A daptiv e small-scale fisheries in the eastern Cantabrian coast through reliance on essential species

In recent decades, small-scale fisheries (SSF) activity along the Basque coast (eastern Cantabrian) has declined, which has led remaining vessels to undergo notable shifts in their targeted species and therefore the fishing gears used, aimed at enhancing efficiency. Within that context, this study combines logbooks and sales notes spanning from 1995 to 2022 to assess inter-annual and seasonal variations in fishing activity and the main target species across different fishing gears, namely ‘fleet segments’. Results reveal that the spring Atlantic mackerel ( Scomber scombrus ) and summer albacore ( Thunnus alalunga ) seasons, with an intensified harvesting under favourable conditions during the past decade, affected the activity of all other segments throughout the year. In the face of climate change affecting harvested species, a scenario where mackerel and/or albacore seasons are disturbed would lead the SSF to predominantly depend on European hake, mainly caught by declining longlines and set nets, as well as on complementary species. Assessing essential species targeted by each SSF segment relies on is crucial for stak eholder s as it helps manage interactions between fleets targeting the same species (e.g. SSF vs. industrial and recreational fisheries), and understand gear shifts by vessels targeting specific species in certain seasons.


Introduction
Despite their relatively low volume of catches and economic importance in global terms, small-scale fisheries (SSF) hold social importance and are an integral component of the European coast (Guyader et al. 2013 ).However, knowledge on SSF has been inadequately documented, with reduced data completeness and/or quality (Cope et al. 2023 ) leading to lower perceived importance in data collection, stock assessment, and management advice, compared to large-scale fisheries (Guyader et al. 2013, Kennelly and Borges 2018, Pascual-Fernández et al. 2020 ).In part influenced by the lack of a common definition for this fleet (e.g.García-Flórez et al. 2014, Smith and Basurto 2019, Murillas-Maza et al. 2023 , and references therein), as well as by the wide diversity of different gears used within the same vessel throughout the year (Maynou et al. 2011 , García de la Fuente 2020 , Pascual-Fernández et al. 2020, Villasante et al. 2021 ), the management of this fleet has historically been challenging (Pascual-Fernández et al. 2020 ).This fleet operates mostly along shorelines, close to the coast, and making short trips.
Although the SSF plays a significant role for the local economy and addressing social benefits (Kittinger et al. 2013, Schuhbauer and Sumaila 2016, Garza-Gil et al. 2020 ), the sustainability of this sector is jeopardized by pressing issues, namely the problem of generational succession, which supposes a significant threat to its near future viability (García-Lorenzo et al. 2023 ).Communities such as the SSF, dependent on natural resources, are likely to be affected by rapid environmental change and environmental and socio-cultural displacements (Young et al. 2019 ).This way, in the Basque Country (eastern Cantabrian), the picture of most harbours has changed during the last decades, which responds to the generalized decreasing trend of the SSF fleet in different Iberian and European regions (Tzanatos et al. 2005, Cordón Lagares et al. 2016, Lloret et al. 2018, García de la Fuente 2020, Pascual-Fernández et al. 2020 ).On the Basque coast, the SSF fleet is characterized as an artisanal fleet employing traditional fishing gears.Reflecting the cultural heritage of the region, it primarily comprises small to medium-sized vessels with a length overall (LOA) between 6 and 18 m (Murillas-Maza et al. 2023 ).These vessels make short trips along the shoreline, close to the coast, with minimal crew onboard that who handcraft different gears throughout the seasons of the year (Murillas-Maza et al. 2023 ).This enables SSF to take advantage from their ability to adapt to resource availability, intensifying their fishing effort on species that are either highly abundant or of significant economic value in the local fish market (Villasante et al. 2021(Villasante et al. , 2022 ) ), and increasing fishing strategy diversity to adapt to changing ecological conditions (Yletyinen et al. 2018 , White andScheld 2024 ).
Within the context of changing oceanic conditions, vessels primarily using certain fishing gears and heavily rely-ing on specific commercial species face increased vulnerability (Young et al. 2019 ) due to the potential loss of fishing opportunities (Pinsky et al. 2021 ), as these species may undergo future changes (Pansch and Hiebenthal 2019 ).In the same way, species predominantly harvested by the SSF, such as seabass, sole, or striped red mullet, are considered as 'data limited' stocks according to the ICES stock classification (ICES 2023a ).These species may experience substantial impacts due to potentially intensified and technologically advanced fishing activities (Pascual-Fernández et al. 2020 ).On the other hand, a good ecological status of certain target species and/or higher abundances closer to the coastline may increase their catchability, which would affect the fish species composition and catch weights on their seasonal landings.However, the SSF are vulnerable not only to the mentioned resources (i.e.catchability and landed species' diversity; Young et al. 2019 , White andScheld 2024 ) but also to other factors.These include cultural services (e.g.gastronomic traditions and festivities related with the consumption of specific fish; Pascual-Fernández et al. 2020, Murillas-Maza 2024 ), local food systems (e.g.increased attention to health and safety, ensuring healthy and nutritious food products are produced safely and in an environmentally sustainable manner; Arthur et al. 2022 ), administrative decisions, and potential interactions with other fishing fleets.Thus, stakeholders and policymakers would benefit from knowledge regarding the adaptive behaviour of the SSF (Prosperi et al. 2019 ), through multiple preferred gears and targeted species (e.g.Maynou et al. 2011, Pascual-Fernández et al. 2020 ), to manage local fisheries in a changing environment so they can contribute to an ecosystem-based management with their decisions (Jackquet and Pauly 2008, Quetglas et al. 2016, Villasante et al. 2021 ).
Our study first attempts to define the SSF fleet segmentation based on the diversity of landed species by vessels operating with each of the main used fishing gears.Our assessment includes the identification of those species that are particularly essential for the SSF, as they may play a pivotal role in potential future scenarios, where a SSF fleet strongly reliant on certain species that might face unfavourable conditions, thereby reshaping fishing activities within this regional fleet over time.Accordingly, the fishing activity of the past three decades is assessed in terms of fishing days, number of active vessels and landings, to determine whether it varies significantly depending on year and/or fleet segment.Based on that, the primary objective of the present study is to explore how the SSF has transformed in the Basque Country during the last decades, in response to a general declining fleet size and the strategic shifts between different gears, e.g. with vessels becoming increasingly specialized in targeting specific species or stratifying into seasonal fisheries.Our hypothesis therefore posits that the reduction in the SSF fleet over recent decades has resulted in notable adaptations in fishing preferencesi.e.fishing diversification behaviour (White and Scheld 2024 ) through higher effort allocation to certain fishing gears-as a response mechanism to changing environmental and socialpolitical (Fuller et al. 2017, Yletyinen et al. 2018, Murillas-Maza et al. 2023 ) conditions.Notably, we anticipate certain temporal trends on fishing activity regarding seasonal fisheries that might exhibit heightened importance, which may indirectly affect SSF vessels dedicated to other fishing gears since they would allocate less fishing effort on other specific target species in which they rely throughout the year.Conclusions drawn from this study may have broader applicability beyond the Basque region, providing valuable insights for assessing and managing SSF in other regions worldwide that are experiencing similar changes in their fishing activity and fleet composition.

SSF data collection
The present study is focused on the active SSF fleet based in the Basque Country, in the eastern Cantabrian Sea, and operating from 1995 to 2022.This comprises fishing activity in external waters, mostly within the 200-m isobath, where the SSF and operate together with large-scale fleets (e.g.purse seiners, trawlers), and within the boundaries of the internal waters, where the SSF is the main operating fleet ( Fig. 1 ; please refer to Murillas-Maza et al. 2023 for details).
As members of the European Union, vessels in this region are subject to the Control Regulation (EU 2009 ).Specifically, vessels with a LOA < 10 m have no legal obligation for directly reporting fishing activity using logbooks or to be fitted with Vessel Monitoring Systems (VMS) that provide spatial information.Additionally, LOA < 15 m vessels have certain exemptions regarding the use of electronic logbooks and VMS requirements: logbooks are mandatory for LOA > 12 m vessels, whereas VMS exemptions apply for LOA < 15 m vessels when trip duration is < 24 h and when fishing occurs, as mentioned, within national waters (EU 2009 ).Thus, fishing trips (e.g.departure and arrival dates, operating fishing gear) and catch information (e.g.landed species' weight and sale value) were gathered by combining first sales notes (for vessels with LOA < 10 m and vessels between 10 and 15 m without logbook records) and logbooks (for vessels with logbook records between 10 and 18 m).For the smallest vessels, which did not provide information about the duration of their fishing trips ( < 10 m LOA vessels), we assumed one-day trips (Murillas-Maza et al. 2023 ) based on their sale dates, which are primarily daily.
Only landings from the Basque SSF fleet were considered in the analysis, excluding trips and landings from vessels with base ports outside the designated area.Price details (i.e. total value of landings and the price per kilogramme and species) were derived from sales records.Trips and sales with incomplete information (e.g.unknown or incorrectly assigned gears, missing departure or arrival dates, etc.) were removed from the analysis.Once all the data were cleaned, the final dataset comprised almost 134 000 trips conducted by 187 vessels spanning from 6 to 18 m in LOA (see Supplementary Table S1 ).

Fleet segmentation
In the study region, the SSF fleet is restricted to using a single gear per fishing trip, and thus, is not permitted to switch between gears during the same trip, neither in external waters (Spanish General 2000).Accordingly, we grouped all fishing trips by the SSF depending on the fishing gear used, into the following 'fleet segments': netters (including bottom gillnets and trammelnets), bottom longlines, trolling-lines targeting northern albacore ( Thunnus alalunga , hereafter referred to as 'albacore'), handlines targeting Atlantic mackerel ( Scomber scombrus , hereafter referred to as 'mackerel') and pots.Such segmentation has also been previously used to assess different SSF activities in the region (Murillas-Maza et al. 2023 ).
Given that the composition of landed species can provide valuable insights into fishing preferences and primary fishing gears, particularly during specific seasons, we evaluated species diversity, in terms of richness (i.e.number of species), drawing on data from the past decade, which was the most consistent data source (i.e.2012-2022) and encompassed a total of 207 different species landed by the SSF fleet under study.With such data, we applied a non-metric multi-dimensional scaling (NM-MDS) ordination to initially validate the fleet segmentation employed in our analyses ( Table 1 ).This technique (Bakker 2024 ) classifies all trips based on the composition of landed species, disregarding any preassigned membership regarding fishing gears.This way, we were able to corroborate our fleet segmentation by examining the distances between the created groups, defined by a multivariate homogeneity of group dispersions test.

Fishing activity and gear-shifting patterns
Then, we assessed the fishing activity by characterizing the fleet size and the fishing effort.This involved plotting the number of vessels and fishing days allocated to each segment, respectively, throughout the entire study period ; Table 1 ).To fit smoothing regression lines to empirical data, we used the 'loess' tool (Jacoby 2000 ).Subsequently, we conducted a two-way ANOVA ( F test) to determine whether the fishing effort (i.e.fishing days) per vessel varies significantly depending on year and/or fleet segment (i.e.here considered as categorical independent variables).
The use of such fishing effort per vessel accounted for cases where vessels changed their primary fishing gears from 1 year to another, thereby allocating different numbers of days to different segments.To detect such shifts, we examined changes in the total number of vessels within each segment from year to year, and we assessed the percentage distribution of the fishing effort per vessel, by calculating the average number of fishing days per vessel allocated to each segment, over the years ( Table 1 ).To identify which fishing gears may replace the primary fishing gear of each segment, affecting the relative distribution of effort significantly, we computed Cohen's D estimates of the size effect for the fishing effort per vessel, adjusted with Tukey method, and for each pairwise segment comparison, and we extracted their corresponding correlation coefficients ( Table 1 ).Pots were excluded from the analyses concerning shifts between segments because they are not replaced by other fishing gears but rather used in combination with them (i.e.within the same trips).

Temporal trends and seasonal fishing adaptations of the SSF during the past decade (2012-2022)
Focussing on the decline of the SSF over the past decade (2012-2022; Supplementary Table S1 ), we delved deeper into the analysis of this period, examining ∼50 000 trips by 94 vessels.In this case, we assessed not only the number of vessels and fishing days but also the landings (in kilogrammes per species) of each fleet segment.To determine whether certain fleet segments have gained importance compared to others showing a reduced allocated effort, we conducted AN-COVA analyses to assess significant differences in the temporal progression between fleet segments ( Table 1 ).The AN-COVA (Neter et al. 1990 ) permits the inclusion of quantitative continuous variables (i.e.year as covariate), related to the dependent variable of the variance model, which is why ANCOVA was appropriate for the evaluation of whether the effects of the fishing activity operating within different fleet segments were independent.Specifically, we compared linear regressions (using F tests for slopes) with year as the explanatory covariate and including the interaction term between year and fleet segment.This way, we tested the effect of different fleet segments on the variation of the fleet size, fishing effort, and landings, while controlling for the effect of time (year), and whether the relationship between year and the response variables varied among different fleet segments.For the purpose of this analysis, we considered netters as the reference fleet segment.Additionally, we conducted Mann-Kendall tests to identify significant temporal trends for each fleet segment separately across the same response variables ( Table 1 ).In the case of landings, we considered the total annual catches to remove the seasonal component of the data.This is because seasonal patterns typically occur within a year, and by aggregating the data on an annual basis, we effectively averaged out any intra-year sea-Table 1. Summary of the main statistical approaches applied to each specific purpose (assessment) and their corresponding period of application.

Fleet segmentation
Landings (catch per species, in kg) NM-MDS ordination plot based on the dissimilarity on the landed species.

Fishing activity Tests for inter-annual differences
Number of vessels Regression lines ('loess' smoothing tool), per fleet segment.

1995-2022
Fishing days Number of vessels Count of vessels operating within each segment from 1 year to the next.

1995-2022
Fishing effort per vessel Test for differences between years and/or segments: two-way ANOVA ( F tests).

1995-2022
Number of vessels ANCOVA: comparison between fleet segments' regression lines ( F tests for slopes), with year as explanatory covariate and including interaction between year and fleet segment.

Gear-shifting patterns
Fishing effort per vessel % Distribution of the fishing effort per vessel (average values for each segment, over years).

1995-2022
To define significant shifts between segments: correlation coefficients of Cohen's D estimates, adjusted with Tukey method, for each pairwise segment comparison.

Temporal trends
Number of vessels Mann-Kendall test for temporal trends, for each segment separately.

2012-2022
Target species Landed species' diversity (i.e.richness) Mann-Kendall test for temporal trends, for each segment separately.

2012-2022
PERMANOVA: comparison of diversity between fleet segments and between years.

2012-2022
Species essentiality index Calculated for each fleet segment and year.Then, annual catches of essential species are plotted for each corresponding fleet segment.

Relevance of seasonal fisheries
Number of weeks engaged in catching seasonal target species (Atlantic mackerel and northern albacore) and catch-per-unit-effort (CPUE) Duration of seasonal fisheries (in weeks) vs. years.

2012-2022
Spearman's rank correlation between the duration of seasonal fisheries (i.e.number of fishing days) and CPUE.
2012-2022 sonality.Therefore, the trends that the Mann-Kendall test identified are interannual, meaning they represent changes from year to year rather than within a single year.Such Mann-Kendall tests calculate a z -statistic ( τ ), of which positive values indicate an upward trend and negative τ values a downward trend, while τ = 0 reflects a lack of any significant trend (Gilbert 1987 ).Since we conducted multiple Mann-Kendall tests (one for each fleet segment), the chance of observing a significant result just by chance (Type I error) increases.To control the family wise error rate, we applied the Benjamini-Hochberg correction procedure, which controls the false discovery rate for multiple comparisons (Cortés et al. 2020 ).

Target species
To assess significant changes in species richness (hereafter referred to as diversity), examining both inter-annual variations and differences between fleet segments, we conducted a PER-MANOVA analysis (see McArdle and Anderson 2001 ).Also in this case, we employed a Mann-Kendall test to identify tem- poral trends in species diversity changes within each fleet segment ( Table 1 ).Subsequently, we identified the main targeted species within each fleet segment ( Table 1 ), based on the Essentiality Index ( ∃ ), as defined by Dorta and Martín-Sosa (2022) .This index was designed to reflect the economic viability of a fishery, determined by factors such as the frequency of species caught, the ability of the fleet to incorporate these species into their fishing strategies, and the income derived from these species.Its use allowed us both to comparatively characterize fishing communities with SSFs of differing characteristics based on the same yearly data (Dorta and Martín-Sosa 2022 ) and gauge the relative importance of specific species for each fleet segment and year.Integrating the relative number of vessels targeting each species concerning the entire SSF fleet, the relative number of days during which these certain species were fished in comparison to all days with fishing activity, and the relative income generated from each species relative to the total income derived from landings, we categorized the essential ( ∃ ≥ 0.5), fundamental ( ∃ ≥ 0.3 and < 0.5), and complementary ( ∃ < 0.3) species for each fleet segment and year.
Then, we also examined temporal trends in their landings but solely considering their corresponding essential species.This approach may unveil seasonal dependencies or any specialization in targeting certain species by each segment ( Table 1 ).

Relevance of seasonal fisheries
Finally, recognizing the potential relevance of specific seasonal fisheries in shaping the dynamics and trends of SSF, namely those involving handlines targeting mackerel in spring and trolling-lines targeting albacore in summer, we investigated changes over the years (2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020)(2021)(2022) in the duration of these seasons, assessed with the total number of weeks dedicated to each fishery ( Table 1 ).To exclude landings of mackerel or albacore from other segments, we considered only vessels operating with the two corresponding fishing gears (i.e.handlines and trolling-lines, respectively), in each season.In this context, a shorter fishing season could potentially result in higher daily landings, leading the fleet to reach the quota within a shorter timeframe, and vice versa.Therefore, we also represented the total allowed catch (TAC) for the Spanish fleet excluding trawlers and purse seiners (based on values published in the Official State Gazette 2012-2022), and we then used Spearman's rank correlation to test for linear association between CPUE (defined as daily catches) and season duration (number of fishing days), with an anticipated rejection of a negative slope ( Table 1 ).Dividing the total catch of mackerel and albacore (for handlines and trolling-lines, respectively) by the total number of fishing days (i.e.CPUE), we exclude the effect of having relatively larger number of fish in fewer days, in contrast with a more extended season (i.e. with more frequent landings of relatively smaller size).

Statistical software and packages
We used R v. 4.3.0(R Core Team 2023 ) and package ggplot v. 3.4.2(Wickham 2009 ) for all analyses and graphical representations, respectively.Figure 1 was performed by using the function worldHires from the 'mapdata' package, combined with the getNOAA.bathyfunction from 'marmap' package to get the bathymetry (isobaths).Fishing days were calculated using the calc_fishing_effort function from 'fecR' package v. 0.0.2 (Scott et al. 2017 ).The functions and pack-ages used for the statistical models were the following: from the 'stats' package, the loess function for plotting the temporal trends, lm and var.test functions for comparing then the regression slopes (i.e.F tests for slopes) between fleet segments during the last decade, and cor.test function for Spearman's rank correlation tests; mann_kendall function from the 'Kendall' package v. 2.2.1 (McLeod 2022 ) to determine the significance of the temporal trends; lsmeans and pairs functions from 'lsmeans' package and rcorr function from 'Hmisc' package to get the parameters regarding paired comparisons of effort per vessel between segments in Table 1 ; and adonis and scores functions from 'vegan' package v. 2.6.4 to perform the PERMANOVA analysis of the diversity of the landed species and to plot the corresponding NMDS, respectively; within the NM-MDS analysis, we used the vegdist function to perform the betadisper (multivariate homogeneity of group dispersions) test.Summarized information was obtained using 'data.table' package v.1.14.8 (Dowle and Srinivasan 2022 ).

Fleet segmentation
There are clear distinctions in the species landed by handlines, trolling-lines, and pots, whereas longlines and netters show greater similarity, i.e. suggesting a higher overlap in their targeted species ( Fig. 2 ).Accordingly, the multivariate homogeneity of group dispersions test revealed variations in dispersion across fleet segments in the NM-MDS ordination space.On average, pots exhibited the highest distance to the centroid (0.20), followed by trolling-lines (0.16), handlines (0.11), longlines (0.08), and netters (0.03).

SSF fishing activity and gear-shifting patterns
The fishing activity in different fleet segments has been fluctuating from 1995 up to date, with an overarching gradual declining trend in fleet size (i.e. total number of vessels; Supplementary Fig. S1 ) and therefore in fishing effort (i.e.fishing days per month, Fig. 3 ).
From 1995 to 2005-2006, the fishing effort across all segments except for netters (which maintained their activity) showed a decline.Subsequently, a period characterized by the stabilization of the entire SSF fleet activity might be observed until 2012, primarily sustained by an increase in fishing days by netters and longlines.Finally, in the last decade, there has been once again a generalized decline in fishing activity, particularly due to diminishing numbers of netters and longlines, as well as a reduction in their operating fishing days.However, during this period, trolling-lines and handlines bucked this trend, by increasing their fishing effort ( Fig. 3 ; Supplementary Fig. S1 ).
Most fishing vessels worked with different fishing gears within the same year, therefore contributing to the effort on different fleet segments.Significant differences were observed regarding the distribution of their fishing effort per vessel, from year to year as well as between fleet segments (two-way ANOVA; year: F = 5.43, d.f.= 27, P = 2.00 × 10 −16 ; fleet segment: F = 735.75,d.f.= 3, P = 2.00 × 10 −16 ; year × segment interaction: F = 1.30, d.f.= 81, P = 0.04).When comparing the count of vessels operating within each fleet segment from 1 year ( y ) to the next ( y + 1 ), no discernible trend emerged for a decrease in the number of vessels within a particular segment in a given year, which might be compensated for by an increase in the fleet within another segment the following year ( Supplementary Fig. S2 ).Hence, it seems clear that the relative allocation of fishing effort was influenced by shifts in fishing gear choices made between seasons within each year, rather than vessels changing their primary fishing gear over the years.Accordingly, the percentage distribution of the fishing effort per vessel across fleet segments remained relatively stable over time ( Supplementary Fig. S3 ).Overall, netters exhibited the highest relative fishing effort per vessel among fleet segments, followed by longlines and handlines during the whole time series ( Fig. 4 ; Supplementary Fig. S3 ).Notably, it was during instances of gear shifting among netters that relative differences became more significant (i.e. as evidenced by the highest Cohen's D estimates and significant correlation coefficients for pairs involving netters; Table 2 ; Figs 3 and 4 ).For instance, in years with fewer vessels engaged with nets, there was an increase in the number of vessels using trolling-lines, and a similar trend was observed for handlines when fewer fishing days were allocated to netters ( Supplementary Fig. S3 ).Consequently, the shift of netters to handlines and trolling-lines during specific seasons, indicated by negative correlation coefficients, could influence the relative distribution of the fishing effort more notably than the shifts between other segments ( Table 2 ).
Regardless of the fishing effort allocated to each fleet segment, the total catch by each segment can offer valuable insights into the most significant fishing activities.In fact, over the entire decade, handliners' fishing activity accounted for 57% of landings, followed by netters (17%), longlines (14%), trolling-lines (12%), and pots (0.3%) ( Supplementary Fig. S4 ).
In this case, it should be highlighted the noteworthy contribu-tion of trolling-lines, despite not always ranking at the top in terms of annual landings, since their increased activity has led to nearly doubling their landings over the past decade ( Fig. 5 ).

Target species
As inferred from the fleet segmentation used throughout the study, the observed differences in the diversity of landed species (e.g.Fig. 2 ) were statistically significant when comparing fleet segments (PERMANOVA, F = 57.70,P = 1.01 × 10 −3 ).However, regarding inter-annual variations, we did not detect significant differences in diversity (PER-MANOVA, F = 0.16, P = 0.79).
However, rather than solely focussing on species with relatively higher landings (landings of the top 20 targeted species per fleet segment and year are presented in Supplementary Table S3 ), it might be worth to identify the species upon which each fleet segment relies, considering their significance in terms of effort, catchability, and revenue.Focussing on essential and fundamental species for each segment and year, throughout the entire decade, handlines and trolling-lines show a clear specificity for mackerel and albacore, respectively, while pots predominantly target crustaceans and molluscs, such as common octopus ( Octopus vulgaris ) ( Table 3 ).Conversely, longlines primarily target European hake ( Merluccius merluccius ), with conger ( Conger conger ) and seabass ( Dicentrarchus labrax ) also emerging as fundamental species across most years.Netters primarily targeted hake, but in addition, other species like stripped red mullet ( Mullus surmuletus ) or common sole ( Solea solea ) are also essential.Notably, netters exhibit a wide range of species preferences, including monkfish ( Lophius piscatorius ), black-bellied angler ( L. budegassa ), and pouting ( Trisopterus luscus ) ( Table 3 ).

Increasing relevance of mackerel and albacore seasonal fisheries
Previous results (Sections 3.2 and 3.3; Figs 3 and 4 ) reflect a significant increase in the activity of handlines targeting mackerel and trolling-lines targeting albacore over the past decade.Moreover, it seems that the duration of these two fishing seasons has been extended in recent years, with the mackerel season increasing from an average of 3 −5 weeks and the albacore season increasing from 4 to 5 weeks ( Fig. 7 ).Such an extension of both fishing seasons might lead to a protracted     timeframe for the fleet to reach the quota, especially for mackerel, which has decreased over the past decade ( Fig. 7 ), potentially resulting in decreased daily landings.For this species, the Spearman's rank correlation revealed a moderate negative correlation between CPUE and season duration ( ρ = −0.58,P = 0.04), indicating that prolonged mackerel seasons tend to coincide with reduced CPUE.For albacore, with an increasing total allowed catch, the relationship between CPUE and season duration was not linear ( ρ = −0.39,P = 0.23; Fig. 7 ).

Discussion
Despite the absence of a universally accepted definition for artisanal fisheries (García-Flórez et al. 2014, Smith and Basurto 2019, Murillas-Maza et al. 2023 ), our study is in accordance with the predefined segmentation of the SSF fleet within the Basque region.Considering < 18 m LOA vessels operating mostly on trips that generally last 1 day (with exceptions for albacore trolling-lines fisheries in summer), and primarily using handcrafted gears (Murillas-Maza et al. 2023 ), its fishing gear-based segmentation aligns notably with the diversity of landed species ( Fig. 2 ).
The SSF fleet employs multi-purpose fishing approaches and therefore tends to switch fishing gear and targeted species throughout the year (e.g.Guyader et al. 2013, Horta e Costa et al. 2013, Palmer et al. 2017 ).The relative allocation of fishing effort (average fishing days per vessel and segment, Fig. 3 ) has varied over the last two decades, most probably driven by sea-sonal shifts in fishing gear choices made by the fleet (Palmer et al. 2017, Herrón et al. 2020 ).Notably, an overarching decline in fishing activity is evident within the Basque SSF fleet as a whole over recent decades, aligning with general trends observed in both Iberian and European SSF fisheries (Cordón Lagares et al. 2016, Lloret et al. 2018, García de la Fuente 2020, Pascual-Fernández et al. 2020 ).
Prior to 2005, the decline in both the number of vessels and fishing days observed may be attributed to the overall ageing of the SSF fleet, which prompted the government to provide financing for the scrapping of the oldest vessels (Cordón Lagares et al. 2016 ).At that time, netters were the only segment that kept constant.
In the following period (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012), the increased fishing activity of the netters might be related with the good ecological status of the coastal stocks of the main target species, such as hake (Goikoetxea andIrigoien 2013 , ICES 2022 ), striped red mullet (ICES 2023b ), or sole (ICES 2021 ).In contrast, handlines and trolling-lines dropped to historical minimum values.The reduced dedication to the mackerel season, which generally extends from March to May (Murillas-Maza et al. 2023 ), might be attributed to the inability to compete with the high landings by the industrial fleet (Jackquet andPauly 2008 , Astorkiza anddel Valle 2018 ).This, in fact, exceeded the total allowed catches at that time, and resulted on the subsequent reduction of the quotas for 2011-2023 as a fine for the whole commercial fleet (EU 2011 ).On the other hand, albacore, usually caught from June to August −September (Rodríguez-   During the last decade (2012-2022), the effort allocated to each fishing gear (and therefore to each targeted species) seems  3 ), during the last decade.Note that ' M. merluccius ' shows the landings from both netters (light grey) and longlines (dark grey).Scomber scombrus , T. alalunga , and O. vulgaris landings are specific for different segments, as defined in Table 3 .
to be more driven by factors related with the main seasonal fisheries in the region: the Atlantic mackerel season, mostly operated with handlines, and the northern albacore season, operated with trolling-lines ( Table 4 ).In fact, these two segments have increased their activity with respect to the others (netters, longlines, and pots), collectively accounting for > 70% of the total annual weight of landings.This characterizes the Basque SSF, i.e. similar to that of closer Asturias Downloaded from https://academic.oup.com/icesjms/advance-article/doi/10.1093/icesjms/fsae132/7759915 by guest on 22 September 2024 Adaptive small-scale fisheries in the eastern Cantabrian coast through reliance on essential species 11 Figure 7. Violin boxplots to illustrate the number of weeks during which SSF vessels were engaged in catching the two seasonal target species, namely mackerel ( S. scombrus ) and albacore ( T. alalunga ), using the main fishing gears associated with such captures: handlines and trolling-lines, respectively.Jitter dots represent individual fishing vessels, considering only the part of the SSF fleet that operated with the two gears within the same years.Black lines represent the smoothed regression lines for the average number of weeks dedicated to each fishery within each year, and solid and dashed lines denoting a significant or non-significant correlation between CPUE and season duration (i.e.Spearman's rank correlation, P value < 0.05), respectively.Grey lines represent, based on the right axis, the national total allowed catch (TAC) of the corresponding years and species, in tonnes.region (García de la Fuente 2020 ), but more different from other regions, such as Galicia in the western Cantabrian, with a SSF more focused on shellfish and molluscs (Garza-Gil et al. 2020 ).
The decline in species diversity observed in the landings of these two segments over the past decade might be attributed to potentially more selective fishing practices that prioritize obtaining clean landings predominantly comprising their target species.In fact, these two fisheries might have been influenced by a more demanding market and by larger mackerel landings from industrial fleet segments (e.g.purse seiners, trawlers; Astorkiza and del Valle 2018 ).In any event, it should be noted that the operating period for vessels targeting mackerel and albacore has expanded in recent years (specifically, from an average of 3-5 for mackerel and from 4 to 5 weeks for albacore).This extension is likely associated with favourable conditions for mackerel (e.g.might lead them to shoal in higher abundances and closer to the coastline of the Cantabrian Sea.For mackerel, the reduced quotas for the last decade obtained in Spain due to fines imposed starting from 2013 might have led to an extension of the mackerel season.Thus, smaller daily captures spread across a higher number of landing days in harbour (i.e. during longer seasons) might be anticipated.This trend was observed as daily mackerel landings (i.e.CPUE) decreased over the last decade.For albacore, the relationship between CPUE and season duration was non-linear, suggesting that as albacore landings increased, there was likely a corresponding rise in the number of vessels targeting albacore, possibly driven by increased quotas.However, further research is needed to determine the factors leading to the rise of these seasonal fisheries, such as potential improvements in vessels (e.g.allowing the use of a higher number of hooks), economic interests, etc.Indeed, the total landings of both mackerel and albacore exhibit an increasing trend over recent years, and even a higher increase might be expected for the former, now that the restrictions on quotas have been finalized.Underscoring the seasonal nature of mackerel and albacore fisheries, which are crucial but heavily reliant on mackerel (Villamor et al. 2011 ) and albacore (Ortiz de Zarate et al. 2020 ) resources in the region, it seems clear that they directly influence the duration and the effort allocated by SSF in other segments.
The reduction in the fishing activity by gillnets and trammelnets (assessed as 'netters') during the last decade, also reported by previous studies (e.g.García de la Fuente 2020 , Pascual-Fernández et al. 2020 ), appears to result from more vessels shifting from using nets to handlines and trollinglines during their respective seasons, coupled with a reduction in the number of vessels dedicated to nets ( Supplementary Fig. S1 ).Nets, being less selective (Gonçalves et al. 2007, Aydın et al. 2008, Borges et al. 2008, Kalayci and Ye ş ilçiçek 2014, Szynaka et al. 2018 ), tend to show a higher diversity of landed species compared to other fishing segments.However, this diversity has remained stable throughout the last decade, indicating that the primary target species (i.e.identified as 'essential') on which netters rely on are especially hake, striped red mullet, and sole, and for some years, also angler and monkfish.This agrees with the main target species observed for netters in other regions, not only in Asturias, located further west in the Cantabrian Sea (García de la Fuente 2020 ), but also in the Mediterranean (Maynou et al. 2011 ).Moreover, within the Basque SSF fleet, netters are the main contributors to all these species, except for hake, which is the main target species for longliners.Indeed, and in accordance with nearby Asturian fleet (García de la Fuente 2020 ), Basque bottom longliners show a strong dependence on hake as a key species during the last decade, although they are also important as primary suppliers of seabass and conger in the local SSF fishery.Like for netters, the decrease in the annual fishing effort by longliners might be attributed in part, to increased effort allocation to handlines and trolling-lines, but it is also likely influenced by other decisions related to economic viability (Schuhbauer and Sumaila 2016 ).A similar situation applies to vessels exclusively dedicated to pots, which have been in very low numbers during the entire study period and have further declined both in terms of activity and therefore on landings over the last decade.Pots primarily target the common octopus, as it has been identified as essential for this segment over the last decade not only in the Basque coast (this study) but also in other regions from both Cantabrian (García de la Fuente 2020 ) and Mediterranean (Petetta et al. 2021 ) seas.However, in our case, while there are few vessels operating exclusively with pots throughout the whole year, most vessels use pots as complementary to their main fishing gear, which could explain the relatively lower activity in comparison with other fleet segments.
Excluding the primary seasonal species, hake is the principal target species for passive gears (i.e.including netters and longlines).While hake catches are much smaller than those from the handline-captured mackerel, they rank as the third most significant in overall landings and the foremost in terms of relative effort.Notably, the combined fishing effort of longlines and netters accounts for most fishing days each year.Moreover, hake landings have remained stable over recent decades, underscoring its enduring importance and potential competition in local markets.Such a competition might not be so remarkable between different segments within the SSF fleet but rather with hake sourced from industrial fleets, which may offer higher abundances at relatively lower income per kilogramme (Astorkiza anddel Valle 2018 , Villasante et al. 2021 ).In addition, it should be noted that certain species, which may not be primarily targeted by specific fleet segments, could still significantly contribute to fishermen's income on a steady basis, despite representing a relatively low percentage of the catch, e.g.sparids ( Diplodus sargus , Sparus aurata , and Dentex dentex ) or Sepia officinalis (Tzanatos et al. 2006 ).In such instances, the Essentiality Index might underestimate the relative importance of these species, since while they may not be central to the SSF sector's reliance, they serve as consistent, opportunistic sources of income.Overall, higher species selection (i.e.being more essential and/or fundamental linked to a higher Essentiality Index) is associated to a gain efficiency in economic terms.The fleet segments obtained more or, as minimum, the same amount of gross revenues from first sales, for the whole period analysed.It is also true that the associated risk might be increased due to the less diversity of species landed, which might cause a drastic economic impact for both fishers and coastal areas highly dependent on this fishing activity, in case of dropping one of those essential species.Previous literature (Carmona et al. 2020 ) suggested calculating a selection of species with highest expected return but with the same variance (for a given return) or, the same expected return with the lowest variance as an optimal fisher's strategy.Thus, fishers should face important trade-offs, but currently SSF fleet segment benefits seem to compensate for medium-or longterm risks, especially when fishing species with an Essentiality Index close to one.
Continuing the methodological assessment, it is important to acknowledge a significant limitation in the data concerning fishing trips, particularly for the smallest vessels (i.e.< 10 m LOA), as it relies solely on first sales notes, i.e. without logbook records (EU 2009 ).Thus, fishing effort estimates should be treated with caution, particularly for passive gears where the quantity of fishing gears per vessel and the duration of fishing activity remain undisclosed.This might also extend to active gears, such as trolling-lines, as the exact number of hooks is often unknown and therefore not considered in calculations.Throughout this study, we assumed a consistent number of gears per vessel across the studied period, but it is worth acknowledging that this number may have increased over time.Thus, the effort estimates presented here should be considered as conservative or as a minimum baseline.In the same way, certain bias may exist in data sources, particularly con-Downloaded from https://academic.oup.com/icesjms/advance-article/doi/10.1093/icesjms/fsae132/7759915 by guest on 22 September 2024 cerning the diversity of landed species, since logbooks might register fewer species compared to sales records.Besides, such a greater accuracy with sales notes might be tested through further research combining data from both sources, which, in our case, is only feasible for a small portion of the dataset corresponding to the largest vessels.
In summary, our findings highlight the significant role of two specific seasons, the spring Atlantic mackerel season and summer northern albacore season, in shaping the SSF in the eastern Cantabrian region.This specialization, whether viewed as opportunistic interest driven by favourable conditions in certain fisheries or as adaptive behaviour to compensate unfavourable factors in other fishing gears, affects the resilience and reliance of the entire SSF, driving the fishing effort allocated to other segments.Accordingly, the decline in the number of vessels is mainly reflected in a decrease of fishing effort (i.e.fishing days) of netters and longliners, since those that remain active have adapted by allocating more fishing days to using handlines and trolling-lines during seasonal fisheries for mackerel and albacore, respectively, in recent years.However, while fishers may adjust the composition of the main harvested species, this does not mean that a decrease in a locally valuable species can be offset simply by targeting or increasing the fishing effort on others (Calò et al. 2022 ).This is important when particular species are targeted in certain regions, as regulations on catches can differentially affect fishers from different areas and, consequently, the decisions made by stakeholders (McDonald et al. 2016, Astorkiza and del Valle 2018, Garza-Gil et al. 2020, Villasante et al. 2021 ).In this sense, our analysis reveals that each fleet segment maintains a consistent reliance on specific target species (considered as essential or fundamental) over time.Consequently, when these species thrive ecologically and are closer to the coast, increased activity within their respective segments may lead to greater interactions with other fleets, including purse seiners, trawlers, and recreational fisheries (Guerreiro et al. 2011, Bachiller et al. 2022 ).This understanding is relevant for assessing the vulnerability of different fishing segments in the region (Horta e Costa et al. 2013 ), albeit further research is needed to delve into the potential causalities (i.e.drivers).Such research should consider these adaptations as a response to resource availability-e.g. the longer distances and higher effort required to find certain target species (Pinsky et al. 2021 )-as well as social-ecological fisheries networks (Fuller et al. 2017, Yletyinen et al. 2018 ).In any case, in scenarios where setbacks may occur in mackerel and/or albacore seasons, results suggest that the SSF fishery would predominantly rely on hake.Additionally, the diverse array of netters and longlines could lead to heightened exploitation of other species as a compensation mechanism to offset the absence of mackerel and albacore, through catch diversification (Young et al. 2019 , White andScheld 2024 ).Consequently, other emerging species, such as seabass, pouting, or striped red mullet, might gain importance, given that the SSF is the unique source introducing them into the local market.Notably, the mentioned species are considered as data-limited stocks, making it crucial to investigate the potential impacts and interactions within the different SSF segments as well as with other fleets (e.g.industrial and/or recreational fishing).
Given the substantial contribution of the SSF to the species required by the local fish markets (e.g.Arthur et al. 2022 ), future research should prioritize collecting high-quality data on local fishing activities.Integrated research like this one, considering fishing effort, gear-switching patterns within each year, key target species, and temporal trends, is indispensable for understanding how the SSF adapts to changing environmental conditions (e.g.Yletyinen et al. 2018, Pinsky et al. 2021, Ilosvay et al. 2022 ) and resource availability (e.g.Young et al. 2019 ), and is essential in facilitating informed decisions toward sustainable fisheries management by stakeholders.

Figure 1 .
Figure 1.Study area showing the main ports where the Basque SSF fleet is based and from which first sales notes were collected (1995-2022).The straight black line close to the shore represents the boundary of the internal waters.Curved line at sea represents the 200 m isobath.The geographic position of the studied area in the B a y of Biscay is also indicated in the upper left inset (with 200, 500, and 1000 m isobaths).

Figure 2 .
Figure 2. NM-MDS based on the dissimilarity on the landed species composition to illustrate the spatial ordination of different fleet segments.Based on Basque SSF landings from 2012 to 2022.

Figure 3 .
Figure 3.Total number of fishing da y s per SSF fleet segment, from 1995 to 2022.Each fleet segment is dra wn b y a different line type, with mean values per month.In each case, a thicker line represents the smoothed regression line (local regression, 'loess'), with its corresponding shadowed area indicating the standard error.Secondary (right) vertical axis corresponds to the top thick red curved line, which shows the 'loess' for the total number of activ e v essels in the entire SSF fleet (see Supplement ary Fig .S1 for further det ails on the number of v essels).T he area within the bo x represents the last decade (2012-2022).

Figure 4 .
Figure 4. Total number of fishing da y s, calculated f or the B asque SSF fleet operating with each fishing gear (i.e.grouped b y fleet segment) from 1995 to 2022.Pots were removed from this analysis since they correspond to a gear, i.e. usually combined with other gears on the same trip.

Figure 5 .
Figure 5.Total landings (tonnes) derived from each Basque SSF fleet segment during the last decade (i.e. from 2012 to 2022), represented in mean values per month for each fleet segment.In each case, a thicker line represents the corresponding smoothed regression line, solid and dotted lines denoting a significant or non-significant temporal trend (i.e.Mann-Kendall tests, P value < 0.05), respectively.
Darker and lighter grey colours of the cells indicate those cases defined as essential ( ∃ ≥ 0.5) and fundamental ( ∃ ≥ 0.3 and < 0.5), respectively.EssentialFundamental Cabello et al. 2009 ), could have been more difficult to catch for the SSF fleet operating with trolling-lines, since it might have been distributed further from the coastal areas (Goñi et al. 2015 ).Moreover, albacore could have been found in lower abundances, due to a reduced availability of their main prey, anchovy ( Engr aulis encr asicolus ) (Lezama-Ochoa et al. 2010 ), for which there was a fishery closure from 2005 to 2009, due to the low biomass of the species (Uriarte et al. 2023 ).

Figure 6 .
Figure 6.Total landings (tonnes) of the species identified as 'essential' for the different Basque SSF fleet segments (see Table3), during the last decade.Note that ' M. merluccius ' shows the landings from both netters (light grey) and longlines (dark grey).Scomber scombrus , T. alalunga , and O. vulgaris landings are specific for different segments, as defined in Table3.

Table 2 .
Pairwise comparisons of effort per vessel among different fleet segments using Cohen's D effect size with a 95% confidence interval.

segment comparison Cohen's D estimate (SE = 1.72, d.f. = 108) t -ratio 95% CI for D Corr.coef P
CI ranges are presented (note that negative values indicate a decrease in the outcome variable in the first group compared to the second group, consistent with the negative Cohen's D estimate.).Corr.coef corresponds to the correlation coefficient for each comparison, with their corresponding P value ( * represents P < 0.05 significance).

Table 3 .
Species Essentiality Index ( ∃ ) for the different fleet segments and years.

Table 4 .
Summary table of the main findings for the past decade (2012-2022).