Piscivorous Predators Research Articles

Relationships between body length, body mass and otolith dimensions in three Sprat species (Teleostei: Ehiravidae) from the Caspian Sea

AbstractReliable and detailed knowledge regarding the relationship between otolith size and the size of fish is important for fisheries management and for ecological studies on predicting fish size and on predator–prey interactions. Therefore, these relationships are estimated for three sprat (genus Clupeonella) species, including C. caspia, C. engrauliformis and C. grimmi from the Caspian Sea. The relative size and mass of the otoliths corrected for body size and mass were also estimated for the three sprat species. After biometry of collected specimens, the Sagittal otoliths were extracted from the cranium of collected specimens and photographed. Photos were used to estimate length and width of otoliths. The results revealed significant relationships between otolith length and width vs. fish length and otolith mass vs. body mass in all three species (r2 > 0.5). The higher coefficient of determination (r2) for relationships between total length (fish) – Otolith length and width was concluded in comparison with relationships between fish mass and otolith mass in the studied sprat species. Otoliths of C. grimmi showed the highest relative length and were significantly (P < 0.05) heavier than sagittal otoliths of two other sprat species. There is no previous report on size–mass relationships between fish and otolith measurements among the three studied sprat species. These estimated equations can be used in back-calculation studies, especially for these three sprats as the dominant prey for piscivorous predators such as Caspian seals and sturgeons, in their habitats.

Pallas’s Gull Ichthyaetus ichthyaetus and Fish Farming of the Palearctic: Review

The Pallas’s Gull Ichthyaetus ichthyaetus is a piscivorous predator and scavenger, some breeding populations of which are vulnerable and require protection. This study analyzes the status and distribution of Pallas’s Gull in Palearctic fish ponds—man–made bodies of water where fish concentrations are controlled by humans and can be many times higher than natural values. The aim of the study was to assess the state of the Pallas’s Gull in the fish farming of the Palearctic over the last ≈ 60 years. The review was based on > 1100 publications found in the search engines Yandex, Google, Google Scholar, eLybrary. Between the 1960s and 2020s, the Pallas’s Gull was discovered in 46 fish farms in the Palearctic. Breeding has been established in 3 fish farms, breeding has not been established in 38 fish farms, and birds were present in 5 fish farms, but the status was not specified. There were 35 places of contact with fish farms in Europe, and 11 places of contact in Asia. The average area of fish farms with which Pallas’s Gull came into contact was 10.7 km² (n = 21). Fish farms support non–breeding individuals –– vagrants, visitors, summer or winter residents of different age classes. Fish farms cannot be considered as important places for the reproduction of the species. The network of fish farms plays a certain auxiliary, but far from decisive role in maintaining the population and the current multidirectional expansion of the species’ range in the Palearctic. The hypothesis about the possible important role of reservoirs and fish farms in food supply and the distribution of Pallas’s Gull beyond the historical range was not confirmed in studies of fish farms.

Rodenticide contamination of cormorants and mergansers feeding on wild fish

AbstractExposure of wildlife to anticoagulant rodenticides from sewer baiting and bait application is poorly understood. We analyzed residues of eight anticoagulant rodenticides in liver samples of 96 great cormorants, 29 common mergansers, various fish species, and coypu, in different German regions. Results show that hepatic residues of anticoagulant rodenticides were found in almost half of the investigated cormorants and mergansers due to the uptake of contaminated fish from effluent-receiving surface waters. By contrast, exposure of coypu to rodenticides via aquatic emissions was not observed. The maximum total hepatic anticoagulant rodenticide concentration measured in waterfowl specimens was 35 ng per g based on liver wet weight. Second-generation anticoagulant rodenticide active ingredients brodifacoum, difenacoum, and bromadiolone were detected almost exclusively, reflecting their estimated market share in Germany and their continuing release into the aquatic compartment. Overall, our findings reveal that second-generation anticoagulant rodenticides accumulating in wild fish are transferred to piscivorous predators via the aquatic food chain.

Fecal DNA metabarcoding reveals the winter diet of Eurasian otter (Lutra lutra) in Northeast China

As the top predator of freshwater ecosystems, the Eurasian otter (Lutra lutra) plays a vital role in maintaining food web structure and ecosystem stability. Understanding the dietary composition and dynamics of the Eurasian otter is crucial for comprehending its ecosystem function and interspecies interactions, providing vital information for determining conservation and management strategies. Currently, DNA metabarcoding technology has been extensively applied in dietary studies as a more effective and accurate method for identifying prey species. However, there remains an insufficient amount of research on otter diet using this technology, especially in Northeast China. In this study, we analyzed the vertebrate dietary composition and spatial variation of otters during the winter in Northeast China using DNA metabarcoding technology. We confirm 106 fecal samples belonging to Eurasian otter DNA from 118 putative otters fecal samples, and then performed polymerase chain reaction (PCR) amplifications using vertebrate universal primers with the otter blocking primer (OBS1) and the human blocking primer (HomoB) to the sequence. Subsequently, high-throughput sequencing was performed to analyze the dietary composition of Eurasian otter. We identified a total of 34 prey taxa, including 31 fish, 2 frog and 1bird. Our results showed that the winter diet of the Eurasian otter was dominated by fish (60.11 %), (e.g., Cottidae, Cyprinidae), followed by Ranidae (39.88 %). Furthermore, geographical variations in dietary preferences were observed. This study confirms that Eurasian otter is a generalist piscivorous predator, and that its diet could be related to the availability of resources in the habitat. This study enriches the information on the diet of Eurasian otter, and can be used to provide a reference for the development of effective conservation strategies. At the same time, it confirms the reliability of the fecal DNA metabarcoding technique for carnivore predation analysis, and provides a new perspective for the investigation and research of otters and other mammals.

Does phenology influence predation rate on Salmo trutta parr during lake migration?

Acoustic tags fitted with predation sensors, which trigger following ingestion by piscivorous predators, were used to compare direct predation rates during downstream migration (out-migration) of potamodromous (freshwater) brown trout (Salmo trutta L.) parr from their natal river into a large freshwater lake system during spring and autumn. Thirty-eight spring migrants were tagged across two study years (2021 and 2022) of which 13 individuals (34%) were predated. By contrast 40 autumn migrants were tagged (2020 and 2021) of which three individuals (7.5%) experienced predation. The overall predation loss rate for spring migrants was 0.342% day-1 and was 0.075% day-1 for autumn migrants. Most predation events during spring (77%) occurred within the lower river before tagged fish entered the lake, whilst no predation events were recorded within the river in the autumn. Predation events were significantly linked to tagging season (spring or autumn), with the probability of tags remaining untriggered (as a proxy for survival) being higher 93% (95% confidence interval [CI] [87%, 100%]) in autumn than in spring 66% (95% CI [53%, 83%]). The spring migration periods showed significantly lower river discharge (0.321 m3 /s mean daily discharge, April 1 to May 31) to those measured during autumn (1.056 m3 /s mean daily discharge, October 1 to November 30) (Mann-Whitney U-test, U = 1149, p < 0.001). Lower flows, clearer water, and longer sojourn in the river may have contributed to greater predation losses in the spring relative to the autumn.

The enigmatic occurrence, size distribution, and significance of a new macrourid species, Nezumia armentrouti, based on otoliths from the Lincoln Creek Formation (upper Oligocene Section), Washington State, USA

ABSTRACT Teleostean otoliths (112 sagittae) from the Lincoln Creek Formation (upper Oligocene), Washington State, U.S.A., were identified as Nezumia armentrouti n. sp. except for two specimens. The preponderance of one species (98.21%) is very unusual. Equally puzzling is the size of the otoliths that represents almost exclusively large, mature fishes (extant N. aequalis used as an analogue). Otoliths do not reflect various ages (sizes), and there appears to be an absence of larval, juvenile, or subadult representatives. The restricted range (97.32% of specimens 8.1–16.1 mm) of the otolith lengths (and corresponding fish length) is attributed to depth stratification, which is well-known in extant macrourids. Otoliths may be the result of piscivorous predators and subsequent excretion. However, the unusual occurrence of the otoliths (single, or at most, two specimens often associated with thin bone beds) may indicate a different process such as the death and decay of individual fish. This investigation is highly significant on many fronts including the first fossil occurrence of the benthopelagic deep-sea Nezumia in North America (excluding the Caribbean), possible evidence of depth stratification in the paleoenvironment based on otolith length, and otoliths from an outer shelf/shelf break to upper slope paleoenvironment (200–600 m), which are extremely rare in the published fossil record.

Feeding ecology of European hake: Insights from stomach content and stable isotope analyses

The European hake (Merluccius merluccius) has been described as a demersal predator that can also feed on the water columns during migration. They may interact with nearly the entire food web in marine ecosystems. In this study, we investigated the feeding behavior of European hake based on size and seasonal stomach content analysis. In addition, we analyzed 15N and 13C of the muscle bulk tissue, determined the proxy trophic position, and revealed the ontogenetic shift with 15N. Our results confirm that the European hake is a piscivorous predator that feeds on various pelagic and demersal prey. Minor size-related dietary changes were observed, with juveniles consuming more benthic invertebrates and adults mainly consuming Teleost species. An increase in prey richness was found for both size groups during summer. Stable isotope analysis showed increased δ15N values with increasing length due to juveniles’ preference for benthic invertebrates, mainly crustaceans. Combining dietary studies with isotope analysis can provide a better understanding of trophic ecology, which can be helpful for ecosystem-focused management.

Diet of the otter Lutra lutra inhabiting a forest stream in SW Poland

AbstractDiet of the otter inhabiting a forest stream in SW Poland was studied in order to show the impact of the otter on fish and other aquatic animals. The diet was examined by means of spraint analysis. A total of 157 spraints were collected from 14 sites, and 605 prey items were extracted. Fish comprised the staple diet. It was supplemented by frogs, birds, small mammals and invertebrates. Fish were represented by at least 23 species belonging to seven families. Two families Cyrinidae and Percidae dominated the fish component of the diet (together 70.1%). The most numerous fish species consumed were Perca fluviatilis (24.1%) and Rutilus rutilus (12.1%). The otter diet was most diversified in the coldest months of the year (November-April; B = 10.0-10.5), and least in the warmest months of the year (July-August; B = 5.7). The niche breath was wider in 2006 (B = 12.2), compared with 2007 (B = 20.4). However, only the proportions of Gobio gobio and Esox lucius were statistically different in those two years compared. This study confirms previous findings that the otter is a generalist piscivorous predator hunting opportunistically on locally and seasonally most common fish species, mainly of low economic importance.

Reduction in overwinter body condition and size of Pacific sand lance has implications for piscivorous predators during marine heatwaves

Acute anomalous ocean warming events, including marine heatwaves (MHWs), have significant effects on reproduction and survival of piscivorous seabirds. Additionally, MHWs have negative effects on seabird fish prey, exacerbating these consequences and resulting in population implications for seabirds. We evaluated the relative body condition of Pacific sand lance Ammodytes personatus, an important seabird forage species, in Haro Strait, a highly productive region of southern British Columbia, Canada. We compared body condition and length of fish cohorts that experienced the 2016 MHW year (MHW cohorts) with fish hatched during 3 subsequent post MHW years (2017-2019). Age-0 MHW cohorts had a seasonal decline in body condition in age-0 fish from 100% in the summer to 81% in the winter, while age-1 fish showed a decline from summer-fall highs of 93.5% to wintertime low of 79.5%. In comparison, post MHW cohorts had a winter body condition that was 2-4 times higher than their MHW cohorts. Similar to previous studies in Alaska during the MHW, age-1 fish failed to grow and reach the typical size that distinguishes them from age-0 fish. Poor sand lance condition and growth in winter may explain the ramifications of a warming ocean for top predators, including seabirds and Pacific salmon, which depend on these prey fish in Haro Strait. Our results support the idea that Haro Strait, which is influenced by estuarine circulation resulting in cooler temperatures than surrounding areas, serves as a climate refugium for sand lance populations in summer and provides buffering capacity to ocean climate warming events.

Identification of important forage fish and implications of increased predator demand through Ecopath modeling

Fisheries on lower trophic levels act as and compete with predators in aquatic ecosystems for potentially limited prey resources. Multiple predators in a system are often managed to achieve a Bmsy that could result in a total predator consumption level the ecosystem cannot support. We developed an Ecopath model for Pamlico Sound, NC and its tributaries to address this issue. The model is comprised of 43 compartments with an emphasis on piscivores and their prey and represents the 2012–13 time period. We estimated total predator demand for fish prey and identified important species of forage fish and top piscivorous predators in Pamlico Sound. We compared local fishing fleet removals and predator consumption in forage fish, penaeid shrimp, and blue crabs. Finally, we evaluated the impact of increased predator demand on the system, by increasing biomass levels of five predators to equal their management thresholds and using mixed trophic impact analysis. Atlantic menhaden (Brevoortia tyrannus), anchovy (Anchoa hepsetus and A. mitchilli), spot (Leiostomus xanthurus), and Atlantic croaker (Micropogonias undulatus) were the most important forage fish in the system, representing over 80% of the fish consumed (by weight). Lizardfish (Synodus foetens) and bottlenose dolphins (Tursiops truncates) were top predators based on trophic level, while bluefish and longnose gar (Lepisosteus osseus) were top predators in terms of total fish consumption. The highest overlap in forage fish usage exists between fisheries and piscivores for Atlantic croaker and spot. Total forage fish removals through predation and harvest was greater than 65% of the production for each of the four-forage fish and, under the higher predator biomass model, total removals exceeded production for spot; total removals in either scenario did not exceed the production of penaeid shrimp and blue crab. Thus, the tradeoff between fisheries for forage fish and piscivores should be considered when assessing and managing fisheries in Pamlico Sound.

Paleoecology of a Lower Cretaceous (Barremian) fish community of the Morro do Chaves Formation, Sergipe-Alagoas Basin, NE Brazil

Opportunities to examine the structure of paleocommunities are extremely rare, due to the incompleteness of the fossil record. Regarding the Morro do Chaves Formation, there are many studies about the fauna and flora since 1870. However, paleoecological data are relatively scarce. According to the most recent study, the palynological records of the Morro do Chaves Formation were related to a disturbed paleoenvironment, caused by marine incursions in the northern sector of the Sergipe-Alagoas Basin during Lower Cretaceous. Thus, this paper aims to analyze the paleoecological relationships of the paleocommunity of fishes in the Morro do Chaves Formation, as the possible responses to the paleoenvironmental disturbances. From the basic matrix of abundance data for four fish orders found in 11 pelitic levels, similarity matrices were computed, using the Bray-Curtis distance coefficient. Cluster analysis by the unweighted pair-group method using arithmetic averages (UPGMA) was performed on these matrices, for grouping the levels. The advantages of multivariate analysis in paleoecological studies are also discussed. In addition, the Morro do Chaves Formation is composed of active piscivorous predators, benthophagous and planktiphagous fishes. The aulopiform fishes probably acted as top-down regulators in the paleocommunity, controlling the local fish populations. Mawsonia and “Lepidotes” are usually recorded in similar outcrops and inferred to be associated fauna. While Mawsonia likely possesses a sit-wait strategy, “Lepidotes” would be a relatively more active predator.

An Insight into the Feeding Ecology of Serranus scriba, a Shallow Water Mesopredator in the Northern Adriatic Sea, with a Non-Destructive Method

Serranus scriba is a common member of the coastal fish community in the Adriatic Sea, but knowledge about its feeding ecology is scarce. The aim of this paper is to present new evidence about its food preferences and feeding habits. An innovative non-destructive method of fecal pellet analysis was used for this study. This method does not require sacrificing specimens and the fish can be released back into the sea alive after the laboratory work. The results demonstrated that S. scriba mainly preys on decapods, followed by polychaetes, isopods, fish, mollusks and swarming shrimps. The calculated index of trophic diversity (ITD) value of 0.89 indicates that it is an opportunistic feeder that feeds on a wide range of different prey. According to the calculated trophic level of 3.43, which is higher than that of other members of the community, S. scriba is also an important piscivorous predator. With age, S. scriba undergoes an ontogenetic shift. The proportion of crustaceans, gastropods and polychaetes decreases with age and body size, while the proportion of fish increases.

In situ management options to improve crucian carp (Carassius carassius, L.) and brown trout (Salmo trutta, L.) population status in Central Europe: A case study from the Czech Republic.

The crucian carp (Carassius carassius, L.) and the brown trout (Salmo trutta, L.) are vanishing from freshwater ecosystems of central Europe. To conserve both species, tailor‐made conservation management of habitats and populations of both species was implemented and tested in the Czech Republic (central Europe). This management was adjusted to reflect the ecological needs of both species. This study aimed to describe the results of a tested in situ management and to analyze the population growth of brown trout and crucian carp under ideal conditions. An experiment was performed at 14 small gravel pit lakes. Seven of them were adjusted to fit the crucian carp habitat requirements while the other seven were treated as a control group. The same experiment was done on 14 smaller streams and with brown trout. The occurrence and growth of crucian carp and brown trout were surveyed over 2 years. A significantly faster growth of both crucian carp and brown trout was observed on the adjusted lakes and streams in comparison to the control group ones. Trout and carp prospered on small streams and gravel pit lakes (respectively) that were free of angling, fish stocking, pollution, piscivorous predators, and competition with hybridizing species like Prussian carp (Carassius auratus, L.) or hatchery‐reared brown trout.

Prospects for the monitoring of the great cormorant (Phalacrocorax carbo sinensis) using a drone and stationary cameras

Great cormorants (Phalacrocorax carbo sinensis) are piscivorous predators that cause high losses of fish in both aquaculture facilities and natural water bodies. Their monitoring (direct counting) in Central European carp (Cyprinus carpio) ponds is currently the only possible source of information for the evaluation of the extent of losses they cause to fish farmers. This method of monitoring is based on regular (optimally daily) counting by farmers, who are the applicants for compensation; however, this method can be easily biased by irregular observations and mistakes made in the counting of individual birds, particularly when cormorant flocks consist of tens or even hundreds of individuals. Such monitoring is not supported by any kind of record, except for the observer's notes on counting and can, therefore, be considered subjective to some extent. We introduce a new objective methodology for cormorant monitoring which eliminates the mistakes caused by the human factor, automatizes bird counting, and provides a record for the evaluation of the monitoring quality. The methodology is based on the use of drones equipped with a thermal camera and/or stationary 360° cameras placed on the monitored pond. The system automatically detects the arrival of cormorants to the pond and counts the individuals in the drone images. The methodology can be adapted to many other bird species on the ponds or appropriate water bodies.

Assessing the catch efficiency of predators in the presence of prey using experimental gillnets in a temperate estuary

Fishery-independent sampling is designed to representatively sample faunal communities based on the effort-standardized catch rates of individual gears. In estuaries, experimental gillnets are widely used due to their ability to passively sample mobile fish communities with multiple panels of decreasing mesh sizes. To test if concurrently collected prey in experimental gillnets create a trophic-related sampling bias for predatory or scavenging (hereafter, predators) species, we set large mesh gillnets comprising two treatments, baited (n = 80) and unbaited (n = 78), using a paired design in Back Sound, North Carolina. Furthermore, we analyzed data from the North Carolina Division of Marine Fisheries (NC DMF) estuarine gillnet monitoring program with boosted regression tree models to correlate estuarine predator occurrence with environmental factors (salinity, temperature), habitat presence, and families of common prey species as predictor variables. In our experimental manipulation, neither total catch nor community composition statistically varied between treatments, determined using permutational multivariate analysis of variance (PERMANOVA). However, species richness estimated using species accumulation curves was higher in baited gillnets, with one frequently caught species (Atlantic sharpnose sharks) collected exclusively in baited gillnets. In NC DMF surveys, prey group variables were more important (average model importance; 10% ± 8.8% SD) than habitat composition (2% ± 1.7%) to the presence of predators, but less than abiotic environmental variables (21.1% ± 13.1%). This combined manipulative and mensurative study revealed mixed evidence towards increased catch efficiency of predatory fish collected in widely used experimental gillnets. These results should be considered in refining abundance estimations for estuarine predators, as catch efficiency for some piscivorous predators may vary in relation to the abundance and catch efficiency of prey.

Shoaling in the Trinidadian guppy: costs, benefits, and plasticity in response to an ambush predator

AbstractShoaling, the formation of social groupings in fish, can provide benefits including reduced predation risk. However, it can also inflict costs including increased competition for resources, transmission of parasites, and salience to predators. Trinidadian guppies exhibit inter-population variation in shoaling behavior where individuals coexisting with large piscivorous predators (high predation localities) spend most of their time in shoals and those coexisting with an ambush predator, Rivulus hartii (recently, Anablepsoides hartii), that preys primarily on smaller guppies (low predation localities) do not. It has been suggested that this predator selects for reduced shoaling because doing so reduces salience to the predator. Here, as far as we know, we perform the first test of this idea. First, we investigated the effectiveness of shoaling in encounters with this predator. In survival trials, where one rivulus interacted with a group of guppies, we found that the predator was more likely to attack individuals in shoals than singletons. However, we also found that attacks directed at shoals were less likely to succeed. This suggests that the optimal strategy for guppies co-existing with this predator is to reduce shoaling to reduce the probability of being attacked, and to form shoals when an attack is initiated. We then asked if guppies modified their shoaling behavior in response to visual and olfactory cues from this predator during development. We found changes in guppy behavior in response to the treatment: guppies increased shoaling behavior when there was heightened risk of predation.

Mini DNA barcodes reveal the details of the foraging ecology of the largehead hairtail, Trichiurus lepturus (Scombriformes: Trichiuridae), from São Paulo, Brazil

Abstract The largehead hairtail, Trichiurus lepturus, is an opportunistic, voracious, and piscivorous predator. Studies of fish feeding behavior based on the analysis of stomach contents are limited by the potential for the visual identification of the ingesta. However, molecular tools, in particular DNA barcoding, have been used successfully to identify stomach contents. When morphological analyses are not possible, molecular tools can precisely identify the components of the diet of a fish based on its stomach contents. This study used mini barcoding to identify food items ingested by T. lepturus off the northern coast of São Paulo State, Brazil. Forty-six sequences were obtained and were diagnosed as belonging to six different fish species: Pimelodus maculatus, Paralonchurus brasiliensis, Isopisthus parvipinnis, Opisthonema oglinum, Harengula clupeola, and Pellona harroweri or as belonging to the genera Lycengraulis and Sardinella. Trichiurus lepturus is an opportunistic predator that will exploit an available prey of an appropriate size. The results indicate that these fish migrate to warmer waters, such as those found in estuarine environments, at certain times of the year, where they exploit prey species that reproduce in this environment. One example was Pimelodus maculatus, which was the prey species most exploited based on the analysis of the material collected.

Tooth Structure and Replacement of the Triassic Keichousaurus (Sauropterygia, Reptilia) From South China

The small-sized sauropterygianKeichousaurus huiwas one of the most abundant marine reptiles from the Triassic Yangtze Sea in South China. AlthoughKeichousaurushas been studied in many aspects, including the osteology, ontogeny, sexual dimorphism, and reproduction, the dentition of this marine reptile was only briefly described in external morphology. In this study, we provide new information onKeichousaurustooth implantation, histology, and replacement based on a detailed examination of well-preserved specimens collected in the past decades. The tooth histology has been investigated for the first time by analyzing cross-sections of premaxillary teeth and the tooth attachment and implantation have been further revealed by X-ray computed microtomography. We refer the tooth replacement ofKeichousaurusto the iguanid replacement type on the basis of the observed invasion of small replacement tooth into the pulp cavity of the functional tooth. Given the resemblance to other extinct and modern piscivorous predators in the morphology and structure of teeth,Keichousaurusmight mainly feed on small or juvenile fishes and some relatively soft-bodied invertebrates (e.g., mysidacean shrimps) from the same ecosystem.

Diel vertical movements of a coastal predator, the roosterfish (

The roosterfish (Nematistius pectoralis) is a piscivorous predator targeted extensively in recreational fisheries throughout the eastern tropical Pacific; however, its biology is poorly understood. To address these shortcomings, we investigated vertical habitat use and behaviour of roosterfish in coastal Panama using pop-up satellite archival tags. Nearly 5000 h of vertical movement data across 274 days from five fish showed that roosterfish largely used the upper 10 m and 20 m of the water column during the night-time and daytime respectively, and rarely left the mixed layer. Roosterfish diving behaviour showed a clear diurnal pattern, with oscillatory dives beginning during dawn and continuing through dusk. Accelerometer data showed that this period was also associated with a sharp increase in activity during dawn and a decrease around sunset. Whereas previous work in shallow systems (&lt;20 m) with limited structure showed that roosterfish were vertically active sporadically throughout the day and mostly during crepuscular periods, our study showed that in a habitat with continuous structure, roosterfish were continuously vertically active from dawn till dusk, possibly because foraging behaviours were limited by light levels rather than prey-congregating structure. Such changes in dive patterns illustrate how habitat influences behaviour and the importance of studying organisms throughout their range.

Harvest Rates of Rheophilic Fish Vimba vimba, Chondrostoma nasus, and Barbus barbus Have a Strong Relationship with Restocking Rates and Harvest Rates of Their Predator Silurus glanis in Lowland Mesotrophic Rivers in Central Europe

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.