Analysis of Fishery Records from Cow Green Reservoir, Upper Teesdale, 1971–1980

Apart from some irregularities reflecting changes in permit costs (1975) and the effects of drought (1976), there were increases in angler-visits, catch per angler-visit and number of fish caught during the first 5 years of the fishery. Thereafter, there were about 1000–1500 angler-visits per season, a mean catch of 1.0–1.2 trout per angler-visit and an annual catch of 1200–1800 trout. Between 1971 and 1980 the mean weight of the fish caught fell from 472 to 349 g. During the period 1976–1980 the mean catch per angler-visit was 1.2 fish. This compares favourably with results from a selection of upland and lowland British reservoirs. The mean weight of individual trout caught was 362 kg and this value is typical of both stocked and unstocked upland reservoirs. The mean annual catch during 1976–1980 was about 2 kg ha^?1. This is similar to the values observed in other unstocked upland reservoirs. The gross yield from such reservoirs can be increased by stocking but the limited data available suggest that at stocking rates above about 5 kg ha^?1 the net yield (i.e. weight caught — weight stocked) becomes negative.     

Effect of supplementary stocking of juvenile brown trout,Salmo trutta,on yield in a Norwegian mountain reservoir

Abstract The effect of supplementary stocking of juvenile (age 0+), hatchery‐reared, brown trout, Salmo trutta L., on annual yields was assessed in a Norwegian mountain reservoir between 1979 and 2007. Fishing was mainly carried out by local fishermen with benthic gillnets. During the study period, annual stocking ranged from 0 to 52 500 fish (19.8 ha^?1). No stocking has been carried out since 1997. Annual yield varied from 1650 to 5653 kg, corresponding to 0.62–2.13 kg ha^?1. Exploitation rate in terms of number of gillnets and mean weight of 6+ fish (age when catchable size was reached) explained 64% of the variability in catches. Stocked fish contributed very little to the yield or catch‐per‐unit‐effort, exhibiting no positive correlation with stocking density. The lack of contribution from stocked fish was probably caused by a competitive bottleneck in the eroded epibenthic zone, causing high juvenile mortality. If stocking continues, it is recommended that fish with body lengths >15–20 cm are used.     

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.     

Performance of rainbow trout, Salmo gairdneri Richardson, in a put-and-take fishery, and influence of anglers' behaviour on catchability

Abstract. Stock, catch and fishing effort statistics for a 12·5-ha lowland pul-and-lake trout fishery have been used to compute the ‘catchability’ of rainbow trout, Salmo gairdneri Richardson, during the fishing seasons 1980–1983. Seasonal trends in the fishes’ susceptibility to capture by fly-fishing are apparent but there was no indication that, in this fishery, newly stocked fish were more vulnerable than the longer-term residents. This consistency of recapture rates of rainbow trout, relative to the population available, is a function both of the fish's behaviour and that of the anglers themselves, and it is suggested that for management purposes the latter must be taken into account. In the fishery studied rainbow trout grew well at fish densities below 60 kg ha^?1, but even with overall recapture levels exceeding 80% the yield of the fishery was less than the weight of fish stocked. The selection of strains of rainbow trout which satisfy the requirements of sport fisheries is discussed.     

The status of host fish populations and fish species richness in European freshwater pearl mussel (Margaritifera margaritifera) streams

• 1. The status of host fish populations and fish species richness was investigated at 36 sites of 20 extant freshwater pearl mussel populations, including the drainages of the Elbe, Danube, Rhine, Weser, Aulne, Kemijoki and Tuuloma in Germany, the Czech Republic, France and Finland, by carrying out comparative electrofishings.
• 2. Brown trout (Salmo trutta f. fario) were found to be the available host fish for pearl mussels in all except one of the streams investigated with mean densities of 2861 ha^?1 (range 0–8710 ha^?1) and a mean biomass of 119 kg ha^?1 (range 0–478 kg ha^?1). Streams that had been frequently stocked with brown trout had higher trout biomass and densities of host fish than natural populations, but trout stocking had no positive effect in two of the streams investigated.
• 3. Fish species richness ranged from 2 to 16 species per stream and showed a negative correlation with host fish biomass and host fish densities. Undisturbed oligotrophic pearl mussel headwater streams usually only yielded a low number of fish species. Habitat degradation can reduce competitiveness of specialized trout and result in an increased abundance of ubiquitous or atypical species.
• 4. A link between the lack of juvenile pearl mussels and a lack of suitable host fish was only rarely observed. Functional pearl mussel populations with relatively high numbers of juveniles had significantly lower densities and biomass of host fish than pearl mussel populations without recent recruitment.
• 5. This study suggests that 0+ host fish are not necessarily required to sustain functional pearl mussel populations. Low densities of host fish can be compensated by the higher glochidia carrying capacity of older host fish with limited previous contact with pearl mussel glochidia, by the long reproductive period of mussels, and by low mortality rates of juvenile mussels during their post‐parasitic phase.

Copyright © 2005 John Wiley & Sons, Ltd.     

Culture-based fisheries in small reservoirs in northern Vietnam: effect of stocking density and species combinations

This study was conducted in 20 reservoirs, ranging in size from 4 to 30 ha, in the mountainous, northern region of Vietnam, in ThaiNguyen and YenBai provinces, over two growth cycles in 2002/03 and 2003/04. The reservoirs are leased by farmers for fishery activities from the provincial administration, and the trials were managed by the lessee farmers. Three species combinations in ratios (by fingerling weight) of grass carp: silver carp: bighead carp: common carp: mrigal 1:2:1:1:3 (A), 1:3:1:1:2 (B) and 1:2:1:1:2 (C) were used as seed stock. The overall mean yield of stocked fish in 2002/03 and 2003/04 growth cycles in reservoirs in ThaiNguyen and YenBai provinces was 165 (±21) and 190 (39), and 287 (±22) and 325 (±24) kg ha^?1 respectively. The yield in reservoirs in both provinces, in both growth cycles and irrespective of the species combinations, increased in relation to stocking density. In reservoirs in ThaiNguyen Province, the species combination B gave the lowest yield (both growth cycles and overall), and differed significantly (P<0.05) from combinations A and C. The stocking efficiency (ratio of the yield of stocked fish in kg ha^?1 to the weight of the stocked fish in kg ha^?1) in reservoirs in ThaiNguyen Province ranged from 2.9 to 5.1 over the two growth cycles and that in YenBai from 2.8 to 3.9. There was no discernible trend between growth cycles and/or between species combinations. The major cost incurred was for fingerling procurement. In all instances, a net profit was accrued. The mean (±standard error (SE)) net profit ha^?1 (in 10³VN dong; approximately 15 500 VND=1 US$) was 885 (±270) and 864 (±214), and 1322 (±176) and 1600 (±150) for the growth cycles 2002/03 and 2003/04 for reservoirs in ThaiNguyen and YenBai provinces respectively. Between the two growth cycles, the net profit increased in eight and three reservoirs from YenBai and ThaiNguyen, respectively, the maximum increase being recorded in Khuan Gio (165%) and Dong Man (39%) reservoirs.     

Evaluation of large-scale stocking of early stages of brown trout, Salmo trutta, to angler catches in the French–Swiss part of the River Doubs

Around 500 000 brown trout, Salmo trutta L., alevins are stocked annually in the 24‐km section of the River Doubs under study. All the alevins stocked in the period 1994–1996 were identifiable by fluoromarking their otoliths with tetracycline chlorhydrate. Anglers' catches, between June 1997 and September 1998, comprised trout aged 1+ to 7+ , but most (90% +) were 2+ to 3+ or 4+ , with the majority at 2+ and 3+. There was no significant difference in the size for a given age between marked and unmarked angled trout. The contribution of stocked fish in anglers' catches was around 22% for the 1995 cohort. The contribution of stocking (cohorts 1994 to 1995–1996) to the 1998 catches was around 23% (95% confidence limits: 19–27%). The estimated recapture rate was three to four trout per 1000 alevins stocked for the 1995 cohort. The major contribution (78%) of natural recruitment to anglers' catches suggests that the fishery management based on natural recruitment is still realistic in this part of River Doubs.     

Stocking of sea trout, Salmo trutta, in Lake Veere, south-west Netherlands

Lake Veere (1750–2050 ha), a brackish water lake in south‐west Netherlands, is a former branch of the Oosterschelde. The lake was closed off by the construction of two dams in 1961. Since the early 1970s Lake Veere has been regularly stocked for recreational and commercial fisheries with rainbow trout, Oncorhynchus mykiss (Walbaum), brown trout, Salmo trutta L., and glass eel, Anguilla anguilla (L.). Between May and September 1996 an experimental stocking of 18 054 trout of sea trout parentage (15–16 cm; 776 kg) was carried out to study their potential for recreational fisheries. The growth and mortality of the stocked trout were estimated from recaptures in eel fyke nets. The production and consumption of the stocked trout were estimated with a bioenergetics model. After 3.5 years (May 1996–November 1999) the stocked trout measured between 50 and 70 cm. The estimated annual total mortality was 84%. During the winter of 1996–1997, the biomass of the stocked trout reached a maximum of about 1800 kg. By November 1999 the biomass was estimated to be 100 kg. The maximum daily consumption by the trout population was 60 g ha^?1 in October 1996 and in June 1997. The total consumption of the stocked trout population over the 3.5‐year period was estimated as 54 244 kg. The analysis suggested that the stocked trout used about 0.2% of the average annual primary production of the lake system. Although the growth and initial production of the population are attractive from the perspective of a recreational fishery, the high mortality and infestation with the salmon louse, Lepeophtheirus salmonis (Krøyer), are serious drawbacks for a future stocking programme with trout in Lake Veere.     

Culture-based fisheries in non-perennial reservoirs in Sri Lanka: production and relative performance of stocked species

Abstract In Sri Lanka, there is a great potential for the development of culture-based fisheries because of the availability of around 12 000 non-perennial reservoirs in the dry zone (<187 cm annual rainfall) of the island. These reservoirs fill during the north-east monsoonal period in October to December and almost completely dry up during August to October. As these non-perennial reservoirs are highly productive, hatchery-reared fish fingerlings can be stocked to develop culture-based fisheries during the water retention period of 7–9 months. The present study was conducted in 32 non-perennial reservoirs in five administrative districts in Sri Lanka. These reservoirs were stocked with fingerlings of Indian (catla Catla catla Hamilton and rohu Labeo rohita Hamilton) and Chinese (bighead carp Aristichthys nobilis Richardson) major carps, common carp Cyprinus carpio L., genetically improved farmed tilapia (GIFT) strain of Nile tilapia, Oreochromis niloticus (L.) and post-larvae of giant freshwater prawn, Macrobrachium rosenbergii De Man, at three different species combinations and overall stocking densities (SD) ranging from 218 to 3902 fingerlings ha⁻¹, during the 2002–2003 culture cycle. Of the 32 reservoirs stocked, reliable data on harvest were obtained from 25 reservoirs. Fish yield ranged from 53 to 1801 kg ha⁻¹ and the yields of non-perennial reservoirs in southern region were significantly (P < 0.05) higher than those in the northern region. Naturally-recruited snakehead species contributed the catches in northern reservoirs. Fish yield was curvilinearly related to reservoir area (P < 0.05), and a negative second order relationship was evident between SD and yield (P < 0.05). Chlorophyll-a and fish yield exhibited a positive second order relationship (P < 0.01). Bighead carp yield impacted positively on the total yield (P < 0.05), whereas snakehead yield impact was negative. Bighead carp, common carp and rohu appear suitable for poly-culture in non-perennial reservoirs. GIFT strain O. niloticus had the lowest specific growth rate among stocked species and freshwater prawn had a low return.     

The potential of mixed culture of genetically improved farmed tilapia (Oreochromis niloticus) and freshwater giant prawn (Macrobrachium rosenbergii) in periphyton-based systems

The production performance of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) in periphyton‐based systems were studied in farmers' ponds at Mymensingh, Bangladesh. Fifteen ponds (200–300 m² area and 1.0–1.5 m in depth) were used to compare five stocking ratios in triplicate: 100% GIFT, 75% GIFT plus 25% prawn, 50% GIFT plus 50% prawn, 25% GIFT plus 75% prawn and 100% prawn. Ponds were stocked at a total density of 20 000 GIFT and/or prawn ha^?1. Bamboo poles (mean diameter 6.2 cm and 5.5 pole m^?2) were posted in pond bottoms vertically as periphyton substrate. Periphyton biomass in terms of dry matter (DM), ash‐free DM and chlorophyll a were significantly higher in ponds stocked with prawn alone than in ponds with different combinations of GIFT and prawn. Survival of GIFT was significantly lower in ponds stocked with 100% GIFT (monoculture) whereas, that of prawn was significantly higher in its monoculture ponds indicating detrimental effects of GIFT on prawn's survival. Individual weight gains for both species were significantly higher in polyculture than in monoculture. The highest total fish and prawn yield (1623 kg GIFT and 30 kg prawn ha^?1) over 125–140 days culture period was recorded in ponds with 75% GIFT and 25% prawn followed by 100% GIFT alone (1549 kg ha^?1), 50% GIFT plus 50% prawn (1114 kg GIFT and 68 kg prawn ha^?1), 25% GIFT plus 75% prawn (574 kg GIFT and 129 kg prawn ha^?1) and 100% prawn alone (157 kg ha^?1). This combination also gave the highest economic return. Therefore, a stocking ratio of 75% GIFT plus 25% prawn at a total density of 20 000 ha^?1 appeared to be the best stocking ratio in terms of fish production as well as economics for a periphyton‐based polyculture system.     

A comparison of growth, survival rate, and number of marketable fish produced of swordtails, Xiphophorus helleri Heckel (Family Poeciliidae), between two types of culture systems

To test the effect of stocking density on growth, survival rates and size distribution of juvenile swordtails, Xiphophorus helleri Heckel, under different environmental conditions, fish were stocked at rates of 1, 3 and 6 fish I^?1. Growth was monitored over a 14-week period. Fish were weighed in six groups of 20 fish per tank. Size variation was determined at the end of the growth period by measuring the total length of each fish to the nearest mm. Fish were stocked in two different systems at three stocking densities (1, 3, and 6 fish I^?1) in replicate. The systems were an indoor aquarium system and a tunnel system under semicommercial conditions. In each system, increasing stocking rates resulted in a significant reduction of growth rates. In the aquarium system, survival rate was not related to stocking density, whereas in the tunnel system, fish at the highest stocking density had a lower survival rate than those kept at the two lower stocking densities. The number of marketable fish above a set size limit of 40 mm total length was not higher in fish stocked at 6 fish I^?1 than at 3 fish I^?1 at the end of the study. Therefore, a stocking rate of 3 fish I^?1 would be optimal. At the end of the study, fish were categorized into males, females and immature fish. Fish with a clearly visible gonopodium were classified as males, those with typical female characteristics as females, and small fish that were not yet differentiated as immature fish. The ratio of females to males was highly skewed in both systems, favouring a higher percentage of females. As stocking density increased, the female:male ratio was significantly reduced, which would result in a greater number of saleable pairs at increased stocking density. The implications of these results for the management of intensive production of swordtails are discussed.     

Assessing culture fisheries practices in small waterbodies: a study of village fisheries in north-east Thailand

Extensively managed culture fisheries systems in small, communal waterbodies in north-east Thailand were analysed using statistical methods and a simple population model. Villages stocked the waterbodies with a variable mixture of carp species and Nile tilapia, and held annual fishing days where individual fishing was allowed upon payment of a fee to the village. Yields ranged from 26 to 2881 (median 652) kg ha^?1 year^?1 and were strongly related to the trophic status of the waterbody and to stocking density (with an optimum at 9800 fish ha^?1 year^?1). Stocking performance varied greatly between species and was also influenced by the trophic status of the waterbody. Catches were dominated by tilapia in the most fertile waterbodies and by carp species in all others, but catch species composition did not significantly influence yield when the effect of trophic status was accounted for. The optimization of stocking regimes is identified as the most promising option to improve village fisheries, on the basis of feasibility and predicted benefit (median increases in yield of 22-75%). Further empirical analyses, possibly combined with experimental management, are suggested to identify optimal stocking regimes.     

The large‐scale stocking of young anadromous whitefish (Coregonus lavaretus) and corresponding catches of returning spawners in the River Tornionjoki,northern Baltic Sea

Stocking and fishing effort are two important potentially conflicting factors in fish stock management that require appropriate assessment to ensure a sustainable fishery. In the River Tornionjoki, which discharges into the northern Baltic Sea, a summer‐ascending whitefish, Coregonus lavaretus L., stock has long been a target by traditional dipnet fishing. Enhancement stocking of young whitefish started in the River Tornionjoki in the 1970s after a collapse in catches, with millions of age‐0 whitefish stocked annually in the river, but after about three decades, the stocking rates were considerably reduced. As a result, dipnet catches of whitefish in the Kukkolankoski Rapids rose simultaneously, peaking in the 1980s and 1990s, and then subsequently decreased. There was a significant positive correlation between stocking intensity and catch, both in weight and in numbers, revealing a strong relationship between whitefish releases and dipnet catch. Changes in gillnet fishing effort in the sea affected dipnet catches in weight as well as in mean size of captured whitefish. When the combined effect of stocking and gillnet effort was evaluated, only stocking significantly affected dipnet catches.     

Changes in commercially exploited populations of tench, Tinca tinca (L.), in littoral zones of lakes of northeastern Poland

Commercially exploited tench, Tinca tinca, (L.) populations in 480 lakes in the northeastern Poland were analyzed on the basis of the fishery data from 1949 to 1994. The long-term changes in tench catch were studied in four categories of lakes with respective proportions of littoral zones (<30, 31–60, 61–90 and <90% of total lake area). The analyses were performed with using relative catch (kg ha⁻¹ month⁻¹) of tench. Mean relative catch of tench for 1949–1994 ranged from 0.36 kg ha⁻¹ month⁻¹ in lakes with smallest littoral zone (>30%) to 0.93 kg ha⁻¹ month⁻¹ in lakes with the largest littoral (<90%). Mean relative catch increased with increasing proportions of littoral zones in lakes. However, long-term trends in mean relative catch of tench showed decreasing tendencies in all lakes. The beginning of these tendencies was found about ten years earlier in lakes with smaller littoral (<60%) in comparison to lakes with larger littoral zones (>60%). Mean stocking rates of tench (number of 1-year-old fish per ha of littoral) for 1949–1994 were not significantly different in lakes of studied categories. However, lakes with proportionally less littoral zone had reduced stocking efficiency estimated as number of stocked fish per ha of littoral to require 1 kg ha⁻¹ month⁻¹ of tench.     

Quantitative estimates of freshwater fish stocking practices by recreational angling clubs in France

Although freshwater fish stocking is widely used by managers, quantitative assessments of stocking practices are lacking in many countries. The general objective of the present study was to determine the quantity and characteristics of fish stocking in metropolitan France. Using a survey-based approach, stocking practices for 2013 by recreational angling clubs in France were quantified, which represented the bulk of fish stocking undertaken in that year. Stocking was found to be practiced by 88.6% of angling clubs in France, representing, on average, 65% of their annual budget. Overall, 22 species were stocked, including 13 native and nine non-native species, with strong variations among species in terms of life stages and body sizes used for stocking. Using Bayesian modelling, a total biomass of 2.029 t, representing approximately 90 million fishes, was estimated to be stocked in France in 2013. In terms of biomass, the most widely stocked species were rainbow trout Oncorhynchus mykiss (Walbaum), brown trout Salmo trutta L., roach Rutilus rutilus (L.), common carp Cyprinus carpio L. and northern pike Esox lucius L. A stocking volume of approximately 60 fishes or 1.5 kg of fish biomass per angler per year seems commonplace in industrialised countries for which data are available.     

Evaluation of nitrogen cycling and fish production in seasonal ponds (‘Fingerponds’) in Lake Victoria wetlands,East Africa using a dynamic simulation model

A dynamic model was developed to simulate nitrogen (N) flows and fish production in seasonal wetland fish ponds (Fingerponds) based on organic manuring and natural food production. The model incorporates pond water depth, food availability, fish stocking densities, fish and fingerling weights at stocking, reproduction rate, manure type and application rates. The ponds were fertilized fortnightly with 1042 kg ha⁻¹ chicken manure. The model captured the dynamics of hydrology, nutrients and fish and demonstrated that similar fundamental processes underlie fish production in these systems. The model predicted annual fish yields of up to 2800 kg ha⁻¹. Simulated fish production, chlorophyll a and dissolved inorganic N concentrations were comparable with field measurements. Using the model, N budgets and estimates of all N flows were made. Most of the N input into the ponds (60–70%) accumulated in the bottom detritus of the pond and only 8–10% was converted into fish biomass, of which about half consisted of small fish. Fish production in Fingerponds was limited by turbidity induced light limitation and by nutrient limitation. Reduction of variability of fish production should come from reduced turbidity and sufficient nutrient input to minimize light limitation and maximize fish growth.     

Effect of Stocking Density on Growth,Yield, and Costs of Producing Rainbow Trout,Oncorhynchus mykiss,in Cages

Abstract

Rainbow trout, Oncorhynchus mykiss, were raised in culture cages (1 m³) to determine the effect of stocking density on growth, survival, and percentage of market-size fish. Large fingerling rainbow trout (20-25 cm, 232 g average weight) were stocked into six cages located in a 0.4-ha pond. Two stocking densities (100 or 200 fish/cage) were used, and fish were grown for 140 days (2000-April 2001). Average total harvest weight (35.0 kg) in the low-density cages was approximately one-half the average total harvest weight (61.2 kg) in the high-density cages. Average weight gain (11.7 kg to 15.1 kg) and feed conversion (1.2 to 1.5) were also smaller for the low-density cages. Average survival was 96.7% for the low-density cages and 94.2% for the high-density cages, with the percentage of market-size fish (< 29 cm) averaging 50.3% and 52.0%, respectively. Production costs for the actual experiment and the revenues from fish sold at the end of the study were collected. An enterprise budget based on the experimental results for the two densities was developed to determine if a culture operation of this size would produce a net return. Production costs and revenues from the experiment resulted in a large negative return (-$3,124) and high breakeven price ($13.53/kg).     

Evaluation and impact assessment of culture‐based fisheries to enhance fish yield in small reservoirs in Odisha State,India

The present study investigates the success of stocking fingerlings of Indian major carps ‐Gibelion catla (Hamilton), Labeo rohita Hamilton and Cirrhinus mrigala Hamilton – to enhance fish yield in 58 small reservoirs in Odisha State, India. Fish stocking and yield data were collected from State Fisheries Department, Odisha. The relationships between area, stocking density and fish yield of different size groups of reservoirs were assessed using the Pearson correlation coefficient (r). Fish yield increased significantly (p < 0.05, t‐test) from 204 kg/ha/year in 2012–13 to 323 kg/ha/year in 2013–14 due to adoption of CBF. The corresponding per capita fish production increased from 398 kg fisher^?1 year^?1 to 702 kg fisher^?1 year^?1 benefitting more than 8,000 fisher households. Reservoirs in the size group 100–500 ha showed the highest response of fish yield with respect to stocking of fingerlings. The size of fingerlings at stocking and area of the reservoir had greater impact on enhancing fish yield. Stocking had a profound positive impact on fish yield. This study forms a baseline evaluation of the impact of stocking on small tropical reservoirs in India. It also recommends management measures and discusses issues, and the way forward for sustainable fisheries enhancement in small tropical reservoirs in eastern India.     

Factors influencing the yield of brown trout, Salmo trutta m. lacustris L., in northern Finnish lakes

Abstract Lake-to-lake variation in brown trout, Salmo trutta m. lacustris L., yield from stocking was examined in 34 lakes in northern Finland. The trout were mainly stocked as 2–3-year-old fish. Catch statistics were compiled with information on water quality, water level fluctuations, fishing effort and lake geomorphology. Absolute brown trout yields (kgha^-1) increased with increasing stocking rate, but there was an indication of non-linearity at higher stocking densities. Relative yields (kg per thousand trout released) were highest at low stocking rates. Stepwise multiple regression analysis was used to determine the best predictive model for lake-to-lake variability in brown trout yields. Seventeen measured regressands were used initially, and then replaced with scores obtained in a principal component analysis of highly correlated water quality variables and species-specific fish yields. Three major determinants of brown trout yields in these lakes were found in both analyses: fish community, stocking rate and fishing effort. Brown trout yields from stocking were higher in lakes with proportionally high yields of vendace or vendace and whitefish and proportionally low yields of pike.     

Fisheries and cage culture of three reservoirs in west Java, Indonesia; a case study of ambitious development and resulting interactions

Abstract The interactions between cage culture and wild fishery activities in three Indonesian reservoirs, Saguling, Cirata and Jatiluhur, of the greater Ciratum watershed, West Java, were evaluated using historical data and interviews with cage culture operators. In all three reservoirs, cage culture of common carp, Cyprinus carpio L., and later of common carp and Nile tilapia, Oreochromis niloticus (L.), were encouraged as an alternative livelihood for persons displaced by the impoundment. Currently, a two‐net culture system, locally known as ‘lapis dua’, in which in the inner cage (7 × 7 × 3 m) is used for common carp culture and the outer cage (7 × 7 × 5/7 m) is stocked with Nile tilapia, is practised. On average each cage is stocked with approximately 100 kg fingerlings each of common carp and Nile tilapia. The numbers of cages and production of cultured fish has increased in the reservoirs, but total and per cage production began to decline from about 1995 in Saguling from 2200 kg cage^?1 in 1989 to <500 kg cage^?1 in 2002, and in Cirata from a peak of approximately 2300 kg cage^?1 in 1995 to approximately 400 kg cage^?1 in 2002. In Jatiluhur, which has a considerably lower cage density, total fish production and production per cage has increased since 2000, and currently is approximately 4000 kg cage^?1, close to production in the early years of cage culture activities. The cage culture operations also resulted in substantial nutrient loading, estimated at 3.2, 15.2 and 3.1 t of nitrogen and 134, 636 and 128 kg of phosphorous per year in the maximum years of production for Saguling, Cirata and Jatiluhur reservoirs, respectively. In later years, when cage culture production was high, fish kills occurred in the cages, and in Jatiluhur reservoir coincided with a dramatic decline in wild fishery catches. An attempt is made to determine the maximum number of cages for each of the reservoirs that will bring long‐term sustainability of cage culture operations and the wild fisheries in the three reservoirs.