Measuring depth of settlement in the red rock lobster,Jasus edwardsii     

John D. Booth  Andrew D. Carruthers  Colin D. Bolt  Robert A. Stewart 《新西兰海洋与淡水研究杂志》2013,47(2):123-132

Settlement of the puerulus stage of Jasus edwardsii (Decapoda: Palinuridae) near the shore takes place over a wide depth range. It occurs intertidally, and, as determined by crevice collectors, also takes place down to depths of at least 50 m. At sites along the east coast of the North Island of New Zealand, depth of greatest settlement found on collectors varied with locality and time, but was within the upper 11.5 m. Surface‐buoyed collectors caught fewer animals than did collectors at greater depths. Settlement levels generally increased with depth to about 10–12 m, then decreased with increasing depth and distance from shore. The ability of/, edwardsii to settle over a wide depth range may improve its chances of recruitment. A device (closing crevice collector) for measuring puerulus settlement of J. edwardsii at depth is described.  相似文献   

First records of Scorpaena onaria (Scorpaeniformes: Scorpaenidae) from the southwestern Pacific Ocean,and comparisons with the Northern Hemisphere population     

Hiroyuki Motomura  Chris D. Paulin  Andrew L. Stewart 《新西兰海洋与淡水研究杂志》2013,47(4):865-880

Scorpaena onaria Jordan & Snyder (Scorpaeniformes: Scorpaenidae), previously known only from the northwestern Pacific Ocean, is reported from the southwestern Pacific Ocean for the first time on the basis of 19 specimens. The southwestern Pacific specimens are regarded as a southern population of S. onaria, characterised by a shorter supraocular tentacle and larger body size compared with the northwestern Pacific specimens. The southern population is described in detail including comparisons with all known Indo‐Pacific species of the genus Scorpaena. Analyses of 37 measurements of the southern population of S. onaria found that relative orbit diameter and second anal‐fin spine length became significantly smaller with growth. Initially cycloid, the scales enclosed by the posterior tips of the upper and lower opercular spines and opercular margin change to ctenoid with growth at c. 160–170 mm standard length. A mature female differed from an immature female and males in having a longer upper jaw, steeper dorsal profile of the snout, and shorter nasal spine. As a consequence, the species previously reported as S. neglecta from the Andaman Sea and northwestern Australia was re‐identified as S. onaria.  相似文献   

Combining passive integrated transponder tags with conventional T‐bar tags to improve tag reporting rates in a rock lobster trap fishery     

Stewart D. Frusher  David Hall  Paul Burch  Caleb Gardner 《新西兰海洋与淡水研究杂志》2013,47(1):347-353

Tag reporting rate is an important parameter required for estimating fishing and natural mortality in fished populations. It is an extremely difficult parameter to estimate and can vary both during the fishing season and between fishing years. Improving tag reporting rates has been identified as a cost‐effective way of improving precision in fishing and natural mortality estimates derived from tagging data. In this study we evaluated the use of passive integrated transponder (PIT) tags to improve tag reporting rates in a lobster (Jasus edwardsii) trap fishery. To minimise the risk of PIT tag ingestion by consumers, we tested insertion of the PIT tag into the base of the antennae, the base of the walking leg, and the base of the telson. The base of the antennae proved to be the best option for lobster health although impacts were observed at all tag insertion sites. We further developed and tested a hybrid tag that combined a conventional external T‐bar tag with a PIT tag embedded within the shaft. PIT tag scanners were positioned in bottlenecks in the capture process so that all lobsters retained on board the vessel were passed through a scanner. Thus, the tag reporting rate was expected to be 100% for the subsample of the fleet fitted with scanners when scanners were operational. Scanner malfunction was a major issue and further engineering solutions are required to ensure that scanners are reliable when working in harsh marine conditions such as on‐board fishing vessels. Advantages of the hybrid tag are: the ability to be detected by both automatic detectors and fishers; known tag‐induced mortality and tag loss rates from previous research; and PIT tagging without risk of human ingestion.  相似文献   

Negative diffusion in planetary rings with a nearby moon     

Mark Lewis  Glen Stewart 《Icarus》2011,213(1):201-217

This paper analyzes a process that has been observed in simulations of numerous systems where ring material is strongly perturbed by a nearby moon. If the ring particles can be imparted with a forced eccentricity on the order of 10⁻⁵ in a single pass by the moon, particle orbits are observed to move towards regions of higher density as a result of the organized collisions that occur in the dense peaks of the satellite wake. The width of the ring can decrease by as much as 90% if the forced eccentricity is greater than 3 × 10⁻⁵ and the unperturbed geometric optical depth is greater than 0.03. The fractional change in ring width is relatively insensitive to the particle size so long as the particle radius is much less than the product of the semimajor axis and the forced eccentricity. Including a power law particle size distribution with slope of −2.8 spanning a decade in particle radius reduces the fractional width change by about 10% compared to the uniform particle-size case. Adding gravitational interactions between ring particles only has a significant effect on ring confinement if the unperturbed geometric optical depth exceeds .03, but a 40% reduction in ring width is still achieved in a self-gravitating ring of geometric optical depth 0.3 if the forced eccentricity exceeds 3 × 10⁻⁵. This process does not require the material to be in resonance with the moon, nor does it have any minimum mass constraints because particle self-gravity is not required. The collisional damping of satellite wakes therefore provides a simple mechanism by which a single moon can reduce the radial extent of any ringlet that is close to it and has sufficient optical depth for collisions to be significant.  相似文献   

Radio mapping of the heliospheric current sheet     

R. T. Stewart 《Solar physics》1971,109(1):139-147

Synoptic plots of solar radio noise storms in the interval 1973 to 1984 are described. The dividing line between opposite noise storm polarities appears to be a good representation of the heliospheric current sheet out to displacements in latitude of ± 50° from the solar equator. This result is surprising, because noise storms are closely associated with closed magnetic field regions near sunspots. The possibility that noise storm polarity is determined by mode coupling high in the corona, where field lines are open, can be ruled out by the available evidence. This leads us to conclude that it is the clustering in longitude of active region complexes which determines the sector structure of the interplanetary magnetic field.  相似文献   

The jet in M87     

P. Stewart 《Astrophysics and Space Science》1971,14(2):261-264

The jet is assumed to be ejected from the nucleus supersonically into a gas which is at rest; the knots that result are related to those which are observed and an estimate of the jet temperature follows. The magnetic field and particle density inside the jet are discussed and observations are suggested.  相似文献   

The detrital zone in the shorty crater cores     

J. Stewart Nagle 《Earth, Moon, and Planets》1978,18(4):499-517

The lower part of lunar cores 74002/1 contains pure fine-grained black soil grading upward to orange soil. The section, however, between 10 cm and the lunar surface contains a mixture of orange and dark soil with a clast-in-matrix texture and some agglutinates. Therefore, this upper section is interpreted as a detrital zone. Although Shorty Crater was formed approximately 30 m.y. ago, all indicators of soil age give a much shorter time for residence of the detrital zone. Both absolute agglutinate content and authigenic agglutinate content indicate a surface residence of less than 8 m.y. for the detrital portion of the core. Most calculated ages of the detrital zone cluster are around 3 m.y. Grain size distribution is characteristic of an immature soil and there is little evidence, indicated by lack of upward fining and decrease in coarsest grain sizes, ofin situ maturation of the section. Mixing with adjacent soils is very low, even though such soils lie only 0.5 M from the sampling site. Four of the five sub-strata in the upper 10 cm could have been produced by the impact event that produced the 20 M wide boulder field near the sampling site on the Shorty Crater rim. This event would distribute perched clasts over the sampling site. Thickness of the detrital part of the section is in keeping with its being ejecta from the boulder bed crater. The thickness of the agglutinate-rich zone, 1.5 cm, is reasonable for a less-than 4 m.y. residence time.  相似文献   

On the contraction of the Earth     

A. D. Stewart 《Earth, Moon, and Planets》1979,21(1):123-124

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Evolution of polar coronal holes and sunspots during cycles 21 and 22     

S. Bravo  G. Stewart 《Solar physics》1994,154(2):377-384

A very good correlation between the evolution of polar coronal hole size and sunspot number half a solar cycle later was found by Bravo and Otaola for solar cycle 21. In this paper we use a more complete set of data to reanalyse the relationship for solar cycle 21 and investigate the same relationship for solar cycle 22. We find that the complete set of data for cycle 21 yields a slightly different time shift for the best correlation between sunspots and holes and that the time shift for cycle 22 is different from that of cycle 21. However, because of limited availability of data of cycle 22, we consider it necessary to wait until the end of this cycle in order to decide if the difference is statistically significant or not. We also found that the time between successive peaks of smoothed polar hole area and smoothed sunspot number is the same in both cycles. This may provide a useful tool for the forecasting of future sunspot maxima. The constant of proportionality between polar coronal hole area and sunspot number can be seen to be different in both cycles. We discuss this difference and interpret it in terms of a different magnitude of the polar field strength in the two cycles.  相似文献   

Some newly discovered coronal emission lines from high altitude infrared observations of the 7 March, 1970, solar eclipse     

Kenneth H. Olsen  Charles R. Anderson  John N. Stewart 《Solar physics》1971,21(2):360-371

A survey of the infrared coronal spectrum between 1 and 3 was made from a high altitude aircraft during the 7 March, 1970, solar eclipse. The observations were made with a Fourier transform spectrometer and were confined to the outer chromosphere and inner corona. In addition to well known chromospheric lines of Hi and Hei, nine additional lines were seen. Evidence is presented for the tentative assignment of these lines to forbidden transitions in highly ionized atoms of magnesium, aluminum, silicon, sulphur, and chromium.  相似文献