共查询到20条相似文献，搜索用时 93 毫秒
1.
Julio L. Lancelotti Luciana M. Pozzi Pablo M. Yorio María C. Diéguez Miguel A. Pascual 《水产资源保护:海洋与淡水生态系统》2009,19(5):497-505
- 1. The Strobel Meseta, a basaltic plateau of Patagonia (Santa Cruz Province, Argentina), holds thousands of shallow fishless lakes that are prime habitat for many species of waterbirds, including some considered ‘near threatened’. In recent years, several lakes have been stocked with trout which has created uncertainty about the potential effects on the recipient ecosystem.
- 2. Limnological and topographical analyses were performed in a group of 32 lakes of the Strobel Meseta in order to characterize and classify individual lakes of the meseta based on their limnological and topographic features, analyze the association between lake type and use by aquatic birds in general and by the endemic hooded grebe (Podiceps gallardoi) in particular, and evaluate the overlap between trout aquaculture and critical habitat for waterbirds.
- 3. The lakes were classified by multivariate analyses into four characteristic types: turbid, high conductivity lakes (T), small vegetated lakes (SV) and larger lakes which were subdivided into either vegetated (LV) or unvegetated (LU). In general, macrophyte cover was the main classificatory variable, whereas conductivity, pH, surface, and depth contributed moderately. Large vegetated lakes were generally found to be important for waterbirds and provided critical habitat for the hooded grebe, whereas trout farmers largely favoured large unvegetated lakes. However, since some large vegetated lakes have already been stocked, there is some level of geographical overlap between waterbird habitat and trout farming.
- 4. The existence of some level of spatial segregation between production and critical waterbird habitat affords opportunities for designing a spatially‐based management system for trout aquaculture.
2.
Doris Soto Ivan Arismendi J. Andres Olivos Cristian B. Canales-Aguirre Jorge Leon-Muñoz Edwin J. Niklitschek Maritza Sepúlveda Felipe Paredes Daniel Gomez-Uchida Yuri Soria-Galvarro 《Reviews in Aquaculture》2023,15(1):198-219
Here, we review extensive information to estimate environmental risks from escaped non-native salmonids based on the assessments of hazard, sensitivity and exposure of discrete water bodies in Chile. In 2020, the country harvested about 1 million tons salmonids from net pens located along 1500 km of highly biodiverse coastline. We base our analysis on existing scientific information and authors' expert opinions including an assessment of knowledge gaps and uncertainties. Risks of environmental impacts differed by salmon species, being lowest for Atlantic salmon due to its estimated lower survival, lower ability to feed after escaping and lower reproductive capacity in the wild compared to coho salmon and rainbow trout. Overall risks due to escapes of any of the species were highest in areas of both high farming intensity and low capacity of mitigating escapes (by wild predators and fishers) such as Aysén District. At same time, risk was higher in the most farmed areas that also presented suitable habitats to support reproduction and juvenile salmonid rearing. However, the risk estimation certainty differed among species being lowest for Atlantic salmon due to insufficient monitoring of their fate in the wild. Monitoring the fate and impacts of escaped salmonids, specially in higher risk areas is recommended to improve risk projections and to prevent and mitigate further impacts. Since Atlantic and coho salmon are not yet successful invaders in Chile, research attention is urgently needed to assess the environmental consequences of escapes of these species. The present approach can be applied to any aquaculture system given the availability of information on farmed species and receiving ecosystems. 相似文献
3.
- Aquaculture in arid Patagonia is potentially affecting the hooded grebe (Podiceps gallardoi), a critically endangered endemic waterbird. Exotic rainbow trout (Oncorhynchus mykiss) were stocked from 1994 in naturally fishless lakes, the primary reproductive habitat of this grebe.
- Trout and grebes are visual predators, whose diets overlap. Consequently, trout could reduce the abundance of prey of the hooded grebe.
- This study compared the size distribution and abundance of the pelagic zooplankton fraction preyed upon by trout in four fishless lakes and three lakes stocked with trout, including vegetated and unvegetated lakes.
- The mean size of Daphnia spp. was 45% and 35% larger in fishless lakes than in stocked lakes, for unvegetated and vegetated lakes, respectively. Boeckella spp. were larger in fishless than in stocked vegetated lakes.
- Fishless and stocked lakes had highly contrasting biomasses of large pelagic crustaceans. Amphipods were absent from the water column of all stocked lakes analysed, and were abundant in fishless lakes. Parabroteas sarsi was absent from the two large unvegetated lakes, stocked with trout.
- These shifts in the abundance and size spectrum of the zooplankton may reflect competition between trout and hooded grebe, affecting the survival of the latter species.
- The current conservation status of this rare aquatic bird demands the application of management tools to reduce the detrimental effects of aquaculture on their primary reproductive habitat.
4.
5.
Nicholas T. Simpson Alexander P. Bybel Michael J. Weber Clay L. Pierce Kevin J. Roe 《水产资源保护:海洋与淡水生态系统》2021,31(7):1831-1846
- Many fish species of greatest conservation need (SGCN) in Iowa and Minnesota, USA, have been in decline for decades. A key reason for the decline is the alteration and degradation of naturally flowing streams owing to land use changes resulting from agricultural practices. Populations of several fishes have been adversely affected by widespread stream channelization that has resulted in more homogeneous stream habitats throughout Iowa and Minnesota.
- The goal of this study was to determine the abiotic and fish assemblage characteristics associated with the presence of these rare fishes. Electrofishing and seining were used to sample fish assemblages and 43 abiotic characteristics were measured at 111 sites in the North Raccoon and Boone River basins in central Iowa and the Rock River and Beaver Creek basins in north-west Iowa and south-west Minnesota during 2016 and 2017.
- Six SGCN, including the federally endangered Topeka shiner (Notropis topeka), were included in statistical modelling to determine habitat and fish assemblage characteristics associated with their presence.
- Species-specific nonmetric multidimensional scaling ordinations indicated that abiotic characteristics and fish assemblages often differed between sites where SGCN were present and absent. Random forest and logistic regression models suggested that the presence of four of six SGCN were positively associated with species richness, whereas all other 10 important abiotic and fish assemblage variables were unique to only one or two of the six SGCN.
- Topeka shiners were present at 36% of sites and were positively associated with orangespotted sunfish (Lepomis humilis) catch per unit effort while being negatively associated with canopy cover and fantail darter (Etheostoma flabellare) catch per unit effort.
6.
- The pet trade has been responsible for many introductions of non‐native species. Freshwater ornamental plants and animals originating from the pet trade are stocked to garden ponds. The present survey focused on awareness and responsible behaviour related to biological invasion risks of companies that designed, built, and stocked garden ponds.
- A representative number (n = 124) of companies (commercial garden pond architects and builders) in the Czech Republic were surveyed regarding the offer of non‐native, invasive and threatened native species. The survey was conducted over the entire warm period (from 1 May 2015 to 31 September 2015) while using personal visits, correspondence and interviews to list the species on offer.
- ‘Traditional’ ornamental species were offered by 39.1% of surveyed vendors, non‐traditional ‘marginal’ species by 5.6%, common native species by 6.5% and threatened native species by 2.4%.
- The findings of this study support the hypothesis that ‘garden pond’ vendors offer non‐native species with a risk of biological invasion; moreover, threatened native animals were also on sale. It is probable that a similar situation exists in other countries. It is important for the conservation of native aquatic biota to raise awareness of the need to reduce risk through responsible behaviour of those involved in the pet trade. It is also essential to prohibit stocking of potential invaders and to enforce the illegal capture and sale of native species.
7.
Marjorie Biffi Anaïs Charbonnel Laëtitia Buisson Frédéric Blanc Mélanie Némoz Pascal Laffaille 《水产资源保护:海洋与淡水生态系统》2016,26(4):761-774
- The implementation of effective and appropriate protection actions is frequently hindered by lack of thorough knowledge on species ecology especially in the case of endemic, vulnerable and elusive species.
- Using a recently updated and unpublished dataset describing the spatial distribution of the Pyrenean desman (Galemys pyrenaicus) in its northern range (French Pyrenees), an Ecological Niche Factor Analysis (ENFA) was conducted to provide a quantitative estimate of local habitat use by this endangered semi‐aquatic mammal. A comparative approach was used to investigate potential differences in habitat use among the three main hydrological regions of the French Pyrenees.
- The Pyrenean desman was identified as a marginal and specialist species concerning the selection of its local habitat in the French Pyrenees. Key habitat variables corresponded mainly to river‐bed characteristics (i.e. high heterogeneity of shelters and river substrates, fast flowing water facies, low amounts of fine sediment) and river‐bank characteristics (i.e. high proportion of rocks, low proportion of earth). A difference in habitat selection between the three hydrological regions of the French Pyrenees was also highlighted. A decrease in marginality and specialization from west to east as well as differences in habitat variables driving the ecological niche of the Pyrenean desman and its range suggested a spatial structure in desman populations regarding local ecological factors.
- These results stress the importance of effective and sustainable river management for the habitat quality of this endangered species and also demonstrate the importance of taking into account the variability in habitat preferences that can exist between geographically distinct populations. This finding has important implications for conservation planning that should thus be conducted at the population level instead of the traditional species level in order to target the specific needs of each hydrological region.
8.
1. The habitat of Texas wild‐rice (Zizania texana Hitchcock), known only from the spring‐fed upper San Marcos River in Central Texas, was classified in terms of physical and chemical conditions, depth, current velocity, associated aquatic macrophytes, and substrate composition. 2. Randomly selected transects in sites with and without Texas wild‐rice were evaluated during May, August and January 1994–1995. Physical and chemical conditions (temperature, dissolved oxygen, specific conductance, pH) were found to be nearly constant and uniform both among transect types and sampling dates. Chemical analysis of the substrate likewise showed few differences among transect types. Turbidity was found to be significantly different among transect types on only one sampling date (Kα0.05=0.60; p=0.009), but even non‐significant levels of turbidity may present biologically significant impacts to wild‐rice plants. 3. Differences in substrate particle size were highly significant (Kα0.05=0.71; p=0.001) with Texas wild‐rice occupying sites having moderately coarse to coarse sandy soils (73%) compared with the moderately fine to fine clay soils found at non‐rice sites (82%). However, no significant differences were found in organic matter content among rice and non‐rice transects ( =2.09 and 2.56%, respectively). 4. Texas wild‐rice was found primarily in shallow areas of the river (<1 m) and at higher current velocities than those of non‐rice sites ( ≥0.46 m s−1 and ≤0.22 m s−1, respectively). 5. Texas wild‐rice appears to be more commonly associated with other native species rather than exotic species. Mean percentage composition of exotic macrophytes did not exceed 29% in areas where Texas wild‐rice grew, but they accounted for nearly 47% of the composition in areas where rice did not grow. 6. The results of this study will allow for reliable and accurate identification of the remaining suitable habitat of Texas wild‐rice in the San Marcos River for possible reintroduction and development of management plans. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
9.
Zachary W. Culumber Garrett W. Hopper Nicholas Barts Courtney N. Passow Samuel Morgan Anthony Brown Lenin Arias‐Rodriguez Michael Tobler 《水产资源保护:海洋与淡水生态系统》2016,26(6):1155-1167
- Effective conservation measures for endangered species require basic knowledge of habitat use and critical environmental variables influencing the species' occurrence. However, setting priorities may be difficult when multiple endangered species inhabit the same area and differ in habitat use.
- This study characterized the physical and chemical environment at 30 sites along a 2.5 km stretch of stream associated with the Baños del Azufre hydrogen sulphide spring complex, home to the only population of the widemouth gambusia (Gambusia eurystoma) in existence. Also present in the spring is Poecilia sulphuraria, a narrowly endemic and endangered species known from only a few populations. This study provides the most detailed report to date for physical and chemical drivers of species density in this small, extreme environment.
- Gambusia eurystoma were generally rare throughout the stream, and stream flow and substrate size were the best predictors of G. eurystoma densities. Conversely, P. sulphuraria were considerably more abundant, but no physical or chemical variables predicted their density among sites. Size distributions of adult P. sulphuraria were significantly influenced by stream flow and water chemistry, indicating a cost to living in greater proximity to toxic springs with high hydrogen sulphide concentrations.
- Overall, the results provide the first extensive report of environmental variation and factors associated with G. eurystoma densities, and indicate that conservation measures prioritizing environmental conditions for G. eurystoma will also benefit P. sulphuraria. Fish in sulphide springs provide prime examples of narrowly endemic species in desperate need of conservation, and their habitats face conservation challenges similar to those found in other springs with sympatric, endemic species in the world's arid regions.
10.
《水产资源保护:海洋与淡水生态系统》2018,28(2):282-295
- Seagrass meadow degradation and loss is one of the major threats to fish biodiversity in coastal marine and lagoon ecosystems in the Mediterranean. Pipefishes and seahorses (family Syngnathidae) are particularly affected by loss of seagrass meadows and other structured habitats, on which they rely for survival and reproduction. Despite their charismatic appearance and peculiar behaviour, their habitat ecology is still poorly understood in Mediterranean coastal waters.
- This study focuses on syngnathid assemblage composition and diversity in the shallow waters of the Venice lagoon (Italy), aiming at highlighting habitat preferences and providing insights into the conservation of biodiversity in these ecosystems. Generalized Additive Models were used in order to disentangle the potential effect of habitat typologies and different architectures of seagrass meadows from that of other environmental parameters.
- Most abundant taxa and whole syngnathid assemblage indicators were positively associated with seagrass meadows. Only few species, however, were seagrass specialists in shallow waters, and preferred meadows with taller canopies.
- Despite that, other structured habitats including short‐leaved seagrass meadows and macroalgal beds were important for some species and overall assemblage diversity.
- Managers in Mediterranean coastal lagoons should thus limit human pressures that lead to the depletion of seagrass meadows, with particular attention to long‐ and broad‐leaved species in less confined areas. Nevertheless, syngnathid assemblages would benefit from the preservation and restoration of the overall habitat diversity characterizing shallow waters in coastal lagoon.
- Future studies should aim at investigating the potential role of habitats at greater depths in supporting syngnathids.
11.
Nicholas T. Simpson Alexander P. Bybel Michael J. Weber Clay L. Pierce Kevin J. Roe 《水产资源保护:海洋与淡水生态系统》2019,29(10):1735-1748
- In the USA, the Topeka shiner (Notropis topeka) is a federally listed endangered species that has been in decline for decades. A key reason for the decline is the alteration of naturally flowing streams and associated oxbow habitats resulting from land‐use changes. The focus of recent conservation efforts for Topeka shiners has been the restoration of oxbow habitats by removing sediment from natural oxbows until a groundwater connection is re‐established. This restoration practice has become common in portions of Iowa and south‐west Minnesota.
- The goals of this study were to compare the occurrence and abundance of Topeka shiners in restored and unrestored oxbows and to determine the characteristics that influenced their presence in these systems.
- In 2016–2017, 34 unrestored and 64 restored oxbows in the Boone, Beaver Creek, North Raccoon and Rock River basins in Iowa and Minnesota were sampled for their fish assemblages and abiotic features. Topeka shiners were present more often and with higher average relative abundances in restored oxbows.
- Nonmetric multidimensional scaling ordinations indicated that fish assemblages found in oxbows where Topeka shiners were present were less variable than assemblages found at oxbows where they were absent, but that abiotic characteristics were similar between oxbow types.
- Logistic regression models suggested that the presence of Topeka shiners in oxbows was positively associated with species richness, brassy minnow (Hybognathus hankinsoni) catch per unit effort (no. fish/100 m2; CPUE), orangespotted sunfish (Lepomis humilis) CPUE, dissolved oxygen and turbidity, and negatively associated with oxbow wetted length. These results highlight the use of restored oxbows by Topeka shiners while also providing new information to help guide restoration and conservation efforts.
12.
Amaiur Esnaola Jorge González‐Esteban Arturo Elosegi Aitor Arrizabalaga‐Escudero Joxerra Aihartza 《水产资源保护:海洋与淡水生态系统》2018,28(3):600-609
- The Pyrenean desman (Galemys pyrenaicus) is an endangered, semi‐aquatic, insectivore mammal, endemic to the northern Iberian Peninsula and the Pyrenees. Owing to its small populations, evasive behaviour, and nocturnal activity, knowledge of its ecological requirements is still limited. Continuing population decline over most of its distribution range – even in regions where water quality has clearly improved – points to other factors as the main conservation threat. Nevertheless, at present there is a lack of information on its habitat preferences within its area of occupancy (e.g. stream microhabitat characteristics), a key point for assessing or improving its habitat.
- This study used radio‐telemetry data to determine the use of space at microhabitat level by the desman, and how this changed depending upon environmental conditions.
- Desmans were studied in two contrasting rivers in the Basque Country (northern Iberian Peninsula): Elama, a nearly pristine stream, and the Leitzaran, a clean‐water stream affected by hydropower diversions. Fifteen desmans were captured and radio‐tracked in Elama and 16 were captured and radio‐tracked in the Leitzaran, and nocturnal activity points were assigned to one of three habitat types: riffles, runs, or pools. Habitat use was compared against availability to measure habitat selection in each stream and between streams.
- Desmans selected riffles positively and pools negatively, with this selection being stronger in the Leitzaran.
- The results highlight the ecological relevance of riffles as foraging habitats of desmans, and therefore as key features for their conservation. It suggests that channel modifications that reduce the areal cover of riffles impair habitat quality for this species. In addition, water diversion for hydropower is likely to be detrimental for desmans, as it reduces discharge and flow velocity in the bypassed river sections.
13.
Francesc Domènech Irene Álvarez de Quevedo Manuel Merchán Ohiana Revuelta Gabriela Vélez‐Rubio Sebastián Bitón Luis Cardona Jesús Tomás 《水产资源保护:海洋与淡水生态系统》2015,25(5):678-689
- A questionnaire‐based survey of fishermen was conducted in the Valencia region (eastern Spain) to assess the levels of marine turtle bycatch. Interviews covered 41.3% of the bottom trawling fleet in the region and included 111 fishermen (one per boat). Results were combined with those from previous studies conducted in neighbouring regions using the same methodology to assess the global impact of bottom trawling on the western Mediterranean stock of the loggerhead turtle (Caretta caretta).
- Estimated turtle catch per unit effort (CPUE) is 0.09 turtles per vessel per month, according to the information reported by fishermen. As a consequence, the whole fleet of bottom trawlers operating off the Valencia region was involved annually in 238 turtle bycatch events (95%, CI: 173–304).
- Ivlev's electivity index revealed that bottom trawling bycatch was higher than expected according to fishing effort in the northern part of the study area, where the continental shelf widens.
- The fishermen's perception was that the local stock of loggerhead turtles is declining, and that drifting longlines and bottom trawling are, at least in part, responsible for this trend.
- According to previous studies as well as the current results, bottom trawlers operating off mainland Spain capture mainly loggerhead turtles from the rookeries in the eastern Mediterranean, with only a low percentage of turtles of Atlantic origin.
- Loggerhead turtle bycatch by bottom trawling deserves more attention in the Valencia region, particularly in its northern part. Conservation measures in the area are discussed.
14.
- Habitat degradation and destruction arising from rapidly increasing urbanization represents one of the most significant threats to biodiversity. Human populations are continuing to increase around coastal regions, and as marine habitats are displaced by artificial structures it is important to understand how marine species may be impacted by these changes in habitat availability. The endangered seahorse Hippocampus whitei has been observed inhabiting protective swimming nets in Sydney Harbour, Sydney, Australia, even in the presence of natural habitats.
- This study tested whether the presence of a swimming net results in increased seahorse numbers at sites around Sydney Harbour, or whether seahorses are attracted away from natural habitats. Density surveys and mark–recapture population estimates were done at sites with pre-existing swimming nets and compared to control sites where only natural habitat was present. A manipulative experiment was conducted in which panels of swimming net material were installed at two sites in Sydney Harbour, with comparisons to control sites over a period of 14 months (April 2018 to June 2019) to test whether the installation of swimming nets would affect seahorses on surrounding natural habitat or increase site abundance.
- The pre-existing and installed swimming nets were found to support greater densities of H. whitei as well as some increases in site-scale abundance, with no effects on seahorse density on natural habitats. It is likely that increased seahorse production is occurring on the nets, with no evidence that seahorses are being attracted away from natural habitat; however, effects may vary across survey occasions and sites. Furthermore, swimming nets may serve as a useful replacement habitat in locations where natural habitat has become sparse or absent.
15.
1. Profundulus hildebrandi, the San Cristóbal pupfish, is a small cyprinodontiform fish endemic to the closed basin of San Cristóbal de Las Casas, a fast‐growing city in highland Chiapas, Mexico. This study constitutes the first population study of this endangered taxon. 2. In order to judge its conservation status, its distribution and habitat were described, and its population size was estimated through a capture–recapture technique. To the extent possible, present conditions of its habitat were compared with historic information, mainly old city maps and photographs. 3. Introduction of largemouth bass (Micropterus salmoides) coincided with local extirpation of P. hildebrandi. Other risk factors related to urban growth include pollution of streams, as well as habitat destruction, fragmentation, and modification; about 60% of the original pupfish habitat is heavily polluted by sewage. 4. Although its population size is apparently large (probably more than 8000), its very restricted distribution, its shrinking habitat and the increasing risk factors provide justification to consider P. hildebrandi as an endangered fish, according to the Mexican Official Norm and the Red Book of the IUCN. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
16.
Megan R. McCusker Janelle M.R. Curtis Nathan R. Lovejoy Nicholas E. Mandrak 《水产资源保护:海洋与淡水生态系统》2017,27(4):780-788
- A spatially explicit metapopulation viability model was created within RAMAS‐GIS to address questions related to the conservation and management of a freshwater species at risk (Notropis anogenus). Population viability analysis was conducted to evaluate extinction risk and sensitivity analyses were undertaken to identify the most important spatial and non‐spatial parameters influencing extinction and decline.
- As biodiversity offsets are increasingly used to compensate for habitat loss, the population model was also used to explore the effectiveness of four potential offsetting mechanisms. In particular, this study addressed whether the impact of habitat loss on a species at risk could be compensated by: (i) increasing habitat elsewhere; (ii) increasing vital rates; (iii) increasing abundance; and (iv) increasing connectivity.
- Results suggest that extinction risk is low for this metapopulation and that the risk of extinction was most sensitive to vital rates.
- Compensating habitat loss with habitat gain, the most straightforward approach explored, was by far the most effective type of compensation. Increasing vital rates was the second most promising approach. Although increasing abundance and increasing connectivity could not be categorically ruled out, their effectiveness was much more limited.
- Overall, this study provided insight into the influence of spatial and non‐spatial parameters on abundance, patch occupancy, and extinction risk of an aquatic species. This approach can be applied to a wide variety of species to evaluate the effect of ecosystem perturbations and inform management options.
17.
Concern about the overexploitation of wild aquatic resources, the slow recovery of the groundfish fisheries and the need to encourage the diversification of the mariculture industry of the province of Quebec (Canada) all provided strong incentive to explore the potential of a wide selection of marine and anadromous fish species for cold‐water mariculture. Starting from a list of over 45 indigenous fish species of potential commercial interest, a biotechnical review was initiated. Technical sheets for each species were produced and aquaculture‐based selection criteria covering three aquaculture approaches of development (complete life cycle, on‐growing and stock enhancement) were examined. Species were ranked according to their degree of suitability for the given biological parameters. The final classification analysis within the complete life cycle production strategy positioned the Atlantic wolffish as the top candidate species (91%) followed by the spotted wolffish and Arctic charr (87%). Growth rate, optimal growth temperature, duration of the weaning period, minimal lethal temperature, larval size and feed requirements were the determining criteria. The on‐growing scenario final results ranked Arctic charr first (84%) followed by Atlantic cod (79%) and Atlantic halibut (74%) mostly owing to their growth rate at low temperature and optimal growth temperature criteria. Stock enhancement programmes should concentrate their efforts on the striped bass (56%), the haddock (54%) and the Atlantic sturgeon (34%) based on their growth rate, fishery status, landing price and the availability of impact studies. 相似文献
18.
19.
Edwin J. Niklitschek Doris Soto Alejandra Lafon Carlos Molinet Pamela Toledo 《Reviews in Aquaculture》2013,5(3):172-195
Chile is the second largest producer of farmed salmon in the world. After reaching a peak harvest of 631 000 tonnes in 2008, a severe sanitary and production crisis triggered a major legal and operational reorganization, and an imminent expansion of the industry into the Aysén Fjords System (AFS). This expansion has caused increasing national and international concern about its potential negative impact upon this pristine area, which holds a mosaic of unique ecosystems and three World Biosphere Reserves. This paper reviews and provides some upper bounds to potential impacts under two feasible production scenarios. It is concluded that severe but highly localized mid‐term damage to the sea‐floor bottom may affect up to 6200 ha. Although this surface area represents only 0.5% of the AFS, the high heterogeneity and limited scientific knowledge of local ecosystems increase the risks of damaging sensitive habitats, communities or populations. While additional inputs of up to 60 000 t of nitrogen and 8000 t of phosphorus can be predicted, the estimation of carrying capacities is a pendant and urgent task to be accomplished in this area. If current escape rates are not reduced, the average number of escaped salmon may exceed 4.4 million individuals each year, able to consume up to 6600 t of pelagic prey from local ecosystems. We recommend following a strict precautionary approach, not granting new farming leases until sufficient information about the risk and magnitude of these impacts is obtained and transformed into effective management actions. 相似文献
20.
Hiromichi Mitamura Yasushi Mitsunaga Nobuaki Arai Yukiko Yamagishi Metha Khachaphichat Thavee Viputhanumas 《Fisheries Science》2008,74(4):787-795
Abstract: The horizontal and vertical movements of eight immature hatchery-reared Mekong giant catfish Pangasianodon gigas were monitored using acoustic telemetry in Mae Peum Reservoir, Thailand between 2003 and 2004. The fish were monitored for between eight days and more than 9 months. All of the fish moved over the entire reservoir within approximately 40 days after release. Subsequently, the home range became small approximately 40 days after release. The fish preferred deep areas in the reservoir. The fish displayed diel horizontal and vertical movement patterns. The fish showed larger-scale horizontal movement during the daytime than at night. The fish repeatedly showed active vertical movement during the day, whilst there was little variation in swimming depth at night. Our results imply that the vertical movements of the fish were related to the environmental condition of the reservoir. 相似文献