Artemia parthenogenetica in Lake Hayward, Western Australia. I. Interrupted recruitment into adult stages in response to seasonal limnology     

Alan Savage  Brenton Knott 《International Journal of Salt Lake Research》1998,7(1):1-12

Lake Hayward, Western Australia, is a pristine, monomictic coastal lake with a residual brine (depth=1.5 m) of 200 gL⁻¹: stratification in winter (May to October) followed the input of ground water and rain. The epilimnion had temperature ranges of 10–30°C, and salinity from 65–110 g L⁻¹. Maximum depth in winter was 2.4 m. The population structure of the brine shrimpArtemia parthenogenetica, the dominant metazoan grazer in Lake Hayward, was studied from September, 1989, to February, 1991. The L. Hayward population ofA. parthenogenetica is predominantly ovoviviparous with little recruitment into the adult population. Cyst production occurs in summer, and there was evidence for recruitment from cyst hatching in the winters of 1989 and 1990. Nauplii were continuously present throughout the study period. Nevertheless, recruitment through to adult stages as defined by the presence of gravid females occurred only twice: in October–December, 1989 and in December, 1990. Based on limited observations of long-term survival of laboratory cultures, we believe that the major mechanism controlling nauplius survival and recruitment ofArtemia in Lake Hayward is food quality and quantity.  相似文献   

A fishery in a changing lake environment: The naked carpGymnocypris przewalskii (Kessler) (Cyprinidae: schizothoracinae) in Qinghai Hu,China     

K. F. Walker  I. G. Dunn  D. Edwards  T. Petr  H. Z. Yang 《International Journal of Salt Lake Research》1995,4(3):169-222

Quinghai Hu is a large, high-altitude, saline lake in north-western China, and supports a fishery based on an endemic species of naked carp (snow trout). The fish take seven years to attain maturity and a marketable weight of 300 g, and have a lifespan of 14–21 years under the present fishery regime. They seasonally migrate from the lake to spawn over the gravel beds of inflowing rivers, but these areas have been reduced by weirs and irrigation diversions and recruitment may have declined. The population may have been affected also by a 1.85-m fall in the lake level over the past 30 years, and by associated changes in salinity. The fishery was opened to large-scale exploitation in 1958. Yields declined sharply (max. 28,523 tonnes, 1960) as the larger, older fish were removed, and then more slowly (min. 2523 tonnes, 1983). Since 1987 the fish factory has been limited to an annual quota of 1200 tonnes, taken by a fleet of four pair trawlers. Another 800 tonnes are taken by licensed fishermen, mainly using gill nets, and perhaps 1000 tonnes are taken illegally. The estimated total catch in 1992 was 3000 tonnes. New trawlers introduced in 1989–90 substantially increased the factory's catch per unit effort, and in 1990 the quota was virtually filled in one month in a zone within 20 km of the factory. Although this could suggest that the stocks will be conserved if the quota is retained, at least half of the catch in 1989–92 consisted of immature individuals. Trawling operations recently were suspended following a further decline in the catch after 1992. While the new trawlers are capable of a major increase in effort, neither the changing environment, the fish stocks or the present markets favour intensified pressure. Gillnets may provide better control over the minimum size limit and may cause less damage than trawling. Other options to improve the viability and profitability of the fishery include improvements in handling, processing and marketing. Failure to develop the fishery may encourage attempts to introduce exotic fish, at some risk to survival of the local species.  相似文献   

Geo-questionnaires in urban planning: recruitment methods,participant engagement,and data quality     

Michał Czepkiewicz  Piotr Jankowski  Marek Młodkowski 《制图学和地理信息科学》2017,44(6):551-567

ABSTRACT

Recent focus on sustainable urban development and livability has increased the demand for new data sourcing techniques to capture experiences and preferences of urban dwellers. At the same time, developments of geospatial technologies and social media have enabled new types of user-generated geographic information and spatially explicit online communication. As a result, new public participation GIS methods for engaging large groups of individuals have emerged. One such method is geo-questionnaire, an online questionnaire with mapping capabilities, which has been used to elicit geographic data in variety of topics and geographical contexts. This article presents two recent cases, in which geo-questionnaires have been used in Polish cities to obtain public input on quality of life and development preferences in local land use planning. The article evaluates participant recruitment methods focusing on sample representativeness, participant engagement, and data quality. Recruitment via social media was found to increase bias towards younger population. Paper questionnaires used along the online version provided for better representation of target population’s age structure, but did not reduce bias related to educational attainment. We discuss how these issues relate to data usability and generalizability in the context of digital divide, and suggest directions for future research.  相似文献   

A potential source of recruitment of Acartia pacifica nauplii: viable benthic resting eggs     

WANG Guizhong  JIANG Xiaodong  LI Shaojing  WU Lisheng  WU Dingxun 《海洋学报(英文版)》2005,24(2):151-158

Many estuarine and coastal planktonic copepods depend on the hatching of benthic resting eggs for recruitment of nauplii to the water column population. The distribution and abundance of viable resting eggs of Acartia pacifica in the Xiamen Bay were determined by the presence of nauplii in the laboratory. The number of viable eggs varied temporally and spatially. The maximum number (9.2×10⁴m^-2) of viable eggs was in summer. In spring the average abundance of viable eggs was 5.6×10⁴ m^-2. The abundances of viable eggs in fall and winter were similar, respectively 2.7×10⁴ and 3.3×10⁴ m^-2, which were the lowest in the year. The numbers of viable eggs inside the stations of the Xiamen Bay were higher than those outside the stations. The viable eggs were found at all depths (0～10 cm),although not in every station. The maximin number did not necessarily occur in the uppermost centimeter of the sediments but often occurred several centimeters below the water-sediment interface. The accumulation of viable eggs in the seabed of a subtropical bay constitutes a potential source of recruitment of nauplii into the pelagic population.  相似文献   

Recruitment indices of European hake, Merluccius merluccius (Linnaeus 1758), in the Northwest Mediterranean based on landings from bottom-trawl multispecies fisheries     

Goni  Raquel; Adlerstein  Sara; Alvarez  Federico; Garcia  Mariano; Sanchez  Pilar; Sbrana  Mario; Maynou  Francesc; Viva  Claudio 《ICES Journal of Marine Science》2004,61(5):760-773

  相似文献   

Impact of climate and hydrodynamics on sole larval immigration towards the Tagus estuary, Portugal     

C. Vinagre  M.J. Costa  H.N. Cabral 《Estuarine, Coastal and Shelf Science》2007,75(4):516-524

Spawning grounds of the soles, Solea solea and Solea senegalensis, are distant from the estuarine nurseries where juveniles concentrate. Recruitment of these species is highly dependent on the success of the larval migration towards the inshore nursery grounds. Unfavourable climate and hydrodynamic circulation may lead to high mortality rates at this stage. The relation between river drainage, NAO index and the North-South wind component intensity over the three months prior to the end of the estuarine colonization and the densities of S. solea and S. senegalensis in the nursery grounds were investigated for both species based on a discontinuous historical dataset (from 1988 to 2006) for the Tagus estuary. Multiple linear regression models were developed for sole density and environmental data (separately for each species). Results showed that river drainage is positively correlated with juveniles’ densities of both species, possibly due to the existence of chemical cues used by larvae for movement orientation. NAO index and the North-South wind component intensity relations with soles densities were non-significant. It was concluded that the high complexity of the Portuguese upwelling system makes it hard to detect causal relations of the environmental variables tested. The importance of river flow for coastal ecosystems was stressed. Since climate change scenarios predict a strong decrease in rain fall over the Portuguese river basins, as well as a concentrated period of heavy rain in winter, it was hypothesised that future river drainage decrease over much of the year may lead to lower recruitment success for soles, especially for S. senegalensis.  相似文献   

Occurrence and recruitment of fish larvae in a northern New Zealand estuary     

D. S. Roper 《Estuarine, Coastal and Shelf Science》1986,22(6)

The occurrence of fish larvae and the effect of diel and tidal variation on catches was studied at about biweekly intervals for a year in Whangateau Harbour, a small well mixed northern New Zealand estuary. Larvae from 31 taxa were identified. The annual pattern of larval occurrence was typical for fish in temperate waters, with a major peak of abundance in early summer. For six taxa, larval densities were significantly greater in night-time than in daytime catches, and analysis of length-frequency distributions suggested that for two species this was due to daytime net avoidance.No significant differences were found between the densities of larvae caught on flood and ebb tides, but changes in length-frequency distributions were significant for two species. Recently hatched larvae of an unidentified goby were found leaving the harbour, where they were probably spawned, while older larvae of this species appeared to be recruiting back in. Larvae of the flounder Rhobosolea plebeia were also apparently recruiting into the harbour. In the absence of a two-layered circulation pattern larvae relied upon tidal transport for recruitment, and probaby ensured their retention by rapidly settling to the bottom.  相似文献   

Comparative analysis of statistical tools to identify recruitment-environment relationships and forecast recruitment strength   总被引：1，自引：0，他引：1  

Megrey  Bernard A.; Lee  Yong-Woo; Macklin  S. Allen 《ICES Journal of Marine Science》2005,62(7):1256-1269

  相似文献   

Marine survival of North American and European Atlantic salmon: effects of growth and environment   总被引：2，自引：3，他引：2  

Friedland  K. D.; Reddin  D. G.; Kocik  J. F. 《ICES Journal of Marine Science》1993,50(4):481-492

  相似文献   

Stock and recruitment: generalizations about maximum reproductive rate, density dependence, and variability using meta-analytic approaches   总被引：3，自引：3，他引：3  

Myers  Ransom A. 《ICES Journal of Marine Science》2001,58(5):937-951

  相似文献