Abstract
Empirical assessments of the influence of invasive species on native species are infrequent because the required long-term data are rarely available. The invasion of silver carp in the Upper Mississippi River System (UMRS) provides a unique opportunity to assess the influence of this invasive species on native fishes because a highly standardized, long-term monitoring program has been sampling the fish communities in six reaches of the UMRS for over 20 years. We analyzed fish abundance (catch per unit effort from electrofishing) and water-quality data collected from 1994 to 2013 from three reaches where silver carp populations have been established since 2000, and three reaches where they are not established. Our results provide empirical evidence of a negative effect of invasive silver carp on native sport fish in the UMRS. Although water temperature, suspended solid concentration, and flooding also differed substantially between control and invaded reaches, only silver carp abundance had a direct negative relationship with the abundance of adult sport fish. Our analyses suggest that the mechanism for this decline may be competition for zooplankton between silver carp and larval/juvenile sport fish. In reaches where silver carp is established, recruitment of juvenile sport fish appears to be constrained relative to reaches where silver carp is not established.
Highlights
Invasive species are an increasing global threat to ecosystems and the subject of much scientific inquiry, actual empirical assessments of the effects of invasive species on native species are relatively scarce because of the rarity of the long-term data needed to examine these effects while accounting for other drivers and anthropogenic stressors (Capinha et al 2015; Clavero and Garcia-Berthou 2005; Grarock et al 2014; Trexler et al 2000)
We found a negative empirical relationship between silver carp and adult sport fish abundance that varied with year
We found empirical evidence of a negative influence of silver carp on the abundance of sport fish in the Upper Mississippi River System (UMRS)
Summary
Invasive species are an increasing global threat to ecosystems and the subject of much scientific inquiry, actual empirical assessments of the effects of invasive species on native species are relatively scarce because of the rarity of the long-term data needed to examine these effects while accounting for other drivers and anthropogenic stressors (Capinha et al 2015; Clavero and Garcia-Berthou 2005; Grarock et al 2014; Trexler et al 2000). Rigorous approaches to detecting the effects of invasive species on native species require standardized data collection on the abundance of native biota before and after the establishment of the invasive species, in multiple invaded areas and multiple control areas where the invasive species is not established (Blossey 1999; Underwood 1992, 1994) Such data are uncommon, but the invasion of silver carp (Hypophthalmichthys molitrix) in the Upper Mississippi River System (UMRS; Upper Mississippi River and its navigable tributaries) provides a unique opportunity to empirically examine the effects of this invasive species on native species. Data from the LTRM element are ideally suited for such an evaluation because this ongoing standardized monitoring program precedes the establishment of silver carp in the UMRS. This monitoring occurs in three reaches that have been invaded by silver carp and three reaches where silver carp is not yet established
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