FATHOMS PLUS TRAPS

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 by a decline in landings as the population is reduced by overfishing (1987-91). 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 3 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. 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 efforts target spiny or slipper lobsters. 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.

Stock assessment of the lobster resource is hindered by the relatively short catch and effort time series and our inability to age lobsters. 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.

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 in 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 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 nmi northwest, from Nihoa Island to Kure Atoll. The fishery targets two species: the endemic spiny lobster and the common slipper lobster.

RESEARCH

ABSTRACT

CASE STUDY OF LOBSTER IN HAWAII

After initial research cruises documented lobster concentrations in the NWHI in 1976, research focused on the biology of the spiny lobster. Trapping surveys mapped the spatial distribution of the spiny lobster in the NWHI and indicated that the highest catch rates ranged from depths of 55-73 m in the southeast portion of the NWHI to 19-54 m in the northwest portion of the Hawaiian Archipelago. The settlement of post-larval lobster, puerulus, were monitored at Kure Atoll, French Frigate Shoals, and Oahu with surface collectors. Puerulus settlement appeared seasonal at the ends of the Hawaiian Archipelago; the greatest settlement occurred during the summer at Kure Atoll and during the winter at Oahu while at French Frigate Shoals, more centrally located, settlement appeared more uniformly throughout the year.

Research conducted during 1984-87 developed escape vents to reduce the catch and hence mortality of sub-legal spiny lobster (<50mm tail width) and sub-legal slipper lobster <56 mm Tail width) without reducing legal catches.

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 un-baited lobster traps. The results indicate that lobsters using the traps for shelter are able to exit, and no mortality from the retention of slipper or spiny lobster in traps was observed.

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 local oceanography studies suggest that long-term differences in lobster densities between banks in the NWHI are caused by 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. The mechanisms responsible for the apparent link between sea level and lobster recruitment are not known and are the subject of current research. The El Niño Southern Oscillation (ENSO) is thought to play a factor in the variation in relative sea level throughout the archipelago.

The return on investment as a function of vessel size has been studied. The most profitable vessels in the fleet are midsize vessels. The vessels are 20-30 m long, have five to nine crew members, and are able to set 600-820 traps per day.

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A COMMERCIAL SHELLFISH TRAP MADE BYFATHOMS PLUS®IS USED BY ALL THE FISHERMAN. THIS IS A DOME-SHAPED, SINGLE-CHAMBERED TRAP MADE OF MOLDED BLACK POLYETHYLENE WHICH MEASURES 980 BY 770 BY 295 MM, WITH A MESH SIZE OF 45 BY 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 ESCAPE OF SUB-LEGAL LOBSTERS (LOBSTERS UNDER MINIMUM LEGAL HARVEST SIZE). THE TRAPS ARE TYPICALLY BAITED WITH CHOPPED MACKERAL AND FISHED IN STRINGS OF SEVERAL HUNDRED TRAPS PER STRING MOST FREQUENTLY SET IN DEPTHS FROM 20 TO 70 M.

MANAGEMENT

SUMMARY

The original design of the Fathoms Plus Traps used in the Hawaii case study

This is a discussion of the lobster fisheries in Hawaii, addressing harvest levels, biology, and research. The fishery is a limited entry trap fishery with 1991 landings of 200 metric tons.

Banded Spiny Lobster, Maui, Hawaii

Fathoms Plus Traps used in the Hawaii case study

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 with a tail width of <56 mm and spiny lobster 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.

INTRODUCTION

Hawaii Lobster Fishery

Lobster concentrations in the NWHI were documented by research cruises in 1976, and commercial trapping began in 1977. Since 1983, the lobster fleet has ranged from 9 to 16 vessels (15-to 35-m-long), each averaging three trips per year. A typical vessel 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 (1 million lobsters), valued at about U.S.$6 million ex-vessel. Since 1988, about 80% of the landings have been spiny lobster.