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Spearfishing data reveals the littoral fish communities’ association to coastal configuration
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Jordi Boada1*, Oscar Sagué2, Ana Gordoa1
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1. Centre d’Estudis Avançats de Blanes (CEAB-CSIC). Accés a la Cala Sant Francesc, 17300,
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Blanes, Girona, Spain.
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2. International Forum for Sustainable Underwater Activities (IFSUA). Carrer València
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231, Bxs., Apartat correus 36003, 08007, Barcelona, Spain.
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[email protected]
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Highlights
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1. We used data obtained from spearfishing contests to evaluate littoral fish communities.
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2. Two different communities were determined from the analyses related to habitat
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configuration.
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3. Labrids and Congers characterised rocky substrates, while mugilids and Sarpa salpa
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defined soft bottoms.
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4. No changes in the community composition were found over the study period (16 years).
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5. Fishing contest data are valuable complementary tool for monitoring fish communities.
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Abstract
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Increasing the knowledge about littoral fish communities is important for ecological sciences,
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fisheries and the sustainability of human communities. The scarcity of baseline data at large
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spatial scales in a fast-changing world makes it necessary to implement special programs to
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monitor natural ecosystems. In the present study, we evaluate littoral fish communities using
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data from spearfishing contests. The Catalan Federation of Underwater Activities (FECDAS)
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regularly organizes fishing contests across ca. 600km of coast. Catch records made over the
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last sixteen years were used to study the fish communities along the coastline. We found two
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different communities that are closely related to the habitat configuration at a regional level.
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Interestingly, contests held on the northern coast were mainly grouped together and were
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characterized by species that inhabit complex rocky habitats, and contests held on the
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southern coast were grouped together and were mainly determined by soft bottoms species
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(i.e. mugilids and Sarpa salpa). In the south group the white sea bream was also very abundant
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compared to the north group. No significant changes in the community composition were
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found in the studied period and we successfully set descriptive baselines. Finally, based on
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these results we propose that studying the data from fishing contest records can be used to
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complement the available tools for monitoring fish communities.
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Keywords: fishing contests, fish communities, spearfishing, sport fishing, substrate, habitat
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configuration.
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1. Introduction
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Characterizing fish communities has interested oceanographers and ecologists through history
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(Andréfouët and Wantiez, 2010; Lees et al., 2006). Describing the species composition is not
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only relevant for determining the marine diversity but also for developing appropriate
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resource management measures to ensure the sustainability of certain societies (Bailey and
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Pomeroy, 1996; Beck et al., 2001). Fish communities are distributed over space according to
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their environmental tolerance and habitat preferences (Stuart-Smith et al., 2013). On a global
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scale, environmental gradients generally determine the distribution of shallow littoral fish
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communities (Hillebrand, 2004). However, at regional scales, the habitat, which provides food
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resources and protection, is most probably the main factor that influences fish assemblages
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(Marshall and Elliott, 1998). In addition, the habitat distribution is not homogeneous at a
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landscapes scale and the presence, absence or relative proportion of certain habitats can
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strongly influence fish communities (Chapman and Kramer, 2000).
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The world's seas and oceans are changing fast particularly in coastal areas and marine fish
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communities are reacting to these changes (Halpern et al., 2008). Recording and predicting
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shifts in fish communities has always been a big challenge. In fact, the ‘mere’ description of
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littoral fish communities itself, has sometimes resisted to ecologists because of the complexity
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of methodologies and the lack of regular monitoring programs (except in marine reserves)
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(Ackerman and Bellwood, 2000; Sale and Douglas, 1981a). Underwater Visual Censuses (UVC)
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are the traditional method for describing fish communities and perhaps among the most
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precise. More recently, visual censuses have been substituted for underwater cameras in
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either fixed and transect fish counts (Holmes et al., 2013). Fishing techniques have also been
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used extensively (i.e. trawling) and have proved to be very representative (Franco et al., 2012).
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These methods, however, are less and less preferred and undestructive technics generally
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prevail. But none of the available tools is completely unbiased making critical the use of
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several complementary techniques. Using alternative data sources can provide valuable
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information at a low cost to early identify changes in fish communities in relation to fishing,
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warming, pollution or the introduction of alien species among others (Rabalais et al., 2009;
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Vergés et al., 2014a; Ojaveer et al., 2015). Some already existent examples on the use of
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alternative methodologies to respond particular objectives include the use of angling
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information and spearfishing data (Parker et al., 2016; Coll et al., 2004; Pita et al., 2014).
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In the Mediterranean, ancient civilizations early depended on the goods and services this sea
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provides as a source of food and transport route. They also represent the dawn of an interest
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in describing the resident fish communities. Historical overfishing heavily altered coastal fish
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communities in the Mediterranean (Coll et al., 2008; Jackson, 2001; Pauly et al., 1998). More
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recently, the tourist sector has increased, adding pressure to the coastal systems. Activities like
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recreational fishing and diving have also increased, which has influenced benthic and fish
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communities (Sala et al., 1996; Tsikliras et al., 2013). The recent effects of warming and species
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invasions continue to alter Mediterranean populations (Azzurro et al., 2011; Vergés et al.,
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2014b). Here as well, communities are prone to shifts as a result of human impacts and
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warming with very relevant ecological consequences (Vergés et al., 2014a). It is therefore
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crucial to be able to track community changes over time and develop more sustainable
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management measures for marine resources (Smallwood et al., 2011). Indeed, much effort is
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needed to identify shifts in fish communities as even when monitoring is successful, only small
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areas can generally be extensively controlled.
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One popular activity that relies on Mediterranean fish resources is recreational fishing. There
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is a large number of recreational fishers, perhaps due to the mild weather and generally calm
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waters of this sea. Associations of different recreational fishing modalities regularly hold
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fishing contests that we believe could be very useful supplementary tools for monitoring
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littoral fish assemblages. Here, we aim to describe the fish community composition of a wide
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stretch of the NW Mediterranean coast to obtain representative baselines that can be used in
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the future to determine changes. We use a 16-year time series of spearfishing contests records
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to: i) characterize the littoral fish communities, and ii) determine potential changes over time
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within this time period. In addition, since fish communities are good indicators of the nature of
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waters we attempt to describe the littoral system based on the catch compositions of spear
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fishing contests (Azzurro et al., 2010; Seytre and Francour, 2009).
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2. Material and Methods
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2.1. Study site and fishing contest data. The Catalan coast is located in the NW Mediterranean
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(NE Spain) with a total length of ca. 600km. It accounts for a great range of Mediterranean
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littoral habitats from coastal cliffs to sandy bottoms and beaches (Marinani et al., 2014). Rocky
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shores are the most abundant substrates mainly dominating the northern coast (Costa
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Brava >200km) followed by beaches found mainly in the southern part (Costa Daurada, ca.
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100km) (Marinani et al., 2014). The central coast is an area where a mix of rocky shores and
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large and heavily anthropized beaches are present and harbour docks and breakwaters are
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common.
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For this study, we have analysed catch records from spearfishing contests provided by the
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Catalan Federation of Underwater Activities (FECDAS). FECDAS is responsible for organizing
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spearfishing contests along the Catalan coast and for providing catch reports to the Fisheries
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Department of the local government. Contests are held each year generally in the same
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locations over the entire region (Figure 1). The records analysed are from the official fishing
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contests held between 2000 and mid 2016 and include data on total catch per species, the
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number of participants, total duration time of the contest, total number of individuals caught
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per species and weight (although total weight per catch was not always recorded), and the
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location and date (day, month and year) of the contest. Just a few contests were developed in
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winter limiting the robustness of conclusions for species with high prevalence in this season.
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Some contests that we considered to be misrepresentative were removed from the analyses
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(see below). A total of 244 contests were finally analysed. Information was recorded globally
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and not to individual participants. We assume that the overall experience of fishers is
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maintained constant between the studied contests.
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To properly analyse and interpret data from spearfishing contests, several considerations need
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to be taken into account. In contrast to the recreational activity in Spain, participants in fishing
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contests generally have no catch limits. This free-of-limits applies for total number and weight.
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However, there are self-enforcement measures concerning the minimum weight of catches
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(i.e. >300g) and certain catch limits for some species of particular vulnerability (e.g. minimum
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catch weight for Epinephelus marginatus). Competitions indirectly enhance the participation of
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the most experienced fishers. Total number and weight of catches together with the number
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of species of the catch (this last since 2004) are valued. Actually, this bonus on diversity, could
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in theory enhance the representative value of contests on the species pool although
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differences in catch records between contests previous and after 2004 were found. This has an
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effect on the catch composition in tournaments, which is consequently mainly characterized
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by relatively large species, when they are present. Finally, the rules of fishing competitions
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may have changed a little during the recorded period but these changes have been small and
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have affected all the tournaments simultaneously, which allows us to compare data across
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locations.
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2.2. Data pre-treatment and CPUE calculations. Before calculating the catch per unit effort
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(CPUE), contests were evaluated for representation. As mentioned above, some tournaments
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were not included due to misrepresentation of the fish community. These contests were those
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where the number of participants was not sufficient to catch the overall group of target
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species present in a particular location (i.e. < 10 participants, see Supplementary Figure 1). In
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fact, additionally, the current regulation states that contests with less than 10 participants
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must not be considered as competitions. The analysis of the distribution of the number of
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participants in contests and the pool of species caught was used to determine the
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misrepresentative contests. Above 10 participants, the variability of the number of species
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caught remained fairly constant suggesting that the targeted community of species present in
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a particular location or time was sufficiently represented. CPUE was calculated for the rest of
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the contests (n=244) as the ratio between the number of individuals caught per species and
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the number of fishing hours, as follows:
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CPUE (Nºfish·hour-1) = Number of individuals / Fishing hours
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where fishing hours results from multiplying the number of participants by the contest length
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in hours.
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2.3. Data analyses. We used the contest CPUE values for each species to describe the fish
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communities. In most of the contests, species could be identified to family or genus levels.
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Finally, a total of 38 species/groups were identified and analysed. As mentioned above, data
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from spearfishing contests could be very useful for characterizing fish communities, evaluating
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potential changes in the region and determining possible shifts in the community composition
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over time (from 2000 to 2016). We used the ‘cooccur’ package in R to describe the species co-
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occurrences in the studied dataset. This package makes it possible to determine the species
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co-occurrences based on species presence-absence values. Then, to be able to describe the
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fish communities, we constructed a log10-transformed matrix of CPUE values for each species
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per contest. A dissimilarity matrix (Bray-Curtis) was calculated afterwards. Dendrogram
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classification techniques were used to make a preliminary exploration of the contest data.
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Hierarchical clustering techniques were used to identify groups in contests. Silhouette analyses
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were performed to evaluate how good tournaments were represented by the identified
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clusters. We used similarity percentage analyses (SIMPER) to identify the species that describe
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the identified groups. We also ran an ADONIS permutation test to evaluate the significance of
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the SIMPER results (Oksanen et al., 2015). All the statistical procedures were performed in R
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software for statistical analyses (R Core Development Team, 2013). We used the ‘vegan’
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package for the multivariate analyses (Oksanen et al., 2015).
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After characterisation, we looked for any long-term changes in catches of species of particular
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interest (either economically or of conservation interests). We looked for possible species
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catch seasonality and long-term trends over the recorded period (from 2000 to 2016). To do
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this, we preliminarily performed a Redundancy Analysis (RDA) to find potential relationships of
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species catches with seasons and year. Then, Generalized Additive Models (GAMs) were used
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to further explore trends in species in relation to season and year when
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necessary. Redundancy analysis and generalized additive models were also performed in R
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software using the ‘mgcv’ package (Wood, 2017; R Development Core Team, 2013).
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3. Results
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3.1. Fishing contests. A total of 56 species were registered during the recorded years (2000-
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2016). However, the species of the family Mugilidae were grouped together and the species of
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the generas Symphodus and Mullus were grouped respectively as well. Nevertheless,
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Symphodus tinca and Mullus surmuletus were the main species within the last two groups
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respectively. L’Escala and Mataró were the locations where the largest numbers of
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species/groups were recorded (22 out of 38). Contrariwise, the contest with the least species
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caught was in Tarragona on the south coast (5 out of 38). It is important to mention the large
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variability found in the number of species within locations. However, these results are
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individual records; the largest average values per contest were recorded in Tamariu and Port
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d’Aro with 20 and 19 species recorded (out of 38) respectively. Meanwhile, Llavaneres and
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Montgat (central coast) recorded the lowest mean values of species caught in tournaments.
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The species co-occurrence analysis found that 27.3% of species were non-randomly linked to
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others. Of these, 24% were positive and 3.3% negative, the other 73.7% were random co-
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occurrences. The Symphodus group together with the white sea bream were the species most
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fished in contests with ~18% of the individuals fished each in total during the studied period
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(Figure 2). The next most abundant groups were the family Mugilidae and the species Labrus
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merula (Figure 2). Neither the sea bass Dicentrarchus labrax nor the seabream Sparus aurata,
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which are important commercial species, were fished in large numbers compared with the
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previous species (~1.5% and ~1% of the individuals respectively). Only between 1 and 3
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individuals of several species were caught during the whole studied period (i.e. Uranoscopus
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scaber, Spicara smaris, Scomber scombrus, Pagellus acarne, Macroraphosus scolopax, Brama
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brama, Campogramma glyacos, Serranus hepatus, Polyprion americanus, Labrus mixtus and
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Labrus bimaculatus).
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3.2. Fish communities. Dendrogram classification techniques allowed us to identify two main
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groups within contest records (Figure 3, dissimilarity = 0.98). Interestingly, contests held on the
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north coast (including most of those corresponding to the central coast) were mainly grouped
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together while the tournaments held on the south coast were configured in the second group.
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From now on we will refer to contests developed on the central coast as part of the north
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coast for the sake of simplicity. A total of 155 tournaments were classified in group 1 (north
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coast; NC) and 89 in group 2 (south coast; SC). The number of species recorded in NC was 38
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out while in SC was 35. The silhouette analysis (mean silhouette width = 0.13, Supplementary
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Figure 3) revealed 22 contests (out of 244) with negative silhouette widths (potentially
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incorrectly classified within groups; 7 for the first group NC and 15 for the second group SC).
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For the north coast group, 4 of the 7 contests with negative silhouette widths were actually
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contests held on the south coast. Similarly, 8 of the 15 incorrectly classified in the second
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group were contests held on the north coast. Only three contests held on the north coast were
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classified in the second group, SC, with positive silhouette widths (from dendrogram and
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silhouette analyses). Within groups, several contests were more similar with each other,
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specifically for group 2 (SC), within which several tournaments appeared clustered in a
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subgroup (Figure 3 C, height = 0.89 and 0.71).
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ADONIS results showed high significance for differences between the two described groups (p
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< 0.01). SIMPER analyses showed that the species that contributed greatly to differentiating
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the two groups were Symphodus species (15%) followed by Diplodus sargus (12%), Mugilids
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(12%) and Labrus merula (11%). Overall, all the 38 groups/species were represented in group
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1, NC, whereas 35 of the 38 species were fished in group 2, SC. However, the three species not
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present in SC were low-presence species in general with very few individuals fished in the
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studied period (i.e. Zeus faber, Pagellus erithrynus and Chelidonichtys lucerna). In fact, Z. faber
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and C. lucerna are characteristic of deeper waters and non-representative of spearfishing
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contest grounds. Co-occurrence analysis showed a positive relationship between Symphodus
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species and Conger conger, Labrus viridis, Phycis sp and Scorpaena scrofa with probabilities of
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above 50% of co-occurrence (see Supplementary Figure 2). This first group of species mainly
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characterized the NC group community. Mugilid species positively co-occured with Sarpa salpa
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and Dicentrarchus labrax with co-occurrence probabilities of above 60%; these species
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characterized the SC group. The white seabream Diplodus sargus was the second most
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important species that characterized groups, mainly due to its frequency of appearance (Figure
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3). This species co-occured with Sparus aurata and Diplodus cervinus.
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3.3. Temporal trends in communities and species. We did not observe any significant long-term
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changes in the community composition over the studied years. As mentioned above, the main
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clusters were related to the spatial classification. Nor did we observe major temporal trends at
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the species level. In fact, the RDA outputs show high significance for RDA1 and RD2 (p-values =
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0.01), which are related to the factors Year and Season respectively but the cumulative
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proportion is very small (
