We examined the effects of adult common carp (Cyprinus carpio) on shallow aquatic ecosystems and compared the effects with those of a native benthic fish, channel catfish (Ictalurus punctatus). Experimental ponds contained enclosures (0.06 ha) with a low carp biomass (174 kg·ha1), high carp biomass (476 kg·ha1), high catfish biomass (416 kg·ha1), and no fish. We measured abiotic factors (turbidity, suspended solids, total phosphorus), as well as effects on adjacent trophic levels (aquatic macrophytes, zooplankton, and aquatic macroinvertebrates) from July to September. Common carp was positively related to total phosphorus, turbidity, suspended solids, and zooplankton biomass, and negatively related to macrophyte and macroinvertebrate abundance. Suspended solids in the carp treatments consisted primarily of inorganic particles. Carp were either positively or negatively related to phytoplankton, depending on zooplankton abundance. A high biomass of carp had greater effect on nutrients, turbidity, and suspended solids than a low biomass. Channel catfish was positively related to total phosphorus concentrations and altered zooplankton composition, but did not affect turbidity, suspended solids, macroinvertebrates, and macrophytes. These results suggest that common carp have a stronger influence on water quality and aquatic community structure than benthic fish native to North America.
Fisheries-induced evolution and its impact on the productivity of exploited fish stocks remains a highly contested research topic in applied fish evolution and fisheries science. Although many quantitative models assume that larger, more fecund fish are preferentially removed by fishing, there is no empirical evidence describing the relationship between vulnerability to capture and individual reproductive fitness in the wild. Using males from two lines of largemouth bass (Micropterus salmoides) selectively bred over three generations for either high (HV) or low (LV) vulnerability to angling as a model system, we show that the trait "vulnerability to angling" positively correlates with aggression, intensity of parental care, and reproductive fitness. The difference in reproductive fitness between HV and LV fish was particularly evident among larger males, which are also the preferred mating partners of females. Our study constitutes experimental evidence that recreational angling selectively captures individuals with the highest potential for reproductive fitness. Our study further suggests that selective removal of the fittest individuals likely occurs in many fisheries that target species engaged in parental care. As a result, depending on the ecological context, angling-induced selection may have negative consequences for recruitment within wild populations of largemouth bass and possibly other exploited species in which behavioral patterns that determine fitness, such as aggression or parental care, also affect their vulnerability to fishing gear.ize-selective fishing, or even just an elevated level of fishing mortality, has the potential to induce rapid evolutionary change in a range of production-related traits in fish populations (1, 2). Theoretically predicted and empirically supported fisheriesinduced adaptive change involves the modification of life history traits, including reductions in age-and size-at-maturation, increases in reproductive investment, and changes in pre-and/or postmaturation growth rates (1-3). Changes in life history traits in response to fishing often collectively reduce adult size-at-age and fisheries yield and result in fish populations that only slowly rebound from overexploited states (4-7). There is little consensus, however, concerning the prevalence of fisheries-induced evolution and its relevance to management (1,(8)(9)(10). Perspectives range from calls for "evolutionarily enlightened management" (11) to positions that argue that evolutionary change induced by fishing is slow, thereby rendering it largely unimportant to fisheries management (9).One important tool to predict long-term population-level consequences of fisheries-induced evolution involves the construction and analysis of individual-based models (5, 12) or more simplified stage or age/size-structured (7) population models. Suitable models to study the potential for fisheries-induced evolution include ecological feedbacks resulting in density-and frequencydependent selection that shapes fitness landscapes and ev...
The development and application of fish bioenergetics models have flourished in recent years, due in part to the complexity of the issues being faced by fisheries biologists. As with any model, the accuracy of bioenergetics models can be hampered by uncertainty in model parameters. A review of the literature showed that field and laboratory tests of bioenergetics models often result in poor agreement between model predictions and independent data. Nonetheless, bioenergetics modeling continues to be used to make important management decisions. Recent tests of model predictions have shown that parameter uncertainty is influenced by factors such as feeding rate, physiological adaptations, and prey composition and abundance. In an attempt to reduce the uncertainty in modeling applications, we propose a framework that highlights the importance of (1) model evaluation, (2) hypothesis-based parameter testing, and (3) improved communication between model developers and model users. Adherence to this framework will help reduce uncertainty in modeling applications and simultaneously contribute to a broader knowledge of fish physiology and feeding ecology.
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