch rates ranged from depths of 55-73 m in the southeastern portion of the NWHI to 19-54 m in the northwestern portion of the Hawaiian Archipelago (Uchida and Tagami, 1984). The settlement of post-larval lobster, puerulus, were monitored at Kure Atoll, French Frigate Shoals, and Oahu with surface collectors (MacDonald, 1984). Puerulus settlement appeared seasonal at the ends of the Hawaiian Archipelago; the greatest settlement occurred in the summer at Kure Atoll and in the winter at Oahu while at French Frigate Shoals, more centrally located, settlement appeared more uniformly throughout the year (MacDonald, 1986).
Research conducted during 1984-87 developed escape vents to reduce the catch and hence mortality of sublegal spiny lobster (<50 mm tail width) and sublegal slipper lobster (<56 mm tail width) without reducing legal catches. A circular vent design takes advantage of the different morphology of the spiny and slipper lobsters to allow escapement at different tail sizes for each species. Specifically, research found that traps equipped with two vent panels consisting of four 67 nim diameter circles placed at the bottom of the trap caught 83% and 93% fewer sublegal spiny and slipper lobsters than did nonvented control traps, without significantly reducing legal catches of either species (Everson et al., In press).
An estimated 2,000 plastic traps are lost annually in the NWHI. Concern has been raised that lobsters entering those lost traps may be unable to exit and therefore die. Recent field and tank studies have investigated whether lobsters can escape unbaited lobster traps. The results indicate that lobsters using the traps for shelter are able to exit, and no mortality due to the retention of slipper or spiny lobster in traps was observed (Parrish and Kazama, 1992).
Ongoing research is directed toward understanding the factors responsible for observed spatial and temporal variation in adult lobster abundance within the Hawaiian Archipelago. Results from larval tows and studies on local oceanography suggest that long-term differences in lobster densities between banks in the NWHI are not due to local larval densities but to differences in the amount of relief provided by the benthic habitat on the banks.
Temporal variation in spiny lobster stocks at the two most productive banks in the fishery, Maro Reef and Necker Island, has been studied with both commercial and research data. Research and commercial trapping data both show a wide variation in recruitment to the fishery for spiny lobster at Maro Reef relative to Necker Island, 360 n.mi. to the southeast. A high correlation is observed between recruitment to the fishery at Maro Reef and the relative sea level between French Frigate Shoals and Midway Island four years earlier. Geosat altimeter data indicate that the variation in relative sea level between French Frigate Shoals and Midway is linked to the El Nino Southern Oscillation (ENSO). The mechanisms responsible for the apparent link between sea level and lobster recruitment are not known and are the’ subject of current research. However, the sea level index may prove to be a useful forecast of recruitment to the fishery at Maro Reef four years later (Polovina and Mitchum, 1992).
One economic study (Clarke and Pooley, 1988) has examined the return on investment as a function of vessel size. The most profitable vessels in the fleet are the midsize vessels. These vessels are 20-30 m long, have 5-9 crew members, and are able to set 600-820 traps per day. Larger vessels face cost constraints while smaller vessels face operational problems.
The fishery has been managed under Federal jurisdiction with a fishery management plan (FMP) administered by the Western Pacific Regional Fishery Management Council (WPRFMC) since 1983. Currently the plan prohibits the harvest of slipper lobster (S. squammosus) with a tail width of <56 mm and spiny lobster (P. marginatus) with a tail width of <50 mm, prohibits the retention of egg-bearing females, requires that all traps have escape vents to reduce handling and release-induced mortality on sublegal lobsters, and mandates that vessels submit logbooks recording daily catch and trapping effort. A decline in CPUE from 1.25 lobster per trap-haul in 1988 to 0.6 in 1990 as well as concerns that vessels from other fisheries in worse condition were considering entering the lobster fishery, motivated the fishermen to work with the WPRFMC to develop a limited entry and harvest quota plan. Further, to protect the spawning biomass of the stock while the plan was being developed the WPRFMC passed emergency regulations to close the fishery for 6 months (May through October, 1991). In March 1992, the lobster FMP was amended to include provisions for a limited entry system for a maximum of 15 vessels, an annual fleet harvest quota, and a closed season from January through June to protect the spawning biomass before the summer spawning. The quota is set to achieve an average CPUE over the fishing season of 1.0 lobster per trap-haul. A preseason quota is set using an estimate of the population size at the end of the previous fishing season and estimates of natural mortality and recruitment. A final quota is set after the first month of fishing based on the CPUE during that month. Information from research surveys can also be used in the quota calculations. Currently, fishermen and managers are considering whether an individual quota would be an improvement over the current fleet quota.
The lobster fishery has sufficient management regulations, which if applied correctly, should make the fishery sustainable and economically profitable. However, environmental factors may result in both considerable annual as well as decadal-scale variation in the exploitable lobster population and hence landings.
The Shrimp Fishery
Deepwater pandalid shrimp are found in some abundance throughout the tropical and subtropical Pacific (King, 1984; Moffitt and Polovina, 1987). In Hawaii, research trapping showed that Heterocarpus laevigatus (Fig. 5) and the smaller and more shallow dwelling species, H. ensifer, could be readily caught in the depth range 350-825 m in baited traps (Struhsaker and Aasted, 1974). During the past decade there have been two periods when the resource, particularly the more valuable species H. laevigatus, has been the target of fishing. In the early 1980’s a small trap fishery was initiated around the main Hawaiian Islands. The vessels typically used large, pyramid-shaped traps with a volume of almost 2 [m.sup.3], and a large vessel might set up to 50 traps a day (Tagami and Barrows, 1988). Landings from this fishery peaked in 1984 at over 190 metric tons of H. laevigatus with an ex-vessel value of $1.5 million ($7.85/kg) from 7 vessels, 23-40 m in length (Ralston and Tagami, 1992). However by the late 1980’s most of the vessels had left the fishery as declining catch rates and the high cost of the deep trapping made the fishery unprofitable. There was a resurgence in the fishery in 1990, when landings of over 100 t were reported, primarily the result of intensive fishing by a single vessel but this level of production was not sustainable at a profitable CPUE(3). Currently there are no management regulations for this resource.
Recent research has conducted submersible surveys of shrimp densities on different habitats and estimated shrimp biomass from an intensive trapping depletion study (Moffitt and Parrish, 1992; Ralston and Tagami, 1922). The submersible surveys observed that H. ensifer tended to group around large anemones and other benthic relief over an otherwise flat, sandy bottom and were very active in the presence of a baited trap (Gooding et. al., 198 8; Moffitt and Parrish, 1992). However, H. laevigatus were solitary and showed little activity around baited traps. Greater densities of H. laevigatus were observed on volcanic than on coralline substrata (Moffitt and Parrish, 1992). The depletion study based on intensive trapping estimated a catchability coefficient which when applied to trapping data around the main Hawaiian Islands estimated an exploitable biomass of H. laevigatus of 271 t (Ralston and Tagami, 1992).
While the deepwater shrimp resource may support a very limited local fishery or perhaps periodic heavy pulse fishing, it is unlikely to be the object of heavy sustained exploitation. Initial high catch rates appear to drop rapidly, gear loss is appreciable and costly due to the trapping depths, and markets are not well established. (1) J. J. Polvina. 1991. Status of lobster stocks in the Northwestern Hawaiian Islands, 1990. U.S. Dep. Commer., Natl. Mar. Fish. Serv., Southwest Fish. Sci. Cent. Admin. Rep. H-91-04, 16 p. (2) Mention of trade names or commercial firms does not imply endorsement by the National Marine Fisheries Service, NOAA. (3) Commercial Landings, State of Hawaii, Division of Land and Natural Resources, Division of Aquatic Resources, 1990.
Clarke, R. P., and S. G. Pooley. 1988. An economic analysis of lobster fishing vessel performance in the Northwestern Hawaiian Islands. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-SWFC-106, 45 p. Everson, A. R., R. A. Skillman, and J. J. Polovina. In press. Evaluation of rectangular and circular escape vents in the Northwestern Hawaiian Islands lobster fishery. N. Am. J. of Fish. Manag. Gooding, R. M., J. J. Polovina, and M. D. Dailey. 1988. Observations of deepwater shrimp, Heterocarpus ensifer, from a submersible off the island of Hawaii. Mar. Fish. Rev. 50(1):32-39. King, M. G. 1984. The species and depth distribution of deepwater caridean shrimps (Decapoda, Caridea) near some Southwest Pacific islands. Crustaceana 47:174-191. MacDonald, C. D. 1984. Studies on recruitment in the Hawaiian spiny lobster, Panulirus marginatus. In R. W. Grigg and K. Y. Tanoue (Editors), Proceedings of the second symposium on resource investigations in the Northwestern Hawaiian Islands. Vol. 1, May 25-27 1983 Honolulu. Univ. of Hawaii, HI, UNIHI-SEAGRANT-MR-8401, p. 199-220. –. 1986. Recruitment of the puerulus of the spiny lobster Panulirus marginatus in Hawaii. Can. J. Fish. Aquat. Sci. 43(11):2118-2125. Moffitt, B. M., and F. A. Parrish. 1992. An assessment of the exploitable biomass of Heterocarpus laevigatus in the main Hawaiian Islands Part 2: Observations from a submersible. Fish. Bull. 90(3):476-482 Moffitt, R. B., and J. J. Polovina. 1987. Distribution and yield of the deepwater shrimp Heterocarpus resource in the Marianas. Fish. Bull. 85:339-349. Morin, T. D., and C. D. MacDonald. 1984. Occurrence of the slipper lobster Scyllarides haanii in the Hawaiian Archipelago. Proceedings of the Biological Society of Washington 97(2):404 407. Parrish, F. P., and T. K. Kazama. 1992. Evaluation of ghost fishing in the Hawaiian lobster fishery. Fish. Bull. 90:720-725. Polovina, J. J., and G. T. Mitchum. 1992. Variability in spiny lobster Panulirus marginatus recruitment and sea level in the Northwestern Hawaiian Islands. Fish. Bull. 90:483-493. Ralston, S., and D. T. Tagami. 1992, An assessment of the exploitable biomass of Heterocarpus laevigatus in the main Hawaiian Islands. Part 1: trapping surveys, depletion experiment, and length structure. Fish. Bull. 90(3):494-504. Struhsaker, P., and D. C. Aasted. 1974. Deepwater shrimp trapping in the Hawaiian Islands. Mar, Fish. Rev. 36(10):13 21. Tagami, D. T., and S. Barrows. 1988. Deep-sea shrimp trapping of Heterocarpus laevigatus in the Hawaiian Archipelago by a commercial fishing vessel. U. S. Dept. Commerce, NOAA Tech. Memo. NMFS, NOAA-TM-NMFS-SWFC-103, 14 p. Uchida, R. N., and D. T. Tagami. 1984. Biology, distribution, population structure, and pre-exploitation abundance of spiny lobster, Panulirus marginatus (Quoy and Gaimard 1825), in the Northwestern Hawaiian Islands. In R. W. Grigg and K. Y. Tanoue (Editors), Proceedings of the second symposium on resource investigations in the Northwestern Hawaiian Islands, Vol. 1, May 25-27, 1983 Honolulu. Univ. of Hawaii, HI. UNIT41-SEAGRANT-MR-84-01, p. 157-197.
Jeffrey J. Polvina is with the Honolulu Laboratory, Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, 2570 Dole Street, Honolulu, Hawaii 96822-2396. Mention of trade names or commercial firms does not imply endorsement by the National Marine Fisheries Service, NOAA.
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