Local Ecological Knowledge (LEK) Can Guide Decision-Making in Inland Fisheries Management

Abstract

Evaluating and integrating local ecological knowledge held by fishers into decision-making processes has the potential to significantly enhance fisheries management. The present study aimed to collect information on fishery practices and to assess the ecological knowledge of local professional fishers through interviews, evaluating its importance in managerial design. As a case study, Polyphytos Reservoir in Greece, which supports substantial fisheries, was selected. During the summer of 2023, thirty-seven interviews were conducted to document fishing efforts, methods, catches, biological information, and fishers’ perspectives on lake management, and economic/demographic details. In addition to gathering data on fishing activities, the study seeks to understand fishers’ perspectives on managerial deficiencies and necessities, thereby revealing their valuable ecological knowledge. The integration of this knowledge into decision-making processes can empower stakeholders and enhance local participation in fishery management. Ultimately, this approach has the potential to address long-standing conflicts, foster inclusive processes, and ensure better collective outcomes.

1. Introduction

Scientists often express reservations about the reliability of fishers’ Local Ecological Knowledge (LEK). The term ‘anecdotal knowledge’ remains commonly used to characterize fishers’ LEK, and its translation into scientific knowledge and management is still limited [1]. Consequently, fishers frequently assert that their LEK needs to be acknowledged, challenging the scientific information that serves as the foundation for fishery policy and management decisions [2]. However, fishers’ LEK is gaining recognition, as a valuable complement to Conventional Scientific Knowledge (CSK). CSK which is obtained and interpreted following scientific methodologies, conceptual models, and hypotheses finds enhanced efficacy when combined with fishers’ LEK, proving particularly beneficial for improvement outcomes, especially in cases where scientific research is scarce in both marine and freshwater ecosystems [3,4,5,6,7,8].

Indeed, LEK can provide valuable insights into species ecology, behavior, and population trends, as well as stocks’ status, fishery production, socio-economic practices, and even the spatiotemporal dynamics, degradation, or changes in ecosystems [7,9,10,11,12]. This information is essential for developing management measures, primarily aimed at protecting and restoring fish stocks [13,14]. However, assessing the LEK reliability for its incorporation into fishery management is of paramount importance [4,11]. Nevertheless, the approaches employed to collect LEK often reveal dissatisfaction among locals [15]. This dissatisfaction arises from a lack of decision-making power, neglect of their interests, improperly established management practices that fail to protect fisheries resources, or a lack of trust in scientific advice. This underscores the importance of further integrating LEK into decision-making processes. Doing so can empower stakeholders, potentially increase local user involvement in management, conservation, and research, address long-standing conflicts, and create more inclusive processes that ensure better collective outcomes [15]. Note that the sustainability of fisheries requires, among other factors, the integration of traditional fisheries management practices and scientific information, coupled with effective information dissemination and communication among users and stakeholders. Additional crucial elements include socio-economic evaluations, education of users, marketing outreach, management plans, and informed decision analysis [16,17].

Inland fisheries management and research in Greece generally face low social priority and contend with inadequate research and funding. Consequently, inland fisheries suffer from inefficient data, primarily limited to the registration of professional fishers by fisheries authorities and the issuance of relevant licenses [18]. However, the existing registries, confirming active fishers in inland water systems, require updating. Additionally, reliable records of landings (annual catch quantities) are lacking, a deficiency primarily attributed to the absence of organized fish markets [18]. This data gap complicates fisheries management and poses a potential threat to the long-term sustainability of fish stocks.

To address these gaps, the present research aimed to collect comprehensive data on the landings of professional Greek inland fishers operating in a dam lake (Polyphytos Reservoir), alongside ecological information derived from their experiences and knowledge, and to evaluate their reliability compared to scientific data. Furthermore, the study sought to document the fishers’ perspectives on fisheries management, investigating whether this information could contribute to the preservation of the fishery and serve as a complementary tool for fisheries managers.

2. Materials and Methods

2.1. Fisheries in Polyphytos Reservoir

Polyphytos Reservoir (Northwestern Greece) is a large dam lake, covering an area of 74 Km² (depending on the water level fluctuations), constructed for electric power production within the Aliakmonas River basin (Figure 1).

The professional fishers’ association in the reservoir comprises 142 registered members, including 45 ordinary members and 97 crew members on vessels with fishing licenses. The reservoir has a total of 68 licensed fishing vessels. However, only a considerably smaller group of fishers are actively engaged in fishing. Notably, between 2016 and 2020, the reservoir experienced a significant increase in fishery production, driven primarily by Danube crayfish (Pontastacus leptodactylus) harvesting. This surge resulted in substantial economic gains for local fishers [19], contributing to the development of lakeside communities. During this period, approximately 85 individuals exclusively pursued crayfish fishing. The lucrative profits from crayfish fishery served as an incentive, attracting individuals with no prior experience who focused solely on crayfish harvesting, utilizing traps as their primary fishing gear excluding other methods. The intense fishing pressure on this specific stock led to its decline culminating in a fishing ban in 2021 to allow the remaining stock to recover. Consequently, the number of active fishers in the reservoir was reduced, nearly returning to pre-crayfish boom levels.

In the subsequent years up to the present day, approximately 15 fishing vessels have consistently been engaged in fishery, with two individuals working on some of them. Crayfish fishing was once again permitted in June 2023. However, the crayfish population has significantly dwindled to the extent that its fishing is no longer economically viable.

2.2. Questionnaire’s Structure

A questionnaire comprising 43 questions, categorized into three sections, was developed and used. The first section focused on demographics, and delved into various aspects of the fishers’ personal information. This included their age, place of birth, father’s employment, marital status, educational qualification, and income. In the second section, which explored involvement in fishing, questions were tailored to gather detailed insights into responders’ fishing participation. This covered the initiation of their fishing engagement, vessel characteristics, sources of information on fishing-related matters, fishing effort, technical aspects of fishing methods (utilizing the fishing tactics typology by [18,20,21]), seasonality of fishing activity, frequency and duration of fishing, recording of commercial and discarded catches, identification of areas with specific fishing interest, fishing equipment, target species sizes, and more. The final section documented the opinions of the fishers on the state of the stocks and the ecosystem, and the adequacy of existing legislation. It also provided an opportunity for the fishers to propose management interventions and share their ecological knowledge. Specifically, the questionnaire addressed their view on the challenges of their employment, environmental issues in the lake, overfishing of stocks, existing fishing legislation, and suggestions for lake management. It also explored the potential for necessary interventions to support the sustainable development of the area, the prospects of the sector, and the possibility of developing secondary activities such as fishing tourism, to supplement fishers’ income and preserve the local population and traditional fishing practices. Additionally, three questions were dedicated to exploring the ecological knowledge of the fishers. Specifically, they were asked to name other non-commercial fish species that inhabit the lake as well as their awareness of the reproductive period and the size of the first sexual maturity of commercial species (here the length of the smallest mature specimen).

The questionnaire underwent a pre-test with a test group consisting of two professional fishers who fish in another inland Greek freshwater body. The objective was to enhance the clarity of certain questions.

2.3. Conducting Interviews

In total, 37 professional fishers were interviewed during the summer of 2023. The interviews took place with both the respondent and a researcher present. Each fisher was interviewed separately so that their responses would be independent. The completion of each questionnaire was conducted anonymously, ensuring that no information that could potentially lead to the identification of the respondent was recorded to uphold the honesty of the responses. Before the interview, each respondent was informed about the identity and role of the researcher, the guarantee of anonymity, and the purpose of the research, including its main goals. Any doubts about methods, potential benefits, and risks, were clarified before the interview.

2.4. Data Analysis

The analysis was initiated by conducting a descriptive examination of the data collected during the interviews. This involved comparing the frequency of responses to present information on the demographic data of the fishers, their fishing practices, catch data, and perspectives. Following this, an assessment was conducted to evaluate the agreement among fisher responses regarding the length or weight at first maturity. It is noteworthy that the inquiry about the length at which the species attains maturity posed significant challenges for fishers with many preferring to respond by mentioning weight (e.g., Prussian carp reproduces for the first time at a weight of 100–200 g). This aspect was considered concerning the standard deviation (SD) estimated for their responses. Concerning the spawning period, the alignment in fishers’ responses was evaluated using a three-measure scale: high agreement for common responses provided by more than 70% of fishers; medium agreement for common responses provided by 30–69% of fishers; and low agreement for common responses provided by less than 29% of the interviewed fishers. Fishers who did not respond to specific questions due to a lack of knowledge were not considered in these analyses.

To explore the alignment between LEK and CSK, a non-parametric Mann–Whitney U Test was applied after log(x) transformation of the data to compare the length at maturity cited by fishers for the commercial fish species with the length reported in the literature. Additionally, the alignment between LEK and CSK regarding the reproductive period of the most commercially important catch species in the Polyphytos Reservoir was investigated. Finally, the non-parametric Spearman correlation was employed to investigate whether fishers’ fishing experience (expressed by fisher’s age, total catches per year, and the year entering the profession) was correlated with reliable ecological knowledge. In this analysis, three pre-assigned measures of LEK were utilized: High, Medium, and Low. These measures were determined based on our assessment of fishers’ responses regarding species reproduction. The above analyses were conducted using IBM SPSS Statistics (version 27).

3. Results

Τhe results obtained from the interviews with the fishers are presented and categorized into three sections: (i) Demographic data, (ii) Involvement in fishing, and (iii) Fishers’ perspectives, corresponding to the structure of the questionnaire.

3.1. Demographic Data

Most respondents were men (86.5%), with women (13.5%) engaging in fishing alongside their spouses (

Table 1. Summary of demographic characteristics of the study participants (n = 37).

Demographic Parameter	Categories	n	Percentage (%)
Gender	Male	32	86.5
	Female	5	13.5
Age group (years)	19–40	14	37.8
	41–65	20	54.1
	>65	3	8.1
Born area	Broader Kozani’s area	35	94.6
	Other	2	5.4
Father involved with fishing	Yes	166	43.2
	No	21	56.8
Educational level	Primary school	9	24.3
	Middle school	7	18.9
	High school	9	24.3
	Technical school	9	24.3
	Higher education institution or college	3	8.1
Marital situation	Singles	8	21.6
	Married	25	67.6
	Divorced	4	10.8
Main occupation	Fishing	13	35.1
	Other	24	64.9
Income	0–6000 €	5	16.1
	6000–12,000 €	13	41.9
	12,000–20,000 €	7	22. 6
	>20,000 €	6	19.4

). A significant portion (54.1%) fell into the 41–65 age group, with a notable presence of younger fishers in the 19–40 age group (37.8%). Approximately 94.6% were born in the broader Kozani area (Kozani is the biggest city near Polyphytos Reservoir). About 43.2% mentioned that their fathers were either exclusively or partially involved in fishing, sometimes alongside other occupations. The educational level of the participants exhibited significant variation, ranging from individuals with elementary school education to those holding university degrees. The majority of the interviewers were married (67.6%) and, on average, had 1.7 children, ranging from 0 to 4. In seven cases, their children were also involved in fishing. However, many fishers (81%) expressed a preference for their children not to pursue a career in fishing, especially following the cessation of crayfish fishing.

Roughly 35.1% of respondents (13 individuals, one of whom is retired but still fishing) considered fishing as their sole employment, while others were simultaneously engaged in various sectors. Regarding annual income, 41.9% reported earnings between 6000 and 12,000 euros, and 22.6% between 12,000 and 20,000 euros. These percentages were calculated based on the responses of 31 individuals. In five cases where the spouse was involved in fishing, the total household income was provided. One fisher did not respond to the income question. In 49% of the cases that answered this question (with exceptions mentioned), respondents stated that their entire annual income came from fishing or the sale of fish. Conversely, individuals who had ceased fishing, particularly those exclusively engaged in crayfish fishing, reported that their income from fishing was now zero.

3.2. Involvement in Fishing

The most experienced fishers initiated their fishing activities in the 1970s, while the majority (51.4%) started during the “boom” of crayfish fishery, specifically in the years 2017–2019 (Figure 2a). Four fishers (10.8%) were exclusively involved in crayfish fishing and mentioned that they would not engage in fishing again unless the crayfish stock recovers to the point where its fishery becomes profitable again. They ceased fishing between 2020 and 2021, along with five others, making a total of nine individuals comprising 24% of the group (Figure 2b). Except for one person who mentioned fishing only in the spring, the remaining fishers (68%) were continuously engaged in fishing from the time they started until today, throughout the year, except during the fishing ban period. Additionally, two women (5%) occasionally fish with their husbands, who fish regularly (Figure 2b).

Overall, the surveyed fishers had 36 vessels, with 27 owning one or more licensed vessels. Those who did not own vessels fished with their colleagues or spouses. On average, the vessels were about 5 m in length, with sizes ranging from 3 m to 7 m. The average engine power was around 30 hp, varying from 5 hp to 125 hp, and these boats were primarily constructed from polyester after the year 2000.

Most of the fishers (32 individuals, 86.5%) indicated that they either currently sell or used to sell their entire catch to wholesalers, while a small percentage sold less than or equal to 50% of their catch at the retail level. Due to the cessation of crayfish fishing, the interviews focused solely on fish catches aiming to document the current situation. Therefore, these estimates only pertain to the fishers who were still active (occupied in 19 vessels). Based on their responses, the target species holding commercial value include common carp (Cyprinus carpio), wels catfish (Silurus glanis), Prussian carp (Carassius gibelio), northern pike (Esox lucius), and to a lesser extent, European perch (Perca fluviatilis) and roach (Rutilus rutilus). Notably, the last two are preferred by those fishers who sell a portion of their catches at the retail level. Consequently, the primary target species for professional fishers in Polyphytos Reservoir range from 4 to 6 species.

Wels catfish and northern pike were primarily caught using long lines, while common carp, Prussian carp, European perch, and roach were caught by crystal-clear gillnets (with mesh sizes ranging from 36 mm to 110 mm). The height of the gillnets varied, ranging from 1.5 m to 7 m, and the total length of the gillnets set per day extended from 500 m to 7 km. The depth at which fishing gear was set varied according to the season and the specific area within the reservoir where each fisher was fishing. Generally, during spring and summer, fishers focus on shallow-water fishing, predominantly in the coastal areas, while in autumn and winter, they shift to deeper waters.

The range of catches per vessel and season is shown in Figure 3. Across all seasons, high values were observed for certain species, mainly common carp, European perch, and Prussian carp, which can be attributed to the reports of 1–2 fishers (Figure 3). The mean values of all reported quantities are presented in

Table 2. Mean vessel catches per species and season based on the statements of the interviewed fishers in Polyphytos Reservoir. Number of vessels: 19, SD: standard deviation.

Season	Catches ± SD (Kg)
	Wels Catfish	Common Carp	European Perch	Prussian Carp	Roach	Northern Pike	Total
Spring	409 ± 510.3	3563 ± 4434.9	406 ± 687.1	2188 ± 4456.3	18 ± 55.8	429 ± 606.1	7014 ± 9021.7
Summer	566 ± 722.8	922 ± 1354.7	1937 ± 4579.9	240 ± 327.3		89 ± 142.0	3754 ± 6032.5
Autumn	369 ± 514.7	1522 ± 1533.3	1011 ± 1071.2	1395 ± 2626.0		668 ± 871.7	4965 ± 5092.4
Winter	185 ± 478.3	1541 ± 2034.9	754 ± 1061.9	1830 ± 2688.4	263 ± 653.4	1096 ± 1569.2	5669 ± 6169.5
Total							21,402 ± 22,203.3

.

3.3. Fishers’ Perspectives

Non-compliance with fishing regulations was identified as the most significant issue affecting the fishery in the Polyphytos Reservoir, as reported by 25 individuals (67.5%) (Figure 4a). Furthermore, the lack of law enforcement and basic fishing infrastructure were also considered substantial problems.

Other significant problems from the fishers’ perspective included: (i) the absence of an ichthyologist in the responsible department of the region, (ii) the lack of comprehensive lake management, (iii) non-conductance of stockings, (iv) a large number of seasonal fishers (primarily those who fish only in the spring or solely for crayfish), and (v) a significant number of anglers fishing in the reservoir without adhering to the legislation. Furthermore, a small number of fishers (16.2%) reported that problems arise from fluctuations in water levels, mainly when fish have deposited their eggs in the coastal zone, affecting the stocks. They also mentioned the high cost of fuel, which increases the expenses of their activities, as well as the absence of subsidies and compensations for fishers, especially following the collapse of the crayfish stock. Other issues are related to false catch reports (some do not issue invoices), the increase in lake temperature, which they believe has impacted fish stocks, the absence of maximum allowable discharge quantities (they request the implementation of discharge limits) leading to overfishing, and the lack of processing units (manufacturing/industrial) that would add value to their fishing products.

Regarding the stocks in the Polyphytos Reservoir, most fishers (35 individuals, 91.9%) stated that crayfish and common carp are overfished (Figure 4b). However, some believe that common carp get overfished only during the spring season. In response to the question of how much they believe the catches have decreased compared to 25 years ago, most fishers answered that the reduction percentage was 0–25% and 50–75% (30% of the respondents in both cases) (Figure 5a). Fishers mentioned overfishing as the primary cause of the reduction (25 fishers, 67.6%) (Figure 5b). However, 56% of the fishers attribute this reduction in water temperature to the decrease in the lake’s water renewal time due to the construction of the upstream Ilarionas Dam (resulting in the construction of the homonymous reservoir) in the upper part of the Aliakmonas River basin and climate change (Figure 5b).

3.4. Fishers’ Ecological Knowledge

3.4.1. Species Composition

The ecological knowledge of the fishers regarding the species composition of the reservoir’s fish fauna was investigated by inquiring about the fish species they were familiar with, aside from their target ones. One person mentioned that he was not aware of any, while several others identified various species (Figure 6).

3.4.2. Length at Maturity

Four of the interviewed fishers stated that they had no knowledge regarding the size of first maturity for any of the commercial species. For the others, the inquiry about the length at which the species attains maturity posed significant challenges and they preferred to respond by mentioning weight (Figure 7). In all cases (except wels catfish) the mean L_m of the fish species based on fishers’ perspectives was between the range for the L_m parameter referred to the Fishbase (

Table 3. Length (L_m, cm) and weight at first maturity (W_m, Kg) ± standard deviation based on the perspectives of interviewed fishers for the commercial catch species in Polyphytos Reservoir (PR). The mean L_m values and the range (in parentheses) at which L_m is attained based on literature [22,23] are also provided.

Parameter	Species
	Wels Catfish	Common Carp	European Perch	Roach	Northern Pike	Danube Crayfish
Lm PR	60.0 ± 17.32	32.5 ± 5.00	12.6 ± 2.07	11.7 ± 3.03	30.0	6.8 ± 2.28
Wm PR	2.07 ± 1.417	0.97 ± 0.358	0.18 ± 0.083	0.15 ± 0.080	1.35 ± 0.629	0.03 ± 0.013
Lm literature	87.5 (86–108)	34.8 (25 ± 36)	16.3 (11 ± 23.4)	14.0 (8–?)	39.9 (25–63)	9 (7–?)

). Based on the conducted Mann–Whitney U test, there were no differences between the L_m values reported in the literature and the ones reported by local fishers in the framework of the present study (p > 0.05) for species common carp, roach, European perch, and northern pike. This analysis was not performed for wels catfish due to insufficient data.

3.4.3. Reproductive Period

The fishers’ responses regarding the spawning periods of the species are depicted in Figure 8. In the case of crayfish and common carp, there was a high agreement among their responses (as more than 70% of the interviewed fishers mentioned one or two specific months) regarding the main reproductive peak for the species. A medium agreement was estimated among their responses for the spawning period of European perch, wels catfish, northern pike, and roach. In general, according to the fishers, common carp, European perch, and roach reproduce during the spring season. Additionally, two fishers noted a second reproductive episode in common carp (a small portion of the population) in early autumn. They also mentioned that wels catfish reproduce during the summer. Finally, the fishers stated that Danube crayfish release their hatchlings mainly during May and June (Figure 8). Overall, LEK agreed with scientific data concerning both the maturity length and the spawning period for most species.

The Spearman correlation among the year of entering the employment, total catches/year, fisher’s age, and LEK on reproduction revealed a potentially significant positive correlation between total catches/year and LEK on reproduction (

Table 4. Spearman correlation results among the year of entering the profession, total catches/year, fisher’s age, and Local Ecological Knowledge (LEK) on reproduction.

Parameter	Year of Entering the Employment	Total Catches/year	Fisher Age	LEK
Year of entering the employment	1.000	−0.371 *	−0.561 **	−0.159
Total catches/year		1.000	−0.052	0.538 **
Fisher age			1.000	0.116
LEK				1.000

*. Correlation is significant at the 0.05 level (2-tailed), **. Correlation is significant at the 0.01 level (2-tailed).

).

3.4.4. Environmental Problems Facing Polyphytos Reservoir

In response to whether they have observed any environmental degradation of the lake, 54% of the fishers answered affirmatively, 43% negatively, and 3% stated they did not know. Specifically, among the most significant problems reported by those who answered affirmatively were eutrophication and the presence of debris and pollution that is attributed to the lack of education and respect for the environment. Some mentioned the presence of livestock units in the area that do not properly handle their waste. In addition, many expressed doubts about the proper functioning of the biological treatment units for urban sewage from neighboring settlements. Lastly, few referred to the increase in water temperature due to the construction of the Ilarionas Dam and climate change and the reduction in the population of crayfish.

3.5. Fishers’ Managerial Proposals

Regarding whether they consider the fishing legislation for the lake and, more generally, the inland waters of Greece to be sufficient, the majority of fishers responded negatively, expressing beliefs that regulations are not enforced, and relevant inspections are lacking. A small percentage pointed out that there are many ambiguities. Concerning the above, a significant portion (>25%) mentioned that the prohibition period is arbitrarily defined and delayed (each time after the start of the reproductive period of the common carp). Furthermore, 92% of the surveyed fishers expressed a desire for increased law enforcement.

The fishers’ management proposals for Polyphytos Reservoir included, among others:

• Conducting stockings mainly with common carp and crayfish.
• Imposing an absolute prohibition on fishing in the lake during the common carp reproduction period. In this context, they propose initiating the prohibition earlier than usual after monitoring the water temperature.
• Conducting inspections to ensure compliance with fishing regulations.
• Staffing the fisheries department of the region with an ichthyologist, or ideally, establishing a management body.
• Updating the registry of fishers to indicate who fishes regularly.
• Providing training for fishers to make them aware of the importance of resource protection.
• Creating infrastructure to facilitate fishing (shore roads, fish ramps, mooring sites), as well as promoting the tourism development of the area (viewing points, kiosks, wooden floating docks).
• Establishing maximum allowable catch limits per professional fisher to prevent overfishing.
• Providing compensation to professional fishers due to the economic loss they incurred from suspending crayfish fishing.

4. Discussion

This study addresses a critical gap in scientific knowledge concerning the fishery of Polyphytos Reservoir, a dynamic socio-ecological system, through questionnaire research. It is situated within the broader context of efforts to enhance the scientific understanding of Greek inland ecosystems and implement effective management measures. Previous studies conducted in other Greek lakes such as Lake Volvi and Lake Trichonida focused on collecting fisheries-related information to shape management strategies [18,24]. However, the present research takes a significant step forward by assessing the ecological knowledge held by local fishers for potential integration into management practices. The study aimed to gain an in-depth understanding of their perspectives on existing managerial deficiencies and necessities. This is crucial for sustaining inland fisheries, necessitating not only scientific information but also social participation in decision-making and effective communication among users and stakeholders [16].

4.1. Demographic Data

The fact that almost all interviewed fishers were born in the broader area of the reservoir’s basin indicates a strong connection with the region and its resources. The gradual aging trend observed in the fishers’ population in other European marine and freshwater fisheries [18,25] was not evident here, indicating that the fishery in the reservoir had significant untapped economic potential. However, the historical trend of passing down the fishing profession from generation to generation [26] was observed, as more than 43.2% of the fishers had fathers who were either exclusively or partially involved in fishing. Τhe fact that fishers with children preferred their offspring not to pursue a fishing career indicates their concerns about the sustainability or economic viability of the profession and sets the stage for a potential upcoming inter-generational discontinuity in the fishery. Similar trends have also been noted in other Greek freshwater ecosystems [18,24], as well as throughout Europe, where inland fisheries, in general, are in decline [27]. This decline results from decreasing fisheries’ productivity due to overfishing, habitat degradation, low demand for freshwater fish, and, subsequently, low economic productivity leading to an increased marginalization of freshwater fisheries [16,18,27].

Given that the research targeted professional fishers, fishing activity was expected to be the sole or primary source of income. However, the findings revealed a notable diversity among fishers in terms of their reliance on fisheries. Specifically, fishers here could be categorized as full-time, part-time, or even subsistence fishers. This diversification is a common characteristic of small-scale European inland fisheries [18,27], driven by the need for supplementary income that motivates individuals to engage in multiple activities.

Participants exhibited a varied range of educational backgrounds, from elementary school to university degree holders. This diversity underscored the heterogeneous educational experiences within the fishing community. From a socio-economic standpoint, it also highlighted the challenges associated with securing employment in rural areas of Greece. In these regions, individuals with higher education degrees are often compelled to engage in agriculture or fisheries, due to a scarcity of job opportunities commensurate with their qualifications [28]. Collectively, these factors create an environment where flexible arrangements can be more easily established and maintained.

4.2. Fishing Involvement

The fishery in Polyphytos Reservoir is currently undergoing a transition phase. After a peak in Danube crayfish fishing for approximately five years until 2021, the number of fishers has declined and a return to pre-crayfish fishing levels is expected. Crayfish were caught using hoop nets, some of which were introduced from China, that were less selective and enhanced catch efficiency. Sold primarily for export, at around 3 euros per kilogram to wholesale companies, this lucrative crayfish exploitation has contributed significantly to the economic welfare of the wider area, often referred to by fishers as a “gold mine”.

Despite the limited socio-economic importance of inland fisheries at the national level [27], with approximately 400 people engaged in the country’s inland fisheries, the sector holds significant economic importance for local communities, especially in rural areas.

The fishery in the Polyphytos Reservoir targets 4–6 species (common carp, wels catfish, Prussian carp, northern pike, and, to a lesser extent, European perch and roach), utilizing various fishing methods, representing a “multi-species” approach uncommon in most Greek lakes, that often focuses on a single species such as common carp (e.g., in lakes Volvi, Mikri Prespa, and Kastoria), or big-scale sand smelt Atherina boyeri Risso, 1810 (in Lake Trichonida) [24].

The mean annual catches estimated per vessel in the present study, based on fishers’ responses, were up to four times higher than those in other freshwater fisheries nowadays [18], underscoring the economic significance of this fishery to the local community. However, while fish stocks in Polyphytos Reservoir seemed to recover during the crayfish fishing period, they now face increased pressure, with expectations for this pressure to rise further. In addition, the fact that no national catch monitoring data system exists, that would enable the early detection of the decline of the fish stocks signs, raises concerns regarding their status. To this framework, the implementation of conservation measures, including potential bans on specific fishing gear to allow stocks to recover, should be considered.

The observed variability in fishing practices and gear dimensions among fishers is attributed to significant changes in the reservoir’s bathymetry induced by its dam origin. Fishers must adapt their practices and gears to the specific conditions of the area they fish.

Increased fishing activity during spring, driven by the common carp’s reproductive cycle, poses a threat to the stock. Despite awareness of the consequences, fishers take advantage of this period before the spring fishing ban, underscoring the need for stricter and more comprehensive prohibition during this critical reproductive period.

Unlike other Greek lakes [18], fishers in the Polyphytos Reservoir do not encounter distribution issues for their catches, likely due to the presence of relevant exporting companies in the region that also provide additional employment in the broader fisheries sector. However, establishing a processing unit for fisheries products could enhance value, benefiting local fishers and the local economy.

The collapse of the Danube crayfish stocks, once a significant contributor to the regional economy, underscores the inadequate protection of the country’s natural resources. Research to investigate the reasons for this collapse in the Polyphytos Reservoir is crucial and could guide restocking trials.

4.3. Fisher’s Perspectives

Most local professional fishers in the Polyphytos Reservoir expressed criticism of fisheries management, effectively highlighting the main issues affecting inland fisheries throughout Europe (see [27]). Specifically, their concerns revolved around the effectiveness of existing regulations and the urgent need for improved enforcement mechanisms, the lack of sufficient monitoring, limited conservation attention, isolation in traditional management practices, intersectoral conflicts, and conflicts with environmental concerns, alongside financial challenges. They were also dissatisfied due to a perceived lack of decision-making power, while distrust of scientific advice was documented. In contrast, the acknowledgment of fish stock overexploitation, with 67.6% of fishers attributing the decline in catches to overfishing, signifies their recognition of the need to address the mismanagement of fish stocks.

The above underscores the importance of researching and uncovering fishers’ perceptions of management and sustainability, as it becomes crucial to assess their willingness to support conservation or management actions [15]. In light of this, effective fisheries control enforcement should be rooted in social participation, with the potential for small-scale commercial fishers to serve as custodians of traditional fisheries [29].

The fishers have requested the implementation of yearly stockings. In addition, they voiced concerns about fish stocks being impacted by various issues including fluctuations in water levels, especially during fish egg deposition, and changes in water temperature and discharge quantities due to the construction of the Ilarionas Dam and climate change. Unfortunately, these concerns have not yet been acknowledged by the scientific community, primarily because monitoring programs are absent. Anthropogenic perturbations, such as pollution, eutrophication, hydropower development, water abstractions, and even overexploitation of stocks have been widely identified as contributors to declining yields [16,27]. This underscores the need to continue stocking efforts to sustain the fishery’s profit. However, for a fishery to remain sustainable, it is crucial to identify the underlying causes of the general decline in fish stocks and implement appropriate actions to address them.

Considering the complete absence of educational programs at a national level aimed at fishers regarding sustainable fisheries management, the observations outlined above demonstrate that fishers possess the ability to identify and articulate deficiencies in managerial practices. Their capacity to highlight key issues affecting inland fisheries throughout Europe, despite the lack of formal education on the subject, underscores the value of their long-term occupation and intimate connection with the natural environment and resources. This suggests that fishers can contribute meaningfully to discussions on fisheries management, offering insights and proposals grounded in their practical experiences and deep familiarity with the ecosystems they operate within [16,30]. The absence of formal education does not diminish their role as key stakeholders and potential contributors to the sustainable management of fisheries.

4.4. Fishers’ Ecological Knowledge

LEK has proven valuable in providing insights into the presence, abundance, population trends, biology, and ecology of fish species (i.e., [4,5,31]). Such studies have been conducted globally, primarily encompassing coastal areas in developing countries where scientific information is often insufficient for effective fisheries management [1,4,7,32]. Among these studies, a considerable amount of research has focused on the reproductive cycles of various fish species, revealing information about the timing of spawning events, preferred spawning grounds, changes in fish behavior associated with reproduction, and even length at maturity [11,33,34]. LEK on length at maturity, yielding numerical data, offers the opportunity for statistical comparison with CSK and has been used as an index of overfishing [11]. It is important to note that formal statistical comparison between CSK and LEK is often challenging [35], although scientists argue that efforts should be made to align them in similar terms for the purpose of comparison [11,29].

The fishers of the Polyphytos Reservoir are primarily familiar with species of economic importance. Mentions of Anguilla anguilla in their responses reflect historical knowledge, as this species can no longer reach the reservoir due to downstream dam construction along the Aliakmonas River that has interrupted its continuity.

The length at first maturity, as reported by local fishers in this study, occasionally differed from the lower limit documented in the existing literature. It is crucial to highlight that in the literature, information on sexual maturity may refer to the median or mean length at which 50% of the population achieves maturity for the first time. This distinction might not be apparent to the fishers, who were specifically asked about the length of the smallest mature specimen. The lack of awareness among many fishers concerning the size of first maturity stems from their common use of large-sized nets or hooks, primarily targeting larger individuals. This results in a lack of personal observations on the maturity of smaller-sized individuals. Fishers’ observations on the breeding periods of commercial species closely align with the literature’s findings [22,36]. Most species typically spawn during spring. However, according to the literature, northern pike, typically reproduces during the winter months, generally between February and April [22]. It is essential to recognize that these studies were conducted in northern countries with colder winter temperatures, which may differ from those in southern Mediterranean countries, such as Greece. Hence, the interviewed fishers may accurately believe that the species’ spawning peak is in February. In contrast, wels catfish, based on various sources [22,37], is reported to spawn from April to June. Nevertheless, some sources suggest a more extended spawning period from early June to August [38], consistent with the observations from interviewed fishers. Given the substantial presence of giant individuals of this species in the ecosystem, a focused study on its reproduction in the lake would be particularly valuable.

From the above, it becomes clear that the fishing ban period in the Reservoir does not encompass the entirety of the commercial species targeted by professional fishers, such as the northern pike and the wels catfish. These specific species are mainly caught with fyke nets, therefore, contemplating a prohibition on the use of these specific fishing tools during their reproductive periods could be examined as an additional management measure for their protection. Additionally, the initiation of the fishing prohibition period in the lake should be reconsidered. According to the consensus among fishers, the start of the prohibition period is later than the onset of common carp reproduction, leading to overfishing of the species stock. Implementing a complete ban on common carp fishing throughout its reproductive period would contribute to its protection.

The substantial convergence between LEK and CSK underscores fishers’ adeptness at consistently and informally assessing fish biological parameters with remarkable accuracy. This highlights a significant potential to engage fishers in upcoming collaborative monitoring initiatives, leading to estimates that are not only scientifically valid but also aligned with the fishers’ experience. The synergy between scientists and fishers can yield meaningful insights and foster mutual benefits.

Integrating LEK as complementary information in the management of small-scale fisheries, as exemplified in the case of Polyphytos Reservoir, can significantly enhance the overall understanding of ecological dynamics. This integrated approach promises to develop more effective management strategies and promote sustainable practices. To achieve this collaborative, community-driven approach, it is essential to foster co-operation among fishers, local authorities, and relevant stakeholders, ensuring the practical effectiveness of implementation. For the Polyphytos Reservoir, the ultimate objective is to advance the sustainability of the small-scale fishery, aspiring to establish a model for effective management that prioritizes both ecological integrity and the livelihoods of those dependent on these resources.

In conclusion, this study highlights the effectiveness of questionnaire-based research in acquiring LEK to bridge knowledge gaps in the realm of fisheries. The findings not only contribute to a better understanding of fisheries dynamics but also shed light on the socio-economic dimensions associated with this sector. Notably, the relatively low cost of employing this method underscores its practical applicability, making it a viable option even under budgetary constraints. The synergy between the scientific exploration of fisheries and the valuable insights provided by local communities showcases the potential for collaborative and cost-effective approaches in fisheries management. Moving forward, integrating such methods into broader research initiatives can enhance our comprehensive understanding of ecological and socio-economic aspects, thereby paving the way for more informed and sustainable fisheries management strategies.