Is whale shark tourism ecologically sustainable in Mozambique?
Running head: Whale shark tourism in Mozambique
Peter J. Haskell¹´², Andrew McGowan¹, Anna Westling³, Adriana Méndez-Jiménez³, Christoph A.
Rohner²´⁴´⁵, Kym Collins3, Marcela Rosero-Caicedo³, Jodi Salmond3, Ara Monadjem⁶, Andrea D.
Marshall²´⁷´⁸, Simon J. Pierce²´³´⁷´⁸ *
¹University of Exeter, School of Biosciences, Cornwall Campus, Penryn, Cornwall, TR10 9EZ, UK
²Marine Megafauna Association, Tofo Beach, Inhambane, Mozambique
³All Out Africa Research Unit, Lobamba, Swaziland
⁴Biophysical Oceanography Group, School of Geography Planning and Environmental
Management, The University of Queensland, St Lucia QLD 4072, Australia
⁵Climate Adaptation Flagship, CSIRO Marine and Atmospheric Research, EcoScience Precinct,
Dutton Park QLD 4102, Australia
⁶All Out Africa Research Unit, Department of Biological Sciences, University of Swaziland,
Kwaluseni, Swaziland
⁷ECOCEAN USA, Tofo Beach, Inhambane, Mozambique
⁸Ocean Revolution (Mozambique), Tofo Beach, Inhambane, Mozambique
*Email: simon@marinemegafauna.org

ABSTRACT:
The whale shark (Rhincodon typus) is a popular focal species in the global marine tourism industry.
While this business can create an economic incentive for the conservation of this threatened species, tourism itself can negatively impact on sharks in some circumstances. We analysed 689 encounters with at least 142 individual sharks over 2.5 years to assess the behaviour of whale sharks in the presence of swimmers at Tofo Beach in Mozambique. Sharks ranged in size from 3.0 to 9.5 m in total length, with males constituting the majority (74%). Avoidance behaviours were displayed by the sharks during 64.7% of encounters. Encounter duration decreased significantly from 12 minutes 37 seconds to 8 minutes 25 seconds in cases where the sharks expressed avoidance behaviours, indicating that tourist interactions did affect the short-term behaviour of sharks. The presence of injuries or scars on a shark, its feeding activity and the number of swimmers present all had a significant positive relationship with encounter duration. Mean encounter duration, the overall expression of avoidance behaviour, and the likelihood of an individual shark exhibiting avoidance behaviours did not show a significant trend over the study period. Although potential tourism impacts are likely to be mitigated by the non-breeding status and transient behaviour of sharks at this aggregation site, the repeated exposure of some sharks to tourists suggests that concerted effort should be made to implement best-practice standards amongst operators to ensure long-term sustainability.
KEY WORDS: behavioural observations, ecotourism, conservation, monitoring, risk assessment

INTRODUCTION
Viewing sharks in their natural setting is an increasingly popular tourism activity (Smith et al. 2010,
Gallagher & Hammerschlag 2011) and the income accrued can create a powerful incentive to manage these charismatic species as a non-consumptive resource (Brunnschweiler 2010, Vianna et al. 2010, Clua et al. 2011). In some cases, shark tourism can even provide a direct economic alternative to fishing (Pine et al. 2007, Gallagher & Hammerschlag 2011). With this in mind, tourism has been mooted as a potential component of shark conservation strategies (Topelko &
Dearden 2005) and has been a primary consideration in increased legal protection for elasmobranchs or their habitats in a number of countries (e.g. Topelko & Dearden 2005, Graham
2007, Pine et al. 2007, Anderson et al. 2011). However, recent studies have documented situations in which marine tourism has negative impacts of its own on focal elasmobranch species in the form of behavioural changes and increased energetic costs (Pierce et al. 2010, Smith et al. 2010,
Fitzpatrick et al. 2011). An improved understanding of the actual or potential effects of tourism interactions on focal species is important for mitigating or avoiding longer-term effects, and therefore ultimately safeguarding employment and tourism infrastructure. This leads us to the main question posed in this paper: is whale shark Rhincodon typus tourism in Mozambique likely to have a detrimental impact on this threatened species?
The whale shark is the world’s largest fish and an iconic tourism species (Gallagher &
Hammerschlag 2011). Commercial whale shark interaction tours began at Ningaloo Reef, Western
Australia, in 1993 after a seasonal aggregation of the species was discovered within the Ningaloo
Marine Park (Davis et al. 1997).Whale shark tourism industry was valued at AU$6.0 million annually in 2006 at this site (Catlin et al. 2010). Whale shark tourism industries have now developed at several locations in all three tropical oceans. Most of these destinations are based on the presence of predictable seasonal feeding aggregations of sharks exploiting ephemeral bursts in local productivity such as mass fish, or coral, spawning events (Taylor 1996, Heyman et al. 2001; de la Parra Venegas et al. 2011). Whale shark tourism provides a significant boost to many regional economies, particularly in developing countries where the majority of established destinations are located. The total global revenue from whale shark tourism was provisionally estimated to be
US$42 million in 2007 (Graham 2007).
Until recently, whale sharks were targeted by fisheries in several countries including the
Philippines (Alava et al. 2002), India (Pravin 2000), the Maldives (Anderson & Waheed, 2001) and
Taiwan (Chen & Phipps 2002), which led to declining catch rates and eventual fisheries closures.
The species was assessed as globally Vulnerable on the IUCN Red List of Threatened Species
(Norman 2005) and is one of the few shark species listed on international conservation conventions such as the Convention on International Trade in Endangered Species (Appendix II) and the Convention on Migratory Species (Appendix II). While the economic value or potential for whale shark tourism has helped to justify legal protection for the species in some of these countries, such as the Philippines and the Maldives, concerns have also been raised that specialist tourism industries could negatively impact the sharks. Sightings of whale sharks at Gladden Spit in
Belize declined between 1998 and 2003 (Graham & Roberts 2007) and, based on further anecdotal reports from guides, stayed low up until at least 2007 (Graham 2007). Graham (2007) suggested that the rapid increase in diver numbers 89 at this site may have led to disturbance of snapper spawning behaviour (the main driver of whale shark presence) and the whale sharks themselves, although a dedicated study on diver disturbance at this site did not find such an effect (Heyman et al. 2010). Propeller injuries on whale sharks from small boats have also been noted at several aggregation sites (Cárdenas-Torres et al. 2007, Rowat 2007, Rowat et al. 2007, Speed et al. 2008,).

Examination of the short-term behavioural responses of sharks to tourists and boats at Ningaloo
Reef (Norman 1999), Donsol in the Philippines (Quiros 2007) and Tofo Beach in Mozambique
(Pierce et al. 2010) demonstrated that sharks routinely display avoidance behaviours, including banking, eye-rolling, fast swimming and diving, in response to close approaches by swimmers or boats.
The ecological, social and economic sustainability of whale shark tourism at Ningaloo Reef was reviewed by Mau (2008). Although long-term empirical data on whale shark behaviour was not available from the area, the industry was judged to be ecologically sustainable based on the lack of observed interruption of feeding behaviour, which may take place largely at night or at least outside tourist interaction times (Taylor 2007), the regular re-sightings of philopatric sharks
(Holmberg et al. 2008, 2009), and the lack of reproductive behaviour observed in this juvenile male-biased population (Meekan et al. 2006, Norman & Stevens 2007). However, concerns were raised about the potential for injury from boat strikes (Speed et al. 2008) and an apparent decline in mean size over time (Bradshaw et al. 2008). Aside from Ningaloo Reef, where the industry has been relatively well-studied, the longer-term sustainability of shark tourism has not been explicitly considered. Studies on marine mammals have concluded that tourism can cause long-term cumulative impacts on the focal 111 species, such as habitat shifts (Bejder et al. 2006b; Allen and
Reid 2000), heightened stress (Bejder et al. 1999), and a reduction in foraging behaviour (Carrera et al. 2008). Individuals who are forced to divert their energies from normal behaviours, such as feeding, to avoidance behaviours may suffer from an overall reduction in biological fitness (Bejder et al. 1999). Given the threatened status and economic value of whale sharks, this topic is evidently worthy of further exploration.
In this study we examine the tourism industry at Tofo Beach (Praia do Tofo) in Mozambique, an international hot-spot for whale shark encounters (Pierce et al. 2010). Whale shark interactions are a key draw for international divers visiting the country, but no official management has been instituted to date raising questions over the sustainability of the industry (Pierce et al. 2010,
Tibiriçá et al. 2011). A relatively high density of whale sharks are present throughout the year in conjunction with localised productivity and meso-scale oceanographic features that may transport whale sharks through the study site (Rohner et al. In press). Previous work at Tofo Beach has examined how interactions can be managed so as to minimise the potential for short-term negative impacts on the sharks (Pierce et al. 2010). Here we extend and expand upon that dataset to evaluate whether longitudinal encounter data reveal evidence of an increasing frequency of avoidance behaviours overall, and whether individual-based analyses show evidence of changing avoidance behaviours over time. The implications of these data are then explored to evaluate the longer-term implications for the ecology of whale sharks at this site.
MATERIALS AND METHODS
Study site and commercial snorkelling trip procedures
The small village of Tofo Beach (23°51’ S, 35°32’ E) is situated in the Inhambane province of
Mozambique, approximately 400 km north-east of the country’s capital city, Maputo (Fig. 1). A full site overview and description of the commercial whale shark tourism industry in Tofo was provided by Pierce et al. (2010). Briefly, operators offer daily two-hour ‘ocean safari’ snorkelling trips that aim to find and swim with whale sharks and other marine megafauna. Trips generally take place between 11 am and 2 pm, when high light penetration into the water aids the visual search for animals. During each trip, vessels typically survey a 6 km stretch of coastline south of

Tofo between the surf line and 1000 m from the shore in waters ranging in depth from approximately 5 to 30 m. All trips were conducted from a single tour operator using an 8.2 m rigidhull inflatable boat. Sharks were located through visual inspection of the water surface, where it was often possible to spot their large, dark silhouettes or exposed fins. The boat was then positioned in relation to the shark’s direction of travel and clients entered the water to interact with the shark.
Data collection
Data were collected from January 2008 until June 2010, except July and August 2008 when no sampling trips took place. Upon locating a whale shark, observers entered the water alongside clients and recorded pre-determined observations whilst snorkelling 155 with the shark. The total number of swimmers and environmental characteristics, including weather conditions
(categorised as sunny, slightly overcast, overcast, or raining), Beaufort sea state and underwater visibility were recorded. The total length (TL) of the shark was estimated visually (Rohner et al.
2011) and the sex identified by the presence or absence of claspers on the pelvic fins. The presence and location of any injuries or scars were noted and categorised post-hoc as either
‘major’ or ‘minor’ following the definitions of Speed et al. (2008). A basic ethogram of each shark’s behaviour in the presence of swimmers was also produced to record the following characteristics: slow swimming (SS), equating to normal behaviour; fast swimming (FS), where there was an obvious increase in the shark’s tail-beat frequency; diving (D), where the shark dived away from the surface; banking (B), where the shark rolled its back toward swimmer/s; changing direction
(CD), where the shark altered its direction of swimming in the presence of swimmers; and any other obvious avoidance behaviours (A), such as the violent shudder reported by Quiros (2007).
Observations of feeding behaviour were also noted when they occurred. The total encounter duration, defined as the time between the first swimmer entering the water and the last swimmer returning to the boat, was recorded (in minutes) following each interaction. When possible, standardised identification (ID) photographs of both the left and right flanks were taken for each shark and uploaded to the global ECOCEAN whale shark photo-identification library (Arzoumaniam et al. 2005). Each of these encounters were then assigned to a new or previously-identified shark in the library.
Defining avoidance behaviours
A lack of opportunity to observe the animal under undisturbed conditions is a common difficulty when evaluating the impact of human presence on animal behaviour (Bejder and Samuels 2003;
Quiros 2007). It was difficult to establish whether behaviours that were exhibited by whale sharks in the presence of swimmers would also occur in a natural, undisturbed setting. Within-effect comparisons (i.e. behaviour in the presence of swimmers) were therefore employed instead of attempting to determine ultimate cause and effect relationships. This approach is useful in cases where there is no baseline or control data, and focuses on assessing behavioural responses under gradations of the effect (Bejder and Samuels 2003). Avoidance responses are not mutually exclusive and lie along a gradient ranging from no response to a high level of response in cases where multiple avoidance behaviours are exhibited (Quiros 2007). Behaviours that are typically classified as avoidance behaviours in whale sharks include FS, D, B and CD (Norman 1999, Quiros
2007, Pierce et al. 2010). When these or A were observed during an interaction they were each assigned a score of one. The total score at the end of each encounter was thus equal to the total number of avoidance behaviours observed, which was then used as the overall avoidance score

during analysis. All statistical analyses were carried out using R version 2.11.0 (http://Rproject.org) with additional software packages “MASS” and “nlme”.
Analysis of short-term responses
The relationship between avoidance score and encounter 198 duration was tested using a
Generalised Linear Mixed Model (GLMM) approach. Encounter duration, log transformed to ensure that error structure was normally-distributed, was used as the response variable.
Avoidance score was used as the explanatory variable and shark ID was added as a random effect to avoid pseudo-replication. Due to the significant relationship between avoidance score and encounter duration (see results, and also Pierce et al. 2010), encounter duration was used in all further analyses as a proxy measure for avoidance. A further GLMM was fitted to determine which variables significantly affected encounter duration. Encounter duration was entered as the response variable and tested against nine main effect explanatory variables: whale shark variables
(size, sex, presence/absence of scarring or feeding behaviour, respectively), environmental variables (weather [clear, partially overcast, overcast or rain], sea state (0-4) and underwater visibility), number of swimmers present during an encounter and the Julian day (Day 1 = 9th
January 2008). Second order interactions were tested between all combinations of whale shark variables, all combinations of environmental variables, size, sex and scarring with all environmental variables and between the number of swimmers and underwater visibility. Year and month of the encounter were entered as nested random effects. Only encounters in which shark ID had been confirmed were used in the analysis; a single interaction was randomly selected from those individuals for which multiple encounters had been recorded. A generalised linear model (GLM) was used to test for a significant relationship between the level of scarring on an individual and its total length.
Analysis of longitudinal responses
A GLM was fitted using the number of encounters as the response variable and search effort (in hours) and year as explanatory variables to establish whether encounter rate changed over the course of the study. As the dataset ended in June 2010, a second GLM was fitted to six-monthly periods using the number of encounters as the response variable and search effort and six month block as explanatory variables. A quasipoisson error structure was used for both analyses due to over dispersion of residual deviance. A third GLM was used to test for a change in encounter duration during the study period using log-transformed encounter duration as the response variable and month and year as explanatory variables. Chi-square was used to test for a population-level increase in avoidance response over the five six-month periods. A generalised
LME model was used to test whether the likelihood of avoidance was related to the number of previous encounters in which the whale shark had been successfully identified and its behaviours recorded over the study period. The ECOCEAN library was used to establish how many previous encounters had been recorded for each individual shark. A binomial score for avoidance was used as the response variable, encounter number as the explanatory variable and shark ID as a random factor. Significance was accepted at the 95% confidence interval in all analyses. The standard deviation for all appropriate data values is presented.
RESULTS
Encounter data

A total of 689 whale shark encounters were recorded from 328 trips between January 2008 and
June 2010, with a total search effort of 476.5 hrs. Between 0 and 14 encounters were recorded on each trip, with an overall mean of 2.73 ± 0.17 trip-1, equating to 1.46 ± 0.10 sharks hr-1 of search effort. At least one shark was spotted on 77.1% of trips. There was no significant trend in sightings over the course of the study (Linear Regression, 27 d.f., P = 0.260) (Fig. 2). A total of 142 individual sharks were positively identified using the ECOCEAN photo-identification library. Of 128 sexed sharks, 33 were female (25.8%) and 95 were male (74.2%) which was significantly different from a 1:1 sex ratio (Chi-square, χ1 249 = 30.031, P = <0.001). Size ranges were 3.0 to 8.5 m TL for female sharks (mean 5.85 ± 1.28 m) and 3.0 to 9.5 m TL in male sharks (mean 6.14 ± 1.24 m) (Fig.
3), with no significant difference between the sexes (t-test, t = -1.144, df = 125, P = 0.255). The total number of encounters (counted as the number of days in which interactions with that shark were recorded) with identified sharks ranged from one to five over the course of the study, although the inclusion of additional data from the ECOCEAN library showed that the individual whale sharks considered in this study had been exposed to swimmers up to 12 times before June
31st 2010, with a mean of 3.08 ± 2.13 encounters (Fig. 4). The reliance on suitable photographs having been submitted to the library means that these figures represent the minimum number of previous encounters. Scarring was observed on 53.3% of identified individuals and whale sharks were observed feeding during 19.5% of all encounters.
Short-term encounter duration and avoidance responses
Overall mean encounter duration was 9 minutes 46 seconds ± 263 8 minutes 18 seconds (N = 613).
One or more avoidance responses were recorded during 67.5% of encounters. A total of 184 encounters, from 132 identified sharks, were evaluated to determine that encounter duration was significantly related to expressed avoidance response (GLMM, χ23 = 15.046, P = 0.002). The mean duration of an encounter when a shark showed no avoidance was 12 minutes 37 seconds ± 8 minute 58 seconds (N = 190), significantly longer than encounters with sharks that exhibited avoidance (GLMM, χ21 = 14.255, P < 0.001). Durations did not differ significantly among encounters where one or more avoidance behaviours were expressed (GLMM, χ22 = 0.791, P =
0.673), which had a mean encounter duration of 8 minutes 25 seconds ± 7 minutes 21 seconds (N
= 397).
All potential explanatory variables were present in 170 encounters and, after controlling for multiple encounters with individual sharks, 120 encounters were available to test for other significant variables affecting encounter duration. An LME model, with year and month retained as nested random effects, demonstrated that scarring was highly significant (LME, χ22 = 10.953, P =
0.004). Encounters with individuals that had no apparent scarring were significantly shorter than individuals that had some degree of scarring (LME, χ21 = 7.927, P = 0.005), with scar type (e.g.
“major” or “minor”) not significantly affecting encounter duration (LME, χ21 = 3.027, P =0.082).
There was no significant relationship between the total length of an individual and the degree of scarring observed (ANOVA, F (2,627) = 2.390, P = 0.122). Encounter durations were significantly longer when a shark was observed feeding during an encounter (LME, χ21 = 5.608, P = 0.018) and when a higher number of swimmers were present during an encounter (LME, χ21 = 5.580, P =
0.018) (Fig. 5).
Longitudinal encounter rate, duration and avoidance responses

The number of whale sharks encountered was not associated with search effort between years
(ANOVA, F (1,249) = 1.134, P = 0.288). There was a significant difference in encounter rates between years (ANOVA, F(2,249) = 5.446, P = 0.005) but, when broken up into six-month blocks, the source of this difference was the second half of 2008, for which July and August were not included (ANOVA, F(4,247) = 8.591, P = <0.001). Encounter rate was generally low during the austral winter, so excluding these two months may have affected this result. No other variables were significant. There was no significant difference in the frequency of avoidance behaviours expressed between the five six-month periods (Chi-square, χ24 = 4.34, P = 0.362) (Fig. 6).
Encounter duration was significantly shorter in 2008 (8 minutes 2 seconds ± 8 minutes 32 seconds) than in 2009 (10 minutes 38 seconds ± 8 minutes 7 seconds) and 2010 (10 minutes 37 seconds ± 7 minutes 56 seconds) (ANOVA, F (2,610) = 17.925, P = <0.001) (Fig. 7). A total of 204 encounters from 142 individual whale sharks were analysed to establish that the number of previous encounters with swimmers did not affect the whale shark’s likelihood of displaying avoidance behaviour (GLMM, χ2 1 = 1.693, P = 0.193).
DISCUSSION
Are whale sharks 306 being affected by tourism?
We found no significant longitudinal effects on encounter duration or the raw proportion of avoidance behaviours expressed over the 30 month study period. There was also no significant relationship between the number of previous tourist encounters and the likelihood of avoidance behaviours being displayed by individual sharks. Therefore, at this stage, there is no evidence of short-term avoidance behaviours translating into medium- to longer-term behavioural change within the sharks present in Mozambican waters.
The potential negative impacts of tourism may be ameliorated by the ecology and population structure of whale sharks in Mozambique. The majority of sharks encountered were male (74%).
Maturity in male sharks occurs at approximately 8.0 m TL based on records from Ningaloo Reef
(Norman and Stevens 2007) and >8.7 m TL in female sharks based on South African and other records (Beckley et al. 1997, Norman and Stevens 2007). Given that no sharks over 9.5 m or less than 3 m TL were encountered, most sharks were immature and likely to be several years old at the time of first sighting (Wintner 2000). No observations of possible courtship or mating behaviours were made amongst the few adult sharks sighted, and social interactions between sharks were rarely observed. Therefore, tourism at this site is unlikely to interfere with reproduction, if it does in fact occur in these waters. The majority (52%) of sharks had only one or two encounters recorded on the ECOCEAN photo-identification library by June 30th 2010 (with the earliest from May 2005) suggesting that many of the sharks are transient to the area as noted in other aggregations at Ningaloo Reef (Holmberg et al. 2008) and the Seychelles (Rowat et al. 2009).
There was no evidence of learnt avoidance behaviour amongst individual sharks and, based on data from the Philippines (Quiros 2007), a degree of habituation may be more likely to occur.
The percentage of whale sharks observed feeding during daylight hours at Tofo in the present study (19.5%) is consistent with the 19.4% reported earlier by Pierce et al. (2010) for the same site, and is comparable to the rates reported at Donsol in the Philippines (13% in 2004 and 36% in
2005) (Quiros 2007), but substantially lower than the 69% reported from Bahía de Los Angeles,
Mexico where researchers were targeting feeding whale sharks (Nelson & Eckert 2007). It has not been established whether significant feeding activity occurs at night off Tofo, as has been recorded at Ningaloo Reef (Taylor 2007). Contrary to results from the Philippines, where feeding

sharks were 1.84 times more likely to exhibit a dive response in the presence of swimmers (Quiros
2007), encounter durations in this study were significantly longer when feeding behaviour was observed. In particular, sharks often appeared to be disinterested or oblivious to swimmers while actively feeding on surface zooplankton (PJH, pers. obs.). Whale sharks are flexible in their foraging strategies depending on prey type and vertical distribution (Graham et al. 2006, Nelson &
Eckert 2007, Taylor 2007, Brunnschweiler et al. 2009, Motta et al. 2010, Brunnschweiler & Sims
2012), so the impacts of tourism on feeding are likely to be context-specific.
Whale shark encounters were spatially aggregated along 9 km of coast immediately south of Tofo
Beach. Opportunistic aerial surveys (Cliff et al. 2007, Rohner et al. In press) and commercial tourism operator search patterns (Pierce et al. 2010) suggest that this small coastal strip contains the highest density of whale sharks. Although the sharks are also sighted more widely along the
Mozambican coast (Cliff et al. 2007, Rohner et al. In press), the small size of the primary aggregation area and its almost complete daily search coverage by commercial operators does suggest a possibility for displacement if whale sharks have negative interactions with swimmers or boats. Over half (53%) of identified sharks in this study had some form of body scarring present, although not all of these were from anthropogenic sources such as propeller strikes. This rate is lower than that recorded from some locations such as the Seychelles (scars on 67% of identified sharks; Speed et al. 2008) and Djibouti (propeller or boat strike scars on 65% of identified sharks;
Rowat et al. 2007), but emphasises the importance of working with skippers to ensure that a safe minimum distance from the sharks is maintained (Pierce et al. 2010). While there has been no perceived shift in whale shark distribution amongst operators, the lack of standardised spatial sampling coverage in this study precludes a definitive assessment.
Lessons for monitoring and managing the impacts of tourism
Accurate quantification of avoidance behaviour is a challenge when investigating the impact of tourism on large marine animals. Our results support the use of encounter duration as a means of measuring the impact of swimmer presence on whale shark behaviour, as sharks that are disturbed will routinely end an encounter by diving or increasing their swimming speed. It is important to note however that encounter duration, while proving to be a useful proxy of avoidance, may only be able to provide resolution at the binomial scale (i.e. ‘avoidance’ or ‘no avoidance’). Encounter duration has previously been used to quantify avoidance of Hector’s
Dolphins Cephalorhynchus hectori to swimmers in New Zealand (Bejder et al. 1999) and for assessing long-term trends in encounters with Dwarf Minke Whales Balaenoptera acutorostrata on the Great Barrier Reef, Australia (Birtles et al. 2002). However, their definition of encounter duration varied, with Bejder et al. (1999) defining it as the length of time that a swimmer spent within 200 m of the nearest dolphin, and Birtles et al (2002) defining it as the time between the first sighting of a whale and the end of the vessel’s contact with that whale.
In this study we defined encounter duration as the time between the first swimmer entering the water in the presence of a whale shark and the last swimmer returning to the boat. We found a positive relationship between the number of swimmers and the encounter duration. This result may be an artefact of the definition in use, as larger groups of swimmers are likely to contain members with a wider range of swimming abilities. The presence of more able swimmers is likely to lead to an increase in encounter duration, as they are able to maintain visual contact with a shark for longer than slower or less fit individuals. However, the method used in this study does represent a simple and easily replicable measure of encounter duration. A mean of 11.4 swimmers per encounter was recorded. This exceeds the maximum recommended by most management

plans, which limit swimmer numbers from three in Mexico (Remolina Suárez et al. 2007), to ten in
Australia (Catlin & Jones 2010), although these set numbers may be partially influenced by operational constraints in those locations. Future studies that rely on in-water observers could trial re-defining encounter duration as the time between the observer’s first and last visual contact of the shark underwater or, in cases where the observer remains on board the vessel, the time between 50% of swimmers entering the water to when 50% of swimmers have returned to the vessel. In this way the approximate mean duration would be recorded, reducing the influence of swimming ability and group size on overall encounter duration. Another important point to consider in future work is the number of swimmers that are actually ‘in contact’ with the shark from a behavioural perspective; i.e. investigating how swimmer proximity may influence these results. From a management perspective it is also important to consider the customer’s level of satisfaction with the experience, which can be significantly reduced in highly crowded scenarios
(Davis et al. 1997).
Quiros (2007) reported from the Philippines that the probability of a shark exhibiting an avoidance response significantly increased if it was touched by a swimmer or had its path obstructed. While swimmer behaviours were not recorded during the present study and could not be directly taken into consideration during analyses, pre-trip briefings were conducted before every sampling trip during which clients were specifically told that these behaviours were strictly prohibited.
Compliance was high and, as such, the number of encounters when one or both of these behaviours occurred represented a small proportion of the total recorded. Consistent with results from Quiros (2007), but contrary to Norman (1999), encounter duration was significantly longer with scarred whale sharks. This could be because scarred individuals have slower reaction times and a reduced level of agility as a consequence of their previous injuries. However, the severity of scarring did not significantly alter encounter duration in the present study. Another hypothesis could be that older individuals, 416 who would presumably be more likely to have accumulated scars, show less avoidance than younger individuals. However, we found no significant relationship between shark size and the severity of scarring. A third plausible explanation is that some sharks have a slower natural reaction time to potential threats and are therefore more likely to accumulate injuries or express avoidance behaviour toward boats or swimmers. Further research is required to confirm or refute these hypotheses.
The inclusion of well-defined and easily observed parameters of known significance that can be recorded by either trained specialist (e.g. researchers) or non-specialist (e.g. tour operators or volunteers) observers would vastly increase the amount of information available, enabling routine sustainability assessments and facilitating inter-site comparisons (Graham 2007). We have created a template data collection sheet, presently in use in Mozambique, which can be freely downloaded from the supplementary material section for this publication. In addition, we encourage the submission of standardised photographs of all whale sharks encountered into the global Whale Shark Photo-identification Library ( www.whaleshark.org
). This facilitates the incorporation of individual-based analyses to be incorporated into future studies, while concurrently enabling more accurate regional and ocean-wide studies of population size and interconnectivity (i.e. Graham 2007, Brooks et al. 2010).
Is whale shark tourism ecologically sustainable?
It is important to explicitly point out that the 30 months of data represented 437 by this study does not provide sufficient context for allowing a definitive assessment of the ecological sustainability, or lack thereof, of whale shark tourism in Mozambique. On-going evaluation and

adaptive management of the industry is necessary, particularly in light of evidence that short term studies of tourism impacts on dolphins do not necessarily identify longer-term detrimental impacts (Bejder et al. 2006a). Also, as these data were collected in conjunction with a single operator, it is presently impossible to say whether our results are fully representative. However, we are cautiously optimistic for the future of whale shark tourism in the country. Recent tagging results (Brunnschweiler et al. 2009) and the low number of repeat sightings observed in this study suggest that whale sharks range widely from the study area. Therefore, most individual sharks are exposed to tourists infrequently, even though the tourism industry is concentrated on a relatively small length of coast. Unlike in Belize, where tourism may disturb feeding behaviours (Graham
2007), there appears to be no significant impact on feeding or reproductive activities in
Mozambique. With increasing global interest in human interactions with whale sharks, there is a clear need for the implementation of monitoring initiatives at major tourism sites so as to understand and avoid long-term anthropogenic impacts. Many other important whale shark tourism sites, such as those in Mexico, the Seychelles and Western Australia, have similar characteristics in terms of residency and population structure. The results of this study demonstrate that encounter duration is a useful metric for assessing whale shark behaviour, and provides a template for future studies in Mozambique and other locations.
The overall success rate of commercial trips observed in this study 459 (77.1%) was lower than the
87% success rate recorded between January 2008 and August 2009 (Pierce et al. 2010); supporting a perception amongst local commercial operators that sightings of whale sharks are decreasing.
Whether this apparent decline is a temporary spatial shift in abundance or behavioural change, or is representative of a broader ongoing reduction in numbers, is unclear. While anthropogenic threats to whale sharks, such as boat strikes and accidental capture in gillnets, do occur in
Mozambique (Speed et al. 2008, SJP pers. obs.), whale shark sightings are also closely correlated with biological and oceanographic drivers (Rohner et al. In press). The general lack of historical data on whale shark populations globally means there is little information on long-term patterns in whale shark abundance available to draw inferences from, although work on this topic is currently underway. This aggregation site in Mozambique is the only sizeable ‘hot-spot’ for the species in the world that presently has no species- or habitat level protection or focused management in place. Given that the presence of whale sharks at this location is a powerful draw for international dive tourists (Tibiriçá et al. 2011); there is a strong economic as well as ecological rationale for improved management.
Acknowledgements. Thanks to All Out Africa volunteers and staff for their efforts collecting the majority of the data used in this study, and to the Marine Megafauna Association staff, volunteers and students who also contributed. The support of Tofo Scuba and Casa Barry Lodge throughout the field portion of the project is greatly appreciated. This study was made possible by support from Project AWARE Foundation, the Rufford Small Grant Foundation, PADI Foundation, Ocean
Revolution, Foundation Ensemble and one private donor. Thanks also to Adrian Gutteridge and
Conrad Speed for their comments on 481 an earlier version of this manuscript.
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Fig. F1F. Geographic location of the study site, Tofo Beach, in south-eastern Africa

Fig. 2. Rhincodon typus. Mean (± S.D.) sightings over the 30-month sampling period. Numbers above the mean denote the number of sampling days within that month
Fig. 3. Rhincodon typus. Population structure of all photo-identified sharks

Fig. 4. Rhincodon typus. The total number of sightings (unique encounter days) for each identified shark
Fig. 5. Relationship between mean (± S.D.) encounter duration and the number of swimmers present. The numbers above the mean denote the number of encounters

Fig. 6. The percentage of encounters featuring avoidance behaviour for each time period.
The numbers for each time period represent the total encounters
Fig. 7. Mean (± S.D.) encounter durations over time. The numbers above the mean denote the number of encounters