Mollusk Habitats and Fisheries in Kiribati: An Assessment from the Gilbert Islands1 Frank R. ThomaslThomas2 Abstract: Biological and ecological attributes of24 species ofedible bivalves and gastropods from thethe Gilbert Islands Group, Kiribati, Micronesia, were assessed for their resilience by examining size at maturity, intertidal burying, adjacent subtidal populations, benthic mobility, and larval type. Foraging for mollusks is largelylargely confined to the intertidal and shallow subtidal regions, although modern diving gear and outboard motors now provide human foragers access to offshore resources. Changes brought about by human demographic pressures have re­ sulted in overexploitation of a number of molluscan resources. It isis suggested thatthat the sustainable use of invertebrates and other marine species for food and nonfood purposes in Kiribati rests on a remodeled form of marine tenure. ATOLLS PRESENT A variety of marine envi­ from resilient resources, and their effect on ronments and molluscan resources that have subsistence. provided subsistence living to generations of Can traditional ecological knowledge be Pacific islandersislanders (Tebano(Tebano et al. 1993, Taniera wedded with modern technology to revive thethe 1994). Kiribati (Figure 1) is but one of more fisheries? Because the thrust of this paper isis thanthan 20 nations in the Pacific, each of which limited to prey biology and ecology in thethe possessed a rich inshore fisheries tradition context ofmollusk fisheries, details of analytic and lore.lore. InIn recent years, however, traditional methodology related to foraging efficiency ecological knowledge (TEK) has suffered the are not discussed here, but can be found inin inevitableinevitable decline that characterizes similar Thomas (1999). bodies of knowledge throughout most of Data on molluscan resources of the Gil­ Oceania. High human population density, bert Islands date back toto thethe 1950s when urban drift, more efficient extractive tech­ Banner and Randall (1952) described thethe in­in­ nologies, and expanding market opportu­ vertebrates of Onotoa Atoll, but identifica­identifica­ nities all have inevitably affected the ocean tions were poor and there were few detailed resourcesresources of these islands. In this study, I descriptions of exploitive strategies. A major examined the prey biology and ecology of interdisciplinary environmental survey on mollusk fisheriesfisheries in Kiribati, Gilbert Islands, the main atoll ofTarawa, Republic ofKiribati lookinglooking at factors distinguishing vulnerable (Abbott and Garcia 1995), expanded species identification and habitat description, and provided an assessment of the impact of 1 Financial support from the University of Hawai'i's human activities (Figure 2). The Tarawa La­ Arts and Sciences Advisory Council; funds provided by goon Project of 1992-1994 (Paulay 1995) is a Alison Kay throughthrough a University of Hawai'i Foundation major study of the lagoon, and data from thatthat Grant and Research Assistantship; Sigma Xi (The Scien­ tifictific Research Society) Grant-in-Aid of Research nos. project are included in this study. 2710 and 8326; thethe Hawaiian Malacological Society; two grants fromfrom Conchologists of America, Inc.; and travel fundsfunds provided by Temakei Tebano at the University of MATERIALS AND METHODS thethe South Pacific. Manuscript accepted 1 February 2000. 22 Ogden Environmental and Energy Services, 680 Several communities engaged in subsistence lwileiIwilei Road, Suite 660, Honolulu, Hawai'i 96817. and commercial exploitation ofmollusks were investigated intermittently between 1993 and 1998. Research focused on four atolls in the Pacific Science (2001), vol. 55, no. 1:77-97 1998. Research focused on four atolls in the © 20012001 by University of Hawai'i Press central Gilberts: Abaiang, Tarawa (both ur­ All rightsrights reservedreserved banized and rural sectors), Maiana, and Abe- 77 78 PACIFIC SCIENCE· January 2001 ...~;;;/Makin~",;Makin 180° .\Po.... U.S.·Admlnl.t.~dU.S.·Admlnlst.~dIslsnds'.'.nd. .s;~ ButaritariButarilari ·:=1;Sularilari';:;;Sutarilari In the Central Pacific < TatluaeranTat>uaeran 0, 100 200300 ..... KiritimaliKlrIllmal' Maiana!tarawa\!tarawa HowlandHOwland \ !I I !I ~ IslandISland'-=- STATUTE MilES ~Abemama '= '!.'!IAbemama Il'I.!.' Baker Island N JarvIsJarvIS Island.,ISland.~, <:.:~ 0° 1>,~ BanabaSanaba •.f.\Nonouti\Nonouti Tabileuea\;tlli~STabi(euea\:t~~S .",.,,-., ' Marakei 2°N PHOENIX ~"/o~?IO ISLANDS ~ I "'.J""~ Abaiang TamanaTamana.:l~ ~ Arorae O/'''O/....,/~.":l!;Enderbuty../~.':$Enderbury KIRIBATI ~ :f) 0., ~Il':~ t: ~Rawaki~ Rawaki '\....... Tarawa GILBERT ISLANDS ., 0., to Malden ::..':. NikumaroroNikumarOtO...... ~lf.~tl< ~Manra 160 W ~.SlartlUCk~.Slart>uCk ;)Maiana.:)Maiana 'Ii>'ti> Abemama ~ .",:--Il"~,:,\ GILBERT ISLANDS <:) ° Kuria~~KUria~'~~ 'I.... 0 50 100 o ° 'DO "\"\KanlanKanlan VOSlok"VO'lok" lJIU' .,.\' 10 00 Aranuka I! !I II CarolinelOrr 0 STATUTE MilES 3 S Flint·'Flinl" PHOENIX ISLANDS 'Enderbury 0 50 '00'DO .y,,, I I I NonOuli '~«i~;k'?'~\ • Birnie NonOuli STATUTE MILES McKean • RawskiRaWSki !~. .• Nikunau 4° r8biteuea":t:JTabiteuea":.~ Beru~~~Beru~\ , \:'Orona -ManraaManra Nikumaroro, ':'Orona Onolo/::> . 1~40W 172° 2°S 0 173 E 175°0 Tamana·Tamana' '75 Arorae'l\)Arorae~ FIFIGUREG URE 1. The Republic ofKiribati (modified from Motteler 1986:1986:16;16; reprinted with permission from Bishop Museum Press, Honolulu, Hawai'i). mama, and one atoll in the Southern Group, along the southern portion of Tarawa Atoll, Tabiteuea North (Thomas 1999). Data on with samples taken between December 1992 various aspects of mollusk gathering were and February 1994. This information greatly obtained by participant observation, inter­ expanded the sample size of foraging events, views, and from the Shellfish Gatherer Sur­ with 83 foraging trips covering 26 days and vey (SGS) of the Tarawa Lagoon Project approximately 191 hr of foraging time (257 (TLP), in cooperation with BioSystems, Inc., forager-hours). Mean group size was 1.3 for­ of Santa Cruz, California. agers (SD = 0.7, n = 112). I accompanied foragers, both individuals Prey type identifications and basic habitat and groups, on 73 foraging trips covering 69 information are based on Cernohorsky (1971, days, for a total of 139.63139,63 hr of direct obser­ 1972), Eisenberg (1981), Abbott and Dance vation (286.92 forager-hours). Mean group (1982), Paulay (1995), and personal observa­ size was 2.6 foragers (SD = 0.9, n = 146).146), tions. For each prey type, five factors were Fifty-nine different individuals took part in examined to assist in distinguishing vulnera­ these activities. When it was not possible to ble from resilient resources: (1) size at matu­ record foraging activities directly, the rele­ rity; (2) intertidal burying; (3) adjacent sub­ vant information was elicited via interviews. A tidal populations; (4) benthic mobility; and total of 65 foraging trips was recorded over a (5) larval type (see Catterall and Poiner 1987). period of 51 days, for an estimated total of In a number of cases, the description of rele­ 88.5 hr offoraging effort (161 forager-hours). vant properties was limited, reflecting gaps in Mean group size was 3.1 foragers (SD = 0.7, the data. n = 148).148), A total of 19 different individuals was interviewed. Atoll Zonation and Molluscan Patch Types Information was also derived from data sheets made available by personnel of the From windward to leeward (Figure 3), the TLP. These data originated from landings basic zones and molluscan patch types char- Mollusk Habitats and Fisheries in Kiribati . Thomas 79 FIGURE 2. Tarawa Atoll (modified from Paulay 1997: fig. 1; reprinted with permission from Gustav Paulay). acteristic of the open atolls of the Gilbert Is­ THE SEAWARD REEF: The seaward reef lands are the: (1) reef slope; (2) submarine slope descends steeply from the upper limit terrace; (3) reef front; (4) reef margin; (5) of vigorous hermatypic corals at a depth of moat; (6) reef crest; (7) reefflat; (8) shoreline; about 18 m to the deepest seaward portion of (9) lagoon reef flat including mangrove, sand the reef between 4000 and 6000 m. In the flats, and sea grass beds; (10) lagoon slope and Gilberts, little is known of the biota below floor; and (11) leeward reef. 40 m, but mollusks commonly found in the 80 PACIFIC SCIENCE· January 2001 r- -. -:-:.'.. ' ' ..., " . " " ..... 0"' " , ... ", '.':.,',','", . ', .. ' . .. " ::-... " '.. " ,', .. ..~" :.:.:GR.o.V(l. c..c..~ ....la.polUllolU '0010,"'4' ..10, 4 .t...lI>uc.lc.l.. Aft" REffREfF fl([rfl(fr n." CRESftRESf RU,.RUF S-OP5LOP fAO/oITfR~T FIGURE 3. Schematic diagram of atoll features of the Gilbert Islands (modified from Richmond 1993:17, fig.fig, 5; re­ printed with permission from the South Pacific Applied Geoscience Commission [SOPAC]).[SOPAC), upper reaches of this zone include Pinctada demarcates the seaward limit ofthe reefflat; it and Trochus (Wells 1957), which also occur supports the gastropod Turbo setosus. The reef on the submarine terraces between depths of flat itself is commonly exposed or barely 15 and 18 m. The dominant mollusks on the awash at lowest tide. It consists of a truncated reef front, the shoreward face of the seaward floor zoned by the tides, which effect varying reef slope where coral growth is sparse and degrees of exposure and temperature between heavy surf dominates, are gastropods such as seaward edge and inshore margin. The sur­ Patella and Trochus (Demond 1957). The face of the reef flat supports Cypraea, Thais, seaward reef