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Complex ecological pathways underlie perceptions of conflict between green turtles and fishers in the Lakshadweep Islands
Article in Biological Conservation · November 2013 DOI: 10.1016/j.biocon.2013.07.014
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Complex ecological pathways underlie perceptions of conflict between green turtles and fishers in the Lakshadweep Islands
a,b, a a,b a Rohan Arthur ⇑, Nachiket Kelkar , Teresa Alcoverro , M.D. Madhusudan a Nature Conservation Foundation, 3076/5, Gokulam Park, Mysore 570002, India b Centre d’Estudis Avançats de Blanes (CSIC), Accés a la Cala St. Francesc, 14, Spain article info abstract
Article history: Managing human–wildlife conflict is often complicated by apparent mismatches between community Received 5 January 2013 perceptions and measures of directly incurred losses. Fishers in Agatti Island (Lakshadweep, India) asso- Received in revised form 2 July 2013 ciate recent increases in green turtle (Chelonia mydas) populations with declining fish catches, resulting in Accepted 12 July 2013 targeted killing of turtles. We compared fisher perceptions in Agatti with a very similar atoll, Kadmat, with much lower turtle densities. Nearly 90% of Agatti fishers interviewed blamed turtles for declining catch compared with 20% in Kadmat and proposed two mechanisms for this decline: direct interference Keywords: (e.g., turtles damaged gear) which we define as first order conflict, and indirect mechanisms (second Human–wildlife conflict order conflict): turtles overgrazed seagrasses, thereby reducing fish catch. We evaluated the magnitude Conflict perceptions Indirect pathways of gear loss with interviews and tested proposed indirect mechanisms with a turtle density gradient, Green turtles before–after comparisons (taking advantage of an increase in turtles in Kadmat and concurrent decrease Fisheries in Agatti) and a natural herbivore exclosure. These complementary approaches supported fisher-pro- Seagrass meadows posed second-order mechanisms: at high densities, turtles heavily grazed seagrasses, significantly reduced canopy heights, lowered fish recruit abundance, food fish biomass and catch. Estimates of losses 1 1 incurred in Agatti show that first-order conflict cost fishers USD 0.6 fisherÀ yearÀ , while second-order 1 1 pathways accounted for USD 887 fisherÀ yearÀ . Our results show that local perceptions are fueled by often-complex mechanisms that, though not always straightforward to measure, are very important in generating conflict. Reconciling the human–wildlife interface requires an adequate accounting of direct and indirect mechanisms to more completely reflect true losses communities bear for living with wildlife. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction 2007; White et al., 2009). Ecological factors underlie foraging decisions made by animals, which, in may turn, directly affect As resource demands grow and natural habitats shrink, the un- humans or inflict material damage to their production systems. easy coexistence between humans and wildlife is becoming While economics helps contextualize such damage as monetary increasingly fragile (Messmer, 2009). While wildlife depredation loss and is useful in assessing its impact, a suite of cultural fac- takes a considerable toll on human lives and livelihoods, species tors determines how humans respond to such losses (Dickman, continue to decline as a direct result of conflict-related reprisals 2010; McCoy, 2003). Yet, without unifying interdisciplinary (Thirgood et al., 2005; Woodroffe et al., 2005b). More significantly, frameworks, our understanding of conflict remains fragmentary human–wildlife conflict erodes goodwill and support for wildlife at at best. Conflict management recommendations continue to be large (Peterson et al., 2010), making conflict management a critical based on a partial and reductionist understanding of the prob- challenge for conservation (Sillero-Zubiri et al., 2007; Woodroffe lem by practitioners of different disciplines, or are governed by et al., 2005b). the expediencies of those managing conflicts in the field. Unsur- Human–wildlife conflict involves a complex interplay of ecol- prisingly, many authors emphasize the ineffectiveness or unsus- ogy, economics and culture (Dickman, 2010; Marshall et al., tainability of conflict alleviation measures (Gore et al., 2008; Thirgood et al., 2005; Webber et al., 2007; Woodroffe et al.,
Corresponding author. Address: Nature Conservation Foundation, 3076/5, 4th 2005a). ⇑ Cross, Gokulam Park, Mysore 570002, India. Tel.: +91 821 2515601; fax: +91 821 A particular challenge posed by a fragmented understanding of 2513822. conflict is the chasm between peoples’ perception of conflict and E-mail addresses: [email protected] (R. Arthur), [email protected] its scientific measurement. Often, the intensity of these responses (N. Kelkar), [email protected] (T. Alcoverro), [email protected] (M.D. Madhu- may appear quite disproportionate to the extent of directly sudan).
0006-3207/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biocon.2013.07.014 26 R. Arthur et al. / Biological Conservation 167 (2013) 25–34 measurable losses, often leading to targeted killing of implicated 2. Materials and methods species. Such reactions are usually considered aberrant, but a clo- ser analysis suggests that they sometimes arise from critical indi- 2.1. Study area and study design rect costs that remain unseen and unmeasured (e.g., crop guarding, reduced sense of security, etc., see Dickman, 2010). The Lakshadweep Archipelago, Indian Ocean, comprises 12 cor- Understanding conflict perceptions is vital since they ultimately al atolls enclosing 27 small islands (8°N–12°N, and 71°E–74°E, drive stakeholder responses. Despite increasing robustness in Fig. 1). Local fishing communities depend on oceanic skipjack tuna quantifying conflicts, we remain quite ignorant about factors as a primary income source (Silas et al., 1986). A few atolls have underlying conflict perception (Kretser et al., 2009; Manfredo extensive seagrass meadows, confined to shallow lagoons (Jagtap, and Dayer, 2004; Marshall et al., 2007), rarely treating them as 1991, 1998). These meadows support a subsistence fishery which serious inputs into scientific understanding and conflict resolution. becomes a primary protein source during the stormy monsoon Although easy to dismiss as merely idiosyncratic or ‘less rational’ months (Hoon et al., 2003). Fishers predominantly use demersal representations of the problem, these disproportionate reactions set-gillnets in the meadow. Although green turtles have always may well conceal a nuanced understanding of the human–wildlife occasionally occurred here, using beaches to nest, the scant past interface, synthesized from a community’s lived experience of it surveys indicate that they have never been abundant in Agatti over space and time. since the 1970s (Bhaskar, 1978; Tripathy et al., 2002, 2007). In We examined the underlying drivers of perceived human–wild- the last 15 years however, turtle densities in Agatti have substan- life conflict in a fishing community in the Lakshadweep Archipel- tially increased (Lal et al., 2010), concurrent with similar increases ago, India. Fishers at one of the Lakshadweep atolls (Agatti) across the Indian Ocean and elsewhere (Bourjea et al., 2007; Laur- associate fish catch declines from lagoonal seagrass meadows to et-Stepler et al., 2007; Scott et al., 2012). This has precipitated a vo- an increase in resident green turtle (Chelonia mydas) densities since cal conflict with fishers in Agatti including persecution and killing around 2000, putatively as a result of highly successful local and of adult turtles and targeted destruction of nests (personal regional conservation measures across the Indian Ocean (Bourjea observations). et al., 2007; Lal et al., 2010; Lauret-Stepler et al., 2007). This has We interviewed fishers to identify perceived drivers of con- led to clandestine killing of adult turtles, destruction of nests and flict, classifying them based on whether they involved direct open hostility against green turtles in Agatti (personal observa- interactions between fishers and turtles or invoked more com- tions). To understand the drivers of this conflict, we compared per- plex indirect mechanisms. We compared perceptions in Agatti ceptions in Agatti with Kadmat, an atoll similar to Agatti in most with Kadmat, an atoll similar in size, fisher density, meadow ex- socio-ecological metrics except that it had very low densities of tent, and other human use variables (Table 1), but with much resident green turtles in seagrass meadows. We interviewed fish- lower green turtle densities reported until 2010 (Bhaskar, 1978; ers to understand the mechanisms they perceived linking herbivo- Tripathy et al., 2007). By 2011, the Kadmat lagoon saw major in- rous green turtle densities with declines in fish catch. We then creases in turtle densities while at Agatti, numbers declined con- tested these mechanisms with complementary field studies: (i) comitantly allowing ideal before–after comparisons at both correlative approaches across a gradient of turtle densities, (ii) be- lagoons that helped validate ecological mechanisms underlying fore–after comparisons, taking advantage of a sudden increase of this conflict. All fishers we interviewed (between 20 and 90 years turtles in Kadmat and a concomitant decrease in Agatti at the old) reported that they could not recall turtle numbers close to end of our study and (iii) comparisons of natural herbivory exclo- present densities in their lifetime, conforming with published re- sures with adjacent grazed areas. Finally we attempted to evaluate ports of low turtle densities from the Lakshadweep (e.g., Bhaskar, the relative economic costs of conflict derived from direct and indi- 1978). rect mechanisms. While quantifying the costs of direct interactions was rela- tively straightforward, indirect conflict mechanisms proposed by
Fig. 1. Map of the Lakshadweep Archipelago, Indian Ocean (center) with details of the studied atolls, Agatti (right) and Kadmat (left). The spatial distribution of turtle density at both locations in 2010 is shown with the shaded circles. R. Arthur et al. / Biological Conservation 167 (2013) 25–34 27
Table 1 A comparison of the biophysical and socio-economic characteristics of Agatti and Kadmat lagoons, Lakshadweep, India. The major difference between these atolls was the density of resident turtle densities in the lagoons in 2010. For details of how turtle density was estimated, refer to Section 2.
Island characteristics Agatti Kadmat Lagoon area (ha) 1680 2090 Orientation North–South North–South Tidal influence Three entrance points (North, Central and South) Three entrance points (North, Central and South) Mean depth at high tide (m) 2.5 2.2 Seagrass cover (ha) 702 776 Population (2009 estimates) 8145 6440 Number of households 1065 940 Fisher density (per km2 of lagoon/day) 3.75 ± 0.95 (SD) 3.89 ± 1.42 (SD) Average lagoon fishers per household 1.56 1.30 Total lagoon fishers 1661 1222 2 Turtle density in 2010 (turtles kmÀ of meadow) 27.58 ± 2.40 (SD) 3.57 ± 0.40 (SD)
fishers required further field investigations. Principally, fishers 2.3. In-situ testing of indirect conflict proposed that, at high densities, turtles intensively grazed seag- rasses reducing available habitat for fish, resulting in declining The principal indirect mechanism identified for reductions in catches. Our earlier studies confirmed that green turtles at Agatti fish catch in Agatti was that turtles, by grazing heavily on seagrass, could significantly overgraze meadows (Lal et al., 2010), and for reduced fish usage and recruitment. We used three different ap- the present study, we focused on determining if turtles could re- proaches to validate these perceived conflict drivers: duce seagrass canopies and cause fish decline. We used natural herbivore exclosures to determine if turtles could influence can- 2.3.1. Meadow and fish changes across a green turtle density gradient opy structure. We validated this with field comparisons of turtle We tested the relationship between turtle grazing and fish de- densities, seagrass canopies and fish biomass at Agatti and Kad- cline across a natural gradient of turtle density in six different mat in 2010 as well as comparisons before and after turtles in- meadows. We first mapped green turtle distributions in both la- creased in Kadmat. In addition, we examined how seagrass goons at two sampling times (February and March) in 2010 using canopies, adult and recruit fish biomass varied across a gradient a 300 m 300 m grid-based sampling across the lagoon. We inter- of turtle herbivory across these two lagoons. Finally, we esti-  polated spatial distributions of turtles and substrate categories mated the relative economic costs of direct and indirect conflict from point data and calculated turtle densities from this distribu- mechanisms, comparing losses in Agatti and Kadmat generated tion (for more details of turtle sampling methods, see Lal et al., through each conflict pathway. 2010). The distribution of turtles closely tracked the spatial distri- bution of seagrass meadows in the Agatti lagoon; at Kadmat, turtle densities were consistently low in 2010. Six localities were chosen 2.2. Documenting fisher perceptions in Agatti and Kadmat (three at each) representing a gradient of tur- tle density (see Fig. 1). While all attempts were made to choose We used focus group and individual interviews to explore con- locations relatively similar in environmental conditions, one local- flict perceptions and its drivers. Interviews were conducted when ity, close to a channel subject to dredging, experienced higher sed- turtle numbers were at their peak in Agatti and were low in Kad- imentation levels than others. At each locality we measured mat (2010). We conducted focus group sessions with village canopy height, turtle herbivory rates, fish recruitment and fish bio- councils (Panchayat), key informant fishers and other community mass. We estimated canopy height (cm) from the substrate to the stakeholders (artisanal and tuna fishers, NGO and government plane of the canopy at 50 random seagrass shoots in each meadow. representatives). These discussions centered on fishing and the To estimate natural rates of turtle herbivory in the meadow, we local economy as well as stakeholder attitudes towards large sampled randomly selected shoots (n = 50). We tagged each shoot, marine animals (sharks, dolphins, turtles, etc.). Based on these and, without detaching it underwater, measured leaf number, leaf initial responses, we conducted semi-structured interviews with length and width, and the number and type of bite marks (i.e., fish individual fishers at Agatti (n = 65) and Kadmat (n = 31). We col- or green turtle, Lal et al., 2010). We lightly pierced shoot bases to lected information on demographic and socio-economic descrip- measure leaf elongation and collected shoots 7 days later. Biomass tors of interviewees (age, education, dependents, income loss was estimated as the difference between initial and final shoot sources, dependence on fishing, number of boats, gear, etc.), and length at the time of collection, corrected for leaf elongation. We explored fisher perceptions of: (1) trends in lagoon fish catch; attributed herbivory to turtles or fish based on the distinctive leaf (2) factors responsible for these trends; (3) specific mechanisms bite marks. Since our objective was to account for large spatial dif- through which these factors influenced catch; and (4) proposed ferences, losses resulting from leaf fall were ignored; consequently, solutions for catch decline. In addition, we asked fishers if they final herbivory values may be slightly underestimated. Herbivory 1 1 had encountered turtle mortality as a result of bycatch in gillnets. rates were expressed in length cm shootÀ dÀ . To assess the im- We ensured that no leading questions were posed and asked fol- pact of turtle grazing on meadow structure, we plotted seagrass low-up questions relating to turtles only when they were specif- canopy heights against herbivory rates. ically identified as conflict triggers. When fishers identified turtles We recorded fish species in 50 5 m visual belt transects  as responsible for fish decline, we determined perceived trends in (n = 10), sampled by snorkelling at each location. Individual fish resident turtle densities. We reduced detailed descriptions of per- was assigned to size classes (<5 cm, 5–10 cm, 10–20 cm, 20– ceived factors affecting fish catch to the most frequent recurrent 30 cm, 30–40 cm, >40 cm), which were visually estimated. Before themes and collated them in a 1/0 matrix based on whether sampling began, we calibrated visual estimates with actual fish respondents alluded to themes or not. We summarized these re- sizes using scaled photographs. We calculated fish biomasses using sponses to analyze fisher perceptions. All interview data was ana- standard volumetric conversions: W = a Lb, where W is weight, L is Á lyzed anonymously. estimated length (midpoint of size-class) and a and b are 28 R. Arthur et al. / Biological Conservation 167 (2013) 25–34 species-specific constants obtained from FishBase (Froese and tively free of the effects of pseudoreplication. We determined Pauly, 2012). Biomass densities were estimated for Parupeneus bar- differences between samples by visually comparing the 95% CIs berinus (Mullidae) and Lethrinus harak (Lethrinidae), identified by of the measured variables. fishers as the principal targets of lagoon fishery. These species are dominant in seagrass meadows across the Indo-Pacific (Uns- worth and Cullen, 2010; Unsworth et al., 2007, 2008), and both 2.3.3. Natural herbivore exclosures adult and juvenile stages preferentially use meadows to feed and We used natural exclosures in Agatti to test if green turtles can find refuge. In addition, we used a separate set of visual transects influence seagrass structure in the long term. The ungrazed exclo- at these six sites to estimate the abundance and biomass density sures consisted of small patches of seagrass growing on sandy sub- of Acanthurid fish recruits (during a recruitment pulse in March strate, between branches of naturally occurring Acropora spp. The 2010). coral branches served as an effective refuge from herbivory, as We tested for relationships of adult and recruit fish biomass in has been reported for other marine macrophytes (Bennett et al., response to seagrass canopy height, total shoot density and sea- 2010). To reduce the potential influence on seagrass biomass by grass composition, across meadows along the turtle density gradi- coral structures themselves (e.g., through fish fertilization or mod- ent, using Generalized Linear Mixed-Effects Models (GLMMs), ification of currents), we restricted our sampling to small coral based on Zuur et al. (2009). ‘‘Island’’ and ‘‘Meadow’’ identities were patches (Kelkar et al., in press). We measured canopy height and used as random effects in these models to hierarchically partition turtle herbivory marks inside and outside exclosures (n = 20) and the variation explained by ecological predictor variables (fixed ef- tested for differences between grazed and ungrazed plots with a fects) in both regressions, from the random variation caused by one-way ANOVA using the software R 2.15.0 (R Development Core site- or island-specific differences in response variables. Random Team, 2012). effects were estimated in order to address pseudoreplication issues that likely arose from transect-level data, when analyzed without accounting for meadow-level or island-level effects. The error 2.4. Economic valuation of losses in direct and indirect conflict structure of the GLMMs was modeled with parameters for the Neg- ative Binomial distribution with a zero-inflation factor. We chose We evaluated monetary losses to fishers caused by direct (i.e., the error distribution based on visual analysis of the frequency dis- gear damage) and indirect (i.e., intensive turtle herbivory, seagrass tribution of fish biomass, which showed clustering in space and reduction, reductions in fish biomass and catch) interactions with many zero values. GLMMs were fit using a maximum-likelihood turtles. We estimated losses to gear from interviews comparing estimation (MLE) procedure with Laplace approximation. Model (i) rates of damage/loss caused directly by turtles and (ii) the cost selection for each set of GLMMs was performed using the Akaike of purchasing a new net per fisher per year in Agatti and Kadmat. Information Criterion (AIC) and nested candidate models were These estimates were obtained in 2010, before turtle numbers in- compared using Likelihood Ratio Tests. All analyzes were per- creased in Kadmat and decreased in Agatti. We obtained estimates formed with the statistical programme R 2.15.0 (R Development of total monetary loss due to gear damage by multiplying individ- Core Team, 2012) using the ‘‘glmmADMB’’ package for GLMM anal- ual costs with the number of lagoon fishers for each island. To esti- ysis (Skaug et al., 2012). mate indirect cost we used published estimates of ‘resource flows’ as catch per unit effort (CPUE) for Agatti (Tamelander and Hoon, 2.3.2. Before–after comparison of turtles and seagrass variables in 2008), and replicated this methodology in Kadmat for comparable Agatti and Kadmat estimates: 16 fishers engaged in a participatory exercise recording To additionally test the overall effects of turtles on meadow and daily catch and effort from the lagoon over a 4-months period from fish parameters, we compared atoll-wide averages of turtle den- which we estimated CPUE of food fish species (Appendix S2 in Sup- sity, canopy height and food fish biomass (see Section 2.3.1 for de- porting information). We estimated the total monetary value of tails on the methods) between Agatti and Kadmat in 2010. In fish catch available based on local market rates (as of January addition, we investigated effects of a sudden increase in turtle den- 2011) of fish species in Agatti and Kadmat and multiplied average sities in Kadmat and a concomitant decline in Agatti that occurred CPUE at each island with the average number of fishing days ob- at the end of our study to confirm these trends in a before–after tained from interviews (200 days per year, Table 4). The difference framework. No other environmental variables (sedimentation, hu- between these estimates was used as a proxy of monetary oppor- man disturbance, etc.) had changed within this short period. We tunity costs borne due to indirect impacts of turtles on fish abun- repeated turtle density surveys at both atolls in 2011 (two surveys dance by fishers in Agatti. one in February and one in March), within a year of turtle densities increasing, and measured canopy height and food fish biomass (see Section 2.3.1 for details). We used a resampling approach to esti- 3. Results mate means and 95% confidence intervals for turtle density, sea- grass canopy height and fish biomass to avoid problems of 3.1. Documenting fisher perceptions pseudoreplication that could arise with estimates from our grid- based sampling of each lagoon (see Section 2.3.1 for details). To re- 3.1.1. Declines in fish catch duce possible non-independence effects, we used ‘Importance In both focus group sessions as well as individual fisher inter- Sampling’ (Efron and Tibshirani, 1993; Good, 2005), a weighted views conducted in Agatti and Kadmat, the overwhelming percep- Monte Carlo method, useful for subsampling datasets of rare tion was that fish catch had declined considerably in both lagoons. events whose means are often influenced by outlying values. In Agatti, diminishing catch was attributed to green turtles (74%, Importance Sampling performs well with a small number of sub- n = 48 respondents) or seagrass decline (associated with increasing sample runs (permutations), controls for inflated ‘effective sample turtle populations, 23% (n = 15) respondents). In contrast, less than size’ and reduces the degrees of freedom that multiple pseudo-rep- a fifth of respondents (n = 5) in Kadmat identified turtles as respon- licated points within a single sampling unit may cause (due to spa- sible for catch decline; the main factors identified instead were in- tial or other hierarchical effects). We calculated means and creases in fisher density and changes in gear use, along with other variances from the sub-samples generated with Importance Sam- factors such as oceanography or climate (current patterns, ocean pling, and calculated more reasonable confidence intervals rela- temperatures, see Table 2). R. Arthur et al. / Biological Conservation 167 (2013) 25–34 29
Table 2 based on whether they reduced catch directly or through indirect Causes of decline in lagoon fish catch identified by fishers in Agatti and Kadmat mechanisms (Table 3). Direct mechanisms identified were that tur- lagoons. Fishers in Agatti clearly perceived turtles as the major cause of catch decline, tles: (1) drive fish away from nets and (2) break nets and lines. Of while fishers from Kadmat ascribe the decline to other factors. the interviewed fishers in Agatti, 52% had their fishing gear either Recognized causes of Agatti (percent and Kadmat (percent and partially or irreparably damaged by turtles within the last year. declines in lagoon fish catch number of number of Fishers in Kadmat also identified these direct mechanisms as play- respondents) respondents) ing a role in reducing fish catch, but, for instance, while 70% of Green turtles/decline in 89.2 (n = 58) 20 (n = 6) respondents in Agatti mentioned gear breakage as a mechanism seagrass abundance Increased fisher density and 32.3 (n = 21) 83.3 (n = 26) of catch decline, less than 17% identified this as important in Kad- change in gear usage mat (Table 3). The indirect mechanisms identified were that green techniques turtles: (1) ‘overgraze’ seagrass meadows, (2) reduce adult fish Oceanographic and climatic 23 (n = 15) 16.7 (n = 5) usage by reducing seagrass biomass, and (3) reduce fish recruit- changes ment in seagrass meadows (Table 3). For the most part, these more complex indirect mechanisms were proposed largely by Agatti fishers (Table 3). 3.1.2. Conflict with green turtles A majority of fishers in Agatti perceived turtle numbers increas- 3.2. In-situ testing of indirect conflict ing (85%), while at Kadmat, no interviewed fishers perceived changes in turtle numbers. Fishers in Agatti first noted increased 3.2.1. Before–after comparison turtle numbers between 5 and 10 years ago (between 1995 and In 2010, turtle densities (resampled estimates) in Agatti were 2000). Conflict with turtles was a dominant and recurrent theme 2 on average 27.6 turtles kmÀ while at Kadmat densities were much in both focus group discussions and individual interviews in Agat- 2 lower (3.6 turtles kmÀ , Fig. 1). However, by 2011, densities at Kad- ti: nearly 90% (n = 58) of interviewed fishers related catch declines 2 mat increased nearly ten-fold (30.8 turtles kmÀ lagoon, Fig. 2), either directly or indirectly to increases in turtle densities (Table 2). 2 while at Agatti they reduced considerably (3.9 turtles kmÀ , A majority of fishers (64.6%, n = 42 respondents in Agatti) believed Fig. 2). Seagrass canopies reflected these differences and were al- that controlling turtle numbers was the only sustainable solution, most fivefold lower in Agatti compared with Kadmat in 2010, be- with around 55% (n = 36, in Agatti) suggesting managed culling or fore turtle numbers increased. In Kadmat, a few months after lifting turtle hunting bans as potential options. Among other solu- densities increased, there was a clearly visible reduction in canopy tions suggested by fishers in Agatti included more careful deploy- height (Fig. 2); in Agatti, after turtle numbers declined, there was a ment of nets (n = 5 respondents, 7.7%), restricting turtle movement small but noticeable increase in canopy height. Similarly, the bio- by fencing (2 respondents) and compensation for broken gear (1 mass of food fish species was several orders of magnitude higher respondent). A quarter of all 96 respondents across Agatti and Kad- in Kadmat with respect to Agatti in 2010. Fish biomass showed a mat (25%, n = 24) believed that there were no solutions to the con- major reduction in Kadmat in 2011 after turtles increased, while flict. Fishers mainly reported tearing and breaking of set nets by at Agatti increases in fish biomass was marginal after turtles de- turtles, with no reported bycatch or mortality due to entangle- clined here (Fig. 2). ment. In our own observations, we never documented turtle mor- tality due to nets or gear. Although difficult to quantify, we recorded occasional clandestine retaliatory killing of turtles princi- 3.2.2. Meadow and fish changes across a green turtle density gradient pally in Agatti, with only a few isolated records in Kadmat. Most Seagrass canopy height was negatively correlated with the pro- 1 1 commonly in Agatti we observed green turtles killed (decapitated, portion of biomass consumed by turtles (cm shootÀ dayÀ ); flippers sliced) on the shore and occasionally saw live turtles in the (Fig. 3a), although one site with very low canopy height but med- lagoon with broken harpoons embedded in their carapace. Fishers ium grazing intensity deviated from this trend. This site was sub- in Agatti also anonymously admitted to occasionally destroying ject to high levels of sedimentation from occasional dredging, turtle nests. potentially influencing canopy heights. Apart from this anomalous site, there was to be a clear negative relationship between turtle herbivory rates and canopy height. Total biomass density of sea- 3.1.3. Mechanisms of conflict grass-associated fish recruits (of Acanthurus auranticavus) was 1 In Agatti, fishers identified several mechanisms by which turtles about 12 times higher in Kadmat (148.4 g haÀ ± 1SE 60) than in purportedly reduced fish catch. We classified these mechanisms Agatti (12.92 ± 1SE 3.6), consistent across all meadows (Fig. 3b).
Table 3 Mechanisms of conflict with green turtles identified by fishers from the Agatti and Kadmat lagoons, Lakshadweep. These perceptions reflect the period in which turtles were present at high densities in Agatti, and were almost absent in Kadmat.
Perceived conflict mechanisms Agatti (percent and Kadmat (percent and number of respondents) number of respondents) Direct causes Driving fish away: green turtles create a disturbance around nets that scares fish away from nets, thereby 10.8 (n = 7) 3.3 (n = 1) reducing catch Breaks nets and lines: green turtles swim through nets and break fishing lines. This often happens when 70 (n = 45) 16.7 (n = 5) green turtles are startled from resting spots when gear are laid out Indirect causes Overgrazes seagrass: green turtles eat seagrass, and at high numbers, overgraze the meadow 40.0 (n = 26) 3.3 (n = 1) Reduce adult fish usage: adult fish from the coral reef are less inclined to enter the meadow because it is 35.4 (n = 23) 3.3 (n = 1) overgrazed Reduce fish recruitment in seagrass meadows: overgrazed meadows have lower fish recruitment and 40.0 (n = 26) 0 (n = 0) juvenile settlement in them 30 R. Arthur et al. / Biological Conservation 167 (2013) 25–34
and Likelihood-Ratio tests we found adequate support for the model with canopy height as a fixed effect (see Appendix S1 details of model selection). The random variation in biomass due to island and meadow effects across islands was negligible (random vari- ance term = 0.0001 ± SE 0.0002). Fish biomass (natural logarithm transformed) of both species increased linearly with seagrass can- opy height across meadows (Fig. 3c and d).
3.2.3. Natural herbivory exclosures In Agatti, seagrass canopy height was three times higher inside natural Acropora exclosures than at grazed locations within the same meadow, where most shoots (80%) had turtle grazing marks (ANOVA: F = 144.33; d.f. 1.54; p < 0.001; Fig. 4).
3.3. Economic valuation of losses in direct and indirect conflict
3.3.1. Direct costs of conflict Frequency of gear repairs per fisher by turtles was much higher in Agatti than in Kadmat, and the total cost of these losses per fish- 1 1 erman was higher in Agatti (nearly 0.6 USD fisherÀ yearÀ ) com- 1 1 pared with Kadmat (around 0.11 USD fisherÀ yearÀ , Table 4).
3.3.2. Indirect costs of conflicts Costs associated with catch decline were calculated with values of fish catch at both islands. CPUE was estimated to be almost four- fold greater in Kadmat than Agatti (Table 4). The average market price of food fish species reflects differences in effort, and was 55% higher in Agatti (Appendix S2). Despite this market offset, total annual harvest per fisher was nearly 2.5 times higher in value for fishers in Kadmat. A rough approximation of opportunity costs in 1 1 Agatti represented USD 887.28 fisherÀ yearÀ (Table 4).
4. Discussion
Fishers in both Agatti and Kadmat see declining catches as a major concern, but the agencies by which they construct this nar- rative are considerably different. While fishers in Kadmat, inter- viewed before turtles increased, attribute catch decline to a suite of factors including overfishing, in Agatti, the overwhelming per- ception was that this decline was caused by increases in green tur- tle densities. This perception was the basis of major conflict between turtles and fishers in Agatti, which was not observed in Kadmat. As perceived by fishers in Agatti, conflict arose through two qualitatively distinct pathways (Fig. 5). The first involved di- rect material costs and was based on quantifiable losses, associated largely with gear destruction and disturbance caused by turtles. Fig. 2. Estimates based on resampled values of (a) turtle density, (b) seagrass canopy height, and (c) fish biomass in Agatti 2010, Kadmat 2010 (before turtles We term these first order conflicts, since they arise from a clear, di- increased) and Kadmat 2011 (after turtles increased). Error bars represent standard rect interaction between turtles and fishers. More interestingly deviations. Resampling is based on an Importance Sampling (IS) procedure to derive however, many fishers also perceived conflicts that did not involve means and variances of these three variables, and associated 95% confidence directly measureable losses, which could, nevertheless, result in intervals are provided. significant declines in fish catch. Fishers invoked complex ecologi- cal interactions—intensive grazing of seagrass by turtles and its The positive relationship between recruit biomass and seagrass consequent impacts on food fish species - to support this percep- canopy height was weak but significant (log(recruit bio- tion. These mechanisms represent a more indirect interaction be- mass) = 0.259 canopy height 2.08, p = 0.013), even when we ac- tween fishers and turtles, which we term second-order conflicts à À counted for meadow-level random effects (random variance term (Fig. 5). These second order conflicts, though difficult to measure, 0.66 ± SE 0.34). This indicated both the influence of seagrass struc- may represent a much larger proportion of perceived and real ture as well as meadow-level random variation in recruitment. losses, and conflict management needs to engage more completely More importantly, the selected GLMMs showed that adult bio- with them for effective resolution. mass of food fish species (L. harak and P. barberinus) was influenced Local communities commonly generate propositions to explain mainly by seagrass canopy height (log(fish biomass) = 0.324 can- observed trends in natural resource distribution, forming the basis à opy height + 0.94, p < 0.001, AIC = 404.3). Other nested candidate of much traditional ecological knowledge (Berkes et al., 2000). GLMMs (with the additional covariates ‘‘total shoot density’’, ‘‘sea- These are seldom treated as valid inputs in the management of so- grass composition’’ and meadow-level random effects had higher cio-ecological systems. Our study shows that, when taken seri- AIC values than the chosen model (range: 407–415). Based on AICs ously, they can help identify important pathways that may R. Arthur et al. / Biological Conservation 167 (2013) 25–34 31
1 1 Fig. 3. (a) Reduction in seagrass canopy height (n = 50 each) with increase in proportion of herbivory (cm shootÀ dÀ ) of total seagrass production, as estimated from herbivory assays (n = 10 each) along six seagrass meadows, (b) differences in biomass of fish recruits across Kadmat and Agatti seagrass meadows, (c) biomass of Lethrinus harak, and (d) biomass of Parupeneus barberinus; both from fish transects (n = 30 each) along the gradient of seagrass canopy heights. Error bars represent standard deviations. otherwise be ignored. Resident green turtle populations reached remarkable increases in turtle populations are, most likely, the re- 2 high densities in the Agatti lagoon (nearly 27 turtles kmÀ lagoon), sult of decades of effective conservation efforts including protec- reflecting a trend documented in several other locations over the tion of nesting beaches, hatchery programmes and bycatch last two decades (Bourjea et al., 2007; Lauret-Stepler et al., 2007; reduction initiatives. A recent analysis of satellite tracking data Ballorain et al., 2010; Christianen et al., 2012). At these densities showed that green turtles may be responding directly to these the resultant grazing offtake can often exceed seagrass production measures, aggregating in significantly higher numbers at marine capacity, as our on-going research suggests (Lal et al., 2010). These protected areas (MPAs) across ocean basins (Scott et al., 2012). These trends have led researchers to re-examine if green turtles can still be considered globally endangered (Broderick et al., 2006). Although the Lakshadweep does not have MPAs, green tur- tles are strictly protected under Indian law, matched with con- certed efforts by local management authorities to curb
Table 4 Evaluating the costs of direct and indirect conflict to fishers in Agatti and Kadmat. (A) Cost of direct conflict: economic losses incurred by fishers due to breakage of gear by turtles. (B) Estimates of costs of indirect conflict: catch per unit effort (CPUE) and value of offtake by fishers in Agatti and Kadmat lagoons per year (effective fishing time per year = 200 days). For details on CPUE, see Supplementary information.
Attributes Agatti Kadmat A. Cost of direct conflict Percent respondents who suffered gear losses to turtles 70 16.7 in the previous year (n = 45) (n = 5) 1 1 Cost of gear repair (USD fisherÀ yearÀ ) 0.6 0.11 B. Estimated cost of indirect conflict 1 1 Catch per unit effort (kg fisherÀ dayÀ ) 1.66 6.27 1 Fig. 4. Seagrass canopy height in the presence (outside exclosure) and absence Average market rates (USD kgÀ ) 1.86 1.20 1 1 (inside exclosure) of green turtle herbivory in Agatti atoll, Lakshadweep, India. Error Total value of fish offtake (USD fisherÀ yearÀ ) 617.52 1504.8 bars represent standard deviations (n = 20). 32 R. Arthur et al. / Biological Conservation 167 (2013) 25–34
Fig. 5. Schematic diagram representing the nature of direct and indirect conflict pathways between fishers and green turtles in the Lakshadweep Islands, India. persecution of nesting females, hatchlings and foraging adults or process in reverse; after grazing pressure had reduced, canopies juveniles. and food fish numbers showed mild increases, indicating that the Whether these current densities are merely an anomaly or rep- recovery of these systems subject to sustained herbivory may re- resent a promising trend towards a more pristine past is difficult to quire significantly longer after its cessation. Our findings add to say in the absence of adequate baselines from this area. Our inter- growing evidence that fish communities can be heavily influenced views with even the oldest fishers in Agatti indicate that they have by canopy height and shoot density in seagrass meadows (Hori never encountered turtles at these densities in their lifetime, and et al., 2009; Unsworth et al., 2007). More interestingly, our results survey efforts from the 1970s (Bhaskar, 1978) confirm that these clearly support patterns perceived by lagoon fishers in Agatti and lagoons were not a major rookery or foraging ground for green tur- represent an indirect pathway important enough to result in major tles in the recent past. Current numbers in the Lakshadweep do not conflicts. In the absence of adequate historical baselines we cannot approach historical estimates from the Caribbean and other loca- speculate if, in the past, fishers may have adapted their targets to tions (Jackson, 2001), but given the limited extent of seagrass fish species less dependent on seagrass meadows when turtle den- meadows within the archipelago’s shallow lagoons it is unclear if sities increased in these lagoons. It is also clear that many other this region could have supported significantly higher densities un- factors currently impact fish populations in these meadows, not less past meadows were much more extensive than they are right least the increasing populations of fishers themselves. Regardless now. The present increase is likely linked, at least in part, to regio- of these other potential drivers, in the perceptions of Agatti fishers, nal declines in top predators like tiger sharks (Heithaus et al., the green turtle is the principal actor around which their narrative 2008). Regardless of these uncertainties, the current conflict has of conflict is built and our results indicate that the mechanisms clearly been triggered by a more near-historical shift in turtle den- they identify have considerable validity. sities in the last few decades. Distinguishing first and second-order interactions may help One of the clearest influences of high turtle densities was in- better understand the many-dimensioned experience of lived con- creased herbivory in Agatti resulting in a marked reduction in sea- flict between humans and wild species. First-order conflicts arise grass canopy height compared with Kadmat, where turtle densities when animals directly utilize resources valued by humans, for in- were historically low (see also Lal et al., 2010). This trend was con- stance crop-raiding, livestock depredation (Sillero-Zubiri et al., firmed by comparisons between the natural exclosures in Agatti: 2007; Treves and Karanth, 2003) or through direct competition protected from herbivory, seagrass canopies inside the exclusion with fishers (e.g., Fanshawe et al., 2003). Resource conflicts aside, grew to lengths substantially higher than in grazed plots. This direct conflict may have significant and often devastating conse- reduction in canopy height was also observed across the turtle her- quences for human life and livelihoods (Thirgood et al., 2005). bivory gradient and was, in turn, correlated with considerable First-order conflicts stem from visible evidence, with direct and reduction in biomass of important food fish species and with re- unambiguous actions of wild species resulting in losses to humans, duced fish recruit biomass. Meadow-level differences were negligi- and losses to wildlife by human retaliation. There is clear identifi- ble compared with the negative effects of reduced canopy height cation of and antagonism towards the agent of conflict (wild ani- on fish biomass. A powerful confirmation of these trends was that mals). This makes first-order conflicts relatively easy to quantify, less than a year after turtle numbers increasing in Kadmat (in providing a crucial first step towards developing resolution strate- 2011), canopies reduced substantially and food fish species de- gies. In Agatti, several fishers held turtles directly responsible for clined significantly, most likely driven by increased turtle foraging. scaring fish away from nets and breaking gear, both first-order Although a similar ‘control survey’ in Agatti was not possible, the interactions that could result in significant costs (Fig. 5). Gear dam- concomitant decline in turtles in 2011 allowed us to document this age was an important source of conflict in Agatti, affecting c.70% of R. Arthur et al. / Biological Conservation 167 (2013) 25–34 33
fishers. Although the cost of repairing a net was relatively low (Ta- meadows may require managers to assist fishers in adapting to ble 4), there were other opportunity costs associated with gear loss changing turtle densities by shifting fisheries targets to non-sea- that we have not quantified, but could represent significant direct grass species (shoaling, sand-loving fish such as Gerres or Trachino- losses for fishers. Because they are the most visible manifestations tus spp. for instance) for as long as meadows are exposed to high of conflict, most conflict resolution initiatives focus on these first- turtle grazing. This will require a collaborative approach towards order pathways with compensatory or insurance schemes for conflict management, acknowledging fishers as important stake- material losses (Dickman et al., 2011; Thirgood et al., 2005; Treves holders in conservation with genuine ecological insights that could and Karanth, 2003). Our results suggest that the limited success of inform management efforts. these efforts is because first-order mechanisms often represent only a small fraction of the costs borne by communities for sharing 5. Conclusions spaces and resources with wild species. In contrast, second-order conflicts may not result in direct Our results contribute to explaining why attempts at resolving physical harm to humans, nor do they involve direct competition human–wildlife conflict with compensatory or insurance schemes over shared resources. We define second-order conflict as arising are often ineffective (Gore et al., 2008; Thirgood et al., 2005; Web- when the species in question modifies a resource of no direct value ber et al., 2007). Offsetting direct losses is considered the instru- to people but whose modification results in the measurable loss of ment of choice in resolving conflict, yet these may represent a another resource that is directly valued. Because these conflicts do small fraction of true costs incurred by communities living at the not lend themselves to easy quantification, they are potentially human–wildlife interface (Dickman et al., 2011). While these lar- more difficult to identify, evaluate and resolve. Estimating their ger losses may be more difficult to quantify, they are often re- economic cost is not straightforward since it involves determining flected in community perceptions and responses. While it is opportunity costs of complex ecological pathways. Our first important to tease apart the interweaving skeins of bias, culture, approximation of these costs for the Lakshadweep is admittedly economics and ecology that together shape perceptions (Dickman, coarse, but enables a relative evaluation of the potential hidden 2010), they can serve as valid inputs in the understanding of the costs of second-order conflict (Table 4). The relatively minor losses human–wildlife interface. Engaging with these perceptions is a to fishing gear cannot explain the apparently disproportionate con- useful gateway to understanding the intensity and drivers underly- flict in Agatti with clandestine killing of turtles and regular ing second-order conflict. Managing this interface may involve destruction of nests. Comparing catches between Agatti and Kad- adjusting compensatory schemes to account for indirect costs, mat helps place the perception of losses incurred to turtles in con- designing outreach programmes to explicitly address the fishing text. Kadmat and Agatti (in 2010, before turtles numbers changed community’s concerns and, where possible, managing the underly- at these atolls) showed major differences in catches, fish prices, ing ecological pathways to improve livelihoods. The green turtle and the per-capita value of lagoon fishing. With fish offtake values example represents an encouraging reminder that given the right from Kadmat as a baseline, a naïve estimate of lost opportunity kind of concerted conservation efforts, species can recover from costs for fishers in Agatti amounts to as much as USD 1 1 serious endangerment (Broderick et al., 2006; Scott et al., 2012), 887.28 fisherÀ yearÀ (see Table 4), assuming 200 fishing days and it would be unfortunate to surrender these gains by alienating per year. This represents the best first-approximation of the cost the human constituencies whose livelihoods they may directly af- of second-order conflict to Agatti fishers, several orders of magni- fect. Local communities often bear a disproportionate burden for tude higher than directly-incurred losses. These trends would conservation, yet may be the most important constituency in likely change after the recent increases in turtle densities in Kad- ensuring its effectiveness. Acknowledging that complex pathways mat and it would be interesting to test if our documented declines often drive discord in conservation hotspots will help us move to- in meadow structure and economically important fishes generate wards a less fraught coexistence. first- and/or second-order conflict in the coming years. Managing this fisher-turtle interface in face of such vocal con- flict is a complex challenge. It is clear that, left to themselves, fish- Acknowledgments ing communities in Agatti would resort to actively culling turtles and destroying nests – this was the overwhelming response of We thank the community of Agatti and Kadmat Islands, fishers, interviewed fishers when asked for potential solutions. However, Panchayat leaders and village officials for giving generously of their the Lakshadweep Archipelago is one of a few areas where green time. We would also like to thank the Lakshadweep Administration turtle numbers are currently high and may represent a globally for supporting our work. The LCRMN team helped in the interview important turtle conservation hotspot which local environmental surveys and R. Raghunath helped with GIS analysis. The manu- authorities are mandated to protect. It could be argued that this script benefited greatly from discussions with G. Inglis, J. Pages, conflict may be self-limiting as turtles move to other atolls after K. Shanker, C. Mishra and N. Marbà. This work was supported by seagrass resources decline (as they likely did in 2011), but are the Ford Foundation, Rufford Small Grants Programme and Norwe- likely to carry conflict with them to these new pastures. In addi- gian Institute for Nature Research (NINA). T.A. was partially funded tion, while the reduction of turtles will significantly reduce first- by the Project CTM2010-22273-C02 (Plan Nacional I + D + I, Spain). order conflict, the effects of second-order conflict are likely to linger until meadow function and fish numbers recover from sus- Appendix A. Supplementary material tained grazing. Compensating for these losses needs to account for the considerable opportunity costs associated with these eco- Supplementary data associated with this article can be found, in logical pathways. At present, fisheries authorities in the Lakshad- the online version, at http://dx.doi.org/10.1016/j.biocon.2013. weep are conceiving compensation schemes to mitigate direct 07.014. material losses to conflict. Our results suggest that these efforts would be much more effective if directed towards habitat conser- vation measures for seagrass meadows; controlling other anthro- References pogenic stresses (dredging, sedimentation, pollution, etc.) that Ballorain, K., Ciccione, S., Bourjea, J., Grizel, H., Enstipp, M., Georges, J.Y., 2010. may negatively affect meadow function and reduce fish abun- Habitat use of a multispecific seagrass meadow by green turtles Chelonia mydas dance. An understanding of the complex roots of conflict in these at Mayotte Island. Mar. Biol. 157, 2581–2590. 34 R. Arthur et al. / Biological Conservation 167 (2013) 25–34
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