Manning Et Al. Case Study of Carrying Capacity in Alcatraz

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Journal of Sustainable Tourism

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Research to Estimate and Manage Carrying Capacity of a Tourist

Attraction A Study of Alcatraz Island

Robert Manning; Benjamin Wang; William Valliere; Steven Lawson; Peter Newman

To cite this ArticleManning, Robert, Wang, Benjamin, Valliere, William, Lawson, Steven and Newman, Peter(2002)'Research to Estimate and Manage Carrying Capacity of a Tourist Attraction: A Study of Alcatraz Island', Journal ofSustainable Tourism, 10: 5, 388 404

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Research to Estimate and ManageCarrying Capacity of a Tourist Attraction:A Study of Alcatraz Island

Robert Manning, Benjamin Wang, William Valliere, Steven Lawson, PeterNewmanRecreation Management Programme, School of Natural Resources, 356Aiken Center, University of Vermont, (802) 6563096, USA

Carrying capacity has been a long-standing issue in management of parks, outdoor

recreationand tourism. Contemporary carrying capacity frameworks rely on formula-tion of indicators andstandardsofquality todefineandmanage carryingcapacity.Thispaper describes a programme of research to support estimation and management ofcarrying capacity of Alcatraz Island, an historic site within Golden Gate NationalRecreation Area, California, USA, and a heavily visited tourist attraction. Researchincluded: (1) a survey of visitors to AlcatrazIsland to identify indicators andstandardsof quality for the visitor experience; and (2) development of a computer simulationmodel of visitor use to estimatemaximum daily use levelswithout violatingstandardsof quality. Study findings are used to estimate a range of carrying capacities for theprison cellhouse and for the island as a whole.

Carrying Capacity

The question of how much public use can be accommodated in a park orrelated tourist attraction is often framed in terms of carrying capacity. Indeed,much has been written, in both the scientific literature and popular press, aboutthecarrying capacity of parks and related touristattractions(e.g. Manning, 2001;Mitchell, 1994; Stankey & Manning, 1986; Wilkinson, 1995). The underlyingconcept of carrying capacity has a rich history in the natural resource profes-

sions. In particular, it has been applied inwildlife andrange management whereit refers to the number of animals that can be maintained in a given habitat(Dasmann,1964).Carryingcapacity has obvious parallels and intuitiveappeal inthe field of park and tourism management. However, the first rigorous applica-tions of carrying capacity to management of parks and related areas did notoccur until the 1960s.

These initial scientific applications suggested that the concept was morecomplex in this new management context. At first, as might be expected, thefocus was placed on the relationship between visitor use and environmental

conditions. The working hypothesis was that increasing numbers of visitorscause greater environmental impact as measured by soil compaction, destruc-tion of vegetation and related variables. It soon became apparent, however, thatthere was another critical dimension of carrying capacity dealing with socialaspects of the visitor experience. Wagar (1964), for example, in his early and

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important monograph on the application of carrying capacity to outdoor recre-ation, reported that his study

was initiatedwith the view that carrying capacityof recreation landscouldbe determined primarily in terms of ecology and the deterioration of areas.

However, it soon became obvious that the resource-oriented point of viewmust be augmented by consideration of human values.

Wagars point was that as more people visit a parkorrelated area, not only canthe environmental resources of the area be affected, but the quality of the visitorexperience as well. Again, the working hypothesis was that increasing numbersof visitors cause greater social impacts as measured by crowding and relatedvariables. Thus, as applied to parks and related tourist attractions, carryingcapacity has two components: environmental and social.

The early work on carrying capacity has since blossomed into an extendedliterature on the impacts of visitoruse and their application to carrying capacity(e.g. Graefeet al., 1984; Hammitt & Cole, 1998; Kusset al., 1990; Lime & Stankey,1971;Manning, 1985,1999; Shelby & Heberlein, 1986; Stankey & Lime, 1973). Butdespite this growing scientific literature, efforts to determine and apply carryingcapacity have sometimes failed. The principal difficulty lies in determining howmuch impact, such as crowding, is too much. Theoretical development, backedup by empirical research, generally confirms that increasing use levels andencounters among visitors leads to increased environmental and social impacts.

But how much impact shouldbe allowed? This basic question is often referred toas the limits of acceptable change (Frissell & Stankey, 1972; Lime, 1970). Givensubstantial demand for public use of parks and related areas, some decline orchange in the quality of natural/cultural resources and the visitor experienceappears inevitable.But how much decline or change is acceptable or appropriatebefore management intervention is warranted?

Carrying Capacity of a Tourist Attraction 389

Visitor Use

X1 X2

Y2

Y1Crowding

A

B

Figure 1Hypothetical relationships between visitor use and crowding

21

1

2




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This issue is illustrated graphically in Figure 1. This figure addresses thesocialimpact of crowding, and two hypothetical relationships between visitoruse andcrowding are shown. It is clear from both that visitor use and crowding arerelated: increasing numbers of visits cause visitors to feel increasingly crowded.However, it is not clear at what point carrying capacity has been reached. The

hypothetical relationships in Figure 1 suggest that some crowding is inevitable,giveneven relatively low levels ofvisitoruse.Thus, some level of crowding mustbe tolerated if parks and related tourist attractions are to remain open for publicuse. For the relationship defined by line A, X1and X2represent levels of visitoruse that result in differing levels of crowding as defined by points Y 1and Y2,respectively. But which of these points Y1or Y2, or some other point along thisaxis represents the maximum amount of crowding that is acceptable? Ulti-mately, this is a value judgement. Again, the principal difficulty in carryingcapacity determination lies in deciding how much crowding (or of some otherimpact) is acceptable. Empirical relationships such as those in Figure 1 can behelpful in making informed decisions about carrying capacity, but they must besupplemented withother informationand,ultimately,management judgements.

To emphasise and further clarify this issue, some writers have suggested distin-guishing between descriptive and evaluative (or prescriptive) components ofcarrying capacity (Shelby & Heberlein, 1984, 1986). The descriptive componentof carrying capacity focuses on factual, objective data such as the types of rela-tionships in Figure 1. For example, what is the relationship between the number

of visitors entering a park and the number of encounters that occur amonggroupsofvisitors?Or what is therelationship between the level ofvisitor use andvisitor perceptions of crowding? The evaluative or prescriptive component ofcarrying capacity determinationconcerns the seemingly moresubjective issueofhow much impact or change in resource conditions and the quality of the visitorexperience is acceptable. For example, how many contacts between visitorgroups are appropriate? What level of perceived crowding should be allowedbefore management intervention is needed?

Recent experience with carrying capacity suggests that answers to the above

questions can be found through formulation of management objectives anddevelopment of associated indicators and standards of quality (Graefeet al.,1990; Manning, 1997, 1998; Manninget al., 1998; National Park Service, 1997;Stankey et al., 1985). This approach to carrying capacity focuses principalemphasis on defining the degree of resource protection and the type of visitorexperience to beprovided andmaintained,monitoringconditionsover time, andadopting management practices to ensure that acceptable conditions have beenmaintained.

Management objectives arebroad, narrative statements that define the degree of

resource protection and the type of visitor experience to be provided. They arebased largely on review of the purpose and significance of the area under consid-eration. Formulation of management objectives may involve review of legal,policy and planning documents; consideration by an interdisciplinary planningand management team; historic precedent; local, regional, national or interna-tional context of the park or related tourist attraction; and public involvement.

Indicators of quality are measurable, manageable variables that reflect theessence or meaning of management objects; they are quantifiable proxies or

390 Journal of Sustainable Tourism




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measures of management objectives. Indicators of quality may include elementsof both the biophysical and social environments.Standards of qualitydefine theminimum acceptable condition of indicator variables.

An example of management objectives, indicators and standards may behelpful. Review of the US Wilderness Act of 1964 suggests that areas of the

National Wilderness Preservation System are to be managed to provide oppor-tunities for visitor solitude. Thus, providing opportunities for solitude is anappropriate management objective for mostwilderness areas.Moreover, researchon wilderness use suggests that the number of visitors encountered along trailsand at campsites is important to wilderness visitors in defining solitude. Thus,trail and camp encounters may be good indicators of quality and help to makethegeneral management objective of solitudemoreoperational.Further researchsuggests that wilderness visitors may have normative standards about howmany trail and camp encounters are acceptable before the quality of the visitorexperience declines to an unacceptable degree (Heberleinet al., 1986; Lewis et al.,1996; Manninget al., 1996a, 1996b, 1999a; Roggenbuck et al., 1991; Shelby &Vaske, 1991; Vaskeet al., 1986; Whittaker & Shelby, 1988). Such data may helpdefine standards of quality.

By defining indicators and standards of quality, carrying capacity can bedetermined and managed through an associated programme of monitoringandmanagement. Indicators of quality can be monitored and management actionstaken to ensure that standards of quality are maintained. If monitoring suggests

that standards of quality have been violated (or may soon be violated), thencarrying capacity has been exceeded and management action is required. Thisbasic approach to carrying capacity is central to contemporary park, recreation,and tourism management frameworks, including Limits of Acceptable Change(LAC) (Stankeyet al., 1985), Visitor Impact Management (VIM) (Graefeet al.,1990), and Visitor Experience and Resource Protection (VERP) (National ParkService, 1997).

When and where feasible, the above approach to carrying capacity might besupplemented by computer simulation modelling. Computer simulation models

of visitor use have been developed to estimate the relationship between visitoruse levels and selected indicators of quality, such as the number of encountersamong hiking groups (Manning & Potter, 1984; Potter & Manning, 1984;Schechter & Lucas, 1978; Smith & Krutilla, 1976; Wang & Manning, 1999). Suchmodels couldbe used to estimate the maximum use level that could beaccommo-dated in a park or related area without violating specified crowding-relatedstandards of quality. In this way, carrying capacity could be estimated.

Research to Estimate Carrying Capacity of Alcatraz IslandThis paper describes a programme of research to help estimate and manage

carrying capacity of Alcatraz Island. The island is an historic site within GoldenGate National Recreation Area, a unit of the US National Park System, and is aheavily visited tourist attraction. It is located in San Francisco Bay and is widelyknown for its history as a federal prison for incorrigible criminals. This historyhas been romanticised and popularised in several books and movies. Conse-quently, demand to visit Alcatraz is high, visitation exceeds several hundred





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touring the cellhouse?). Finally, respondents were asked Which photographlooks most like the number of visitors you typically sawon your tour of thecellhouse today?.

Computer simulation model

The second component of research focused on developing a computer-based

simulation model of visitor use at Alcatraz Island. The primary purpose of themodel was to determine the relationship between the number of visitors andpotential standards of quality for the maximum PAOT in Michigan Avenue ofthecellhouse. In this way, carryingcapacity could be estimatedin relationship tocrowding-related standards of quality for the cellhouse. The model wasconstructed using the commercial object-oriented dynamic simulationpackage,Extend,developed by Image That, Inc. Model input was basedondetailed visitorcounts and observations, including number of visitors per ferry, frequency of


Figure 2Study photographs




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ferries, length of time between debarkation of visitors on the island and theirarrival into the cellhouse audiotour ticket line, time spent in the cellhouseaudiotour ticket line, and time spent touring the cellhouse.

The structure of the model was built with hierarchial blocks that representedspecific components of the Alcatraz Island visitor system. A block labelled

Dock generated simulatedvisitorgroups as theydisembarked from ferry boats.A block labelled Up the Hill represents the time that visitors take to walk fromthe dock to the prison cellhouse. Blocks labelled Audio Tour Line and Cashierrepresent the time visitorsspend in line waiting to enter theprisoncellhouse andpurchase their audio tour tape and player. Blocks labeled Tour Beginning,Tour Middle and Michigan Avenue represent the time that visitors take toproceed through sections of the tour of the prison cellhouse. The data used tobuild and operate these blocks were derived from the detailed counts and obser-vations of visitor use described above. More detailed information on thisapproach to simlation modelling and its application to outdoor recreation andtourism can befound inLawsonandManning (2002),Wang andManning(1999),and Wanget al.(2001).

A short survey was also administered to 187 visitors as they completed thecellhouse audiotour to determine the relationship between PAOT in MichiganAvenue as reported by visitors using the computer-edited photographs and theactual PAOT in Michigan Avenue as estimated by the simulation model.

Study Findings: Estimates of Carrying CapacityThe sample of visitors to Alcatraz Island was characterised by the following

socioeconomic and demographic descriptors:

Most visitors come in small groups of family and friends. Most visitors (71%) are from the United States, with 46 states and Wash-

ington, DC represented among the sample. A plurality of visitors are fromCalifornia.

A sizable minority of visitors (29%) are from outside United States, with 30

countries represented among the sample. A plurality of international visi-tors are from the United Kingdom.

The vastmajority ofvisitors (82%)report that English is their first or nativelanguage. Among those who did not report English as their first or nativelanguage, the vast majority (86%) reported that they understood Englisheither very well or pretty well.

Visitors stay on Alcatraz Island an average of about two hours. The vast majority of visitors (86%) are visiting Alcatraz Island for the first

(and probably only) time.

Nearly all visitors (93%) took the audiotour of the prison cellhouse.

Indicators and standards of quality

The first component of research yielded information on potential indicatorsand standards of quality for the visitor experience at Alcatraz Island. Responsesto open-ended questions were coded verbatim, and then grouped into similarcategories. Frequency distributions and mean values were calculated forresponses to close-ended questions. Based on this analysis, the number of





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visitors in the prison cellhouse emerged as especially important in defining thequality of the visitor experience at Alcatraz. The vast majority of respondents(75%) reported that the audiotour of the cellhouse was the element of their expe-rience that they enjoyed themost.Moreover, thenumber of visitorson the tour ofthe cellhouse was rated by respondents as the most problematic of six potentialissues on the island; 54% reported that this was either a big problem or a smallproblem. Thus, the number of visitors in the cellhouse is a good indicator ofquality in that it is measurable, manageable, and important in defining thequality of the visitor experience.

Data on standards of quality for the number of people in the cellhouse areshown in Figure 3 and Table 1. Figure 3 graphs the average acceptability ratingsfor thesix study photographs.As this norm curve illustrates,44 PAOT in Mich-igan Avenue represents a threshold of acceptability the point at whichaggregate sample ratings fall out of the acceptable range and into the unaccept-able range.Table1 reports summaryfindings for all three evaluative dimensionsexplored acceptability, preference, and management action. Respondentswould prefer to see an average of 25 PAOT in Michigan Avenue, think the


-4

-3

-2

-1

0

1

2

3

4

10 22 34 46 58 70

PAOT in Michigan Avenue

Acceptability

Figure 3Norm curve

Table 1Alternative crowding-related norms (PAOT) for Michigan Avenue

Evaluative dimension

Preference Acceptability Management Action

25 44 44




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National Park Service should allow a maximum of 44 PAOT, and (as notedabove)would finda maximum of 44PAOTtobeacceptable. These datasuggest apotential range of crowding-related standards of quality. Neither of the pointsdefining this range (25 to 44), nor any of points along this range, are necessarilyany more valid than any other. Each point has potential strengths and weak-nesses. For example, standards of quality based on preference-related normsmay result in very high quality visitor experiences but would restrict access to arelatively low number of visitors. In contrast, standards of quality based onacceptability or management action allow access to a greater number of visitorsbut may result in visitor experiences of lesser quality. Findings that offer insightsinto multiple evaluative dimensions provide a potentially rich base of informa-tion and maylead to formulationof themost thoughtful andinformed standards

of quality. Such dataallow moreexplicitunderstandingof thepotential tradeoffsbetween use level and quality of the visitor experience.

Computer simulation model

The second element of research developed a computer-based simulationmodel of visitor use at Alcatraz Island. The model was used to estimate themaximum total daily use levels (i.e. daily carrying capacities) that could beaccommodated without violating the normative crowding standards shown inTable 1. Model output could be generated in several graphic and numerical

forms. For example, Figure 4 traces minute-by-minute PAOT levels in MichiganAvenue over the duration of a simulated day. This particular model run wasgenerated using an averagesummer day total use level of 4464 visitors (derivedfrom the counts of visitor use taken to construct the model). It can be seen fromthe graph that the number of visitors in Michigan Avenue fluctuates betweenabout 50 andabout 90throughout mostof the day.The modelwas ultimately runmultiple times (to average out the randomnessassociated with each individualmodel run) to estimate the maximum total daily use levels that could be


0

10

20

30

40

50

60

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80

90

100

110

0 480

Time of Simulation Day

PAOT

9:30 am 5:30 pm

Figure 4PAOT in Michigan Avenue over the minutes of a simulated day




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accommodated on the island without violating each of the crowding-relatednorms shown in Table 1 more than 10% of the time, and findings are shown inTable 2. (This 10% allowance isdiscussed later in the paper.) It is clear fromTable2 that there is a range of daily carrying capacities (from approximately 2500

visitor per day to approximately 4800 visitors per day) for Alcatraz Islanddepending upon the crowding-related standard of quality that is selected. Adaily carrying capacity could be implemented relatively easily through manage-ment of the ferry system serving the island.

As noted earlier, a short survey was also administered to 187 visitors as theycompleted their audiotour of the cellhouse. Visitors were asked to select one ofthe study photographs of Michigan Avenue (described above) that looked mostlike the PAOT they typically saw at this location. The PAOT in the photographsselectedby respondents averaged 35. The simulationmodel estimates that on the

days when the survey was conducted there was an average of 70 PAOT in Mich-igan Avenue. This suggests there is a 2 to 1 ratio of the actual PAOT in MichiganAvenue and the number ofpeople that can be seenat any one time. This is due tothe fact that people in the foreground and middle ground tend to obscure somepeople in the middle ground and background. Thus, the crowding-relatednorms derived by the photographs underestimate the actual PAOT that can beaccommodatedinMichigan Avenue by about half.That is, if visitors report that amaximumof 44 PAOT is acceptable in Michigan Avenue (the PAOT visitors find

acceptable to see), then there can actually be approximately 88 PAOT in Mich-igan Avenue.

A final analytical approach used in this study employed thecomputer simula-tion model of visitor use to explore the effect of alternative ferry schedules oncarrying capacity. Currently, ferries depart San Francisco for Alcatraz Islandevery half hour from 9.30 a.m. to 5.30 p.m. If ferry departures were reduced toevery hour, daily carrying capacity would also be substantially reduced. Rela-tively large numbers of visitors arriving at the same time would result in manyvisitors seeing relatively large PAOTs in Michigan Avenue. For example (as

reported inTable2), using theacceptabilityand management actionstandardsofquality of 44 PAOT, the computer simulation model estimates that approxi-mately 4800 visitors per day could be accommodated on Alcatraz Islandwithout violating that standardof quality more than 10%of the time. This anal-ysis is based on the existing ferry schedule of departures every half hour.However,when ferries depart only every hour, thecomputer simulationmodelestimates that only 3200 visitors per day could be accommodated withoutviolating the 44 PAOT standard of quality more than 10% of the time. Similarly,


Table 2Alternative daily carrying capacities of Alcatraz Island

Standards of quality Daily carrying capacity

Preference (25 PAOT) 2560

Acceptability (44 PAOT) 4800Management action (44 PAOT) 4800




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for the preference based standard of quality, daily carrying capacity drops fromapproximately2500visitorsperdayunder theexisting ferry schedule toapproxi-mately 1840 visitors per day under the reduced ferry schedule. Comparableincreases in carrying capacity are not possible in this case by increasing thefrequency of ferry service beyond the existing schedule. Forexample, increasing

the frequency of departures to every 15 minutes would increase acceptabilityand management action based carrying capacity from approximately 4800 visi-torsper day (under existing ferry service) toapproximately 4896visitorsper day,andwould increasepreference basedcarryingcapacityfrom approximately2560visitors per day to approximately 2656 visitors per day.

Discussion

The programme of research described in this paper raises a number of issuesregarding estimationand management of carrying capacity of parks and relatedtourist attractions.As notedat the beginning of this paper, anemerging principleof carrying capacity is that decision-making must be guided by managementobjectives and associated indicatorsand standardsof quality. A corollary of thisprinciple is that there is no one inherent carrying capacity of a park or touristattraction. Rather, each park or tourist attraction (or even site within such anarea) has a range of capacitiesdepending upon thedegree of resource protectionand type of visitor experience to be provided.

Data developed in this study illustrate this point. The number of peopleencountered (PAOT) in the prison cellhouse is a potentially good indicator ofquality. Study findings show that nearly all visitors take the audiotour of theprison cellhouse, and feel this is the highlight of their visit. However, there areindications that visitors are concerned with growing use levels in the cellhouse.Visitors rated crowding in the cellhouse as the most problematic of severalvisitor-related issues. Moreover, visitor perceptions of current use levels in thecellhouse are approaching the maximum PAOT judged acceptable (as reportedin Table 2). Finally, visitors rated the prison cellhouse as somewhat crowded

(an average of 4.2 on a 9-point crowding scale that ranged from 1 (not at allcrowded) to 9 (extremely crowded)), and this represented the highest level ofcrowding for any location on the island. However, standards of quality for thisindicator vary substantially, depending upon the evaluative dimension used inthestudy (i.e. the type ofvisitor experience). Crowdingnormsranged from a lowassociatedwith preference (a very high quality experience) to a high associatedwith acceptability and management action (a lower quality experience). Thecarrying capacity of the prison cellhouse, and ultimately Alcatraz Island as awhole, varies accordingly.

A related principle of carrying capacity is that some element of managementjudgement must be exercised. Again, the data developed in this study illustratethis principle. What point (or points) along the range of standardsof quality andassociated carrying capacities should be selected for management purposes?This is ultimately a judgement that should consider a variety of other factorsinherent in carrying capacity, including the purpose and significance of the area(as may be defined in law or policy), the fragility of natural and/or culturalresources, financial and/or personnel resources available for management,





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cellhouse. For example, using a response scale from 1 (strongly agree) to 5(strongly disagree) visitors were asked the extent to which they agreed ordisagreed with the statement I enjoyed my visit to Alcatraz Island. The averagescore was1.52.This suggests thatmanagementdecisionsabout carryingcapacityof AlcatrazIsland shouldnot be made exclusively on the basis of crowding in the

prison cellhouse.As noted above, it may be wise to consider a range of standards of quality and

associated carrying capacities for Alcatraz Island. Since the island is relativelysmall andtheprisoncellhouse is the icon visitorattraction,it may not be feasibleto do this in a spatial or geographic way. However, alternative standards ofquality and associated carrying capacities could be established on a temporalbasis. For example, a relatively high carrying capacity could be established forthe summer peak visitor use seasonand a lower carrying capacity during the offseasons.Moreover, the NationalParkServicehas recently begun special eveningtours of theisland,andthese could be managedto a different standardofquality,thereby providing a diversity of visitor experiences.

Finally, study findings illustrate that carrying capacity can be influenced byalternative management practices. For example, the frequency of ferry depar-tures can substantially affect daily carrying capacities.

The programmeofresearchdescribed inthis paper relies on several distinctivemethodologicalapproaches. First, visitor surveys provide the empirical founda-tion for the indicators and standards of quality developed, and the carrying

capacities ultimately derived. This is importantas it involves those who are mostdirectly interested in this site and who have much to gain or lose as a result ofmanagement decisions. It may be wise, when and where feasible, to expand thisresearch to other interest groups as well, including residents of local communi-ties and even the general population (Manninget al., 1999a).

Second, a visual approach is used to measure crowding-related norms. Avisual approach may be more realistic and valid than conventional narrativeand numeric approaches (i.e. asking respondents to evaluate encounteringselected numbers of other people), especially in relatively high use contexts

(Manning et al., 1999a). Research suggests that visitors may process someencounters withotherpeople ata subconsciouslevel, especially when suchpeopleareperceived to be like the respondent in terms of recreationactivity, behaviour,andotherappearance.A visualapproachtomeasuringcrowdingnormsallowsforsubconscious processing, while narrative/numerical approaches call explicitattention to allpersons encountered. When and where feasible, visual approachesmight be extended to normative evaluation of other recreation-related impactssuch as resource impacts to trails and campsites, litter, vandalism and graffiti.

Third, multiple evaluative dimensions (preference, acceptability, and manage-

ment action) were employed in asking respondents to evaluate alternative uselevels. Resulting data are complex, but provide empirical, detailed insights intohow visitors feel about alternative use levels, including how use levels affect thequality of the visitor experience, and tradeoffs visitors might make betweenavoiding crowding and maintaining reasonable public access to parks andrelated tourist attractions (Lawson & Manning, 2001; Manninget al., 1999a).

Fourth, computer simulation modelling was used to estimate carrying capaci-ties. Contemporary carrying capacity frameworks such as LAC and VERP





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suggest that carrying capacityis determined throughmonitoring of indicatorsofquality. When monitoring suggests that standardsof quality havebeen violated,carrying capacity has been reached. However, computer simulation modellingallows estimation of visitor use levels (i.e. carrying capacities) that will violateselected standards of quality. This facilitates a more proactive approach to

defining and managing carrying capacity, and enables estimates of carryingcapacity under alternative management scenarios such as more or less frequentferry schedules.

Clearly, theprogrammeofresearch described in this paper hasimportant limi-tations.First, it addresses social carrying capacityonly. The resource componentof carrying capacity noted at the beginning of this paper also needs research andmanagement attention. However, the methodological approaches outlinedabove may have some application to the resource component of carryingcapacity, or at least the interaction between these components. For example,recreation impacts to soil and vegetation at campsites have a potentially impor-tant aesthetic component, and the visual approach to measuring normativestandards for such impactsmay be useful in formulating standards of quality forthese resource-related indicators of quality.

Second, even within the social component of carrying capacity, this studyaddresses onlycrowding-related indicatorsand standardsof quality. The visitorsurvey conducted at Alcatraz Island suggests the importance of crowding-related indicators, but also suggests other potential indicators of quality such as

noise, availabilityof information/educationabout the island,andvisitorcompli-ance with rules and regulations. Expandedtreatmentofother potential indicatorvariables and associated standards is warranted.

Third, estimation of carrying capacities from the computer simulation modelallowed for standards of quality to be violated up to 10% of the time. This allow-ance was factored into modelling because it may not be reasonable to prescribethat standardsof qualitywill never be violated.Visitor use of parks and relatedtourist attractions has an inherent random element that tends to result in occa-sional peaks or spikes of activity andassociated encounters. The graph in Figure

4 tracing minute-by-minute PAOT levels in Michigan Avenue is representative.Occasionally, by happenstance, a number of visitor groups may arrive at anattraction site simultaneously, and this may result in isolated spikes in PAOTlevels. Totaluse levels wouldhaveto bekept very low toensure that these spikesnever (or rarely) occur, and this may not serve public interests for reasonableaccess to parks and related tourist attractions. A 10% allowance was adopted inthis study, but this figure wasarbitrarilychosen.Additionalresearch is warrantedto derive a more empirically sound basis for specifying this allowance.

Finally, it should be noted that the concept of carrying capacity of parks and

related tourist attractions has been controversial. Carrying capacity has beenvariously characterised as slippery (Alldredge, 1973), elusive (Graefeet al.,1984) and illusive (Beckeret al., 1984). In fact, a recent special issue of the

Journal of Sustainable Tourism Vol. 9, No. 5 was devoted to assessing thecomplexity of carryingcapacity and related topics.However, there is emergingconsensus that management-by-objective approaches, such as the VERP frame-work, are most appropriate for analysing and managing carrying capacity(Manning, 2001; McCool & Lime, 2001). There remains disagreement on some





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aspects of carrying capacity, including the ability to specify a numerical carryingcapacity (McCool & Lime, 2001). However, in the case of this study of AlcatrazIsland, numerical carrying capacities are thought to be justified because (1) theprimary indicator of quality of the visitor experience is the number of other visi-tors in the prison cellhouse, and (2) a computer simulation model of visitor use

was developed to estimate the maximum daily use level of Alcatraz withoutviolating standards for this indicator variable.

Conclusions

The programme of research described in this paper was designed to supportapplication of the concept of carrying capacity to Alcatraz Island,an historic sitewithin the US National Park System, and an important tourist attraction. Inparticular, it was designed to provide an empirical foundation for application of

the contemporarycarrying capacity framework,VERP. Study findings suggest apotentially important crowding-related indicator of quality (PAOT within theprison cellhouse), a range of potential standards for this indicator variable, andassociatedcarrying capacities for the prison cellhouse and the Island as a whole.Management judgements will still have to be rendered in choosingamong alter-native standards of quality and associated carrying capacities (or perhaps morethan one standardand carrying capacity to facilitate a diversity of visitor oppor-tunities at the island). However, study data help toprovide an informed basis forsuch management judgements.

Within the field of parks and outdoor recreation, the concept of carryingcapacity has traditionally been applied to resource-based parks and relatedareas.Nevertheless, the researchdescribedin this paper suggests that contempo-rary, indicator-based carrying capacity frameworks such as LAC and VERP,along with an associated programme of research, can be applied to heavily usedhistoric sites and tourist attractions that include significant elements of the builtenvironment. In such cases, indicators of quality may vary from those conven-tionally used in outdoor recreation, such as the number of encounters with other

groups along trails per day and resource impacts to trails and campsites.Recentand current research, for example in highly developed, urban recreation areas,suggests that visitors are concerned with crowding and other recreation-relatedimpacts, but that these impacts are manifested in other ways. For example, apotential indicator of quality for the visitor experience at Statue of LibertyNational Monument is the time required to wait in line to enter the Statue(Manning etal., 1999b),and potential indicatorsofquality for thevisitorexperienceat Boston Harbor Islands National Recreation Area include the amount of litter,vandalismandgrafittiseen (Manning etal.,2001).Applicationofcarryingcapacity

frameworks and associated programmes of research should be expanded to afull spectrum of parks and relatedtourist attractions toensure protection of theirresource base and the quality of the visitor experience.

Correspondence

Any correspondence should be directed to Professor Robert E. Manning,School of NaturalResources, University of Vermont, 356Aiken Centre, Burlington,VT 05405, USA ([email protected]).





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Documents

Manning Et Al. Case Study of Carrying Capacity in Alcatraz