Recent settlement trends in Panulirus argus (Decapoda: Palinuridae) pueruli around St. Thomas, U.S....

8/7/2019 Recent settlement trends in Panulirus argus (Decapoda: Palinuridae) pueruli around St. Thomas, U.S. Virgin Islands

1/8

23

Recent settlement trends in Panulirus argus (Decapoda: Palinuridae)pueruli around St. Thomas, U.S. Virgin IslandsB.L. Kojisr, N.J. Quinn2 & S.M. Caseau'-3lDivisionofFishandWildlife,629lEstateNazareth, l01,St.Thomas,U.S.VirginIslands00802.E-mail: bkoj [email protected] of the West Indies, Discovery Bay Marine Lab, Discovery Bay, St. Ann, JamaicaCunently with the St. John National Park Service, Cruz Bay, St. John, U.S. Virgin lslands

(Received 09-VIII-200 1 . Corrected 26-VI-2002. Accepted 09-I-2003)

Abstract: Puerulus settlement olthe western Atlantic spiny lobster, Panulirus argus,was monitored using modifiedWithanr collectors from December 1996 to March 1998 at seven sites around St. Thomas, U.S. Virgin Islands. A totalol 605 pueruli were collected from 553 samples lor a catch per unjt ellort (CPUE) for all sites of 1.09 pueruli. Thegreatest settlement occurred on sites within a recently declared marine reserve, which had an overall CPUE of 1.77pueruli. Settlement in non-reserve sites was much lower with an overall CPUE of 0.31 pueruli. Pueruli recruitmentdeclined 67% at inshore sites and 53% at ofTshore sites between July 1992 - April 1994 and February 1997 - March1998. Also, only l0% of montlts sampled in 1997-98 had a CPUE > 0.5 compared to 55% in a previous study in 1992- 1993. Despite the decline in pueruli CPUE in 1997-98 comparedto 1992-94, the commercial lobster catch in the2000-01 fishing season, and by inference the adult lobster population (legal lobster size in the US Virgin Islands is >3.5 cm carapace length), remained stable.Key words: Marine protected areas, lobster, recruitment, catch efforl, fisheries, Caribbean.

The westem Atlantic spiny lobster, Panulirusargus (LaIreille 1804), is fished commerciallyin the US Virgin lslands (USVI) by traps, freediving, and scuba diving and recreationally byfree diving and scuba diving. Spiny lobsterlandings in the USVI increased from an aver-age of 19 tons between 1980-88 (NOAA 1992)to approximately 39-41 tons between 1996-2001 (Tobias et al. 2000, this paper). Today,the spiny lobster is an imporlant component ofthe USVI commercial fishery comprising 9%of the total commercial catch. Selling aI anaverage retail price of $7 pound t 1$ t 5.4 kg t;,it comprises 16%o of the total income derivedfrom the commercial catch (Tobias et al.2000). In St. Thomas/St. John District, thefocus of this study, there were 38 licensed

Rev. Biol. Trop.,51, Supl.4: l7-24,2003www.rbt.ac.cr. www.ucr.ac.cr

commercial fishermen who landed lobster in1999-2000 (33 trap fishermen, 5 divers).Acknowledging the impoftance of this in-dustry and the potential for overfishing, regu-lations were adopted by both the CaribbeanFishery Management Council and USVI Gov-emment in 1985. These regulations restrictharvest to lobsters with a minimum carapacelength of 3.5 inches (89 mm), prohibit harvestof females with eggs, require landing lobsterswhole, and prohibit the use of poisons, drugs,spears, hooks or gigs when harvesting lobster.

Despite the adoption of these regulations,two recent studies indicate that the USVIspiny lobster hshery is showing signs of over-fishing (Bolden 2001, Mateo and Tobias2001). The over fished status ofthese stocks is


2/8

18 REVISTA DE BIOLOGIA TROPICAL

based on data indicating a decline in the lengthclass containing the majority of spiny lobsters,a significant negative trend in the mean annualcarapace length, a decline in sex ratios, and adecrease in trap catch per unit effort (Bolden2001). Finally, a stock assessment study ofspiny lobster on St. Croix, based on yield perrecruit analysis and surplus production mod-els, found that the St. Croix spiny lobster iscurrently harvested beyond their optimumexploitation levels (Mateo and Tobias 2001).An understanding of population dynamicsof a species is essential for determining the"predictability" of recruitment to a fisherybased on larval abundance. Changes in thelevels of recruitment to fishery stocks oftenresult from changes in the survival of young(Cushing 1973). Puerulus settlement data havebeen used to predict forward commercialcatches. Since 1981, Westem Australia hasused puerulus settlement to provide a 3-4 yearforward estimate of catch of the rock lobster.Panulirus cygnus (Brown and Phillips 1994).Witham collectors have given a good relativemeasure of the number of pueruli in an area(Witham et al. 1968) and have been used tomake general comparisons of abundance ofpueruli among sites (Quinn and Kojis 1997)and regions (Little and Milano 1980).Knowledge of trends in pueruli abundancescan assist in the management of marine pro-tected areas and possibly help to regulate catchlimits.We used modified Witham collectors to ex-amine the spatial and temporal variation oflobster pueruli settlement within Caribbeancoastal waters adjacent to the east end of St.Thomas. Specifically this study examines: 1)the distribution and abundance of pueruliwithin and outside St. Thomas marine re-serves, 2) changes in pueruli abundance be-tween 1992-94 and 1991-98, and 3) the rela-tionship between pueruli settlement rates andcommercial lobster catches in St. Thomas/St.John District.

MATERIALS AND METHODSSampling was done using modified Withamcollectors identical to those used in Quinn and

Kojis (1997) and Quinn et al. (1998) on sevensites on the east and south sides of St. Thomas.Four sites, Christmas Cove, Great St. JamesIsland, (CC) (18"18.75'N; 64"50'W); Cas Cay(CCa) (18"18.5' N; 64"51'W); Nazareth Bay(NB) (18"19.1' N; 64o51 .3'W); and MangroveLagoon (ML) (18"18.4'N; 64'52.5'W), werewithin the Mangrove Lagoon /Cas Cay and St.James Marine Reserves. Three sites, BuckIsland (BI) (18"16.5'N; 64"53.8'W), LovangoCay (LC) (18"21.9'N; 64"41.9'W) and SharkIsland (SI) (18"20.25'N; 64"50.7'W), wereoutside the marine reserves adjacent to smallislands. Three replicate collectors were set ap-proximately 15 m aparl at each site except Slwhere only two were installed. Collectorswere set at a depth of 3 m in water approxi-mately 8 m deep except for the CCa and MLsite where collectors were set I m below thesurf-ace in water approximately 2 m deep.Collectors were installed between Decemberi 996 and January 1997 . ML and CCa collec-tors were located in a mangrove estuary. Theremaining collectors were set over sand sub-strate approximately 100 m fiom rocky shore-lines inhabited by coral communities.Of the sites sampled in 1997-98, ML, wasidenticai to the site sampled by Quinn andKojis (1997) in 1992-94; CC was within thesame bay in both 1992-94 and 1997-98; andBI, an offshore island south of St. Thomas,was similar to Saba Island, a site also sampledby Quinn and Kojis (1991). The data liomthese three sites were used to compare varia-tion in pueruli settlement rales 1992-94 andt991-98.From December 1996 - January 1991through May 1997, collectors were sampiedapproximately weekly at all sites except CCa.Weekly sampling commenced at CCa in May1997. From June 1997 to March 1998, collec-tors were sampled every two weeks approxi-mately five days after the new and full moonphases in a procedure identical to Quinn andKojis (1997). All pueruli were removed fromthe collector, staged (Lewis et al. 1952, Quinnand Kojis 1997), counted, and released. Catchper unit effort (CPUE) was determined bydividing the total number of pueruli caught percollector at each srte by the number of collec-tors sampled at the site on each sampling date.


3/8

ASSOCIATION OF MARINE LABORATORIES OF THE CARIBBEANTABLE 1

St. Thomas, USVI: Number o/Panulirus argus pueruli of dffirentstages settling at each site (Dec. 1996 to Mar. 1998)

Site N Juvenile Clear Semi- Pigmented TotalpigmentedBucklsland 55 0 0 1 6 7Cas Cay 54 9 10 21 121 16lChristmas Cove 128 0 4 8 13 25Lovango Cay 10 0 3 2 18 23Mangrove Lagoon 109 9 5 18 97 129Nazareth Bay 87 2 48 76 115 241Shark lsland 50 1 2 4 12 19Total 553 21 12 130 382 605N : total nomber of samples (onc sample : the number ofpueruli on one collector at one sampling datc).

TABLE 2Comparison ofcatch per ttnit effort (CPUE) oJ Panulirtts argus pueruli between sitesinside and outside the St. Thomas Cas Cay /Mangrove Lagoon and

Great St. James Marine Reserves. Der:. 1996 to Mar. 1998Marine Reserve Sites CPUE Standard Eruor % sampling dayspueruli present

Cas Cay 2.98 0.91 19Christmas Cove 0.23 0.17 59Mangrove Lagoon 1.20 0.25 11Nazareth Bay 2.65 0.57 84Mean 1.17 75Non-marine Reserve SitesBuck IslandLovango CayShark IslandMean

0.1 5 0.07 220.38 0.14 410.39 0.t2 370.31 33

RESULTShe statistic is directly comparable with thatused by Quinn and Kojis (1997). Catches fromthe weekly sampling were pooled yielding A total of 605 pueruli were collected fromsamples similar to the fbrtnightly sampling 553 samples (Table 1) fbr a mean CPUE,period. (MCPUE) for all sites of 1.09 pueruli. Settle-Commercial fisheries statistics were derived ment of at least one individual was observed infrom commercial landings reported by the 55%ofthesamples.Amaximumof2l puenuliDivision of Fish and Wildlife (Tobias 1997; settled on a single collector at a single sam-Tobias et al. 2000') and directly from Division pling time. Seventy-two (1'1.9oh) of the pueruliof Fish and Wildlife databases. The commer- collected were clear, 130 (21 5%) serni-pig-cial lobster catch was standardized by calcu- mented, and 403 (66.6%) pigmented/juverfilelating the percentage of fisherman reporting (Table 1).compared with the total number of licensed Three of the four sites within the marine lre-commercial fishermen in the St. Thomas /St. serve had the highest levels of settlemgnt.John District and adjusting the reported catch There was a significant difference between the(Tobias eta/.2000). MCPUE for reserve and non-reserve siltes

l9


4/8

20 REVISTA DE BIOLOGiA TROPICAL

940o(,)330IEzoO

2.5A

A1^ O,99' g* \qq' .f"

15 =lrt

co0.5

Commerical Catch Pueruli

(One Way ANOVA, N: 9; p :0.03). Pueruliwere present at each of the four marine reservesites on 590/o to 840/o of sampling days andthese sites had an overall CPUE of 1.77 puer-uli (Table 2). Settlement was highest at CasCay (CCa) and Nazareth Bay (NB) (Table 2).The CCa site borders the Mangrove Lagoonwhile the NB site is east of the Lagoon. TheMangrove Lagoon (ML) site, located in achannel in the inner lagoon, had the thirdhighest CPUE. However, it was less than halfof CCa and the NB sites. The other four siteswere at offshore cays and their CPUE rangedfrom 0.15 to 0.39 pueruli (MCPUE of 0.29pueruli) or less than 15o/o of the CCa and NBsites (MCPUE of 2.8) (Table 2).The total commercial landings for St. Tho-mas/St. John District from the 1992-93 fishingyear to 1997-98 (the fishing year extends fromJuly I to June 30) varied befween 35 to 50tons. There is no statistically significant trendfor commercial lobster catches (N : 7, r:0.39,n.s.). The correlation coefficient for puerulisettlement CPUE by years is signihcant (N =6, r:0.83, p : 0.04) (see Fig. 1).

g* 9d', g{, ,C

0

-0.5-lgtr

"""t ".*C ommercial lobster catch

DISCUSSIONThis study showed a statistically significantdecline in pueruli settlement rates between

1992-94 (Quinn and Kojis 1997) and 1991-98(this study), while the commercial lobsterlandings remained nearly static (Fig. 1). Ifpueruli settlement is a predictor of futurelandings and spiny lobster take approximatelythree years to achieve legal size (89 mm cara-pace length) (Moe 1991), then the low puerulisettlement rate observed in 1997-98 shouldresult in a decline in commercial lobstercatches in the 2000-01 fishing year. In con-trast, the commercial lobster catch in 2000-01was 40.9 tons, similar to previous years. Thedecline in pueruli CPUE does not appear to beeffective in forecasting the commercial lobstercatch for the 2000-01 fishing season, and byinference estimating the reproductive lobsterpopulation. However, because no size meas-urements were taken to provide the age distri-bution of the commercial catch, the value ofsampling P. argus pueruli to predict the com-mercial lobster catch in the Virgin Islands still

Pueruli

Fig. 1. Comparison between commercial fisher's landings of Panulirus argas (Tobias, 1997; Tobias et al2000) and pueruli settlement in St. Thomas, USVI.


5/8


6/8

s92-94 n 97-98

REVISTA DE BIOI,OGtA TROPIC]AI-

NIL CC OffshoreSampling Sites

Fig. 3. St. Thomas, USVI: Percentage of months that thePanulirus argrls pueruli settlement was > 0.5 CPUE. 1992-1994 data from (Quinn and Kojis 1997), 1997-1998 (hisstudy). CC : Christmas Cove, ML - Mangrove Lagoon.Oflshore : Saba Island (Quinn and Kojis 1997) and BuckIsland (this study).

Saba Islands, and Christmas Cove was 1.2, 0.1and 0.5 pueruli compared with 2.5, 1.3 and2.4pueruli in 1992-94, respectively. In 1997-98,less than 10oh of the months sampled at thethree comparable sites had a pueruli settlementrate > 0.5 MCPUE compared with an averageof more than 55o/o of the months during 1992-94 (Fig. 3) (Quinn and Kojis 1997, Quinn elal. 1998).Previous work in St. Thomas (Quinn andKojis 1997, Quinn el al. 1998) showed that theareas now designated as marine reserves had ahigher pueruli settlement rate than other sites.This study reports similar results. Four of thesites in this study are within the Cas CayAvlangrove Lagoon and St. James MarineReserves and Wildlife Sanctuaries, and threeof these sites had the highest MCPUE forpueruli. Knowledge of the ecological charac-teristics associated with areas of high settle-ment is necessary to develop managementstrategies for identilj'ing and preserving habi-tat ofparlicular concern for spiny lobster puer-uli. Additional studies describing the sites indetail and identifying factors that make thempref'er-red settlement sites are required onceareas of high settlement are identified.A high CPUE at the Nazareth Bay and CasCay sites may have been, in pafi, the result ofconcentrations of pueruli caused by the iargeisland mass and partially enclosed bay. Tidal

and easterly trade wind driven currents drivewater into the Mangrove Lagoon and NazaretitBay. When easterly trade winds blow greaterthan 7 m sec-' 1.1 4 knots), wind driven surfacecurrents at the entrance to Cas Cay and theMangrove Lagoon reach 0.l m sec-' (Nicholsand Towle 1977). This funneling of water intothe bays could result in a higher volume olwater passing around the collectors in this areaincreasing the numbers of pueruli available forsettlement. However, since the protectedMangrove Lagoon site aiso had a high CPUE,we suggest that one of the primary reasons forthe high settlement rates at these sites is thatthey lie within or adjacent to preferred puerulisettlement habitat.Legislation designating the Mangrove La-goon and Great St. James Marine Reserveswas approved in September 1994. The re-serves are closed to the take of all inverte-brates and plants and only allow fishing bypermit with cast net within -15 m of shore andwith hook and line. No take of any kind ispemitted in the inner Mangrove Lagoon.

The relatively high CPUE in the three sitesnearest the n-iangroves is consistent with thehypothesis that mangrove en\ ironments areimportant juvenile nursery areas in the lifehistory of lobsters (LitIle 1977). Establishmentol marine reserves protecting these habitats isan important step toward maintaining andenhancing lobster stocks. However, the Man-grove Lagoon/Cas Cay Marine reserve issubjected to non-point source pollution, e.g.sediment and toxins from upland sources, aswell as point source pollution, e.g'. sewage.These pollutants are curently seriously af'-fecting the water quality within the Cas CaylMangrove Lagoon Marine Reserve (Nicholsand Towle, 1977, Wernicke and Towle, 1983,Anonymous 1984) A new sewage treatmentplant scheduled lor completion in 2002 isexpected to eliminate point source sewagedischarges into the Mangrove Lagoon. Thisplant will also treat leachate fiom the landfillthat currently seeps into the Lagoon. Furtherstudy is necessary to determine whether ananticipated improvement in water qualityresults in an increase in settlement of pueruliand survival of juvenile spiny lobster withinthe marine reserve.


7/8

ASSOCIATION OF MARINE LABORATORIES OF THE CAR]BBEAN z)

ACKNOWLEDGEME,NTSStaff of the Virgin Islands Department ofPlanning and Natural Resources, Division ofFish and Wildlife assisted in data collection.We would like to particularly thank Steve

Meyers for initiating this study and JosephBarbel for his diligence in assisting with field-work. The Caribbean NMFS Cooperative SEAMAP Grant NA77F50094 tunded this project.RESUMEN

El asentamiento de puerulos de la langostaespinosa del Caribc, Panulirus arglrs fue mo-nitoreado usando coiectores modificados tipoWitham, entre diciembre de 1996 y marzo de1998 en siete sitios alrededor de St. Thomas,Islas Virgenes. En general, para todos los sitiosestudiados se colectaron un total de 605 pueru-los en 553 lxuestras, que representan ur esf'uer-zo por unidad de captura (EPUC) de 1.09puerulos. El rnayor asentamiento registradoocurri6 en sitios declarados recientemente Re-servas Marinas, para los cuales se alcanz6 unEPUC de 1.77 puerulos. El asentamiento en si-tios no protegidos fue m6s bajo (EPUC : 0.31puerulos). El reclutamiento de puerulos des-cendi6 53o/o en lugares hacia mar af uera entrefebrero de 1997 y marzo de 1998. Solamenteen el 10% de los meses muestreados (entre1997 y 1998) se alcanz6 un EPUC > 0.5, com-parado al alcanzado en un 557o de los mesesde rnonitoreo en un estudio previo entre 1992y 1993. A pesar del decline del EPUC entreestos dos periodos cornparados, la captura co-mercial de langostas durante la ter.nporada depesca 2000-2001, y por inferencia la poblaci6nadulta de este crust6ceo (la talla minirna legalde captura de langosta en las Islas Virgenes esde >3.5 cm longitud del caparazon), permane-ce estable.

REFERENCESAnonvmous. I984. Final Environmental Impact Statementfbr thc Mangrove Lagoon /Turpentinc Run Waste-watcr F'acilities Plan. U.S. Envirorrmental ProtectionAgenc;. St. Thonras. USVI. 2.1 p.

Bolden, S.K. 2001. Status of the U.S. Caribbean spinylobster fishery 1980 - 1999. USDOCA,IMFS, MiamiLaboratory Contribution No. PRD-99/00- I 7. 69 p.Brorvn. R.S. & B.F. Phillips. 1994. The curent status ofAustraiia's rock lobster flsheries, p. 33-63. ln B.F.Phillips, .I.S. Cob & J. Kittaka (eds.). Spiny LobsterManagement. Blackw'ell Scientifi c, Oxford.Cushing, D.H. 1973. Recruitment and parent stock in fishes.Univ. Washington Sea Grant Publ. WSG 73-1. 197 p.Lewis, J., H. Moore & W. Babis. 1952. The postlarvalstages of the spiny lobster, Panulirus argus. BullMar. Sci. 2:324-337.Little, E.J., lr. 1997. Observations on recruitment of postlalval spinv lobsters, Panulirus arglts, to the SouthFlorida coast. Fla. Mar. Res. Publ. No. 29: 35 p.Little. E.J., Jr. & G.R. Milano. 1980. Techniques tomonitor recruitment of postlarual spiny lobsters,Ponulirus argils. to the Florida Keys. Fla. Mar. Res.Publ. No. 37. 16 p.Mateo. I. & W.J. Tobias. 2001. Preliminary estimations ofgro\\th, mortality and yield per recruit lor the spinylobster Panulirt6 orgus in St. Croix, USVI. Proc.GulfCaribb. Fish. Inst. 53. (in press).Moc Jr., M.A. 1991. Lobsters: Florida, Bahamas, the Carib-

bean. Grcen Turtle Publications, Plantation, FL. 5 I 0 p.Nichols" M. & E. Towle. 1977. Water. Sediments andEcologl'olthe Mangove Lagoon and Benner Bay, St.Thomas. Tech. Rep. 1. Island Resources Foundation,U.S. Virgin lslands. 158 p.NOAA. 1992. Our living oceans. Report on the status olU.S. living rnarine resources, 1992. NOAA Tech.Mem. NMFS-F/SPO-2. 150 p.Quinn, N.J. & B.L. Kojis. 1997. Settlement variations of thespinl lobster (Panrlirus argls) on Witham collectorsin C'aribbean coastal waters around St. Thomas, United

States Virgin lslands. Carib. .1. Sci. 33: 251-262.Quinn, N.J.. B.L. Kojis & C. Chapman. 1998. Spinylobster (Panrllrus argus) recruitment to artiflcialhabitats ir.r waters ofT St. Thorr.ras. United StatesVirgin Islands. Proc. 45'h Session Gulf Carib. Fish.Inst.15:759-'777.Tobias, W. 1997. Three Year Summary Repoft, April I 994- March 1997. Cooperative Fishery Statistics Proglam.VI Dcpartment ol Planning and Natural Resources,Division of Fish and Wildlifb. St. Thomas, USVI. 41 p.Tobias. W., R. Gomez, I. Mateo & B. Kojis. 2000. ThreeYear Summary repon, I April 1997 - 3l March 2000,Cooperative Fishcry Statistics Program. VI Depart-ment ol Planning and Natural Resources, Division of

Fish and Wildlife. St. Thomas, USVI. 34 p.


8/8

24 REVISTA DE tsIOLOGIA TROPICAI,Wernicke, W. & E. Tow.le. 1983. Vessel waste controlplan for the U.S. Virgin Islands. Prepared lor V.l.Department ol Conservation and Cr:ltural Affairs, byIsland Resourccs Foundation, St. Thomas, USVI.

Witham, R., R.M. Ligle & E.A. Joyce Jr. 1968. Physio-logical and ecological studies ol Panulirus argLrslrom the St. Lucie estuary. Fla. Board Cons. Mar.Res. Lab. Tech. Ser. No. 53. 31 p.

Recent settlement trends in Panulirus argus (Decapoda: Palinuridae) pueruli around St. Thomas, U.S....

Documents

Transcript of Recent settlement trends in Panulirus argus (Decapoda: Palinuridae) pueruli around St. Thomas, U.S....