Abstract. - A deepwater trap- 

 ping sun'ey for Heterocarpits laeviga- 

 tus was conducted around the main 

 islands of the Hawaiian Archipelago 

 to estimate exploitable biomass and 

 potential yield. Stratified sampling 

 by depth zone and island was con- 

 ducted over a 3-year period to evalu- 

 ate shrimp catch rates. Catchability 

 of the traps was estimated from a 

 12-day intensive fishing experiment 

 performed at a small, isolated site in 

 the Kaulakahi Channel; habitat areas 

 were determined by digitizing nauti- 

 cal charts. 



Results from a Leslie analysis of 

 the depletion experiment showed that 

 H. laevigatus is very susceptible to 

 capture by traps (i.e., catchability q 

 = 9. 48 ha/trap-night). There was no 

 ewdence of a change in size structure 

 through the course of the experiment. 



Shrimp catch rates varied greatly 

 by island and depth of capture. Ex- 

 ploitable biomass was greatest in the 

 460-640 m depth range; negligible 

 amounts of shrimp occurred shallow- 

 er than 350 m and deeper than 830 m. 

 Catch rates were highest at Niihau 

 and lowest at Oahu. The total ex- 

 ploitable biomass of shrimp in the 

 main Hawaiian Is. was estimated to 

 be 271 MT, a figure substantially less 

 than previously believed. 



Analysis of multiple size-frequency 

 distributions for each sex showed no 

 evidence of modal size progression. 

 Assuming equilibrium conditions, 

 application of the Wetherall et al. 

 (1987) method to these data resulted 

 in estimates of M/K =1.01 for female 

 shrimp and 0.74 for males. From 

 these results and estimates of L„ 

 we calculate that F(i.i/M = 0.75 for 

 females and 0.86 for males. 



An assessment of the exploitable 

 biomass of Heterocarpus laevigatus 

 in the main Ha\A/aiian Islands. 

 Part 1: Trapping surveys, depletion 

 experiment, and length structure 



Stephen Ralston 



Tiburon Laboratory, Southwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 3150 Paradise Drive, Tiburon, California 94920 



Darryl T. Tagami 



Honolulu Laboratory, Southwest Fisheries Science Center 



National IVIanne Fisheries Service. NOAA 



2570 Dole Street, Honolulu, Hawaii 96822-2396 



The caridean shrimp, Heterocarpus 

 laevigatus Bate 1888, is an abundant 

 deepwater inhabitant of the Hawaiian 

 Is., where it has been fished sporad- 

 ically since 1970 (Anon. 1979). Two 

 early research surveys (Clarke 1972, 

 Struhsaker and Aasted 1974) showed 

 that large catches of this species, and 

 its smaller congener H. ensifer, could 

 readily be taken in baited traps in 

 water depths of 365-825 m (200-450 

 fm).* Based on catch rates from around 

 the island of Oahu, the deepwater 

 shrimp resource seemed sufficiently 

 abundant to support a commercial 

 fishery (2. 6 kg/trap-night fori/, laein- 

 gatus and 6. 6 kg/trap-night fori/, en- 

 sifer; Struhsaker and Aasted 1974). 

 To date, however, attempts to har- 

 vest the resource have met with lim- 

 ited success, even though 75 MT of ii. 

 laevigatus were landed by one vessel 

 during a 14-month period (Tagami 

 and Barrows 1988). At its peak in 

 1983-84, a short-lived fishery devel- 

 oped, involving as many as 7 me- 

 dium-sized (23-40 m) boats. At that 

 time over 190 MT of H. laevigatus 



Manuscript accepted 27 May 1992. 

 Fishery Bulletin, U.S. 90:494-504 (1992). 



'Depths are given in meters with fathom 

 equivalents (1.0fm= 1.83 m). although con- 

 touring and stratification were based on 

 nautical charts in fathoms. 



were landed, with an ex-vessel value 

 of $1.5 million ($7.85/kg; Hawaii Dep. 

 Land & Nat. Resour., Div. Aquat. 

 Resour.). The fishery soon failed, 

 however, primarily due to problems 

 with gear loss, product processing, 

 and localized stock depletions. Even 

 so, the product was well received by 

 the public, and rejuvenating the 

 shrimp fishery remains a fishery 

 development goal of the State of 

 Hawaii (Anon. 1984). 



With this interest in developing the 

 Hawaiian fishery, major gaps in our 

 knowledge of local H. laevigatus 

 shrimp stocks have become apparent 

 (see Gooding 1984, Dailey and Ral- 

 ston 1986), although elsewhere in the 

 Pacific more extensive data are avail- 

 able (e.g.. Wilder 1977, King 1984 

 and 1986, Ralston 1986, Moffitt and 

 Polovina 1987). Particularly lacking 

 are estimates of the absolute abun- 

 dance of the H. laevigatus stock in 

 Hawaii and its ability to withstand 

 sustained fishing pressure. 



The primary objective of the work 

 presented here was to estimate the 

 exploitable biomass of H. laevigatus 

 in the main Hawaiian Is. A secondary 

 objective was to estimate growth 

 and mortality rates through analysis 

 of length-frequency data. Together 



494 



