INTRODUCTION

Megalops atlanticus Valenciennes, 1847 is a bony fish of the Megalopidae family, commonly known as sábalo (in the Caribbean), sábalo real (in the Colombian Pacific) or tarpon (in Anglophone America). It is widely distributed in tropical and subtropical waters of the Atlantic Ocean, both in American and African coasts; it is found from Virginia (in North America) to southern Brazil and from Mauritania to southern Angola (1). From the record of Hildebrand in 1937, its passage through the Panama Canal is assumed, thus its presence on the Pacific coast of Panama (2), extending its distribution to northern Costa Rica, although this has not been strictly documented (3).

Its lifecycle mainly includes estuarine and marine environments, but it is also found in freshwater, since specimens have been found in inland waters several hundred kilometers from the coast (4). Tarpon’s variability in environment occupation at the different stages of its lifecycle makes it an interesting and attractive species to be used in fattening projects, as in Belize, Colombia, and Guyana (5). In Florida (United States of America) and Mexico, its large body and combative behavior has made it a fish of great value in game fishing, investing millions of dollars each year in this practice (5).

On the other hand, in countries such as Belize, Cuba, Puerto Rico, Nicaragua, Costa Rica, Trinidad, and Colombia, it has been exploited as a fishing resource, which has led to a decline in its population, placing it in the “Vulnerable” category of threatened species according to criterion “A” of the classification of the International Union for Conservation of Nature (6). In the case of Colombia, several threats have been mentioned that have contributed to the decline in tarpon’s populations, including the mishandling of crops, deterioration or loss of habitat, and overfishing. This latter has been mainly generated by the use of inappropriate fishing techniques, such as dynamite, which has caused a reduction in tarpon’s capture volumes along the Caribbean coast of Colombia (7).

Different researches carried out in the Pacific coast of Colombia (8,9,10) have not mentioned the species and its presence of tarpon in the country has not been formally documented. Therefore, the occurrence of Megalops atlanticus in the Colombian Pacific is recorded for the first time in this work, which also provides information about its use and exploitation as a resource by the surrounding coastal communities.

MATERIALS AND METHODS

Study area. The study covered the jurisdiction of the municipalities of Nuquí and Bahia Solano, in the North Choco Pacific Coast Environmental Unit (UAC-PN) to the northwestern of the Chocó Province. The UAC-PN has a coastline length of 250 km between Punta Ardita and Cabo Corrientes; this marine-coastal region has a high diversity of habitats, including mangrove forests, muddy flats, sandy bottoms, rocky substrates, cliffs, and coral formations (11)(Figure 1).

According to the Holdridge system, the UAC-PN is located in a very humid tropical forest area (Bmh-T), which is characterized by high annual rainfalls (between 5000 and 7000 mm), as it is located in the Inter-tropical Convergence Zone (ITCZ) where the trade winds converge (11). The rainfall pattern is bimodal with a rainy season that runs from April to December and a short period of low rainfall from January to March. The annual average temperature ranges between 25 and 27 °C. Tides are regularly semidiurnal, showing two highs and two lows over a period of 12.25 h; salinity ranges from 20 to 33 in stations far from the coast (11).

Field methods. To obtain information about the distribution, use and exploitation levels of tarpon, surveys were conducted from May 2013 to February 2014 among artisanal fishermen from several communities in the municipalities of Nuquí and Bahia Solano. The survey was composed of ten questions related to the areas of distribution, frequency of capture, fishing methods, time of year where it is most often seen, current abundance of the resource, time present in the region, size, weight, maturity, uses and marketing. In addition, material was examined from specimens landed at communities and samplings were conducted with fishermen from the region, using local gear forms such as hook and spinel as capture method.

The specimens collected were recorded photographically and data on total length (TL) and total weight were taken. Sex differentiation and gonadal maturity was determined using the criterion applied to the species. Subsequently, specimens were returned to fishermen. Tarpon’s morphometric and meristic information was obtained from the literature on Atlantic fish (1).

RESULTS

In total 50 catches were recorded in the Cupica and Tribugá Gulfs, in addition to two records outside the study area, one in the mouth of the San Juan River, in front of Charambirá (to the south of the Chocó Province) and another record in the mouth of the Mira River (to the south of the Nariño Province). The latter measured 132 cm TL (Figure 2). Regarding the specimens examined, six in total, these were captured in the area of the community of Jurubirá (Table 1).

Diagnostic features: compressed and fusiform body, oblique or upper mouth, prominent lower jaw, very small teeth arranged in villiform bands in the jaw, ventral gular plate between the two branches of the lower mandible, 32 to 36 gill rakers on the lower part of the first arch; 23 to 27 branchiostegals rays; simple and spineless dorsal fin with 13 to 16 rays, the last being a very long ray, anal fin with 21 to 25 soft rays, pectoral fins with 13 to 15 soft rays, pelvic fins with 10 or 11 soft rays; 37-42 large cycloid scales along the lateral line (Figure 1).

Coloration. In fresh, bright silver body, gray back, silver belly and gray fins.

Maximum size. 1.97 m and 44 kg weight. Regarding the maturity stage, five males and one female were captured, all in stage III of gonadal maturity.

According to the results of the surveys, the landing sites where more catches have been registered are Jurubirá (15 records) and Nuquí (12 records); 23 records were detected in the communities of Coquí, Arusí, Bahia Solano, Guachalito, Panguí, and Cabo Corrientes. As to exploitation areas, the results of the surveys showed that in each one of the towns there are some fishing sites with the highest tarpon catches, these are: in the Gulf of Tribugá, in Jurubirá, to the rocky reefs in front of the town and at the mouth of the Jurubirá river; in Nuquí, in the mouth of Tribugá and in front of Jurubirá; in Coquí, in the deltaic mouth of the estuary; in Guachalito and Arusí in Cabo Corrientes and in the reef in front of Arusí; in the Gulf of Cupica, in Bahia Solano; at the mouth of the Cupica, Piña and Juradó Bay(Figure 3).

Four fishing gear used to catch tarpon were found: hand line (hooks with sizes between 3 and 9), spear, gillnet, and fishing rod. In general, the capture method consists of using live bait (often Opisthonema libertate) and leaving the hook on shallow waters (what is called trolling), and once the tarpon is attracted to the bait it is captured with the spear.

Regarding the months of capture, although tarpon can be fished the entire year, 20% of the catches occurred in October, 10% in September, 8% in August and June and less than 6% in the other months of the year or have no date of capture. However, fishermen argue that the period when they are most often seen is from April to May due to the migration of O. libertate.

With respect to the sizes reported by the fishermen and the specimens collected, only about one third of the individuals measured (32.14%) had sizes between 0 and 1 m and little more than two thirds (67.86%) had sizes between 1 and 2.5 m; in other words, only one third of the individuals captured corresponds to small-sized specimens. The vast majority of the sizes found corresponded to adult individuals (Figure 4).

On the other hand, the uses in the Colombian Pacific are self-consumption (65% of respondents), handcrafts (20%), sale (7%), and game fishing (8%), although the use and the importance of the species varies from one community to another (Figure 5). In the case of the community of Jurubirá, its meat is sought after by the Embera indigenous group in the region, who exchange bananas and other foods to consume it. Instead, in black communities, scales are used for the manufacturing of handcrafts such as lamps, costumes, necklaces, and bracelets, among others, using them in their natural form or colored with anilines. The sale price of scales per half a kilo is $10.000 Colombian pesos (approx. US $5).

In the communities of Nuquí, Arusí, Panguí, Cabo Corriente, Coquí, and Tribuga, given the low income of these communities (using wooden boats and artisanal and rudimentary fishing gear) and due to the large size and combative behavior of tarpon, it is a strenuous activity for the fishermen, who make incidental catches and in some cases specimens are returned to the sea provoking beaching. Therefore, they are traded in a very low proportion in Nuquí because it is the most important municipality in this region, making deliveries from there to Quibdó to be then marketed in the rest of the country. In contrast, on the beaches of Guachalito, an important tourist area, as in Bahia Solano, tarpon is exclusively used in game fishing; making this practice more technical with sport fishing rods and hooks (rapalas), which are more appropriate for its capture (Figure 6).

DISCUSSION

From what has already been written on the traversing of this species through the Panama Canal (2) and the anecdotal records on the Costa Rica coasts, this becomes the first tarpon record for the Colombian Pacific, showing a process of dispersion in the Pacific and an evident invasive phenomenon. According to the information gathered, it can be asserted that tarpon has certainly spread to the south of the Colombian Pacific through the Gulfs of Tribugá and Cupica, reaching the mouth of the Mira River (border with Ecuador); hence, this record shows that the species has travelled about 1.300 km, starting from the Caribbean Sea through the Panama Canal to the southern Colombian Pacific.

The main use of this resource in the Colombian Pacific is own consumption as a food supplement; however, it is not very appreciated by locals who use it for other purposes such as making handcrafts and in game fishing. Despite being an important species with economic potential in the region, exploited by commercial fishing and game fishing, and being a priority species for researching, the current status of the migration of the population and the status of the invading population is still unknown. This prevents the implementation of management plans and/or control policies, thus becoming a potential danger not only at ecosystem level, since it is a predatory species, but at social and economic levels, because it can become a problem for the fishing industry in the area.

The presence of tarpon in the Chocó Pacific area is estimated at approximately 30 years, according to the incidental catches made by local fishermen. It is found both in muddy environments in bays and mangroves and in rocky substrates. This shows that it is a species that, in addition to being resistant to marked environmental changes, is in a continuous search for resources.

Therefore, studies are needed to provide important data to assess and determine not only the structure, genetic diversity, and phylogeographic patterns of this species in the Pacific coastal area and the Caribbean, but also to establish whether there is any influence of evolutionary, such as dispersion, and/or ecological events in shaping the distribution patterns of this species. This will reveal the adaptive and evolutionary potential of tarpon populations, leading to the identification and prioritization of monitoring, management, and conservation areas (12,13). Thus, policies governing the fishing of this species in both the Pacific and Caribbean coastal regions are required (12).

An important aspect that must be analyzed by national academic and administrative authorities is the status to be given to the presence of tarpon in Colombian Pacific waters. It may be considered a transplanted native species as it is a native species of the Colombian Caribbean, according to the guidelines of the Ministry of the Environment. However, its dispersion and reproduction in the Pacific Ocean is presumed, for which it may be classified as an established species that can become invasive at the same time, displacing native species in the Pacific and creating ecological imbalances and altering the genetic structure of natural populations (14).

Acknowledgements

To the fishermen and residents of the area for their help. To Fundacion MarViva for spatial information, To Cristian Vanegas for Figure 6. This work was partially funded by the Young Researchers and Innovators Program, Administrative Department of Science, Technology and Innovation – Colciencias. Contribution 414 Cecimar, Caribbean campus of Universidad Nacional de Colombia.

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