Blue catfish (Ictalurus furcatus) have been widely introduced throughout the United States and are invasive in Chesapeake Bay. Despite this proliferation, little is known about the diet of this ...large, predatory catfish. We used stratified random sampling to collect stomachs from 14,488 blue catfish in Chesapeake Bay. Canonical correspondence analysis (CCA) was used to identify key drivers of the diet of blue catfish, and generalized additive models (GAMs) were used to explore trends in rates of predation by blue catfish on depleted or commercially valuable native species, including American shad (Alosa sapidissima), blueback herring (A. aestivalis), alewife (A. pseudoharengus), American eel (Anguilla rostrata), and blue crab (Callinectes sapidus). Results of CCA reveal that diets were significantly correlated with season, salinity, and total length (TL) of blue catfish, and those from our GAMs reveal the circumstances associated with greater predation on these species. For example, we found that Alosa species were most susceptible to predation by large catfish (>600 mm TL) in freshwater areas during the month of April. This paper describes methods for identifying times, locations, and other circumstances that are associated with maximal predation rates upon certain taxa. The information gained from these approaches can be used to inform management strategies, with the goal of reducing effects of predation on specific organisms.
Amazonian goliath catfishes are widespread in the Amazon Basin. Recently, otolith 87Sr:86Sr analyses using laser ablation–multi‐collector–inductively coupled plasma mass spectrometry (LA‐MC‐ICPMS) ...revealed a >8,000 km trans‐Amazonian natal homing in Brachyplatystoma rousseauxii among fish caught and hatched in the largest Amazon River tributary, the upper Madeira basin. Although also suspected for fish in the upper Amazon, homing could not be demonstrated owing to less distinct environmental 87Sr:86Sr gradients along the Amazon mainstem. Using scanning X‐ray fluorescence microscopy (SXFM), a separate study provided evidence that Se:Ca and Sr:Ca are useful markers for identifying migration into Andean headwaters and the estuarine environment.
We analysed otoliths of known 87Sr:86Sr profiles using SXFM mapping to test if Sr:Ca and Se:Ca patterns could demonstrate natal homing for three fish caught in the upper Amazon, using as reference two individuals that were natal homers and two forced residents (hatched after the construction of hydroelectric dams on the Madeira River) from the upper Madeira River.
As hypothesised, although the Sr isotope profiles of the upper Amazon individuals were uninformative, two of them presented similar alternating mirror patterns of Sr:Ca and Se:Ca to those of the upper Madeira natal homers, indicating migrations out of the Andean region and into the estuary area. Both were therefore natal homers from the upper Amazon.
The third individual from the upper Amazon presented similar Sr:Ca and Se:Ca patterns to those of the upper Madeira residents, suggesting it was a natural resident from the upper Amazon.
By combining the results of 87Sr:86Sr analyses (LA‐MC‐ICPMS) and Sr:Ca and Se:Ca mappings (SXFM) that are completely independent of one another, we demonstrated that B. rousseauxii also performs natal homing in the upper Amazon. Our results indicate that the life cycle of B. rousseauxii is more complex than previous literature hypothesised, with the existence of partial migration, even in absence of physical barriers. Quantifying the relative importance of these different life‐history strategies will have important implications for fisheries management. Our results also lay the groundwork for conservation efforts in the context of hydropower development in the Amazon Basin and set testable hypotheses of the potential impacts of the Madeira River dams.
Current understanding of mercury (Hg) dynamics in the Arctic is hampered by a lack of data in the Russian Arctic region, which comprises about half of the entire Arctic watershed. This study ...quantified temporal and longitudinal trends in total mercury (THg) concentrations in burbot (Lota lota) in eight rivers of the Russian Arctic between 1980 and 2001, encompassing an expanse of 118 degrees of longitude. Burbot THg concentrations declined by an average of 2.6% annually across all eight rivers during the study period, decreasing by 39% from 0.171 μg g–1 wet weight (w.w.) in 1980 to 0.104 μg g–1 w.w. in 2001. THg concentrations in burbot also declined by an average of 1.8% per 10° of longitude from west to east across the study area between 1988 and 2001. These results, in combination with those of previous studies, suggest that Hg trends in Arctic freshwater fishes before 2001 were spatially and temporally heterogeneous, as those in the North American Arctic were mostly increasing while those in the Russian Arctic were mostly decreasing. It is suggested that Hg trends in Arctic animals may be influenced by both depositional and postdepositional processes.
► We assessed the sustainability of multispecies small-scale fisheries in the Lower Amazon. ► Exploitation levels are below the predicted maximum potential. ► Five of the nine most caught species ...appear to be overexploited. ► Concentration of fishing effort and unsustainable fishing practices threaten the sustainability of higher value, target species.
Resource assessments of small-scale fisheries in the Amazon are rare, making it difficult to improve fisheries management. This study assessed the sustainability of small-scale fishery resources in the Lower Amazon region using data from over 20,000 interviews collected in three floodplain fishing communities between 1992 and 2007. The data were analyzed with respect to theoretical maxima of catches and historical trends of (i) catch per unit effort (CPUE), (ii) species composition of the catch, and (iii) mean body length of the most-caught species. The most important results were: First, observed catches have been about 54–58% of theoretical maxima in all communities. Second, CPUE has remained stable over time in all communities. Third, there has been no substitution of fish species in the catch. Fourth, mean body lengths of five of the nine most-caught species were below length-at-first-reproduction, and the body lengths of some have increased overtime while that of others have remained stable or decreased. Overall, fishery resources in the region appear to be moderately exploited, with some key species showing typical signs of overexploitation. This would indicate that the principal threat to the sustainability of fishery resources is excessive concentration of fishing effort on a few target species combined with unsustainable fishing practices. Management and research recommendations are proposed.
Tropical small-scale fisheries are highly heterogeneous with respect to a wide range of fisheries characteristics, but that heterogeneity has generally not been adequately studied or considered in ...management. This study investigated fisheries heterogeneity and the extent to which it is accounted for in management regulations in eight small-scale fishing communities located in floodplain ecosystems of the Amazon basin. Analyses of 29,844 fishery landing interview data revealed that fisheries heterogeneity with respect to gear, habitat, species composition, and total catch and fishing effort was high across all communities, but low over the years in the same communities, indicating that each community must be considered as a distinct management unit. Data analyses also revealed that many important community fisheries characteristics were not accounted for by government- and community-based management regulations. Total catch and fishing effort were largely unregulated; there were no size or closed season limits for one-third of the most important fishery species; and the nursery habitats used by most fishery species were not protected in any fashion. Clearly, increased attention to cross-community fisheries heterogeneity can improve the design and implementation of management regulations. The management problems created by the heterogeneity of small-scale fisheries are discussed, and the potential of the “barefoot ecologist” concept to address them is considered.
► Little scientific and management attention is paid to the heterogeneity of tropical small-scale fisheries. ► Fisheries heterogeneity was found to be high across eight fishing communities. ► Many key community fisheries characteristics were not accounted for by management regulations. ► Management can be improved through better consideration of the heterogeneity of small-scale fisheries.
A major trend in global trade in forest, animal, and agricultural products is the implementation of importation policies and development of private sector standards and certification mechanisms to ...promote the sustainable management of natural resources in the countries of origin. In many cases, ensuring sustainable origins involves requirements that small-scale rural producers and fishers cannot meet. This article investigates the formalization of community-based floodplain fisheries in the Brazilian Amazon, including (a) the development of federal and state fisheries management policies, (b) the parallel development of community management systems, and (c) the role of these processes in the evolution of fisheries management in the Lower Amazon region. We argue here that market-oriented solutions, such as third-party certification, are insufficient. Government support for and collaboration with producers and industry are essential to creating conditions that enable fishing communities to sustainably manage their fisheries.
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