Quantifying shark depredation events while commercial, charter and recreational fishing in Western Australia

Marine Policy 109 (2019) 103674

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Quantifying shark depredation events while commercial, charter and recreational fishing in Western Australia

T

Karina L. Ryana,∗, Stephen M. Taylora, Rory McAuleyb, Gary Jacksona, Brett W. Molonyc a

Department of Primary Industries and Regional Development, Western Australian Fisheries and Marine Research Laboratories, PO Box 20, North Beach, WA 6920, Australia b Minderoo Foundation, PO Box 3155, Broadway, Nedlands, WA 6009, Australia c CSIRO Oceans & Atmosphere, Indian Ocean Marine Research Centre, Crawley, WA 6009, Australia

ABSTRACT

Shark encounters while fishing in Western Australian waters have been perceived to be increasing by some fishers in recent years. A lack of quantitative information remains a significant obstacle to determining the nature and magnitude of these encounters. A probability-based survey was implemented to assess the occurrence of and attitudes toward shark encounters by commercial fishers, charter tour operators and private boat-based recreational fishers during 2015/16. Of the 906 fishers interviewed, 52% indicated they had experienced at least one shark encounter while fishing during the previous year. The loss or damage of fish was involved in over half of these encounters while charter fishing and nearly a third while recreational fishing. The level of concern towards shark depredation was highest among charter tour operators state-wide and all sectors in the Gascoyne bioregion. Multiple logistic regression analyses indicated fishing method and bioregion were the most important predictors of encounters. Depredation through fish loss below or at the surface was highest for pelagic or demersal line fishing in the North Coast and Gascoyne bioregions. Overwhelmingly, the majority of fishers in all sectors were satisfied with their fishing experience despite the occurrence of shark encounters. Future research on shark depredation would benefit from focusing on fishing methods and bioregions where depredation events were highest, with consideration of associated behavioural and environmental characteristics likely to influence depredation rates. The approach outlined here could easily be applied to other humanwildlife interaction studies where representative views of stakeholders are required for policy development and effective management.

1. Introduction Depredation through the removal of, or damage to, captured fish by marine predators is common in many commercial and recreational fisheries around the world [1–7]. A wide range of marine fauna have been implicated in depredation of fish in commercial fisheries, including killer whales (Orcinus orca) [8], sperm whales (Physeter macrocephalus) [9], dolphins (Tursiops truncates) [10], pinnipeds [11], colossal squid (Mesonychoteuthis hamiltoni) [12], large teleost species such as goliath groper (Epinephelus itajara) [13] and aquatic birds such as cormorants (Phalacrocorax carbosinensis) [14]. Depredation by sharks is a global phenomenon that has gained attention in high value pelagic longline commercial fisheries for tuna and billfish [15–17]. In these fisheries, a wide variety of sharks have been identified as responsible for damaging catches, including porbeagle (Lamna nasus), shortfin mako (Isurus oxyrhinchus), blue shark (Prionace glauca), thresher (Alopias spp.), hammerhead (Sphyrna spp.), crocodile (Pseudocarcharias kamoharai) and numerous species of whaler sharks (Family Carcharhinidae) [4,15,17–19]. Studies of shark depredation in recreational fisheries, however, are limited [20].

Depredation of target species can lead to a range of issues for fishery management agencies and can contribute to higher levels of fishing mortality that potentially increases the risk of overfishing [15]. However, data to quantify this typically ‘cryptic’ source of mortality is generally lacking and this may have important implications for assessment and management of fishery resources [21,22]. For example, in situations where depredation is anecdotally known to occur but quantitative data are unavailable, stock assessments may rely on inaccurate assumptions of mortality and resultant management arrangements may be either insufficient or overly-restrictive [23,24]. Depredation can have other detrimental consequences for fishers themselves, including increasing their costs by forcing expensive avoidance behaviours, e.g. travelling further or changing fishing location more frequently, increasing the length of time it takes to land the desired catch or bag limits, as well as increasing costs of bait usage and replacing damaged fishing gear [17,25]. In a broader societal context, increasing shark depredation rates can affect the experiential values of recreational fishing, cause misperceptions about shark abundance and associated public safety risks (particularly in regions with histories of shark attacks), which can lead to negative attitudes towards shark conservation,

Corresponding author. E-mail addresses: [email protected] (K.L. Ryan), [email protected] (S.M. Taylor), [email protected] (R. McAuley), [email protected] (G. Jackson), [email protected] (B.W. Molony). ∗

https://doi.org/10.1016/j.marpol.2019.103674 Received 31 January 2019; Received in revised form 19 August 2019; Accepted 26 August 2019 0308-597X/ Crown Copyright © 2019 Published by Elsevier Ltd. All rights reserved.

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research and management. Despite the significance of these issues, other than for some pelagic longline fisheries, the extent of shark depredation is poorly reported and understood for the vast majority of fisheries. The Western Australian coastline extends more than 12,889 km and spans sub-tropical and temperate regions that support numerous commercial, charter and recreational fishing activities [26,27]. Domestic and foreign commercial fishing fleets around Western Australia have targeted gummy (Mustelus antarticus), whiskery (Furgaleus macki), dusky (Carharhinus obscurus) and sandbar (C. plumbeus) sharks since at least 1941 [28–30]. In response to concerns about increasing commercial fishing effort, stock sustainability and bycatch risks, both targeted commercial shark fishing and retention of shark bycatch in nontarget commercial fisheries have been incrementally restricted since the mid-1980s [31–33]. These restrictions have had the cumulative effect of: reducing targeted commercial shark fishing effort in the southern half of the State by approximately 60%; eliminating shark bycatch retention in non-target commercial fisheries; permanent closures to commercial shark fishing off the State's capital city (Perth) and in the north-west; and cessation of targeted commercial shark fishing off the north coast [30,34]. Nevertheless, commercial shark fishing in the southern half of Western Australia, remains one of the largest sources of finfish production in the State, with annual landings of about 1000 tons (live weight) per annum [30]. Restriction of commercial shark fishing, together with the listing of several shark species under State and National conservation legislation, are often cited as de-facto evidence that shark abundance off the Western Australian coast is increasing [35,36]. Despite this popular perception, however, CPUE indices from commercial shark fisheries show limited recovery of historically overexploited stocks [30]. Anecdotal and media reports of encounters between fishers and sharks, together with concerns about the potential ecological and economic impacts of shark depredation, have been observed to increase across many Western Australian fishing sectors in recent years. For example, in meetings with fishery management officials, commercial fishers regularly express concerns about the impacts of shark depredation on the economic viability of the line fishery for pink snapper (Chrysophrys auratus) in the Gascoyne Coast (Fig. 1). Operators in the State's largest and most valuable fishery for Western Rock Lobster (Panulirus cygnus), have also reported that increasing numbers of sharks scavenging discarded (under-size or setose) lobsters might be undermining stock sustainability, as well as creating a crew safety issue. Charter tour operators have also reported high depredation rates at numerous locations around the State; shark ‘bite-offs’ are a commonlydiscussed topic in online recreational fishing fora; reports of sharks ‘interacting’ with recreational fishers are a regular feature of television and print news media; and a recent study in the Ningaloo Marine Park and Exmouth Gulf revealed that shark depredation occurred on more than a third of fishing trips [20]. However, given that anecdotal reports about increasing depredation rates are not a new phenomenon (DPIRD, unpublished data), assessing the scale of recent changes according to fishing method and/or spatial or temporal differences, and whether fishery management responses are required, is hindered by a lack of quantitative information on the issue. This study was undertaken to provide fishery managers and stakeholders with the first systematically derived data to describe the extent and nature of shark encounters and depredation rates across commercial, charter and recreational fishing sectors in Western Australia. The specific aims were to identify: (i) the level of concern with shark encounters (including depredation) among fishing sectors, and (ii) fishing methods and geographic areas associated with shark encounters. Understanding activity and location-specific differences in the frequency and type of encounters and associated levels of concern, along with importance, participation and satisfaction with fishing, will assist in the development of appropriate and effective responses to managing shark depredation concerns and provide a baseline against which future

changes can be measured. 2. Methods 2.1. Study area and fisheries management arrangements The Western Australian coastline is divided into four broad marine bioregions (Fig. 1). In 2016, there were 2179 licences issued to commercial fishers employing line, beach seine, purse seine, gillnet, trawl, trap and pot methods. Each of the State's commercial fisheries operates under a specific set of management arrangements designed to ensure catches are kept at sustainable levels [26]. More than 752,000 people were estimated to have participated in recreational fishing during 2016 [27]. Of the 170,094 recreational fishing licences issued in 2015/16, approximately 82% (139,485) were Recreational Boat Fishing Licences (RBFL) that are required when recreational fishing from powered vessels in Western Australian waters, with the remainder of licences issued for individual species (rock lobster, abalone and marron) or fisheries (netting and freshwater angling) [27]. A licence is not required for shore-based recreational fishing. 2.2. Survey design A telephone survey of commercial fishers, charter tour operators and private boat-based recreational fishers was conducted between August and November 2016 to recall their participation in different fishing activities in marine (including coastal and estuarine) waters in Western Australia during the previous 12 months (2015/16) and whether (or not) they had experienced any shark encounters while fishing. Random samples of commercial fishers and charter tour operators were selected from logbooks that had reported active fishing records in the previous 12 months. Private boat-based recreational fishers were randomly selected from a database of RBFL holders that were initially selected for a state-wide survey of recreational fishing [37]. All fishers were deemed eligible for this study if they fished in marine waters at least once during the previous 12 months (i.e. active fishers). A minimum age criterion of 18 years was applied to all sectors. As samples were taken from three discrete sampling frames (i.e. administrative lists of commercial fishers, charter tour operators and RBFL holders), potential duplicate respondents were excluded. No substitution of respondents occurred during the survey and no proxies were allowed. This study was guided by principles of informed consent, voluntary participation, confidentiality, and collection of only relevant information. Human Ethics approval was obtained from Edith Cowan University and respondents provided verbal consent to participate. The survey utilised Computer Assisted Telephone Interviews (CATI) and survey instruments to facilitate collection and recording of data, including: a structured questionnaire (see Supplementary Material Appendix A) and interviewer guidelines in accordance with standard interviewing conventions. CATI testing and interviewer briefings were conducted prior to and during the survey to ensure data were collected at consistent standards. The first section of the questionnaire included questions to identify the types of fishing activities that respondents participated in during the previous 12 months. The importance of each activity type (i.e. fishing gears and methods) was measured on a fivepoint Likert scale from ‘very important’ (1) to ‘not at all important’ (5) [38]. Participation in each activity type was measured according to five a priori categories: less than 5 days, 5–9 days, 10–14 days, 15–19 days and 20 or more days [37]. Satisfaction with fishing (across all activity types) was measured for the number, variety and size of fish caught and the environment where fishing occurred on a five-point Likert scale from ‘very satisfied’ (1) to ‘not at all satisfied’ (5). The second section of the questionnaire included questions to assess perceptions of shark encounters, including depredation. The level of concern toward each type of shark encounter (i.e. sighting, contact, fish loss below the surface, fish loss at the surface, landing damaged fish and 2

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Fig. 1. Marine bioregions fished by commercial, charter tour operators and private boat-based recreational fishers in Western Australia.

sharks eating released fish) was measured on a five-point Likert scale from ‘very concerned’ (1) to ‘not at all concerned’ (5). For each activity type, fishers were asked to recall the bioregion (North Coast, Gascoyne Coast, West Coast or South Coast) and austral season fished [spring (September–November), summer (December–February), autumn (March–May), or winter (June–August)]. As the reliability of recall data is limited by respondent's ability to accurately recall past events (Pollock et al., 1994), fishers were not asked to quantify how many encounters they had while fishing in the previous 12 months. Instead they were asked to recall the occurrence of specific types of shark encounters (presence/absence) for each activity type, bioregion and season they had fished, thus multiple types of shark encounters could be reported for an individual fishing ‘event’. Respondents' perceived changes in shark encounters were also compared with the prior 12

Table 1 Sample size and response rates from telephone surveys of commercial fishers, charter tour operators and recreational fishers in Western Australia.

Gross sample Sample loss Net sample Non-contact Refusals Fully responding Eligible sample Response rate

Commercial

Charter

Recreational

Overall

254 30 224 36 2 186 188 83%

127 25 102 5 2 95 97 93%

953 n/a 953 n/a 328 625 953 66%

1334 55 1279 41 332 906 1238 71%

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months (2014/15), although the accuracy of this observation is more likely to be compromised by recall bias. Sample loss was attributed to disconnected telephone numbers, or contacts where respondents were not known, known but no longer at listing, or away for the survey period (Table 1). A minimum eligible sample of 150 commercial fishers, 100 charter tour operators and 600 recreational fishers (i.e. 150 from each bioregion) was achieved with ~70% of respondents fully responding (i.e. completed all required interview questions) (Table 1). The majority of non-responses were from non-contacts, despite 20 attempted calls to each respondent over a range of times and days of the week. Non-response from refusals (~1% of the net sample) was low for all sample groups.

Table 2 Fishing activity types (number and percent of total) by commercial fishers, charter tour operators and boat-based recreational fishers. Fishing activity Line fishing (handline, dropline and longline) Pelagic line fishing for large pelagic species Beach seine, including haul seine Purse seine for small pelagic fish Gillnet, including shark fisheries Trawl for invertebrates Trap for scalefish Trap for invertebrates

2.3. Statistical analysis Multiple Logistic Regressions were used to compare the occurrence of shark encounters as a whole and then individually for different types of shark encounters from the binary outcome reported for each fishing ‘event’, with zero (0) for nil encounters and one (1) for at least one encounter. Logistic models describe the outcome from a dichotomous dependent variable (i.e. likelihood of an encounter) as a function of three categorical independent variables (activity type, bioregion and season) reported for each fishing ‘event’. A logit link function was used to determine the Odds Ratio (i.e. the ratio of the probability of an event occurring in one categorical group to the probability of it occurring in another). The logit (or log odds) is the natural log of the probability of an event divided by the probability of it occurring in another categorical group [39]. Activity type categories for commercial fishers were different to those for charter tour operators and recreational fishers, and observations of shark encounters for each fishing ‘event’ were variable among activity type and bioregion (see Supplementary Material Fig. S1). Consequently, separate analyses were conducted for commercial fishers, charter tour operators and recreational fishers for each type of shark encounter. Season was included in exploratory models for activity types with ‘events’ reported across bioregions and seasons, but was not included as an independent variable in any of the final models due to non-significance. Multiple Logistic Regressions were fitted and Odds Ratios calculated from model coefficients using the ‘glm’ function in base R (R Core Team 2016).

Pelagic line fishing (e.g. trolling for mackerel) Game fishing (e.g. for marlin) Boat-based demersal line fishing Boat-based nearshore and estuarine line fishing Any shore-based line fishing Any diving-based fishing (e.g. spearfishing) Any potting-based fishing

Commercial n (%) LINEF

69 (28)

TROLL

13 (5)

BEACS PURSS GILLN TRAWL TRAPF TRAPL

19 (8) 10 (4) 56 (23) 10 (4) 3 (1) 65 (27) Recreational n (%)

TROLL

Charter n (%) 40 (29)

GAMER DEMER NEARR

14 (10) 57 (41) 15 (11)

30 (3) 218 (20) 353 (32)

SHORE DIVER

1 (1) 7 (5)

240 (22) 42 (4)

POTTR

4 (3)

83 (7)

131 (12)

reported infrequently in some bioregions (e.g. diving- and pottingbased fishing by charter fishers) (see Supplementary Material Fig. S1). 3.2. Likelihood of shark encounters The survey of 906 fishers provided fishing data for 3653 events, with shark encounters reported for 2124 events (58%). The most frequent encounter type was sighting (38%) followed by loss of fish below the surface (35%). Lower encounter rates were reported for contact with gear (13%), loss of fish at the surface (14%), landing damaged fish (7%) and sharks eating released fish (4%). For commercial fishing, the likelihoods for all encounter types associated with depredation (i.e. loss of fish below or at the surface, landing damaged fish or sharks eating released fish) were higher for demersal line fishing than every other activity type. Odds Ratios and 95% confidence intervals predicting the odds of shark encounters while fishing by sector, activity type and bioregion are presented in Table 3. Relative to demersal line fishing, the likelihoods of depredation encounters were generally similar within individual activity types. For example, the Odds Ratio for different depredation encounters ranged from 0.00 to 0.10 for invertebrate trapping, 0.08 to 0.20 for gillnetting and 0.18 to 0.20 for trawling (Table 3). However, notable differences in likelihoods for depredation encounters were observed for surface-based activity types, such as purse seine and trolling, while the likelihood of fish loss at the surface (0.99 and 0.34, respectively) was much higher than of fish loss below the surface (0.22 and 0.05, respectively). For charter tour operators, the likelihood of depredation encounters did not vary significantly from demersal line fishing for all activity types, except boat-based nearshore and estuarine line fishing. Only fish loss below the surface while diving (i.e. free-diving or SCUBA) (0.21), landing damaged fish during pelagic fishing (0.46) and all depredation encounters while boat-based nearshore and estuarine line fishing (0.17 to 0.26), were significantly less likely to occur than while demersal line fishing. For recreational fishing, the likelihoods of fish loss at the surface (2.68) and landing damaged fish (3.65) were significantly higher while pelagic fishing, and the likelihoods of landing damaged fish (2.37) or sharks eating released fish (3.90) were significantly higher while potting, than demersal line fishing. The likelihood of fish loss below the surface

3. Results 3.1. Importance and participation in fishing The most common activity types for commercial fishers were line fishing (28%), invertebrate trap fishing (27%) and gillnetting (23%) (Table 2). The most common fishing activity types for charter tour operators were demersal line fishing (41%) and pelagic (e.g. mackerel) line fishing (29%). The most common fishing activity types for recreational fishers were boat-based nearshore and estuarine line fishing (32%), any shore-based line fishing (22%) and boat-based demersal line fishing (20%). At a state-wide level, fishing was ‘very important’ to commercial fishers (89%), charter tour operators (86%) and recreational fishers (60%) (Fig. 2) and was consistently ‘very important’ across all bioregions. Most commercial fishers (58%) and charter tour operators (50%) participated in fishing for ‘20 or more days’ (in the previous year), while most recreational fishers (60%) participated in fishing for ‘less than five days’ in the previous year (Fig. 2). While importance and participation varied among activity types and main bioregion fished for all sectors, some fishing activity types were not reported (e.g. purse seining in the North Coast, trap fishing in the Gascoyne and West Coast bioregions by commercial fishers and shore-based line fishing in the North Coast, Gascoyne and West Coast bioregions by charter fishers) or

4

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Fig. 2. Importance, participation and satisfaction in fishing by commercial fishers, charter tour operators and boat-based recreational fishers within four marine bioregions (North Coast (NC), Gascoyne Coast (GC), West Coast (WC), South Coast (SC) in Western Australia (WA).

was significantly less while diving (0.48), game fishing (0.38), boat-based nearshore and estuarine (0.43) and shore-based (0.32) line fishing. 3.3. Perceptions of change in shark encounters The majority of commercial and recreational fishers thought the number of encounters were similar in 2015/16 and 2014/15 (55% and 62%, respectively), followed by a perceived increase in 2015/16 compared with 2014/15 (36% and 28%, respectively) (Table 4). Similar proportions of charter tour operators thought the number of encounters were similar in both periods (50%) and increased in the last 12 months (50%). Only a small proportion of commercial fishers (9%) and recreational fishers (8%) thought encounters had declined over the same timeframe. Similarly, only small proportions of fishers (up to 13%) across all sectors and bioregions thought the number of encounters had declined in the last 12 months. Most thought the number of encounters were similar in both periods in the North Coast (56–67%) and South Coast (66–71%), as did recreational fishers in the West Coast (67%). Perceptions were divided between increased and similar number of encounters for recreational fishers in the Gascoyne Coast (41 and 46%), and commercial fishers in the Gascoyne Coast (45% for both) and West Coast (66 and 71%). The majority of charter tour operators thought encounters in the Gascoyne Coast (57%) and West Coast (61%) had increased in the last 12 months. 3.4. Concerns about shark encounters while fishing Concerns regarding shark encounters varied among sectors, with sightings (22%) and contact with gear (17%) the main concerns for commercial fishers and complete loss of fish below the surface the main concern for charter tour operators (50%) and recreational fishers (26%) followed by sightings as the second main concern for both sectors. Of less concern to all sectors were complete loss of fish at the surface, landing fish that are damaged, and sharks eating released fish (Table 5). Of the non-depredation encounter types, most fishers were ‘not at all concerned’ about sightings (Fig. 3). Commercial fishers were more likely to be concerned about sightings in the North Coast, Gascoyne Coast and West Coast and less likely to be concerned in the South Coast, while charter tour operators and recreational fishers were ‘not very concerned’ or ‘not at all concerned’ with sightings in all bioregions. Similarly, there were differences among sectors in the level of concern about contact with gear, with commercial fishers (25%) and charter tour operators (35%) most likely to be ‘very concerned’, while recreational fishers (27%) were most likely to be ‘not very concerned’ (Fig. 3). Most commercial fishers were either ‘very concerned’ or ‘quite concerned’ in the North Coast (67%) and Gascoyne Coast (70%) compared with the West Coast (37%) and South Coast (27%). Most charter tour operators were ‘very concerned’ or ‘quite concerned’ about contact with gear in all bioregions, while most recreational fishers were ‘not very concerned’ or ‘not at all concerned’ about contact with gear in all bioregions. With respect to depredation encounters, there were differences among sectors in their level of concern regarding loss of fish below the surface, loss of fish at the surface, landing fish that are damaged and sharks eating released fish (Fig. 3). For commercial fishers, there were differences in the level of concern among main bioregion fished for all depredation encounters. Most commercial fishers were either ‘very concerned’ or ‘quite concerned’ about: loss of fish below the surface in the North Coast (83%) and 5

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Table 3 Odds Ratios (95% confidence intervals) predicting the odds of shark encounters while fishing by sector, activity type and bioregion (95% confidence intervals of nonsignificant Odds Ratios include the value 1). Fishing activity types are defined in Table 2. Commercial Encounter (ENCOUNT) Intercept 18.4 (7.14–57.8) LINEF = ref BEACS 0.22 (0.10–0.46) GILLN 0.65 (0.41–1.02) PURSS 4.41 (1.58–15.7) TRAPF 0.13 (0.02–0.50) TRAPL 0.47 (0.30–0.73) TRAWL 0.12 (0.04–0.33) TROLL 1.21 (0.56–2.67) NC = ref GC 2.43 (0.60–10.6) WC 0.18 (0.06–0.47) SC 0.05 (0.02–0.14) SIGHTING Intercept 1.11 (0.58–2.13) LINEF = ref BEACS 0.25 (0.11–0.55) GILLN 0.30 (0.19–0.48) PURSS 1.01 (0.46–2.19) TRAPF 0.52 (0.14–1.63) TRAPL 1.36 (0.91–2.04) TRAWL 0.25 (0.10–0.61) TROLL 1.52 (0.75–3.09) NC = ref GC 6.29 (2.74–15.0) WC 1.13 (0.58–2.18) SC 0.51 (0.27–0.99) Contact with fishing gear (CONTACTB) Intercept 1.05 (0.52–2.08) LINEF = ref BEACS 0.75 (0.33–1.58) GILLN 0.52 (0.31–0.85) PURSS 7.86 (3.50–19.1) TRAPF NA TRAPL 0.21 (0.11–0.38) TRAWL 0.54 (0.21–1.31) TROLL 0.20 (0.06–0.54) NC = ref GC 1.49 (0.67–3.34) WC 0.28 (0.13–0.58) SC 0.32 (0.15–0.67) Complete loss of fish below the surface (LOSSFBEL) Intercept 3.08 (1.44–6.70) LINEF = ref BEACS NA GILLN 0.08 (0.04–0.16) PURSS 0.22 (0.07–0.57) TRAPF NA TRAPL 0.09 (0.05–0.16) TRAWL 0.20 (0.07–0.50) TROLL 0.05 (0.01–0.17) NC = ref GC 0.87 (0.36–2.13) WC 0.26 (0.12–0.57) SC 0.15 (0.06–0.34) Complete loss of fish at the surface (LOSSFSUR) Intercept 2.04 (0.93–4.63) LINEF = ref BEACS 0.08 (0.00–0.42) GILLN 0.20 (0.09–0.42) PURSS 0.99 (0.33–2.60) TRAPF NA TRAPL 0.00 (0.0–5571) TRAWL 0.18 (0.05–0.54) TROLL 0.34 (0.10–0.97) NC = ref GC 0.56 (0.22–1.40) WC 0.08 (0.03–0.20) SC 0.07 (0.03–0.16) Landing fish that are damaged (LANDINGF) Intercept 1.16 (0.51–2.58) LINEF = ref

Charter

Recreational

Intercept DEMER = ref DIVER GAMER NEARR PELAR POTTR SHORE

9.29 (5.04–18.1)

3.66 (2.81–4.78)

0.28 0.47 0.21 0.81 0.27 NA

0.91 1.73 0.70 1.74 0.59 0.51

NC = ref GC WC SC

0.71 (0.37–1.37) 0.41 (0.21–0.77) 0.14 (0.05–0.39)

1.25 (0.97–1.61) 0.17 (0.13–0.21) 0.09 (0.07–0.12)

(0.11–0.67) (0.20–1.17) (0.10–0.45) (0.42–1.58) (0.10–0.73)

(0.60–1.39) (0.77–4.48) (0.52–0.93) (1.18–2.58) (0.43–0.81) (0.38–0.69)

Intercept DEMER = ref DIVER GAMER NEARR PELAR POTTR SHORE

0.85 (0.53–1.36)

0.66 (0.52–0.83)

1.37 0.76 0.56 0.45 6.42 NA

2.24 0.71 1.10 1.35 1.05 1.46

NC = ref GC WC SC

0.64 (0.36–1.10) 0.98 (0.58–1.67) 1.57 (0.57–4.36)

0.96 (0.78–1.19) 0.53 (0.42–0.67) 0.29 (0.22–0.39)

0.75 (0.44–1.27)

0.10 (0.07–0.15)

0.71 0.22 0.22 0.15 NA

0.73 3.76 1.46 1.62 1.18 2.16

Intercept DEMER = ref DIVER GAMER NEARR PELAR POTTR SHORE NC = ref GC WC SC

(0.60–3.15) (0.36–1.54) (0.27–1.12) (0.26–0.77) (2.27–23.1)

(0.26–1.75) (0.08–0.51) (0.08–0.54) (0.07–0.30)

(1.55–3.25) (0.36–1.36) (0.84–1.44) (0.97–1.88) (0.78–1.42) (1.12–1.92)

(0.32–1.52) (1.71–7.93) (0.92–2.35) (0.94–2.78) (0.69–2.04) (1.40–3.41)

1.15 (0.59–2.20) 0.51 (0.26–0.97)

0.96 (0.70–1.32) 0.24 (0.14–0.40) 0.66 (0.44–0.96)

Intercept DEMER = ref DIVER GAMER NEARR PELAR POTTR SHORE

2.50 (1.52–4.23)

1.71 (1.34–2.18)

0.21 1.11 0.26 1.60 1.12 NA

0.48 0.38 0.43 0.78 0.86 0.32

NC = ref GC WC SC

1.78 (0.96–3.35) 0.51 (0.29–0.88) 0.08 (0.02–0.25)

1.16 (0.93–1.45) 0.23 (0.17–0.29) 0.12 (0.08–0.17)

(0.08–0.52) (0.50–2.58) (0.13–0.54) (0.90–2.92) (0.42–3.23)

(0.32–0.71) (0.20–0.72) (0.33–0.58) (0.55–1.09) (0.64–1.17) (0.24–0.43)

Intercept DEMER = ref DIVER GAMER NEARR PELAR POTTR SHORE

0.91 (0.56–1.47)

0.24 (0.17–0.33)

0.70 0.75 0.17 0.93 0.98 NA

0.75 0.75 0.62 2.68 1.22 1.04

NC = ref GC WC SC

0.53 (0.31–0.91) 0.38 (0.21–0.66) 0.35 (0.10–1.08)

0.74 (0.56–0.98) 0.34 (0.24–0.49) 0.13 (0.07–0.22)

0.39 (0.21–0.68)

0.05 (0.03–0.09)

Intercept DEMER = ref

(0.26–1.75) (0.36–1.55) (0.05–0.43) (0.54–1.59) (0.36–2.45)

(0.40–1.33) (0.27–1.75) (0.40–0.94) (1.79–4.04) (0.81–1.84) (0.71–1.55)

(continued on next page) 6

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Table 3 (continued) Commercial BEACS NA GILLN 0.20 PURSS NA TRAPF NA TRAPL 0.06 TRAWL 0.21 TROLL NA NC = ref GC 0.99 WC 0.23 SC 0.12 Sharks eating released fish (RELEASEF) Intercept 0.15 LINEF = ref BEACS NA GILLN NA PURSS NA TRAPF NA TRAPL 0.10 TRAWL 0.80 TROLL 1.91 NC = ref GC 2.45 WC 0.76 SC NA

Charter

Recreational

(0.02–0.15) (0.06–0.61)

DIVER GAMER NEARR PELAR POTTR SHORE

NA 0.67 0.21 0.46 0.15 NA

0.17 0.96 1.71 3.65 2.37 0.91

(0.38–2.64) (0.09–0.56) (0.04–0.31)

NC = ref GC WC SC

1.03 (0.53–1.98) 0.39 (0.17–0.85) NA

1.02 (0.67–1.54) 0.39 (0.21–0.66) 0.03 (0.00–0.15)

(0.09–0.40)

(0.04–0.42)

(0.02–0.37) (0.21–2.55) (0.46–6.81) (0.73–9.83) (0.23–3.03)

North Coast n (%)

Commercial More 4 (33) Less 0 (0) Same 8 (67) UNSURE 0 (0) Charter More 8 (31) Less 1 (4) Same 17 (65) UNSURE 0 (0) Recreational More 55 (36) Less 8 (5) Same 85 (56) UNSURE 3 (2)

0.30 (0.16–0.53)

0.03 (0.01–0.05)

0.96 1.12 NA 1.63 0.52 NA

NA 1.64 1.04 0.38 3.90 1.07

NC = ref GC WC SC

0.73 (0.38–1.38) 0.23 (0.10–0.51) NA

Gascoyne Coast n (%)

West Coast n (%)

South Coast n (%)

State-wide

9 2 9 0

(45) (10) (45) (0)

34 (41) 11 (13) 38 (46) 0 (0)

20 (28) 3 (4) 47 (66) 1 (1)

67 (36) 16 (9) 102 (55) 1 (0)

12 (57) 0 (0) 9 (43) 0 (0)

25 (61) 0 (0) 16 (39) 0 (0)

2 0 5 0

(29) (0) (71) (0)

47 (50) 1 (0) 47 (50) 0 (0)

58 (42) 11 (8) 67 (49) 1 (1)

36 (20) 20 (11) 123 (67) 3 (2)

29 (19) 11 (7) 110 (71) 5 (3)

178 (28) 50 (8) 385 (62) 12 (2)

Sighting Contact with fishing gear Complete loss of fish below the surface Complete loss of fish at the surface Landing fish that are damaged Sharks eating released fish Other None

Commercial n (%)

Charter n (%)

Recreational n (%)

SIGHTING CONTACTB LOSSFBEL

42 (22) 31 (17) 25 (13)

12 (13) 4 (4) 47 (50)

81 (13) 34 (5) 161 (26)

LOSSFSUR

5 (3)

8 (8)

28 (5)

LANDINGF

2 (1)

0 (0)

10 (2)

RELEASEF

2 (1) 7 (4) 72 (39)

5 (5) 3 (3) 16 (17)

9 (1) 34 (5) 268 (43)

(0.21–3.31) (0.47–2.62) (0.84–3.21) (0.08–2.02)

(0.24–6.85) (0.40–2.75) (0.06–1.54) (1.82–9.33) (0.42–2.85)

1.32 (0.75–2.34) 0.30 (0.12–0.67) NA

Gascoyne Coast (60%); fish lost at the surface in the North Coast (75%) and Gascoyne Coast (65%); landing damaged fish in the North Coast (67%) and Gascoyne Coast (65%); and released fish being eaten by sharks in the Gascoyne Coast (75%). Similarly for recreational fishers, there were differences in the level of concern among main bioregion fished for all depredation encounters. Most recreational fishers were either ‘very concerned’ or ‘quite concerned’ about: loss of fish below the surface in the North Coast (45%) and Gascoyne Coast (56%); fish lost at the surface in the North Coast (41%) and Gascoyne Coast (48%); landing damaged fish in the North Coast (42%) and Gascoyne Coast (46%); and released fish being eaten by sharks in the North Coast (35%) and Gascoyne Coast (48%). In contrast, charter tour operators were consistently ‘very concerned’ or ‘quite concerned’ about loss of fish below the surface, fish lost at the surface, landing damaged fish and released fish being eaten by sharks in all bioregions (Fig. 3). 3.5. Satisfaction with fishing Despite the likelihood of shark encounters while fishing and levels of concern about these encounters, the majority of commercial fishers (88%), charter tour operators (91%) and recreational fishers (87%) were either ‘very satisfied’ or ‘quite satisfied’ with their fishing experiences (Fig. 2). Similarly, most commercial fishers (67%), charter tour operators (79%) and recreational fishers (75%) were ‘very satisfied’ or ‘quite satisfied’ with the variety of fish caught (Fig. 2). Fishers from most sectors reported high satisfaction overall, in the number of fish caught and the variety of fish caught. The majority of commercial fishers (86%), charter tour operators (77%) and recreational fishers (74%) were ‘very satisfied’ or ‘quite satisfied’ with the size of the fish caught while fishing in the previous 12 months (Fig. 2). Most commercial fishers (86%), charter tour operators (88%) and recreational fishers (93%) were ‘very satisfied’ or ‘quite satisfied’ with the environment where they fished (Fig. 2). Commercial fishers had highest satisfaction with the size of fish they caught, while recreational fishers had highest satisfaction with the environment where they were fishing. There were minimal differences in satisfaction with number of fish caught, variety of fish caught, size of the fish

Table 5 Main issue of concern with regard to shark encounters while fishing (number and percent of total) by commercial fishers, charter tour operators and boatbased recreational fishers. Shark encounter type

(0.01–0.85) (0.15–3.62) (0.90–3.38) (1.91–7.30) (1.25–4.71) (0.43–1.94)

Intercept DEMER = ref DIVER GAMER NEARR PELAR POTTR SHORE

Table 4 Perceptions of change in shark encounters while fishing between the survey period and the previous 12 months (number and percent of total) by commercial fishers, charter tour operators and boat-based recreational fishers. Sector

(0.28–1.53) (0.05–0.64) (0.22–0.91) (0.01–0.78)

7

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Fig. 3. Level of concern with regard to shark encounters while fishing by commercial fishers, charter tour operators and boat-based recreational fishers within four marine bioregions (North Coast (NC), Gascoyne Coast (GC), West Coast (WC), South Coast (SC) in Western Australia (WA).

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caught and environment where fishing occurred among sectors and main bioregion fished (see Supplementary Material Fig. S2).

Fishery (G Jackson, by obs.). Higher depredation rates in northern bioregions (North Coast and Gascoyne Coast) compared with southern bioregions (West Coast and South Coast) could be attributed to the distributions of species that predate recreationally targeted fish species. In Western Australia, sharks tend to be more commonly encountered in tropical and subtropical waters than temperate waters [30,66]. Additionally, some fishers suggest shark abundance has increased in the north of the State following prohibitions on commercial shark fishing between Cape Vlamingh (NW Cape) and Steep Point (Shark Bay) in 1994 and between Cape Vlamingh and 120° E longitude in the North Coast in 2006 to reduce the risks of over-exploitation for dusky (Carcharhinus obscurus) and sandbar (Carcharhinus plumbeus) sharks [34]. These closures ensure that areas of sub-tropical marine waters have had no commercial shark fishing for one to two decades and recreational fishing has been concentrated into smaller areas [19]. Higher encounter rates, including higher likelihood of shark sightings, were reported in the North Coast and Gascoyne Coast bioregions by all fishing sectors. The higher depredation rates reported by charter tour operators may reflect the tendency for charter fishing to occur repeatedly in specific areas (DPIRD, unpublished data) according to a trade-off between accessibility (as determined by the cost of fuel) and reliability of good catches for fee-paying fishers. Although shark depredation was reported in commercial, charter and recreational fisheries, in many cases concerns for depredation were low and satisfaction in fishing was high. This demonstrates that for most fishers, the potential negatives of encountering a shark while fishing is outweighed by the social or economic benefits that fishing provides. Furthermore, not all types of encounters (e.g. sightings) may be perceived to be negative. Nevertheless, the results indicated that for some fisheries, concerns were high and that some fishers perceived the frequency of depredation events were increasing. These perceptions were often attributed to changes in the distribution and abundance of sharks due to management and environmental change, as well as changes in the distribution of fishing activity due to spatial management, including Marine Parks. The relatively high cost of commercial fishing gear provides an obvious explanation for the relatively high level of concern about this type of encounter. The reason(s) for charter tour operators being noticeably more concerned than boat-based recreational fishers (who charter tour operators service) may reflect the business costs and client expectations associated with charter fishing.

4. Discussion This study represents the first broad-scale survey to quantify levels of shark depredation among commercial, charter and recreational fishers in Western Australia. Many surveys of stakeholder groups rely on ‘opt-in’ or non-probability-based designs to collect information (e.g. [36]). For contentious issues such as shark depredation, results from these types of surveys are prone to bias because respondents' encounter rates and views may not accurately reflect the target population. A key advantage of this study is that interviewed-fishers were recruited from licence-based sampling-frames as part of a robust, probability-based design. The high survey response rate (~70%, Table 1) strongly suggests that encounter rates and fishers' views for the survey period were representative of all commercial, charter and boat-based recreational fishers in Western Australia. Such an approach avoids the tendency for placing too much confidence in human judgement (perceptions, anecdotal reports) and responding to difficult questions with simple answers [40]. This approach assists in the testing of perceptions against determining reality. In addition, it allows the limited resources of a natural resource management agency to be focussed on responding to genuine high priority issues, allowing for hypothesis generation and the potential for adaptive management. 4.1. Human wildlife interactions Human-wildlife interactions are contentious, as conservation measures often seek to increase the abundance of vulnerable species, while management intervention is often expected following negative impacts on human activity [41]. Increases in the number of humans and the extent of anthropogenic activities, coupled with reduced and lower quality habitats (especially in terrestrial systems), potentially contribute to more frequent human-wildlife interactions. Most studies on human-wildlife interactions have been based on terrestrial predators [42–44], including terrestrial apex predators, such as bears [45,46], cougars [47], dingos [48,49], panthers [50] and wolves [51,52]. While there has been less focus on aquatic predators, research has involved cormorants [14], seals [53], and apex predators, such as sharks [15,17,18,20,25,54–56]. Attitudes to wildlife interactions can become polarised when sectors of the community feel that their livelihood or leisure is negatively impacted by these interactions [57,58]. Shark encounters attract high levels of community interest [59,60]; however, little is known about the nature of encounters between sharks and fishers [7], who encounter sharks more frequently than any other sector of the community.

4.3. Implications of depredation Depredation of captured fish by sharks is likely to have implications for maintaining ecosystem health, fisheries management, ensuring the social and economic value of fishing and shark welfare [67–69]. The loss or damage of fish through depredation comprises an additional source of mortality that could alter ecosystem structure, particularly if this is not explicitly incorporated in stock assessments [4,7,70]. Sharks species are rarely targeted by recreational fishers and typically have high release rates [37]. The direct effects of hook damage [71] and the repeated hooking of sharks can cause capture stress and physiological responses that can lead to mortality or reduced reproductive function [72]. As most fishers indicated they were satisfied with their fishing experience, the social and economic effects of depredation (at present) are likely to be highest for the commercial and charter fishing sectors where depredation rates were highest. Quantifying these effects was outside of the scope of the current study but could be addressed in subsequent research.

4.2. Rate of shark encounters and attitudes towards depredation Prior to this study, limited information was available on the ways in which fishers encounter sharks in Western Australia, despite the high diversity of sharks [61], long history of commercial shark fishing [28–30] and intense media scrutiny surrounding shark bite incidents [62–65]. The state-wide data obtained from all types of fishers in Western Australia have identified broader geographical areas (i.e. bioregions) where the probability of encountering sharks is higher. Although shark depredation has been reported by fishers across all sectors, bioregions and methods of fishing, the results suggest that these encounters typically occur more in the tropical and sub-tropical waters in the North Coast and Gascoyne Coast. The finding that fish loss below the surface was highest for pelagic or demersal line fishing in the North Coast and Gascoyne Coast is consistent with results of recent research on shark depredation and recreational fishing in the Ningaloo Marine Park and Exmouth Gulf [20] and anecdotal reports in recent years by commercial fishers operating in the Gascoyne Demersal Scalefish

4.4. Where to from here? The results from this study provide a contemporary snapshot of shark encounters for over 752,000 boat-based recreational fishers in Western Australia (Department of Fisheries 2016), in addition to 9

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commercial fishers and charter tour operators. Fishers that hold a RBFL usually possess other licence types and participate across all recreational fishing activities, including shore-based recreational fishing. Data from RBFL holders can, therefore, inform the propensity of shark interactions with unlicensed fishers. Periodic reassessment will assist in determining any temporal changes in shark encounters, including whether or not potential management actions introduced to mitigate shark depredation [e.g. 65,70] have the desired outcome or whether fishers' attitudes toward shark encounters change over time or identify any broad-scale changes in encounters among sectors, fishing gear and/ or bioregions. By virtue of the survey design (12-month recall), fine-scale spatial and temporal information on shark depredation (e.g. dates and locations fished for individual fishing events) was not recorded in this study. For example, a fisher may have recalled depredation to be low even though a potentially large number of sharks may have been encountered during an individual fishing event. The collection of depredation data at finer resolution would be beneficial for developing and evaluating management policies and recommendations for changes in fishing practices, and for assessing the social and economic impacts of shark depredation. For the recreational sector, individual fishing event data could be collected through on-site surveys of recreational fishers at boat ramps [19]. This would also allow the potential effects of fishing method and targeting practices in relation to depredation to be closely examined, along with potentially assessing patterns in relative abundance and distribution of shark populations [66,74], to assist in estimating how many fish are lost through shark depredation (within the scope of such surveys). Modifications to commercial logbooks and charter tour operator returns would also enable depredation data to be routinely reported for individual fishing events. Understanding which species are responsible for depredation is also important to develop specific management actions; however, the collection of quantitative data on those species involved in depredation is challenging. In the current study, it was not possible to confirm which shark species were responsible for recalled depredation events, or whether other predators, such as teleosts, seals, birds or cetaceans could have been responsible. The deployment of in situ cameras to observe depredation events while fishing or simulating fishing methods [75] or DNA methods [76] would enable identification of the species responsible and development of species-specific management responses. Given that shark catches and bycatch are carefully regulated in Western Australia to ensure ecosystem function and the sustainability of fisheries that rely on sharks [26,30], non-destructive approaches to dealing with concerns about shark depredation will need to be developed, communication and education will continue to be critical to informing on-going debate and any potential future research on shark depredation in Western Australia will likely involve further analysis of the survey data collected for this study.

responsible for depredation and associated behavioural and environmental characteristics likely to influence depredation rates. These studies would inform recommendations that could minimise depredation, including mitigation by policy agencies (with consideration of associated costs and benefits) or behavioural changes by fishers (such as removing gear and moving to another suitable fishing location). Funding None. Declarations of interest None. Acknowledgements We acknowledge contributions from the commercial, charter and recreational fishers that were interviewed and staff from the Survey Research Centre (Edith Cowan University) for conducting the phone surveys. Staff from the Surveys, Assessment and Data Analysis branch (DPIRD) provided assistance with the commercial and charter sampling frames and searching scientific literature. We thank Agata Zabolotny for compiling Figure 1. Patrick Cavalli, Ainslie Denham, Shane Walters, Stephen Newman and Brent Wise provided constructive comments in reviewing the manuscript. The authors also thank the anonymous reviewers for their useful comments. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.marpol.2019.103674. References [1] G.D. Raby, J.R. Packer, A.J. Danylchuk, S.J. Cooke, The understudied and underappreciated role of predation in the mortality of fish released from fishing gears, Fish Fish. 15 (2014) 489–505, https://doi.org/10.1111/faf.12033. [2] J.R. Powell, R.S. Wells, Recreational fishing depredation and associated behaviors involving common bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida, Mar. Mamm. Sci. 27 (2011) 111–129, https://doi.org/10.1111/j.1748-7692.2010. 00401.x. [3] E. Karpouzli, R. Leaper, Opportunistic observations of interactions between sperm whales and deep-water trawlers based on sightings from fisheries observers in the northwest Atlantic, Aquat. Conserv. Mar. Freshw. Ecosyst. 14 (2004) 95–103, https://doi.org/10.1002/aqc.595. [4] J.W. Mandelman, P.W. Cooper, T.B. Werner, K.M. Lagueux, Shark bycatch and depredation in the U.S. Atlantic pelagic longline fishery, Rev. Fish Biol. Fish. 18 (2008) 427–442, https://doi.org/10.1007/s11160-008-9084-z. [5] S.R. Dorman, B.W. Molony, S.J. Newman, S. Blight, A. Denham, J. Santana-Garcon, C.B. Wakefield, S.R. Dorman, A. Denham, S. Blight, B.W. Molony, S.J. Newman, Risk versus reward: interactions, depredation rates and bycatch mitigation of dolphins in demersal fish trawls, Can. J. Fish. Aquat. Sci. 75 (2018) 1–29, https://doi. org/10.1139/cjfas-2017-0203. [6] A.R. Rafferty, E.O. Brazer, R.D. Reina, Depredation by harbor seal and spiny dogfish in a Georges Bank gillnet fishery, Fish. Manag. Ecol. 19 (2012) 264–272, https:// doi.org/10.1111/j.1365-2400.2011.00837.x. [7] J.D. Mitchell, D.L. McLean, S.P. Collin, T.J. Langlois, Shark depredation in commercial and recreational fisheries, Rev. Fish Biol. Fish. (2018), https://doi.org/10. 1007/s11160-018-9528-z. [8] M.J. Peterson, F. Mueter, K. Criddle, A.C. Haynie, Killer whale depredation and associated costs to Alaskan Sablefish, Pacific Halibut and Greenland Turbot longliners, PLoS One 9 (2014) e88906, , https://doi.org/10.1371/journal.pone. 0088906. [9] A. Janc, G. Richard, C. Guinet, J.P.Y. Arnould, M.C. Villanueva, G. Duhamel, N. Gasco, P. Tixier, How do fishing practices influence sperm whale (Physeter macrocephalus) depredation on demersal longline fisheries? Fish. Res. 206 (2018) 14–26, https://doi.org/10.1016/j.fishres.2018.04.019. [10] C.B. Wakefield, J. Santana-Garcon, S.R. Dorman, S. Blight, A. Denham, J. Wakeford, B.W. Molony, S.J. Newman, Performance of bycatch reduction devices varies for chondrichthyan, reptile, and cetacean mitigation in demersal fish trawls: assimilating subsurface interactions and unaccounted mortality, ICES J. Mar. Sci. 74 (2016) fsw143, https://doi.org/10.1093/icesjms/fsw143. [11] T. Götz, V. Janik, Acoustic deterrent devices to prevent pinniped depredation: efficiency, conservation concerns and possible solutions, Mar. Ecol. Prog. Ser. 492

5. Conclusions While loss of social amenity and economic costs associated with shark depredation may affect fishing in some areas, our results suggest that the level of concern and occurrence of depredation in marine waters off Western Australia is not as high as individual anecdotal reports initially suggested. Furthermore, the level of concern and occurrence of depredation is not uniform among sectors, activity type or bioregion. The likelihood of encounters that could contribute to depredation through fish loss below or at the surface was highest for pelagic or demersal line fishing in the North Coast and Gascoyne Coast. These fishing methods are designed to target pelagic or demersal species and may also attract sharks that depredate on target species. The diversity of activity types and large geographical range considered in this study suggests future research on shark depredation would benefit from focusing on the activity types and bioregions where depredation rates were highest, with consideration of the species most likely to be 10

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[38] [39] [40] [41] [42]

[43] [44] [45] [46]

[47] [48]

[49]

[50] [51] [52] [53] [54] [55] [56]

[57] [58] [59]

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