Effects of biological,economic and management factors on tuna and billfish stock status          下载免费PDF全文

Maite Pons  Trevor A Branch  Michael C Melnychuk  Olaf P Jensen  Jon Brodziak  Jean M Fromentin  Shelton J Harley  Alan C Haynie  Laurie T Kell  Mark N Maunder  Ana M Parma  Victor R Restrepo  Rishi Sharma  Robert Ahrens  Ray Hilborn 《Fish and Fisheries》2017,18(1):1-21

Commercial tunas and billfishes (swordfish, marlins and sailfish) provide considerable catches and income in both developed and developing countries. These stocks vary in status from lightly exploited to rebuilding to severely depleted. Previous studies suggested that this variability could result from differences in life‐history characteristics and economic incentives, but differences in exploitation histories and management measures also have a strong effect on current stock status. Although the status (biomass and fishing mortality rate) of major tuna and billfish stocks is well documented, the effect of these diverse factors on current stock status and the effect of management measures in rebuilding stocks have not been analysed at the global level. Here, we show that, particularly for tunas, stocks were more depleted if they had high commercial value, were long‐lived species, had small pre‐fishing biomass and were subject to intense fishing pressure for a long time. In addition, implementing and enforcing total allowable catches (TACs) had the strongest positive influence on rebuilding overfished tuna and billfish stocks. Other control rules such as minimum size regulations or seasonal closures were also important in reducing fishing pressure, but stocks under TAC implementations showed the fastest increase of biomass. Lessons learned from this study can be applied in managing large industrial fisheries around the world. In particular, tuna regional fisheries management organizations should consider the relative effectiveness of management measures observed in this study for rebuilding depleted large pelagic stocks.  相似文献   

Red swamp crayfish,Procambarus clarkii,found in South Africa 22 years after attempted eradication          下载免费PDF全文

Ana L. Nunes  Andries C. Hoffman  Tsungai A. Zengeya  G. John Measey  Olaf LF Weyl 《水产资源保护:海洋与淡水生态系统》2017,27(6):1334-1340

1. No freshwater crayfish are indigenous to continental Africa, but four species have been introduced to the continent. One of these is the North American red swamp crayfish Procambarus clarkii, which has been introduced into several African countries, mainly for aquaculture, and has had demonstrable impacts where it has escaped captivity. In South Africa, the documentation of this species in farm dams near Dullstroom and the adjacent Crocodile River in 1988 resulted in an eradication attempt in 1994, with unknown results. 2. In order to evaluate the status of P. clarkii in South Africa, dams on the previously invaded farm and the Crocodile River were sampled four times between December 2015 and June 2016 using visual surveys, trapping, dipnetting and electrofishing. This yielded a single reproductively active male P. clarkii from one of the farm ponds, while many other native aquatic species were found in high numbers. 3. It is clear from this study that P. clarkii was not eradicated in South Africa and that individuals have been surviving in the wild (i.e. outside captivity or cultivation) for at least 28 years in the location where it was introduced. Containment and eradication of the species are proposed as management actions, which have major importance in preventing undesirable further spread or translocation of this species into new aquatic environments in South Africa.  相似文献   

Temporal dynamics of snags and development of snag habitats in wet spruce–fir stands in east-central British Columbia     

S. Craig DeLong  Glenn D. Sutherland  Lori D. Daniels  Ben H. Heemskerk  Ken Olaf Storaunet   《Forest Ecology and Management》2008,255(10):3613-3620

Patterns of tree mortality, rates and type of tree and snag fall, and relationships between snag characteristics and potential wildlife habitat value were estimated for hybrid spruce (Picea glauca (Moench) Voss × engelmannii Parry ex Engelm.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) in east-central British Columbia in order to provide important parameters for deadwood modelling. We sampled 172 snags (52 spruce and 120 fir) for species, size, morphological, and habitat attributes, and used dendroecological techniques on a subsample of these (n = 158) to estimate year of death. Input of snags appeared to occur at a nearly constant rate in these stands. Estimated annual tree fall, including live trees and snags, was 5.3% for hybrid spruce and 6.1% for subalpine fir and stem breakage was more frequent than uprooting. Long-term annual snag fall rates were 4.6% for hybrid spruce and 2.9% for subalpine fir. Discriminant analysis based on time since death correctly classified snags into three decay classes for 85% and 72% of spruce and fir, respectively. Snags that potentially could provide important functions for wildlife habitat were more prevalent in fresh and intermediate classes for hybrid spruce and in intermediate and old classes for subalpine fir. The results provide valuable parameters for further development of deadwood models, which are an important tool for development of best practices for deadwood management.  相似文献   

Break crop benefits in temperate wheat production   总被引：4，自引：0，他引：4  

John Kirkegaard  Olaf Christen  Joseph Krupinsky  David Layzell   《Field Crops Research》2008,107(3):185-195

Changes in the sequence of crops grown on agricultural land are well known to enhance the yield of grain crops such as wheat. A survey of the literature gathered from around the world show mean yield benefits of up to 20% or more. Much is known about the principal mechanisms responsible for these benefits, including effects on disease control, improved nitrogen nutrition and water supply, although researchers continue to be challenged by inexplicable “rotation effects” that have yet to be documented or fully understood. This review summarizes our current understanding of the ‘better-known’ mechanisms of crop rotation, and discusses other mechanisms (e.g. changes in rhizosphere biology, allelopathy or soil structure) that may help to account fully for the rotation benefits that have been observed by agricultural producers for more than 2000 years. Where possible we emphasise new techniques employed to investigate these less well-understood aspects of the “rotation effect”. At the farm level, the inability to capitalize on the benefits of break crops may owe more to economics, the availability of suitable break crops and the complexity of the crop response. Computer-based decision support tools have been developed to assist growers to apply the information gathered from scientific studies, although efforts to integrate this information at whole-farm scales are embryonic.  相似文献   

Pan‐national identities: representations of the Philippine diaspora on the world wide web     

James A. Tyner  Olaf Kuhlke 《Asia Pacific viewpoint》2000,41(3):231-252

This paper shows how the world wide web can facilitate the transformation of a trans‐national identity into a global, or pan‐national identity. Specific to the Philippines diaspora is the concept of tahanang, or home as a metaphor for a pan‐national Philippine identity. Not only does the web facilitate the spatial interactions of diasporic communities but it also fosters the representation of national identity. In the case of the Philippine diaspora we find that social networking, via the web, operates at and through a variety of spatial scales, including intra‐diasporic, inter‐diasporic, diaspora‐host, and diaspora‐homeland.  相似文献   

Prognosis for long‐term sustainable fisheries in the African Great Lakes     

K. Irvine  C. A. Etiegni  O. L. F. Weyl 《Fisheries Management and Ecology》2019,26(5):413-425

Declines in fish yields and shifts in species composition are serious concerns in the African Great lakes of Tanganyika, Malawi (Nyasa/Niassa) and Victoria. Despite management and regulatory structures, all the lakes remain open‐access fisheries, severely depressing yields, economic returns and threatening biodiversity. While the lakes require an ecosystem‐based approach to management, this has not been realised because of a lack of institutional capacities, insufficient political will or simply being overwhelmed by the scale of the endeavour. Sustainable fisheries management can only be achieved through a refocus towards a stronger socio‐ecological approach and re‐evaluating how to realistically improve fish yield and environmental protection. This requires a combination of the following: (1) acceptance of suboptimal fish yields; (2) community‐enforced regulations that restrict access to fisheries and destruction of inshore habitats; (3) enhanced national and local institutional capacities and collaboration among the riparian states; and (4) major awareness and educational efforts that demonstrate the national and international importance of these lakes for food supply and biodiversity in pursuance of the Sustainable Development Goals. Without such actions, the prognosis for long‐term sustainable fisheries is bleak, and international projects and conferences will merely bear witness to further degradation of resources and the livelihoods they support.  相似文献   

Successful mechanical eradication of spotted bass (Micropterus punctulatus (Rafinesque, 1819)) from a South African river     

Johannes A. van der Walt  Sean M. Marr  Marius J. Wheeler  N. Dean Impson  Craig Garrow  Olaf L.F. Weyl 《水产资源保护:海洋与淡水生态系统》2019,29(2):303-311

Vertebral column deformity with curved cross-stitch vertebrae in Norwegian seawater-farmed Atlantic salmon,Salmo salar L.     

Cathrine Trangerud  Håvard Bjørgen  Erling Olaf Koppang  Randi Nygaard Grøntvedt  Hege Kippenes Skogmo  Nina Ottesen  Agnar Kvellestad 《Journal of fish diseases》2020,43(3):379-389

Pathological changes in the vertebral column of farmed Atlantic salmon in Norway have been reported since the 1990s. Based on the characteristic radiographic findings, we here present a vertebral column deformity named “curved cross-stitch vertebrae” that mainly affects the middle aspect of the vertebral column. Sixty fish, from the west/northwest coast of mid-Norway, were sampled at slaughter and examined by radiography, computed tomography (CT), necropsy, macrophotography, and histology. The vertebral deformities were radiographically graded as mild, moderate, or marked. The main differences between these grades of changes were defined by increased curving of the peripheries of endplates, reduced intervertebral spaces, and vertical displacement of the vertebrae. The curved rims of endplates were located peripheral to a continuous and approximately circular borderline. The CT studies revealed small, multifocal, hypo-attenuating, round to crescent-shaped areas in the notochord, compatible with the presence of gas. Additionally, histology revealed that the axial parts of endplates had circular zones with perforations, through which either notochordal tissue prolapsed into the vertebrae or vascularized fibrochondroid proliferations extended from the vertebrae into the notochord. Inflammation was present in many vertebral bodies. To the best of our knowledge, this is the first report of gas in the notochord of fish.  相似文献   

Retention of T-bar anchor and dart tags by a wild population of African sharptooth catfish, Clarias gariepinus     

Anthony J. Booth  Olaf L.F. Weyl 《Fisheries Research》2008,92(2-3):333-339

A double-tagging experiment is presented that estimates tag retention by plastic dart and T-bar anchor tags in a wild population of Clarias gariepinus. It is shown that plastic dart tags are the most suitable tag as there was 100% initial retention and long-term loss of 2% per annum. T-bar anchor tags had an initial tag retention rate of 81% and no measurable long-term loss. A combination of tag design is attributed to the poor performance of T-bar anchor tags as the T-piece of the tag does not properly anchor behind the pterygiophores.  相似文献   

Rapid invasion of a subtropical lake fishery in central Mozambique by Nile tilapia,Oreochromis niloticus (Pisces: Cichlidae)     

Olaf L.F. Weyl 《水产资源保护:海洋与淡水生态系统》2008,18(6):839-851

• 1. Lake Chicamba, Mozambique (19°08′S; 33°08′E) is a large (116 km²) impoundment in the headwaters of the Buzi River system, which was invaded by Oreochromis niloticus in 1996 from a small (<0.3 km²) upstream reservoir.
• 2. Experimental and artisanal catch data showed no O. niloticus until January 1996; after this O. niloticus was recorded in up to 83% of experimental seine net catches, 33% of experimental gill net catches, 43% of boat angling and 23% of shore angling catches, and in 48% of artisanal gill net catches.
• 3. During the period January to March 1997, O. niloticus mean (upper, lower 95% confidence interval) yields in the artisanal fishery were 5.2 (3.6, 7.0) t month^?1.
• 4. The rapid invasion of this lake illustrates the significant invasion threat that small point‐sources of this species pose to southern African freshwater systems.
• 5. The study recommends: (1) that this species should not be used for aquaculture or fisheries enhancement in catchments that have not been invaded, and (2) that the eradication of potential point sources of O. niloticus in non‐invaded catchment systems should be considered.

Copyright © 2007 John Wiley & Sons, Ltd.  相似文献