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Moore, M. N.; Lowe, D. M.; Gee, J. M.
doi: 10.1093/icesjms/38.1.6pmid: N/A
Localised metaplastic changes in the gut epithelial cells of Mytilus edulis were found to be associated with the presence of the parasitic copepod, Mytilicola intestinalis. These changes involved the replacement of the ciliated columnar cells by non-ciliated cuboidal cells. Experimental thermal stress induced a significant increase in the numbers of macrophages in the connective tissues of both infected and uninfected mussels, but there was no evidence of any synergistic effect in infected hosts. A number of lysosomal hydrolases are associated with the gut cells of the parasite where they may be involved in intracellular digestion. It is concluded that Mytilicola intestinalis has no significant effect on the basic cellular functions in Mytilus edulis
Bayne, B. L.; Gee, J. M.; Davey, J. T.; Scullard, C.
doi: 10.1093/icesjms/38.1.12pmid: N/A
Various levels of infestation by Mytilicola had no effect on the rates of oxygen consumption by Mytilus edulis in laboratory experiments. However, high levels of infestation (> 10 parasites per mussel) caused a depression in the feeding rate of the host at high temperatures (22° or 23° C) and low ration (maintenance or sub-maintenance). This depression of feeding resulted in a decline in the scope for growth, which would result in time in a decline in the “condition” of the host. It is concluded that similar effects may occur in the field when large numbers of small parasites are present at a time of high metabolic demand and low food availability.
doi: 10.1093/icesjms/38.1.18pmid: N/A
Estimates were made of the annual food consumption of North Sea and Faroe haddock and cod of various sizes. Two methods of computation have been used. One is based on estimates of the energy required for maintenance, growth and reproduction, the other is based on mean stomach content weights.Estimates based on energy requirement made use of the following sources of data: (1) observations on the relationship between growth and feeding under aquarium conditions; (2) observations on the relationship between oxygen consumption and swimming speed; (3) observations on the relationship between oxygen consumption and body weight; (4) observations on annual growth rates; and (5) estimates of energy content of eggs produced.From an analysis of the available data, equations were determined for estimating the annual energy requirements of a fish. Equation (10) takes account of the energy required for growth and maintenance and is applicable to the immature fish. Equation (11) takes account also of the energy required for reproduction and is applicable to the mature fish.An alternative method of estimation was also investigated using mean stomach content weights. This method is based on the fact that on average, the rate at which food enters a stomach must be equal to the rate at which it is eliminated. To a first approximation therefore, estimates of the rate of elimination of food (based on stomach content weights) should be equivalent to estimates of the rate of food intake.Estimates of food intake were made by both methods and it was concluded that:(1) for both haddock and cod, energy intake can be treated as proportional to (body weight) b; for haddock the coefficient b varied from 0·77–0·80, for cod, the values ranged from 0·80–1·3, depending partly on the range of body weights involved, and(2) weight for weight, North Sea and Faroe cod require more energy than North Sea and Faroe haddock.
doi: 10.1093/icesjms/38.1.28pmid: N/A
A distinction is drawn between methods for counting single fish and estimating biomass. Biases in both systems are indicated, and the most important of these is the capacity of the biomass method to record signals from animals smaller than desired. The best system would count individual fishes and record integrated signals from shoals and in this way the biases in either system are minimized.
doi: 10.1093/icesjms/38.1.33pmid: N/A
A large scale sonar map offish schools in the Los Angeles Bight is described and used to determine the amount of sampling required to estimate the number of schools at various levels of precision. About 8 nautical square miles (2744 ha) must be directly surveyed to get an estimate offish schools with a 25% level of precision: 47 nautical square miles (16121 ha) must be sampled for a 10% level of precision using the observations and assumptions of this paper. Although spatial autocorrelation indicates independent observations can be taken at 5 nautical miles (9km) spacing or greater, there is a possibility of exclusion or reduction of the number of schools at 7 to 15 nautical miles (13 to 28 km) range which should be further investigated.
Dickson, R. R.; Langhorne, D. N.; Millner, R. S.; Shreeve, E. G.
doi: 10.1093/icesjms/38.1.41pmid: N/A
In October 1974, a sector scanning sonar adapted for operation in side-scan mode was used to examine a channel dredged in 1971 within the sandwave field at Longsand Head (Outer Thames Estuary). Trials of the system were successful. The range and resolution of the records obtained were comparable with those of EG & G side-scan sonar but the provision of automatic gain control permitted the detection of seabed features which had hitherto been unresolved by side-scan sonar.Resurvey of a channel dredged through the sandwave field off Longsand Head showed that sections of the major sandwaves removed by dredging had shown only a limited tendency to reform in the 3-year period since the close of dredging operations. A system of dunes (5 m wavelength) had developed in the fine infill material which covers the floor of the channel. Intermittent noise signals due to sediment movement were recorded by the modified scanner system during each survey leg and provide some qualitative impression of the patchiness of sediment movement on sandwave crests.
doi: 10.1093/icesjms/38.1.48pmid: N/A
The use of high speed plankton samplers is inevitably accompanied by the risk of damage to the specimens in the catch. The techniques used by the Lowestoft laboratory are designed to minimize this damage during collection, fixation and preservation of the catch. To this end a special collecting bag is used in the plankton sampler and the sample is fixed with a new formaldehyde-based fixative marked with eosin dye. This fixative, together with a new observation and preservation fluid used during sorting, results from the recommendation of the SCOR/UNESCO working group on fixation and preservation of zooplankton.Finally the use of polarized light as an aid to counting the myotomes of clupeoid larvae is described and illustrated. This technique is put forward as the only reliable means of differentiating between small or damaged specimens of herring, sprat and pilchard larvae.
doi: 10.1093/icesjms/38.1.54pmid: N/A
A two year study of lobsters off the coast of North Wales showed that fecundity was linearly related to carapace length by the equation: egg numbers = 217·74 carapace length (mm) − 12 490·30. Embryonic development was rapid during the autumn, slow during the winter and then rapid again in the spring.
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