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1.
Long‐whiskered catfish, Sperata aor (Hamilton 1822), is commercially important in food, ornamental and sport fisheries. The fish is mainly caught from the wild populations because its aquaculture practices are not commercialised. Inland fishery in the Ganga basin is mostly unorganised; hence, no published report is available on the trend of S. aor production from the selected habitat. In India, S. aor has been categorised vulnerable mainly due to natural and anthropogenic threats. Otolith chemistry shows variation with changing physico‐chemical conditions of the fish habitat. Therefore, the present study was conducted with the objective to analyse spatio‐temporal variations in water chemistry in relation to environmental factors; relationship between water and otolith chemistry; and spatio‐temporal variations in otolith chemistry to discriminate the stocks of S. aor inhabiting the River Ganga. Most of the element: Ca ratios in water samples did not show significant correlations with environmental factors, viz. temperature and conductivity. Only few element: Ca concentrations in otoliths were positively correlated to their corresponding ratios in the ambient water. In the selected study area, the S. aor populations were discriminated into four stocks possibly because of heterogeneous water chemistry at the sampling sites, and physical barriers. In the present study, otolith chemistry showed relatively low temporal variability as compared to spatial variability; thus, the classification accuracy of individuals to their original populations remained consistent over the selected time period. The findings could be useful in devising scientifically sound management strategies and/or any conservation plans for the vulnerable S. aor populations inhabiting the River Ganga.  相似文献   

2.
Floods are known to be the major source of natural variability and disturbance in stream ecosystems. However, the management and channelisation of large rivers have impacted the fluvial geomorphology and disconnected the main channel and floodplains used as nurseries by many species of fish. This study examines the influence of a first autumnal flood event of the Ardèche River on the roach population, Rutilus rutilus (Linnaeus, 1758), in the Caderousse reach on the Rhône River. This influence was evaluated through an analysis of the spatial distribution for the abundance and size of juvenile roach and an analysis of otolith shape. Juvenile roach from the three sections of the reach formed well‐defined local populations before and after the flood event. Juvenile roach were always more abundant in the less modified section (BPS) of the river than in the other sections (RES and TAIL). While the original primary river channel was directly impacted by the flash flood, no significant difference in otolith shape was observed before or after the flash flood. Our results suggest that this part of the reach provides refuge habitats used by fish during high flow events.  相似文献   

3.
Abstract Telemetry was used to examine spawning migration of sea trout, Salmo trutta L. (n = 126), in two rivers in northern Sweden. The spawning areas defined by radio‐tagged fish differed between the river systems. In the River Vindelälven, sea trout spawned in the main stem and 80% of tagged individuals returned to areas where hatchery‐reared juveniles had been previously stocked. In the River Piteälven, 74% of tagged sea trout ascended tributaries for spawning. Tagged fish were categorised into three groups of migratory pattern. cart (classification and regression tree) analysis indicated that distance from tagging location to spawning site (Sdist) explained the migratory patterns. Large Sdist separated fish with stepwise upstream migration from those with up‐ and downstream migrations and one‐directional direct migration. Fish tagged early in the season migrated the longest distance to spawning areas. Stocking locations and sex explained the large search behaviour up‐ and downstream in the rivers. The findings are important for the sustainable management of sea trout in the Gulf of Bothnia.  相似文献   

4.
We studied the otolith microstructure and growth of sardine, Sardina pilchardus, in the North Aegean Sea (eastern Mediterranean Sea), using samples of larvae and juveniles that had hatched in winter (November–January) and winter–spring (February–May), respectively. The juveniles had developed during an extended period coinciding with marked pelagic ecosystem changes (from winter, mixed conditions to summer, stratified waters). To examine the relationship between environmental changes and the observed variability in their otolith increment–width trajectories (width‐at‐age), we summarized the shape of trajectories with a four‐parameter set estimated from a growth model fit to each width trajectory. The individual parameter sets were then related to the potential oceanographic conditions that fish experienced during their development, derived from a hydrodynamic–biogeochemical model (POM‐ERSEM), implemented in the sampling area. Substantial seasonal effects were demonstrated on the otolith microstructure (platykurtic versus leptokurtic trajectories in winter‐mixed versus summer‐stratified conditions), which were related to the progressive sea surface warming. In a subsequent step, in order to study the effect of oceanographic conditions on larval and juvenile daily growth rates, a GAM (Generalized Additive Model) analysis of otolith increment widths was carried out, using model‐derived oceanographic parameters and taking into account the ‘inherent otolith growth’, expressed by the explanatory variables ‘previous increment width’ and ‘Age’. Results showed a strong and positive, linear effect of temperature on the growth rate of winter‐caught larvae, whereas in juveniles, which had developed within a wide range of temperatures, an optimum temperature for growth was observed at around 24°C.  相似文献   

5.
This is the first comprehensive study on the occurrence and distribution of piscine reovirus (PRV) in Atlantic salmon, Salmo salar L., caught in Norwegian rivers. PRV is a newly discovered reovirus associated with heart and skeletal muscle inflammation (HSMI), a serious and commercially important disease affecting farmed Atlantic salmon in Norway. A cross‐sectional survey based on real‐time RT‐PCR screening of head kidney samples from wild, cultivated and escaped farmed Atlantic salmon caught from 2007 to 2009 in Norwegian rivers has been conducted. In addition, anadromous trout (sea‐trout), Salmo trutta L., caught from 2007 to 2010, and anadromous Arctic char, Salvelinus alpinus (L.), caught from 2007 to 2009, were tested. PRV was detected in Atlantic salmon from all counties included in the study and in 31 of 36 examined rivers. PRV was also detected in sea‐trout but not in anadromous Arctic char. In this study, the mean proportion of PRV positives was 13.4% in wild Atlantic salmon, 24.0% in salmon released for stock enhancement purposes and 55.2% in escaped farmed salmon. Histopathological examination of hearts from 21 PRV‐positive wild and one cultivated salmon (Ct values ranging from 17.0 to 39.8) revealed no HSMI‐related lesions. Thus, it seems that PRV is widespread in Atlantic salmon returning to Norwegian rivers, and that the virus can be present in high titres without causing lesions traditionally associated with HSMI.  相似文献   

6.
Between 1979 and 1991, hatchery-reared 1+ and 2+ rainbow trout were released in May and June in the Boknafjord at the mouth of the River Imsa, and from April to June in the Oslofjord, southern Norway. The fish were recaptured in the fjords of release, in rivers emptying there and from rivers and sea further along the Norwegian coast. Of the total recaptures, 35.6% ascended rivers in the year of release. Some fish released at the River Imsa returned to the area of release after spending 1 to 3 years at sea. Among those that were recaptured in rivers, 11.9% were recaptured in other rivers than the Imsa. The growth rate of the fish varied inversely with size at release. The growth rate was higher in the Oslofjord than in the Boknafjord, and in both areas the growth rate decreased with time after release. Rainbow trout that had escaped from local fish farms entered the River Imsa between March and December. Adults ascending in spring remained a shorter time in the river (37 days) than those ascending in autumn (200 days). Fish entering in autumn decreased more in weight during their river stay than those ascending in spring, and females more than males. Spawning took place in April-May. The monthly mean river stay of juvenile entrants ranged from 2 weeks to 6 months. In total, 27.8% of the rainbow trout escaped from fish farms and captured in the Imsa strayed to other rivers for repeat spawning. There is no evidence for continuing survival of escaped Norwegian rainbow trout in the wild.  相似文献   

7.
Abstract – The objectives of this study were, first, to assess the usefulness of otolith microstructure analysis to examine winter size‐selective mortality of young‐of‐the‐year (YOY) Atlantic salmon and, secondly, to validate various hypotheses relating to the dynamics of two populations with different winter survival. By examining otolith microstructure, we back‐calculated body size at hatching and at emergence of YOY salmon sampled in fall 2000 and in early summer 2001 on the Petite Cascapédia River and the Bonaventure River (Québec, Canada). The results of the study did not reveal any size‐selective mortality of YOY salmon in the Petite Cascapédia River, while in the Bonaventure River, size‐selective mortality of the smaller individuals of the cohort was detected. This case study allowed not only a better comprehension of the population dynamics of those rivers but demonstrated the usefulness of otolith analysis to detect winter size‐selective mortality under a natural environment.  相似文献   

8.
Accuracy of angler‐reported data on steelhead, Oncorhynchus mykiss (Walbaum), harvest in Idaho, USA, was quantified by comparing data recorded on angler harvest permits to the numbers that the same group of anglers reported in an off‐site survey. Anglers could respond to the off‐site survey using mail or Internet; if they did not respond using these methods, they were called on the telephone. A majority of anglers responded through the mail, and the probability of responding by Internet decreased with increasing age of the respondent. The actual number of steelhead harvested did not appear to influence the response type. Anglers in the autumn 2012 survey overreported harvest by 24%, whereas anglers in the spring 2013 survey under‐reported steelhead harvest by 16%. The direction of reporting bias may have been a function of actual harvest, where anglers harvested on average 2.6 times more fish during the spring fishery than the autumn. Reporting bias that is a function of actual harvest can have substantial management and conservation implications because the fishery will be perceived to be performing better at lower harvest rates and worse when harvest rates are higher. Thus, these findings warrant consideration when designing surveys and evaluating management actions.  相似文献   

9.
Thibault I, Hedger RD, Dodson JJ, Shiao J‐C, Iizuka Y, Tzeng W‐N. Anadromy and the dispersal of an invasive fish species (Oncorhynchus mykiss) in Eastern Quebec, as revealed by otolith microchemistry. Ecology of Freshwater Fish 2010: 19: 348–360. © 2010 John Wiley & Sons A/S Abstract – Rainbow trout (Oncorhynchus mykiss) is invading rivers bordering the St. Lawrence Estuary (Quebec, Canada). Some rivers in Eastern Quebec support self‐sustaining populations while adult vagrants are frequently captured in rivers where no reproduction has been confirmed. We hypothesised that the development of anadromy has promoted the species dispersal. Otolith Sr:Ca analyses revealed that although all fish captured in the upstream stocking region were freshwater residents, both anadromous and freshwater resident phenotypes were found downstream in Eastern Quebec. The proportion of fish exhibiting the anadromous life cycle increased with the distance from the stocking zone. Eastern Quebec steelhead migrated to sea at the same age but at a larger size than steelhead within their native range. Age at first reproduction was similar to that observed in native populations. The development of the anadromous life cycle enables this species to colonise new rivers following long‐distance migrations along the St. Lawrence Estuary corridor.  相似文献   

10.
Fishways have historically been constructed to restore and preserve the ecological connectivity for fish in fragmented rivers. However, the fishways are often selective on species due to different size and swimming capacity. As the proportion of dammed rivers is still increasing, there is a growing need for more information on wild fish and their migration potential. In this study, we compared the swimming capacity of wild caught brown trout (Salmo trutta) and European grayling (Thymallus thymallus) until the fish were exhausted in a critical swimming speed (Ucrit) test, under three different naturally occurring stream temperatures in Norway: 1.7, 5.5 and 10°C. The results indicated that trout swim better at the warmer temperatures than at colder temperatures. The grayling showed consistent swimming patterns with little variation across all tested temperatures. The results therefore signify the need to have operational fishways already early in the spring when the grayling migration starts and highlight the need for more studies on fish migration abilities across a wider range of species and seasons.  相似文献   

11.
For effective management, information on the stock composition of a fishery is essential. Here, the utility of a resident trout, Salmon trutta L, microsatellite baseline to determine the origins of sea trout entering the rivers Tamar, Tavy and Lynher in south‐west England is highlighted – all share a common estuary and have major runs of sea trout. There is a high degree of geographical structuring of the genetic variation in the baseline rivers. Testing with simulated and real data sets showed fish can be assigned to reporting group with a high degree of accuracy. Mixed stock analysis of >1000 sea trout showed that fish entering the Tamar and Tavy constituted mixed stocks. Significantly, in the Tamar, non‐natal origin sea trout are restricted to the lower catchment. As well as providing insight into sea trout behaviour, this study also has important implications for the management of recreational rod and line fisheries.  相似文献   

12.
Exotic species present a great threat to native fish conservation; however, eradicating exotics is expensive and often impractical. Mechanical removal can be ineffective for eradication, but nonetheless may increase management effectiveness by identifying portions of a watershed that are strong sources of exotics. We used mechanical removal to understand processes driving exotic brown trout (Salmo trutta) populations in the Logan River, Utah. Our goals were to: (i) evaluate the demographic response of brown trout to mechanical removal, (ii) identify sources of brown trout recruitment at a watershed scale and (iii) evaluate whether mechanical removal can reduce brown trout densities. We removed brown trout from 2 km of the Logan River (4174 fish), and 5.6 km of Right Hand Fork (RHF, 15,245 fish), a low‐elevation tributary, using single‐pass electrofishing. We compared fish abundance and size distributions prior to, and after 2 years of mechanical removal. In the Logan River, immigration to the removal reach and high natural variability in fish abundances limited the response to mechanical removal. In contrast, mechanical removal in RHF resulted in a strong recruitment pulse, shifting the size distribution towards smaller fish. These results suggest that, before removal, density‐dependent mortality or emigration of juvenile fish stabilised adult populations and may have provided a source of juveniles to the main stem. Overall, in sites demonstrating strong density‐dependent population regulation, or near sources of exotics, short‐term mechanical removal has limited effects on brown trout populations but may help identify factors governing populations and inform large‐scale management of exotic species.  相似文献   

13.
Abstract. Analysis of 4 years’ club records shows that, on average, the anglers fishing for brown trout in the lower River Don, Aberdeenshire, Scotland made 9 trips/y of 4 hours duration, caught 0·8 fish/trip at the rate of 0·2 fish/h, making a total of 7 fish/season, having an average weight of 350g. There was, however, considerable variation in the results. Guests tended to fish for longer, and to catch less, than regular members. Most (95%) of the fish were caught by only 30% of the anglers, who accounted for 80% of the fishing effort. Angler efficiency increased with the number of seasons spent fishing the club waters during the period; it decreased with increase in water temperature and flow and, early in the season, tended to decrease slightly with increase in catch in the preceding month.  相似文献   

14.
Salmon from different locations in a watershed can have different life histories. It is often unclear to what extent this variation is a response to the current environmental conditions an individual experiences as opposed to local‐scale genetic adaptation or the environment experienced early in development. We used a mark–recapture transplant experiment in the Shasta River, CA, to test whether life‐history traits of juvenile Chinook salmon Oncorhynchus tshawytscha varied among locations, and whether individuals could adopt a new life history upon encountering new habitat type. The Shasta River, a Klamath River tributary, has two Chinook salmon spawning and juvenile rearing areas, a lower basin canyon (river km 0–12) and upper basin spring complex (river km 40–56), characterised by dramatically different in‐stream habitats. In 2012 and 2013, we created three experimental groups: (i) fish caught, tagged and released in the upper basin; (ii) fish caught at the river mouth (confluence with the Klamath River, river km 0), tagged and released in the upper basin; and (iii) fish caught at the river mouth, tagged and released in the lower basin. Fish released in the upper basin outmigrated later and at a larger size than those released in the lower basin. The traits of fish transplanted to the upper basin were similar to fish originating in the upper basin. Chinook salmon juvenile life‐history traits reflected habitat conditions fish experienced rather than those where they originated, indicating that habitat modification or transportation to new habitats can rapidly alter the life‐history composition of populations.  相似文献   

15.
Abstract – Management policies balancing harvest and conservation of natural populations of fish are difficult to establish, both scientifically and politically. This issue is particularly difficult when those populations represent native genetic resources. Since 1997, several brown trout populations in the eastern Pyrenees Mountains (Spain) were designated as ‘genetic refuges’ under varying fishing regulations, where releases of hatchery‐origin fish are not permitted. We analysed genetic variation in samples of brown trout from six of those refuge populations and four non‐refuge populations within the same region. Each population was sampled in four separate years: 1993, 1999, 2004 and 2006. Our analyses were based on a diagnostic allele (LDH‐C*90) that distinguishes native and exogenous hatchery populations. Comparisons were based on stocking histories before and after refuge designations and on three management strategies: fished, unfished and catch‐and‐release. Overall, we detected significant genetic introgression resulting from past stocking practices despite the current restriction of hatchery releases imposed by the recent genetic refuge policy. However, this new policy has prevented detectable introgression from increasing throughout the region and together with additional measures on length and number of captured fish is contributing to self‐sustained fisheries that are achieving conservation goals. Quick acceptance of ‘genetic refuges’ by anglers in one particular river, the Ter River basin, has been a key factor in protecting native gene pools compared with the Segre River basins where refuges were not readily accepted.  相似文献   

16.
To predict recreational‐fishing impacts on freshwater fish species, it is important to understand the interplay between fish populations, anglers and management actions. We use an integrated bioeconomic model to study the importance of fish life‐history type (LHT) for determining (i) vulnerability to over‐exploitation by diverse angler types (generic, consumptive and trophy anglers), who respond dynamically to fishing‐quality changes; (ii) regulations [i.e., minimum‐size limits (MSLs) and licence densities] that maximize the social welfare of angler populations; and (iii) biological and social conditions resulting under such socially optimal regulations. We examine five prototypical freshwater species: European perch (Perca fluviatilis), brown trout (Salmo trutta), pikeperch (Sander lucioperca), pike (Esox lucius) and bull trout (Salvelinus confluentus). We find that LHT is important for determining the vulnerability of fish populations to overfishing, with pike, pikeperch, and bull trout being more vulnerable than perch and brown trout. Angler type influences the magnitude of fishing impacts, because of differences in fishing practices and angler‐type‐specific effects of LHT on angling effort. Our results indicate that angler types are systematically attracted to particular LHTs. Socially optimal minimum‐size limits generally increase with LHT vulnerability, whereas optimal licence densities are similar across LHTs. Yet, both regulations vary among angler types. Despite this variation, we find that biological sustainability occurs under socially optimal regulations, with one exception. Our results highlight the importance of jointly considering fish diversity, angler diversity and regulations when predicting sustainable management strategies for recreational fisheries. Failure to do so could result in socially suboptimal management and/or fishery collapse.  相似文献   

17.
The proportion of angled Atlantic salmon Salmo salar L. being caught and released has increased. If individuals are repeatedly captured, this may have fish welfare consequences. Of 995 Atlantic salmon tagged during catch and release in eight Norwegian rivers, 10% were captured twice, while 3% were captured three times within the same fishing season. The probability that released salmon were captured again decreased with decreasing time left of the fishing season, decreased for larger‐sized fish and varied among rivers/years. Increased exploitation rates within the river, indicating an increased fishing pressure, strongly increased the probability that fish would be recaptured. However, the proportion of salmon caught a second time was much lower than the total exploitation rates in the same rivers (which was on average 46%). For fish tagged in the sea, the likelihood of being angled decreased with time since entering the river, which may explain why the recapture rates of caught and released fish were lower than the total exploitation rates.  相似文献   

18.
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.  相似文献   

19.
To apply otolith microstructure to examination of age and growth of juvenile chum salmon Oncorhynchus keta inhabiting coastal waters, formation of otolith increments was investigated for juveniles reared in a seawater aquarium and in net pens. In all otoliths examined, a distinctive check was formed at the time of sea entry of the fish. The deposition of otolith increments after the check was daily for rearing both in the aquarium (57 days) and in the net pens (26 days). Check formation associated with sea entry was also observed in otoliths of juvenile salmon collected 1 km off the coast of Shari, Hokkaido, Japan. Transmitted light observation of otoliths of those fish revealed a transition in otolith increment appearance from dark to light. Otolith Sr: Ca ratio remarkably changed from a low to a high level, coinciding with the transition in otolith appearance. It is suggested that the transition was associated with individual sea entry. This study demonstrated that the check and/or transition associated with sea entry are applicable to a benchmark for otolith increment counts of juvenile chum salmon inhabiting coastal waters.  相似文献   

20.
Sea trout (Salmo trutta L.) stocks on the West Coast of Scotland and Ireland have decreased due to reduced survival during the marine phase of their life cycle. Lice‐infested sea trout returning to rivers could indicate that parasite burdens are contributing to the decline. Salmon farms represent a potential source of substantial quantities of sea lice, leading to a conjectured link between parasites on salmon fish farms and infestations on wild sea trout. To investigate the potential infective pressure on sea trout in Loch Shieldaig, offshore and sub‐littoral plankton samples were collected and analysed for sea lice nauplius and copepodid stages. During the plankton survey, numbers of sea lice on a fish farm in the loch reached a maximum in November 2001. Soon after, numbers of sea lice larvae peaked in open‐water samples and then in sub‐littoral samples. Nauplii were found adjacent to the farm and occurred less elsewhere. This study reports a concentration of sea lice larvae at the head of Loch Shieldaig and indicates a possible relationship between sea lice numbers on the fish farm and lice larvae densities in the open‐water of the loch and in the sub‐littoral zone.  相似文献   

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