Abstract
Small-scale fisheries of lagoon-estuarine complexes (LECs) in Northwest Mexico were investigated using official landings data. Species groups found in landings were clustered into three categories according to their life cycle and habitat distribution: Lagoon-estuarine (LE), Transition zone (TZ) and Coastal (CO). Average landings were highest for LE (19,606 t yr−1), followed by TZ (7,234 t yr−1), and CO (3,155 t yr−1). In contrast, the total number of fished species groups had an opposite pattern: LE, TZ, and CO bore 31, 66 and 74 species groups respectively. The number of species groups in LE category significantly increased towards LECs of southern latitudes. The families with highest landings in LECs were Penaeidae, Portunidae, Mugilidae, Scombridae, and Lutjanidae. The area of LECs was significantly correlated with the amount of landings recorded for LE category. A similarity analysis of LECs species groups revealed a latitudinal clustering of northern and southern LECs. Overall, fisheries in LECs produced millions of $US per year, which support socioeconomic activities at the local, regional, and national scale. Although the information and landings data on LECs fisheries in Northwest Mexico have limitations for data analysis, our results suggest that changes in fisheries management of LECs, such as bottom-up management actions where resource users can participate, could help establish more sustainable fishing practices in these ecosystems and allow coastal communities to continue obtaining economic benefits and food supply from LECs in Northwest Mexico.
Keywords
Introduction
Small-scale fisheries worldwide account for more than half the world's catch, employ more than 90% of all people engaged in fisheries, and provide food security for hundreds of millions of persons [1, 2]. However, small-scale fisheries are frequently undervalued, seldom studied, and generally not taken into account by assessments or management programs [3].
In northwestern Mexico, small-scale fisheries generally use fiberglass skiffs known as “pangas” to catch diverse fish, shellfish, and invertebrates, which are found in varied ecological environments [4, 5]. However, some fishers of lagoons and estuaries in northwestern Mexico still employ more traditional fishing practices, such as manually throwing cast nets in shallow areas of LECs to catch shrimp and fish [6]. The Mexican National Commission of Fisheries and Aquaculture (CONAPESCA) reports that the Gulf of California harbors about 29,000 pangas officially registered for small-scale fisheries, 82% of which are found in the northwest Mexican Pacific coast, including the states of Sonora, Sinaloa and Nayarit, with 7,234, 11,828, and 4,442 pangas, respectively [7].
Northwestern Mexico's Pacific coast fisheries have been important for centuries [6]. Today, more than 50% of Mexico's small-scale and large-scale fisheries landings in this region are from inland water bodies connected to the sea such as estuaries, coastal lagoons, and bays [8, 9]. Here we define estuaries and coastal lagoons as lagoon-estuarine complexes (LECs) following Day and Yañez-Arancibia (1982) [10]. LECs are coastal ecotones connected to the sea in a permanent or ephemeral manner. They typically have shallow depths, variable volumes of water (depending on local climatic and hydrologic conditions), oscillations in temperature and salinity, muddy-sandy bottoms, seasonally high turbidity, and irregular topography. Primary production in the shallow waters of LECs (usually < 10 m depth) is sustained by nutrient inputs released by wind-induced sediment suspension [11, 12], and by the inflow of freshwater from rivers and their connection with the sea [13]. These ecosystems have very high primary productivity, usually ∼10–15-fold higher than adjacent environments [14].
Few studies have systematically explored the small-scale fisheries of LECs. This is mainly because small-scale fisheries information is scarce and frequently reported inadequately [15–17]. For example, in Mexico, current fisheries statistics from CONAPESCA use coarse taxonomic categories that include multiple trophic levels, and landings data give no detail on fishing method or location of capture [18]. In spite of these limitations, CONAPESCA data currently represent the most complete and systematic information available for small-scale fisheries landings in Mexico. CONAPESCA fisheries data have proven useful in the development of macro-scale studies of the importance of mangrove forests for fisheries [21], and of fishery regions in the Gulf of California and northwestern Mexico [18].
Using CONAPESCA landings data and multivariate analysis, Erisman et al. (2011) demonstrated a connection between the spatial distribution of species groups of commercial fisheries landings and the latitude of primary coastal habitats of the Gulf of California, which include mangroves, wetlands, rocky reefs, and soft seabed habitats [18–20]. These results have been useful in the development of management plans that consider the direct spatial connection among coastal habitats, harvested species groups, and fishing activities within each fishery region [18].
Other studies, which also underscore the ecological and economic importance of LECs small-scale fisheries, show the Gulf of California produced more than 11,000 tons of fish and blue crab from 2001 to 2005 [21]. These fishery landings were dependent on mangrove forests in LECs from northwestern Mexico and the Baja California Peninsula, and were worth more than 19 million dollars in economic benefits for local fishers [21]. Carrasquilla-Henao et al. (2013) report that in the 1990–2009 period, volume captures of shrimp, blue crab, stripped mullet, snapper, and cockles of the San Ignacio-Navachiste-Macapule lagoon in northwestern Mexico were significantly correlated to mangrove cover [22]. In general, diverse physical, ecological and fisheries aspects of lagoon-estuarine ecosystems are more broadly reported in other coastal areas of Mexico, such as the Gulf of Mexico and the Caribbean, [see 23–25].
Overall, fishing in LECs of northwestern Mexico is focused on the Penaeidae (shrimp) and Portunidae (blue crab) families [6, 26]. The shrimp fishery is the most economically important in the studied LECs and occurs from September to March [27]. From April through August shrimp-fishing has been banned by the Mexican government since the early 1960s [6]. The blue crab (Callinectes sp.) fishery is considered second in economic importance in the region [26], and took place all year round until 2012, when fishing was banned from May to August of every year [28].
Regionally, little is known about how the fisheries of groups other than shrimp and blue crab occur in LECs of northwestern Mexico. More importantly, it is not known how these fisheries relate to the seasonality of the shrimp fishery. Although the fisheries of other species groups are not as profitable as those of shrimp (e.g., Litopenaeus spp.) and blue crab, they are important regionally, providing a continued flow of income and food resources for local communities. We examined how the landings of other groups caught in LECs may change with the seasonality of the shrimp-fishing season and whether these changes occur differently among LECs at different latitudes.
Our study provides a regional description of small-scale fisheries landings and their revenues in seven LECs of northwestern Mexico (see Table 1 for names), within one of the fishery regions proposed by Erisman et al. (2011). Our results can give managers a better understanding of LEC fishery dynamics, and can help in actions that aim to better understand the fising effort in the region for single species, such as shrimp or blue crab, and may also help to develop management actions for sustainable fishing and natural resource conservation of LECs in northwestern Mexico.
Lagoon-estuarine complexes names and map labels.
Methods
Conapesca landings database
We obtained a nine-year database (2001-2009) with 258,166 daily records of small-scale fishery landings from C
LECs of Northwest Mexico. Coastal area of Sonora (SON), Sinaloa (SIN) and Nayarit (NAY). LECs are represented by colors: purple (Guaymas-Bahía Lobos GBL), orange (Huatabampo-Bahía Agiabampo HA), yellow (Topolobampo TOP), red (Bahía de Santa María La Reforma BSM), green (Pabellones PAB), pink (Mazatlán-Laguna Huizache Caimanero MLH), and magenta (Marismas Nacionales MN). Black circles with numbers represent local fishery offices from which landings arrival records were collected.
Classification of species groups in conapesca landings database
The small-scale fishery landings reports in the C
(A) Diagram of the classification of species groups. (B) Number of species groups and families for each category. Circles are proportional to the amount of species groups in each category.
Data analysis
Families caught in LECs
We used descriptive statistics to identify the relevant species groups and their families caught in LECs.
Families were considered relevant if their landings were within the 85% of the total catch for each species group category during the nine years of study.
Relationship between the landings of LECs and the number of species groups with the area and latitude of LECs.
We developed three hypotheses based on previous studies by: (1) Aburto et al. (2008), which show the area of mangrove fringe is positively correlated to fishery yields in coastal lagoons of the Gulf of California [21]; (2) Pérez-Rufaza (1989) and Pérez-Rufaza et al. (2006) which found that the positive relationship between species richness and lagoon volume, a synthetic expression of surface and depth, is consistent with the expectation that larger lagoons could provide a greater diversity of environments and types of bottoms with specific assemblages [16, 33]; and (3) Hillebrand (2004), which reports on the latitudinal gradient as a spatial pattern in taxa of aquatic and terrestrial environments where biodiversity is higher towards tropical latitudes and decreases towards higher latitudes [34].
Our first hypothesis was that mean annual landings for each family in each species group category in LECs would increase as the area of the LEC increases. The total area of LECs was used for the analysis, including mangrove cover (Rhizophora mangle, Laguncularia racemosa, Avicennia germinans, and Conocarpus erectus) together with the open water area of LECs, which also includes other submerged aquatic vegetation such as bottom-rooted seagrasses (Ruppia maritima, Halodule wrightii, Syringodium filiformis, Zostera marina, and Thalassia testudinum). Like mangroves, seagrass beds are also known to enhance fishery yields [35, 36]. Our second hypothesis was that the number of species groups would increase as the area of the LEC increases. Our third hypothesis was that the parameters of average annual landings and the number of species groups will vary depending on the latitude of each LEC. To test these hypotheses, four different relationships were tested via regression analysis: first, the area of the LEC in km2 against (i) average annual landings and (ii) the number of species groups, and, secondly, the latitude of each LEC against these same factors.
Analysis of similarities of species groups among LECs
To determine whether species groups were similar among LECs, we used a non-parametric analysis of similarities, and a cluster analysis [37, 38]. For the non-parametric analysis of similarities, a presence–absence matrix of species groups as descriptors and LECs as units of the analysis was used. This test uses distance measures converted to ranks, and the test statistic R ranges from 0 to 1. A large positive R means dissimilarity between groups. If the non-parametric analysis of similarities revealed a significant p value <0.05, a step-down sequential Bonferroni post-hoc test was used to test for significant differences in LECs. The post-hoc test was done between the significant (p value <0.05) pairwise results of all gropus obtained from the non-parametric analysis of similarities; significant comparisons for the post-hoc test were at p value <0.05 [38]. For the cluster analysis PAST v. 2.12 uses unweight pair-group averages, where clusters are joined based on the average distance between all members in the two groups. The distance matrix for this analysis was made using the Bray-Curtis similarity index [38].
Testing for the causes of dissimilarities in fishery species groups among LECs.
To test hypotheses on the causes of dissimilarity between LECs, we used the same presence-absence matrices used for the non-parametric analysis of similarities for each fishery group category, and subjected them to a Principal Component Analysis. The resulting axes were tested against external variables such as latitude or lagoon size, in order to detect potential drivers of the differences in fishery composition between LECs.
Average annual landings of families caught in northern and southern LECs
We obtained the average annual landings of each relevant family in northern and southern LECs in each species group category and used a one-way analysis of variance (ANOVA) to examine differences between the average annual landings of the same families from northern and southern LECs for each species group category. Calculations of fishing method or catch-per-unit were not possible to analyze from the C
LECs fisheries during shrimp-fishing season and shrimp-fishing ban
We selected 19 species groups from the C
Revenues of LECs fisheries
We analyzed the ex-vessel price, which is the price given to fishermen for catches when landed at the dock. Ex-vessel price information was available from the C
Results
FAMILIES CAUGHT IN LECs
The daily records of C
A qualitative description of the families and species groups in the different categories is shown in Figs. 2B and 2C. Overall, the amount of species groups was higher for the coastal area and lowest for the lagoon-estuarine area, but the landings values had an opposite pattern. The highest average landings were for species groups inside the lagoon. LE category had 19,606 t yr−1, followed by TZ and CO categories with 7,264 t yr−1 and 3,179 t yr−1, respectively (Fig. 3B). Landings differed significantly between categories (F2,24 = 24.77, p = 0.00). Post-hoc comparison revealed significant differences in landings production between LE and TZ categories (Bonferroni-corrected t = 5.130; p < 0.0001) and LE and CO categories (Bonferroni corrected t = 6.738, p = 0.00). ZI and CO categories did not differ significantly (Bonferroni corrected t = 1.608; p = 0.3625) (Fig. 3B).
(A) Percent of total landings for families and species groups caught in LECs for which landings were 85% or more of the total catch in each category. (B) Average landings for each category of species groups.
RELATIONSHIPS BETWEEN THE LANDINGS OF LECs AND THE NUMBER OF SPECIES GROUPS, TO THE AREA AND LATITUDE OF LECs.
As expected, larger lagoons harbored higher landings (Fig. 4A), but this pattern was only significantly correlated for species groups that live inside the LECs (Fig. 4B). On average, each km2 of LEC was associated with an increase in LE average landings by 5.226 tons (y = 5.226 x + -2,438; p < 0.032, r2 = 0.63). There was no significant relationship between the area of the LEC and the landings of TZ and CO categories, and the area of the LEC and the number of species groups in each category were not significantly related, either. Similarly, the relationship between latitude and average landings was not significantly different for any of the species group categories. However, the relationship between latitude and the number of species groups was significant only for LE category. On average, each latitudinal degree towards the north was associated with a decrease of 3 LE species groups (y = -2.8 x + 85.54; p < 0.023, r2 =0.68; Fig. 4C).
(A) Shows the sum of average landings in Lagoon-estuarine complexes for LE (grey), TZ (white), and CO (black). (B) Relationship between the lagoon-estuarine area (km2) and average landings (metric tons). (C) Relationship between the latitude of LEC and species groups richness. (B) The dotted black line shows the linear regression for LE (y = 5.226 x + −2,438; p < 0.032, r2 = 0.63); (C) The strait black line shows the linear regression for LE (y = 2.8 x + 85.54; p < 0.023, r2 = 0.68). Species group's categories are represented by grey circles (LE), white squares (TZ), and black triangles (CO). LECs are labeled see Table 1.
ANALYSIS OF SIMILARITIES OF SPECIES GROUPS AMONG LECs.
The non-parametric analysis of similarities showed low dissimilarity between the species groups caught in all categories of LECs: LE (R = 0.06), TZ (R = 0.02), and CO (R = 0.03). However, pairwise post-hoc Bonferroni tests revealed significant differences between species groups caught in LECs (Table 2). These differences clustered LECs according to latitude for all categories in a very robust way (Fig. 5A–5C). For LE category the species groups caught formed two clusters, one composed of the northern LECs (Guaymas-Bahía Lobos and Huatabampo-Agiabampo) and the other composed of the southern LECs (Pabellones, Mazatlán-Laguna Huizache Caimanero and Marismas Nacionales). Species groups caught in Bahía de Santa María La Reforma (located in the central latitudes of our study area) were more similar to species groups of northern latitudes. In contrast, species groups caught in the northern LEC of Topolobampo were more similar to the ones caught in southern LECs (Fig. 5A).
Pairwise post-hoc Bonferroni test for the non-parametric analysis of similarities between LECs for the different species groups categories in LECs (see table 1 for LECs labels). Bold numbers denote significant differences between LECs with Bonferroni.
Dendograms for the presence-absence of species groups in LECs for each category (A) LE, (B) TZ, and (C) CO. The Bray Curtis similarity index was used for this analysis. Abbreviations for each LEC are shown on the right (see Table 1 and Fig. 1 for color labels of LECs). Principal Component Analysis for all three categories D (LE), E (TZ), and F (CO). This first multivariate axis was significantly correlated with latitude for all categories (r= −0.83, p=0.02 for LE; r= −0.83, p=0.02 for TZ; and r= −0.92, p=0.003 for CO).
For TZ category the species groups caught in LECs also formed two clusters, one of northern LECs (Guaymas-Bahía Lobos, Huatabampo-Agiabampo, Topolobampo), and the second joining the central (Bahía de Santa María La Reforma and Pabellones) and southern LECs (Mazatlán-Laguna Huizache Caimanero and Marismas Nacionales) (Fig. 4B). For the CO category, a clustering pattern similar to that for the LE category occurred. However, in the CO category the species groups caught at LEC Bahía de Santa María La Reforma were more similar to species groups caught in southern LECs (Fig. 5C). The Principal Component Analysis largely confirmed the results of the analysis of similarities. For all three categories (LE, TZ, and CO), a single dominant axis ordered the regional LECs from north to south, following a latitudinal gradient (Fig. 4D–4F). This first multivariate axis was significantly correlated with latitude (r = −0.83, p = 0.02 for LE; r = −0.83, p = 0.02 for TZ; and r = −0.92, p = 0.003 for CO).
AVERAGE ANNUAL LANDINGS OF FAMILIES CAUGHT IN NORTHERN AND SOUTHERN LECs.
Because of the latitudinal association among LECs, we present the average annual landings for those families that concentrated 85% or more of the catch in northern and southern LECs. For the LE category the Penaeidae family landings in northern and southern LECs were not significantly different. The Portunidae family landings were significantly higher in northern LECs (F1,1 = 32.63, p < 0.0001; 7,119 t yr−1). Portunidae family landings were 97% less in southern LECs (183 t yr−1) (Fig. 6A). For the TZ category, only the Mugilidae family landings did not show a significant difference between northern and southern LECs. All the other families analyzed had significant differences between their landings in northern and southern LECs. For the Penaeidae family, landings were 79% less in southern LECs (F1,16 = 22.35, p < 0.00)1; 207 t yr−1) than in northern LECs (1014 t yr−1) (Fig. 5B). The opposite pattern was seen for families Ariidae (F1,16 = 22.35, p < 0.0001; 46 t yr−1), Veneridae (F1,16 = 8.66, p < 0.0001; 120 t yr−1), Gerreidae (F1,16 = 37.21, p < 0.0001; 124 t yr−1), Sciaenidae (F1,16 = 5.12, p = 0.03; 318 t yr−1), Lutjanidae (F1,16 = 17.91, p < 0.0001; 87 t yr−1), and Triakidae (F1,16 = 13.03, p = 0.002; 154 t yr−1), for which landings in northern LECs were significantly less. The landings values for all of these families increased in southern LECs by 100% or more (Fig. 6B).
Average landings of relevant families caught in northern (GBL, HA, TOP, BSM) and southern (PAB, MLH, MN) LECs. (A) LE category, (B) TZ category and (C) CO category. Stars indicate p values for ANOVA comparisons between landings of northern and southern LECs, *** (p value < 0.001), ** (p value < 0.01), * (p value < 0.05).
For the CO category, landings in northern LECs were significantly higher for families Scombridae (F1,16 = 7.68, p = 0.013; 826 t yr−1), Lutjanidae (F1,16 = 33.53, p < 0.000; 299 t yr−1), Serranidae (F1,16 =21.23, p < 0.0001; 188 t yr−1), and Balistidae (F1,16 = 6.87, p < 0.018; 107 t yr−1). The landings of the aforementioned families decreased by over 40% in southern LECs. The landings of diverse shark families were not significantly different among LEC latitudes (Fig. 6C). The Muricidae family only had landings in northern LECs, and Chaenidae and Osteridae family landings were mainly from southern LECs.
LECs FISHERIES DURING SHRIMP-FISHING SEASON AND SHRIMP-FISHING BAN
The 19 species groups for which landings were analyzed during the shrimp-fishing season (September-March) and the shrimp-fishing ban (April-August) showed landings of blue crab and grouper (cabrilla, Mycteroperca sp., Epinephelus sp.), pufferfish (Sphoeroides sp.), red snapper (Lutjanus sp.), and rays (e.g. Rhinoptera sp., Myliobatis sp.) were significantly higher during the shrimp-fishing ban (p<0.05 for ANOVA comparisons). On the other hand, hound shark (Mustelus sp.), mojarra (e.g. Eucinostomus sp., Gerres sp., Diapterus sp., Eugerres sp.), catfish (chihuil, Bagre sp.), corvina (Cynoscion spp.), snapper (Lutjanus spp., Holopargus sp.), snook (Centroppmus spp.), sierra (Scomberomorus sp.), and gulf coney (Epinephelus sp.) had significantly higher landings (p <0.05 for ANOVA comparisons) during the shrimp-fishing season. The landings of mullet (Mugil spp.), flatfish (Paralichthys sp, Bothus sp.), pampano (e.g. Selene sp., Trachinotus sp.), shark (Carcharhinus spp. Sphyrna sp., among others not identified), manta (Myliobatus sp., Mobula spp., Rhinoptera sp., Dasyatis spp.) and cusk eel (Brotula sp.) were not significantly different between fishing seasons (p > 0.05 for ANOVA comparisons; Table 3).
ANOVA results for landings of 19 species groups caught in LECs during shrimp-fishing season and shrimp-fishing ban. Stars indicate p values for ANOVA comparisons *** (p < 0.001), ** (p < 0.01), * (p < 0.05). Ns refer to non-significant ANOVA comparisons. One-way ANOVA used landings as main effect for both fishing seasons; ANOVA effects shows results for a two-way ANOVA between groups, which examined the interaction of fishing season and LECs.
The discriminant function analysis (Fig. 7A) revealed separation of species groups primarily among fishing seasons and latitude of LECs (Fig. 7B). The discriminant function analysis generated two significant discriminant functions (Wilk's Lambda 0.119, p<0.0001), which accounted for 98.6% of total variance. The first discriminant function was related to latitude (it separated northern LECs from southern LECs). The second discriminant function had an effect only in northern LECs, where there are changes in the species groups caught during the different seasons. The plot of the group centroids on the first two discriminant functions reveals the 19 species groups associated into three distinct clusters: (1) species groups (corvina, flatfish, gulf coney, hound shark (cazon), manta, mullet, pampano, sierra, and snapper) that are being fished in northern latitudes during shrimp-fishing season, are in the upper right quadrant; (2) species groups (blue crab, cusk eel, grouper (cabrilla), mojarra, pufferfish, red snapper, sea catfish (chihuil) and shark) that are being fished in northern latitudes during the shrimp-fishing ban are in the lower right quadrant; and (3) in southern latitudes the 19 species groups did not form any clusters during the shrimp-fishing season, except for snook which is being fished in southern latitudes during shrimp-fishing season and mantarraya which is being fished in southern latitudes during the shrimp-fishing ban (Fig. 7A and 7B).
(A) Discriminant function analysis performed on 19 species groups in northern and southern LECs during shrimp-fishing season and shrimp-fishing ban. The discriminant function analysis generated two significant discriminant functions, which accounted for 98.6% of total variance. (B) Group centroids (within group mean for each discriminant function) for the first and second discriminant functions.
REVENUES OF LECs FISHERIES THROUGHOUT THE SHRIMP-FISHING SEASON AND LATITUDE OF LECs.
Based on the discriminant function analysis results, we documented the revenues from fisheries from northern and southern LECs throughout the different fishing seasons and related these revenues to the areas of LECs, the number of people inhabiting around each LEC, the number of species groups, and the value of revenue diversity (this last variable was calculated using Simpson's Index to estimate the economic diversity that the revenues of species groups in LECs are providing; see Fig. 8).
Revenues for species groups caught in Northern and Southern LECs during the shrimp-fishing season and the shrimp-fishing ban. * Revenue diversity was calculated using the Simpson Index and it refers to the economic diversity that the revenues of species groups in LECs are providing. See Appendix 2 for details.
The numbers of species groups in Northern LECs do not change much between fishing seasons. However, the discriminant function analysis reported shifts in what is being fished between seasons (Fig. 7). The revenue diversity in Northern LECs during the shrimp-fishing season is low and produced by five species groups (estuarine shrimp, blue shrimp, shrimp, blue crab, and sierra), of which shrimps are responsible for 73% of the total US$ 128 million revenues. On the other hand, during the shrimp-fishing ban the revenue diversity is also low, provided mainly by shrimp, blue crab and red snapper. Even though there is a ban on shrimp, the data collected report 45% of the total US$ 65 million revenues were obtained from shrimp.
Although in Southern LECs there is a higher number of species groups during the shrimp-fishing season (n = 127), the discriminant function analysis showed there were no shifts in what is being fished between seasons (Fig. 7). In Southern LECs what changes between seasons is the proportion of species groups caught. Revenue diversity was also low for Southern LECs. During the shrimp-fishing season estuarine shrimp is responsible for 70% percent of the total US$ 202 million generated. On the other hand, during the shrimp-fishing ban the revenue diversity is mainly from six species groups (shrimp, blue crab, pleasure oyster, pufferfish, snook, snapper and corvina). Despite the ban on shrimp, the data collected report 32% of the total US$ 42 million revenues were obtained from shrimp. The low revenue diversity matters for management purposes and for the future conservation and sustainability of fishery ecosystem services in LECs of northwestern Mexico.
DISCUSSION
Our results underscore the importance of the area of LECs for fishery production, at least for fish and invertebrates that use LECs during their entire life cycle or are temporary residents at one stage of their life cycle, and are mainly fished inside the LEC (Fig. 4B). These results support two previously-posed ideas: (1) that coastal lagoons and estuaries can harbor species groups of economic importance for small and large-scale fisheries in high quantities [25, 40]; and (2) that mangroves and seagrass beds (both present in the studied LECs) are critical for fisheries enhancement [21, 22, 35, 36].
Because area and landings were correlated, we expected that LECs with larger areas could harbor a higher number of species groups. Pérez-Rufaza (1989) and Pérez-Rufaza et al. (2006) report that the positive relationship between species richness and lagoon volume, a synthetic expression of surface and depth, confirms the expectation that larger lagoons could provide a greater diversity of environments and types of bottoms with specific assemblages [16, 33]. Our results did not confirm this relationship, possibly because, besides area, the interaction of physical (hydrology, salinity, bathymetry) and biological (chlorophyll concentration) factors can also be at play in defining the amount of species groups in LECs [41, 39]. Additionally, although lagoon-estuarine areas are highly productive, there are cases where a few species can dominate the biotic community [42].
Another factor that can influence these unexpected results is fishing. Although the information presented here does not suggest overfishing, the influence of fishing pressure on the ecosystem cannot be entirely discarded, since fishing patterns can influence the presence and abundance of species in ecosystems [43]. The history of coastal resource use in the LECs studied here is millenary, and there is good evidence that the abundance and diversity of estuarine and coastal fauna in this region were higher in the past than they are today [31, 44–46]. Supporting this argument, Sala et al. (2004) have documented overfishing in shallow coastal areas all along the region [4].
Each latitudinal degree towards the north was associated with a decrease in species group diversity within the LE category (Fig. 4C). This agrees with the general latitudinal gradient seen in taxa of aquatic and terrestrial environments, where biodiversity decreases towards higher latitudes [34]. However for the TZ and CO categories the latitudinal pattern is absent. The wider habitat ranges and higher mobility of species groups in TZ and CO can influence this trend.
In contrast, the analysis of similarities among LECs showed that there is a variation in the fishery catches according to latitude. Within each category there was a biotic gradient that grouped species with affinities to tropical waters in southern LECs and species with affinity to temperate waters in northern LECs (Fig. 5A–C). Previous work by Erisman et al. (2011) demonstrated a connection between the spatial distribution of species groups of commercial fisheries landings and the latitude of primary coastal habitats throughout the Gulf of California, including mangroves, wetlands, rocky reefs, and soft seabed habitats [18–20]. Based on these geographic trends, the authors defined five fishery regions using C
Although our analysis occurs in a narrower spatial scale of six latitudinal degrees compared to Erisman et al. (2011), our results support the latitudinal regionalization of the landings, as given by the analysis of similarities and by the strong correlation between latitude and the multivariate PCA axes (Fig. 5D–5F). These results are useful for management because they highlight the importance of understanding and managing small-scale fisheries at the LEC scale. A regional management for small-scale fishers in the Gulf of California was suggested by Erisman et al. (2011) based on the existence of distinct fisheries regions with distinct ecological and socio-economic traits, in contrast with current management as a single region by the Mexican government [47].
Quantitatively, we found significant differences between the landings of families caught in LECs for all categories (Fig. 6). This agrees with previous studies showing that LEC fishery yields can be uneven, with some systems being more productive than others. Qualitatively, our results demonstrate that families fished in LECs have uneven fishing pressure [48–50]. For the nine years of this study, only 9–15% of the families in each category were preferentially targeted and caught (Fig. 3A). These preferences for specific families (e.g. Penaeidae) in LECs are part of an ancestral tradition in northwestern Mexico [46, 49, 50]. However, in the last half of the 20th century fishing preference for certain families has been exacerbated by (i) the coastal population boom, as people switched from agriculture to fishing, (ii) the high economic value of shrimp, (iii) government policies that promoted resource extraction, and (iv) the use of highly effective fishing gear [7, 27, 48, 49].
Increased fishing selectivity has had visible results. In the past, higher trophic level fish (groupers TL 4, corvinas TL 4, snapper TL 3.6, and snook TL 3.8) were commonly caught in the LECs studied [7, 46, 49, 50]. Today these are severely reduced, and lower trophic level fish families (mullet TL 2.13, sea catfish TL 3.6, mojarra TL 3.17) are the most common catch. Also, the high fishing selectivity reported here for families Portunidae (blue crab) and Penaeidae (estuarine shrimp) raises management issues of food security and future socioeconomic stability in the region.
The differences in landings of families among LECs are also linked to the physical and ecological characteristics of the LECs. Blue crab comes mainly from Topolobampo, a dry-climate LEC with a more oceanic environment, as it is a permanently open lagoon with well-defined tidal circulation, strongly influenced by winds and well-mixed vertically [9]. This is a crucial environment for completion of the blue crab life cycle [51]. Female blue crabs spawn in the mouth of the LEC; the planktonic phase individuals migrate offshore and return to the LEC as adults [52]. On the other hand, Marismas Nacionales had the highest estuarine shrimp landings. This LEC is an alluvial plain composed of a complex of tidal channels, coastal lagoons, rivers, and seasonal flood plains, with the most extensive northern mangrove forest in North America [40]. Ecologically, this LEC has a suitable environment for the proliferation of shrimp, where mangroves provide refuge and food sources for the shrimp larval stages before they leave the estuarine and coastal lagoon waters for their pelagic life phase [8]. Such information is scarce or absent for most of the other species groups caught in LECs, and together with data on the ecology and seasonality of LECs fisheries is needed for management actions tailored to specific needs of LEC species groups.
For example, here we show that in northern LECs the catch composition of species groups can change between the shrimp-fishing season and shrimp-fishing ban. However, this situation is not present in southern LECs. Locally it is known that fishermen of LECs would switch from fishing bluecrab to shrimp when the shrimp-fishing season is over [26]. Here we demonstrate this tendency with landings statistics across northern LECs and show how blue crab is mainly available in northern LECs (Fig. 7A).
Our finding that grouper (cabrilla) is fished more in northern LECs during the shrimp-fishing ban is important for management, because there is so little knowledge of the actual state of Serranid populations in the Gulf of California (Fig. 7A, Table 3). Here their spawning aggregations have been heavily fished in recent decades [31]. Grouper (cabrilla) coastal landings in Nayarit peak in the month of April, during the spawning aggregations of their reproductive season [15, 31]. April also coincides with the shrimp-fishing ban in northwestern Mexico, a policy that reinforces the springtime fishing pressure on groupers in the northern LECs.
Arreguín-Sánchez and Arcos-Huitrón (2011), found the grouper (cabrilla) fishery from 1956 to 2009 for the coastal area of Sonora and Sinaloa to be overfished, and the coastal Central Pacific grouper fishery (including the states of Nayarit, Guadalajara, Colima, Morelia and Guerrero, see Appendix 3) to be collapsed. Although these data are at the state scale, the authors warn of the threats groupers (cabrilla) face [53]. Red snapper provides a similar example of higher landings during the shrimp-fishing ban (Table 3). Available fisheries data show red snapper is caught year round and is one of the most important resources for small-scale fisheries in Mexico's Pacific coast, both by catch volume and by market value. However, the status of the fishery is unclear [6, 15]. Arreguín-Sánchez and Arcos-Huitrón (2011) consider this fishery to be fully exploited for the coastal area of Sonora and Sinaloa and overfished for the coastal Central Pacific.
The latter examples place fisheries managers in a difficult situation, because lack of information about LEC fisheries species groups makes it hard to establish appropriate regulations. Mexico recently issued regulations for blue crab, hound shark, mullets, rays and sharks that involve a fishing ban [28]. Even the most basic descriptive studies of to LECs fisheries are therefore valuable for management purposes.
Although we present a high diversity of species groups found in LEC fisheries, only a handful of these are highly profitable (Table 4). Because price values used for this analysis were obtained using the ex-vessel price, revenues can increase when the resources enter the local, national, and international markets. Using partial information for eight fish families and blue crab that depend on mangroves, Aburto et al. (2008) reported that ∼US$ 19 million are yearly obtained from these resources all along the Gulf of California. This amount can considerably increase if the fishery revenues from other families (e.g. Penaeidae) caught in LECs are taken into account (see Fig. 8). A clearer perspective of revenues could be given if precise fisher numbers were available. This is important because illegal fishing is a common activity in the region. However, fishers' statistics are scarce. In the year 2012, the states of Sonora, Sinaloa and Nayarit had 12,740; 36,912; and 12,784 fishers respectively, but these data do not distinguish between small-scale or large-scale fishers [54]. In general, our revenue results demonstrate that a considerable amount of the revenues were obtained from shrimp during the shrimp-fishing ban, which should prompt better enforcement strategies in the region.
Lastly we acknowledge that the results presented here have data limitations, since official fisheries landings from C
Implications for conservation
Thousands of fishers receive a direct economic benefit from LECs of northwestern Mexico. Over 2 million people living around the LECs also receive indirect economic benefits from fishing activities (Fig. 7). Nevertheless LECs fisheries and their habitats continue to be undervalued by government and society [27, 55]. Historically, the government has encouraged the increasing fishing effort, unsustainable fishing practices, and societal issues occurring in LECs [7, 27, 48, 55]. For example, at Marismas Nacionales pork meal is used to attract shrimp when fishing. This activity is considered an everyday practice for shrimp fishing. Similarly, the use of cyanide and of nets with illegal mesh size is widespread [56]. Currently, similar information for other LECs studied here is unavailable.
Our study narrows the gap of information on Mexico's small-scale fisheries. Despite the data caveats mentioned previously regarding C
In closing, there is a need for the Mexican government to reconsider the management of LECs fisheries for more sustainable use of their resources. For this purpose, even the most basic descriptive studies related to LECs fisheries are needed. In the near future this information will also have to be supplemented by the introduction of “bottom-up efforts” that include participation by communities and fishers. This is also suggested for small-scale fisheries in the northern Gulf of California, where the social organization and participation of fishers have improved fishery practices and resource conservation in some coastal towns [5, 58–60]. The latter recommendations will preserve coastal ecosystem functions provided by LECs in northwestern Mexico, which are tightly coupled to successful fisheries and the socioeconomic well-being of coastal communities.
Footnotes
Acknowledgements
We thank the headquarters offices of C
Appendix 1.
Families, species groups, and total landings for lagoon-estuarine species group category.
Appendix 2.
Revenues Shrimp-fishing season Northern LECs
Appendix 3.
Appendix 3. Coastal states of Mexico's Pacific coast.