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Influences of mean advection and simple behavior on the distribution of cod and haddock early life stages on Georges Bank 总被引：2，自引：0，他引：2
FRANCISCO E. WERNER FRED H. PAGE DANIEL R. LYNCH JOHN W. LODER R. GREGORY LOUGH R. IAN PERRY DAVID A. GREENBERG MICHAEL M. SINCLAIR 《Fisheries Oceanography》1993,2(2):43-64
Results of a modeling study designed to explore the influences of physical advection and certain biological mechanisms on the distribution of cod (Gadus morhua) and haddock (Melarwgrammus aeglefinus) early life stages on Georges Bank are described. Using a late-winter/early-spring 3-D circulation field driven by the M2 tidal current, mean wind stress and Scotian Shelf inflow, we examine the distribution of cod and haddock larvae spawned on the Northeast Peak of the Bank. The sensitivity to a March-April baroclinic field is also explored. Results indicate that larvae remaining in the surface Ekman layer are generally advected off-bank. However, downwelling associated with Ekman layer convergence near the shelf break provides a mechanism for larvae to exit from the off-bank surface drift. Larvae below the surface layer are transported south-westward along the southern flank of Georges Bank and are retained on the Bank if their position immediately upstream of the Great South Channel is shoalward of (roughly) the 70 m isobath. Within the Great South Channel region and between the 50 and 70 m isobaths, retention can depend on the phase of the tide. Spawning shoalward of the 50 m isobath on the Northeast Peak greatly increases the chances of retention. These results apply to passive larvae and to those with specified vertical distributions and migration based on observations. Directional on-bank swimming at rates of 0.5 to 1 body length per second would substantially enhance shoalward displacement, resulting in larval distributions during the first 2 months that are consistent with field observations. 相似文献
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The effect of pH on the incorporation of six 14C-labelled amino acids and a dipeptide into humic acid extracted from a podzolic soil was examined. Maximum incorporation was found to occur at a pH which coincided with the apparent dissociation constants of their α-amino groups. Incorporation took place, into forms which were both acid-hydrolysable and non-hydrolysable, the latter accounting for between ten and twenty per cent of the total. 相似文献
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P. J. DAVIS L. A. LAIDLER P. W. PERRY D. ROSSINGTON R. ALCOCK 《Journal of fish diseases》1994,17(2):99-110
Abstract. The need to accurately, reliably and economically screen large populations of brood salmon for infectious pancreatic necrosis virus (IPNV) prompted a fresh approach to the use of ELISA and cell cultures. The result is an integrated procedure that recognizes the limitations of each method while building upon the strength of both in the way that they are brought together, ELISA tests can never be sensitive enough to detect the very low virus levels typical of carrier fish, but are able to detect virus in infected cell cultures, both specifically and objectively. Cell cultures provide the means to detect very low virus levels, but without specificity and only through subjective observation. Without a suitable ELISA, the need to keep cell monolayers in a condition in which viral effects can be observed imposes strict demands on inoculation and culture procedures. In contrast, the new procedure described in this paper provides a simpler culture method in which the inoculum is retained throughout a single, uninterrupted 14-day culture cycle. This culture duration allowed maximum opportunity for viral replication in healthy cells, even though the monolayers became disorganized. However, the cultures were tested in the standardized ELISA, eliminating the need for microscopic observation and virus neutralization tests. Thorough validation studies confirmed the system's adequacy in practice. 相似文献
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1. This paper reviews evidence from 15 experiments, reported over a span of 44 years, in which pullets were reared from hatching to sexual maturity on 2 or more constant photoperiods. 2. The evidence strongly indicates that earliest age at first egg (AFE) was observed when pullets were held on constant 10 h days (though earlier maturity is easily induced by increasing the photoperiod during rearing). The pair of equations which best describe the relationship between AFE (y,d) and photoperiod (x,h) are for x < 10 h, y = 175.8- 1.731x; for x > 10 h, y=155.5 + 0.301x. 3. This 2-straight-line model, hinged at 10 h, should be used in preference to curvilinear models published earlier, which wrongly predict that pullets reared on long days (14h to 17h) mature faster than birds reared on constant 10 h. 相似文献
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Spatial variations in feeding and condition of juvenile pink and chum salmon off Vancouver Island, British Columbia 总被引：1，自引：0，他引：1
R. IAN PERRY N. BRENT HARGREAVES BRENDA J. WADDELL DAVID L. MACKAS 《Fisheries Oceanography》1996,5(2):73-88
Spatial variations in feeding and condition of juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon, and their implications for growth, were examined on the Vancouver Island continental shelf in early summer 1992. Juvenile pink salmon off northern Vancouver Island had more material in their stomachs, were in better condition, and had higher potential growth rates (from a bioenergetics model) than pink salmon off southern Vancouver Island. These variations were consistent with spatial differences in zoo-plankton biomass, there being more plankton in the northern region. There was a significant positive relationship between condition of pinks and the amount of material in their stomachs, suggesting a positive feedback on feeding success. Juvenile chum in the north also had more material in their stomachs than chum to the south. However, condition factor was not significantly different between southern and northern regions nor was there a significant relationship between condition factor and the weight of stomach contents for chum on the southern shelf. A bioenergetics model suggests that chum in the south were food limited. Stable carbon isotope data also indicated different feeding histories for some chum in the southern region, which may have been recent migrants onto the continental shelf from near-shore areas, or possibly a nearby hatchery. Estimation of the energy required by juvenile salmon to migrate north in a continental shelf area with low zooplankton biomass and a weak northerly current (inner shelf), compared with an area with higher zooplankton biomass but a strong southerly current (outer shelf), indicated sufficient surplus energy only in the inner shelf, consistent with observations of northward migrations predominantly through this area. Spatial variations in current velocity and zooplankton biomass can affect feeding, condition, and potential growth of juvenile pink and chum salmon off Vancouver Island. 相似文献
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A varied population of cucumber mosaic virus from peppers 总被引：1，自引：0，他引：1
A varied population of Cucumber Mosaic Virus (CMV) isolates is reported from peppers ( Capsicum annuum ) in Australia. Isolates representing both CMV subgroups (serogroups) I and II have been obtained from the same field at the same sampling time. The CMV isolates were typed into subgroup I (eight isolates) and subgroup II (two isolates) using both a nucleic acid hybridization assay and an immunological assay with monoclonal antibodies. The immunological assay described allows the typing of strains in crude sap extracts, obviating the need for purified virions. The spatial and temporal coincidence of both CMV subgroups presents a situation in which pseudorecombinants with reassorted genomic components might arise. 相似文献
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No significant relationship (p greater than 0.05) was found between age at puberty in heifers and the age and scrotal circumference at puberty in related bulls. There was a significant effect (p less than 0.01) of genotype and sire on age at puberty of heifers and a significant effect (p less than 0.05) of genotype on weight at puberty in heifers. There was a significant effect of genotype on age (p less than 0.01) and weight (p less than 0.05) at puberty of bulls. A significant difference (p less than 0.05) in age at puberty of bulls was found between the 2 methods of assessing puberty. It is possible that the assessment of puberty of heifers at 2-month intervals may not have been precise enough to detect such a relationship and/or that the variation in genotypes and ages in this study were too great to establish such a relationship. 相似文献