Abstract
Exotic freshwater fish can have deleterious effects on local biodiversity, although these impacts often only become apparent many years after the introduction. Local Ecological Knowledge (LEK) may be a useful source of information in situations where formal technical studies are insufficient, but few works have examined the reliability of information generated through this approach. We examined the reliability of LEK by investigating the impacts of Nile tilapia on fishery stocks in an artificial reservoir in northeastern Brazil. We gathered LEK from 29 experienced fishermen and then confronted this information with official fishery statistics from the same site. Twenty-two fishermen stated that total catch in the Gargalheiras Reservoir had declined over the years, 68% (N=15) of them began fishing before 1976 (the year Nile tilapia was introduced into reservoir). Of those 15 fishermen, 87% (N=13) stated that tilapia has not negatively affected other species, which ran counter to analyses of fishery statistics. Our study suggests that the LEK of fishermen is not a useful source of information concerning the impacts caused by exotic tilapia. However, the LEK added an overfishing hypothesis of the decline in fishery stocks in the Gargalheiras reservoir.
Highlights
There is no universally accepted definition of local ecological knowledge (LEK), the concept considers components of: (i) local and empirical ‘knowledge’ of species and other environmental phenomena; (ii) ‘practice’, the manners in which people use natural resources for survival purposes, including fishing, hunting, and agriculture; and (iii) ‘beliefs’ that define human relationships with their immediate environments (BERKES, 2008)
According to the fishermen involved in the research project (29 individuals) the main fish species captured in the reservoir were: tilapia (O. niloticus), pescada (Plagioscion squamosissimus, HECKEL, 1840), and tucunaré (Cichla ocellaris, Bloch; Schneider, 1801) (Table 2), as can be seen in the graph of fishery statistics (Figure 1a)
Not directly questioned on the subject, 31% (N = 10) fishermen interviewed attributed the success of tilapia to their high reproductive capacity - as expressed in statements such as: ‘tilapia spawn a lot’, ‘they lay eggs all the time, while other fish species depend on the season’
Summary
There is no universally accepted definition of local ecological knowledge (LEK), the concept considers components of: (i) local and empirical ‘knowledge’ of species and other environmental phenomena; (ii) ‘practice’, the manners in which people use natural resources for survival purposes, including fishing, hunting, and agriculture; and (iii) ‘beliefs’ that define human relationships with their immediate environments (BERKES, 2008). The impacts of non-native fish may not, become fully apparent until years or even decades after their initial introduction, and in many cases little or no information is available about the baseline ecological conditions of inland aquatic ecosystems prior to their introduction (CANONICO et al, 2005; STRAYER et al, 2006). Experimental approaches are important for providing mechanistic understandings of ecological phenomena, but often fail to incorporate context-dependent impacts of invasive species (CUCHEROUSSET; OLDEN, 2011). In situations where technical (scientific) information is insufficient, LEK may be a useful source of information, but there have been few attempts to closely examine the reliability of the information generated through this approach (GILCHRIST et al, 2005)
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