Showing papers in "Fisheries Management and Ecology in 1998"
TL;DR: With increasing pressure on the world's inland and coastal marine fisheries, increases in production and quality of yield are being sought through the application of a range of enhancement techniques which of these is applied depends on the attitude to the natural resource by societies at different levels of economic development as mentioned in this paper.
Abstract: With increasing pressure on the world's inland and coastal marine fisheries, increases in production and quality of yield are being sought through the application of a range of enhancement techniques Which of these is applied depends on the attitude to the natural resource by societies at different levels of economic development The range of enhancement techniques involves increasing levels of human input and control which raise productivity significantly, but which also raise costs Introductions have raised production in many areas of the world at the price of the risk of environmental disruption Stocking is extremely widespread but has generally been applied uncritically A variety of models are proposed to serve as a basis for more rigorous evaluation of biological and economic effectiveness of this practice Fertilization of water bodies is used to raise levels of production further Elimination of unwanted species then becomes necessary to maximize benefits from the target species Adjustments to the habitats within the water body assist in raising general levels of productivity which culminate in the conversion of areas of the water into fish ponds or for cage culture This process has important implications for the social, economic and policy context which necessitates shifts in ownership, finance and education among populations where these types of development occur
162 citations
TL;DR: Fish is the most important source of animal protein for this region, with an annual mean consumption rate of 550 g capita−1 day−1, and the fishery has changed from a subsistence to a commercial scale, which was associated with increasing cattle ranching activities.
Abstract: Questionnaires were used to collect data from the low-Solimoes/high-Amazon region, Brazil, between December 1992 and February 1994. Gillnets, fishing rods and castnets were the preferred gear used. Gillnets were used throughout the year whilst other gears were used only in certain periods of the year. The fish caught tended to supply family needs but a high proportion were sold in regional markets. Curimata (Prochilodus nigricans), pacu (various Myleinae) and ruelo (young Colossoma macropomum) were the most frequent species caught. Around 50% of the fish caught in these fisheries was consumed fresh, and the remainder was stored under ice or salted. Fish is the most important source of animal protein for this region, with an annual mean consumption rate of 550 g capita−1 day−1. The fishery has changed from a subsistence to a commercial scale, which was associated with increasing cattle ranching activities. This may have serious social and economic implications.
103 citations
TL;DR: The Girnock Burn, a tributary of the River Dee, has been used as a monitoring site for Atlantic salmon, Salmo salar L., populations since 1966 as discussed by the authors.
Abstract: The Girnock Burn, a tributary of the River Dee, has been used as a monitoring site for Atlantic salmon, Salmo salar L., populations since 1966. The burn drains a catchment of 30 km2 and is a third order stream at the catchment outlet; its width ranges from 1 m in the headwaters to around 15 m in its lower reaches. During the period 1966–1996, the mean number of fish (average lengths; males = 0.64 m and females = 0.68 m) entering the burn for spawning averaged 126 (range 38–293) with a mean male:female ratio of 0.96 (range 0.58–1.66). Typically, 85% of the adults were 2-sea winter fish. Redd counts in 17 spawning seasons showed that the number of redds constructed during the spawning season ranged from 13 to 141 with a mean of 79. Redds were generally 2–3 m long, 1–1.5 m wide and 0.2–0.3 m deep. Redd distributions showed that parts of the river were used more frequently for spawning than others. This paper describes the main physical characteristics of the river that influence spawning habitat. This characterization occurs at two scales; the overall Girnock system and individual river reaches. At the large scale, bed slope exerts a strong influence on spawning distribution by controlling the distribution of spawning-calibre sediment. Additionally, river flow during the spawning period appears to have a significant influence on accessibility and the subsequent distribution of redds. At the reach scale, local hydraulic (depth, velocity and Froude number) and sedimentary (particle size distribution) variables were found to be increasingly important. Mean utilized depth, velocity and Froude number for 93 redds were 0.248 m, 0.536 m s–1 and 0.344, respectively. Samples of utilized sediment had a mean median particle size (D50) of 20.7 mm and a mean fines (particles < 1 mm diameter) content of 5.4%. It was suggested that the Froude number may be a useful single descriptor of hydraulic habitat, as it is dimensionless and is thus comparable between different sizes of river and fish species.
101 citations
TL;DR: Density-dependent factors related to a beaver dam, which limited spawning distribution, may have contributed to poor survival and increased fry emigration in one year and environmental factors, particularly winter conditions, in streams such as Catamaran Brook may act as bottlenecks to natural production of Atlantic salmon.
Abstract: A biological model was developed to calculate annual survival between life stages of juvenile Atlantic salmon, Salmo salar L, in Catamaran Brook, a small stream basin (52 km2) in the Miramichi River catchment in New Brunswick, Canada Seven years’ data (1990–1996) were used in the model Input variables included: daily fish counts and measurements of parr (3–4 age classes), smolts, and adult salmon at a fish-counting fence near the stream mouth; biennial quantification of all habitat types along the watercourse; fish density estimated by electric fishing at 30 sites; and estimates of young-of-the-year emigration via stream drift Continuous recording of stream discharge provided data to assist in interpretation of survival estimates Annual survival for juvenile salmon in their first 3 years of life in the stream averaged between 31% and 34% The greatest annual variation (CV = 0699) occurred at the egg to 0+ (summer) stage with a low of 92% survival recorded for a winter with an atypical midwinter flood event; parr and pre-smolt survival were similarly affected Survival from egg deposition (after correction for losses caused by predation and retention/non-fertilization) to smolt emigration was between 016% and 052%, which is low relative to estimates from many other studies Survival of smolts to returning 1-sea-winter adults (grilse) averaged 85% Potential errors in the computation of the model are discussed, eg inaccurate counts of spawning adults during high autumn stream flow A possible explanation for the low egg to smolt survival was the environmental conditions experienced during various winters Mean egg survival was 13 times higher (393%) and egg to smolt survival increased to 103% when the two winters characterized by extremely low discharge or midwinter freshets were excluded from the calculation Density-dependent factors related to a beaver dam, which limited spawning distribution, may also have contributed to poor survival and increased fry emigration in one year Environmental factors, particularly winter conditions, in streams such as Catamaran Brook may act as bottlenecks to natural production of Atlantic salmon
100 citations
TL;DR: The demersal fish stocks in southern Brazil were assessed from landings and catchper-unit effort data trends between 1975 and 1994, available information on the life history patterns, and population dynamics of the most important species.
Abstract: The demersal fish stocks in southern Brazil were assessed from landings and catchper-unit effort data trends between 1975 and 1994, available information on the life history patterns, and population dynamics of the most important species. The fishing gears, mostly otter and pair bottom trawls in the 1970s, diversified towards double-rig trawls for fish and shrimp and bottom gill nets in the mid 1980s, and bottom longlines in the upper slope in the early 1990s. There were also some less successful attempts with traps for fish and crabs. The demersal fisheries are more intensive in winter when migratory species move northward, associated with the seasonal displacement of the western boundary of the Subtropical Convergence. Landings between 1975 and 1994 were mostly of sciaenid fishes (>70%) and elasmobranchs (10%) and oscillated around 59 000 t. There was not a decrease in total landings but a shift from more to less exploited stocks. Since 1989, 4% of the landings came from depleted stocks of Pagrus pagrus (L.), Netuma barba (Lacepede), Pogonias cromis (L.) and Rhinobatos horkelli (Muller & Henle); 37% from overexploited stocks: Micropogonias furnieri (Desmarest), Paralichthys patagonicus Jordan, Squatina guggenheim Marini, and Galeorhinus galeus (L.); 24% from heavily exploited stocks of Umbrina canosai Berg, and Macrodon ancylodon (Bloch & Schneider); and 35% of Cynoscion guatucupa (Cuvier) and small stocks with unclear status. The demersal fisheries are virtually unmanaged and future landings are expected to decrease if fishing pressure remains high. Effective management will require the participation of all three countries in the region because most of the stocks fished in southern Brazil are shared with Uruguay and Argentina.
98 citations
TL;DR: The feasibility of participation by local fishermen in scientific fisheries data collection for stock assessment is described in this article, where the authors show that with this method, it is possible to obtain large quantities of reliable and relatively cheap length-frequency data that allow for a full length-based stock assessment, including cohort analysis.
Abstract: The feasibility of participation by local fishermen in scientific fisheries data collection for stock assessment is described. Artisanal fishermen from the Bangweulu Swamps, Zambia, collected length-frequency data for 1 year from their catch using the main fishing methods employed in the swamps as well as experimental gears. It is shown that with this method, it is possible to obtain large quantities of reliable and relatively cheap length-frequency data that allow for a full length-based stock assessment, including cohort analysis. There are also indications that with a proper feedback of the findings by the research institutions to the fishing communities, this sampling method might enhance the awareness of exploitation patterns and the management consequences. This may be seen as a first step in preparing the communities to take up their role in a community-based approach in the management of the fish resources.
81 citations
TL;DR: A fishway consisting of vertical slot and Denil sections was constructed at the lowest dam on the River Kemijoki, northern Finland, in 1993 as mentioned in this paper, and nearly 1000 adult salmonids passed through the fishway despite heavy fishing below the dam.
Abstract: A fishway (fish pass), consisting of vertical slot and Denil sections, was constructed at the lowest dam on the River Kemijoki, northern Finland, in 1993. The river was one of the best salmon rivers in Europe until 1949, when the dam and the hydropower plant were completed close to the river mouth. From 1993 to 1995, nearly 1000 adult salmonids passed through the fishway despite heavy fishing below the dam. Of environmental variables measured, water temperature, headwater level, and discharge through the power plant in relation to season changes explained most of the variation in Baltic salmon, Salmo salar L., numbers. They had a minor effect on trout, Salmo trutta L. Migratory whitefish, Coregonus lavaretus (L.), entered the fishway but were not observed in its uppermost pool. River lamprey, Lampetra fluviatilis (L.), passed through the vertical slot section of the fishway after plastic bristles were fastened into the bottom of the slots.
73 citations
TL;DR: In this article, an impact assessment examined the effects of a new flow management system introduced in 1992 for the lower reaches of the Bregenzerach, a river in western Austria, has been affected by heavy hydro-peaking discharges (up to 60 m3 s−1) for several decades.
Abstract: The lower reaches of the Bregenzerach, a river in western Austria, have been affected by heavy hydro-peaking discharges (up to 60 m3 s−1) for several decades. In conjunction with a plan to construct a new power plant, mitigation measures were developed to reduce the adverse effects of hydro-peaking in this river reach.
The impact assessment examined the effects of a new flow management system introduced in 1992. The study concentrated on three main components: abiotics (morphology, hydrology, hydraulics), fish and benthic fauna.
Prior to mitigation, both the fish and invertebrate fauna were heavily affected by the peaking. Benthic biomass was less than 15% of that predicted by an altitude model. After mitigation benthic biomass recovered to about 60% of the model prediction. No post-mitigation improvement was found with respect to fish biomass.
Flow velocity distribution data showed that rising surge releases had two distinct phases, a bed-filling and a flow acceleration phase. The present flow management system, based on a dual-flow logistic, resulted in increased base flows and reduced peak flows, but did not alter the ramping rates. The reduction of the adverse effects of the bed-filling phase was apparently responsible for the recovery of the benthic fauna. However, the unaltered ramping rate of the acceleration phase may have inhibited the development of the fish community.
An analysis of the hydrograph demonstrated the possibility of adjusting the present management strategy to reduce the ramping rate of the acceleration phase, smoothing out the peak duration curve.
65 citations
TL;DR: In this article, the uses of trap-and-transport systems to enhance recruitment of catadromous anguillid eels into fresh water can be discussed in relation to key biological and hydraulic management criteria.
Abstract: Immigration of catadromous anguillid eels into fresh water can be impeded by barriers such as barrages, weirs and dams. The uses of passes and trap-and-transport systems to enhance recruitment are reviewed. Pre-construction studies of the needs for passes and traps are discussed in relation to key biological and hydraulic management criteria. Recommendations for pass and trap designs and placement are made in the context of site-specific biotic and abiotic factors. Reference is made to experience gained from eel passes and trapping systems in use throughout the world, and to experimental and pre-and post-construction monitoring studies. Practical recommendations are made for the design and use of eel passes and traps for monitoring studies and for trap-and-transport stocking.
59 citations
TL;DR: It was concluded that exposure to an artificial rearing environment during ontogeny can affect both the phenotype and the behaviour of the reared individuals, and thereby, their potential for survival after release into the wild as well.
Abstract: The main question which must be raised when planning to enhance natural populations through sea ranching is whether reared organisms are fit for a life in the wild, or more specifically, whether there are differences between reared and naturally resident individuals. The causes and effects of these differences are reviewed, and results from the Norwegian enhancement programme, which compared reared and wild individuals of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L., are discussed with emphasis on morphological and behavioural differences. It was concluded that exposure to an artificial rearing environment during ontogeny can affect both the phenotype and the behaviour of the reared individuals, and thereby, their potential for survival after release into the wild as well. Suggestions are made as to how to diminish observed differences, and thereby, improve the survival potential.
47 citations
TL;DR: The tolerance of incubating salmon embryos to spawning gravel sedimentation was examined under hatchery conditions and also in the natural state on the River Bush, County Antrim, Northern Ireland, and mean survival was found to be better than that recorded in the hatchery, although no clear relationship was established between the level of fines and percentage survival in the wild.
Abstract: The tolerance of incubating salmon embryos to spawning gravel sedimentation was examined under hatchery conditions and also in the natural state on the River Bush, County Antrim, Northern Ireland. In a laboratory assessment alevin survival was closely related to the level of fine material. The number of individuals was reduced at the 10% fines level while >15% fine material was found to be deleterious to survival. Mean survival on the river (19.26%) was found to be better than that recorded in the hatchery, although no clear relationship was established between the level of fines and percentage survival in the wild. The mean fines accumulation (13.59%) in the river incubators at the end of the experiment was shown to be statistically similar to the background substrate. The role of high flow events in the contamination of gravels scoured by spawning fish is discussed.
TL;DR: External morphological characteristics were used to identify escaped farmed Atlantic salmon, Salmo salar L., in a coastal salmon fishery in County Antrim, Northern Ireland during four fishing seasons and at an adjacent freshwater location during a 5-year period to show correlation between presence in the marine fishery and in fresh water.
Abstract: External morphological characteristics were used to identify escaped farmed Atlantic salmon, Salmo salar L., in a coastal salmon fishery in County Antrim, Northern Ireland during four fishing seasons and at an adjacent freshwater location (R. Bush) during a 5-year period. Out of a total of 36 326 adult salmon examined in the fishery, 883 (2.4%) were identified as having escaped from sea cages. Annual average values ranged from 0.26% to 4.04% of the fish caught. Occurrence of escapees entering an adult trap in fresh water averaged 0.88%, with a range of 0.13–2.62%, depending on year. No correlation between presence in the marine fishery and in fresh water was evident, the latter year-round figures probably being more indicative of presence of escapees in spawning stocks. Entry to fresh water was significantly later on average for escaped farmed salmon, compared with wild salmon.
TL;DR: The cumulative effects of growth rates estimated from the new model and lower losses through predation could imply a higher contribution of winter eggs to the autumn fishery, but further evaluation is needed to properly quantify the trade-offs between settlement and recruitment to the fishery.
Abstract: Settlement, growth and mortality of the brown shrimp, Crangon Crangon L., were studied in the north Frisian Wadden Sea over a period of 19 months to fill existing gaps regarding the species' life cycle, and thereby to clarify points related to the fishery. Settlement of postlarval shrimp in the shallow areas occurred in three batches: in May; during summer; and an overwintering batch. Compared with an earlier model based on laboratory-derived data, a new growth model based on field data predicts similar growth rates for the earlier phase of the shrimp life cycle, but higher rates for the later stages of the cohorts. Mean growth rate of the different cohorts over the size range sampled was 0.23 ± 0.08 mm day−1. Of the factors tested, only temperature significantly influenced growth rates. Preliminary estimates of instantaneous total mortality values for shrimp cohorts from these shallow areas ranged from 0.03 to 0.12 day−1. Salinity explained most of the variation in mortality rates, but this most likely indicates an indirect effect of depth on emigration. The cumulative effects of growth rates estimated from the new model and lower losses through predation could imply a higher contribution of winter eggs to the autumn fishery. This, however, needs further evaluation to properly quantify the trade-offs between settlement and recruitment to the fishery, as well as the growth and mortality rates.
TL;DR: In this paper, the authors analyzed the data collected at the cooling water intake screens of West Thurrock power station located 35.5 km downstream of London Bridge on the Thames estuary during the decade 1980-1989.
Abstract: Fish samples collected at the cooling water intake screens of West Thurrock power station located 35.5 km downstream of London Bridge on the Thames estuary during the decade 1980–1989 were analysed. Seasonal and long-term changes in the abundance of the 15 most numerous fish species and in several fish community parameters were analysed. The majority of species were highly seasonal in their distribution and abundance. Species diversity was lower in the summer (May–August) compared with spring/winter (October–February). Evidence of long-term changes in species diversity and community structure over the decade is presented. The changes were consistent with a period of relative stability (1980–1984) followed by a period of change (1985–1989) and may reflect a deterioration in water quality in the second quinquennium. It is argued that the monitoring of fish communities in estuaries should be based on a multi-metric approach as no single indicator alone can describe the complex community structure.
TL;DR: The results indicate that instream cover from submerged macrophytes may be important for maintaining high 0 + trout densities in small and medium-sized streams where other types of instREAM cover are in short supply.
Abstract: The effect of instream cover on the density of juvenile sea trout, Salmo trutta L., in two streams in southern Sweden was studied. One of the streams, Vallkarrabacken, was narrow (2–3 m) and had few sympatric species, whereas the other stream, Braan, was wider (6–8 m) and had many sympatric species. Three treatments were used: (1) addition of artificial vegetation; (2) an undisturbed control; and (3) removal of natural vegetation. Only the first two treatments were tested in Braan, whereas all three treatments were tested in Vallkarrabacken. The 0 + trout density was higher in sections containing artificial vegetation than in control sections, which in turn had higher densities than sections where natural vegetation was removed. Moreover, the effect of adding artificial vegetation on trout density was most pronounced at the end of the summer. The results indicate that instream cover from submerged macrophytes may be important for maintaining high 0 + trout densities in small and medium-sized streams where other types of instream cover are in short supply.
TL;DR: Habitat–hydraulic modelling results were similar between the PHABSIM and EVHA with respect to flow vs. suitable habitat curves, but there were important differences between HABITAT and PHA BSIM/EVHA.
Abstract: Habitat–hydraulic models simulating habitat productive capacity for fish have met with limited success. Limitations of hydraulic modelling, particularly related to spatial scale relevant for hydraulic field data collection and model simulations, have attracted little attention. The hypothesis that hydraulic field sampling procedures and modelling scale per se affect results was tested using three habitat–hydraulic models that employed the same fish habitat data and similar hydraulic models.The PHABSIM, EVHA and HABITAT habitat–hydraulic models were compared on a 5.56 km long, 12–35 m wide, river segment in Newfoundland, Canada. Approaches to hydraulic data collection allowed higher spatial resolution in the EVHA and HABITAT models on selected subsegments representing habitat types (with from 12 to 14 transects per subsegment), while the PHABSIM models covered the entire segment but at lower resolution (a total of 14 transects representing four habitat types placed along the entire segment).Habitat–hydraulic modelling results were similar between the PHABSIM and EVHA with respect to flow vs. suitable habitat curves, but there were important differences between HABITAT and PHABSIM/EVHA. These differences were attributed mainly to different biological models because the hydraulic models performed similarly. Weighted usable area (WUA) curves gave less information than separate suitability curves for habitat variables. It is important that habitat–hydraulic data be collected, and model simulations conducted, at scales that are relevant to habitat selection by species and age classes of interest.
TL;DR: It is believed that the higher biomass growth in habitats 2 and 3 may have reflected differences in cover afforded by the deeper water and coarser substrates and/or improved foraging opportunities facilitated by the larger volumes of water in the deeper habitats in which the trout could search for prey.
Abstract: The effect of habitat on the growth and diet of brown trout, Salmo trutta L., stocked at the same densities in nine stream enclosures, comprising three habitat types of different quality, were tested. The habitats, which were created based on microhabitat preference data, were a shallow water habitat lacking cobbles (habitat 1), a deeper, mixed cobble-bottomed (128-384 mm diameter) habitat (habitat 2) and a large cobble-bottomed (256-384 mm) habitat of intermediate depth (habitat 3). Brown trout were found to have greater increases in total biomass in habitats 2 and 3 than in habitat 1. The pattern for length did not follow that of biomass as trout had greater increases in total length in habitat 2 than in the other two habitats. Biomass of food in trout diets reflected habitat-specific fish biomass changes, with a greater total biomass of prey as well a greater biomass of the leech, Erpobdella, in habitats 2 and 3 than in habitat 1. There were no habitat-specific differences in the biomass of benthic or drifting invertebrates in the enclosures, with the exception of a tendency for an effect of habitat on the biomass of Erpobdella. Although there may have been habitat-specific differences in food resources that were not detected, it is believed that the higher biomass growth in habitats 2 and 3 may have reflected differences in cover afforded by the deeper water and coarser substrates and/or improved foraging opportunities facilitated by the larger volumes of water in the deeper habitats in which the trout could search for prey.
TL;DR: In this paper, fish assemblages in two reaches of the Hawkesbury-Nepean River were studied to determine the separate and combined effects of modifications to the riparian vegetation and nutrient enrichment on the composition of fish assembls.
Abstract: Fish assemblages in two reaches of the Hawkesbury–Nepean River were studied to determine the separate and combined effects of modifications to the riparian vegetation and nutrient enrichment on the composition of fish assemblages. Fish were sampled along vegetated and degraded banks where no vegetation was present, and upstream of and within zones of nutrient enrichment, associated with discharge of treated sewage effluent into the river and run-off from nearby urban areas. Although the species composition differed between river reaches, both the number of fish species and total fish abundance were significantly greater in habitats adjacent to vegetated banks. Five species [Anguilla reinhardtii Steindachner, Macquaria novemaculeata (Steindachner), Cyprinus carpio L., Hypseleotris compressa (Krefft) and Myxus petardi (Castelnau)] were significantly (P < 0.05) affected by riparian degradation, with mean abundances ranging from 3.3 to 13.0 times larger than adjacent to vegetated banks. Species richness, total abundance and abundance of M. novemaculeata and H. compressa were also higher in zones with low levels of nutrient enrichment. Multivariate analyses showed that while eutrophication has a major effect on fish assemblages in the Hawkesbury–Nepean River, even greater effects may result from clearing of riparian vegetation leading to bank degradation.
TL;DR: Evidence is presented that indicates a delay in spawning in silver pomfret in Kuwait waters, which means that only an insignificant level of spawning takes place in April, which, from the management point of view, may be ignored.
Abstract: The spawning periodicity of silver pomfret, Pampus argenteus (Euphrasen), was investigated against a background of conflicting evidence on the onset of spawning in this species. Contrary to the existing view that silver pomfret in Kuwait waters begin to spawn in March–April, evidence is presented that indicates a delay in spawning until May. Only an insignificant level of spawning takes place in April which, from the management point of view, may be ignored. The species has a prolonged spawning period extending from May to August in females, although the males mature in April and ripe specimens are encountered in monthly samples until September. There are two spawning peaks, the first one in May and the second in August.
TL;DR: The first bullhead was observed in the River Utsjoki in the far north of Finland for the first time in 1979 as mentioned in this paper, which is a tributary of the sub-Arctic River Teno, which flows into the Arctic Ocean and is one of the most important salmon rivers in northern Europe.
Abstract: The bullhead, Cottus gobio L., was observed in the River Utsjoki in the far north of Finland for the first time in 1979. This river is a tributary of the sub-Arctic River Teno, which flows into the Arctic Ocean and is one of the most important salmon rivers in northern Europe. The bullhead does not belong to the natural fish fauna of the Finnish river systems flowing into the Arctic. It was probably introduced by anglers as bait or accidentally during the water exchange activities as salmon fry were transferred from Finnish hatcheries to northern Norway. A viable bullhead population has dispersed through the River Utsjoki catchment. In 1995 its range extended from the lowest part of the river to a point 43 km upstream. It is highly probable that it has also entered the mainstem of the River Teno.
TL;DR: In this article, three lakes were repeatedly sampled at night using boat electric fishing, experimental gill netting, and fyke netting from May to November 1993 to evaluate the feasibility of using proportional stock density (PSD) to monitor warm-water fish populations in Washington State, USA.
Abstract: Three lakes were repeatedly sampled at night using boat electric fishing, experimental gill netting, and fyke netting from May to November 1993 to evaluate the feasibility of using proportional stock density (PSD) to monitor warm-water fish populations in Washington State, USA. Additionally, average night-time boat electric fishing catch-per-effort of largemouth bass, Micropterus salmoides (Lacepede), from 30 Washington lakes was also analysed to determine the amount of effort required to obtain adequate samples for precise PSD estimates. Temporal variations in PSD were not large enough to affect the management of warm-water fish populations in the small Washington lakes studied. However, the considerable effort required to obtain precise PSD estimates may limit its usefulness for warm-water fisheries surveys in the Pacific Northwest. On average, from three to 13 nights of electric fishing effort are needed to capture enough stock-length largemouth bass for PSD estimates, depending on the precision desired (80–95%) and the location of the lake (eastern or western Washington). Catch of stock-length fish can be maximized by using electric fishing for centrarchids and gill netting for yellow perch, Perca flavescens (Mitchill), in June or September. Adequate samples for precise PSD estimates can be difficult to obtain from Pacific Northwestern lakes, even when using recommended gear at optimum sampling times. Inability to capture an adequate sample size for precise PSD estimates may be responsible for some of the fluctuation in PSDs in some studies of warm-water fish populations in northern areas. Managers in other northern climates may find that low sample size may account for large variations in PSDs reported.
TL;DR: A genetic study based on polymorphic tissue enzymes found significant differences at the IDDH-1*, PGM-1* and GPI-2* loci were found when data from a sample of transferred wrasse caught in southern Norway were compared with local wrasse in the recipient areas.
Abstract: The application of goldsinny wrasse, Ctenolabrus rupestris (L.), as parasite cleaners in the salmon farming industry has led to transport of live wrasse between regions in Norway. Owing to the operation of salmon farms, some of the transferred wrasse escape from the salmon net pens and can therefore mix and potentially interbreed with the local populations. The genetic effects of such interbreeding are unknown and information about the genetic population structure of this species in Norwegian inshore waters is needed to evaluate the potential effects. A genetic study based on polymorphic tissue enzymes was therefore carried out. Four of the 35 protein coding loci screened were polymorphic at the 99% level, and only two at the 95% level. The allele frequencies of the IDDH-1*; PGM-1*; GPI-1* and GPI-2* loci were compared in wrasse samples (1442 specimens) collected at 12 localities. Significant differences were found for PGM-1* among the samples collected at two inner fjord localities. Significant differences at the IDDH-1*, PGM-1* and GPI-2* loci were found when data from a sample of transferred wrasse caught in southern Norway were compared with local wrasse in the recipient areas.
TL;DR: The bullhead was observed for the first time in the River Utsjoki, a tributary of the River Teno, in 1979 and statistical analysis showed that the presence of the bullhead had not affected juvenile salmon densities.
Abstract: A newly introduced species, the bullhead, Cottus gobio L., was observed for the first time in the River Utsjoki, a tributary of the River Teno, in 1979. The River Teno is one of the most important Atlantic salmon, Salmo salar L., rivers in Northern Europe and its tributary the River Utsjoki is an important salmon spawning and nursery area. The densities of bullhead were lowest in the areas to which the species has spread most recently and highest in the areas downstream of its introduction point. Densities were markedly lower upstream. Statistical analysis showed that the presence of the bullhead had not affected juvenile salmon densities in the River Utsjoki.
TL;DR: In this article, a framework is described which proposes a sequential series of questions to guide the fisheries manager or student of fisheries through the process of planning and managing an inland fishery.
Abstract: A framework is described which proposes a sequential series of questions to guide the fisheries manager or student of fisheries through the process of planning and managing an inland fishery. It proceeds from such general issues as the place of inland fisheries in national and regional sector plans to prescriptions for the application of specific techniques for the assessment of the fishery and the implementation of management procedures.
TL;DR: In this article, three methods were used to estimate coarseness of substrate within experimental stations in four Newfoundland rivers: (1) a categorical rating was derived by estimating proportions of types of all the substrate within an area; (2) a similar type of rating, but from substrate types within 30 cm sections delineated on a lead rope stretched across the station; and (3) an index of coarsereness of the substrate was measured from a depth sampler constructed of 11 sliding rods supported within a 1 m long frame.
Abstract: Three methods were used to estimate coarseness of substrate within experimental stations in four Newfoundland rivers: (1) a categorical rating was derived by estimating proportions of types of all the substrate within an area; (2) a similar type of rating was derived, but from substrate types within 30 cm sections delineated on a lead rope stretched across the station; and (3) an index of coarseness of the substrate was measured from a depth sampler constructed of 11 sliding rods supported within a 1 m long frame. The rod, or depth, sampler was considered to provide the least subjective method and could therefore provide an index to validate the other methods. Compared with the standard deviations of depths for the rod sampler, the categorical ratings from the general estimate had an rs= 0.85, and the 30 cm sampler an rs= 0.86. It was deduced that the two methods of visually estimating substrate types in shallow clear rivers are reasonably adequate methods for describing coarseness, but that the depth sampler would be the more precise under certain conditions.
TL;DR: The results indicate that the tag and tagging operation had no influence on either growth or mortality, although tag retention was poor compared with other studies, and alternative tagging locations may improve retention rates and the visibility of the tag.
Abstract: In tropical fisheries where ageing fish is often difficult, tagging programmes offer an important means to estimate growth parameters and mortality rates. The majority of tags are large and attached externally via a puncture in the muscle. These characteristics may cause significant biological effects which bias parameter estimates. Visible implant (VI) tags offer a more benign means to individually mark fish. The utility of VI tags for marking five species of tropical river fish was examined. The results indicate that the tag and tagging operation had no influence on either growth or mortality, although tag retention was poor compared with other studies. For three of the five species, the only suitable tagging location was highly inconspicuous and therefore inappropriate for tagging programmes that rely upon fishermen to return tagged fish. Alternative tagging locations may improve retention rates and the visibility of the tag.
TL;DR: Among brown trout, males showed a significantly greater propensity to eat and to stay in the upper part of the stream near the stocking site compared with females, and brown trout with natural food items in their stomachs had significantly lower mean length than trout without such items.
Abstract: Hatchery-reared, juvenile European grayling, Thymallus thymallus (L.), and brown trout, Salmo trutta L., were each stocked six times into an area of a semi-natural stream. The order in which the two species were released was switched after every second experimental stocking. Temporal and spatial post-stocking dispersal, effects of previously stocked species, feeding behaviour and the influences of sex and size were studied. During each 48-h experimental release period, some fish were recaptured in a trap situated 200 m downstream from the stocking site, and fish remaining in the stream after each experimental release were caught by electric fishing. Significantly more grayling than trout moved downstream and left the semi-natural stream. Proportions of stocked grayling recaptured in the trap within 2 h and from 2 to 48 h post stocking in the stream were 36.4% and 10.0%, respectively. Corresponding recapture rates for brown trout were both 1.5%. Most of the grayling and brown trout that did not leave the stream early were recaptured in deep, slow-moving water at low velocities in the release area. The presence of grayling at the time that the brown trout were stocked resulted in significantly fewer brown trout staying in the upper part of the stream. Within 48 h of their release, 33.3% and 22.8% of the grayling and brown trout, respectively, had eaten natural food items. The mean length of brown trout recaptured in the upper part of the stocking area was significantly lower than that of fish recaptured in the lower part and in the trap. Among brown trout, males showed a significantly greater propensity to eat and to stay in the upper part of the stream near the stocking site compared with females. Brown trout with natural food items in their stomachs had significantly lower mean length than trout without such items. No sex- or size-related differences were found in the spatial distribution or feeding activity of grayling.
TL;DR: Fisheries management strategies based on habitat protection require definitive assessment of fish habitat affinities, but most habitat association information is based on disparate data from multiple sampling strategies.
Abstract: Fisheries management strategies based on habitat protection require definitive assessment of fish habitat affinities, but most habitat association information is based on disparate data from multiple sampling strategies. Habitat affinities were quantitatively defined using consistently collected data with a 16-m high-rise otter trawl at 314 Virginian Province (US) sites from 1990 to 1993. Catch rates and field-recorded salinity, depth, sea bed type, and geography (coastal system) associated with each trawl were analysed. Habitat affinity was quantified by comparing the concentration of fish in a particular habitat with the prevalence of that habitat. Fishes exhibited a specific habitat affinity even though they occurred across a range of environmental gradients. Fish were most associated with salinity (14 of 19 species/life-stage groups had a significant affinity for at least one salinity zone). Three-quarters of the flatfish displayed an affinity for a selected sea bed type; the same percentage of sciaenids had an affinity for a particular salinity zone.
TL;DR: In this paper, angling data collected between 1971 and 1991 were analyzed before, during, and after logging operations for 20 lakes located within 200 m of a clear-cutting area and 16 reference lakes undisturbed by logging.
Abstract: Brook trout, Salvelinus fontinalis (Mitchill), angling data, collected between 1971 and 1991, were analysed before, during, and after logging operations for 20 lakes located within 200 m of a clear-cutting area and 16 reference lakes undisturbed by logging. The mean weight of catches by anglers remained unchanged over the three periods, while catches per unit of effort (CPUE) and biomass per unit of effort (BPUE) decreased, respectively, by 18% and 22% after clear-cutting. These changes reflected a significant modification in population dynamics probably caused by logging operations. Results indicated that the negative impacts on aquatic fauna were felt more strongly on water bodies located in watersheds where deforestation was more severe; CPUE was inversely correlated with a cumulative cutting index (CI) developed from physiographic parameters. An increasing interannual trend of the spring-flood discharge in the order of 8% was noted. It was hypothesized that this increase might damage spawning and nursery habitats, hence affecting recruitment and offering a possible part of the explanation for the variations in fishing success. The cause-to-effect links and the mechanisms associated with changes affecting fish populations following deforestation remain to be clarified.