## 2 Materials and Methods  
### Study Area  
The data for this study were collected through the whole Bohemian region, which covers overall 70% of the Czech Republic (52,065 km\({}^{2}\)). The Czech Republic is in central Europe. Over 3% of the Czech population engages in recreational fishing, which results in 250,000 anglers visiting the local streams approximately 1 million times per year (data from the year 2020) [7]. The numbers of anglers and fishing visits increased by 5% between the years 2000 and 2018 [10].  
There are 82 streams in the study area, which are further separated into 198 individual fishing sites (stretches of streams) that are divided by a visible structure (a weir, a dam, or a bridge). Rivers wider than 5 m were excluded from this study. The total area of the fishing sites is 204 hectares of water surface. They are all smaller (0.2-10 ha of surface area, with a median value of 1.2 ha). The streams are located in the temperate zone. They belong either to the North Sea Basin, to the Black Sea Basin, or to the Baltic Sea Basin. The streams are located mostly in the lowlands (200-600 m above sea level), are 2-8 m wide (the median value is 3 m), have mesotrophic or eutrophic nutrient levels, and have a fish biomass of 150-300 kg per hectare. They are dominated by brown trout _Salmo trutta_ and gudgeon _Gobio gobio_[11].  
In total, 170,000 fish weighing 87 tons were harvested in the streams of the Bohemian region in the year 2020 [12]. This number is declining every year and fell by 10% over the years 2000-2018 [11]. Anglers mostly harvested salmonids, mainly rainbow trout _Oncorhynchus mykiss_ (70% by biomass), brown trout _Salmo trutta_ (10%), and European grayling _Thymallus thymallus_ (2%). The remaining fish harvested consisted of common carp _Cyprinus carpio_ (5%), followed by other cyprinids (bream _Abramis brama_, European chub, vimba bream _Vimba vimba_, roach, and bleak _Alburnus alburus_--4% altogether) and predatory fishes (European catfish _Silurus glanis_, northern pike _Esov lucius_, perch _Perca fluviatilis_, and pikeperch _Sander lucioperca_--4% altogether). The remaining 27 harvestable species of fish formed 5% altogether [12]. Rainbow trout is stocked using the put-and-take fisheries management and so it dominates the streams over several weeks during the trout fishing season (April and May) before anglers catch most of them [7].  
Recreational fishing in the study area is heavily regulated by the state. Many fish species that are targeted by anglers have bag and slot limits that prevent anglers from overfishing the fish populations. Brown trout has a minimum legal angling size of 25 cm TL (total length) and a closed season from 1 September to 16 April [7].  
The state aquaculture sector focuses little on production of brown trout--it forms under 1% of Czech aquaculture production [7]. Instead, the traditional fish such as common carp, rainbow trout, or European catfish form over 80% of the aquaculture production [7]. The aquaculture provides larger fish (30 cm TL and larger) for food and smaller fish (1-20 cm TL) for stocking purposes. It is approximately 10 times cheaper to stock small 0 + brown trout instead of large adult ones, so the financial returns of stocking small fish are better [7].  
Owners of small hydropower plants are obliged to keep the water level on the streams on a minimum of 50% of the full capacity of the stream [7].