Geology topics

Marco Milardi

Publications and source records attributed to Marco Milardi.

7 recordsLinked to original sources

USGS2025

Global recreational consumption of non-native inland fish: Higher economic benefits, but lower nutritional value and climate resilience

Inland recreational fisheries are globally significant leisure pursuits, with well-documented benefits to human health and well-being, but also one of the principal drivers of non-native fish introductions to enhance fishing opportunities, whether for sport or sustenance. In this study, we assess the relative reliance of global inland recreational fisheries on non-native versus native species for harvest. We further examine how this reliance varies by economic and nutritional value as well as the climate vulnerability of the species involved. We demonstrate that, of the 1,325,851 t of inland recreational fishes recreationally harvested for consumption worldwide in 2021, non-native fish were a small proportion (4 %; 53,651 t). On a global scale, non-native fish contributed a net positive 38.2 % economic value to inland recreational harvest. However, they also contributed a net negative −21.9 % nutritional value to inland recreational harvest. Non-native fishes were also more climate vulnerable (i.e., higher average climate vulnerability index values) and thus proportionally increased overall estimates of climate vulnerability with a net positive of 70.9 %. Our results quantitatively demonstrate that non-native species play a more important role in inland consumptive recreational fisheries than their mere harvest volume would suggest. However, many nuances were seen on the continent and country scale, which reflect the complexity of fisher behavior, fish distribution and socio-economic factors. Our findings help unravel the complex effects of non-native species on human activities and underscore the need to evaluate their global impacts holistically.

Science of the Total Environment↗

USGS2024

Inland recreational fisheries contribute nutritional benefits and economic value but are vulnerable to climate change

Inland recreational fishing is primarily considered a leisure-driven activity in freshwaters, yet its harvest can contribute to food systems. Here we estimate that the harvest from inland recreational fishing equates to just over one-tenth of all reported inland fisheries catch globally. The estimated total consumptive use value of inland recreational fish destined for human consumption may reach US$9.95 billion annually. We identify Austria, Canada, Germany and Slovakia as countries above the third quantile for nutrition, economic value and climate vulnerability. These results have important implications for populations dependent on inland recreational fishing for food. Our findings can inform climate adaptation planning for inland recreational fisheries, particularly those not currently managed as food fisheries.

Nature Food↗

USGS2022

Global dataset of species-specific inland recreational fisheries harvest for consumption

Inland recreational fisheries, found in lakes, rivers, and other landlocked waters, are important to livelihoods, nutrition, leisure, and other societal ecosystem services worldwide. Although recreationally-caught fish are frequently harvested and consumed by fishers, their contribution to food and nutrition has not been adequately quantified due to lack of data, poor monitoring, and under-reporting, especially in developing countries. Beyond limited global harvest estimates, few have explored species-specific harvest patterns, although this variability has implications for fisheries management and food security. Given the continued growth of the recreational fishery sector, understanding inland recreational fish harvest and consumption rates represents a critical knowledge gap. Based on a comprehensive literature search and expert knowledge review, we quantified multiple aspects of global inland recreational fisheries for 81 countries spanning ~192 species. For each country, we assembled recreational fishing participation rate and estimated species-specific harvest and consumption rate. This dataset provides a foundation for future assessments, including understanding nutritional and economic contributions of inland recreational fisheries.

Scientific Data↗

USGS2022

Overturning stereotypes: The fuzzy boundary between recreational and subsistence inland fisheries

Inland recreational fisheries provide numerous socio- economic benefits to fishers, families and communities. Recreationally harvested fish are also frequently consumed and may provide affordable and sustainable but undervalued contributions to human nutrition. Quantifying the degree to which recreationally harvested fish contribute to food security and subsistence is impeded by lack of data on harvest and consumption and by the difficulty in differentiating among recreational and subsistence fisheries. Recreational harvest records tend to be limited to wealthy, food- secure countries and well- monitored fisheries with clear regulations or permitting systems. These records often neglect components of recreational harvest among food- insecure fishers who are potentially more likely to have consumption as a motivation. Here, we highlight the ‘fuzzy boundary’ that can exist between inland recreational and subsistence fisheries and argue that unreported consumption is likely to be a hidden contributor to food security in some populations. We draw on local case studies from around the world to highlight specific instances where recreationally harvested fish species contribute food and subsistence benefits to participating communities. We use these examples to highlight the diversity of ways that inland recreational fisheries contribute to human nutrition, knowledge gaps in understanding recreational fishing for food, and consequences of not accounting for them as food fisheries in policy and management. The aim of this paper is to draw the attention of resource managers and policy makers, create greater social awareness of the importance of recreational fisheries and bring to light this hidden contribution of inland fisheries to nutrition and subsistence.

Northern Territory, Virginia↗

USGS2020

Could a freshwater fish be at the root of dystrophic crises in a coastal lagoon?

Eutrophication has a profound impact on ecosystems worldwide. Grass carp Ctenopharyngodon idella , an herbivorous fish, has been introduced to control aquatic plant overgrowth caused by eutrophication, but could have other, potentially detrimental, effects. We used the Po di Volano basin (south of the Po River delta, northern Italy) as a test case to explore whether grass carp effects on canal aquatic vegetation could be at the root of historical changes in N loads exported from the basin to the Goro Lagoon. We modeled the aquatic vegetation production and standing crop, its denitrification potential, and its consumption by introduced grass carp. We then examined whether changes in historical nitrogen loads matched the modeled losses of the drainage network denitrification function or other changes in agricultural practices. Our results indicate that introduced grass carp could completely remove submerged vegetation in the Po di Volano canal network, which could – in turn – lead to substantial loss of the denitrification function of the system, causing in an increase in downstream nitrogen loads. A corresponding increase, matching both timing and magnitude, was detected in historical nitrogen loads to the Goro Lagoon, which were significantly different before and after the time of modeled collapse of the denitrification function. This increase was not clearly linked to watershed use or agricultural practices, which implies that the loss of the denitrification function through grass carp overgrazing could be a likely explanation of the increase in downstream nitrogen loads. Perhaps for the first time, we provide evidence that a freshwater fish introduction could have caused long-lasting changes in nutrient dynamics that are exported downstream to areas where the fish is not present.

Po River basin↗

USGS2019

Ligation and division of ductus deferens does not produce long term sterility in most bighead carp or grass carp

Invading species are most easily eradicated or controlled if detected early and rapid action can be taken, but locating and eradicating small numbers of aquatic invaders is extremely difficult. Bighead carp ( Hypophthalmichthys nobilis ) and grass carp ( Ctenopharyngodon idella ) are Asian cyprinids that have been widely introduced and are considered undesirable and detrimental invasive species in many parts of their introduced range. The relatively novel “Judas fish” technique is used to locate aggregations of fish in the wild by strategically releasing individuals equipped with surgically implanted transmitters. However, releasing Judas fish that are capable of reproducing is problematic because it could add to the invasion problem by contributing to recruitment if not recaptured. We thus tested whether surgical ligation and division of the ductus deferens could effectively sterilize adult diploid bighead and grass carp. If effective, surgical sterilization would result in a superior Judas fish by maintaining the reproductive motivation derived from intact gonads while blocking the reproductive potential. This technique was initially successful, but ultimately most individuals were able to recanalize the surgically-severed ducts and produce milt, and were thus potentially able to reproduce during the following spawning season. Thus, ligation and division of the ductus deferens does not seem to be a viable procedure to sterilize bighead carp or grass carp for deployment as Judas fish where long term sterility of the fish is paramount in importance.

Missouri↗

USGS2017

First evidence of bighead carp wild recruitment in Western Europe, and its relation to hydrology and temperature

Bighead carp ( Hypophthalmichthys nobilis ) have been introduced throughout Europe, mostly unintentionally, and little attention has been given to their potential for natural reproduction. We investigated the presence of young-of-the-year bighead carp in an irrigation canal network of Northern Italy and the environmental conditions associated with spawning in 2011–2015. The adult bighead carp population of the canal network was composed by large, likely mature, individuals with an average density of 45.2 kg/ha (over 10 fold more than in the main river). The 29 juvenile bighead carp found were 7.4–13.1 cm long (TL) and weighed 9.5–12.7 g. Using otolith-derived spawning dates we estimated that these juveniles were 94–100 days old, placing their fertilization and hatch dates in mid-to-end-June. Using this information in combination with thermal and hydraulic data, we examined the validity of existing models predicting the onset of spawning conditions and the viability of egg pathways to elucidate spawning location of the species. While evidence of reproduction was not found every year, we determined that potentially viable spawning conditions (annual degree-days and temperature thresholds) and pathways of egg drift suitable for hatching are present in short, slow-flowing canals.

PLoS ONE↗