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Beyer, F.; Feyn, E.; Ruud, J. T.; Totland, E.
doi: 10.1093/icesjms/31.1.5pmid: N/A
Because of pollution problems there is an increasing need for better knowledge of the exchange of water through the narrow and shallow Dröbak Sound. Transport computations as well as current measurements are impeded by the abrupt changes, both with depth and time, that occur in the sound. Giving current velocity and direction as well as depth ofthe instrument instantaneously and continuously, the new electric flowmeter described proved a useful tool in studying such changes. The range of the instrument is 3 cm/sec, to 300 or 350 cm/sec. During calm meteorological conditions a well developed counter-current was found to be due to internal waves. The maximum rates of velocity changes were 24 cm/sec, per metre of depth, and 6 cm/sec, per minute at one and the same depth.
doi: 10.1093/icesjms/31.1.27pmid: N/A
Percentage water (42.8–97.57), total nitrogen (0·33–11·99) and calorific values (0·502–7·538 K. Cal/g dry weight) of entire organisms of 22 species from a tropical freshwater community were measured on the basis of dry weights. The values determined were found to bear no relation to the nature of food, physical habitat, size of the species, larvalstages or taxonomic position but may be associated with the ratio of inert to labile matter. For most of the organisms these values compared favourably with those of temperate forms.The high calorific value recorded for Branchiodrilus semperi was associated with high rate of asexual reproduction.
Wolfe, Douglas A.; Schelske, Claire L.
doi: 10.1093/icesjms/31.1.31pmid: N/A
C14-labelled phytoplankton on filter papers were counted with a gas-flow geigercounter, then combusted in oxygen combustion flasks. C14O2 was recovered with hyamine, andthe absolute activities of the original samples weredetermined by liquid scintillation counting. Geiger counting efficiency, based on the absolute activities, was 25·8% ± 1·19. Intact filter papers containing C14-phytoplankton also were counted directly by liquid scintillation. Comparison of liquid scintillation and geiger activities for the same samples showed that the absolute activity of C14-phytoplankton on filter paper can be determined by direct liquid scintillation counting of the intact sample.
Mahnken, C. V. W.; Jossi, J. W.
doi: 10.1093/icesjms/31.1.38pmid: N/A
Experiments on the dynamics of flow into conical plankton nets were conducted at the US Navy's David Taylor Model Basin. A pitot tube and a telemetering flowmeter were used to measure the distribution of flow across the mouths of three 1 m diameter nets with mesh apertures of 0.281 mm, 0.221 mm, and 0.111 mm. Velocity profiles at the mouth of bridled nets consistently showed maximum velocity near the margin of the mouth, and a distinct minimum at the centre. The velocity was uniform across the mouth of an unbridled net that was tested. The filtration efficiency of all nets was high at normal towing speeds and remained high up to speeds of 257 cm/sec. Sustained high efficiencies weredue in part to stretching of the nylon material from which the nets were constructed.
doi: 10.1093/icesjms/31.1.46pmid: N/A
Zooplankton samples were collected in northern, western, and southwestern British waters in September-October, 1963 and in the western and middle part of the North Seain November, 1963. The origin of water masses was determined by identifying indicator species among the chaetognaths and copepods. The age-structure of predominant species was used as indicator of the similarity between water masses within the area. Temperature and salinity data bearing upon population age-structure are also given.
doi: 10.1093/icesjms/31.1.56pmid: N/A
The study of the major growth changes in North Sea herring which have taken place in the last fifteen years or so has until now been based mainly on mean length-for-age data.Such data have limitations, but despite the increased scope that back-calculation of annular rings on scales might be expected to allow, the use of methods incorporating data obtained from scales has been limited. This paper, the first of a series, describes a method which allows accurate and reliable comparisons of growth to be made for each year-class and each year of life, based entirely on back-calculated estimates of mean length-for-age. The method is applied to growth of I-group herring sampled in the East Anglian fishery, which is then compared over a period from 1939 to 1963. There were quite large changes in I-group growth in the 1940s, equally big changes in the 1950s, and in 1963 an increase of such a magnitude as to imply that a major change in growth conditions had occurred in that year.The precision of growth estimates derived from backreading can be determined because the reappearance of a year-class in the fishery each year allows successive, and to a large extent independent, estimates to be made of the same year's growth. In the data considered the precision reached is very satisfactory, allowing reasonably firm conclusions to be drawn for differences of 1 or 2% in growth between years. This is despite the occurrence of LEE'S phenomenon which, in fact, by revealing an age- (and length-) dependent bias in growth estimates, allows its effect to be estimated and removed, wholly or partly, when comparisons are made. The method does not rely on theoretical models of growth processes, for reasons which are discussed, but does allow the comparisons made to be defined in quasi-experimental terms.
doi: 10.1093/icesjms/31.1.77pmid: N/A
Whole blood proteins from a sample of cod (Gadus morhua L.) caught in the North Sea off Aberdeen have been analysed by electrophoretic and immunological techniques. The observed frequency of the haemoglobin allele Hbl1 was 0.55, a value consistent with that observed in nearby areas. Eleven abnormal haemoglobin patterns, corresponding to three ‘rare’ types were observed and were associated with non-agglutinating erythrocytes. Individual variation in the occurrence of erythrocyte and serum protein antigens detected by normal human sera and specific rabbit anti-cod sera respectively are observed and discussed.
de Figueiredo, Maria José; Thomas, H. J.
doi: 10.1093/icesjms/31.1.89pmid: N/A
In view of the wide distribution, differences in the biology of Nephrops norvegicus are to be expected. The size composition of the stocks, which varies considerably, appears to be unrelated to latitude. The largest are found off Portugal and the smallest in the Irish Sea. The size of females at maturity also varies in a manner apparently unrelated to latitude. The 50% level of maturity in the High Adriatic is reached at 27 mm carapace length as compared with 33 mm off Portugal and 22 mm in the Moray Firth. The sex ratio varies seasonally because of the lower availability of berried females as compared with nonberried females and males. The percentage of females in the catch is lowest during the period between spawning and hatching. The extent of the seasonal variation is very marked in Scottish and Irish waters, but less so off Portugal and in the Adriatic. The period of eggbearing in the Adriatic extends for about 30 weeks from June-July to January. Off Portugal spawning occurs in August-September and development takes only 28 weeks whilst around Scotland and Ireland spawning occurs around a peak in September and the incubation lasts about 34 weeks until hatching in May. Females are most abundant, relative to males, in the lowest size classes. With the onset of maturity the growth rate of the female decreases in comparison with that of the male of corresponding size. This results in a high percentage of females in the length classes about the maturity size followed by a falling off in the proportion of females to males. Annual spawning is normal throughout the distribution of the Norway lobster.
doi: 10.1093/icesjms/31.1.102pmid: N/A
The catch-per-unit-of-effort (CPUE) for one species may affect the CPUE of another species in a multiple-species fishery. This effect is studied by means of a simple stochastic model. The model provides a “competition free” CPUE which is never less than the CPUE obtained under competition, is strongly dependent on the empty space on or in the gear, and varies as a function of the proportion of each species. The multinomial structure of the model enabled the derivation of maximum-likelihood estimators of its parameters.Estimates of the large sample sampling variances and covariance of the parameters are also provided. Application of concepts of the model to other fishery problems is discussed and it is noted that the model also provides a maximum-likelihood estimate for the well-known yield equation.
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