Fishless shallow lakes of Southern Patagonia as habitat for waterbirds at the onset of trout aquaculture

• 1. The Strobel Meseta, a basaltic plateau of Patagonia (Santa Cruz Province, Argentina), holds thousands of shallow fishless lakes that are prime habitat for many species of waterbirds, including some considered ‘near threatened’. In recent years, several lakes have been stocked with trout which has created uncertainty about the potential effects on the recipient ecosystem.
• 2. Limnological and topographical analyses were performed in a group of 32 lakes of the Strobel Meseta in order to characterize and classify individual lakes of the meseta based on their limnological and topographic features, analyze the association between lake type and use by aquatic birds in general and by the endemic hooded grebe (Podiceps gallardoi) in particular, and evaluate the overlap between trout aquaculture and critical habitat for waterbirds.
• 3. The lakes were classified by multivariate analyses into four characteristic types: turbid, high conductivity lakes (T), small vegetated lakes (SV) and larger lakes which were subdivided into either vegetated (LV) or unvegetated (LU). In general, macrophyte cover was the main classificatory variable, whereas conductivity, pH, surface, and depth contributed moderately. Large vegetated lakes were generally found to be important for waterbirds and provided critical habitat for the hooded grebe, whereas trout farmers largely favoured large unvegetated lakes. However, since some large vegetated lakes have already been stocked, there is some level of geographical overlap between waterbird habitat and trout farming.
• 4. The existence of some level of spatial segregation between production and critical waterbird habitat affords opportunities for designing a spatially‐based management system for trout aquaculture.

Copyright © 2008 John Wiley & Sons Ltd.     

Precautionary rules for exotic trout aquaculture in fishless shallow lakes of Patagonia: minimizing impacts on the threatened hooded grebe (Podiceps gallardoi)

• 1. Conflicts between habitat use and conservation are inherent to the management of wetlands. A major challenge for their management is to preserve habitat while addressing the demands from multiple users. In southern Patagonia (Argentina), a growing aquaculture activity based on rainbow trout introductions in shallow lakes is generating concerns about the effects on the waterbird fauna, including some endemic species.
• 2. Generalized linear models (GLM) were used to analyse data on the endemic hooded grebe (Podiceps gallardoi) collected over a diverse set of lakes to: (1) build presence‐absence models as a function of environmental variables; (2) assess current and potential overlap with trout aquaculture; (3) explore the power of alternative lake assignment algorithms based on habitat variables to segregate critical habitat and aquaculture activities; and (4) explore the correlation between the probability of grebe presence and their abundance in given lakes.
• 3. Hooded grebe presence is clearly correlated with macrophyte cover, lake area, and water conductivity. Medium size lakes, with a combination of emerging macrophytes, adjacent to open water areas had the highest probability of both hooded grebe presence and abundance.
• 4. Different lake allocation scenarios are identified that could grant significant protection to hooded grebes without substantial losses for trout producers. The a priori probability to hold hooded grebe, assigned by the model based on lake characteristics, provides a tool that can be used by managing authorities to derive precautionary management rules to regulate aquaculture and to preserve primary hooded grebe habitat. Copyright © 2009 John Wiley & Sons, Ltd.

     

Aquatic macroinvertebrates from littoral vegetated lakes in arid Patagonia: The influence of fish introduction on community structure

1. Wetlands in arid regions are characterized by their great heterogeneity, often including endemic species that contribute to regional aquatic biodiversity. In the Patagonian steppe, most lakes are naturally fishless and sustain a rich aquatic biodiversity, including endemics; however, many of these lakes have been stocked with Oncorhynchus mykiss (rainbow trout) during recent decades. The introduction of predatory fish into aquatic ecosystems naturally devoid of these organisms can produce profound alterations in the structure of the original communities and in the configuration of their biotic assemblages.
2. Aquatic invertebrates play important roles in both the structure and functioning of freshwater ecosystems, including their contribution to global biodiversity and their cascading effects across ecosystem boundaries.
3. The aim of this study was to assess the effect of introduced non-native fish on the pleustonic macroinvertebrate assemblage. Samples were taken from 10 shallow Patagonian lakes (five fishless and five stocked with fish) in two consecutive warm periods.
4. Lakes with fish had higher conductivity and phosphate values. Higher inter-annual differences were also observed in lakes with fish for phytoplanktonic chlorophyll a, nitrate, phosphate, conductivity, and water temperature.
5. The community structure (relative abundance of different taxa, species composition, and diversity index) was affected by the presence of rainbow trout, with the differences mainly driven by the relative abundance of Ostracoda, Hyalella, Chironomidae, and Haliplus species.
6. This approach can be used to assess the required conservation actions in shallow Patagonian steppe lakes, which have been listed as priority areas for waterbird conservation. Specifically, this study provides a baseline for monitoring future trends of the macroinvertebrate communities and for evaluating conservation and management efforts over time.

     

Climate variability and trends in the reproductive habitat of the critically endangered hooded grebe

1. The population of the critically endangered hooded grebe (Podiceps gallardoi) has decreased drastically during recent decades. The effects of climate change on their reproductive area (Southern Patagonia) have been proposed as one of the potential causes of their critical situation. However, there is much uncertainty about climate variability and climate trends at local scales in Patagonia, and their effects on the hooded grebe habitat.
2. Variability and trends in temperature, precipitation, and wind from 1960 to 2016 in one of the most important reproductive areas of hooded grebe – the Lake Strobel plateau – were analysed. A Landsat satellite image series (1973–2016) was used to evaluate changes in lake area in the region.
3. Generalized linear models were used to analyse the relationship between the variation in lake area and climatic variables, including the Antarctic Oscillation Mode (AAO) index, which is the most important year to year pattern in climate variability at high latitudes of the Southern Hemisphere.
4. High inter‐annual variability and increasing coefficients of variation in precipitation and wind were found, as well as a significant positive trend in temperature. Total lake area, as well as the area specifically used by hooded grebe to reproduce, decreased significantly over time, with high inter‐annual variability. Variation in lake area was significantly correlated with variation in precipitation, and with the AAO index.
5. The loss of reproductive habitat may force the hooded grebe to use sub‐optimal environments, such as lakes with lower food supply, lower macrophyte cover, and less protection from wind – a potential major handicap for this declining species.
6. Information on lake variation in response to climatic variability could be used to guide hooded grebe conservation strategies, directing more resources and special efforts to those reproductive lakes that are more resilient to the effects of climate fluctuations.

     

Effects of stocked trout on native fish communities in boreal foothills lakes

Nasmith LE, Tonn WM, Paszkowski CA, Scrimgeour GJ. Effects of stocked trout on native fish communities in boreal foothills lakes.
Ecology of Freshwater Fish 2010: 19: 279–289. © 2010 John Wiley & Sons A/S Abstract – Ecological effects of stocking nonnative trout into lakes are receiving increased attention, especially in alpine environments. We assessed effects of stocked trout on native forage fishes in the boreal foothills of Alberta (Canada) by comparing fish density, population size structure and spatial and temporal activities in stocked and unstocked lakes over 3 years (2005–2007). The numerically dominant dace (primarily Phoxinus spp.) were larger in stocked lakes, consistent with size‐limited predation. Dace were also more crepuscular and concentrated on the lake‐bottom in stocked lakes, compared to more daytime activity in the water column in unstocked lakes. There were, however, no demonstrable effects of trout on the abundance of forage fish. The lack of major population‐level impacts of stocked trout suggests that current stocking practices, characteristics of boreal foothill lakes (e.g. thermal structure, abundant invertebrates, dense macrophytes) and/or behavioural adjustments of forage fish contribute to healthy native fish populations in our stocked lakes.     

Is the decline of birds and amphibians in a steppe lake of northern Patagonia a consequence of limnological changes following fish introduction?

• 1. Laguna Blanca, in Laguna Blanca National Park, is a lake in Patagonia which has been designated as a Ramsar site since 1971 because of bird diversity and abundance and importance for nesting, particularly for the black neck swan, Cygnus melanocoryphus. It is also valued for its populations of endemic amphibians, Atelognathus patagonicus and Atelognathus praebasalticus.
• 2. Avian and amphibian populations have decreased dramatically in recent years. Percichthys colhuapiensis, Percichthys trucha (Pisces, Percichthyidae), Salmo trutta and Oncorhynchus mykiss (Pisces, Salmonidae) were introduced into Laguna Blanca in 1965. Since 1986, no Atelognathus frogs have been found. The abundance of swans and coots, which are strongly associated with macrophytes for nesting and feeding, has diminished drastically, whereas piscivorous birds have increased.
• 3. The fishless condition of some neighbouring small lakes with abundant pond weeds, aquatic birds and endemic amphibians, was assessed in order to compare the physical and chemical characteristics and the quantitative composition of the benthos among lakes. Fish presence at Laguna Blanca and its absence at El Burro, Antiñir and Jabón lakes, were confirmed. Compared with previous results, it seems that the abundance of Amphipoda (Hyalella), Copepoda and Cladocera at Laguna Blanca has decreased, while Acari has increased and Notostraca has disappeared. Water transparency has diminished in Laguna Blanca and now is lower than that of fishless lakes.
• 4. P. colhuapiensis were captured only in Laguna Blanca, with the highest captures in the littoral zone. The population shows rapid individual growth in the early years and an absence of fish older than 6 years. The preponderance of benthos and the presence of macrophytes in the gut contents of adult P. colhuapiensis appear to indicate that they are important consumers of these resources.
• 5. This paper concludes that fish introduction in Laguna Blanca led to a complex trophic cascade effect (fish predation on tadpoles, fish competition for avian food, bottom disturbance, zooplankton reduction) producing deleterious effects on the amphibian and bird populations.

Copyright © 2006 John Wiley & Sons, Ltd.     

Food consumption rates of piscivorous brown trout (Salmo trutta) foraging on contrasting coregonid prey

Knowledge of predator–prey dynamics is essential to understand ecosystem functioning. Quantification of such interactions is important for fisheries management, in particular in the case of stocking programmes. Here, food consumption rates (FCR) were quantified for wild and stocked piscivorous brown trout, Salmo trutta L., in three subarctic lakes with contrasting coregonid (Coregonus spp.) prey communities, using the Wisconsin and the Elliott–Hurley bioenergetic models. FCR was highest for stocked brown trout in lakes with the lowest predator densities, and lowest for wild brown trout. Although FCR estimate may vary somewhat depending on the specific model used, such tools are imperative for the proper impact assessment of brown trout stocking programmes and for the provision of advice on optimal stocking densities.     

Non‐indigenous fish in protected spaces: Trends in species distribution mediated by illegal stocking

1. Many freshwater non‐indigenous species (NISs) are stocked for recreational fishing, in some cases illegally in protected areas. In this study, fish communities were monitored using environmental DNA, electrofishing and anglers’ catches as the sources of samples in a mountainous Biosphere Reserve in Asturias (northern Spain), where stocking is forbidden.
2. Three NISs have been introduced illegally in the protected area and have shown increasing populations in the last two decades. Two species used as fishing bait, Squalius carolitertii (chub) and Phoxinus phoxinus (minnow), are expanding in running waters. Oncorhynchus mykiss (rainbow trout) was also detected and is likely to have been introduced for angling or from fish farm escapes.
3. The results suggest that sustained illegal stocking contributed to the increase of the three NISs. In contrast, Salmo trutta (brown trout) of northern European lineages, identified from *90 alleles at the LDH‐C1 locus, and formerly legally stocked for angling, is decreasing, most likely as a result of climate change. Climate change could also contribute to the expansion of the two non‐indigenous cyprinids to colder upstream areas.
4. Through the application of a social survey, it was found that unlike other population groups, anglers in the region significantly preferred stocking over environmental improvement for the management of fish populations. The results obtained suggest that raising the awareness of anglers about the importance of safeguarding native fish species could help to prevent the spread of NISs in protected areas.

     

Spawning aggregation behaviour in the Creole perch,Percichthys trucha (Percichthyidae): A target species for conservation

1. Habitat fragmentation and loss threaten freshwater biodiversity worldwide. Habitats that are essential as fish spawning and nursery sites are critical, and must be identified for conservation purposes. Littoral zones within Patagonian lakes, especially shallow vegetated areas, represent important areas for the Creole perch, Percichthys trucha.
2. Spawning behaviour has been little studied, so it is not known whether these movements are performed in groups. A particular area of a deep lake in northern Patagonia was studied to identify the environmental conditions under which spawning occurs, and to analyse spawning aggregation behaviour in relation to the lunar cycle.
3. To identify spawning sites, spawning occurrence time, and the environmental parameters that determine it, fish capture data were analysed. Underwater cameras were also set up at three depth strata in the shallow zone to detect spawning aggregation behaviour. Aggregation was scored as the greatest number of individuals present in a single frame, and the number present per depth stratum. The relationship between the lunar cycle and Creole perch abundance by depth was then determined.
4. This is the first visual record of a spawning bed and the spawning aggregation behaviour of Creole perch in Patagonian lakes. The abundance of mature Creole perch in the shallow strata during the austral spring suggests that vegetated areas constitute spawning sites. Spawning aggregation takes place at a shallow depth 2 days before the full moon.
5. As the reproductive behaviours of Creole perch are important phenomena in the life history of the species, the results of this study have important implications for conservation and management.

     

Diet of the Eurasian otter (Lutra lutra) on the River Gradac,Serbia: Predation in a brown trout‐dominated stream

1. Prey preference and seasonal variation in the diet of the Eurasian otter, Lutra lutra (Linnaeus, 1758), were examined by the analysis of 789 spraint samples collected along a 10‐km section of a small lowland salmonid river in Serbia, with a trout farm situated in its lower part, from June 2009 to March 2012. Of particular interest was any possible impact of the otter on brown trout, which is important to investigate for preventing and managing any potential conflicts with fishers and fish farmers.
2. Fish were by far the most important otter prey, followed by crayfish. Cottus gobio Linnaeus, 1758 (the European bullhead) was the most common prey species, probably because of the combination of its abundance and easy catchability. Other prey contributed very little to the diet of the otters. Of 11 fish species present in the river, five were found in the otter diet: the European bullhead, Salmo trutta Linnaeus, 1758 (brown trout), Squalius cephalus (Linnaeus, 1758) (chub), Barbus balcanicus Kotlík, Tsigenopoulos, Ráb & Berrebi, 2002 (the Danube barbel), and Phoxinus phoxinus (Linnaeus, 1758) (the Eurasian minnow). The bullhead was the only positively selected species, however. The share of fish prey in the otter diet was stable throughout the year, except for a decrease noticed during the summer.
3. The results suggest that otters on the River Gradac target smaller, sedentary, and less nutritious prey. Owing to a small percentage of brown trout in otter spraints, we surmise that otters do not represent a major biological or economic threat, either to the native trout population in the river or to the trout from the nearby fish farm.
4. Although there are no reports of otters causing damage to the trout population in the local fish farm, it is advisable to establish mechanisms for the compensation of fish farmers in case such damage does occur.
5. The data presented in this paper can be used to contribute to the conservation of the otter in stream habitats, especially because there are no published studies on the dietary requirements of otter in Serbia.

     

Resource use of native and stocked brown trout Salmo trutta L., in a subarctic lake

Habitat use, food composition and growth of stocked and native brown trout, Salmo trutta L., were studied in the subarctic Lake Muddusjärvi in northern Finland. Stocked brown trout and native brown trout preferred littoral and pelagic areas. Trout were stocked in October. In June stocked trout fed primarily on invertebrates while native fish were piscivorous. From July onwards the composition of the diet of both stocked and native trout was similar and consisted almost entirely of small‐sized whitefish. Brown trout were already piscivorous at a length of about 20 cm. The mean length of prey consumed was about 12 cm. Mean length‐at‐age was similar from the second year in the lake despite of the larger size of stocked fish during the first year in the lake.     

Broad‐scale habitat classification variables predict maximum local abundance for native but not non‐native trout in New York streams

相似文献   

From a research study to a conservation partnership: Developing approaches to restoring common scoter populations

• 1. Like many sea‐duck populations, the British breeding population of common scoters Melanitta nigra has declined markedly. In 2009, a study was established to measure factors affecting lake use by breeding scoters, to inform conservation measures. That study, published in Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) in 2016, showed that lakes used by scoters had relatively more shallow water and large invertebrates. Furthermore, lakes with abundant large invertebrates had relatively few brown trout Salmo trutta. These results probably reflect the importance of foraging habitat (shallow water), prey abundance (large invertebrates), and competition for prey (trout abundance) in influencing scoter lake use.
• 2. To develop this study, additional research, and scoter conservation measures, we formed a long‐term partnership, comprising nature conservation non‐governmental organizations, statutory agencies, fisheries managers and the regional hydropower company. The partnership meets regularly to coordinate and review research and develop conservation measures, building on the earlier lake‐use study.
• 3. At key scoter lakes managed for hydropower, the partnership negotiated a revised water level management regime, favouring shallow water availability in the breeding season. This regime was informed by additional research, showing the value of certain islands for nesting scoters, and water level requirements to maintain these as islands.
• 4. In a different key scoter area — an extensive near‐natural peatland where recreational angling takes place — the partnership established a trial of increased brown trout angling, with increased fish removal, to determine whether this would increase invertebrate prey abundance and benefit breeding scoters. Both conservation interventions are currently being evaluated by detailed monitoring.
• 5. Overall, the earlier study published in AQC, was important in strengthening and informing our researcher–practitioner partnership, as we collaborated within an adaptive management framework to reverse scoter declines. Long‐term interdisciplinary partnerships are likely to have an important role to play in general, for the successful conservation of aquatic biodiversity.

     

Angling catch returns as indicators of the status of upland trout lakes

Abstract. Over the period 1966–1983 angling catches from the Penrhyncoch trout, Salmo trutta L., lakes in mid-Wales showed a steady decline while catches from the nearby Trisant lakes steadily increased. By the early-mid 1970s some of the Penrhyncoch lakes had ceased to exist as viable fisheries. The declining catches from many of the Penrhyncoch lakes appeared to be attributable to the recent acidification of the lakes which has led to a severe decline in the size of the native trout population and a high mortality among stocked hatchery-reared trout, Salmo trutta L. The increase in catches from the Trisant lakes appears to be due to a shift in angling pressure but the relatively high catches are a real reflection of high trout population densities in lakes unaffected by acidification. The average annual angling catch from the Penrhyncoch and Trisant lakes over 1966–1983 was 1·2 and 6·7 kg ha^?l respectively. Catches per unit area from the Trisant lakes compare favourably with other much larger upland reservoirs.     

Hatchery‐reared endangered Colorado pikeminnow (Ptychocheilus lucius) undergo a gradual transition to piscivory after introduction to the wild

1. Disruption of ecosystems by human activities has caused worldwide extinction threats, which has prompted conservationists to implement captive breeding programmes that aid the recovery of imperilled species. Understanding factors that limit the survival of hatchery‐spawned fishes after stocking is critical to future conservation efforts using captive populations.
2. As the size at which juvenile piscivorous fishes shift to consuming other fish can influence their survival, the transition to piscivory by hatchery‐spawned Ptychocheilus lucius Girard, 1856 (Colorado pikeminnow) was investigated after stocking the San Juan River in New Mexico, Colorado, and Utah, USA. The stable isotope ¹⁵N was used to track ontogenetic changes in the trophic position of individuals stocked at age 0, with the expectation that they would become fully piscivorous by age 2. By sampling the isotopic signatures of Colorado pikeminnow across multiple years, the ability of river discharge and densities of fish prey to explain interannual variation in trophic position was also explored.
3. Annual variation in river flow and the densities of fish prey had little predictive power in explaining variation in δ¹⁵N of age‐1 or age‐2 Colorado pikeminnow. After assessing the isotopic signatures of potential prey, a Bayesian isotopic mixing model suggested that invertebrates comprised nearly 25% of the diet of of both age‐1 and age‐2 individuals. The relationship between Colorado pikeminnow size and δ¹⁵N within stocked cohorts indicated that juveniles slowly transitioned to consuming fish prey as they grew, rather than abruptly switching, as indicated from a limited number of dietary studies using wild fish.
4. Together, these results suggest that Colorado pikeminnow stocked into the San Juan River slowly transition to consuming fish prey. If this pattern leads to poor survival and recruitment, the effectiveness of this management action for conservation could be compromised.

     

An experimental test of the genetic component of the ontogenetic habitat shift in Arctic charr (Salvelinus alpinus)

Abstract— Fry of the Arctic charr, Salvelinus alpinus , were experimentally stocked into a small fish-free lake to test the hypothesis that the size-dependent habitat shift from the epibenthic to the pelagic habitat is genetically determined. The charr originated from a nearby lake inhabiting predatory brown trout Salmo trutta. The cohort of stocked charr was investigated for three years. The Arctic charr started to exploit the pelagic habitat in their first summer at a size of 7–9 cm in contrast to about 15 cm in the donor lake. In the next two summers, the pelagic fraction of the cohort increased. The main fraction lived in epibenthic areas, utilizing the same prey as pelagic charr. Water temperature moderated the habitat use of juveniles such that they avoided warm (>16°C) waters and resided in cool, deep areas. The result was consistent with the hypothesis of a tradeoff between feeding benefit and the predation risk producing spatial segregation of Arctic charr and demonstrated that the fish can facultatively respond to predation risk and adjust the size at which they migrate to the pelagic zone to feed on zooplankton.     

Tracing trophic pathways through the marine ecosystem of Rapa Nui (Easter Island)

1. The structure of food webs provides important insight into biodiversity, organic matter (OM) pathways, and ecosystem functioning.
2. Stable isotope analysis (δ¹³C and δ¹⁵N) was used to characterize the trophic structure and the main OM pathways supporting food webs in the Rapa Nui coastal marine ecosystem.
3. The trophic position of consumers and isotopic niche metrics were estimated for different assemblages (i.e. mesozooplankton, emergent zooplankton, reef invertebrates, reef fishes, pelagic fishes, and seabirds). Furthermore, the relative importance of different OM sources (i.e. macroalgae, zooxanthellate corals, and particulate OM [POM]) was assessed for heterotrophic consumers using Bayesian mixing model (MixSIAR).
4. Results show a clear pattern of ¹³C and ¹⁵N enrichment from small-sized pelagic and benthic invertebrates, to reef and pelagic fishes, and seabirds. Most invertebrates were classified as primary consumers, reef fishes as secondary consumers and pelagic predators and seabirds as tertiary and quaternary consumers.
5. Isotopic niche metrics indicate a low trophic diversity for pelagic assemblages (mesozooplankton and pelagic fishes), in contrast to reef fauna (invertebrates and fishes), whose higher trophic diversity suggest the exploitation of a wider range of trophic resources. Overlapping of standard ellipses areas between reef invertebrates and reef fishes indicates that both assemblages could be sharing trophic resources.
6. Mixing models results indicate that POM is the main trophic pathway for mesozooplankton, macroalgae (Rhodophyta) for emergent zooplankton, and a mix of coral-derived OM and Rhodophyta for coral reef assemblages such as macrobenthos and reef invertebrates. In contrast, POM contribution was notably more important for some pelagic fishes and seabirds from upper trophic levels.
7. This study provides key elements for conservation efforts on coral reefs, management planning and full-implementation of the recently created Rapa Nui Multiple Use Marine Protected Area.

     

Constrained by aliens,shifting landscape,or poor water quality? Factors affecting the persistence of amphibians in an urban pond network

1. Freshwater communities and especially pond‐breeding amphibians are extremely vulnerable to land‐use change, alien species introductions and the use of pesticides or other toxic chemicals, as reflected in their worldwide decline. Effective conservation and management of ponds requires a better understanding of the biotic and abiotic factors that shape diversity patterns and species distribution, especially in cases of habitat loss
2. The present study aimed to reveal and classify which pond and landscape characteristics are the most important determinants for the occurrence patterns of amphibian species as well as for the overall amphibian species richness in an urban pond network. To achieve this aim, 17 biotic and abiotic variables were measured for 61 ponds and the dataset was analysed by means of a machine‐learning approach, suitability indices and co‐occurrence modelling
3. The highest probability of Triturus macedonicus occurrence was found at fishless artificial and semi‐natural ponds. The persistence of Lissotriton graecus in ponds was predicted by high pond connectivity and the absence of fish reflecting the species dispersive potential. Pelophylax kurtmuelleri showed a higher probability of occurrence with increased pond connectivity and macrophyte cover.
4. Amphibian species richness was higher in fishless ponds with well‐oxygenated waters located in sites with a low to intermediate road density network. Ponds categorized as ‘average’ in terms of newt suitability were more frequently inhabited by fish than Triturus macedonicus. Alien fish species showed negative associations with both newt species, while both newt species showed a positive association between them.
5. The results support the view that conserving a greater number of water bodies with increased landscape connectivity and without any fish presence could provide amphibian species with alternative habitat choices, especially in sites with human pressure where pond stability is at stake owing to continuous landscape changes.

     

Contribution of Stocked Legal-sized Trout to the Sport Fishery of Three Small Wisconsin (U.S.A.) Lakes*

Legal-sized trout stocked in spring in three lakes in Wisconsin U.S.A. provided a short-term, popular, sport fishery. Frequently, half or more of the stocked fish were caught in the first month of the Fishing season, and few were caught thereafter. Separate estimates of the percentage of numbers (and weight) returned in the first month of the fishing season were 46 (47), 73 (76), 62 (113), and 31 (22) for rainbow trout (Salmo gairdneri) and 64 (81) for brook trout (Salvelinus foutinalis). Most anglers interviewed at two of the lakes were fishing primarily for trout, including in one case 95% of the anglers interviewed over the 9-month season, even though the trout fishery persisted for less than 2 months. Fishing pressure also was highest at the opening of the angling season and declined exponentially thereafter. Of an estimated total of 7,906 angler-hours in one lake, 67% occurred in the first month of the season and 79% in the first 2 months. Because the trout were harvested rapidly, relatively little of the productive capacity of the lakes were channelled into production of trout flesh. Therefore, the stocked trout provided a put-and-take fishery at tittle expense to the existent warmwater fishery.     

Predicting population status of freshwater pearl mussel (Margaritifera margaritifera,L.) in central Sweden using instream and riparian zone land‐use data

相似文献