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Changes in recreational catfish Silurus glanis harvest rates between years 1986–2017 in Central Europe
Journal of Applied Ichthyology
Abstract
The European catfish Silurus glanis is an important fish species in both commercial and recreational fisheries. Catfish is a spreading species that was reported to potentially benefit from increasing temperatures. The goal of this study was to estimate long‐term changes in harvest rates of catfish in Central Europe. This study used individual mandatory angling logbooks collected by the Czech Fishing Union in the Czech Republic (Central Europe) over the course of years 1986–2017 (32 years) to assess harvest rates of catfish. This study discovered that harvest of catfish has been increasing over time. Moreover, rivers that previously showed zero harvested catfish are beginning to display higher harvest rates of catfish. Increasing average air temperature and angling effort in the study area have positively affected harvest rates of catfish. The increased harvest of catfish could not be reliably explained by intensive fish stocking. In conclusion, while other studies show that many fish species are negatively affected by human activities and therefore show decreased harvest rates, catfish angling seems to benefit from anthropogenic changes.
... The European catfish S. glanis is a native large-growing non-migratory piscivorous fish species. A previous study from this area confirmed a strong relationship between the catfish stocking intensity and its yield [12]. Common carp Cyprinus carpio and grass carp Ctenopharyngodon idella are non-native omnivorous cyprinids, while the rainbow trout Oncorhynchus mykiss is a non-native predatory salmonid. ...
... A previous study from this area confirmed a strong relationship between the catfish stocking intensity and its yield [12]. Common carp Cyprinus carpio and grass carp Ctenopharyngodon idella are non-native omnivorous cyprinids, while the rainbow trout Oncorhynchus mykiss is a non-native predatory salmonid. While the local catfish populations were expanding during the years 2000-2018 [12], the non-native fish populations relied on intensive stocking. All four studied species-the common carp, the grass carp, the rainbow trout, and the European catfish-have a cumulative daily bag limit of either 7 kg of fish or two individual fish (whichever comes first). ...
... To the knowledge of the author, this is the first time that a similar result has occurred in scientific literature; other studies usually reported the opposite effect, meaning that higher angling competition led to a lower yield per one angler. This was true, for example, of the common carp and rainbow trout in this study, and also for the perch, brown trout, European grayling, European catfish, nase, vimba bream, and barbel in the study area [12,23]. This was also reported by other studies [34][35][36]. ...
Intensive multi-species fish stocking management is a popular yield enhancement tool that supposedly leads to elevated yields in recreational angling. This study aimed to analyze the relationships between fisheries management of an apex predator and its putative prey. The GAM (generalized additive model) was used to analyze the relationships between the yields and the stocking intensities of European catfish and non-native fish species. The fish yields and stocking intensities were obtained from mandatory angling logbooks collected from 38,000 individual recreational anglers by the Czech Fishing Union on 176 fishing sites during the years 2005–2017 in central Bohemia and Prague (the Czech Republic). Our results show that the stocking intensities of the targeted species positively correlated to their yields. However, intensive catfish stocking negatively correlated to the yields of the non-native fishes. Other factors that were strongly correlated to the yields include the angling effort, size of a fishery, and yield of catfish. In conclusion, a significant relationship is found between the fisheries management of a predator and its putative prey. The results suggest that catfish should not be intensively stocked in the same rivers as non-native fishes.
... The European catfish S. glanis is a native large-growing non-migratory piscivorous fish species. A previous study from this area confirmed a strong relationship between the catfish stocking intensity and its harvest rate [19]. Vimba bream V. vimba and barbel B. barbus are native medium-sized non-migratory omnivorous fish species. ...
... The anglers have gained access to high-quality fishing gear and a great know-how regarding trophy-sized catfish angling. Catfish angling has become a popular sport in Europe over the last 5-10 years [3,4,19]. Its popularity launched introductions outside of the native range of the catfish, and the catfish became an expansive or even an invasive species [3,4,19]. ...
... Catfish angling has become a popular sport in Europe over the last 5-10 years [3,4,19]. Its popularity launched introductions outside of the native range of the catfish, and the catfish became an expansive or even an invasive species [3,4,19]. Angling "selfies" with a catch of a trophy-sized catfish have flooded the angling discussion forums on Facebook and Twitter. ...
The European catfish Silurus glanis (Linnaeus, 1758) is an expanding apex piscivorous predator whose predation may drive fish harvest rates and fish populations. This study aimed to analyze the relationships between intensive catfish stocking/harvesting and harvest rates of putative catfish prey–three rheophilic fish species: vimba bream Vimba vimba, nase Chondrostoma nasus, and barbel Barbus barbus (Linnaeus, 1758). The GAM (generalized additive model) was used to analyze the relationships between the harvest rate and the stocking intensity rate of the catfish and the three rheophilic fish species. The harvest rates and stocking intensity rates were obtained from mandatory angling logbooks collected from 38,000 individual recreational anglers by the Czech Fishing Union on 176 fishing sites over the years 2005–2017 in central Bohemia and Prague (the Czech Republic). Our results show that a higher intensity of catfish stocking and harvesting resulted in a lower harvest rate of rheophilic fishes. Conversely, the stocking rates of rheophilic fishes were not significantly correlated to their harvest rates. In conclusion, a significant negative relationship was found between the harvest rate and the restocking rates of rheophilic fishes and their predator, suggesting that fisheries managers should not perform intensive stocking of both catfish and rheophilic fishes on the same rivers.
... Large-scale angling restrictions are among the most common and effective ways to protect fish populations from overexploitation by anglers and commercial fishermen. There are several types of restrictions: minimum and maximum angling size, a decreased amount of killed fish per day, catch-and-release fishing strategy, closed season, daily fishing hours, limited amount of fishing visits per week, permitted/forbidden fishing techniques (lures, baits, hooks, number of rods, nets, boats, lights), and no-fishing zones (Naslund et al., 2005(Naslund et al., , 2010Powell et al., 2010;van Poorten et al., 2013;Veiga et al., 2013;Tetzlaff et al., 2013;Lew and Larson, 2015;Lenker et al., 2016;Lenox et al., 2016;Rahel, 2016;Cha and Melstrom, 2018;Johnston et al., 2018;Lyach and Remr, 2019a, 2019b, 2019c. Angling restrictions may even change perceptions and behaviour of anglers (Beard et al., 2003). ...
... As previous studies have found, angling restrictions can potentially have either positive or negative effects on protected fish populations. For example, a restriction in minimum angling size can lead to increased fishing pressure on large-sized individuals which arein many fish specieshighly fertile females with high fitness (Arlinghaus et al., 2010;Lyach and Remr, 2019a, 2019b, 2019c. Conversely, other studies reported a recovery of fish populations after a restriction was introduced (Johnston, Arlinghaus et al., 2011;Alós and Arlinghaus, 2013;Askey, 2016). ...
... Fisheries Research 223 (2020) 105438 Fishing sites are defined as stream and river stretches where recreational fishing can be legally conducted. Aa similar dataset was previously used for scientific purposes (Humpl et al., 2009;Jankovský et al., 2011;Boukal et al., 2012;Lyach andČech, 2018a, 2018b;Lyach and Remr, 2019a, 2019b, 2019cLyach and Čech, 2019). ...
... An example of a successful invader in freshwaters able to establish into novel habitat types is represented by the European catfish Silurus glanis L., a large-bodied fish naturally distributed in large freshwater ecosystems of eastern Europe and western Asia [12]. Thanks to its fast growth and the large body size reached, S. glanis is highly appreciated among anglers [13] and is an important resource in aquaculture [14], and this has led to its voluntary introduction into different areas, both within and outside Europe [12,15]. In western and southern Europe, it has established self-sustained populations, raising conservation concerns due to its top-predator position and opportunistic feeding behavior [12,15]. ...
... However, in a few years, the total catfish harvest quintuplicated, and so did its proportional contribution to the total fish harvest (from 3.2% in 2016 to 12.5% in 2020), indicating that commercial fisheries may benefit from harvesting catfish. This is not surprising given that the importance of S. glanis for both recreational and professional angling is increasingly recognized [13] and that catfish populations in their native range cannot reach a carrying capacity due to the high angling pressure [15,48]. However, our data showed that the fish harvest in Lake Maggiore is dominated by those species that were also most consumed by catfish, like coregonids. ...
The ecological features of invasive alien species are crucial for their effective management. However, they are often lacking in newly invaded ecosystems. This is the case of the European catfish Silurus glanis L. in Lake Maggiore, where the species is present since 1990, but no scientific information is available on its ecology. To start filling this knowledge gap, 236 catfish (67 cm to 150 cm of total length) were collected, measured, and dissected for stomach content analyses from three localities and in two habitats (littoral vs. pelagic) in late autumn/early winter. The NPUE and BPUE (individuals (N) and biomass (B, in grams) per unit effort (m²), respectively) of catfish were generally higher in littoral (NPUE > 0.01; BPUE > 96) than in pelagic habitats (NPUE < 0.009; BPUE < 114), but the catfish had, on average, larger sizes in pelagic habitats. Overall, 581 individual prey items were recorded, belonging to 12 taxa. Pelagic catfish specialized their diet exclusively on three prey fish (coregonids, shad, and roach), whilst the diet of littoral catfish was more variable and dominated by crayfish, perch, and roach. These results highlighted for the first time the interaction of larger catfish with the lake’s pelagic food web, and thus possible consequences are discussed, including the potential contrasting role S. glanis may have for the lake’s fishery.
... An example of a successful invader in freshwaters able to establish into novel habitat types is represented by the European catfish Silurus glanis L., a large-bodied fish naturally distributed in large freshwater ecosystems of eastern Europe and western Asia [12]. Thanks to its fast growth and the large body size reached, S. glanis is highly appreciated among anglers [13] and is an important resource in aquaculture [14], and this has led to its voluntary introduction into different areas, both within and outside Europe [12,15]. In western and southern Europe, it has established self-sustained populations, raising conservation concerns due to its top-predator position and opportunistic feeding behavior [12,15]. ...
... However, in a few years, the total catfish harvest quintuplicated, and so did its proportional contribution to the total fish harvest (from 3.2% in 2016 to 12.5% in 2020), indicating that commercial fisheries may benefit from harvesting catfish. This is not surprising given that the importance of S. glanis for both recreational and professional angling is increasingly recognized [13] and that catfish populations in their native range cannot reach a carrying capacity due to the high angling pressure [15,48]. However, our data showed that the fish harvest in Lake Maggiore is dominated by those species that were also most consumed by catfish, like coregonids. ...
Ecological information of invasive alien species are crucial for their effective management. How-ever, they are often lacking in newly invaded ecosystems. This is the case of the European catfish Silurus glanis L. in Lake Maggiore where the species is present since 1990 but no scientific infor-mation are available on its ecology. To start filling this knowledge gap, 236 catfish (67 cm to 150 cm of total length) were collected, measured, and dissected for stomach content analyses from three localities and in two habitats (littoral vs. pelagic) in late autumn/early winter. NPUE and BPUE (individuals and biomass (g) per unit effort (m2)) of catfish was generally higher in littoral (NPUE > 0.01; BPUE > 96) than pelagic habitats (NPUE < 0.009; BPUE < 114) but catfish had, on average, larger sizes in pelagic habitats. Overall, 581 individual prey items were recorded belonging to12 taxa. Pelagic catfish specialized their diet exclusively on three prey fish (coregonids, shad and roach) whilst the diet of littoral catfish was more variable, and was dominated by crayfish, perch, and roach. These results highlighted for the first time the interaction of larger catfish with the lake’s pelagic food web, and thus possible consequences are discussed, including the potential contrasting role S. glanis may have for the lake’s fishery.
... While the natural dispersal of catfish is generally slow, higher water temperatures can accelerate this process [94,95]. In the Iberian Peninsula, the species has spread rapidly in rivers like the Ebro and Tajo [35,96], due to several factors: its trophic plasticity, which allows it to exploit diverse habitats and resources, including surface areas; its high growth rate, enhanced by warm temperatures; and its physiological resilience [7,31,86,97,98]. ...
The European catfish (Silurus glanis Linnaeus, 1758) was introduced into the Ebro Basin in Spain in 1974 for recreational fishing. Since then, the species has spread throughout the country’s river basins, reaching the Iznájar Reservoir (Guadalquivir River Basin) in 2011. This area is of great ecological and economic relevance, especially as it includes the Doñana National Park, one of the most important nature reserves in Europe. Recently, the presence of catfish has been reported in the lower reaches of the river. In this work, we used non-invasive vertical and horizontal hydroacoustic surveys and environmental DNA river sampling to unravel the actual distribution and dispersal pattern of the species in the lower Guadalquivir River. The hydroacoustic profiles and the species-specific detections by real-time PCR (qPCR) and droplet digital PCR (ddPCR) showed that these non-invasive methods allow the detection and quantification of catfish and provide valuable information on the species’ presence. We have confirmed the presence of catfish in most of the study area, including downstream areas of the Guadalquivir Basin. The results suggest the possibility of other isolated introductions and/or human-mediated movements of specimens, and imply that a coordinated catfish prevention and mitigation strategy is therefore urgently needed.
... The monitoring of freshwater fish stocks is essential for the management of artisanal fisheries (Amarasinghe and Da Silva, 1999;Roos and Longo, 2021). Therefore, logbook data are important to support the sustainable management of freshwater fisheries and can be useful in determining the trends in catches, although the reliability of self-reporting of commercial catches was questioned in some cases (Lyach and Remr, 2019;Schubert et al., 2022). In FAO Technical Papers (Group author, 2020), it is stated that in countries where commercial freshwater fishing is important, in most cases the fishers were registered and obliged to report their catches, and Croatia is mentioned as an example based on logbook returns under development. ...
The number of artisanal fishers and consequently their catch in the Sava River have been declining significantly for years. The aim of this study is therefore to examine how this affects the average weight of the most important fish species caught. The average weight increased significantly for bream Abramis brama ( P < 0.01), pike-perch Sander lucioperc a ( P < 0.01) and wels catfish Silurus glanis ( P < 0.05), while this was not the case for common carp Cyprinus carpio and pike Esox lucius ( P > 0.05). Although recreational anglers also catch fish in the same waters, together with the two groups of fishermen from Bosnia and Herzegovina from the other bank of the river, it is expected that the average weight of the main fish caught will not decrease under the current circumstances.
... Logbook data, despite potential limitations, are important to support the sustainable management of freshwater fisheries and can be useful in determining the trend of catches (e.g. Lyach and Remr, 2019;Schubert et al., 2022). For all data, the correlation between the annual catch by species and the respective year was determined. ...
The aim of this study is to analyse the development of artisanal fish catch by species in the Croatian section of the Sava River. For Abramis brama and Silurus glanis , a significant decline in catches (in kg) was observed throughout the study period (2004-2021). Since 2013, this has also been the case for Cyprinus carpio, Esox lucius, Sander lucioperca, other autochthonous species and alochthonous species, while catches of Leuciscus idus have declined significantly since 2014. The catches of three species ( Acipenser ruthenus, Leuciscus aspius and Tinca tinca ) fluctuated without a trend, which can be attributed to the low quantities. This decline in catches of the most sought-after species in the Sava was greater than that of the other less sought-after autochthonous species (mainly other cyprinids), whose share of the total catch increased significantly.
... Non-effective management practices are influenced by the lack of quantitative information on most invasive populations (De Santis and Volta 2021), scarcity of information on habitat use and behaviour, and unsuitable capture techniques . New occurrences of S. glanis populations in southern Europe are the result of illegal introductions and releases in the region (Cucherousset et al. 2018;Lyach and Remr 2019;Vejřík et al. 2019a), which is likely linked to the appreciation of this species by trophy anglers . Some anglers may favour the expansion of nonnative species because they are unaware of the negative consequences their actions may have. ...
The management of Invasive Alien Species (IAS) is often hindered by ecological, social and economic factors, resulting in inadequate biodiversity protection and inefficient use of public money. A clear example of such inefficient management in aquatic ecosystems is the European catfish Silurus glanis L. in southern Europe. Native to central Eurasia, S. glanis is an emblematic and controversial freshwater fish, being the subject of extensive and profitable trophy angling in central Europe and of commercial fishing in eastern Europe. Concurrently, in western and southern Europe where it was introduced in the XIX century, S. glanis is considered a problematic invader. The lack of comprehensive information on S. glanis invasive populations has limited effective management, which is critical to successfully control the spread and minimize negative impacts on native ecosystems and species. LIFE PREDATOR, started in September 2022 with a budget of € 2.85 million and a consortium of six partners from three countries, aims at developing a multidisciplinary and transnational approach to control established populations of S. glanis, and prevent further spreading and future introductions in southern European lakes and reservoirs. The project will develop and test an early warning system based on eDNA and citizen science and identify the most effective and selective capture techniques to reduce the abundance of catfish, particularly in Natura 2000 lakes, actively involving anglers and professional fishermen on this. Massive raising awareness campaigns will be conducted targeting anglers but also the general public, and protocols and best practices will be transferred to management authorities. For the long-term sustainability of the project, a South European Management Group will be created. Additionally, in northern Italy, where the catfish invasion is more advanced, a local circular economy will be implemented, involving the increase in fishing pressure by encouraging catfish consumption as food.
... The meat of this species has a sweet taste and its capacity for growth is among the highest of any fish (Eurostat, 2017). Thus, this catfish is very popular among Europe's sport fishermen as a trophy fish (Lyach and Remr, 2019). ...
... They are a large and very aggressive fish and have reached certain lakes and rivers in Western Europe where they developed quite explosively and sometimes detrimentally to the local fish species [5,6]. European catfish farming has been an increasing trend throughout the last years due to three main factors: it has a tasteful flesh, particularly appreciated by consumers, especially in Eastern Europe and Asia [3,7,8]; it is a useful species in fisheries practising polyculture, providing a good health state of biocenosis [9,10]; and last but not least, it is very appreciated in sport fishing in countries like Spain, the Netherlands, France, and Italy [11][12][13] due to its impressive dimensions and the struggle during the drill. Catfish rearing in different aquaculture systems is closely correlated to the natural environment. ...
Quantitative and qualitative flesh production in the Silurus glanis species was comparatively studied between two fish groups: one from aquaculture (AG) and the other from a natural environment, the Prut River (RG). Morphometry was carried out on the fish, and then biometric and conformational indices were calculated. Better values were found in the aquaculture catfish. The Fulton coefficient was 0.82 in the Prut River fish and 0.91% in the farmed ones. The fleshy index reached 19.58% in the AG fish and 20.79% in the RG fish, suggesting better productive capabilities in the AG fish. Postslaughter, the flesh yield and its quality were assessed at different moments throughout the refrigeration period (0–15 days), and chemical compound loss occurred. In the AG samples, the water content decreased by 8.87%, proteins by 27.66%, and lipids by 29.58%. For the RG samples, the loss reached 8.59% in water, 25.16% in proteins, and 29%in lipids. By studying the fatty acids profile and sanogenic indices, good levels of PUFA (31–35%) were found, and the atherogenic index reached 0.35–0.41 while the thrombogenic index ranged between 0.22 and 0.27. Consequently, it can be stated that fish origin and especially the refrigeration period influence the flesh proximate composition and nutritional value of European catfish.
... Some species that I pooled together into one group (especially native piscivores) may show different trends over time. For example, native piscivores were either decreasing or unchanged, but yield of European catfish (a native megafish and an apex piscivorous predator in freshwaters of central Europe) has been increasing in the 21st century (Lyach and Remr, 2019a). Unlike other piscivorous species, catfish populations have been expanding into new ecosystems (Cucherousset et al., 2018). ...
Introductions of non-native fishes are among the biggest threats to freshwater ecosystems globally. However, the effects of such introductions on fisheries management and fish yields are understudied. This study is trying to fill this knowledge gap by analyzing relationships between yields of native and non-native fishes with regards to important fisheries management factors, such as fish stocking, fishing effort, and the type or size of the fishery. I analyzed the changes in fish yields in the regions of Prague and central Bohemia from 1986 to 2017. Based on the 32 years of reported data that included 60 million harvested fish weighing 80 tons that were harvested by 250,000 anglers, I conclude that while predominately native fish species were harvested by anglers in the 1980, non-native fish species started dominating in the 21st century. This was true on both small trout streams (1-m wide) and medium-sized cyprinid rivers (5-250 m wide). This dominance is partially explained by the decreasing percentage of native salmonids and cyprinids and by the decreasing or stagnating percentage of native piscivores in the overall fish yield. Conversely, the percentage of non-native salmonids in the overall fish yield was increasing on both streams and rivers. Most importantly though, the percentage of non-native cyprinids-which made 60-80 % of all harvested fish-increased by 16 % over 32 years. Fish yield had a strong positive relationship with fish stocking intensity, a strong negative relationship with angling effort, and strong but mixed relationships with size of the fishery. In conclusion, native fishes are being slowly replaced by non-native fishes in the yield of recreational anglers in central Europe.
... Anglers harvested only 1-5% of restocked fish in the case of salmonids and rheophilic fishes (brown trout Salmo trutta, rainbow trout Oncorhynchus mykiss, nase Chondrostoma nasus, vimba bream Vimba vimba, and barbel Barbus barbus) [26,27]. On the other hand, intensively stocked species showed 5-10 times higher yield in comparison to restocking intensity-for example, in the case of European catfish Silurus glanis and common carp Cyprinus carpio [24,25]. The recapture rates of restocked fish usually depend on species and geographical area [50][51][52]. ...
The European eel Anguilla anguilla is a critically endangered catadromous migratory fish species. To conserve eel populations, angling restrictions and stocking activities are often used. This paper aimed to analyze the effect of an increased minimum legal angling size, eel stocking, fishing effort, and important environmental and biological factors on eel yield. This study used data on eel stocking and yield collected by the Czech Fishing Union using angling logbooks. Data regarding 41 tons of harvested eels were collected on 176 fishing sites from 38,000 anglers over the years 2005–2018 in central Bohemia and Prague (the Czech Republic). Eel made up only 0.006% of the overall fish harvest by biomass. It was found that the increased minimum legal angling size led to decreased yield of eel and to a decreased percentage of eel in the overall fish harvested. It also led to larger harvested eels, while the number of fishing sites where anglers harvested eels stayed constant over time. The eel yield was strongly correlated to the angling effort but not to the eel stocking intensity or the environmental and biological factors. In conclusion, implementing the minimum legal angling size did achieve its goal, because it led to decreased eel yield.
... The meat of this species has a sweet taste and its capacity for growth is among the highest of any fish (Eurostat, 2017). Thus, this catfish is very popular among Europe's sport fishermen as a trophy fish (Lyach and Remr, 2019). ...
The European catfish Silurus glanis is attracting growing interest as an object of fisheries and aquaculture, which is reinforced by the expansion of its natural range under climate change. Shaping the effective exploitation strategy for this valuable species requires detailed knowledge of its biology, including feeding and digestion processes, especially near the natural limits of the species range. Meanwhile, the digestion physiology of the European catfish remains poorly explored, including the activity of major digestive enzymes and the possible effect of intestinal parasites on this activity. In this regard, the activity of proteinases and α‐amylase in the intestinal mucosa of the catfish was studied. Adult catfish were collected in the Rybinsk reservoir (Upper Volga) located close to the northern limit of the species range. It was shown that all subclasses of intestinal digestive proteinases, including serine proteinases, metalloproteases and cysteine (thiol) proteinases, function in the gut mucosa of the catfish. The mucosal levels of total proteolytic activity depended on fish size, in contrast to those of trypsin, chymotrypsin and α‐amylase. The level of chymotrypsin activity was significantly higher than that of trypsin activity. It was also found that the incubation medium and extract of the cestodes Silurotaenia siluri parasitizing the catfish gut had a significant inhibitory effect on the activity of serine proteases (trypsin and chymotrypsin) operating in the intestines of the host fish.
Biological invasions are a major component of global change worldwide. But paradoxically, an invasive species might also have threatened populations within its native range. Designing efficient management policies is needed to prevent and mitigate range expansions of invasive alien species (IAS) in non-native areas, while protecting them within their native range. Characterizing genetic variation patterns for IAS populations and deciphering the links between their native and introduced populations is helpful to (i) assess the genetic state of both native and non-native populations, (ii) reveal potential invasion pathways, (iii) define IAS management strategies in invaded areas, and (iv) identify native populations requiring conservation measures. The European catfish (Silurus glanis) is the largest European predatory fish. Introduced since the seventies from Eastern to Western Europe, it has colonized many waterbodies. Yet, little is known about the genetic status of non-native populations and the invasion pathways used by the species. Besides, some native populations are threatened, requiring conservation actions. Here, we describe current patterns of genetic variability of native and non-native S. glanis populations across Europe. Using microsatellite markers, we first assessed genetic variation within and between native and non-native populations. Second, we performed genetic clustering analyses to determine the genetic structure of multiple catfish populations across Europe and highlight their potential links. We revealed that native populations are more genetically diverse than non-native populations, and highlight complex introduction pathways involving several independent sources of introduction, which likely explain the invasion success of this large predatory fish across western Europe.
The Czech Republic has a long tradition of pond production and recreational fisheries. Today, the Czech fisheries sector has two main pillars: (1) production of common carp Cyprinus carpio in semi-extensive pond culture, and (2) rod-based recreational angling of approximately 350,000 people (3 % of Czech population). The production of carp supplies fish protein mainly for the local population, but the Czech Republic is also Europe´s most important exporter of carp meat. A mandatory national licence and reporting system in recreational fisheries has been effective since the 1950s. Anglers purchase a fishing license, and the proceeds are used mainly to stock fish and maintain ecosystems for native fish species. Recreational angling and fish stocking is focused on non-native species – common carp and rainbow trout Oncorhynchus mykiss. Here, I present a short review of pond culture, aquaculture, commercial fisheries, and recreational fisheries, with examples of history, status, management, and regulations.
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.
Engineering design studies and financial feasibility assessments were made for construction, maintenance, equipment, operations, loan requirement, shrimp sales and predicted cash flows for simulated transformations of extensive shrimp farms to intensive shrimp farms in the Mekong Delta, Vietnam. Farms with less than 2.8 ha of feed‐based, aerated production ponds would not be profitable at shrimp yields less than 5 t/ha/year. Profit projections increased in response to greater production area on farms and larger annual pond yields. Farms with 6 ha or more of production ponds and yields of 10 t/ha/year or more had the best profit potential. Greater profitability at higher production intensity resulted from a reduction in the labour cost/product weight ratio as yield per unit area increased. Transformation from extensive to intensive farms would allow greater shrimp production, increase worker income and lessen land and water use. Environmental benefits would include a reduction in sediment starvation of the Mekong Delta, and the option to restore some of the several hundred thousand hectares of mangrove area severely degraded by extensive shrimp farming. These two improvements would be of benefit in retarding erosion along the Mekong Delta coastline. The possibility of intensification and consolidation of the shrimp farming area in the Mekong Delta deserves further consideration.
This study aimed to describe the effect of cormorant predation on newly established Atlantic salmon, Salmo salar, population in three nursery streams in the upper Elbe River basin (Czech Republic). Salmon have been annually stocked into the nursery streams since 1998 as part of a salmon reintroduction programme. Salmon parr density in nursery streams was 3-81 fish per 100 m 2. Only thirteen adult salmon were observed in the study area during two years of research. Altogether 912 cormorant pellets were collected, 5482 diagnostic bones were analysed, and 3915 fish were identified in the diet. Cormorant diet was composed of 24 fish species from six families but no salmon were consumed. The salmon stocking programme produces a reasonable amount of smolts but return rates of adults are very low. The cause of low return rates is not cormorant predation on nursery streams but, most likely, a low survival rate on the passage downstream. We suggest that more studies should focus on monitoring of survival and return rates of salmon in the upper River Elbe to ensure that, in the future, the salmon reintroduction programme will be really successful. Cite as: Lyach R., Čech M. 2017. The effect of cormorant predation on newly established Atlantic salmon population. Folia Zoologica 66 (3): 167-174.
The extreme body sizes of megafishes associated with their high commercial values and recreational interests have made them highly threatened in their native range worldwide by human-induced impacts such as overexploitation. Meanwhile, some megafishes have been introduced outside of their native range. A notable example is the European catfish (Silurus glanis), one of the few siluriforms native to Eastern Europe. It is among the 20 largest freshwater fish worldwide, attaining a total length over 2.7 m and a documented mass of 130 kg. Its distinct phylogeny and extreme size imply many features that are rare among other European fish, including novel behaviours (massive aggregations, beaching), consumption of large bodied prey, fast growth rates, long lifespan, high fecundity, nest guarding and large egg sizes. The spread of the species is likely to continue due to illegal introductions, primarily for recreational angling, coupled with natural range extension associated with climate change. Here, the most recent knowledge on the current distribution and the ecology of the species are reviewed. A series of key research questions are identified that should stimulate new research on this intriguing, yet largely unknown, species and, more generally, on the ecology of freshwater invaders.
Apex predators play a key role in ecosystem stability across environments but their numbers in general are decreasing. By contrast, European catfish (Silurus glanis), the European freshwater apex predator, is on the increase. However, studies concerning apex predators in freshwaters are scarce in comparison to those in terrestrial and marine ecosystems. The present study combines stomach content and stable isotope analyses with diet preferences of catfish to reveal its impact on the ecosystem since stocking. Catfish niche width is extremely wide in comparison to the typical model predator, Northern pike (Esox lucius). Catfish and pike have different individual dietary specialization that results in different functional roles in coupling or compartmentalizing distinct food webs. The role of both species in the ecosystem is irreplaceable due to multiple predator effects. The impact of catfish is apparent across the entire aquatic ecosystem, but herbivores are the most affected ecological group. The key feature of catfish, and probably a common feature of apex predators in general, is utilization of several dietary strategies by individuals within a population: long-term generalism or specialization and also short-term specialization. Catfish, similar to other large-bodied apex predators, have two typical features: enormous generalism and adaptability to new prey sources.
The coefficient of determination R² quantifies the proportion of variance explained by a statistical model and is an important summary statistic of biological interest. However, estimating R² for generalized linear mixed models (GLMMs) remains challenging. We have previously introduced a version of R² that we called for Poisson and binomial GLMMs, but not for other distributional families. Similarly, we earlier discussed how to estimate intra-class correlation coefficients (ICCs) using Poisson and binomial GLMMs. In this paper, we generalize our methods to all other non-Gaussian distributions, in particular to negative binomial and gamma distributions that are commonly used for modelling biological data. While expanding our approach, we highlight two useful concepts for biologists, Jensen's inequality and the delta method, both of which help us in understanding the properties of GLMMs. Jensen's inequality has important implications for biologically meaningful interpretation of GLMMs, whereas the delta method allows a general derivation of variance associated with non-Gaussian distributions. We also discuss some special considerations for binomial GLMMs with binary or proportion data. We illustrate the implementation of our extension by worked examples from the field of ecology and evolution in the R environment. However, our method can be used across disciplines and regardless of statistical environments.
Information about the socioeconomic drivers of Silurus glanis anglers in the UK were collected using questionnaires from a cross section of mixed cyprinid fisheries to elucidate human dimensions in angling and non-native fisheries management. Respondents were predominantly male (95%), 30–40 years of age with <10 yr angling experience for S. glanis; most had received college rather than university education. The majority (34%) were employed with low-moderate income status (<£30k per annum), which may restrict time and expenditure spent on angling. Highest angling expenditure was on equipment and bait with most from southern England (54%) spending >£500 per annum. The proportion of time spent angling for S. glanis was significantly related to angler motivations; fish size, challenge in catch, tranquil natural surroundings, escape from daily stress and to be alone were considered important drivers of increased time spent angling. Overall, poor awareness of: the risks and adverse ecological impacts associated with introduced S. glanis, non-native fisheries legislation, problems in use of unlimited ground bait and high fish stocking rates in angling lakes were evident, possibly related to inadequate training and information provided by angling organisations to anglers, as many stated that they were insufficiently informed.
So far, perch egg strands have been considered unpalatable biological material. However, we repeatedly found egg strands of European perch (Perca fluviatilis) in the diet of European catfish (Silurus glanis) caught by longlines in Milada and Most Lakes, Czech Republic. The finding proves that perch egg strands compose a standard food source for this large freshwater predatory fish. It extends the present knowledge on catfish foraging plasticity, showing it as an even more opportunistic feeder. Utilization of perch egg strands broadens the catfish diet niche width and represents an advantage against other fish predators. Comparison of datasets from extensive gillnet and SCUBA diver sampling campaigns gave the evidence that at least in localities where food sources are limited, multilevel predation by catfish may have an important impact on the perch population.
Effective management of invasive fishes depends on the availability of updated information about their
distribution and spatial dispersion. Forensic analysis was performed using online and published data on the European
catfish, Silurus glanis L., a recent invader in the Tagus catchment (Iberian Peninsula). Eighty records were obtained
mainly from anglers’ fora and blogs, and more recently from www.youtube.com. Since the first record in 1998, S. glanis
expanded its geographic range by �700 km of river network, occurring mainly in reservoirs and in high-order reaches.
Human-mediated and natural dispersal events were identified, with the former occurring during the first years of invasion
and involving movements of >50 km. Downstream dispersal directionality was predominant. The analysis of online data
from anglers was found to provide useful information on the distribution and dispersal patterns of this non-native fish,
and is potentially applicable as a preliminary, exploratory assessment tool for other non-native fishes.
Dualism in activity has been described in many fish species, including larger individuals of European catfish (Silurus glanis), which are able to switch their activities from nocturnal to diurnal in winter and spring. During the multi-year telemetry study, seasonal changes in diel activity of 45 juvenile European catfish were investigated. These juveniles exhibited no dualism in movement and were strictly nocturnal and crepuscular with no period of diurnal activity. During winter, the same juvenile European catfish were completely inactive throughout the 24-hr cycle. Also investigated was the impact of temperature, dissolved oxygen levels and water clarity on fish movement, relocation of resting places and home range size. The only significant correlations were that relocation and home range size increased with rising water temperatures.
The first record of the European catfish Silurus glanis Linnaeus, 1758 in the Guadalquivir River basin
This paper describes the first record of the European catfish Silurus glanis Linnaeus, 1758, introduced into the Guadalquivir
River basin. One individual of the species was captured in the Iznájar Reservoir (Córdoba, Spain) in July 2011. Most likely,
the illegal introduction of the species is due to anglers that brought the fish from other Iberian river basins, where the species
has been present since 1974.
Growth rates are a core characteristic of catfi sh populations that are of in-creasing research interest. However, few studies have synthesized growth data across catfi sh populations and species to examine large-scale drivers of catfi sh growth. Here, a meta-analysis of growth was conducted for channel catfi sh Ictalurus punctatus, blue catfi sh I. furcatus, fl athead catfi sh Pylodictis olivaris, brown bullhead Ameiurus nebulosus, and black bullhead A. melas, and relationships were documented between growth and climate vari-ables, hydrologic habitats (lentic versus lotic), and latitudinal countergradients (a tendency for faster subannual growth in the north). Blue catfi sh, black bullhead, and brown bullhead growth correlated signifi cantly and positively with temperature metrics. Blue catfi sh, fl at-head catfi sh, and brown bullhead growth also correlated signifi cantly and positively with sunshine fraction, wind speed, and evapotranspiration. Channel catfi sh growth did not cor-relate to any climate metrics. After removal of growth effects related to climate, blue catfi sh and brown bullhead had signifi cantly faster growth in lotic than lentic habitats. Channel catfi sh and black bullhead had faster growth in lentic than lotic habitats. Flathead catfi sh showed no difference in growth between hydrologic habitat types. After standardizing growth by postsexual maturation age and the thermal opportunity for growth, signifi cant and highly predictive countergradient growth relationships (mean r 2 = 0.47) were found for all fi ve species across sites (i.e., faster temperature-standardized growth in more northerly populations). Slopes of these relationships did not differ among species, suggesting similar responses to latitude. There may be a genetic basis for countergradient growth in catfi shes that developed over evolutionary scales via selection by a shared environmental factor. Cat-fi sh growth is variable within and among species but can be intensely shaped by all three primary factors evaluated in this study.
Maximum likelihood or restricted maximum likelihood (REML) estimates of the
parameters in linear mixed-effects models can be determined using the lmer
function in the lme4 package for R. As for most model-fitting functions in R,
the model is described in an lmer call by a formula, in this case including
both fixed- and random-effects terms. The formula and data together determine a
numerical representation of the model from which the profiled deviance or the
profiled REML criterion can be evaluated as a function of some of the model
parameters. The appropriate criterion is optimized, using one of the
constrained optimization functions in R, to provide the parameter estimates. We
describe the structure of the model, the steps in evaluating the profiled
deviance or REML criterion, and the structure of classes or types that
represents such a model. Sufficient detail is included to allow specialization
of these structures by users who wish to write functions to fit specialized
linear mixed models, such as models incorporating pedigrees or smoothing
splines, that are not easily expressible in the formula language used by lmer.
Managing fisheries using length-based harvest regulations is common, but such
policies often create trade-offs among conservation (e.g. maintaining natural agestructure or spawning stock biomass) and fishery objectives (e.g. maximizing yield
or harvest numbers). By focusing harvest on the larger (older) fish, minimumlength limits are thought to maximize biomass yield, but at the potential cost of
severe age and size truncation at high fishing mortality. Harvest-slot-length limits
(harvest slots) restrict harvest to intermediate lengths (ages), which may contribute
to maintaining high harvest numbers and a more natural age-structure. However,
an evaluation of minimum-length limits vs. harvest slots for jointly meeting fisheries and conservation objectives across a range of fish life-history strategies is currently lacking. We present a general age- and size-structured population model
calibrated to several recreationally important fish species. Harvest slots and minimum-length limits were both effective at compromising between yield, numbers
harvested and catch of trophy fish while conserving reproductive biomass. However, harvest slots consistently produced greater numbers of fish harvested and
greater catches of trophy fish while conserving reproductive biomass and a more
natural population age-structure. Additionally, harvest slots resulted in less waste
in the presence of hooking mortality. Our results held across a range of exploitation
rates, life-history strategies and fisheries objectives. Overall, we found harvest slots
to represent a valuable option to meet both conservation and recreational fisheries
objectives. Given the ubiquitous benefits of harvest slots across all life histories
modelled, rethinking the widespread use of minimum-length limits is warranted.
Hatchery programmes involving the mass release of cultured fish have been implemented worldwide to supplement wild populations
and to increase harvests. Hokkaido Island is one of the most active regions for Pacific salmon hatchery programmes, with ca.
1.2 billion (109) juveniles released annually along a coastline of ca. 3000 km. During the last quarter of the 20th century, coastal catches
of chum and pink salmon increased dramatically, whereas those of masu salmon did not. In addition to the development of hatchery
technologies, several possible hypotheses may explain these catch trends, including climate change, closing of high-seas fisheries,
rehabilitation of water quality, habitat loss caused by damming and channelling, and increased pressure from recreational
fisheries. Even when these other factors have been accounted for, it is difficult to evaluate whether all hatchery programmes
have actually increased net populations. To use these programmes more effectively, it is necessary to evaluate both their
river- and species-specific benefits and compare hatchery programmes with other management tools, such as fishery controls
and habitat rehabilitation. Future hatchery programmes should incorporate active, adaptive learning approaches to minimize
the risks associated with artificial propagation and to promote sustainable salmon stocks.
Put–grow–take fisheries for channel catfish Ictalurus punctatus provide popular sport fisheries in many small impoundments and lakes throughout the United States. These fisheries are costly to maintain because the fish that are stocked are usually large fingerlings (>175 mm total length). Given the substantial fiscal and human resources required, it is important that these stockings contribute to the fishery. We estimated the exploitation of stocked channel catfish by tagging fish in 14 small impoundments to determine their use. Secondly, we determined whether the stocking rate, stocking size, and angler catch inequality (proportion of tags returned) affected exploitation. Annual exploitation varied more than 10-fold among the impoundments, ranging from 0 to 0.65 for the year after the fall stockings and usually declining thereafter. Cumulative exploitation in the 3 years after stocking ranged from 0 to 0.69, indicating that there is wide variation in the use of the stocked fish. Exploitation was unrelated to the stocking rate but was affected by stocking size, larger fish being more vulnerable than smaller fish to catch and harvest. In several impoundments, one to three anglers accounted for one-third or more of all returned tags, showing that just a few anglers can markedly affect exploitation. These results suggest that exploitation can be dynamic, changing with stocking size and angling clientele. Despite this inherent variability, we found substantial differences in exploitation among lakes. Managers should focus on impoundments where channel catfish are heavily exploited, possibly by stocking more fish or implementing protective harvest restrictions. For lightly exploited lakes, reducing stockings may be necessary to improve the growth and size structure of channel catfish.
Although being a widely introduced and successfully established species, the European catfish Silurus glanis L. (the world's third largest freshwater fish) remains poorly studied in its introduced areas, Here we studied the trophic ecology of non-native European catfish in a large river system in south-western France using stomach content and stable isotope analyses (SIA). We used fin samples for SIA of catfish and hence tested the validity of using fin tissue as a proxy for muscle in SIA. The mean delta N-15 and delta C-13 values analysed from fin tissues did not differ from those analysed from muscle tissue and reflected strong and consistent relationships (r(2) = 0.95 for carbon and r(2) = 0.98 for nitrogen). The delta N-15 values varied almost 5 parts per thousand among the analysed catfish individuals, while delta C-13 values varied > 5 parts per thousand. Total length of these catfish ranged from 200 to 2240 mm and was correlated with delta N-15 and especially with delta C-13 values. Although catfish length and delta N-15 values were positively correlated, the mean trophic positions of catfish increased only slightly from smaller individuals to larger ones (4.3 to 4.7). However, larger catfish were considerably C-13-enriched in their delta C-13 values compared to smaller individuals and had up to 4 parts per thousand higher delta C-13 values than their expected aquatic prey. This might indicate frequent consumption of mammals and/or non-aquatic birds by the larger sized individuals, which were found in the catfish stomachs.
Abstract Recreational fisheries statistics can provide valuable information on the dynamics of fish stocks and their exploitation. For some reservoirs in the Czech Republic, there are conspicuous synchronous fluctuations in catches of different species that might be caused by fishing skills and strategies. This study describes a method that could detect signatures of such phenomena in individual logbooks. It classifies anglers by species reported during 1 year and compares the resulting angler groups by group size, fishing effort, catch per unit effort (CPUE) and annual catch. The method is illustrated by data from one reservoir, showing that the number of generalist anglers who caught several species was higher than expected. Generalists also had higher catches and effort but lower CPUE than specialists who caught only one of the species. The results indicate that generalist anglers with a low degree of specialisation and high effort could contribute to long-term correlations in species catches.
The first telemetry study analysing behaviour of the largest freshwater predator in European rivers, Silurus glanis, was performed bimonthly during the years 2002–2004. Movement of juveniles and adults occurred mostly in the same time intervals. The only statistical differences occurred for nocturnal activity in spring and autumn. In spring and winter, activity was low with the peaks during daylight, and in autumn, maximal movement was recorded during dusk. In summer, the European catfish were active across the whole 24 h even during high-flow conditions. During all other seasons, movement was inversely related to flow rate. Maximal home ranges occurred in summer, being larger for adults. Juveniles and adults were spatially segregated. With increasing flow, fish were displaced, and individuals from both groups got closer to each other. Only juveniles migrated downstream from the upstream isolated river stretch suggesting a negative impact of lateral obstructions on the fish population structure.
Most sources of stress in aquaculture, fish salvage, stocking programs, and commercial and sport fisheries may be unavoidable.
Collecting, handling, sorting, holding, and transporting are routine practices that can have significant effects on fish physiology
and survival. Nevertheless, an understanding of the stressors affecting fish holding can lead to practices that reduce stress
and its detrimental effects. The stress-related effects of short-term holding are influenced by water quality, confinement
density, holding container design, and agonistic and predation-associated behaviors. Physiological demands (e.g., resulting
from confinement-related stresses) exceeding a threshold level where the fish can no longer compensate may lead to debilitating
effects. These effects can be manifested as suppressed immune systems; decreased growth, swimming performance, or reproductive
capacity; even death. Furthermore, holding tolerance may depend upon the species, life stage, previous exposure to stress,
and behavior of the held fish. Water quality is one of the most important contributors to fish health and stress level. Fish
may be able to tolerate adverse water quality conditions; however, when combined with other stressors, fish may be quickly
overcome by the resulting physiological challenges. Temperature, dissolved oxygen, ammonia, nitrite, nitrate, salinity, pH,
carbon dioxide, alkalinity, and hardness are the most common water quality parameters affecting physiological stress. Secondly,
high fish densities in holding containers are the most common problem throughout aquaculture facilities, live-fish transfers,
and fish salvage operations. Furthermore, the holding container design may also compromise the survival and immune function
by affecting water quality, density and confinement, and aggressive interactions. Lastly, fishes held for relatively short
durations are also influenced by negative interactions, associated with intraspecific and interspecific competition, cannibalism,
predation, and determining nascent hierarchies. These interactions can be lethal (i.e., predation) or may act as a vector
for pathogens to enter (i.e., bites and wounds). Predation may be a significant source of mortality for fisheries practices
that do not sort by size or species while holding. Stress associated with short-term holding of fishes can have negative effects
on overall health and well-being. These four aspects are major factors contributing to the physiology, behavior, and survival
of fishes held for a relatively short time period.
Besides various physiological and biological indices, stress in fish can be expressed directly by changes in their behaviour.
Electrofishing point sampling approach based on CPUE (catch per unit effort) was used to evaluate fish density (escapement)
into the littoral zones of four Czech ponds as a reaction to the occurrence and hunting activities of great cormorant (Phalacrocorax carbo sinensis) flocks. The behaviour of two-year-old common carp (Cyprinus carpio) before and after cormorant arrival was compared. Significant differences (P<0.001) in CPUE were recorded in fish density before and after cormorant arrival on all of four ponds under study—Žofinský:
0.04±0.18 and 22.38±26.87 (mean±SD), Starý Hospodář: 0.05±0.29 and 25.49±25.45, Žebrákov: 0.16±0.57 and 28.58±24.75
and Travičný: 0.03±0.19 and 17.18±18.20, respectively. The evaluation of fish wounding in the CPUE fish samples proved
the proportion of fish injured by cormorant attacks ranging from 3.33 to 18.19% in the ponds under study.
KeywordsCPUE (catch per unit effort)–
Phalacrocorax carbo sinensis
–Pond aquaculture–Stress
Catfish have spread across Europe and several countries out of this region within the last decades. Basic knowledge of this apex predator has revealed concerns of invasive behaviour and questions regarding its utilization as a biomanipulation species. However, a method enabling its regulation to a required level has not yet been developed. We simulated the impact of angling on the catfish population by method of hook-lines in two post-mining lakes with a monitored population consisting of tagged individuals and in two reservoirs as reference sites. Further, the efficiency of hook-lines as a reducing device was examined and the economic aspects were determined. Catfish population in localities where the species is unwanted or invasive may be efficiently reduced to a harmless level by hook-lines and angling (depending on the approach of anglers). The most efficient time of the year seems to be spring to early summer with catch efficiency of 5.4 individuals per 10 baits in one day. The catch efficiency markedly decreased during the second part of the year and did not exceed 2.8 individuals per 10 baits in one day. Mean size of catfish had negative impact whereas catfish biomass had positive impact on the catch efficiency. Trophic status and number of catfish in the locality had no impact on the catch efficiency. According to model, 11–18 bait-days per 1 ha per season is efficient to decrease catfish population to 10% of the original size. Both angling and hook-lines are very simple, they are financially and time bearable mechanisms of catfish regulation in any condition. However, catfish play an important role as a biomanipulative species in many localities. In this case where catfish is beneficial, angling presents a real threat of population collapse and loss of the biomanipulative effect.
In Central Europe, European grayling Thymallus thymallus is an endangered and vanishing fish species with high recreational angling value. For that reason, in January 2016, the minimum legal angling size for grayling was increased from 30 to 40 cm in the Czech Republic. This study evaluated if the increase in minimum angling size had any effect on grayling harvest. Data from 229 fishing sites covering the years 2011-2017 were used in this study. The data originated from individual angling logbooks, collected in the regions of Prague and Central Bohemia, Czech Republic. Over the seven years, anglers visited the studied fishing sites 3.6 million times and harvested 105 000 salmonids. Grayling made up only 0.5 % of the overall salmonid harvest. The fishing restriction caused a decrease in grayling harvest-per-visit. It also decreased the contribution of grayling to the overall harvest as well as the number of fishing sites where anglers successfully harvested graylings. Fish stocking was constant during the study period. Increased minimum angling size led to increased average body weight of harvested fish. In conclusion, the increase in minimum angling size significantly affected fish harvest and composition.
This study aimed to assess the relationship between basic metrics in recreational fishing and the size of the fishing ground. Data were obtained from individual angling logbooks collected by the Czech Fishing Union over 12 years on 212 fishing grounds located in the regions of Prague and Central Bohemia in the Czech Republic. Small fishing grounds had the highest catch, yield, numbers of fishing visits and numbers of angling guard controls per hectare. Medium‐sized fishing grounds had the highest catch, yield, and numbers of both fishing visits and angling guard controls per fishing ground. Anglers returned to medium‐sized fishing grounds most frequently. The percentage of anglers who caught and took home at least one fish decreased with increasing size of the fishing ground. In conclusion, basic metrics in recreational fishing are related to the size of the fishing ground, which thus plays an important role in fisheries management.
Capsule: Great Cormorants Phalacrocorax carbo prey on larger fish in late winter compared to early winter.
Aims: This study aimed to describe Cormorant diet and to discover whether prey size changed during winter.
Methods: The diet of Cormorants was studied using regurgitated pellets collected from roosting places at the upper Elbe River, Czech Republic, during winter (from December to March).
Results: The diet consisted of 24 fish species from 6 fish families. Roach Rutilus rutilus dominated in the diet (over 50% of biomass). Size of fish in the diet increased over time during the whole winter. Except for European Chub Squalius cephalus, the increased size applied for the majority of the most frequently consumed fish species: Roach, European Perch Perca fluviatilis and White Bream Abramis brama. Cormorants consumed mostly fish species of lower commercial and angling value.
Conclusion: Fisheries management should reflect on the fact that competition for larger-sized fish is the highest in late winter and in early spring. For that reason, stocking of potentially vulnerable fish could be delayed to the time when overwintering birds leave the area and recreational fishing could be restricted in late winter.
Recreational fishing is a major leisure activity in many European countries but social aspects of angling are still understudied. This study aimed to examine long-term social trends in recreational fishing. Data was obtained from annual angling reports collected by the Czech Fishing Union. Data from annual angling reports is based on data from individual angling logbooks collected from 238 fishing grounds over the course of 11 years in Prague and Central Bohemia, Czech Republic. It was discovered that the numbers of individual anglers and angling visits on fishing grounds have been increasing. An average angler visits higher diversity of fishing grounds but anglers keep on returning to individual fishing grounds less frequently. Frequency of angling guard controls on fishing grounds has been increasing as well. On the other hand, angling yield and catch have been decreasing. The number of anglers who take home at least one fish has been increasing but percentage of anglers who take home at least one fish has been decreasing. In conclusion, recreational fishing is on the rise but fish catch and yield are decreasing.
Standardised angler diaries could produce useful proxy data for assessing fish population density and size distribution, but few rigorous studies about their utility exist. We use 62 years of angling diary data (1949–2010), from a large mesotrophic lake, to investigate population structure (abundance, mean size and record size) of European perch (Perca fluviatilis L.) in relation to the impact of three commercial fishers with different fishing strategies, pike (Esox lucius L.) predation and temperature. We found that anglers’ harvest rates of perch varied by a factor of 10 over time, indicating large variation in population abundance over decadal time scales. Our statistical analysis revealed that the anglers’ harvest rates of perch were related to pike CPUE (proxy of pike predation), temperature and commercial fishing directly through the harvest of perch and indirectly through the harvest of pike, the top predator of the lake. The size distribution and growth rates of perch caught by anglers also changed substantially during the study period, most likely controlled by density-dependent mechanisms as well as size-selective commercial harvest. The effect of selective harvest on size-structure was stronger than ecological density dependence. We conclude that commercial harvesting may exert strong impacts on the quality of the angling experiences, at least in the studied case. Moreover, our work showcases the value of detailed angler diaries to study and monitor changes in freshwater fish populations, but it also underlines the need for supplementary data on biotic and abiotic factors to reach the full potential of angler diary data.
Stocking of hatchery-reared fish into streams is a common practice in fisheries industry as it provides catches for recreational anglers and support for native fish populations. The Eurasian otter Lutra lutra is one of the most important freshwater piscivorous predators in Europe. Impact of otters on stocked fish is a source of conflict between fisheries industry and environmental protection. This study aimed to describe differences between otter diet and catches of anglers on a lowland trout stream with salmonid stocking. Otter diet was studied during winter, using spraint analysis. Fish dominated otter diet (85% of biomass). Gudgeon Gobio gobio was the most important otter prey (38% of biomass). Catches of otters and catches of anglers on the stream were significantly different. Otters mostly preyed upon small-growing fish species of medium or no angling value while anglers took large-growing fish species of medium and high angling value. Otters took fish with average weight of 10 g while anglers took fish with average weight of 290 g. Stocked salmonids made up 13% of estimated biomass in otter diet. Otters targeted significantly different fish species of different sizes than anglers did.
Information on fishing effort, catch, harvest, and survival is important for formulating management policies in freshwater fisheries and for understanding the dynamics of aquatic ecosystems. Fisheries managers often use creel surveys to assess fisheries statistics. The mean‐of‐ratios estimator has been traditionally used for estimating catch rates from incomplete angler trips, whereas the ratio‐of‐means estimator is preferable for estimating catch rates from completed trips. Recent studies have demonstrated persistent bias when comparing the two estimators based on catch data from incomplete and completed trips from the same sample of anglers; these studies have promoted the use of linear regression models to correct for apparent bias in catch rates based on incomplete trips. However, the reported bias in catch rate estimates may be an artifact of measurement error in incomplete‐trip angler surveys rather than bias from the estimates themselves. Furthermore, we contend that ordinary least‐squares linear regression is inappropriate to correct for this apparent bias because measurement error is present in both the response variable (e.g., catch rate estimated from completed trips) and the explanatory variable (e.g., catch rate estimated from incomplete trips), leading to low estimates of the slope of the relationship. Alternatively, when both variables contain measurement error, model II regression methods provide less‐biased estimates. Using interview data (incomplete trips) from roving creel surveys and a catch card survey (completed trips) conducted on the same sample of anglers, we compared catch rates derived from both estimators. Our results show that linear regression underestimates the slope of the relationship and that model II regression reduces bias and provides a more accurate estimate.
Received April 26, 2014; accepted November 26, 2014
In culture-based fisheries, managers strive for high stocking efficiency, the ratio between the total weight of caught and stocked fish. Here we present a new time series approach to examine the dependence of reported anglers’ catches on stocking and external events, using data on carp (Cyprinus carpio L.) from 14 reservoirs in the Czech Republic. Average stocking efficiency varied between 0.25 and 2.2, with values close to unity in most reservoirs. The lowest efficiencies occurred in three reservoirs receiving cold hypoxic water from a large upstream reservoir, while the highest efficiencies were found in two shallow, highly productive reservoirs. Analyses further indicate that stocked carp are typically caught during the year of release or the year after; but also that the mean time lag between stocking and capture increases with reservoir area. External events can be important: major floods in the years 2002 and 2006 were in many cases followed by large, up to 10-fold, increases in catches in subsequent years; we attribute the surplus catch to carp washed down from upstream aquaculture and river stretches. In contrast, the “Velvet Revolution” (demise of the communist regime in 1989) had no discernible effect on catches in subsequent years. In conclusion, the proposed method can simultaneously estimate the likely mean survival time of stocked carp and identify the impact of major environmental and societal events on recreational fisheries. The approach thus sheds light on the performance of current stocking practices at individual reservoirs, and could be used to monitor and improve stocking strategies and management of culture-based recreational fisheries.
We implemented a statewide volunteer angler diary program for the 1995 fishing season to determine whether angler diaries can provide data that are useful for the management of the principal sport fishes in waters throughout Mississippi. Of 1,153 anglers volunteering to participate, 224 (19%) returned diaries with at least one recorded fishing trip that was usable for data analysis. We found no significant (P < 0.05) correlations between angler diary catch per unit effort (CPUE; fish/h) and creel survey or electrofishing CPUE for black bass Micropterus spp. and crappies Pomoxis spp. The length distributions of black bass reported by anglers were similar to those obtained from electrofishing samples at five of seven reservoirs when fish smaller than 250 mm were excluded from the comparisons. The length distributions of crappies obtained from diary reports were different from those obtained from electrofishing samples. Low participation by anglers for catfish (Ictaluridae) and sunfish Lepomis spp. precluded similar analyses for those species. The participating anglers differed from the general angling public in Mississippi, possibly biasing estimates of catch rate. Although angler diaries may have value for monitoring angler catch rate trends for diverse types of anglers and in numerous water bodies, our results show that angler diary data should not be used to replace traditional fishery assessment data.
The survival, angler catch, and harvest of several size-groups of channel catfish Ictalurus punctatus, concurrently stocked into a 6.1-hectare impoundment in central Illinois, increased with size at stocking. However, in the presence of an established predator population and adequate forage, even the largest size-group of channel catfish (mean length, 202 mm total length) suffered 55 and 73% natural mortality, after one and two growing seasons, respectively. Based on the results of this study, the greatest return on investment would be obtained by stocking fish of at least 200 mm total length.
Most research on catch-and-release (C&R) in recreational fishing has been conducted from a disciplinary angle focusing on the biological sciences and the study of hooking mortality after release. This hampers understanding of the complex and multifaceted nature of C&R. In the present synopsis, we develop an integrative perspective on C&R by drawing on historical, philosophical, socio-psychological, biological, and managerial insights and perspectives. Such a perspective is helpful for a variety of reasons, such as 1) improving the science supporting successful fisheries management and conservation, 2) facilitating dialogue between managers, anglers, and other stakeholders, 3) minimizing conflict potentials, and 4) paving the path toward sustainable recreational fisheries management. The present work highlights the array of cultural, institutional, psychological, and biological factors and dimensions involved in C&R. Progress toward successful treatment of C&R might be enhanced by acknowledging the complexity inherent in C&R recreational fishing.
Abstract Culture-based fish yield in non-perennial reservoirs of Sri Lanka was related to reservoir morphometry and stocking density. The reservoirs were stocked mainly with fingerlings of one Chinese and three Indian major carp species, common carp, Cyprinus carpio L., and the genetically improved farmed tilapia strain of Nile tilapia, Oreochromis niloticus (L.), at four pre-determined species combinations and a range of stocking densities [SD (fingerlings ha−1)]. Twenty-three reservoirs were harvested successfully at the end of the culture period of 2002–2003. Basic limnological and morphometric parameters, including shoreline development (DL) and shoreline area ratio (RLA), were estimated for each of the 23 reservoirs. Bray–Curtis similarity and non-metric multidimensional scaling using mean values of limnological data revealed that reservoirs could be ordinated into two major clusters, one with intact sample distribution due to similar trophic characteristics and the other with scattered sample distribution. Reservoirs in the cluster with similar trophic characteristics showed significant correlation (P < 0.05) between RLA and total fish yield (Y). A multiple regression equation, Y = −693 + 4810 RLA + 0.484 SD, was generated to estimate fish harvest in relation to SD.
a b s t r a c t . in 1975–2005, we utilized data on water quality (n-nH 4 + , o 2 , Cl -) and number of carp caught (CC) as environmental data, and sport fishery statistics as species data, from three fishing stretches of the Berounka River, Czech Republic. an indirect gradient analysis (DCa) for calculating the strongest gradient affecting the species data, and direct linear gradient analysis (RDa) were used for assessing the relationships among environmental and species data. all RDa models were significant and consecutively explained 45.5, 39.6, and 39.7% of the variability of species data. The strength of environmental variables was evaluated by partial RDa. in the first stretch below the City of Plzeň, with the poor water quality and low carp yields, all environmental variables were significant and the CC data alone explained 26.2% variability of species data. In the second stretch, with intermediate water quality and carps yields, only two environmental variables (o 2 and Cl -) were significant and in the third stretch near the city of Prague, with the same water quality and exceptionally high yields, the environmental variables did not significantly influence the species data. These results indicate that sport fishery statistics can be used as at least one source of information for studies of fish assemblages in streams where other data is lacking.
1. Temperate regions with fish communities dominated by cold-water species (physiological optima <20 °C) are vulnerable to the effects of warming temperatures caused by climate change, including displacement by non-native cool-water (physiological optima 20–28 °C) and warm-water fishes (physiological optima >28 °C) that are able to establish and invade as the thermal constraints on the expression of their life history traits diminish.
2. England and Wales is a temperate region into which at least 38 freshwater fishes have been introduced, although 14 of these are no longer present. Of the remaining 24 species, some have persisted but failed to establish, some have established populations without becoming invasive and some have become invasive. The aim of the study was to predict the responses of these 24 non-native fishes to the warming temperatures of England and Wales predicted under climate change in 2050.
3. The predictive use of climate-matching models and an air and water temperature regression model suggested that there are six non-native fishes currently persistent but not established in England and Wales whose establishment and subsequent invasion would benefit substantially from the predicted warming temperatures. These included the common carp Cyprinus carpio and European catfish Silurus glanis, fishes that also exert a relatively high propagule pressure through stocking to support angling and whose spatial distribution is currently increasing significantly, including in open systems.
4. The potential ecological impacts of the combined effects of warming temperatures, current spatial distribution and propagule pressure on the establishment and invasion of C. carpio and S. glanis were assessed. The ecological consequences of C. carpio invasion were assessed as potentially severe in England and Wales, with impacts likely to relate to habitat destruction, macrophyte loss and increased water turbidity. However, evidence of ecological impacts of S. glanis elsewhere in their introduced range was less clear and so their potential impacts in England and Wales remain uncertain.
Angler diary programmes (n=46, 1979–1997) implemented in Ontario by the Ontario Ministry of Natural Resources are reviewed, and the different uses of angler diary programmes, levels of participation and differences in programme design are reported. In Ontario, angler diary use is common, but successful application is limited. This review revealed a variety of uses and approaches for administering angler diary programmes. Problems arise when programmes are initiated without the complete commitment of the administrators and agency, or when there is no regular review so adaptive changes can be made. If administrators realize the potential biases and problems associated with diaries, and design programmes to control them, angler diaries can provide favorable cost-effective results. With reduced funding and staffing constraints, angler diary programmes could become the primary method of data collection for specialized and remote fisheries.
A popular species for food and sport, the European catfish (Silurus glanis) is well-studied in its native range, but little studied in its introduced range. Silurus glanis is the largest-bodied freshwater fish of Europe and is historically known to take a wide range of food items including human remains. As a result of its piscivorous diet, S. glanis is assumed to be an invasive fish species presenting a risk to native species and ecosystems. To assess the potential risks of S. glanis introductions, published and ‘grey’ literature on the species’ environmental biology (but not aquaculture) was extensively reviewed. Silurus glanis appears well adapted to, and sufficiently robust for, translocation and introduction outside its native range. A nest-guarding species, S. glanis is long-lived, rather sedentary and produces relatively fewer eggs per body mass than many fish species. It appears to establish relatively easily, although more so in warmer (i.e. Mediterranean) than in northern countries (e.g. Belgium, UK). Telemetry data suggest that dispersal is linked to flooding/spates and human translation of the species. Potential impacts in its introduced European range include disease transmission, hybridization (in Greece with native endemic Aristotle’s catfish [Silurus aristotelis]), predation on native species and possibly the modification of food web structure in some regions. However, S. glanis has also been reported (France, Spain, Turkmenistan) to prey intensively on other non-native species and in its native Germany to be a poor biomanipulation tool for top-down predation of zooplanktivorous fishes. As such, S. glanis is unlikely to exert trophic pressure on native fishes except in circumstances where other human impacts are already in force. In summary, virtually all aspects of the environmental biology of introduced S. glanis require further study to determine the potential risks of its introduction to novel environments.
The world's fish species are under threat from habitat degradation and over-exploitation. In many instances, attempts to bolster stocks have been made by rearing fish in hatcheries and releasing them into the wild. Fisheries restocking programmes have primarily headed these attempts. However, a substantial number of endangered species recovery programmes also rely on the release of hatchery-reared individuals to ensure long-term population viability. Fisheries scientists have known about the behavioural deficits displayed by hatchery-reared fish and the resultant poor survival rates in the wild for over a century. Whilst there remain considerable gaps in our knowledge about the exact causes of post-release mortality, or their relative contributions, it is clear that significant improvements could be made by rethinking the ways in which hatchery fish are reared, prepared for release and eventually liberated. We emphasize that the focus of fisheries research must now shift from husbandry to improving post-release behavioural performance. In this paper we take a leaf out of the conservation biology literature, paying particular attention to the recent developments in reintroduction biology. Conservation reintroduction techniques including environmental enrichment, life-skills training, and soft release protocols are reviewed and we reflect on their application to fisheries restocking programmes. It emerges that many of the methods examined could be implemented by hatcheries with relative ease and could potentially provide large increases in the probability of survival of hatchery-reared fish. Several of the necessary measures need not be time-consuming or expensive and many could be applied at the hatchery level without any further experimentation.
Reported improvements in the muskellunge angling fishery on Lake of the Woods, Ontario over the last two decades have paralleled
an increase in the practice of catch and release angling, and an increase in minimum size regulations for this species. The
overall status of muskellunge populations in this large, complex lake has proven difficult to monitor using standard assessment
methods. A volunteer muskellunge angler diary program, established in 1988, has provided a cost effective method of gathering
a large amount of information with which to track this fishery and associated populations. Results from angling diaries indicated
increased angling effort, catch and success rates for muskellunge on Lake of the Woods since the early 1990s. Although the
month of July accounted for the majority of angling effort and catch, angling success rates and sizes of fish reported in
diaries improved monthly into the late fall. Angling success rates were consistently higher in angling diaries than from creel
surveys, but both survey types showed similar long-term trends in the fishery. Angler diary data, incorporating both the numbers
of fish caught and/or seen by anglers, were used to calculate catch equality indices which proved to be sensitive to changes
in population abundance. Increased minimum length regulations for muskellunge during 1987–2001 have been largely responsible
for a decline in harvest rates from an estimated 36% in 1986 to 0% since 1999. Although higher size limits have yet to produce
more quality-sized fish in angler catches, diary survey data, supported by recent improvements in catch rates from assessment
gill nets, would indicate that muskellunge recruitment has increased. This article concludes with a brief review of how muskellunge
angler diary data has been used in the past, including recommendations to minimize biases associated with this survey method.
Abstract In January 2004, 46 wels catfish, Silurus glanis L., between 51 and 135 cm total length were tagged and released into a 0.4 ha recreational, catch and release, lake fishery in the UK, and their recapture by anglers monitored throughout the year. Of the 46 tagged fish, 16 were recaptured by anglers during 170 capture events. Some individual fish were captured up to 26 times. Catfish 100 cm most susceptible. Frequency of captures increased with temperatures >10 °C and peaked between June and August. Selected recapture weight data were used to produce a mass specific growth equation and revealed specific growth rate was a decreasing function of body mass over the size range of the recaptured fish. Their growth was slower than fish from elsewhere in their distribution range.
Using the electrofishing database of the French National Agency for Water and Aquatic Environment (Onema), the time trends of 48 freshwater fish taxa at 590 sites monitored for at least 8 years from 1990 to 2009 were investigated. The results demonstrated that species richness increased steadily from the beginning of the monitoring period. This is congruent with the finding that the number of species displaying a significant increase in spatial distribution or abundance was greater than those showing a significant decrease. Some species, however, had declined both in occurrence and abundance, e.g. tench Tinca tinca, common bream Abramis brama, brown trout Salmo trutta and European eel Anguilla anguilla. The species showing the most spectacular colonization were non-native, e.g. topmouth gudgeon Pseudorasbora parva, wels catfish Silurus glanis and asp Aspius aspius. The time trends in population density were related to the maximal body size, habitat requirement, occurrence and abundance and the status (i.e. native or exotic) but not to the spawning temperature.
Generalized linear mixed models provide a flexible framework for modeling a range of data, although with non-Gaussian response variables the likelihood cannot be obtained in closed form. Markov chain Monte Carlo methods solve this problem by sampling from a series of simpler conditional distributions that can be evaluated. The R package MCMCglmm implements such an algorithm for a range of model fitting problems. More than one response variable can be analyzed simultaneously, and these variables are allowed to follow Gaussian, Poisson, multi(bi)nominal, exponential, zero-inflated and censored distributions. A range of variance structures are permitted for the random effects, including interactions with categorical or continuous variables (i.e., random regression), and more complicated variance structures that arise through shared ancestry, either through a pedigree or through a phylogeny. Missing values are permitted in the response variable(s) and data can be known up to some level of measurement error as in meta-analysis. All simu- lation is done in C/ C++ using the CSparse library for sparse linear systems.
How to cite this article: Lyach R, Remr J. Changes in recreational catfish Silurus glanis harvest rates between years 1986-2017 in Central Europe
How to cite this article: Lyach R, Remr J. Changes in
recreational catfish Silurus glanis harvest rates between years
1986-2017 in Central Europe. J Appl Ichthyol. 2019;00:1-11.