Influence of fishing activity over the marine debris composition close to coastal jetty

Abstract

Worldwide, the marine debris emissions have been provoking impacts in ecosystems, generating massive mortality of different species with commercial interest. In South America, we have a lack of studies to verify the marine debris composition in transitional environments such as adjacent regions of coastal jetties. These are hydraulic engineering constructions used to maintain the navigation channel access between the sea-estuarine interface and are also used by teleost fishes, crustaceans, and mollusks like artificial shelters (reefs), being excellent fishing grounds. Therefore, the present study was devoted to qualitatively evaluate the composition of marine debris in an internal jetty portion of a Laguna Estuarine System (LES) located in South America (Brazil). Six hundred freediving were conducted to collect marine debris in the study region. The in situ campaigns were performed in 2016 during all spring season (sand substrata) in four distinct zones with 26,400 m² each one covering almost all adjacent jetty extension, to evaluate possible spatial changes in the marine debris composition. All material obtained was identified, measured, weighed, and ordered in eight groups, with six groups being related to the fishing activity and two groups related to the tourism/community in the study region. So, it was possible to observe possible relations between the marine debris distribution to artisanal and recreational local fishing. After 600 freediving sampling efforts, 2142 marine debris items were obtained, totaling close to 100 kg of solid waste removed from the inner portion of the coastal jetty. Notably, 1752 units (50 kg) of fishing leads were collected being this item the main marine debris residue found in the four sampled areas, corresponding to nearly 50% of the total weight of the collected waste. Ninety-eight percent of marine debris were derived from the local fishing activities, and just 2% were derived from tourism/community. Considering the total contribution related to fishing, 83% of the marine debris were composed by lead (sinkers) adopted by recreational and artisanal fishing. Notably, the catch activity in this region has a close influence over the marine debris composition. Reductions of marine debris emissions derived from the fishing activities have been a global challenge, once this problem is occurring in practically all marine and estuarine environments under the anthropic action. The presence of marine debris changes the local landscape and can provoke serious environmental problems, such as ghost fishing that affects a wide variability of marine mammals, birds, and fishes. Most of marine debris collected came from recreational and artisanal fishing, being the fishing leads the most prominent material, especially in sector 4. This fact is possibly related to the intense mullet fishing using cast nets, usual in this sample area. In the other sectors, there was a great predominance of grapnel fishing leads, widely adopted by recreational fishermen in open water environments. The "fingernails" present in these fishing leads ensure the sinking of the line for a specific location independently of possible flow oscillations of the tidal current and/or currents generated by winds. The massive quantity of fishing leads into the sectors is a dangerous fact. Notably, lead is a heavy, non-biodegradable, and extremely toxic metal that, due to the anthropogenic activities, has been increasing around the world. Future efforts in our study region should evaluate the seasonal marine debris composition to observe possible changes along the different seasons of the year. In this way, it would be possible to infer quantitatively the emission of marine debris derived from the fishing activity, assessing its impacts and enabling the adoption of environmental management strategies. This effort adopted a qualitative analysis, serving to show the current situation of this region that we now know to be vulnerable to the presence of marine debris derived from the fishing activity.

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