摘要:

AbstractIn recent years, there has been increasing pressure from user groups in Newfoundland and Labrador, Canada, to manage Atlantic salmon,Salmo salarL., on a river‐specific basis. The requirement to maximize benefits to users while ensuring that conservation goals are met has resulted in an initiative to develop river‐specific target spawning requirements. In Newfoundland, anadromous juvenile Atlantic salmon make widespread use of lacustrine habitat for rearing. Depending on the river, lacustrine habitat can account for a substantial proportion of total production. Therefore, target spawning requirements for a number of rivers in several management areas were derived in terms of the contribution of both riverine and lacustrine habitats. The approach adopted, and derivations of associated parameter values, are reviewed, and limitations and research needs are discus

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00109.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractCarlin tagging data for 1980–1991 were used to examine the influence of smolt size and feeding conditions on the post‐smolt survival of ranched River Neva salmon, (Salmo salarL.), in the the Gulf of Finland, which is the native feeding area of the stock, and in the Bothnian Sea, where the stock has been introduced. Because of better feeding conditions, the survival rates were higher and less variable in the Gulf of Finland than in the Bothnian Sea. In the Bothnian Sea, the annual variability in survival decreased and the mean value increased with increasing smolt size from the smallest (14–16 cm) to the largest (28–30 cm) size classes. The survival was positively correlated with growth rates, food resources and sea‐surface temperatures. This suggests that in the Bothnian Sea the annual variability in survival is mainly because variable marine conditions affect growth rates, and, thus, the vulnerability of the post‐smolts to size‐dependent predation. In the Gulf of Finland, the survival advantage of large initial size and rapid growth was counteracted by size‐selective post‐smolt mortality from fishing. The increase in the survival rate with increasing smolt size levelled off at 22 cm, and the correlations between survival, growth and the indices of feeding conditions were mostly insignificant. For large smolts, some negative correlations were recorded, suggesting that the relative significance of mortality from fishing may even exceed that of size‐dependent natural mortality. The implications of the results for manag

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00110.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractLarvae of grayling,Thymallus thymallus(L.) were immersed in tetracycline hydrochloride (TC) and alizarin red S (AL) solutions for 3–4 h at concentrations of 300 and 70 ppm, respectively. Fluorescent marks on the otoliths from the marked fish were identified using a UV‐light microscope. Results obtained with AL were superior to TC in marking otoliths. Fish kept in an aquarium retained good marks for 842 days. Stocking of the Carpathian River Ochotnica with marked grayling larvae revealed good mark retention for 128 days and a survival rate of approximately 12

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00111.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe conflict between the cormorant,Phalacrocorax carbo sinensisShaw, and commercial and recreational fisheries was investigated in the foraging area of a cormorant colony of 5000 breeding pairs in Horsens Fjord, Denmark. Depredation of commercial pound nets was studied by stocking a large net pen with hatchery‐reared rainbow trout,Oncorhynchus mykiss(Walbaum). When avian predation was precluded with a cover net, background mortality was around 15% day‐1. When the cover net was removed, mortality increased to 98% day‐1. Direct observation revealed that a flock of cormorants emptied the pound net in about 30 min, consuming 110 fish weighing a total of approximately 50 kg. The cormorants were able to catch trout weighing more than 1 kg, i.e. almost 50% of their own body weight. The impact of the cormorant colony on recreational fishing in the area was studied by stocking Carlin‐tagged sea trout,Salmo truttaL., smolts into the two rivers that drain into the fjord. The cormorant colony lies between the river outlets and the open sea. Tag recovery from a 3‐year programme was only about 2%, compared with about 10% for smolts stocked in areas of low cormoran

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00112.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA fish resource monitoring programme was undertaken during 1992–1993 in nine Dhofar khawrs (coastal lagoons) of Oman. The khawrs contained a large number of fish comprising mostly milkfish,Chanos chanos(Forsskal), and mullet,Mugil cephalusL. A wide range of species were recorded (47) with Khawr Sawli supporting the highest number (26). Most fish use khawrs as nursery grounds and migrate to the sea for breeding. Mullets matured in winter, milkfish in early spring and the other species in spring‐summer except the sleeper,Ophiocara porocephala(Valenciennes), which breeds all year round. Three species of invertebrates with commercial value were collected: Indian white shrimp,Penaeus indicusH. Milne Edwards, Mud crab,Scylla serrata(Forskal), and swimming crab,Portunus pelagicus(L.). Khawr water temperature followed a seasonal cycle and surface temperatures were higher than the deeper waters. Heavy rains in early spring caused extensive flooding and opening of khawrs to the sea. This had little effect on water salinity in some khawrs (Rawri and Mughsayl), while others displayed marked elevation in salinity (Taqah, Sawli and Jnawf) or reduced salinity by 50% (Qurm al‐Kabir). Sedimentation and organic decomposition added during flooding produced drastic reduction in dissolved oxygen. Khawrs were again connected to the sea during monsoon (June–September) as water levels increased. Intrusion of sea water increased salinity and continued for several months in shallow khawrs (Jnawf); however, freshwater seepage reduced salinity in most khawrs. Massive fish mortality following heavy rains was the most significant seasonal occurrence. Extensive fish losses also occurred when water levels dropped after opening khawrs to the sea, and left many fish stranded in shallow areas. Other environmental perturbations existed in most khawrs (e.g. pollution and overgrazing). However, these khawrs have potential for small‐scale fisheries and different types of aquaculture. Management problems are identified and options for solutions

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00113.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractPractical models for predicting the impacts of introduced biota are urgently required to assess the benefits and risks of introductions. The simple method described predicts the ecological consequences of an introduction through potential competition between species based on elementary niche classifications. The model's predictions are tested against field data for common carp,Cyprinus carpioL., which escaped from fish farms during a study of the feasibility of fish stock enhancement in a large river basin. Recorded effects of carp are based on pre‐ and post‐carp gillnet catches, observations of local villagers, socio‐economic censuses and other sources of data. The predicted ecological interactions of common carp are in broad agreement with those recorded. The method can assist pre‐introduction assessments and is particularly useful where limited data exist. In this particular study, common carp have contributed significantly to an improved capture fishery by fortuitous accident; production from aquaculture was negligible. High niche overlap between carp and certain resident fish species is predicted and this may be of more consequence in highland than lowland regions. Organisms introduced/transferred for aquaculture should be assessed within a much wider forum. The intended impacts of an introduction/ transfer, which in the case study were entirely erroneous, is an area in need of considerable at

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00114.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00115.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Book reviewed in this article:Biological Diversity: The Coexistence of Species on Changing Landscapes. By Michael A Huston.Restoration Planning for the Rivers of the Mississippi River Ecosystem. Edited by L.W. Hesse.Shrimp Capture and Culture Fisheries of the United States. By E.S. Iverson, D.M. Allen&J.B. Higham.

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00116.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY