Pacific Science (1996), vol. 50, no. 4: 393-403 © 1996 by University of Hawai'i Press. All rights reserved

Effect of Exploitation on the gigantea: A Field Study in Baja California (Mexico) and California (U.S.A.)!

2 2 OSCAR ALBERTO POMB0 ,3 AND ANAMARiA ESCOFET

ABSTRACT: Specimens of (Sowerby) from intertidal popu­ lations, artisanal catches, and shell middens were obtained from 1985 to 1988 at 11 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 in­ tertidal exploitation associated with visiting patterns of gatherers, accessibility, and site topography. Maximum and mean size of intertidal populations and artisanal catches decreased along a gradient of increasing exploitation. Mean size was significantly different between catches and the corresponding intertidal population. Mean size of specimens in older middens was significantly larger than in a recent midden. Measurements at the most inaccessible site inmediately after the exceptional extratropical winter storm that swept the California coast on 17-18 January 1988 showed that the storm had removed larger specimens approximating exploitation measuring 1-2 on our scale. Intertidal gathering occurs or has occurred unless it is physically prevented by topography, distance, or some kind of restriction of access. Ecological implications of exploitation were explored utilizing the conceptual model proposed by Catterall and Poiner for assessing potential impact of traditional shell gathering on intertidal mol­ luscs. The model suggests that size at maturity of this and its pelagic larval stage may prevent depletion by harvesting.

MOST INTERTIDAL HABITATS worldwide are issue of substantial interest in contemporary exploited by artisanal harvesters using simple ecology and conservation biology (Catterall tools. The production, which is seldom in­ and Poiner 1987). cluded in official fisheries statistics, is either Studies of the role of humans as predators consumed by individual gatherers or family in the intertidal has focused largely on pop­ groups or sold in small-scale trade (Duran et ulation density and size structure of prey at al. 1987). Artisanal harvesting includes a va­ harvested and nonharvested sites; some stud­ riety of organisms such as lugworms, , ies have analyzed the implications of har­ and gastropods. The effect of human exploi­ vesting in terms of biomass and gonad out­ tation relative to natural processes in popu­ puts (Branch 1975, Blake 1979, McLachlan lations ofharvested marine invertebrates is an and Lombard 1981). The effects of human on intertidal populations have also been analyzed in terms of community ecol­ 1 This article is part of O.A.P.'s M.S. thesis submitted ogy; the concepts of top carnivore and key­ to CICESE. The work was partially supported by Con­ stone species (Paine 1966) as well as the in­ sejo Nacional de Ciencia y Tecnologia, Mexico, through termediate disturbance hypothesis (Connell grant PCEBNA-021264 to A.E. Manuscript accepted 22 January 1996. 1978) have been employed to explain pro­ 2 Centro de Investigaci6n Cientifica y Educaci6n Su­ found changes in species richness, commu­ perior de Ensenada, Apartado Postal 2732, 22800 Ense­ nity structure, and size structure of compo­ nada, B.c., Mexico. International mailing address: P.O. nent species at sites with and without human Box 434844, San Diego, California 92143-4844, U.S.A. predation (Moreno et al. 1984, Hockey and 3 Current address: Department of Environmental Analysis and Design, School of Social Ecology, Uni­ Bosman 1986). versity of California, Irvine, California 92715. On Baja California shores, several species 393 394 PACIFIC SCIENCE, Volume 50, October 1996

of invertebrates are exposed to artisanal riginal shell middens were collected during exploitation (Pombo 1990). Most species are field studies conducted from 1985 to 1988 at removed for direct human consumption: 11 sites along the Pacific coasts of Baja Cal­ (Mytilus californianus Conrad); ifornia (Mexico) and California (U.S.A.) (mainly Pismo , Tivela stultorum Mawe); (Figure 1). A rank scale of 0-4 was used to (Haliotis spp.); keyhole limpet describe the degree of intertidal exploitation ( [Sowerby]); (As­ for each site. Criteria used to rate the inter­ traea undosa [Wood]); owl limpet (Lottia gi­ tidal gathering were as follows: (1) gatherers' gantea [Sowerby]); and gooseneck visiting pattern to the intertidal during the 3­ or leaf barnacle (Pollicipes polymerus Sower­ yr period in which the study was conducted by). Abalone are also collected, as juve­ and in the past, according to reports of local niles, for ornamental purposes. The ghost dwellers; (2) several features of the sites that shrimp (Callianassa californiensis Dana) is could explain degrees of exploitation (to­ used as fish bait. (Stenoplax spp.), pography, distance from mainland or major keyhole limpet, black abalone (Haliotis cra­ human settlements, habits of consumption of cherodii Leach), snail, and owl limpet are intertidal species by local people, existence used as bait in spiny lobster traps. Most spe­ and length of protective management pro­ cies come from the rocky intertidal; snail and grams). all abalone except black are extracted from Individual elements of the scaled intertidal the sublitoral, and ghost shrimp and clams gathering rating system of 0-4 were assigned from soft bottoms. as follows: The owl limpet, Lottia gigantea, is the Rating 0: Sites where intertidal gathering largest limpet in North America. It lives on never occurred because of steep topography exposed and semiexposed rocks and cliffs in that physically prevents access (La Bufadora) high middle and upper littoral zones from or where it was certifiably absent for ap­ northern Washington to central Baja Cal­ proximately the last 30 yr because of pro­ ifornia (Ricketts and Calvin 1939, Stimson tective management (all sites at Santa Cruz 1973, Lindberg and Wright 1985, Wright Island, Channel Islands). 1989). Zedler (1976, 1978) found lower abun­ Rating 1: (1) Lobera, where the local oys­ dance of larger individuals of L. gigantea in ter farm cooperative has banned intertidal areas of greater human use than at the Cab­ gathering since 1984 to promote abalone re­ rillo National Monument, Point Loma, Cal­ covery; only two abalone harvesting seasons ifornia, where collecting is restricted. Gha­ have been allowed since then; (2) Isla Gua­ zanshahi et al. (1983) included L. gigantea in dalupe, where gathering is rare because the the list of species likely to be affected by site is isolated from the mainland and there public use. are no fishing settlements nearby. A small Our data relate different degrees of inter­ number of military personnel at an Ol,ltpost tidal exploitation to the sizes of individuals in collect abalone during very low tides that populations of L. gigantea in 11 localities coincide with official holidays. along the Pacific coasts of Baja California Rating 2: (1) Chorera, a site protected by (Mexico) and California (U.S.A.). We also the local farm cooperative since 1985. investigated the effect of the history of ex­ Only five resident family groups of fishermen ploitation at a site, the effect of human ex­ are allowed in the area. However, their visits ploitation relative to physical disturbance by are frequent, because of feeding habits; gath­ strong storm-generated waves, and the eco­ ering of several species, mostly abalone, was logical implications of exploitation. confirmed in the field; (2) El Campito, where access is free but people are seldom observed (its vicinity to Chorera, a protected area, may MATERIALS AND METHODS deter visitors). Specimens of Lottia gigantea from inter­ Rating 3: Cantiles, a site open to the pub­ tidal populations, artisanal catches, and abo- lic but relatively inaccessible (5 km from a N

VENTURA

LOS ANGELES

~ Q U.S. A.

ENSENADA

1 [sla Guadalupe ([G) 2 EI Campito (CAM) l\.... 1 3 Chorera (CHaR) \J 4 Lobera (LOB) 5 Cantiles (CAN) 6 Punta Papagayo (PP) 7 Bufadora (BUF) 8 Punta Morro (PM) - Channel Islands: Santa Cruz Island 9 Fraser Point ( FP) 10 Fraser Point NW (FPNW) 11 Fourney Cove (FC)

FIGURE 1. The study sites. 396 PACIFIC SCIENCE, Volume 50, October 1996 major town; unpaved roads); gatherers arrive by gatherers was compared with the effect irregularly, usually on major holidays. caused by storm waves. A second set of in­ Rating 4: The highest degree of exploita­ direct measurements was carried out at La tion was assigned to Punta Papagayo and Bufadora immediately after the exceptional Punta Morro, where numbers of gatherers extratropical winter storm that swept the are observed all year round, almost daily. California coast on 17-18 January 1988. In Both sites have free access, are located I Ian the results, Bufadora BS (BUF-BS) and Bu­ from a major city (Ensenada, B. C., Mexico), fadora AS (BUF-AS) respectively indicate and have paved roads. data obtained before and after the January In all the intertidal samples, except those 1988 storm. from La Bufadora, all individuals of L. gi­ To compare shell length, a parametric gantea detected along a randomly chosen analysis of variance (ANOYA) of unbal­ strip 2 m wide across the intertidal were col­ anced design was applied for more than two lected, and shell length (longest axis to the samples. A Student-Newman-Keul's multi­ nearest mm) was measured in the laboratory. ple range at IX = 0.05 (Sokal and Rohlf Specimens were frozen to preserve them for 1979) was used for post-hoc comparisons of later determination of growth rate, sex, and population means in the ANOYA model maturity, as part of more extensive studies when significant among-population differ­ (Pombo 1990). ences (P < 0.05) were detected. For compar­ At La Bufadora, inaccessibility of the wall isons of two samples outside the ANOYA occupied by L. gigantea forced us to make model, a two-tailed t-test at IX = 0.05 was indirect measurements. One person dangled a performed. ruler on the wall with the aid of a sport fish­ Ecological implications of exploitation ing rod while another person took pictures were explored through the conceptual model from the opposite side. The entire wall was proposed by Catterall and Poiner (1987) for covered in bands one film frame high. A 200­ assessing the potential impact of traditional mm telephoto lens and ASA 400 slide film shell gathering on intertidal molluscs. The were employed. The length of the specimens model uses life history and habitat infor­ was calculated by converting the dimensions mation to predict the extent to which a given in projected images. The error of the method intertidal population would be either was calculated by taking pictures of the same susceptible to depletion or resilient. ruler placed by an array of 48 limpet shells of known length, at five different distances equivalent to those in the field. The mea­ RESULTS surement error, using 95% confidence inter­ val was 0.48 ± 0.89 mm. Size Structure at Field Sampling Sites The number and size of limpets collected by present-day artisanal harvesters was re­ In the intertidal populations the size of in­ corded and the catches were returned to the dividuals ranged from 102 to 17 mm (Table I). harvesters. Mean size was significantly different among To explore intertidal exploitation in the sites (F = 92.647; P < 0.05). The multiple past, specimens of L. gigantea were measured range test yielded five groups: (1) values at two Indian shell middens 3 km apart on higher than 50 mm (Bufadora BS); (2) values Santa Cruz Island (California, U.S.A.) where between 45 and 50 mm (Lobera, Fraser the stratigraphic sequence was finely dated Point, and Isla Guadalupe); (3) values be­ by Glassow (1980): Fraser Point (superficial, tween 40 and 45 mm (Chorera and Fraser mussel-dominated strata dated 280 ± 150 yr Point NW); (4) values between 30 and 40 mm B.P.); Fourney Cove (4 m deep; the last ab­ (Cantiles); (5) values lower than 30 mm alone-dominated strata, dated 2310 ± 150 yr (Punta Papagayo and Punta Morro). The B.P.). size of mature individuals ranged from 21 to The magnitude of the effect of harvest 73 mm. The mean size ofmature males varied Exploitation of Lottia gigantea-POMBO AND ESCOFET 397

TABLE I SIZE RANGE (SR) (mm) AND MEAN SIZE (x) (mm) OF Lottia gigantea IN SAMPLES FROM INTERTIDAL, CATCHES, AND MIDDENS AT II SITES WITH DIFFERENT DEGREES OF EXPLOITATION (DE)

SAMPLE FROM

SITE DE INTERTIDAL CATCHES MIDDENS

BUF-BS o SR = 102-30 x = 55.0 ± 13.7 n = 125 BUF-AS, all data o SR = 107-32 x = 50.9 ± 14.6 n = 28 BUF-AS, outlier removed o SR = 72-32 x = 48.8 ± 9.8 n = 27 Channel Islands: o SR = 72-31 SR = 62-26 Fraser Point x = 49.0 ± 9.4 x = 39.9 ± 6.9 n = 61 n = 93 Fraser Point NW o SR = 67-28 x = 42.5 ± 8.7 n = 57 Fourney Cove o SR = 68-26 x = 50.3 ± 7.2 n = 37 Lobera SR = 75-29 x = 49.3 ± 7.6 n = 97 Isla Guadalupe SR = 78-17 SR = 80-42 x = 48.7 ± 13.9 x = 56.7 ± 8.7 n = 131 n = 66 Chorera 2 SR = 57-28 x = 43.9 ±6.1 n = 114 EI Campito 2 SR = 55-46 x = 50.7 ±4.3 n = 90 Cantiles 3 SR = 58-20 x = 37.8 ± 8.3 n = 60 Punta Papagayo 4 SR = 44-20 SR = 33-23 x=29.7±6.2 x = 27.8 ± 5.2 n = 68 n = 119 Punta Morro 4 SR = 49-18 x = 28.4 ± 6.8 n = 103

between 47.0±8.3 and 31.4±6.5 nun; mean 77.6% mortality at La Bufadora (125 organ­ size of mature females varied between 52.2 ± isms detected in 1987, 28 survivors after the 6.5 and 31.2 ± 6.4 mm. Sex ratio varied from storm). Mean size before and after the storm 60% males and 40% females with none or few was not significantly different when all data undetermined individuals at Chorera and were considered (tcalc = 1.355, P > 0.05) but Lobera to 26% males and 38% females with was significantly different when a 107-mm 64% undetermined individuals at Punta specimen suspected to be a methodological Morro. outlier was removed from data (tcalc = 2.22, The January 1988 winter storm caused P << 0.05). Size range before and after the 398 PACIFIC SCIENCE, Volume 50, October 1996 stonn also appeared similar considering all maximum size were similar in both middens. data after the stonn but was quite reduced Mean size ofthe specimens found in the older when the suspected outlier was removed. strata (Fourney Cove) was significantly larger In catches, size of individuals ranged from (tcalc = 7.50, P < 0.05) than in the more re­ 80 to 23 mm. The average size of limpets cent deposit (Fraser Point). At Fraser Point, in catches from each site was significantly mean size of individuals in the midden was different from that of limpets in the cor­ significantly smaller than that of the current responding intertidal populations (Isla Gua­ intertidal population (tcalc = -2.709, P < 0.05). dalupe, tcalc = 4.947, P < 0.05; Punta Papa­ gayo, tcalc 2.313, P < 0.05). The smallest = Effect ofHarvesting individuals in catches were always larger than the smallest individuals in the intertidal. Mean size, maximum size, and size range In the shell middens, the size ofindividuals of intertidal populations decreased along the ranged from 68 to 26 mm. Size range and exploitation gradient (Figure 2). Mean size in

110

100

90

~ 80

:::x::: I- 70 (!) :z lLJ -l 60 -l -l BUF - BS lLJ BUF - AS :::x::: 50 FP (J) BUF-AS* :z

30

20

10 0 j 2 3 4 DEGREE OF EXPLOITATION

FIGURE 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 results were obtained at BUF-AS after the removal of the suspected outlier from data. At exploitation rating 0, limits are set according to BUF-AS values. Exploitation of Lottia gigantea-POMBO AND ESCOFET 399 seven of the nine intertidal populations (Bu­ Fourney Cove and more intense at Fraser fadom BS, Lobera, Isla Guadalupe, Chorera, Point (ratings of 1-2 and 3-4 in our scale, Cantiles, Punta Papagayo, Punta Morro) de­ respectively) and that the storm had removed creased along a gradient of increased ex­ the larger specimens to a degree similar to an ploitation (R2 = 0.395, n = 589). At Fraser exploitation rating of 1-2 in our scale. Point and Fraser Point NW, mean size was smaller than expected at sites without ex­ Ecological Implications ofExploitation ploitation, close to sizes found at sites with degree of exploitation ratings of 2-3 and 1­ The analysis of life history and habitat in­ 2, respectively. Mean size in artisanal catches formation in the model proposed by Catterall also decreased along the exploitation gra­ and Poiner (1987) singled out two attributes dient (Isla Guadalupe-EI Campito-Punta Pa­ that presumably make it unlikely that local pagayo). Difference between mean size of populations of L. gigantea will be driven to catches and those of the corresponding inter­ extinction: their small size at maturity, and tidal populations was maximal (27 mm) at existence of a pelagic larval stage (Table 2). Isla Guadalupe, with a low amount of ex­ Other biological characteristics proposed by ploitation, and minimal (3.0 mm) at Punta the model (intertidal burying, adjacent sub­ Papagayo, with the highest exploitation. tidal populations, benthic mobility) do not Plotting of data from middens and Bufa­ apply to L. gigantea, which only occurs on dora AS within the former scheme suggested intertidal hard substrate and has limited mo­ that exploitation in the past was low at bility in the adult stage.

TABLE 2

BIOLOGICAL ATfRIBUTES CONSIDERED TO BE THE MORE IMPORTANT DETERMINANTS OF THE CONSEQUENCES OF TRADITIONAL GATHERING OF SHELLFISH POPULATIONS (CATfERALL AND POINER 1987) AND ITS ILLUSTRATION IN L. gigantea

ATfRIBUTE MODEL STATEMENT RESULTS

Size at maturity If size at maturity is less than size detectable by Mature females (25.8 mm) and males (25.0 gatherers, a population will always contain mm), close to the size of the smallest reproducing individuals. individuals in catches (23 mm) were registered in the study area. Intertidal burying If individuals large enough to be detectable L. gigantea only occurs on hard substrate have the opportunity to bury themselves (Stimson 1973). within soft substrate, a refuge from preda­ tion or gathering can be attained. Adjacent subtidal If a local intertidal population is depleted, L. gigantea is strictly intertidal (Stimson populations replenishment may be possible through 1973). recruitment of individuals from adjacent subtidal areas. Benthic mobility In species with partially subtidal distribution, L. gigantea is intertidal and has limited if benthic stages are mobile, reproductive mobility as adult (Stimson 1973). individuals may migrate into the exploited intertidal areas, providing an opportunity for local reproduction. Pelagic larvae Irrespective of benthic migration of adults, if L. gigantea has a planctonic larval stage. a species has a pelagic larval stage lasting Duration of planctonic larval stage is long enough to permit settlement of larvae unknown (Stimson 1973). spawned by distant, unexploited popula­ tions, recruitment into exploited areas would continue as long as enough such populations remained. 400 PACIFIC SCIENCE, Volume 50, October 1996

DISCUSSION size in the catches and in the intertidal pop­ ulation: as exploitation increases, both values Since the publication of the pioneer paper became closer to each other (27-mm differ­ by Branch (1975), there have been numerous ence at Isla Guadalupe; 3-mm difference at demonstrations of the effect of exploitation Punta Papagayo). on populations of intertidal invertebrates These results convey that the decrease in (Zedler 1976, 1978, Blake 1979, McLacWan mean size, as a descriptor of the effect of ex­ and Lombard 1981, Moreno et al. 1984, 1986, ploitation, is reinforced by the decrease in Castilla and Dunin 1985, Hockey and Bos­ maximum size and size range of intertidal man 1986, Oliva and Castilla 1986). Most populations (Branch 1975). Our results sug­ comparisons were made between sites with gest that at sites with heavy exploitation, and without exploitation, and the effect of the mean size of intertidal populations and the degree of exploitation has only been ex­ catches may not demonstrate satisfactorily plored by Branch (1975) and Moreno et al. the selection of larger sizes by gatherers. In (1984). our results, the smallest individuals in the Our procedure to rank levels of human catches were always larger than the smallest activity in the intertidal is close to the proce­ individuals in the intertidal, suggesting that dure of Moreno et al. (1984) in considering harvesters are size selective and preferentially proximity and size of settlements or fishing take larger limpets even at sites where heavy communities and existence and length of exploitation has reduced the population size protection as reasonable predictors of inten­ range. This is shown at Punta Papagayo sity of human activity. Also, it is similar to (highest degree of exploitation) where the the procedures of Beauchamps and Gowing mean size of the catch was smaller than in (1982), Ghazanshahi et al. (1983), and Un­ the intertidal population, but selection of the derwood and Kennelly (1990) in considering larger individuals can be shown through dif­ counts of people as a measure of public ac­ ference between size range in the catches and cessibility. in the intertidal population. Our results, showing a reduction in popu­ Consistent lack ofspecimens below 17 mm, lation size range and a decrease of the mean both in intertidal populations and catches, size of specimens of L. gigantea along five suggests that the smallest individuals are different ratings of amount of intertidal ex­ hidden in inaccessible microhabitats or are ploitation, are similar to the results of several inconspicuous (e.g., mussel beds, tufts of al­ other studies. Moreno et al. (1984) reported a gae), which is the case for at least two species similar pattern in the exploitation of Fissur­ in the study area: juveniles of Pachygrapsus ella picta (Gmelin) at four sites with different crassipes Randall are only found among levels of human activity, and Oliva and Cas­ tubes of the sand castle polychaete, Phrag­ tilla (1986) reported reduced size of individ­ matopoma californica (Fewkes) (Escofet et al. uals and reduced abundance of 1992); those of black abalone, beneath tufts crassa Lamarck and F limbata Sowerby at of Pelvetia compressa (c. Agardh), in Bahia harvested versus nonharvested sites. Branch San Quintin (pers. obs.). (1975) reported a reduction in average size The decrease in mean size ofindividuals in and abundance of concolor Krauss at intertidal populations was consistent along 13 individual sites over a 5-yr period of in­ the following sequence: Bufadora BS-Lo­ creasing exploitation. bera-Isla Guadalupe-Chorera-Cantiles-Punta Our results also show that mean size in Morro-Punta Papagayo. Mean size of in­ artisanal catches decreased along the ex­ dividuals at two sites remained unexplained ploitation gradient and that the difference under the exploitation hypothesis: Fraser between mean size in the catches and in the Point and Fraser Point NW, where sizes were intertidal population becomes smaller as ex­ smaller than expected after 20 yr of pro­ ploitation increases. The effect of exploita­ tective management. tion was also evident comparing the smallest For Fraser Point, we propose that the Exploitation of Lottia gigantea-POMBO AND ESCOFET 401 major factor for size reduction is wave expo­ gantea found in the Fraser Point midden de­ sure, a physical stress that may limit max­ note a later stage, where abalone were no imum size of mobile invertebrates either by longer abundant, and extraction of , selective mortality ofthe larger individuals or limpets, and other species began to be more by decreased access to food (Judge 1988). intense. The latter hypothesis is supported by the The relative effect of natural processes can slower individual growth of L. gigantea doc­ be masked where exploitation occurs. In that umented at Fraser Point (Pombo 1990), al­ sense, La Bufadora emerges as a natural ex­ though our data from La Bufadora suggest periment. Because of extreme inaccessibility, that larger individuals are selectively affected exploitation is absolutely blocked, and only by storms. Also, comparison between midden natural factors affect the population; had ex­ and intertidal samples shows that a recovery ploitation occurred there, the effect of physi­ has 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 specimens cannot surpass the limits imposed by the of L. gigantea as large as those reported 50 yr physical stress. This can also be supported by ago (Ricketts and Calvin 1939). After the data from Bufadora AS, where mean size storm (especially when the suspected outlier was close to that at Fraser Point. was removed from the analysis), the average 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 is of stress that imposes physical barriers for also size selective (Judge 1988); its effects on grazing. Although they do not compete with size, at least for the exceptional January 1988 limpets for food, abalone may limit the avail­ storm, which had the highest waves in 50 yr ability of substrata. Currently, the intertidal (Seymour et al. 1989), are comparable with assemblage at Fraser Point NW is unusual; exploitation rating 1-2 in our scale. abalone were once common on California Populations of L. gigantea are subject rocky shores (Ricketts and Calvin 1939) but to heavy exploitation along the California have been heavily exploited at accessible coast, yet have persisted. An analysis of the sites. Our results suggest that the protective life history and natural history of this limpet management at Fraser Point NW allowed the using the factors proposed by Catterall and recovery of the original biological assem­ Poiner (1987) suggests that two factors in blage for semiexposed rocky shores, includ­ particular may be responsible for the species ing abalone, and that this may have resulted persistence: the small size at maturity and in restriction of the L. gigantea population or the pelagic dispersal stage. The occurrence of reduction in the growth rates of individuals. mature females and males at sizes close to Data obtained at the middens can be those of the smallest individuals in catches linked with the general process of human suggests that maturity can be attained before gathering in the intertidal (Reinman 1954, individuals are noticeable or valuable to har­ McKusic and Warren 1959, Meighan 1959, vesters. The existence ofa pelagic larval stage Rozaire 1967, Orr 1968, King 1971, Swald­ and the associated capability for dispersal ing 1976, Glassow 1980, Tellez 1985). As­ may not be important in the persistence of suming that a shift in food preferences of populations if the refuges for the species are aboriginal people occurred after local deple­ few or far from the sites ofintense harvesting. tion of populations of the preferred species (Simenstad et al. 1978), we propose that: (1) species assemblage and larger sizes of L. gi­ ACKNOWLEDGMENTS gantea found in the Fourney Cove midden are indicative of the end of an intense ex­ Careful 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 402 PACIFIC SCIENCE, Volume 50, October 1996 processing, we were helped by J. M. Domin­ public recreational use. J. Environ. Man­ guez and J. C. Burguefio (CICESE). Sugges­ age. 16: 379-394. tions from two anonymous reviewers are also GLASSOW, M. A. 1980. Recent developments gratefully acknowledged. in the archaeology of the Channel Islands. Pages 77-79 in D. M. Power, ed. The California Islands: Proceedings of a Multi Disciplinary Symposium. Santa Barbara LITERATURE CITED Museum of Natural History, Santa Bar­ BEAUCHAMPS, K. A., and M. M. GOWING. bara, California. 1982. A quantitative assessment of human HOCKEY, P. A., and A. L. BOSMAN. 1986. trampling effects on a rocky intertidal Man as an intertidal predator in Transkei: community. Mar. Environ. Res. 7: 279­ Disturbance, community convergence and 294. management of a natural food resource. BLAKE, R. W. 1979. Exploitation ofa natural Oikos 46: 3-14. population of Arenicola marina (L.) from JUDGE, M. L. 1988. The effects of increasing the north-east coast of England. J. App!. drag on Lottia gigantea (Sowerby 1834) Eco!. 16: 663-670. foraging behaviour. Funct. Eco!. 2(3): BRANCH, G. M. 1975. 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