Marine Invasive Alien Species Reshape Small-Scale Fisheries: Case Study in Greek Coastal Waters

Abstract

The spread of non-indigenous species (NIS) in the Mediterranean poses complex challenges for coastal fisheries, yet the perceptions and adaptive responses of small-scale fishers remain poorly understood. This study surveyed 70 professional fishers across Greek insular and mainland ports to assess fishers’ local ecological knowledge, awareness, and operational strategies related to eleven established marine NIS. Semi-structured interviews recorded demographic and effort profiles, recognition rates, perceived environmental and economic impacts, catch frequencies, gear damage, injury incidents, and behavioral changes. Fishers in the study area demonstrated high overall awareness (~95%), but variable recognition of less familiar taxa (e.g., bigfin reef squid, squirrelfish). Venomous and gear-damaging species (pufferfish, lionfish, rabbitfish) were predominantly viewed negatively, with significant reported gear losses (EUR 600–1345 yr⁻¹) and avoidance of high-incidence areas (25–30% of respondents). Conversely, commercially valuable NIS received more positive appraisals and are increasingly targeted. Spatial heterogeneity in perceptions and adaptations underscores the need for regionally tailored management that integrates fishers’ knowledge, promotes safe handling and selective exploitation of marketable NIS, and supports adaptive governance to mitigate ecological risks while enhancing socioeconomic resilience.

1. Introduction

The health of Mediterranean ecosystems is increasingly threatened by human activities and pressures [1]. Among the most significant threats are the invasions of non-indigenous species (NIS), which are internationally recognized as serious risks to the area [2]. The number of NIS has been rapidly increasing in recent decades, with no signs of slowing down, and is now significantly higher than in any other region worldwide. Up-to-date studies reveal that the Mediterranean has seen a 40% increase in established NIS over 11 years, with major invasions from mollusks and crustaceans, which directly impact biodiversity [3].

Major pathways for NIS introduction to the Mediterranean Sea include shipping (via ballast water or hull fouling), entrance through the Suez Canal, aquaculture, and aquarium releases. In the Eastern Mediterranean Sea, the Suez Canal is the primary entry point for species arriving from the Indian Ocean [4]. Recent expansions to the canal, coupled with climate change (increasing average surface water temperatures), have facilitated the spread of thermophilic species from the Indo-Pacific [4,5,6]. Some of these invasive alien species (IAS) cause significant negative impacts on local ecosystems [7]. These effects include reductions in the diversity and abundance of native species, increased extinction risk, genetic alterations in native populations, behavioral changes, and disruptions to ecological processes and ecosystem services [8,9,10,11]. However, some NIS may offer positive contributions by providing new ecological roles or services [8,12]. Some NIS are also poisonous or toxic and negatively affect coastal human activities, such as tourism and fishing [13]. Others, like Silver-cheeked toadfish, Lagocephalus sceleratus (Gmelin, 1789); Striped eel catfish, Plotosus lineatus (Thunberg, 1787); and Yellowspotted puffer, Torquigener flavimaculosus Hardy & Randall, 1983, interfere with fishing activities by damaging gear and catch [14,15], with estimated damages to coastal fisheries in Turkey reaching around EUR 2 million annually [16]. Outbreaks of Rhopilema nomadica Galil, Spannier & Ferguson, 1990, have also resulted in high costs to power plants, due to clogged water intake pipes, and a negative impact on tourism, as their painful stings are a significant concern [17].

In contrast to the negative impacts of NIS, some of them have been commercially exploited by local fisheries in the Eastern Mediterranean, offering economic benefits and contributing to stable fishing yields and local incomes [12,18,19]. Certain NIS can also compensate for lost ecological functions, increase system redundancy, and bolster ecosystem services [8]. To address NIS spread, both the EU and the UN have established legal frameworks and action plans. Scientists have also proposed the culinary use of edible NIS as a practical method to limit their populations [20].

In this context, the systematic recording of fishers’ knowledge has gained importance as a data collection approach, especially when traditional methods fall short [21,22,23]. Professional fishers can provide valuable insights into changes in species composition, temporal trends in fishing, and distinguishing between fishing impacts and environmental ones [21]. Combining these insights is crucial for understanding the impacts of NIS on coastal fisheries, especially on remote islands and in marine areas.

Aim of the Study

In 2019, the campaign “Eat it before it eats them” was launched in Greece by iSea and the Cyclades Preservation Fund, while, in the following years, the project was further supported by the Ionian Environment Foundation, the Argosaronic Environment Foundation, and, more importantly, by the Blue Marine Foundation, which has funded the project for the last 4 years. With the support of professional chefs, it promotes the consumption of edible NIS. The campaign is now implemented as “Pick The Alien”, aiming to raise public awareness about NIS presence and impacts on Greek seas [20].

Most studies to date focus on identifying priority NIS—those likely to cause significant harm to local ecosystems—to guide policy interventions ([12,14] and references herein). More recently, research has explored Greek consumer preferences toward NIS consumption [20,24,25] and the role of seafood retailers and restaurant owners in promoting these species [20]. However, the potential positive contributions of other NIS to fisheries have generally been overlooked. Few studies have examined the operational impacts of marine NIS on Greek seas and especially on coastal fisheries [26]. In this context, the official fishery landing data, reported by the Hellenic Statistical Authority (HELSTAT), which serve as the primary baseline for documenting fishing pressure on ecosystems, do not include non-indigenous species (NIS), thereby hindering accurate assessment of their impacts on Greek fishery resources [27].

Thus, the present study aims to address the aforementioned knowledge gap by investigating possible changes in small-scale fishery (SSF) strategies on the Greek Islands and mainland ports about established NIS in the area. The impacts of geographic regions on professionals’ perceptions were also examined, contrasting those living on islands with those residing on the mainland. Greece’s extensive mainland and insular coastline yield highly heterogeneous small-scale fisheries, characterized by varying levels of dependence, gear use, and economic conditions, which suggests the need for regionally tailored management approaches [28].

2. Materials and Methods

This investigation focused on eleven established marine NIS: L. sceleratus; T. flavimaculosus; Red Sea goatfish, Parupeneus forsskali (Fourmanoir & Guézé, 1976); Devil firefish, Pterois miles (Bennett, 1828); Bluespotted cornetfish, Fistularia commersonii, Rüppell, 1838; Bigfin reef squid, Sepioteuthis lessoniana, Férussac, 1831; Redcoat, Sargocentron rubrum (Forsskål, 1775); Dusky spinefoot, Siganus luridus (Rüppell, 1829); Marbled spinefoot, Siganus rivulatus, Forsskål & Niebuhr, 1775; Yellowstripe barracuda, Sphyraena chrysotaenia/flavicauda, Klunzinger, 1884/Rüppell, 1838; and Pempheris sp. Species selection was based on expert assessments regarding their abundance and interactions within the study area. Additionally, coastal priority species, identified by the joint pilot sub-regional study of the General Fisheries Commission for the Mediterranean (GFCM) and UN Environment/MAP for the Eastern Mediterranean, were considered [12,29].

This study involved small-scale fishers from the three fishing ports of the Cyclades Islands, namely Paros, Amorgos, and Santorini, and four fishing ports from the mainland in the Argolikos Gulf, namely Tolo, Hydra, Spetses, and Nafplio (Figure 1). The survey was focused on the fishers using set nets (gill and trammel nets) and bottom longliners to target demersal species. The number of SSF vessels was derived from the records of the EU Fleet Register for 2023 (https://webgate.ec.europa.eu/fleet-europa/index_en, accessed on 5 May 2025) for the registered fishers who declared the above-mentioned fishing gear types as primary and secondary fishing gear. The percentage of truly active SSF vessels (i.e., fully dependent on fisheries) was derived from [30], which has remained consistent to the present day [28].

Active fishers, those working all year round and more than 125 days per year, were selected for interviews during visits to the ports, and interviews were conducted when fishers returned to the port from a fishing trip, or when they were mending their gear. At the beginning of the interviews, the fishers were aware of the study’s objectives and assured that their responses would remain anonymous, and that the research was independent of any regulatory bodies, to establish trust with the participants. To ensure clear and consistent responses, the interviews were conducted using standardized methods commonly applied in previous fishery research, see [12].

The interviews were conducted primarily at the landing and docking sites of the fishers’ vessels. At the same time, they were engaged in tasks such as net repairs or boat maintenance, either before or after landing, to avoid disrupting their daily routine. The interviews took place in a private setting, through one-on-one meetings, to prevent third-party influence. To minimize misunderstandings and enhance the reliability of the responses, all interviews were conducted by the same individual, using a consistent method of presenting, without prompting or influence. Participants were approached in an informal and friendly manner, being asked if they were willing to answer a few questions regarding their fishing activities.

To prevent data duplication, the interviewees were exclusively owners or captains of the fishing vessels, and only one questionnaire was collected per vessel. Given that fishers often use different or local names for species, some of which may refer to multiple species or vary between communities, species identification guides were used during the interviews to clarify species identity.

The questionnaire developed posed questions (shown in

Table A1. Questionnaire.

Questionnaire for the Small-Scale Fishery of Marine Invasive Alien Species.
Date of interview:							Area:
General information
1. Sex: Male/Female
2. Age:
3. Area of residence:
4. Fishing port:
5. Education level?
a. Not completed primary school
b. Primary school
c. Junior high school
d. High school
e. University student
f. University/Technical Degree
g. MSc/PhD
6. Since when have you been involved in fishing (year)?
7. Member of fisher’ association? YES/NO
8. Owner of a fishing vessel? YES/NO
9. Vessel characteristics:
a. Length
b. Engine horsepower
c. Year of construction
10. How often do you fish each season?
Season		Number of fishing trials			Duration of a fishing trial				Fishing gear			Target species
Winter
Spring
Summer
Autumn
Non-indigenous species
Using a scale from −2 to +2, where −2 = strongly negative, 0 = neutral, and +2 = very positive, to what extent do you believe the following non-indigenous (alien) species affect your fishing activities? 1: Lagocephalus sceleratus; 2: Torquigener flavimaculosus; 3: Parupeneus forsskali; 4: Pterois miles; 5: Fistularia commersonii; 6: Sepioteuthis lessoniana; 7: Sargocentron rubrum; 8: Siganus luridus; 9: Siganus rivulatus; 10: Sphyraena chrysotaenia/flavicauda; 11: Pempheris sp.
	Is it a NIS? (YES/NO)		NIS Impacts. Positive (+), Negative (-), Neutral (/), Do not know	NIS discarded (YES/NO)		Frequency of presence in the catch per fishing trip): 75–100%, 75–50%, 25–50%,5–25%, <5%		Percentage contribution in the overall catch: 75–100%, 75–50%, 25–50%,5–25%, <5%		Gear damages: (per year)	Personal incidents of injury (YES/NO)		Change: (1) of fishing gears, (2) fishing area (3) in the duration of fishing trials
1
2
3
4
5
6
7
8
9
10
11

in Appendix A) in three sections to describe the following: (1) the demographic profile of the fishers; (2) their perceptions about the impacts of NIS; and (3) species-specific knowledge, perceptions, and interactions of fishers with the 11 studied NIS. The common name(s) of each target species were used during the interviews, accompanied by a photo to ensure the respondent was referring to the correct species. For each species, fishers were asked specific questions to assess the following: (a) their awareness of the species’ non-native status in the Mediterranean; (b) their perceptions of the species’ impacts; (c) how often the species were discarded; (d) how frequently they were caught (i.e., likelihood of capture per fishing trip) and their relative contribution to total catch biomass; (e) any damage caused to catches (e.g., through depredation) or fishing gear; (f) any injuries sustained due to the species; and (g) whether they had modified their fishing equipment, location, or effort duration in response to the species’ presence.

The frequency of responses across the whole sample was calculated based on independent variables, such as the demographic profile of the fishers. Statistical associations were analyzed using a one-sample chi-squared (χ²) test for proportions. Relationships between fisher profiles and their responses were evaluated using Pearson’s chi-squared test with Yates’ continuity correction for binary questions (Yates-corrected p > 0.05), or Fisher’s exact test when expected frequencies were below five. For questions using percentage-based scales, differences across species were tested using the Kruskal–Wallis H test, followed by Dunn’s post hoc test with Bonferroni pairwise correction [31].

All statistical analyses were performed using IBM SPSS Statistics version 29.0.2 [32].

3. Results

Overall, 70 professional small-scale fishers participated in the survey. According to the official country data from 2023, the interviews covered more than 10% of the active (approximately 50% of registered fishers) registered SSF vessels in the Cyclades Islands and almost 7% of the active registered SSF vessels in the Argolikos Gulf. The percentage breakdown between island and mainland fishers was higher in the Cyclades (69%) than in the mainland (31%). The average age of the SSFs interviewed was 54.2 (SD: 14.6, range: 22–80). They exhibited an average of 41.6 years of fishing experience (SD: 16.4, range: 10–75). The vast majority (94.7%) of the fishers surveyed were members of the professional fishers’ association, and all of the participants were vessel owners exhibiting an average of 152 (SD: 836.6, range: 25–330) annual fishing days. More than 80% of fishers have been professionally engaged in fishing since the mid-1980s and -1990s, while smaller proportions (15.8% and 4.2%) have been active since the 1950s or the 2010s, respectively. Fishers’ vessels had an average length of 9.6 m (SD: 2.9 m) and an average engine power of 74.8 horsepower (SD: 100.7 HP). There is a significant (F = 30.81, p < 0.05) spatial variation in the average annual fishing days, with fishers from the mainland exhibiting significantly (post hoc Tukey’s test, p < 0.05) higher effort (229.8 days) compared with those originating from the Cyclades (<179.9 days). A significant difference was observed in the average number of fishing hours invested in fishing trials per fishing trial/trip for a single fisher, with those fishing in the Cyclades Islands exhibiting higher numbers of fishing hours than those in the mainland (80.9 vs 31.4 h, respectively). With respect to seasons, the mean number of fishing days significantly differed (F = 25.1, p < 0.05) among seasons, with spring and summer showing significantly (post hoc Tukey’s test, p < 0.05) higher numbers of fishing days (44.1 and 48.4, respectively) compared to autumn and winter (37.0 and 32.8, respectively). In contrast, there were no significant (F = 75.1, p > 0.05) differences for the number of fishing hours among seasons. The majority of the participant fishers (ranging from 60% to 90%, depending on the season) used gillnets, while the rest—more than 15%—used exclusively bottom longlines, especially during the winter (26.8%). The majority of the participants (68.4%) reported, regardless of the season, that their target species generally consisted of various species. A smaller percentage specifically targeted species such as Surmullet, Mullus surmuletus, Linnaeus, 1758, Parrotfish, Sparisoma cretense (Linnaeus, 1758), or Chub mackerel, Scomber japonicus Houttuyn, 1782, while 5.3% indicated that their target species were either Red porgy, Pagrus pagrus (Linnaeus, 1758), White seabream, Diplodus sargus (Linnaeus, 1758), or M. surmuletus.

The vast majority (overall ~95%) of fishers stated that they were aware of what a NIS is, which was significantly (chi-squared (χ²) proportion test, p > 0.05) independent of the area of fishing. Using a scale of –2 to +2 (–2 = very negative, 0 = neutral, and +2 = very positive), more than a third of the fisheries (34.3%) reported that NIS cause neutral impacts to the ecosystem, significantly (Kruskal–Wallis, χ² = 47.7, df = 4, p < 0.05) attributed to the fishers originating from the mainland (45.5%) and Paros Island (56.3%). In contrast, 40% of the fishers stated that NIS cause very negative and negative impacts, significantly (Kruskal–Wallis, χ² = 65.7, df = 4, p < 0.05) deriving from Santorini (61.5%). For the rest of the fishers, 25.7% stated that NIS cause positive or very positive impacts, mostly dependent on fisheries in Amorgos (57.9%) (Kruskal–Wallis, χ² = 84.3, df = 4, p < 0.05).

Four out of the eleven studied species (i.e., S. lessoniana, S. rubrum, S. chrysotaenia/flavicauda, and Pempheris sp.) were not recognized as NIS by more than 47.1% of the fishers, which was dependent (Kruskal–Wallis, χ² = 27.2, df = 4, p < 0.05) on the fishing area. In Amorgos and Santorini, all the above-mentioned species were more often recognized as NIS by significantly higher proportions (more than 60%) than in overall mean estimates (Kruskal–Wallis, χ² = 53.2, df = 4, p < 0.05) (Figure 2). In contrast, the remaining seven species were recognized as NIS by more than 70% of the fishers (Figure 2), independent (Kruskal–Wallis, χ² = 4.3, df = 4, p > 0.05) of the fishing area, with the exception of P. forsskali in the Argolikos Gulf, which were not recognized as NIS by 50% of the fishers.

The commercially important NIS P. forsskali was perceived as positive by 52.9% of the fishers, with perceptions being significantly (Kruskal–Wallis, χ² = 41.3, df = 4, p < 0.05) higher in Amorgos and Santorini, whereas venomous but still edible P. miles was perceived as neutral, an opinion that significantly (Kruskal–Wallis, χ² = 18.4, df = 4, p < 0.05) differed in Amorgos, where the species was perceived as positive. Poisonous L. sceleratus, T. flavimaculosus, S. luridus, and S. rivulatus were perceived as negative by more than 67.1% of the fishers (Figure 2), which was not significantly (Kruskal–Wallis, χ² = 7.3, df = 4, p > 0.05) dependent on area. For the other four NIS (i.e., F. commersonii, S. lessoniana, S. rubrum and S. chrysotaenia/flavicauda, and Pempheris sp.) most fishers (>52.2%) responded they “don’t know”, which was not statistically (Kruskal–Wallis, χ² = 5.8, df = 4, p > 0.05) dependent on area, except S. lessoniana in Amorgos (positive statement by 89.5% of the fishers).

When fishers asked about the probability of catching in a fishing trip and the percentage contribution in the overall catch of each NIS, S. luridus and S. rivulatus were recognized as the most commonly (for more than 50% of the fishing trials and overall catch) caught species by more than 60% of the fishers (Figure 3). A wide range of probabilities and contributions were identified for L. sceleratus, T. flavimaculosus, P. forsskali, and P. miles, as more than 80% of the fishers declared a range of percentages up to 50% (Figure 3). All the above were not statistically (Kruskal–Wallis, χ² = 1.6, df = 4, p > 0.05) dependent on area.

Figure 4 presents the percentage of fishers who had at least one fishing trip during which a single specific NIS was discarded. According to more than half of the participants, F. commersonii, S. rubrum, S. luridus, and S. rivulatus had the highest chances of being discarded (Figure 4), with most NIS responses not significantly (Kruskal–Wallis, χ² = 63.5, df = 4, p < 0.05) different among areas, except F. commersonii in the mainland, where fishers responded in a significantly (Kruskal–Wallis, χ² = 38.7, df = 4, p < 0.05) higher percentage “I do not know”.

For seven NIS, fishers did not report any direct damage to fishing gear; for four NIS, the above was not true. L. sceleratus (72.3%) and T. flavimaculosus (67.1%), significantly (Kruskal–Wallis, χ² = 22.7, df = 4, p < 0.05) higher in Amorgos and Argolikos (70%), S. luridus (46.0%), significantly (Kruskal–Wallis, χ² = 12.4, df = 4, p < 0.05) higher in Paros and Argolikos (>61.5%), and S. rivulatus (44.3%), with no significant (Kruskal–Wallis, χ² = 18.6, df = 4, p < 0.05) difference among areas. For these species, from 9% to 29% of fishers reported average annual financial losses due to gear damage of EUR 600 for S. rivulatus, EUR 620 for S. luridus, EUR 960 for T. flavimaculosus, and EUR 1345 for L. sceleratus were reported.

Fishers did not report any personal incidents of injury from most of the selected NIS apart from P. miles, S. luridus, and S. rivulatus, for which incidents were reported by 25.2%, 77.1% and 44.3% of the participants, independent (Kruskal–Wallis, χ² = 7.3, df = 4, p > 0.05) of area. Regarding the indirect impacts caused by NIS, about 25–30% of the fishers reported that they changed their fishing area, due to the presence of L. sceleratus, T. flavimaculosus (25%), S. luridus, or S. rivulatus in their target area, independent (Kruskal–Wallis, χ² = 14.1, df = 4, p > 0.05) of area.

4. Discussion

The present study assessed the perceptions and adaptive practices of small-scale Greek fishers in selected mainland ports and three Cyclades islands regarding the spread of 11 non-indigenous marine species in their fishing areas. Our survey of 70 professional SSFs constitutes a substantial sample, covering over 10% of active SSF vessels in the Cyclades and nearly 7% in the Argolikos Gulf [27]. The average respondent was 54.2 years old with more than four decades of fishing experience. This age and experience profile aligns with previous studies on Mediterranean SSFs as a traditional occupation with deep local ecological knowledge [21]. The high-frequency membership rate (94.7%) further indicates that our participants are well-integrated into formal governance structures, suggesting that their views may inform policy effectively.

A spatial heterogeneity in fishing effort was documented, with mainland fishers averaging 229.8 fishing days annually, substantially exceeding the 179.9 days reported by fishers in the Cyclades (F = 30.81, p < 0.05). This may reflect differential economic reliance on SSFs between areas [28] or variable environmental conditions (e.g., seasonal closures, tourism pressure). Seasonality also influenced effort, with spring and summer exhibiting higher mean fishing days than autumn and winter (F = 25.1, p < 0.05), consistent with seasonal fluctuations in target species abundance and market demand [28].

Nearly all respondents (~95%) recognized the concept of NIS and demonstrated a general awareness of NIS in the marine environment, regardless of the fishing area. This high awareness likely reflects increased media and management attention to invasives in the Eastern Mediterranean [3]. Recognition rates for each NIS varied, as four species (e.g., S. lessoniana) were unrecognized by nearly half of fishers, with significant area-dependent contrasts (e.g., >60% non-recognition in Amorgos/Santorini; χ² = 53.2, p < 0.05). This might be attributed to the fact that SSFs do not interact with such species. For example, S. lessoniana is more common in recreational fishers’ catches, while Pempheris sp. is mostly seen by divers and snorkelers [6]. On the other hand, this might be attributed to the species abundance in these areas, but such systematic data do not exist for the two target areas. In contrast, seven species achieved > 70% recognition across regions (except P. forsskali in Argolikos). The commercial species P. forsskali was viewed positively by over half of respondents, particularly in Amorgos and Santorini, underscoring its emergent economic importance [18]. This might be attributed to the fact that the common name of this species is “alien red mullet”, similar to the commercially important common red mullet, M. surmuletus, a common target of Greek SSFs. Therefore, this positive attitude might also be influenced by the common name of the species and the perception of the fishers that it will also become a highly priced and commercial species. Attitudes varied markedly by locality, as mainland and Paros fishers tended toward neutral perceptions (34.3% overall), Santorini respondents exhibited predominantly negative views (40%), and Amorgos fishers reported more positive assessments (25.7%). Such divergence may reflect local economic and ecological contexts: areas where NIS contribute significantly to catch or revenue may engender more favorable attitudes [6], whereas locations experiencing gear damage or ecosystem shifts may foster negativity [33]. This mirrors broader Mediterranean patterns, where fishers view marketable NIS, such as Siganus spp. and P. forsskali, as economically beneficial despite their ecological disruptiveness [11].

In contrast, venomous or harmful taxa (e.g., P. miles, L. sceleratus, Siganus spp.) were predominantly perceived as neutral or negative (> 67%), reflecting concerns over human health risks and gear damage [34,35]. More specifically, most of the participants reported gear damage from L. sceleratus (72.3%) and T. flavimaculosus (67.1%), particularly in Amorgos and Argolikos (≈70%; χ² = 41.3, p < 0.05). Incidents of personal injury were noted for P. miles (25.2%), S. luridus (77.1%), and S. rivulatus (44.3%), though these did not vary by region. These results corroborate prior reports of NIS as vectors of economic loss and occupational hazard [7,36], underscoring the need for targeted mitigation measures (e.g., modified gear, fisher training). A significant portion of respondents also reported modifying their fishing strategies, because NIS damage their gear, thus subsequently increasing the time spent fishing to achieve their income. Approximately 25–30% of fishers altered fishing grounds to avoid NIS hotspots, notably for L. sceleratus and T. flavimaculosus. Although there is no direct documentation of gear damage caused by T. flavimaculosus, the species’ high discard rate, toxicity, and increasing frequency in bycatch raise concerns about the economic and operational impacts on small-scale Mediterranean fisheries [37]. Such spatial avoidance, independent of area, may reflect adaptive responses, but could lead to intensified pressure on alternative grounds, with potential ecosystem trade-offs [38]. A structured interview-based study in Cyprus found that venomous and poisonous NIS, particularly L. sceleratus and P. miles, were widely perceived by fishers as harmful. Respondents described personal injuries from handling these species, including bites and punctures from venomous spines, which pose health risks and economic costs. This evidence was gathered from both commercial and recreational fishers [12]. However, in the case of Cyprus, fishers reported, among other strategies, that they further increased the eye of the net to reduce the bycatch of T. flavimaculosus, while Greek fishers did not report such a strategy.

More than 60% of fishers reported frequently catching S. luridus and S. rivulatus, with substantial bycatch probabilities for other taxa (e.g., L. sceleratus, T. flavimaculosus), yet most catches of F. commersonii, S. rubrum, S. chrysotaenia/flavicauda, and Pempheris sp. were largely unknown (“don’t know”). These results are consistent with previous research, such as [7,18], which reported that Siganus spp. were among the most significant NIS in Cyprus in terms of both biomass and commercial value [12]; however, in Greece, Siganus spp. still have very low commercial value, with a retail price of EUR 5 per kg in the case of large quantities and size (information provided by fishers in the Cyclades). Often NIS prices are determined on the basis of comparable species, as, for instance, P. miles is priced the same as Red scorpionfish, Scorpaena scrofa, Linnaeus, 1758, and P. forsskali the same as M. surmuletus (information provided by fishers in the Cyclades). Highly abundant or commercially valuable NIS are readily identified and retained, whereas less familiar species are often ignored or discarded, potentially biasing official landing statistics [12]. Over half of fishers indicated discarding high-incidence NIS (F. commersonii, S. luridus, and S. rivulatus), with area-specific uncertainty (e.g., in the mainland) that is attributed to the low abundance of the species in this area. Although some NIS are now actively targeted in other Mediterranean areas [7,18], discard of NIS in Greece remains high [37]. These findings reinforce the complex cost–benefit trade-offs that NIS present to fishers. As noted in [12], rethinking management to harness the benefits of certain NIS while mitigating their harms requires adaptive governance frameworks.

Establishing a market chain for NIS in Greece and beyond is complex, influenced by market drivers, stakeholder perceptions, and consumer preferences. For instance, the invasive P. miles spurred market development in other regions worldwide (Caribbean coast: ref. [39] and US Virgin Islands: ref. [40]). In the Cyclades, the retail price of P. miles ranges from 10 to 20 EUR/kg deboned, depending on the size (information provided by local fishers). For Siganus spp., consumption potential is limited to local venues and mid-tier restaurants, as chefs cited its bony, low-flesh anatomy as a barrier to gourmet use. While currently only fried preparations were deemed feasible, Cyprus’s experience [18], where Siganus spp. is now a major catch—suggests future fishery significance in the South Aegean [41], pending shifts in gastronomic perceptions fitting into a climate-smart seafood strategy. Red Sea goatfish (P. forsskali) is also considered economically important, due to its high market value as a food fish in both the Red and Eastern Mediterranean [42] Seas. However, sporadic landings and low volumes hinder large-scale market integration. In contrast, P. miles exhibits broader restaurant potential due to its versatile flesh, which is adaptable to ceviche, sushi, grilling, and burgers, dishes that have been successfully prepared in Amorgos and Tolo, with positive consumer feedback [20]. This supports localized supply chains (e.g., fishers to restaurants), already operational in Amorgos. Yet, retail potential remains low: Greek consumers tend to avoid unfamiliar, labor-intensive species for home cooking [41], and their exotic appearance exacerbates this reluctance. While the U.S. market provides vacuum-packed fillets [40], Greece lacks both an ISO certification for P. miles processing and stable year-round landings (especially in winter), deterring supermarket involvement. This supply inconsistency, a universal challenge for NIS in Greece, limits mainstream adoption, despite growing supermarket reliance for fish purchases. Additionally, Greek consumers prefer familiar, easy-to-prepare species, which further restricts mass-market potential [20]. Thus, future efforts should prioritize localized chains (e.g., Siganus spp. in Amorgos, P. miles in Crete), chef collaborations for innovative NIS dishes, and festivals like Thessaloniki’s Blue Crab Festival, implemented under Pick the Alien for four years, with more than 7000 dishes of the invasive Atlantic Blue Crab served to locals [20].

Studies have identified Greek seas, especially areas like the Saronikos Gulf, as key entry points for non-indigenous species (NIS), but efforts to manage these introductions, such as through market use or policy changes, remain less developed compared to in other Mediterranean areas [43]. The threat of biological invasions within Marine Protected Areas (MPAs) and Natura 2000 sites remains underestimated [44], which has clear implications for policy and management decisions, while further MPAs can act as NIS hubs [45]. Surveys across Mediterranean MPAs showed that NIS biomass often exceeded 50% of total fish biomass in the South and East, with warmer waters and proximity to the Suez Canal acting as major facilitators [45]. Coordinated regional efforts, such as through the Barcelona Convention, are crucial to recognizing the transboundary nature of marine invasions and the dual ecological and economic roles that established NIS may have. Scientific research, citizen science, outreach campaigns, and systematic monitoring are indispensable tools for improving understanding, utilization, and management of NIS in the Mediterranean.

5. Conclusions

The present study indicated knowledge gaps on key information about non-indigenous species (NIS), such as how to identify them, their impacts, and management rules. Subsequently, studied fishers relied on ecosystem services that are influenced by NIS, such as fish stocks and gear conditions, supporting calls for more participatory and area-specific management strategies. Nevertheless, the results of the present study should be interpreted in light of its limitations. This research was exploratory in nature and was confined to a small number of fishers in certain areas relative to the whole. Further investigation, with a larger sample and across wider regions, could significantly enhance the validity of this study’s findings, especially those relating to the economic profiling of the surveyed fishers. Involving fishers in monitoring, training them for accurate species identification, and promoting sustainable exploitation of marketable NIS could serve both ecological and socioeconomic goals [12]. The perceptions and experiences of small-scale fishers reveal a nuanced landscape of NIS impacts, shaped by species traits, spatial dynamics, and local knowledge. Effective NIS governance must integrate this heterogeneity through tailored, bottom–up approaches that recognize both the threats and potentials of these species within changing Mediterranean ecosystems.