Este libro nos pone al día en tres grandes bloques, uno inicial donde se aborda el estado del conocimiento tanto desde la perspectiva biótica como física de la cuenca, la geología, hidrología, sedimentología y su relación con los ecosistemas y la biodiversidad acuática; los peces, su diversidad taxonómica y genética, ecología e historias de vida y los servicios ecosistémicos que brindan como recursos pesqueros. En la segunda parte se consideran los conflictos ambientales en la cuenca, desde temas como la contaminación y la modificación del hábitat; los peces introducidos (exóticos y trasplantados y la “presión” de una demanda cada vez mayor de la pesca. En la sección tercera, tras una interpretación concienzuda de los capítulos anteriores y el conocimiento de los investigadores, se hace un análisis detallado de todas las amenazas, así como las estrategias de conservación y manejo del recurso íctico. Todo ello, sienta las bases para una serie de recomendaciones para la toma de decisiones que son recogidas al final de la obra.
Context Overfishing has been historically considered as the main cause of fish stock depletion in the Magdalena River basin, Colombia, whereas the environmental context in which fisheries take place has not been considered. Aims The purpose of this research was to answer the following question: have anthropic activities, other than fishing, influenced the decrease in fishery production in the Magdalena River basin between 1980 and 2015? Methods We analysed diverse variables that were used as proxies for different environmental degradation processes, including sediment load, forest cover, flow rates, reservoir volume <1200 m above sea level, gold production and human population growth. We compared these variables with fishery production between 1980 and 2015 by using cluster analysis, principal-component analysis (PCA) and principal-component regression (PCR). Key results Our findings confirmed that environmental degradation accounts for 61% of the reduction of fishery production. Conclusions The traditional approach of holding fishers accountable for the decline of fishery production is misleading, and, therefore, a better understanding of the overall system is necessary before implementing restrictions on fishing activities. Implications Hence, fishery management should also integrate economic and social variables that affect ecosystem services within the basin into the analysis and decision processes.
Objetivo: Realizar un estudio de las principales variables económicas, biológicas y pesqueras del recurso camarón blanco (Litopenaeus occidentalis) del Pacífico colombiano. Metodología: Se recopilaron 49 años de datos de captura y esfuerzo, complementados con información de tallas y peso que permitieron utilizar modelos de producción excedente y bioeconómicos (modelo Gordon-Schaefer) de esta manera. Resultados: Se determinó que el recurso está siendo sometido a un sobreesfuerzo lo cual ha obligado a la realización de diferentes periodos de veda. Conclusiones: Se pudo determinar que el punto de referencia límite como rendimiento máximo sostenible fue de 808 ton con un esfuerzo correspondiente de 54 motonaves/año y el punto de referencia objetivo como el rendimiento máximo económico de 760 ton con un esfuerzo correspondiente de 41 motonaves/año, los cuales ya han sobrepasado sus niveles registrando capturas anuales que no superan las 200 ton/año.
Classical management has not been able to stop the 65% decrease in fishery production during the last 40 years in the Magdalena-Cauca River Basin. To analyze the effects of selective fishing of multiple species and small scale fisheries we addressed temporal changes at fishing level and the response of fishermen. The fishery reduced production and CPUE (catch per unit effort standardized), decreased the large sizes and growth rates of Prochilodus magdalenae and Pseudoplatystoma magdaleniatum, changed the abundance of trophic levels (decreased carnivores and increase of detritivores, omnivores), and increased exploitation rates. The fishermen have responded by implementing self-control measures, diversifying fishing gear and mesh size, including new species and sizes in the catch with a higher cpue (catch per unit effort) of small sized fish, adjusting the fishing effort to the abundance. We conclude that selective fishing has had ecological effects and fishermen have empirically self-regulated to optimize the cost-benefit ratio of their activity, developing a fishery that is more in line with ecosystemic structures. We address the balanced harvest strategy as a management alternative.
24Overfishing has been historically considered as the main cause of fish stock 25 depletion worldwide. This paradigm has oriented fishery management towards a 26 classical approach, under which externalities to fisheries were not considered as they 27 were difficult to assess and measure. The aim of this study is to describe the dynamics 28 of different environmental, economic, and demographic variables (water flow, forest 29 cover, gold production, population growth, stored water volume, and sediments) in 30 relation to the behavior of the fishery production in the Magdalena-Cauca river basin 31 from 1980 to 2015. Generalized Additive Models were used to determine the variables 32 that best explain fishery production. The findings confirmed that environmental 33 deterioration of the Magdalena River basin explained at least 60% of the reduction in 34 fishery production. Thus, we concluded that the traditional approach of making fishers 35 responsible for the decline of fish production was a misguided argument, and before 36 implementing restrictions on fishing activity, a better understanding of the overall 37 system is crucial. Hence, fishery management should involve the economic and social 38 sectors that affect the offer of ecosystem services within the basin, including fishing. 40 Introduction 41Historically, overfishing was considered to be the main cause of fish stocks 42 depletion in the world. This fact guided fisheries management towards a classical 43 approach that did not adequately consider the impacts of external factors, either because 44 they were difficult to control (1,2), or complex to characterize. This is the case in inland 45 fisheries, being rivers the most impacted ecosystems by human activities over the past 46 100 years. Furthermore, many activities linked to the use of natural resources that imply 3 47 intense human interventions take place in rives, threatening their functionality (flow 48 rates disruption, erosion, alterations of habitats, among others) (3). As a consequence, it 49 is imperative to study the anthropic effects on both, the environment as well as on 50 natural fish populations, before ascribing all impacts to fishing activity (4). Therefore, 51 as fisheries cannot be considered isolated, a multifactorial approach is required for their 52 assessment and management (5). 54According to the abovementioned, inaccurate or incomplete diagnoses of the 55 root causes of overfishing can lead to errors in the formulation and implementation of 56 fishing policies or programs (6). This phenomenon responds to a lack of knowledge on 57 the impacts of other sectors (i.e., agriculture, mining, and transport, among others) in 58 inland fisheries, which together with a northern hemisphere industrial fisheries approach 59 (1) have resulted in the overall reduction of fishery resources. Moreover, these concepts 60 are focused on internal factors such as size, fishing gear, reproductive seasons, and 61 reserve areas, aimed to achieve sustainability only through their management (1,7). 62 63 ...
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