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Assessing Fishing Impacts in a Tropical Reservoir Through an Ecosystem

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Assessing Fishing Impacts in a Tropical Reservoir Through an Ecosystem Rev Fish Biol Fisheries https://doi.org/10.1007/s11160-018-9539-9 (0123456789().,-volV)(0123456789().,-volV) RESEARCH PAPER Assessing fishing impacts in a tropical reservoir through an ecosystem modeling approach Juliana Strieder Philippsen . Carolina V. Minte-Vera . Marta Coll . Ronaldo Angelini Received: 3 August 2017 / Accepted: 19 October 2018 Ó Springer Nature Switzerland AG 2018 Abstract Ecological models are useful for evaluat- drivers explaining catch trends in the Itaipu Reservoir ing fishery management scenarios, as they allow fisheries. The mean trophic level of catch did not researchers to investigate alternative fishing effort, change throughout the analyzed time period and no as well as varying environmental and trophic interac- losses in secondary production from exploitation (L tion scenarios. Through an ecosystem modeling index) were observed, indicating that Itaipu fisheries approach (Ecopath with Ecosim), we addressed the are sustainable regarding ecosystem effects. The possible impacts of small-scale fisheries on the negative impacts of introduced species on native structure and functioning of a tropical ecosystem species seem to be greater than the fishing impacts. (Itaipu Reservoir, Brazil). We found that fishing Fishing simulations from the ecosystem Maximum effects and predator–prey interactions were the main Sustainable Yield (MSY) reduced the biomass of some important species in the local fishery. Regarding management advice, our results indicate that fishing Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11160-018-9539-9) con- efforts should not be increased for curimba (Prochilo- tains supplementary material, which is available to authorized dus lineatus), pintado (Pseudoplatystoma corruscans), users. J. S. Philippsen (&) Á C. V. Minte-Vera R. Angelini PPG Ecologia de Ambientes Aqua´ticos Continentais, Departamento de Engenharia Civil, Universidade Federal Universidade Estadual de Maringa´, Av. Colombo 5790, do Rio Grande do Norte (UFRN), Natal, Brazil Maringa´, PR 87020-900, Brazil e-mail: [email protected] C. V. Minte-Vera Inter-American Tropical Tuna Commission, La Jolla, CA 92037, USA M. Coll Institut de Ciencies del Mar (ICM-CSIC), Barcelona, Spain M. Coll Ecopath International Initiative Research Association, Barcelona, Spain 123 Rev Fish Biol Fisheries and jau´ (Zungaro jahu). Additionally, participative Graaf et al. 2015; FAO 2016). Furthermore, when management methods are important measures for dealing with fisheries in reservoirs, the water demands local fisheries. Finally, additional research is needed to of hydropower production usually take precedence investigate how fishery management can promote the over biodiversity conservation and fishery activities use of multispecific methods (e.g., gillnets) to control when public policies are determined, especially in introduced species. developing countries (Winemiller et al. 2016). When fishery management occurs in reservoirs, it is Keywords Ecopath with Ecosim Á Ecosystem-based usually done through traditional input or output management Á Inland fisheries Á L index Á Maximum controls (Arlinghaus et al. 2016; Agostinho et al. sustainable yield 2016). The main input regulations include fishing gear restrictions, controlled access, and the establishment of fishing seasons. The output controls can limit the minimum size of fish and catch per fisher. Such Introduction controls might not be enough to ensure population sizes and sustain biomass production over time, since Inland fisheries are commonly small-scale and spa- some degree of connection to upstream rivers is tially spread out, involving a large number of artisanal necessary for reproduction (Agostinho et al. 2008). or subsistence fishers whose products are usually sold Moreover, fisheries management in reservoirs should and consumed locally (Welcomme 2011). Tropical be implemented alongside habitat management freshwater fisheries exploit a wide variety of fish (through dam operation) and should consider the species, often using the same fishing gear (Smith et al. negative impacts that water level oscillations have on 2005). The total global freshwater capture production the recruitment of fish species (Arlinghaus et al. 2016; in 2016 was 11.6 million tons, representing 12.8% of Oliveira et al. 2015). the total catch (FAO 2018). Inland capture fisheries are socio-ecological sys- Although the production and overall economic tems with dynamics that depend on human behavior, values of freshwater fisheries are small when com- societal norms, and environmental quality (Ostrom pared to marine fisheries, inland capture fisheries play 2009; Beard et al. 2011). An ecosystem approach to a vital social role as they are the main source of income fisheries (EAF) could encourage sustainable develop- and protein for rural households in remote areas ment and management of inland fisheries by address- (Smith et al. 2005; Bartley et al. 2015). The majority of ing both human and ecological aspects (FAO 2003; the inland fisheries’ catch comes from developing Suuronen and Bartley 2014; Anderson et al. 2015). In countries, where fishing activities are key to food this way, management actions under the EAF try to security and alleviating poverty (Cooke et al. 2016). balance the different dimensions (social, ecological, However, if such fishing is not properly managed, it and human) involved in fisheries, seeking to improve can harm both the exploited fish population and the performance of these dimensions and align with the ecosystem structure and function (Coll et al. 2016). social-ecological systems concept. Besides fishing, freshwater systems are subject to The ecological dimension of the EAF aims to several other impacts, such as invasion by nonnative conserve the ecosystem structure, diversity, and species, climate change, and habitat alteration (Agos- function, while the societal and human objectives tinho et al. 2016; Walsh et al. 2016). Habitat alteration focus on successfully attaining food and livelihood can also negatively influence fishing activities. The (Pikitch et al. 2004). Regarding the ecological dimen- construction of dams can alter the composition of sion, it is possible to use food web modeling as a tool inland catches, affecting species with relatively high to understand ecological processes and to investigate market values and those with low market values, thus the fishing impacts on ecosystems (Angelini et al. reducing revenue and yield (Hoeinghaus et al. 2009). 2013; Coll et al. 2016). The knowledge gained through Despite the remarkable contributions that inland such approach can inform and promote management fisheries make to society, national and international and policy decisions regarding the ecological aspects agendas often neglect this sector. Thus, the stock of fisheries. Also, ecosystem modeling can integrate statuses of most inland fisheries are unknown (De single-species management into a wider ecological 123 Rev Fish Biol Fisheries context by considering impacts on non-target species, Methods structural elements of the ecosystem, and trophic interactions among species (Hilborn 2011; Collie et al. Study area and local fishery 2016; Gascuel et al. 2016). In this study, we adopted an ecosystem modeling The Itaipu Reservoir, which was impounded in 1982, approach to address the possible impacts of fishing on is located in the Upper Parana´ River at the Brazil- the structure and function of the Itaipu Reservoir in Paraguay border (Fig. 1), in a region with a high Brazil. The small-scale commercial fisheries in the concentration of hydroelectric dams (Agostinho et al. Itaipu Reservoir play a fundamental role in providing 2007). The Upper Parana´ River basin comprises an livelihood and protein sources for almost 700 fishers area of 891,000 km2 and in 2007, 146 large dams were (Okada et al. 2012). The majority of catches from the recorded in this basin, with a total area of approxi- reservoir consist of ten species, especially the follow- mately 16,700 km2. The biggest 10 reservoirs (in- ing six species: Pterodoras granulosus, Prochilodus cluding Itaipu) have a total area of 10,270 km2, with lineatus, Plagioscion squamosissimus, Hypophthal- the first reservoir impounded in 1963 (Furnas Dam) mus edentatus, Pinirampus pirinampu, and Hoplias and the last one in 1998 (Porto Primavera Dam) spp. These species are sedentary (non-migratory (Agostinho et al. 2007). The Itaipu Reservoir has a species, except for P. lineatus) and P. squamosissimus surface area of 1350 km2, a mean depth of 22 m, and is an introduced species. After the construction of the an average hydraulic retention time of approximately Itaipu Reservoir, catch declines and changes in catch 40 days. The Itaipu Reservoir is connected to an composition have negatively affected the income of extensive floodplain upstream, which is essential for local fishers (Hoeinghaus et al. 2009; Philippsen et al. maintaining the abundance of reservoir fish popula- 2016). Input and output controls are traditional tions, especially for migratory species (Oliveira et al. strategies that have been adopted by the Secretariat 2015). of Fishery and Aquaculture in Brazil. In addition, fish The composition of catches changed markedly after ladders and stocking actions have been taken by the impoundment of the reservoir for large migratory government managers as an attempt to minimize dam species with high commercial value to sedentary (i.e., impacts, but in general, have been unsuccessful or species that do not migrate) ones with lower market caused
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