Leandro Castello’s research while affiliated with Virginia State University and other places

Freshwater ecosystems contribute substantially to the global fish catch. However, freshwater fisheries face growing human pressures and are underrepresented in global analyses and conservation strategies. Attempts to reconcile conservation and human welfare goals in fisheries have led to comanagement by the government and local communities, along with other stakeholders, but assessments of its effectiveness in freshwater fisheries are lacking. We investigated the effectiveness of comanagement in freshwater fisheries by assessing ecological (fish catch) and economic (fishing revenue) outcomes in a major tributary of the Amazon Basin. Fisheries comanagement in the Amazon is typically implemented through an approach developed by riverine communities called lake management in which floodplain lakes are categorized as open access, subsistence, or protected. Each category has different levels and types of fishing pressure. We analyzed data (e.g., fishing data and management rules) from 1607 fishing trips of 198 fishers over 5 years in 30 riverine communities in 74 floodplain lakes (20 open access, 33 subsistence, and 21 protected). Lake comanagement increased fish catch in protected lakes over time by 12% (2.4 kg) compared with subsistence lakes and by 13% (2.6 kg) compared with open‐access lakes (p = 0.03). Increased fish catch in protected lakes was mainly due to limits on fishing effort. Fishing revenue was 63% greater in protected lakes than in open‐access lakes (p < 0.001), mainly due to increased harvests of species that had small to medium home ranges and were amenable to management at the small geographical areas of these community initiatives. These results show how one locally developed approach to comanagement can reconcile ecological and socioeconomic benefits and provide policy‐relevant evidence that can serve as models to foster freshwater conservation elsewhere.

Finding easily accessible indicators to assess the biodiversity conservation is crucial in regions where long-term monitoring data is deficient. This is particularly true for tropical freshwater ecosystems, which house most of the known fish biodiversity and faces multiple natural and anthropogenic threats. Fish sizes serve as a key ecological indicator of ecosystem productivity and responses to environmental changes. Using length measurements of 354,465 fish produced by multiple projects and researchers, we investigated the spatial patterns and main drivers of fish productivity and mortality across 11 widely distributed basins in the Brazilian Amazon. Specifically, we examined if fish mortality and ecosystem productivity vary among environments, water types, Amazon sampling regions, and landscape metrics. Our findings show that fish size structure vary between water types and sampling regions, with Northern regions of the Amazon Basin exhibiting larger fish sizes and lower mortality than Southern region. Human population demography and forest cover also influenced fish productivity and size-160X/© 2025 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). structure, affecting complexity and diversity of ecosystem trophic chains. We provide evidence that maintaining at least 75% forest cover is critical for supporting fish fauna size structure, highlighting the importance of considering terrestrial-freshwater links in conservation programs aiming to enhance sustainable fishing.

Although sparse, increasing evidence suggests an overlooked population of fishers whose fishing motivations and outcomes overlap across commercial, subsistence and recreational fishing sectors, resulting in underrepresented groups of fishers in management and policy frameworks. These fishers participate in what we frame as “provisioning fisheries,” a concept we propose to highlight the underrepresented values from fishing and fisheries across recreational, sociocultural, psychological, economic, health, and nutritional dimensions. We argue that provisioning fisheries often support underserved groups, provisioning fishers may engage in informal markets, and, that distinction exists from sport-oriented recreational fisheries in power, risks, access barriers, fishing motivation, attitudes, and practices including rule and advisory awareness. We propose that provisioning fisheries should be consciously considered—whether as part of existing fisheries structures or even its own sector to promote more sustainable and inclusive fisheries management. Overlooking this population of fishers may risk further marginalization, conflicts, contaminant exposure, and inaccurate stock estimates. Therefore, we propose provisioning fisheries as a useful analytical category to explore the heterogeneity of fishers and their distinct needs, motivations, and behaviors. As an example of how these fisheries may function, we synthesize what we currently know about provisioning fisheries in North America with hypothesized differences between provisioning and the sport-oriented recreational fisher to encourage greater dialogue and investigation about underrecognized fisheries.

Fish migrate for varied reasons, including to avoid predators and to access feeding, spawning, and nursery habitats, behaviors that enhance their survival and reproductive rates. However, the migratory ecology of many important fishes, especially those in river–floodplain ecosystems, remains poorly understood. One fish of the Amazon Basin whose migratory behavior is poorly understood is the catfish Pseudoplatystoma fasciatum. Here, we used otolith elemental microchemistry to characterize the migration ecology of P. fasciatum in the Amazon Basin. The main research questions of this study were: (1) does P. fasciatum move between waters with different Sr isotopic signatures (⁸⁷Sr/⁸⁶Sr) and chemical compositions? (2) What distance do they migrate? (3) Is the migration of P. fasciatum related to age? And (4) does P. fasciatum migrate mainly upstream, downstream, or in both directions? We assessed whether P. fasciatum migrates between waters with different ⁸⁷Sr/⁸⁶Sr values, comparing the Sr isotopic signature of otolith transects of each individual with the range of Sr isotopic signatures within the respective rivers. We found that 34% of the 71 fish analyzed migrated between rivers with different Sr isotopic signatures and 66% did not. The mean migration distance migrated was 126 km, with most specimens migrating between 72 and 237 km. Apparently, no fish of age one or age six or older migrated. All fish that migrated were between two and five years of age, with 20% of the specimens that migrated being two years old, 40% three years old, 30% four years old, and 20% five years old. Sixty-six percent of all individuals that migrated between rivers with different Sr signatures did so bidirectionally, while 33% moved unidirectionally. According to our definition of homing behavior in which fish migrated back to the same river where they were born, 41% of all fish that migrated displayed apparent homing behavior. Our findings provide insights into the migratory ecology of P. fasciatum, corroborating and refining knowledge reported in the literature. Our results on the migratory ecology of P. fasciatum have implications for sustainable fisheries conservation and management: conserving P. fasciatum requires habitat maintenance and suitable fishing practices in spawning and nursery habitats, and managers must consider large geographic areas for effective fishery management and conservation.

Fish in the South American genus Arapaima Müller, 1843 (hereafter referred to as arapaimas) have attracted interest for commercial aquaculture development thanks to their rapid growth rate and high market value. However, management agencies in the United States have expressed concerns about importing and culturing arapaimas due to records of non-native establishment in certain other countries where arapaimas were released or escaped from captivity. We used the Freshwater Fish Injurious Species Risk Assessment Model (FISRAM) to estimate the probability that arapaimas would be injurious (able to cause harm) to native ecosystems, humans, or the economy of the contiguous United States. Risk assessment model inputs were elicited from arapaima experts around the world. Model results were sensitive to the estimation of climate suitability for arapaimas within the contiguous United States, with predicted probability of injuriousness ranging from 0.784 down to 0.321 with different climate suitability inputs. Expert assessors predicted that competition and predation on native species would be the most likely mechanism of impact and expressed a high degree of uncertainty about potential for impacts from pathogens and parasites. We concluded that due to the cold sensitivity of these tropically adapted fish, establishment within the contiguous United States would be highly restricted geographically, limiting potential impacts if introduced outside climatically suitable areas. Existing regulations already mitigate risk of escape from aquaculture in areas where establishment is plausible, but further research into arapaima parasites and pathogens would help reduce uncertainties and suggest opportunities to enhance biosecurity measures if needed.

Fish growth is a fundamental biological process driven by a multitude of intrinsic (within-individual) and extrinsic (environmental) factors that underpin individual fitness and population dynamics. Interannual variability in river hydrology regarding the intensity and duration of floods and droughts can induce interannual variations in the biotic and abiotic variables that regulate fish growth. However, the understanding of how interannual variability in river hydrology affects fish growth remains limited for most species and ecosystems. We evaluated how inter-annual hydrological variations within the Amazon River basin influence the growth of the catfish Pseudoplaystoma fasciatum. Our research questions were as follows: Do floods lead to the faster growth of P. fasciatum and droughts lead to the slower growth? And do floods and droughts affect all age classes in the same manner? We sampled 364 specimens of P. fasciatum from five sites in the Amazon basin, estimated their growth rates, and related the growth rates to indices of the intensity of floods and droughts. We fitted linear mixed-effects models to test the relationship between growth increments and hydrological indices (with F and D quantifying the intensities of floods and droughts, respectively), age as fixed effects, and basins and Fish ID as random effects. We found an inverse relationship between the increment width in the fish hard parts and hydrological indices. That is, intense floods and droughts negatively affected the growth rates. We also found that the growth of P. fasciatum was no different in years with intense and mild floods across age classes 1–5, although was different for age class 6. However, the growth of P. fasciatum was faster in years of mild droughts for all age classes. Our results showing that the growth of P. fasciatum was slower in years of intense droughts are supported by those of previous studies in the Amazon basin and elsewhere. However, our results showing for the first time that the growth of P. fasciatum is slower in years of intense flooding is the opposite of patterns found in other studies. These results thus suggest that the growth of P. fasciatum is maximized within an optimum range of hydrological conditions, where neither floods nor droughts are intense.

Information on natural resource exploitation is vital for conservation but scarce in developing nations, which encompass most of the world and often lack the capacity to produce it. A growing approach to generate information about resource use in the context of developing nations relies on surveys of resource users about their recollections (recall) of past harvests. However, the reliability of harvest recalls remains unclear. Here, we show that harvest recalls can be as accurate to data collected by standardized protocols, despite that recalls are variable and affected by the age of the recollecting person and the length of time elapsed since the event. Samples of harvest recalls permit relatively reliable reconstruction of harvests for up to 39 years in the past. Harvest recalls therefore have strong potential to inform data‐poor resource systems and curb shifting baselines around the world at a fraction of the cost of conventional approaches.

The Brazilian Amazon is one of Earth’s most biodiverse and ecologically important regions. However, research investments for biodiversity in the biome are disproportionately low compared with other regions of Brazil. In 2022, the Amazon received 13% of master's, doctoral and postdoctoral scholarships and hosted 11% of all researchers working in biodiversity postgraduate programs. Amazonian institutions received approximately 10% of all federal budget spent on grants and scholarships and about 23% of all resources destined to support long-term ecological sites. The cities of Manaus and Belém concentrate about 90% of all grants and scholarships available for the entire region. Despite per capita research investment in the Amazon being equal to or better than that available for the more economically developed regions of Brazil, the distribution of resources by area is highly unequal. Increasing research funding for the Amazon region requires differential input by federal agencies and more transnational collaborations and integration between Amazonian programs and international funds.