The effects of environmental factors and fisheries management on recreational catches of perch Perca fluviatilis in the Czech Republic

The Eurasian perch Perca fluviatilis is an important fish species in both commercial and recreational fisheries. However, there is concern that perch populations in Central Europe are decreasing. This study aimed to assess the effects of environmental factors and management on recreational perch catches. Data from individual angling logbooks collected by the Czech Fishing Union on 229 fishing grounds during the period 2005–2016 were used in this study. In total, almost 60 000 perch weighing 17 500 kg were recorded. During the study period, total perch catches decreased by 60%, catch per fishing visit decreased by 70%, average body weight of caught perch increased by 18%, and percentage of fishing grounds with perch catches decreased by 13%. The results indicated that the decreasing catches were due to increasing fishing pressure. Further, fishing grounds with higher fishing visit rates had higher catches in general but lower catch per fishing visit. Larger and more productive rivers also showed higher catches. In contrast, the intensity of fish stocking did not affect catches. In conclusion, perch populations in Central Europe are likely under high fishing pressure, and the pressure is further increasing

The effect of a large-scale fishing restriction on angling harvest: a case study of grayling Thymallus thymallus in the Czech Republic

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 7 yr, 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

Diet of Eurasian otter (Lutra lutra) in relation to the stocking of brown trout (Salmo trutta m. fario) and grayling (Thymallus thymallus)

Cílem této studie bylo vyčíslit predační tlak ze strany vydry na vysazované pstruhy a lipany. Práce zkoumala složení potravy vydry říční (Lutra lutra) na potoce Chotýšanka (střední Čechy) za zimní období (90 dní). Jako metodu jsme zvolili sběr trusu vydry na stanovené lokalitě a jeho následnou analýzu. Vysazování ryb probíhalo převážně ve druhé polovině roku 2005. V tomto roce proběhlo vysazení 5000 ks potoční formy pstruha obecného (Salmo trutta m. fario) o velikosti cca 10 cm, 480 ks pstruha duhového (Oncorhynchus mykiss) o velikost cca 30 cm a 600 ks lipana podhorního (Thymallus thymallus) o velikosti cca 10 cm. Sběr trusových hrudek proběhl v zimě 2005/2006. V potravě vydry říční bylo identifikováno celkem 1531 ryb. Ryby tvořily hlavní složku potravy vydry na této lokalitě (téměř 85 %). Většina ulovených ryb dosahovala velikosti do 13 cm a hmotnosti do 20 g. Největší podíl potravy tvořily rybářsky nevýznamné druhy ryb, především hrouzek obecný (Gobio gobio). Další významné druhy ryb v potravě byly jelec tloušť (Squalius cephalus), kapr obecný (Cyprinus carpio), okoun říční (Perca fluviatilis), pstruh obecný a pstruh duhový. Většina ulovených ryb dosahovala velikosti do 13 cm a hmotnosti do 20 g. Pstruzi obecní tvořili 1,80 % hmotnosti zkonzumované kořisti, pstruzi duhoví pak 10,90 % hmotnosti....This study aimed to evaluate otter predation on stocked trout and grayling. The diet composition of piscivorous Eurasian otters (Lutra lutra) was studied on the stream Chotýšanka in central Bohemia using spraint (otter faeces) analysis during one winter period (90 days). Stocking took place mostly in the second half of 2005. Around 5000 hatchery-reared brown trouts (Salmo trutta m. fario) of size about 10 cm, 600 graylings (Thymallus thymallus) of the same size and 480 rainbow trouts (Oncorhynchus mykiss) of size about 30 cm were stocked into the stream. Spraints were collected in December 2005 and January 2006. We found and identified 1531 fish in the spraints. The primary food source of otters was fish (almost 85 % of biomass). The main fish prey was small - sized, below 20 g in weight and 13 cm in length. The bulk of otter's diet consisted of less - valued species, especially the gudgeon (Gobio gobio). Other frequently consumed fish species were the European chub (Squalius cephalus), the common carp (Cyprinus carpio), the European perch (Perca fluviatilis), the brown trout and the rainbow trout. Consumption of stocked brown trout was 1,80 %, while cosumption of stocked rainbow trout was 10,90 % of biomass. Otters in this area consumed about 723 - 1446 brown trouts and 72 - 144 rainbow trouts...Institute for Environmental StudiesÚstav pro životní prostředíPřírodovědecká fakultaFaculty of Scienc

The Effect of Fishery Management on the Yield of the Critically Endangered European Eel <i>Anguilla anguilla</i> in Mesotrophic Rivers and Streams in Central Europe

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

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

Abstract 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

Influence of age and rearing conditions of a fish on the chance to survive in the wild

The task of this thesis is to summarize all the most important biotic and abiotic factors that can influence chances of reared fish to survive in the wild. It contains some of the most frequently reared and popular fishes, such as Sander lucioperca (pike perch), Samo trutta (trout), Micropterus salmoides (largemouth bass), Esox lucius (northern pike), Esox masquinongy (muskellunge) and the hybrid of northern pike and muskellunge, the tiger muskellunge. Mainly the factors such as success, survival, rate of growth and mortality have been studied. Survival increases with the size of the fish because of the fact that larger fish can easily avoid predation. Pellet-reared fish show higher mortality than minnow-reared fish because of the loss due to predation and also slightly worse ability to catch living prey and obtain food, even though their diet contains similar species. Temperature can also affect the mortality of the stocked fish, mainly when the temperature difference between the rearing pond or hatchery and the new environment exceeds 10 řC, which brings loss of majority of the stocked fish. It has been revealed that genetics is very important during the process of stocking, while fish from the local population show better abilities to adapt to the environment than those from other geographic..

Diet of Eurasian otter (Lutra lutra) in relation to the stocking of brown trout (Salmo trutta m. fario) and grayling (Thymallus thymallus)

This study aimed to evaluate otter predation on stocked trout and grayling. The diet composition of piscivorous Eurasian otters (Lutra lutra) was studied on the stream Chotýšanka in central Bohemia using spraint (otter faeces) analysis during one winter period (90 days). Stocking took place mostly in the second half of 2005. Around 5000 hatchery-reared brown trouts (Salmo trutta m. fario) of size about 10 cm, 600 graylings (Thymallus thymallus) of the same size and 480 rainbow trouts (Oncorhynchus mykiss) of size about 30 cm were stocked into the stream. Spraints were collected in December 2005 and January 2006. We found and identified 1531 fish in the spraints. The primary food source of otters was fish (almost 85 % of biomass). The main fish prey was small - sized, below 20 g in weight and 13 cm in length. The bulk of otter's diet consisted of less - valued species, especially the gudgeon (Gobio gobio). Other frequently consumed fish species were the European chub (Squalius cephalus), the common carp (Cyprinus carpio), the European perch (Perca fluviatilis), the brown trout and the rainbow trout. Consumption of stocked brown trout was 1,80 %, while cosumption of stocked rainbow trout was 10,90 % of biomass. Otters in this area consumed about 723 - 1446 brown trouts and 72 - 144 rainbow trouts..

Diet of Eurasian otter (Lutra lutra) in relation to the stocking of brown trout (Salmo trutta m. fario) and grayling (Thymallus thymallus)

This study aimed to evaluate otter predation on stocked trout and grayling. The diet composition of piscivorous Eurasian otters (Lutra lutra) was studied on the stream Chotýšanka in central Bohemia using spraint (otter faeces) analysis during one winter period (90 days). Stocking took place mostly in the second half of 2005. Around 5000 hatchery-reared brown trouts (Salmo trutta m. fario) of size about 10 cm, 600 graylings (Thymallus thymallus) of the same size and 480 rainbow trouts (Oncorhynchus mykiss) of size about 30 cm were stocked into the stream. Spraints were collected in December 2005 and January 2006. We found and identified 1531 fish in the spraints. The primary food source of otters was fish (almost 85 % of biomass). The main fish prey was small - sized, below 20 g in weight and 13 cm in length. The bulk of otter's diet consisted of less - valued species, especially the gudgeon (Gobio gobio). Other frequently consumed fish species were the European chub (Squalius cephalus), the common carp (Cyprinus carpio), the European perch (Perca fluviatilis), the brown trout and the rainbow trout. Consumption of stocked brown trout was 1,80 %, while cosumption of stocked rainbow trout was 10,90 % of biomass. Otters in this area consumed about 723 - 1446 brown trouts and 72 - 144 rainbow trouts..

The role of fish-eating predators and socio-economic trends in recreational fishing

Recreational fishing is a very important leisure activity and one of the most important ways how humans influence freshwater habitats and wild fish populations. Both fish-eating predators and socio-economic trends play a major role in recreational fishing. This thesis found that the Eurasian otter feeds mainly of small (5-10 g) and very abundant fish species of low angling value. In this case, gudgeon Gobio gobio dominated in the otter diet. The overlap between catches of otters and anglers was very low, and commercially important salmonids made up only 10 % of the otter diet by biomass. Cormorants also prey mostly on smaller (10-100 g) a very abundant fish species. In this case, roach Rutilus rutilus dominated in the cormorant diet. The overlap between catches of cormorants and anglers was also quite low. Commercially important fish species made up less than 10 % of the cormorant diet. Even though cormorants consume mostly smaller fish, they are potentially removing fish that serve as prey for piscivores, and they are also removing smaller fish that would grow into angling size. The Atlantic salmon Salmo salar reintroduction programme has not yet been successful. However, cormorant predation is not the main reason for its low success. The main problem is somewhere on the lower River Elbe in..

Fisheries Management of the European Catfish Silurus glanis Is Strongly Correlated to the Management of Non-Native Fish Species (Common Carp Cyprinus carpio, Rainbow Trout Oncorhynchus mykiss, and Grass Carp Ctenopharyngodon idella)

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&ndash;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