Papua New Guinea comprises the eastern part of the island of New Guinea and numerous smaller islands in the southwestern Pacific region. Domestic and international tourism greatly expanded at coastal destinations in PNG prior to the COVID-19 pandemic (PNGTPA, 2020; Militz et al., 2021). The influx of tourists brought demand for a new range of goods and services, presenting coastal communities with novel income generating opportunities (IFC, 2016). An unmet demand for souvenirs (IFC, 2016) coupled with a loss of critical income sources, such as bêche-de-mer fisheries (Purdy et al., 2017), appears to have catalyzed local expansion of shellcraft (Simard et al., 2019; Militz et al., 2021). This is particularly true among the Tigak Islands of New Ireland Province where households rely on marine resources for subsistence and income (Kaly et al., 2005; Purdy et al., 2017). Over a span of twenty years, participation in shellcraft among the Tigak Islands expanded from a single household to become an income source supporting at least 6% of residents by 2017 (Simard et al., 2019). The shellcraft sector of the Tigak Islands is now well-established and presents a unique opportunity to evaluate utilization of marine taxa for this increasingly important livelihood activity. With resumption of international tourism to PNG now underway (PNGTPA, 2022), such information comes at an opportune time to provide a basis for future development plans supporting sustainability within this sector.

Past research on the shellcraft sector of the Tigak Islands (Simard et al., 2019) found that artisans concentrated at the Nusa Islands. We conducted a survey at these islands in July 2019 to identify households producing shellcrafts. Households with at least one member that had routinely produced shellcrafts during the previous year were asked to participate in an interview. No household refused participation, and all households (n = 36) that met the inclusion criteria were interviewed.

Interviews were conducted verbally in either English or Tok Pisin, depending on the preference of the participants, and followed a semi-structured format with a questionnaire to guide the interview. Participants were asked to identify all marine taxa their household utilized in the production of shellcrafts. Since it was unreasonable to expect participants to identify taxa by internationally recognized (i.e., scientific) names (Moesinger, 2018), taxa were identified to the lowest taxonomic rank possible using a photographic reference guide and voucher specimens. Nomenclature was based on the World Register of Marine Species (Horton et al., 2022). For each taxon identified, participants were asked to indicate the quantity utilized during the previous year. Additionally, participants were asked to list all locations from where they had obtained (either purchased, traded, or fished) each taxon identified and, if obtained through their own fishing activities, to identify source habitat(s).

Where identified taxa were phenotypically and functionally (as a material) similar, participants were unable to provide species-specific information. Instead, information was provided for a group of taxa. This applied to the black corals Antipathes spp. and Cirrhipathes spp. (hereafter Antipathidae), the cowries Monetaria annulus and Monetaria moneta (hereafter Monetaria annulus/moneta), the nautilus Allonautilus scrobiculatus and Nautilus pompilius (hereafter Nautilidae), and the sea turtles Chelonia mydas and Eretmochelys imbricata (hereafter Cheloniidae). We considered each group as a ‘taxon’ in our study to accommodate the integration of local and traditional knowledge systems with contemporary fisheries science (Moesinger, 2018).

For each taxon utilized, information obtained from interviews was supplemented with biological data gleaned from SeaLifeBase (Palomares and Pauly, 2020). Specifically, ‘common length’ was used as an indicator of the typical size of a given taxon. In cases where data were not available, an appropriate metric of size (antero-posterior measurement, dorso-ventral measurement, carapace width, or colony height, depending on the taxon) was measured from a voucher specimen using either a vernier caliper (for taxa ≤ 15 cm) or measuring tape (for taxa > 15 cm).

Varying systems of measurement were used by participants to indicate the quantities of taxa utilized during the previous year. Quantities were reported as the number of individuals, ‘bottles’, or pieces of a taxon utilized on a weekly, monthly, or annual basis. As these measures were not directly comparable, quantities were standardized as the number of individuals utilized annually. For some measures (i.e., bottles and pieces), this required establishing appropriate conversion factors.

Quantities reported in terms of ‘bottles’ refers to a local practice of storing and trading smaller taxa in 330 mL glass bottles ( Figure 1 ). To establish an appropriate conversion factor for each of the 20 taxa quantified in this manner, the number of individuals within a representative bottle was determined. An appropriate conversion factor was then applied to express the quantity of individuals utilized annually.

Quantities of sea turtles (Cheloniidae), reef sharks (Carcharhinus melanopterus), and black corals (Antipathidae) were commonly reported in terms of taxon-specific pieces. For sea turtles, participants reported the number of carapace scutes utilized ( Figure 1 ), which is a typical measure of sea turtle utilization for shellcraft (Kinch and Burgess, 2009). Since Chelonia mydas and Eretmochelys imbricata were the only sea turtles identified by participants, a conversion factor of 13 scutes to one carapace (i.e., individual) was adopted (Wyneken, 2001). For reef sharks, participants reported the cumulative length, in centimeters, of cartilaginous vertebrae utilized. Since only vertebrae of immature sharks were reportedly utilized, a conversion factor of 42.5 cm to one individual was adopted (White et al., 2017). For black corals, participants reported the cumulative length, in centimeters, of branches utilized. A conversion factor of 100 cm to one individual was adopted, representing a typical Cirrhipathes spp. colony (pers. obs.).

Source habitats were standardized broadly as intertidal benthic, subtidal benthic, or subtidal pelagic. The local ecological knowledge of participants, however, permitted further differentiation of intertidal benthic habitats based on substrates that the taxon was associated with, and a distinction was made between hard substrates (i.e., rock, wood, or sedimentary hardgrounds) and soft substrates (i.e., unconsolidated sediments).

In addition to source habitats, it was also necessary to standardize locations that were identified using vernacular place names. Coordinates from the World Geodetic System 1984 (WGS84) were attributed to all referenced locations from where taxa were obtained. Where the referenced location was not discrete but referred to an island or region, the center of referenced area was used when attributing coordinates.

All statistical computing was performed using R programming (version: 4.1.3), with the stats (R Core Team, 2021), geosphere (Hijmans, 2021), corrplot (Wei and Simko, 2021), and vegan (Oksanen et al., 2020) packages. For all analyses, statistical significance was accepted as P< 0.05 and summaries of data are presented in-text as the mean ± standard deviation.

Diversity, in terms of composition and quantities of taxa utilized, was further represented by two compound indices: Shannon-Wiener index (H′) and Simpson’s index (D). The Shannon-Wiener index was calculated as

where p_i is the proportional quantity of taxon i that was utilized for shellcraft (function: diversity). Simpson’s index was calculated as

where N is the total quantity of all taxa utilized and n is the quantity of taxon i that was utilized for shellcraft (function: diversity). These indices were calculated to express diversity within the shellcraft sector (based on simple-pooling of data from all households) and among artisan households (based on data from each household), the latter being summarized by measures of central tendency and variation (mean ± standard deviation and range). Additionally, multivariate statistics were used to investigate whether composition and quantities utilized differed among artisan households. Specifically, non-metric multidimensional scaling (nMDS) was used to visualize differences in the probability that households utilized a non-identical composition of taxa, based on a Raup-Crick dissimilarity matrix, and to visualize differences in the quantities of taxa utilized, based on a Bray-Curtis dissimilarity matrix (function: metaMDS). A taxa-accumulation curve was also constructed from random permutations of the data to estimate the proportional composition of taxa that were utilized by a random sample of artisan households (function: specaccum).

To examine whether both the composition and quantities of taxa originating from the four source habitats differed, χ²-tests with Yates’ continuity correction were used (function: prop.test). Since the broadly defined source habitats led to an absence of variation in the number of habitats from which a taxon was obtained, this metric was excluded from further analyses describing utilization. In contrast, metrics representing the geographic scale of exploitation (i.e., the number and distance [based on Haversine distances; function: distHaversine] of locations from which a taxon was obtained) had sufficient variation to merit further analysis.

To examine the relational structure among metrics representing various aspects of utilization, a correlation matrix was constructed comparing the number of households utilizing each taxon, the quantity of each taxon utilized, the typical size of each taxon, the number of locations from where each taxon was obtained, and the furthest location from where each taxon was obtained. Kendall’s correlation tests (function: cor.mtest) were used to construct the correlation matrix, controlling for the false discovery rate with the Benjamini and Hochberg (1995) procedure.

Research activities associated with this study were reviewed and approved by University of the Sunshine Coast’s Human Research Ethics Committee (approval number: S191337). Authorization to conduct research activities in PNG was obtained through a Memorandum of Subsidiary Agreement (approval number: FIS/2014/060) between the Australian Centre for International Agricultural Research and the PNG National Fisheries Authority. Permissions to engage with residents of the Nusa Islands were obtained from elected and traditional community leaders prior to obtaining informed consent from households for their participation in this study.

Seventy-three marine taxa from seven classes were utilized within the shellcraft sector of the Tigak Islands ( Figure 2 ). The majority (93.2%) of taxa utilized were mollusks of either class Gastropoda (83.6%), represented by 37 genera, or class Bivalvia (9.6%), represented by four genera. All taxa representing these classes are presented in Figure 2 and Table S1 . Each of the other classes were represented by only a single taxon: for Cephalopoda this was Nautilidae, for Chondrichthyes this was Carcharhinus melanopterus, for Hexacorallia this was Antipathidae, for Malacostraca this was Carpilus maculatus, and for Reptilia this was Cheloniidae.

Annual utilization within the sector was close to 500,000 individuals ( Table 1 ). Gastropoda was the most utilized class (98.7%), followed by Bivalvia (1.0%). Critically, most (90.4%) of the 73 taxa accounted for less than 1.0% of individuals, while a single gastropod, Chrysostoma paradoxum, accounted for 78.5% of all individuals utilized ( Figure 2 ). By comparison, the next most utilized taxa, Euplica scripta, which is also a gastropod, accounted for only 3.0% of all individuals utilized. Among the other classes, the most utilized bivalve was Pinctada margaritifera of which 1,090 individuals (0.2%) were utilized, while 899 (0.2%) Nautilidae, 97 (< 0.1%) Antipathidae, 55 (< 0.1%) Cheloniidae, and 40 (< 0.1%) Carpilus maculatus individuals were utilized ( Figure 2 ). Additional data, pertaining to the quantity of each taxon utilized within the shellcraft sector, are presented in Table S1 .

When considering both the composition and quantities of taxa utilized, a Shannon-Wiener index (H′) of 1.23 and a Simpson’s index (D) of 0.38 was calculated for the shellcraft sector of the Tigak Islands. Excluding Chrysostoma paradoxum, however, showed a more even utilization (H′ = 3.27; D = 0.94) of the remaining taxa.

Composition of taxa utilized for shellcraft varied among artisan households ( Figure 3 ), with 19.1 ± 10.6 (range: 3 – 56) taxa utilized per household. No household utilized the full composition of taxa within the sector (n = 73), and only two of the 36 households (5.6%) utilized more than half (n ≥ 37). The taxa-accumulation curve ( Figure 4 ) shows that with a random sample of 10 (27.7%) households, an estimated 80.3 ± 12.2% of taxa within the sector would be represented, whereas a sample of half the households would represent 92.0 ± 7.3% of taxa. No taxon, or class of taxa, was utilized by all households, with an average of 10.0 ± 9.0 (range: 1 – 33) households utilizing a given taxon ( Table 1 and Figure 2 ). The number of households utilizing each taxon is presented in Table S1 , while the composition of taxa utilized by each household is presented in Table S2 .

Quantities of taxa utilized annually for shellcraft also varied among households, in both absolute and relative terms ( Figure 3 ). A combined 12,744.1 ± 9,289.7 (range: 36 – 31,229) individuals were utilized per household, with taxon-specific utilization spanning from 9,999.3 ± 9,465.6 (range: 0 – 29,400) individuals per household for Chrysostoma paradoxum down to 0.1 ± 0.3 (range: 0 – 2) individuals per household for Ovula ovum. The combined quantity of taxa utilized by each household is presented in Table S2 , while taxon-specific quantities utilized by each household are summarized in Table S1 as the mean ± standard deviation of all households.

A Shannon-Wiener index (H′) of 1.09 ± 0.71 (range: 0.17 – 2.57) and a Simpson’s index (D) of 0.43 ± 0.27 (range: 0.06 – 0.88) represented the composition and quantities of taxa utilized among households. Additional data, pertaining to the H′ and D indices for each household, are presented in Table S2 .

Each taxon was attributed to only one of the four broadly defined source habitats, amongst which the composition of taxa differed significantly (χ ² = 68.4, P< 0.001; Figure 5 ). Intertidal benthic habitats accounted for 91.8% of all taxa, with a similar number of taxa being sourced from hard (n = 35) and soft (n = 32) substrates (χ ²< 0.01, P = 1.0). By comparison, subtidal habitats accounted for only 8.2% of taxa, with the number of taxa sourced from benthic substrates (n = 4) similar to those sourced from the water column (i.e., pelagic; n = 2; χ ² = 0.17, P = 0.68). Notably, gastropods and bivalves were sourced from all benthic habitats. Data pertaining to the source habitat for each taxon are presented in Table S1 .

In terms of quantity, the vast majority (91.4%) of all individuals (n = 458,788) utilized were sourced from intertidal benthic hard substrates ( Figure 5 ). Far fewer individuals were sourced from intertidal benthic soft substrates (8.1%), subtidal benthic (0.4%), or subtidal pelagic (< 0.1%) habitats (χ ² = 1.45×10⁶, P< 0.001).

Taxa were obtained from at least 34 unique locations across three provinces: New Ireland, Manus, and East New Britain ( Figure 6 ). The number of locations from which a given taxon was obtained ranged from one to thirteen (2.3 ± 2.1). Most taxa (94.5%) were obtained from the Nusa Islands and 54.8% of taxa were only obtained from the Nusa Islands. Less than half (45.2%) were obtained from 33 other locations that were, on average, 55.5 ± 84.5 km from the Nusa Islands. Three taxa (Nautilidae, Oliva irisans and Pinctada margaritifera) were obtained from interprovincial locations (Manus and East New Britain) and five taxa (Antipathidae, Cheloniidae, Nautilidae, Pinctada maxima, and Pteria penguin) were obtained from intraprovincial locations (Mussau and Tingwon Islands) more than 100 km from the Nusa Islands, but all locations were within a 500 km radius of the Nusa Islands. Table S1 summarizes the number of locations, distance of furthest location, and the mean ± standard deviation of distances for all locations from which each taxon was obtained.

There were eight significant associations among the metrics selected to represent aspects of taxa utilization within the shellcraft sector of the Tigak Islands ( Figure 7 ). The strongest association (τ_b = 0.74, P< 0.001) occurred between the number of locations and furthest location from which a taxon was obtained, such that taxa obtained from more locations were likely to be obtained further from the Nusa Islands. Taxa utilized by a greater number of artisan households were also likely to be obtained at increasing distances from the Nusa Islands (τ_b = 0.44, P< 0.001), as were taxa utilized in greater quantities (τ_b = 0.36, P< 0.001). The number of locations from which a taxon was obtained was positively associated with the number the artisans utilizing it (τ_b = 0.56, P< 0.001), but unrelated to the quantities utilized (τ_b = 0.14, P = 0.13).

The typical size of a taxon ( Table S1 ), which ranged from 1.0 cm (Engina bonasia and Engina mundula) to 100.0 cm (Antipathidae), had a significant positive association with the number of households (τ_b = 0.19, P< 0.05) and number of locations (τ_b = 0.23, P< 0.05) suggesting that larger taxa were utilized by a greater number of artisan households and obtained from a greater number of locations than smaller taxa ( Figure 7 ). Despite this, typical size had a significant negative association with quantities utilized (τ_b = -0.27, P< 0.01) suggesting that larger taxa were used in lower quantities than smaller taxa ( Figure 7 ).

An absence of information pertaining to taxa utilized within shellcraft sectors, particularly those reliant on artisanal fisheries (Kailola, 1995; Wood and Wells, 1995; Dias et al., 2011), begets value in discussing how the approach taken in our study can be adapted for monitoring shellcraft sectors more broadly. Past studies with a single-species (Kinch and Burgess, 2009) or socio-economic focus (Simard et al., 2019) greatly understated the composition of taxa utilized within the shellcraft sector of the Tigak Islands. Thus, dedicated study on fisheries-dependent shellcraft sectors seems necessary to canvass diversity in its entirety.

Interviewing artisan households was an effective approach to obtaining information on the diversity of taxa utilized within the shellcraft sector of the Tigak Islands as it overcame challenges of geographic scale. Interviewing fishers directly, as opposed to artisan households, would have required a far greater investment in terms of both the number of interviews required and geographic scale over which interviews were conducted. Artisan households obtained taxa from more than 30 locations, up to 417 km away, indicating a dispersal of fishing effort, with monitoring further complicated by the fact that multiple fishers at each location may supply these taxa. A dispersal of fishing effort around a central hub of artisanal activity (either production or sales) is a common aspect of shellcraft sectors as, for example, artisans in Tuvalu, the Philippines, and Indonesia have been reported to source marine taxa from as far as 100, 400, and 500 km away, respectively (Tiraa-Passfield, 1996; Floren, 2003; Nijman et al., 2015). Identifying and targeting these hubs of activity is a recommended approach for monitoring the diversity of taxa utilized within shellcraft sectors, where fishing is potentially extended over a broad geographic scale and across a range of habitats.

Whilst artisan households among the Tigak Islands were highly concentrated, facilitating interviews, this may not be the case with other sectors. Our results suggest that a large proportional composition of taxa utilized can be identified even without sampling all households. Randomly sampling a quarter of households (n = 9) was predicted to identify around 80% of the composition utilized within the sector, which increased to 90% when involving half the households (n = 18). Given the positive association between the number of households utilizing a particular taxon and the quantity utilized within the sector, a subset of all households should help identify the more heavily exploited taxa in addition to those utilized by a large proportion of artisans. Thus, a reasonable account of both composition and relative quantities at which taxa are utilized is likely to be obtained even if not all participants within a sector can be interviewed.

Tourism is widely perceived as a central element of development among island nations of the Indo-Pacific (Connell and Rugendyke, 2008; Connell, 2018) and, through the purchase of souvenirs, tourism and shellcraft sectors are intrinsically linked (Chand et al., 2014; Militz et al., 2021). Prior to the COVID-19 pandemic, tourism expanded rapidly throughout the Indo-Pacific (UNWTO, 2022a). At many coastal destinations, including Madagascar (Gibbons and Remaneva, 2011), Fiji (Chand et al., 2014), and Brazil (Dias et al., 2011), growth in tourism coincided with increasing demand for shellcrafts and, in the case of PNG, local expansion of shellcraft (Simard et al., 2019). Detrimental impacts, such as overfishing of utilized taxa, could arise from such expansion (e.g., Dias et al, 2011). The cessation of tourism attributed to COVID-19 (UNWTO, 2022b) has allowed critical reconsideration of tourism-related development and provides opportunities to accelerate transformation towards more sustainable approaches (Connell, 2018; Gössling et al., 2020). Such opportunities could include implementing community-based resource management, expanding marine aquaculture activities, and strengthening existing governance as part of future development plans supporting greater sustainability within shellcraft sectors.

Within PNG, the existing top-down governance framework for managing fisheries is unlikely to sufficiently mitigate overexploitation of most taxa utilized within shellcraft sectors. Attempts to match resource extraction with productivity through a combination of government-imposed output and technical control measures have a high failure rate at a community level (Wilson et al., 1994) and are largely impractical for shellcraft sectors given the broad composition of taxa for which limited biological data are available (Kailola, 1995; Dias et al., 2011). Whilst existing regulations prevent harvesting ‘sedentary’ taxa (viz. 93.2% of taxa utilized) at night with aid of a torch and establish size restrictions for some species (Pinctada margaritifera Pinctada maxima, Rochia nilotica, and Turbo marmoratus), national and provincial governments often lack adequate funding and personnel for enforcement at a community level (Govan, 2015). Given such challenges, an alternative management framework, such as community-based, centrally governed, and co-managed marine protected areas (MPAs) (Smallhorn-West et al., 2019), are more likely to yield positive ecological and socio-economic impacts within shellcraft sectors. While poaching aggression and a lack of compliance have limited the effectiveness of MPAs for high-value taxa in PNG (Hair et al., 2020), most of the taxa utilized for shellcraft have negligible value as an unworked resource (Kailola, 1995). No-take MPAs appear particularly well-suited for shellcraft sectors, because most positive ecological impacts are associated with rapid recovery of benthic invertebrates following reduced fishing efforts (Thaman et al., 2017; Smallhorn-West et al., 2019). Targeting intertidal and subtidal benthic habitats, specifically, during MPA establishment would best ensure recovery of a large proportion of taxa utilized by artisans.

In addition to community-based resource management, an expansion of aquaculture activities could offer a renewable source of shell material while simultaneously creating additional income-generating opportunities. Several nations, such Fiji, Tanzania, and Tonga, already benefit from community-based farming of pearl oysters to provide a sustainable supply of shell and opportunity for additional income through pearl culture (Southgate et al., 2006; Jiddawi, 2008; Fröcklin et al., 2018; Johnston et al., 2019; Southgate et al., 2019; Saucedo et al., 2022). Whilst similar developments existed in PNG (George, 1978), production has greatly diminished in recent years (Simard et al., 2022) with current operations of marginal relevance to shellcraft sectors. For example, current operations are limited to the production of Pinctada maxima in Milne Bay Province (IPA 2021), to which the shellcraft sector of the Tigak Islands had no direct links ( Figure 6 ). Establishing linkage between shellcraft sectors and existing aquaculture operations should be seen as a priority given that shellcraft can generate 5-10 times more income than the export of unprocessed shell (Friedman et al., 2008; Simard et al., 2019). Beyond this, reinvigorating community-based aquaculture in areas presently producing shellcrafts should be considered, given the apparent importance of pearl oysters within shellcraft sectors (Simard et al., 2019).

Studies have shown that marine taxa threatened with overexploitation, such as Antipathidae, Cheloniidae, and Nautilidae, are heavily trafficked as curios and shellcrafts (Nijman et al., 2015; Nijman and Lee, 2016; Nijman, 2019). Our study found all these taxa utilized within the shellcraft sector of the Tigak Islands. Papua New Guinea, as a Party to the Convention on International Trade in Endangered Species (CITES) since 1976, has acknowledged that international cooperation is essential for the protection of these taxa and is committed to ensuring their utilization is compatible with their survival. Under CITES regulations, transport of shellcrafts comprised of Antipathidae, Cheloniidae, or Nautilidae out of PNG requires a government-issued export permit. Despite this, such regulations have a history of being minimally promoted or policed, as evident from items containing Eretmochelys imbricata being offered for sale within Jackson’s International Airport in Port Moresby (Kinch and Burgess, 2009). Current quantities of Antipathidae, Cheloniidae, and Nautilidae leaving PNG as shellcrafts are unclear, although conservative estimates can be made by examining their utilization within shellcraft sectors. In our study, an estimated 899 shells of Nautilidae, 55 carapaces of Cheloniidae, and 97 colonies of Antipathidae were utilized annually. For Nautilidae, current utilization represents no imminent threat to their survival as the shellcraft sector of the Tigak Islands exclusively utilized drift shells collected from intertidal benthic habitats (Kailola, 1995; Simard et al., 2019). Similarly, with Cheloniidae, scutes and carapaces used in shellcraft are mainly obtained from subsistence or opportunistic catches (Kinch and Burgess, 2009) with the quantity utilized comparatively low compared to other areas of PNG. For example, annual utilization across all households among the Tigak Islands was roughly half that reportedly utilized by a single household based at Hula village, Central Province (Kinch and Burgess, 2009). Given the relatively small quantities utilized for shellcraft, draconian measures to reduce utilization of these taxa within the sector would seem unnecessary. Rather, educating consumers, particularly foreign tourists (Militz et al., 2021), retailers, and relevant authorities would greatly strengthen existing governance to protect these taxa against unregulated international trade. Routine monitoring of shellcraft sectors would also help to detect a change in practices (such as targeted fishing of Nautilidae spp.; Dunstan et al., 2011) that may present a potential threat to the sustainability of both these taxa and the sectors they support.