ICES Journal of Marine Science: Journal du Conseil

Howell, B. R.

doi: 10.1093/icesjms/35.1.1pmid: N/A

The rotifer, Brachionus plicatilis, and the trochophore larvae of the mussel, Mytilus edulis, were compared with Artemia nauplii as foods for larval plaice and sole. The culture techniques for the food organisms are described. An empirically developed culture technique for Brachionus gave a mean daily yield over 80 days of 370000 rotifers from a 30 1 culture to which an average of 4·4 1 of a Dunaliella suspension containing 3000 cells per ul were added daily.Larval plaice and sole gave similar results. Although trochophores were of comparatively little value, Brachionus supported development to metamorphosis. The growth rate on rotifers was less than that on nauplii, but survival was equally good. The daily demand of plaice larvae for rotifers increased from 85 per late stage 2 larva to 1400 per larva approaching metamorphosis.

Saraiva, Maria C.

doi: 10.1093/icesjms/35.1.7pmid: N/A

To estimate the radiosensibility of the benthic copepod, Tigriopus fulvus (Fischer), this species was submitted to gamma ray exposure (60 Co). A method of culture of Tigriopus fulvus is described: The copepods were fed with dense cultures of Dunaliella and Monochrysis. The egged females were irradiated at the same egg-sac maturity.Death of adults was observed at the dose of 128000 rads but did not occur at the lower doses used (i. e. 64000 rads and below). Irradiation doses above 8000 rads induced a delay in the egg-sac formation; this was stopped at a dose of 64000 rads. The hatching rate as well as the number of nauplii formed (and their survival) decreased with increasing gamma doses.

Holden, M. J.; Vince, M. R.

doi: 10.1093/icesjms/35.1.13pmid: N/A

The results of an experiment in which 348 Raja clavata were tagged and injected with tetracycline in November 1968 are described. This drug is deposited in calcified tissues and fluoresces in ultraviolet light, and can therefore be used as a time marker in calcified skeletal structures. There were 86 recaptures from the experiment by mid-October 1971, but only 16 fish were actually returned. Examinations of these showed that tetracycline was deposited in all the calcified skeletal structures present at the time of injection. It was not found in the secondary sexual alar and malar spines of a male ray which was immature at tagging and mature at recapture. The deposition of tetracycline in relation to the opaque and hyaline zones occurring on the centra of the vertebrae is described in detail. Six of these rays had just started the formation of a hyaline zone at the time of injection, and six were still forming an opaque zone; one ray was in a transitional stage. These observations, combined with those on the appearance of the opaque zone at the periphery of the centrum, show that formation of the opaque zone probably occurs in the latter half of the year but usually does not become visible, when the centra are observed by reflected light, until the early months of the subsequent year. By relating the opaque and hyaline zones to the deposition of tetracycline it is proved that one of each type of zone is laid down annually. The difficulties in interpreting the edge structure in relation to the use of the centra for age determination are discussed.

Windom,, H.;Taylor,, F.;Stickney,, R.

doi: 10.1093/icesjms/35.1.18pmid: N/A

Abstract Concentrations of mercury in North Atlantic plankton (on a dry weight basis) vary from less than 0·2 to about 0·4 ppm in unpolluted areas to as high as 5·3 ppm in polluted areas near shore. No correlation in mercury content with species composition of the plankton samples was observed. Variations in concentration appear to be a function of distance from coastal pollution sources. This content is only available as a PDF. © Conseil International pour l'Exploration de la Mer

Cushing, D. H.

doi: 10.1093/icesjms/35.1.22pmid: N/A

The sonar equation for echo level has been used to estimate the average signals at different ranges expected from fishes between 20 and 90 cm in length, at intervals in length of 2·5 cm. The volume sampled (in one transmission, or in each nautical mile) has been determined in range and size of fish. The signal expected at different ranges using a time-varied gain (TVG) for different sizes of fish has been calculated. The height above the bottom and the number of transmissions/target for different sizes of fish at different ranges has been calculated.

Rommel, Sentiel A.; Mccleave, James D.

doi: 10.1093/icesjms/35.1.27pmid: N/A

Several hypotheses exist in the literature suggesting the use of oceanic geoelectric fields in fish orientation, but only surface electric field values are readily available. However fishes may migrate at considerable depths. Standard electrical circuit analysis techniques were utilized to develop a two-dimensional predictive model for the geoelectric fields in ocean current systems. In six cross sections of the Gulf Stream examined as examples, total electric field intensities up to 0·46 μV/cm and current densities up to 0·0175 μA/cm2 were predicted. The electro-sensitivity of the American eel and the Atlantic salmon are within this range. Thus sufficient information is available for possible electro-orientation of at least two migratory fishes.

Lenz, Jurgen

doi: 10.1093/icesjms/35.1.32pmid: N/A

During a quantitative survey of the phyto- and zooplankton standing stock a surprisingly high number of Bolinopsis infundibulum, cited as a rare visitor to the Western Baltic, was observed in Kiel Bight from November 1970 to April 1971. The specimens caught ranged from 1–4 cm in length and were apparently young stages. Their maximum concentration was found to be 49 ind./m3. From January to early April a mean value of 16 ind./m3 was obtained for water masses where salinity exceeded 15·5%. In most cases Bolinopsis outnumbered Pleurobrachia pileus, which is common in this area. It is thought possible that the occurrence of Bolinopsis in the Western Baltic has so far been overlooked because it more or less completely disintegrates in formalin-preserved samples. In our case the specimens were caught by a newly developed plankton pump which provides for very careful sampling, and examined on filter screens before preservation. It is recommended to investigate the interesting penetration of this species into brackish waters by examining fresh plankton samples immediately after hauling.

Boyar, H. C.; Marak, R. R.; Perkins, F. E.; Clifford, R. A.

doi: 10.1093/icesjms/35.1.36pmid: N/A

This study reports observations made on the seasonal distribution of larval herring in the western North Atlantic from November 1962 through April 1970. It summarizes observations made during all months of the year except January and provides a more complete picture than previous studies conducted in autumn, winter, and spring of the 1950's. The seasonal distribution of larval herring from the autumn through the spring (combined with maturity, meristic and biochemical studies of adult herring in the 1960's) provides evidence of at least three discrete major spawning areas in the western North Atlantic: Georges Bank, coastal Gulf of Maine and Nova Scotia. The presence of a clockwise gyre, although it may at times break down in the winter, on Georges Bank retains the majority of larvae spawned on the Bank. The presence of a counter-clockwise current in the coastal Gulf of Maine appears to retain the larvae in these waters and the circulation off the coast of Nova Scotia results in the larvae remaining close to the spawning site or being carried into the Bay of Fundy. Larvae grow at least to a length of 50 to 55 mm (TL) before becoming post-larvae. They grow on the average of 5 mm per month from September through June.

de Campos Rosado, J. M.

doi: 10.1093/icesjms/35.1.52pmid: N/A

The catch statistics of Angola are considered as grossly inaccurate. The catch of yellowfin and skipjack, and the corresponding effort by the local bait-boat fishery were then evaluated by the following method. The estimates XY and Xs of the effort exerted respectively on yellowfin and skipjack off the fishing centre of Benguela were computed by dividing their respective catch statistics into the indices of abundance (catch-per-standard-bait-boat-per-day) UY and Us, evaluated in a previous paper from landing records of a sample of bait-boats. Xy and Xs were then compared with another estimate of the effort, denoted by G and computed from the right side of the expression ∑i=1i=NEigi=NE¯g¯+(N−1)CovE,g where Ei and gi are the relative efficiency and the number of fishing days of bait-boat i. The number NĒ of standard boats was estimated from the registration files maintained by the marine authorities, and g¯ and CovE, g from the sample. It was found that G and Xy are strongly correlated, while G and Xs are not. The skipjack catch statistics were thus dismissed as meaningless, and Xy and G were taken as the minimum effort and the average maximum effort, respectively. The latter was acknowledged as the truer estimate. Hence, the total minimum Angolan effort was evaluated by dividing the total yellowfish catch into Uy, and the total average maximum effort with a prediction equation of G given XY, calculated from the Benguela data. The total average maximum catch of yellowfin and skipjack was then evaluated by multiplying G by Uy and Us, respectively.On fitting Schaefer's logistic model to the Angolan G and Uy series it was found that the reducdion in the yellowfin population observed in the Angolan catches since 1956 was not caused by the local fishing efforts.

Omori, Makoto; Konagaya, Teruo; Noya, Kazuo

doi: 10.1093/icesjms/35.1.61pmid: N/A

Sergestes lucens is a pelagic shrimp which is fished commercially only in Suruga Bay, Japan. The history and present status of the unique fishery are described. Fishing and catch statistics were collected extensively for the years 1955 to 1970. A night fishery of the species has been conducted by haul net since 1894. Recently, the annual catch of the shrimp totals 3800 to 7500 tons (more than 2 500 000 dollars US in landed value). The stocks of S. lucens in the bay seem to be enormous and fishing has not affected the reproduction of the species. The fishable life span of the species is normally not more than about one year, and the catch for a particular year largely depends upon the success of an individual year-class entering the fishery in the previous year. The critical period exists in early larval stages and the fluctuation in the abundance of S. lucens is greatly influenced by the temperature during the breeding season. There is an apparent close correlation between the fluctuations of catches for different year-classes and water temperature around the 50 m level in the bay during June and August. Warm years bring good total catches and cold years poor total catches. Detailed analyses of the data have yielded useful biological information and important fishery parameters such as annual catch, fishing effort, size and age composition, and weightvariation of catches, as well as growth rate. These statistics will be used for further studies to forecast the abundance of stocks of S. lucens in the bay.