Conflicting interests and growing importance of non- indigenous species in commercial and recreational fisheries of the Mediterranean Sea

Non- indigenous species (NIS) are spreading and reshaping Mediterranean Sea biological communities and fishery resources. The present study used fisheries data and structured interviews to assess the impacts of NIS on recreational and commercial fishers in Cyprus. NIS that have been present in Cyprus for more than two decades were mostly perceived by local fishers as native, NIS with high market value were considered to be beneficial, and venomous or poisonous NIS were considered to be deleterious. Pufferfishes (Tetraodontidae) were identified by fishers as causing significant economic damage, which undermines the sustainability of the commercial fishing sector. The most popular and highly priced NIS were rabbitfishes ( Siganus spp.). In terms of commercial landings, six non- indigenous taxa contributed over a quarter of the total landing value and more than half during the summer season. The results of the present study emphasised the multifaceted interactions of NIS with the fishing sector, and how policy objectives may not align with social and commercial fishery interests.

Some NIS become invasive when they cause negative ecological effects. Such effects include reducing native species richness and abundance, increasing the risk of native species extinction, reducing the genetic diversity of local populations, introducing novel parasites or diseases, changing native species behaviour, altering ecological processes and reducing ecosystem services (de Castro et al., 2017;Chaffin et al., 2016;Geburzi & McCarthy, 2018). Invasive NIS have also become a major social issue: inflicting economic losses in a range of millions to billions of dollars per year (Warziniack et al., 2021), impacting human health, and interacting with recreational activities and aesthetic values (Pyšek & Richardson, 2010). A number of recently-introduced invasive NIS in the Mediterranean are poisonous or venomous and so could adversely affect tourism and fisheries (Galil, 2018). For example, pufferfishes (family: Tetraodontidae) have high concentrations of tetrodotoxin (TTX) in their tissues and can be fatal when consumed (Katikou et al., 2009). Some species damage fishing gear and catch, such as the pufferfishes, the striped eel catfish Plotosus lineatus (Thunberg), and the nomad jellyfish Rhopilema nomadica Galil (Galanidi et al., 2018;Kalogirou, 2013).
Positive effects of NIS can in some cases be underestimated due to a perception bias and focus on the negative effects (Katsanevakis et al., 2014b). Some NIS can replace lost ecological functions, add redundancy and enhance ecosystem services (Chaffin et al., 2016;Kleitou et al., 2021a), in addition, some cases becoming target species of the fisheries (Demirel et al., 2021;Ugarković & Crocetta, 2021) that provide potential to stabilise fishery revenues (Michailidis et al., 2019;van Rijn et al., 2019;Saygu et al., 2020).
Relatively little is known about the impacts of NIS on people and society (García-Llorente et al., 2008, 2011. A few recent studies have explored the adverse socioeconomic effects of NIS in the Mediterranean Sea (Galanidi et al., 2018;Peyton et al., 2019Peyton et al., , 2020, but the positive impacts may have been overlooked (Bonanno, 2016;Kleitou et al., 2021a). In principle, risk assessment of NIS to inform decision makers focuses purely on adverse impacts, though under the 2014 EU Regulation (No. 1143/2014) on the prevention and management of the introduction and spread of invasive alien species, possible benefits of a NIS must be mentioned but these are not evaluated so that decision makers may come to an informed decision on NIS, balancing up the adverse impacts and potential positive benefits.
Commercial and recreational fisheries are important to local people of the Mediterranean region (Giovos et al., 2018;Lloret et al., 2018). Inherent difficulties in monitoring (FAO, 2020), such as the diverse structure of fishing fleets (Lloret et al., 2018), the diverse national data collection programmes (Pauly & Zeller, 2016) and a lack of data on recreational fisheries (Pita et al., 2018) all pose challenges for sustainable management of the sector. Non-indigenous species are gradually becoming a source of revenue in the eastern Mediterranean (van Rijn et al., 2019), but insufficient consideration of stakeholder perspectives and priorities when making management decisions mainly or purely on NIS risk assessments that report impacts, can lead to poor policy decisions that lose support at the local management level (Barney & Tekiela, 2020;Oficialdegui et al., 2020). As such, the multifaceted costs and benefits of NIS for local people need to be understood better and incorporated into marine management strategies.
The present study used (i) fishery data from official Cyprus national sources (Department of Fisheries and Marine Research, Ministry of Agriculture, Cyprus) and (ii) structured interviews with commercial and recreational fishers, to assess the socioeconomic interactions, knowledge, norms and intrinsic motivations of fishers with respect to common NIS.
The study focussed on a marine protected area (MPA) adjacent to Cyprus where NIS of Indo-Pacific origin now dominate (Kleitou et al., 2019b;Savva et al., 2020). Two fishing fleets operate in this area: small-scale inshore boats and polyvalent vessels. The smallscale inshore boats (overall lengths of 6-12 m) target predominantly demersal species using mainly bottom-set nets (trammel nets/gillnets) and bottom longlines. The polyvalent vessels (overall lengths of 12-24 m) target pelagic species with drifting longlines, bottom-set trammel/gill nets and bottom longlines. All recreational fishers, irrespective of their fishing technique/tools, were included in the present study. Recreational fishers use traps, spearfishing, boatfishing using bottom fishing, trolling, jigging, bottom longlining, deep dropping and shore fishing using casting, spinning, squid jigging (eging) and shore jigging (Moutopoulos et al., 2021). The catches of recreational fishers are not monitored by official schemes.

| Targeted non-indigenous species
The research is focussed on 12 target NIS (Table 1), which were selected based on their known high abundance or identified as priority species in relation to fisheries (GFCM-UNEP/MAP, 2018).

| National fishery data
Monthly national fishery data (landings quantity (kg), value (€) and effort (landings per trip)) for the selected species were provided by the Cyprus Department of Fisheries and Marine Research (DFMR).
These data derive from various sources of information such as logbook records of fishers and sales notes from fishmongers. Data were acquired for the landings of the four nearest (<15 km distance) to the Cape Greco (MPA) landing areas, namely Ayia Triada, Paralimni, Ayia Napa and Potamos for 2017-2019 ( Figure 1).

| Structured interviews
Structured interviews were conducted with both commercial (CFs) and recreational (RFs) fishers during June and July 2020 at the same landing areas (i.e. Ayia Triada, Paralimni, Ayia Napa and Potamos) and adjacent locations on the coast whilst interviewees were fishing.
Contact details of the licenced CFs were provided by the local fishery associations and the DFMR. Before the interview, fishers were informed that their participation was optional, and that personal data would remain confidential. All interviews were carried out by the same trained person, ensuring that questions were presented in an identical manner. The interviews were held privately, on one-toone sessions, to prevent influence or interference by other people.   (Figure 2b). Since 2019, landings increased sharply for P. forsskali, and the first reports of P. miles were also recorded. The two Siganus species and P. forsskali were the most commercially valuable species with retail prices over €10 per kg ( Figure 2d).

| Interview results
Fifty five fishers were interviewed, 20 of whom were CFs (17 smallscale fishers and three polyvalent corresponding to 25.6% of the licenced CFs of the area) and 35 RFs some of which used more than one fishing mode (five fishing demersal species with boat; five fishing pelagic species with boat; 28 fishing with a rod from the shore; and four fishing with freedive and speargun). These fishers were  as the most commonly caught species. Small deviations were also identified; for example, the two rabbitfishes (S. rivulatus and S. luridus) were reported as being more common than the S. rubrum.
( Figure 6). According to fishers' responses, pufferfish species L. sceleratus and T. flavimaculosus had the most chances of being discarded ( Figure 7); however, responses for the two species varied between CFs and RFs (Figure 7) with the first group reporting less discard rates. This was especially the case for L. sceleratus, which was more likely to be kept by CFs (binomial test, p < 0.05). High discard rates were also reported for Pempheris sp. and P.  Finally, CFs fishers stated that non-indigenous by-catch and subsequent damage to gear increased the time spent fishing to achieve their income (55% of the CFs stated an increase of one to one and a half hour per fishing trip).

| DISCUSS ION
Non-indigenous species are increasingly reshaping the ecosystems of the Mediterranean Sea (e.g. Giovos et al., 2019;Kleitou et al., 2019a;, altering commercially important species assemblages. As native species are overfished, the contribution and interactions of NIS with fisheries have increased (Kleitou et al., 2021a). Some invasive NIS exert adverse impacts whereas others provide welcome revenue, and some may

F I G U R E 5
Perceptions about the impacts (positive, negative or neutral) of the selected NIS as stated by the commercial and recreational fishers (right plot). Left plot shows the number of fishers who reported that they don't know versus those who assessed the impacts. Asterisk (*) represents statistically significant view of species impacts as positive, two asterisks (**) represent statistically significant view of species impacts as negative and three asterisks (***) represent statistically significant "I don't know" responses (p < 0.05, binomial test using proportion of 0.5). Cross (+) represents significant differences between the responses of commercial and recreational fishers (Fisher's exact test or Pearson's chi-squared test, p < 0.05) provide both. These details can inform a management policy that acknowledges the multifaceted interactions of NIS with stakeholder groups.
Six of the selected NIS contributed over a quarter of the commercial fishery catch in the study area, and the catches comprised more than half of both total landings and value in the summer, highlighting the need for fishery reform to optimise their exploitation (Kleitou et al., 2021a). The contribution of the six species was higher than the catch contribution of all non-indigenous species in the Cyprus fleet, which was estimated by  using telephone surveys (about 19%) but comparisons should be made with caution.
The Cyprus government has identified issues with the data re-  Asterisk (*) represents statistically significant retainment, and two asterisks (**) represent statistically significant discard (p < 0.05, 1-sample proportions test with continuity correction or binomial test using proportion of 0.5). Cross (+) represents significant differences between the responses of commercial and recreational fishers (Fisher's exact test or Pearson's chi-squared test, p < 0.05) accuracy and allow for better informed management decisions (Giovos et al., 2020).

Differences between the interview and official landing data
highlighted that monitoring would benefit from an improved reporting system. Official fishery records are data deficient some NIS, e.g.
species at an early stage of their invasion or species that are sold in aggregated categories along with native species, this prevents timely decision making that can enable management of the NIS before they cause economic impact. For instance, the lack of official data for some NIS, which have been reported as relatively frequent catches ( to incentivise fishers to hunt the species and mitigate the impacts. In 2019, the compensation covered (based on the landing value) about 23% of the reported damages (catch and/or gear) that were caused by the pufferfishes (as estimated by the fishers interviewed this study).
Rigorous monitoring is needed to understand better the ecological and socioeconomic effects of this DFMR compensation scheme.
A peak in Lagocephalus spp. catches coincided with the L. sceleratus reproduction peak (Rousou et al., 2014), and it is likely that the species aggregate to spawn during the summer (anecdotal information by fishers). Fishers adapted to fishing pufferfishes in the summer months to benefit from the government subsidies. Aggregations of the Lagocephalus spp. populations could offer opportunities for alternative fishing practices (e.g. fishery-related tourism/pescatourism) and management strategies that would guide massive and targeted removal of the species.
From the structured interviews, it was evident that RFs reported significantly less frequency of catches than CFs for many of the selected NIS, including P. miles, F. commersonii and P. forsskali.
Recreational fishers' motivations often extend beyond key economic drivers and might be driven by traditional norms for larger and 'trophy' fish, which are often keystone top predators (Giovos et al., 2018;Mackay et al., 2018;Sbragaglia et al., 2021).
Future strategies for NIS management need to consider challenging social norms, feelings and moral obligations to enhance fishing pressure to nuisance NIS and alleviate pressure from native keystone species such as groupers (Kleitou et al., 2021a). Spearfishing of lionfish Pterois spp. has been widely recognised as the best control mechanism (Côté et al., 2014;Kleitou et al., 2021c). Spearfishing with free dive is very popular in Cyprus, with over 2000 licences per year (DFMR, 2020), and management strategies can aim to engage and motivate them.
Generally, fishers tended to perceive NIS (as a whole) as negative but when asked about species-specific impacts, their responses were contradictory, and many species were viewed positively and by many respondents considered to be native. Less than half of the species were correctly recognised by fishers as NIS in the  (Giakoumi, 2014;Vergés et al., 2014). Siganus spp.
were also considered amongst the 100 worst invasive species in the Mediterranean in terms of their socioeconomic impacts (Streftaris & Zenetos, 2006). Damage to ecosystems is often not visible to the public, and ecosystem state change can occur without immediate negative economic impacts. Divergent views and knowledge between stakeholder groups need to be exchanged, acknowledged and prioritisation of issues (i.e. ecological vs social and economic issues) needs to be harmonised to coordinate management strategies.
The low market price of NIS was mentioned by respondents as a major driver of discards, and it limited targeting of NIS by fishers.
There is potential for fishers to become part of the management solution to NIS. In instances where fishing effort can play a role in the management of NIS that are invasive, a market-based management approach to increase demand for selected NIS is strongly recommended (Kleitou et al., 2019c(Kleitou et al., , 2021a has had a negative impact on fishing income and, as a result, put at a risk the economic sustainability of the small-scale fishery (STECF, 2020). This is similar to the impact of pufferfishes on the small-scale fishery of Turkey, where a loss of 2 million € (fishing gear and labour losses) per year was estimated (Ünal et al., 2015).
The findings of the study need to be used with caution. A sample of fishers operating in the study area was interviewed, and results cannot be generalised to the entire Cyprus fishery fleet. However, the use of fishers knowledge is frequently used as an alternative source of information when empirical data are not available (Lopes et al., 2019), and the present study provides additional insights and potentially corrects the above-mentioned inherent limitations of the official data. Interview methods also come with limitations such as reliance on fishers, trust between researcher and fisher, fatigue and potential reticence to provide accurate information (Gill et al., 2019;Maurstad, 2002). All of these issues were largely overcome due to the excellent relationships with the fishers, the proper design and the experience of researchers in conducting interviews.

| CON CLUS IONS
The current management strategy against NIS of the Mediterranean is based on the traditional narrative approach of NIS as having only negative effects; it fails to account for positive contribution of species in ecosystems and fisheries. It was evident that the worst socioeconomic effects of NIS are being caused by pufferfish species, and management solutions are urgently needed to mitigate the effects of their invasions. Other species such as rabbitfish were perceived as highly beneficial by the fishers. To decide on the NIS management strategy, an ecosystem-based fishery approach is needed at which fishery revenues and losses are assessed together with the ecological loss costs or benefits in an integrative framework (Kleitou et al., 2021a). Fishers could be important allies if they are properly informed and involved in collaborative and communicative management processes (Morales-Nin et al., 2017). Improved data collection programmes, research, citizen science, market campaigns and monitoring are also vital in improving the management of NIS and consequently the performance and sustainability of the fisheries in region.

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest for this article.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.