ICES Journal of Marine Science: Journal du Conseil

Macer, C. T.

doi: 10.1093/icesjms/31.2.158pmid: N/A

The sampler, which weighs about 30 kg in air, consists of a net mounted on a tubular steel sled, the latter surmounted by a diving plane. The mouth of the net is a rectangular wooden frame, in which revolves a spring-loaded door. This door is held in the open or closed position by one of two pins, which are attached on either side of the pivot of a metal ‘see-saw’ shoe beneath the frame, and which protrude through holes in the frame base into the path of the door. When in contact with the sea-bed, the rear part of the shoe is forced upwards; this withdraws one pin and releases the door, which revolves through 90° to be held by the other pin which has been forced upwards. On leaving the sea-bed, a compression spring forces the shoe downwards, so restoring the pins to their original position and the door revolves through a further 90°, to close the net mouth.Three hauls near the surface are compared with three on the bottom in 5 m depth in Red Wharf Bay (North Wales) and these show that certain of the plankters were more concentrated near the bottom.

Raymont, J. E. G.; Krishnaswamy, S.; Tundisi, J.

doi: 10.1093/icesjms/31.2.164pmid: N/A

The level of succinic dehydrogenase activity in Neomysis integer as determined by the reduction of triphenyl tetrazolium chloride appears to vary seasonally from 1·7 μg formozan/mg wet weight/24 hours in November, to 3·5 μg/mg/24 hours in December, and to 5·3 μg/mg/24 hours in May. Temperature accelerates the enzyme activity. There is an inverse relationship between activity of the enzyme and body weight. A comparison with a few other typical planktonic animals shows that the activity is high as compared with that of cnidarians and ctenophores, but is in the same range as that for chaetognaths and copepods. Of the chaetognaths studied, Spadella shows a higher activity than Sagitla. Similarly, among copepods, Acartia has a far higher activity than Calanus, again indicating possibly an inverse relationship with body weight.

Hempel, G.; Blaxter, J. H. S.

doi: 10.1093/icesjms/31.2.170pmid: N/A

The dry weight of mature herring eggs, measured from samples taken from about 25 spawning grounds, is very variable from ground to ground, while there may also be age and year-to-year differences. The mean weight varies by at least a factor of three, from 1·2 mg per egg in Baltic spawners of the late spring, to 3·7 mg per egg for early winter spawners of the southern North Sea. In general egg weight is high for fish spawning in winter and early spring, and low in late spring, summer and autumn. As a characteristic it can be useful for defining “races” as well as having wide ecological implications. Usually fecundity and egg weight are inversely related. Thus spawners with fewer, heavier eggs will produce few, but large larvae with considerable yolk reserves at a time of poor food supply and a low predator population. Under warmer conditions a larger number of small eggs are produced which can be seen as an adaptation to adequate larval food, but high predation.

Zijlstra, J. J.

doi: 10.1093/icesjms/31.2.196pmid: N/A

Two fishing techniques, trawl and drift-net, gave opposite indications about the trends in abundance of the herring-stock in the northwestern North Sea in the period 1945–1960. The two fisheries exploit different components of the stock (younger and older fish), due possibly to differences in fishing area of the fleets and in behaviour of the two components of the herring stock.

de Veen, J. F.

doi: 10.1093/icesjms/31.2.207pmid: N/A

The sole, normally a demersal fish, occasionally migrates to the surface especially in the period preceding the spawning season in spring. This phenomenon was studied by means of verbal inquiries among Dutch fishermen in the springs of 1963, 1964 and 1965. From a total of 2,500 interviews 441 positive reports revealed that swimming at the surface results in a speedy migration from deeper water to the spawning grounds near the coasts of Holland, Germany and Denmark.Soles only migrated to the surface during the night and only when the tidal streams were flowing to the NE, E, SE or S guaranteeing transport in a favourable direction. Quick transport was secured by swimming to the surface since maximum current velocity may be expected there.At the surface soles, lying nearly immobile, normally were heading NE and E even when they were carried in other directions by the tidal streams. This suggests that two types of orientation are used, namely selection of the appropriate tidal current direction before reaking surface and, after having arrived at the surface, an orientation of the body independant of the tidal currents.A number of possible orientation mechanisms are discussed. The concept of compass orientation seems to be most appropriate. Supporting this is the fact that in a number of observations in a restricted area there emerged a distinct relation between the degree of cloud cover and the degree of orientation towards tidal streams, suggesting that celestial cues may be used in the orientation. It appeared that the moon had no influence in this respect.

Raitt, D. F. S.; Hall, W. B.

doi: 10.1093/icesjms/31.2.237pmid: N/A

Sebastes marinus is an ovo-viviparous fish with an unusual maturity cycle. Estimates of the fecundity from the number of eggs in the ovary prior to self-fertilisation show that these can be related to changes in size and regression equations of fecundity on length are presented for samples from Faroe and Iceland. A comparison of these results with some published data on fertilised egg counts of S. marinus from East Greenland shows the latter to be significantly lower. The relationship between either of these counts and the subsequent numbers of larvae extruded is not known. The appropriate measure of fecundity to be estimated in future will depend on the way in which the data will be utilised.

Hancock, D. A.; Edwards, E.

doi: 10.1093/icesjms/31.2.246pmid: N/A

Determination of annual growth under natural conditions has so far proved difficult in Crustacea, largely due to lack of information on moult frequency. In this paper, recaptures from suture-tagging experiments have been examined, and the results from crabs recaptured on annual anniversaries after their release, including both moulted and unmoulted, combined to provide estimates of annual growth and annual moult frequency. Males and females were considered separately, and annual growth in males became reduced at a smaller size than in females.

Pope, J. A.; Thomas, H. J.

doi: 10.1093/icesjms/31.2.265pmid: N/A

Current size legislation on Norway lobsters is based on overall length, while for scientific purposes the more accurate carapace length is used. The relationships between these measurements, derived from samples of males and females taken in the Moray Firth and the Minch, are obtained. No sex difference is detected, but the overall length (L) at a given carapace length (C) is found to be slightly higher in the Minch than in the Moray Firth. The best fitting relationships for the two areas are found to beMoray Firth: L = 3·004C + 9·2 Minch: L = 3·004C + 10·1 These relationships are compared with ones available for English, Irish, Portuguese and Faeroese stocks and, with the exception of the latter, they are found to be very similar everywhere.Other relationships obtained from the Scottish data are derived. These include the relationship between carapace length and tail width, body weight and tail weight and total weight and carapace length. Sex and area differences in these relationships are studied.