Effect OfExploitation On The Limpet Lottia Gigantea: A .
Pacific Science (1996), vol. 50, no. 4: 393-403 1996 by University of Hawai'i Press. All rights reservedEffect of Exploitation on the Limpet Lottia gigantea: A Field Study inBaja California (Mexico) and California (U.S.A.)!OSCAR ALBERTO POMB0 2 ,3 AND ANAMARiA ESCOFET 2ABSTRACT: Specimens of Lottia gigantea (Sowerby) from intertidal populations, artisanal catches, and shell middens were obtained from 1985 to 1988 at11 sites along the Pacific coasts of Baja California (Mexico) and California(U.S.A.). A scaled rating system of 0-4 was used to describe the amount of intertidal exploitation associated with visiting patterns of gatherers, accessibility,and site topography. Maximum and mean size of intertidal populations andartisanal catches decreased along a gradient of increasing exploitation. Meansize was significantly different between catches and the corresponding intertidalpopulation. Mean size of specimens in older middens was significantly largerthan in a recent midden. Measurements at the most inaccessible site inmediatelyafter the exceptional extratropical winter storm that swept the California coaston 17-18 January 1988 showed that the storm had removed larger specimensapproximating exploitation measuring 1-2 on our scale. Intertidal gatheringoccurs or has occurred unless it is physically prevented by topography, distance,or some kind of restriction of access. Ecological implications of exploitationwere explored utilizing the conceptual model proposed by Catterall and Poinerfor assessing potential impact of traditional shell gathering on intertidal molluscs. The model suggests that size at maturity of this species and its pelagiclarval stage may prevent depletion by harvesting.MOST INTERTIDAL HABITATS worldwide areexploited by artisanal harvesters using simpletools. The production, which is seldom included in official fisheries statistics, is eitherconsumed by individual gatherers or familygroups or sold in small-scale trade (Duran etal. 1987). Artisanal harvesting includes a variety of organisms such as lugworms, limpets,and gastropods. The effect of human exploitation relative to natural processes in populations of harvested marine invertebrates is an1 This article is part of O.A.P.'s M.S. thesis submittedto CICESE. The work was partially supported by Consejo Nacional de Ciencia y Tecnologia, Mexico, throughgrant PCEBNA-021264 to A.E. Manuscript accepted 22January 1996.2 Centro de Investigaci6n Cientifica y Educaci6n Superior de Ensenada, Apartado Postal 2732, 22800 Ensenada, B.c., Mexico. International mailing address: P.O.Box 434844, San Diego, California 92143-4844, U.S.A.3 Current address:Department of EnvironmentalAnalysis and Design, School of Social Ecology, University of California, Irvine, California 92715.issue of substantial interest in contemporaryecology and conservation biology (Catteralland Poiner 1987).Studies of the role of humans as predatorsin the intertidal has focused largely on population density and size structure of prey atharvested and nonharvested sites; some studies have analyzed the implications of harvesting in terms of biomass and gonad outputs (Branch 1975, Blake 1979, McLachlanand Lombard 1981). The effects of humanpredation on intertidal populations have alsobeen analyzed in terms of community ecology; the concepts of top carnivore and keystone species (Paine 1966) as well as the intermediate disturbance hypothesis (Connell1978) have been employed to explain profound changes in species richness, community structure, and size structure of component species at sites with and without humanpredation (Moreno et al. 1984, Hockey andBosman 1986).On Baja California shores, several species393
394PACIFIC SCIENCE, Volume 50, October 1996of invertebrates are exposed to artisanalexploitation (Pombo 1990). Most species areremoved for direct human consumption:mussel (Mytilus californianus Conrad); clams(mainly Pismo clam, Tivela stultorum Mawe);abalone (Haliotis spp.); keyhole limpet(Megathura crenulata [Sowerby]); snail (Astraea undosa [Wood]); owl limpet (Lottia gigantea [Sowerby]); and gooseneck barnacleor leaf barnacle (Pollicipes polymerus Sowerby). Abalone are also collected, as juveniles, for ornamental purposes. The ghostshrimp (Callianassa californiensis Dana) isused as fish bait. Chitons (Stenoplax spp.),keyhole limpet, black abalone (Haliotis cracherodii Leach), snail, and owl limpet areused as bait in spiny lobster traps. Most species come from the rocky intertidal; snail andall abalone except black are extracted fromthe sublitoral, and ghost shrimp and clamsfrom soft bottoms.The owl limpet, Lottia gigantea, is thelargest limpet in North America. It lives onexposed and semiexposed rocks and cliffs inhigh middle and upper littoral zones fromnorthern Washington to central Baja California (Ricketts and Calvin 1939, Stimson1973, Lindberg and Wright 1985, Wright1989). Zedler (1976, 1978) found lower abundance of larger individuals of L. gigantea inareas of greater human use than at the Cabrillo National Monument, Point Loma, California, where collecting is restricted. Ghazanshahi et al. (1983) included L. gigantea inthe list of species likely to be affected bypublic use.Our data relate different degrees of intertidal exploitation to the sizes of individuals inpopulations of L. gigantea in 11 localitiesalong the Pacific coasts of Baja California(Mexico) and California (U.S.A.). We alsoinvestigated the effect of the history of exploitation at a site, the effect of human exploitation relative to physical disturbance bystrong storm-generated waves, and the ecological implications of exploitation.MATERIALS AND METHODSSpecimens of Lottia gigantea from intertidal populations, artisanal catches, and abo-riginal shell middens were collected duringfield studies conducted from 1985 to 1988 at11 sites along the Pacific coasts of Baja California (Mexico) and California (U.S.A.)(Figure 1). A rank scale of 0-4 was used todescribe the degree of intertidal exploitationfor each site. Criteria used to rate the intertidal gathering were as follows: (1) gatherers'visiting pattern to the intertidal during the 3yr period in which the study was conductedand in the past, according to reports of localdwellers; (2) several features of the sites thatcould explain degrees of exploitation (topography, distance from mainland or majorhuman settlements, habits of consumption ofintertidal species by local people, existenceand length of protective management programs).Individual elements of the scaled intertidalgathering rating system of 0-4 were assignedas follows:Rating 0: Sites where intertidal gatheringnever occurred because of steep topographythat physically prevents access (La Bufadora)or where it was certifiably absent for approximately the last 30 yr because of protective management (all sites at Santa CruzIsland, Channel Islands).Rating 1: (1) Lobera, where the local oyster farm cooperative has banned intertidalgathering since 1984 to promote abalone recovery; only two abalone harvesting seasonshave been allowed since then; (2) Isla Guadalupe, where gathering is rare because thesite is isolated from the mainland and thereare no fishing settlements nearby. A smallnumber of military personnel at an Ol,ltpostcollect abalone during very low tides thatcoincide with official holidays.Rating 2: (1) Chorera, a site protected bythe local oyster farm cooperative since 1985.Only five resident family groups of fishermenare allowed in the area. However, their visitsare frequent, because of feeding habits; gathering of several species, mostly abalone, wasconfirmed in the field; (2) El Campito, whereaccess is free but people are seldom observed(its vicinity to Chorera, a protected area, maydeter visitors).Rating 3: Cantiles, a site open to the public but relatively inaccessible (5 km from a
NVENTURALOS ANGELES QU.S. A.ENSENADA1234567891011[sla Guadalupe ([G)EI Campito (CAM)l\. 1Chorera (CHaR)\JLobera (LOB)Cantiles (CAN)Punta Papagayo (PP)Bufadora (BUF)Punta Morro (PM)Channel Islands: Santa Cruz IslandFraser Point ( FP)Fraser Point NW (FPNW)Fourney Cove ( FC)FIGURE1. The study sites.
396major town; unpaved roads); gatherers arriveirregularly, usually on major holidays.Rating 4: The highest degree of exploitation was assigned to Punta Papagayo andPunta Morro, where numbers of gatherersare observed all year round, almost daily.Both sites have free access, are located I Ianfrom a major city (Ensenada, B. C., Mexico),and have paved roads.In all the intertidal samples, except thosefrom La Bufadora, all individuals of L. gigantea detected along a randomly chosenstrip 2 m wide across the intertidal were collected, and shell length (longest axis to thenearest mm) was measured in the laboratory.Specimens were frozen to preserve them forlater determination of growth rate, sex, andmaturity, as part of more extensive studies(Pombo 1990).At La Bufadora, inaccessibility of the walloccupied by L. gigantea forced us to makeindirect measurements. One person dangled aruler on the wall with the aid of a sport fishing rod while another person took picturesfrom the opposite side. The entire wall wascovered in bands one film frame high. A 200mm telephoto lens and ASA 400 slide filmwere employed. The length of the specimenswas calculated by converting the dimensionsin projected images. The error of the methodwas calculated by taking pictures of the sameruler placed by an array of 48 limpet shellsof known length, at five different distancesequivalent to those in the field. The measurement error, using 95% confidence interval was 0.48 0.89 mm.The number and size of limpets collectedby present-day artisanal harvesters was recorded and the catches were returned to theharvesters.To explore intertidal exploitation in thepast, specimens of L. gigantea were measuredat two Indian shell middens 3 km apart onSanta Cruz Island (California, U.S.A.) wherethe stratigraphic sequence was finely datedby Glassow (1980): Fraser Point (superficial,mussel-dominated strata dated 280 150 yrB.P.); Fourney Cove (4 m deep; the last abalone-dominated strata, dated 2310 150 yrB.P.).The magnitude of the effect of harvestPACIFIC SCIENCE, Volume 50, October 1996by gatherers was compared with the effectcaused by storm waves. A second set of indirect measurements was carried out at LaBufadora immediately after the exceptionalextratropical winter storm that swept theCalifornia coast on 17-18 January 1988. Inthe results, Bufadora BS (BUF-BS) and Bufadora AS (BUF-AS) respectively indicatedata obtained before and after the January1988 storm.To compare shell length, a parametricanalysis of variance (ANOYA) of unbalanced design was applied for more than twosamples. A Student-Newman-Keul's multiple range test at IX 0.05 (Sokal and Rohlf1979) was used for post-hoc comparisons ofpopulation means in the ANOYA modelwhen significant among-population differences (P 0.05) were detected. For comparisons of two samples outside the ANOYAmodel, a two-tailed t-test at IX 0.05 wasperformed.Ecological implications of exploitationwere explored through the conceptual modelproposed by Catterall and Poiner (1987) forassessing the potential impact of traditionalshell gathering on intertidal molluscs. Themodel uses life history and habitat information to predict the extent to which a givenintertidal shellfish population would be eithersusceptible to depletion or resilient.RESULTSSize Structure at Field Sampling SitesIn the intertidal populations the size of individuals ranged from 102 to 17 mm (Table I).Mean size was significantly different amongsites (F 92.647; P 0.05). The multiplerange test yielded five groups: (1) valueshigher than 50 mm (Bufadora BS); (2) valuesbetween 45 and 50 mm (Lobera, FraserPoint, and Isla Guadalupe); (3) values between 40 and 45 mm (Chorera and FraserPoint NW); (4) values between 30 and 40 mm(Cantiles); (5) values lower than 30 mm(Punta Papagayo and Punta Morro). Thesize of mature individuals ranged from 21 to73 mm. The mean size of mature males varied
Exploitation of Lottia gigantea-POMBO397AND ESCOFETTABLE ISIZE RANGE (SR) (mm) AND MEAN SIZE (x) (mm) OF Lottia gigantea IN SAMPLES FROM INTERTIDAL, CATCHES, ANDMIDDENS AT II SITES WITH DIFFERENT DEGREES OF EXPLOITATION (DE)SAMPLE FROMDEINTERTIDALBUF-BSoBUF-AS, all dataoBUF-AS, outlier removedoChannel Islands:Fraser PointoSR 102-3013.7n 125SR 107-32x 50.9 14.6n 28SR 72-32x 48.8 9.8n 27SR 72-31x 49.0 9.4n 61SR 67-28x 42.5 8.7n 57SITEFraser Point NWoFourney CoveoMIDDENSx 55.0 SR62-266.993 x 39.9 n SR68-267.2n 37 x 50.3 SRLoberaCATCHES75-297.6n 97SR 78-17x 48.7 13.9n 131SR 57-28x 43.9 6.1n 114 x 49.3 Isla GuadalupeChorera2EI Campito2Cantiles3Punta Papagayo4Punta Morro4SR80-428.766 x 56.7 n SR 55-46x 50.7 4.3nSR58-20x 37.8 8.3n 60SR 44-20x 29.7 6.2n 68SR 49-18x 28.4 6.8n 103 90 between 47.0 8.3 and 31.4 6.5 nun; meansize of mature females varied between 52.2 6.5 and 31.2 6.4 mm. Sex ratio varied from60% males and 40% females with none or fewundetermined individuals at Chorera andLobera to 26% males and 38% females with64% undetermined individuals at PuntaMorro.The January 1988 winter storm causedSR 33-23x 27.8 5.2n 11977.6% mortality at La Bufadora (125 organisms detected in 1987, 28 survivors after thestorm). Mean size before and after the stormwas not significantly different when all datawere considered (tcal c 1.355, P 0.05) butwas significantly different when a 107-mmspecimen suspected to be a methodologicaloutlier was removed from data (tcalc 2.22,P 0.05). Size range before and after the
398PACIFIC SCIENCE, Volume 50, October 1996stonn also appeared similar considering alldata after the stonn but was quite reducedwhen the suspected outlier was removed.In catches, size of individuals ranged from80 to 23 mm. The average size of limpetsin catches from each site was significantlydifferent from that of limpets in the corresponding intertidal populations (Isla Guadalupe, tcalc 4.947, P 0.05; Punta Papagayo, tcalc 2.313, P 0.05). The smallestindividuals in catches were always largerthan the smallest individuals in the intertidal.In the shell middens, the size of individualsranged from 68 to 26 mm. Size range andmaximum size were similar in both middens.Mean size of the specimens found in the olderstrata (Fourney Cove) was significantly larger(tcalc 7.50, P 0.05) than in the more recent deposit (Fraser Point). At Fraser Point,mean size of individuals in the midden wassignificantly smaller than that of the currentintertidal population (tcalc -2.709, P 0.05).Effect of HarvestingMean size, maximum size, and size rangeof intertidal populations decreased along theexploitation gradient (Figure 2). Mean size in11010090 80:::x:::I-70(!):zlLJ-l-l-llLJ:::x:::(J)60BUF - BS50:z tlLJBUF - ASFPBUF-AS*FPNW40:E3020100j234DEGREE OF EXPLOITATIONFIGURE 2. Mean size of Lottia giganrea from intertidal (circles), catches (triangles), and middens (rectangles)along the exploitation gradient, depicted within the limits of the size range of the intertidal population (solid lines)and catches (shaded area). Abbreviations for the sites as in Figure I and text; BUF-AS* indicates that the resultswere obtained at BUF-AS after the removal of the suspected outlier from data. At exploitation rating 0, limits areset according to BUF-AS values.
Exploitation of Lottia gigantea-POMBO AND ESCOFETseven of the nine intertidal populations (Bufadom BS, Lobera, Isla Guadalupe, Chorera,Cantiles, Punta Papagayo, Punta Morro) decreased along a gradient of increased exploitation (R 2 0.395, n 589). At FraserPoint and Fraser Point NW, mean size wassmaller than expected at sites without exploitation, close to sizes found at sites withdegree of exploitation ratings of 2-3 and 12, respectively. Mean size in artisanal catchesalso decreased along the exploitation gradient (Isla Guadalupe-EI Campito-Punta Papagayo). Difference between mean size ofcatches and those of the corresponding intertidal populations was maximal (27 mm) atIsla Guadalupe, with a low amount of exploitation, and minimal (3.0 mm) at PuntaPapagayo, with the highest exploitation.Plotting of data from middens and Bufadora AS within the former scheme suggestedthat exploitation in the past was low at399Fourney Cove and more intense at FraserPoint (ratings of 1-2 and 3-4 in our scale,respectively) and that the storm had removedthe larger specimens to a degree similar to anexploitation rating of 1-2 in our scale.Ecological Implications of ExploitationThe analysis of life history and habitat information in the model proposed by Catteralland Poiner (1987) singled out two attributesthat presumably make it unlikely that localpopulations of L. gigantea will be driven toextinction: their small size at maturity, andexistence of a pelagic larval stage (Table 2).Other biological characteristics proposed bythe model (intertidal burying, adjacent subtidal populations, benthic mobility) do notapply to L. gigantea, which only occurs onintertidal hard substrate and has limited mobility in the adult stage.TABLE2BIOLOGICAL ATfRIBUTES CONSIDERED TO BE THE MORE IMPORTANT DETERMINANTS OF THECONSEQUENCES OF TRADITIONAL GATHERING OF SHELLFISH POPULATIONS (CATfERALL AND POINERAND ITS ILLUSTRATION IN L. giganteaATfRIBUTEMODEL STATEMENTSize at maturityIf size at maturity is less than size detectable bygatherers, a population will always containreproducing individuals.Intertidal buryingIf individuals large enough to be detectablehave the opportunity to bury themselveswithin soft substrate, a refuge from predation or gathering can be attained.If a local intertidal population is depleted,replenishment may be possible throughrecruitment of individuals from adjacentsubtidal areas.In species with partially subtidal distribution,if benthic stages are mobile, reproductiveindividuals may migrate into the exploitedintertidal areas, providing an opportunityfor local reproduction.Irrespective of benthic migration of adults, ifa species has a pelagic larval stage lastinglong enough to permit settlement of larvaespawned by distant, unexploited populations, recruitment into exploited areaswould continue as long as enough suchpopulations remained.Adjacent subtidalpopulationsBenthic mobilityPelagic larvae1987)RESULTSMature females (25.8 mm) and males (25.0mm), close to the size of the smallestindividuals in catches (23 mm) wereregistered in the study area.L. gigantea only occurs on hard substrate(Stimson 1973).L. gigantea is strictly intertidal (Stimson1973).L. gigantea is intertidal and has limitedmobility as adult (Stimson 1973).L. gigantea has a planctonic larval stage.Duration of planctonic larval stage isunknown (Stimson 1973).
400PACIFIC SCIENCE, Volume 50, October 1996DISCUSSIONSince the publication of the pioneer paperby Branch (1975), there have been numerousdemonstrations of the effect of exploitationon populations of intertidal invertebrates(Zedler 1976, 1978, Blake 1979, McLacWanand Lombard 1981, Moreno et al. 1984, 1986,Castilla and Dunin 1985, Hockey and Bosman 1986, Oliva and Castilla 1986). Mostcomparisons were made between sites withand without exploitation, and the effect ofthe degree of exploitation has only been explored by Branch (1975) and Moreno et al.(1984).Our procedure to rank levels of humanactivity in the intertidal is close to the procedure of Moreno et al. (1984) in consideringproximity and size of settlements or fishingcommunities and existence and length ofprotection as reasonable predictors of intensity of human activity. Also, it is similar tothe procedures of Beauchamps and Gowing(1982), Ghazanshahi et al. (1983), and Underwood and Kennelly (1990) in consideringcounts of people as a measure of public accessibility.Our results, showing a reduction in population size range and a decrease of the meansize of specimens of L. gigantea along fivedifferent ratings of amount of intertidal exploitation, are similar to the results of severalother studies. Moreno et al. (1984) reported asimilar pattern in the exploitation of Fissurella picta (Gmelin) at four sites with differentlevels of human activity, and Oliva and Castilla (1986) reported reduced size of individuals and reduced abundance of Fissurellacrassa Lamarck and F limbata Sowerby atharvested versus nonharvested sites. Branch(1975) reported a reduction in average sizeand abundance of Patella concolor Krauss at13 individual sites over a 5-yr period of increasing exploitation.Our results also show that mean size inartisanal catches decreased along the exploitation gradient and that the differencebetween mean size in the catches and in theintertidal population becomes smaller as exploitation increases. The effect of exploitation was also evident comparing the smallestsize in the catches and in the intertidal population: as exploitation increases, both valuesbecame closer to each other (27-mm difference at Isla Guadalupe; 3-mm difference atPunta Papagayo).These results convey that the decrease inmean size, as a descriptor of the effect of exploitation, is reinforced by the decrease inmaximum size and size range of intertidalpopulations (Branch 1975). Our results suggest that at sites with heavy exploitation,the mean size of intertidal populations andcatches may not demonstrate satisfactorilythe selection of larger sizes by gatherers. Inour results, the smallest individuals in thecatches were always larger than the smallestindividuals in the intertidal, suggesting thatharvesters are size selective and preferentiallytake larger limpets even at sites where heavyexploitation has reduced the population sizerange. This is shown at Punta Papagayo(highest degree of exploitation) where themean size of the catch was smaller than inthe intertidal population, but selection of thelarger individuals can be shown through difference between size range in the catches andin the intertidal population.Consistent lack of specimens below 17 mm,both in intertidal populations and catches,suggests that the smallest individuals arehidden in inaccessible microhabitats or areinconspicuous (e.g., mussel beds, tufts of algae), which is the case for at least two speciesin the study area: juveniles of Pachygrapsuscrassipes Randall are only found amongtubes of the sand castle polychaete, Phragmatopoma californica (Fewkes) (Escofet et al.1992); those of black abalone, beneath tuftsof Pelvetia compressa (c. Agardh), in BahiaSan Quintin (pers. obs.).The decrease in mean size of individuals inintertidal populations was consistent alongthe following sequence: Bufadora BS-Lobera-Isla Guadalupe-Chorera-Cantiles-PuntaMorro-Punta Papagayo. Mean size of individuals at two sites remained unexplainedunder the exploitation hypothesis: FraserPoint and Fraser Point NW, where sizes weresmaller than expected after 20 yr of protective management.For Fraser Point, we propose that the
Exploitation of Lottia gigantea-POMBO AND ESCOFET401major factor for size reduction is wave expo- gantea found in the Fraser Point midden desure, a physical stress that may limit max- note a later stage, where abalone were noimum size of mobile invertebrates either by longer abundant, and extraction of mussels,selective mortality of the larger individuals or limpets, and other species began to be moreby decreased access to food (Judge 1988). intense.The latter hypothesis is supported by theThe relative effect of natural processes canslower individual growth of L. gigantea doc- be masked where exploitation occurs. In thatumented at Fraser Point (Pombo 1990), al- sense, La Bufadora emerges as a natural exthough our data from La Bufadora suggest periment. Because of extreme inaccessibility,that larger individuals are selectively affected exploitation is absolutely blocked, and onlyby storms. Also, comparison between midden natural factors affect the population; had exand intertidal samples shows that a recovery ploitation occurred there, the effect of physihas occurred at Fraser Point because of pro- cal disturbance would not have been visible.tective management, but that recovery of size Before the 1988 storm, the site had specimenscannot surpass the limits imposed by the of L. gigantea as large as those reported 50 yrphysical stress. This can also be supported by ago (Ricketts and Calvin 1939). After thedata from Bufadora AS, where mean size storm (especially when the suspected outlierwas removed from the analysis), the averagewas close to that at Fraser Point.For Fraser Point NW we propose that size of individuals was significantly smaller,the presence of abalone might be a source demonstrating that physical disturbance isof stress that imposes physical barriers for also size selective (Judge 1988); its effects ongrazing. Although they do not compete with size, at least for the exceptional January 1988limpets for food, abalone may limit the avail- storm, which had the highest waves in 50 yrability of substrata. Currently, the intertidal (Seymour et al. 1989), are comparable withassemblage at Fraser Point NW is unusual; exploitation rating 1-2 in our scale.abalone were once common on CaliforniaPopulations of L. gigantea are subjectrocky shores (Ricketts and Calvin 1939) but to heavy exploitation along the Californiahave been heavily exploited at accessible coast, yet have persisted. An analysis of thesites. Our results suggest that the protective life history and natural history of this limpetmanagement at Fraser Point NW allowed the using the factors proposed by Catterall andrecovery of the original biological assem- Poiner (1987) suggests that two factors inblage for semiexposed rocky shores, includ- particular may be responsible for the speciesing abalone, and that this may have resulted persistence: the small size at maturity andin restriction of the L. gigantea population or the pelagic dispersal stage. The occurrence ofreduction in the growth rates of individuals.mature females and males at sizes close toData obtained at the middens can be those of the smallest individuals in catcheslinked with the general process of human suggests that maturity can be attained beforegathering in the intertidal (Reinman 1954, individuals are noticeable or valuable to harMcKusic and Warren 1959, Meighan 1959, vesters. The existence of a pelagic larval stageRozaire 1967, Orr 1968, King 1971, Swald- and the associated capability for dispersaling 1976, Glassow 1980, Tellez 1985). As- may not be important in the persistence ofsuming that a shift in food preferences of populations if the refuges for the species areaboriginal people occurred after local deple- few or far from the sites of intense harvesting.tion of populations of the preferred species(Simenstad et al. 1978), we propose that: (1)species assemblage and larger sizes of L. giACKNOWLEDGMENTSgantea found in the Fourney Cove middenare indicative of the end of an intense exCareful readings and comments by B. C.ploitation of abalone and early exploitation Farfan and M. G. Hammann, O. Sosa, S.of other species, including L. gigantea; and Bullok, and V. Ferreira (CICESE) are deeply(2) composition and smaller sizes of L. gi- appreciated. With drawing, tables, and word
PACIFIC SCIENCE, Volume 50, October 1996402processing, we were helped by J. M. Dominguez and J. C. Burguefio (CICESE). Suggestions from two anonymous reviewers are alsogratefully acknowledged.LITERATURE CITEDBEAUCHAMPS, K. A., and M. M. GOWING.1982. A quantitative assessment of humantrampling effects on a rocky intertidalcommunity. Mar. Environ. Res. 7: 279294.BLAKE, R. W. 1979. Exploitation ofa naturalpopulation of Arenicola marina (L.) fromthe north-east coast of England. J. App!.Eco!. 16: 663-670.BRANCH, G. M. 1975. Notes on the ecologyof Patella concolor and Cellana capensis,and the effects of human consumption onlimpet populations. Zoo!. Afr. 10(1): 7585.CASTILLA, J. c., and L. R DURAN. 1985.Human exclusion from the rocky intertidal zone of central Chile: The effects onConcholepas concholepas (Gastropoda).Oikos 45: 391-399.CATIERALL, C. P., and I. R POINER. 1987.The potential impact of human gatheringon shellfish populations, with reference tosome NE Australian intertidal flats. Oikos50: 114-122.CONNELL, J. H. 1978. Diversity in tropicalrain forest and coral reefs. Science(Washington, D.C.) 199: 1302-1310.DURAN, L. R, J. C. CASTILLA, and D. OLIVA.1987. Intensity of human predation onrocky shores at Las Cruces in centralChile. Environ. Conserv. 14(2): 143-149.ESCOFET, A., M. ROBLES, A. MONTIEL, andE. ARIAS. 1992. Bioecologia del cambio detamafio y habitat en organismos bentonicos: Resultados experimentales en el cangrejo intermareal Pachygrapsus crassipes.Pages 185-189 in S. A. Guzman del Proo,ed. Memorias del Taller Mexico-Australiasobre reclutamiento de recursos marinosbentonicos. Sepesca-IPN, Mexico.GHAZANSHAHI, J., T. D. HUCHEL, and J. S.DEVINNEY. 1983. Alteration of southernCalifornia rocky shores ecosystems bypublic recreational use. J. Environ. Manage. 16: 379-394.GLASSOW, M. A. 1980. Recent developmentsin the archaeology of the Channel Islands.Pages 77-79 in D. M. Power, ed. TheCalifornia Islands: Proceedings of a MultiDisciplinary Symposium. Santa BarbaraMuseum of Natural History, Santa Barbara, California.HOCKEY, P. A., and A. L. BOSMAN. 1986.Man as an intertidal predator in Transkei:Disturbance, community convergence andmanagement of a natural food resource.Oikos 46: 3-14.JUDGE, M. L. 1988. The effects of increasingdrag on Lottia gigantea (Sowerby 1834)foraging behaviour. Funct. Eco!. 2(3):363-369.KING, C. 1971. Chumash inter-village economic exchange. Indian Hist. 4: 31-43.LINDBERG, D. R., and W. G. WRIGHT. 1985.Patterns of sex change of the protandricpatellacean limpet Lottia gigantea (Mollusca: Gastropoda). Veliger 27: 261-265.McKuSIC, M. B., and C. N. WARREN. 1959.Introduction to San Clemente Island archaeology. University of California LosAngeles Archaeo
the sublitoral, and ghost shrimp and clams from soft bottoms. The owl limpet, Lottia gigantea, is the largest limpet in North America. It lives on exposed and semiexposed rocks and cliffs in high middle and upper littoral zones from northern Washington to central Baja Cal ifornia (Ricketts and Calvin 1939, Stimson 1973, Lindberg and Wright .
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̶The leading indicator of employee engagement is based on the quality of the relationship between employee and supervisor Empower your managers! ̶Help them understand the impact on the organization ̶Share important changes, plan options, tasks, and deadlines ̶Provide key messages and talking points ̶Prepare them to answer employee questions
Chính Văn.- Còn đức Thế tôn thì tuệ giác cực kỳ trong sạch 8: hiện hành bất nhị 9, đạt đến vô tướng 10, đứng vào chỗ đứng của các đức Thế tôn 11, thể hiện tính bình đẳng của các Ngài, đến chỗ không còn chướng ngại 12, giáo pháp không thể khuynh đảo, tâm thức không bị cản trở, cái được
Le genou de Lucy. Odile Jacob. 1999. Coppens Y. Pré-textes. L’homme préhistorique en morceaux. Eds Odile Jacob. 2011. Costentin J., Delaveau P. Café, thé, chocolat, les bons effets sur le cerveau et pour le corps. Editions Odile Jacob. 2010. Crawford M., Marsh D. The driving force : food in human evolution and the future.
A-Level Business Studies Question and Answers 2020/2021 All copyright and publishing rights are owned by S-cool. First created in 2000 and updated in 2013, 2015 & 2020. 2 Contents People in the Workplace (Questions) . 3 People in the Workplace (Answers) . 4 Budgeting, Costing and Investment (Questions). 6 Budgeting, Costing and Investment (Answers) . 7 Business Objectives and .
