A hydrodynamic study of a modified model of the Clarke Jet Net

A hydrodynamic study of a modified model of the Clarke Jet Net, a high speed plankton sampler, was made using a wind tunnel and an IBM 7040. Modifications allowed a somewhat larger amount of water filtered than in the original model. By adjusting the size of the net chamber exhaust (water control aperture), an average net chamber velocity of about 100 cm/sec could be obtained at any cruising speed. The curvature of the towing cable of the deep tow of a high speed sampler seemed to be determined mainly by the cable characteristics. The stability, vertical and horizontal, of the modified model was satisfactory.Contribution No. 218 from the Seikai Regional Fisheries Research Laboratory, Nagasaki.     

Emploi du chalut pélagique Isaacs-Kidd 10 pieds dans les eaux équatoriales du Pacifique

This paper describes the use of the 10 foot Isaacs-Kidd midwater trawl as a quantitative sampler of the micronektonic standing crop. The use of this gear without an opening-closing mechanism made it necessary to sample by means of oblique hauls. This study, which includes not less than 1500 hauls, is directed towards introducing some degree of uniformity in operating this device so that valid comparisons can be made between catches from oblique hauls made at similar depths, as well as oblique hauls made at different depths. It is emphasized that information must be obtained on the tow path using depth-time and depth-distance recorders simultaneously. As the maximum depth depends largely upon variations in towing speed, it is important to be able to control ship speed carefully. As net speed is a significant factor in avoidance and escapement, care should be taken to sample each layer in an identical manner. The procedure defined here mainly involves (a) modifications of the depressor; (b) application of the winch brake after all the cable has been paid out, during the time required for the trawl to attain maximum depth; (c) paying out and hauling in at high speed by the winch. Resulting hauls show a nearly oblique tow path. Sampling velocities of the net are the same for all water layers: slow during descent, fast during ascent. This allows valid comparisons to be made between a series of hauls. Nevertheless, future progress in quantitative sampling depends largely upon technical improvements, and the evolution of new devices and approaches.     

Design of a rapid-sampling vertical-tow net

Design and operation of a new sampler for zooplankton are described. The sampler facilitates reliable duplicate samples; it can be closed at a defined depth during vertical towing, and can be rapidly reloaded for repeated tows.     

Development of odorous gas sampler and investigation of its practicality

The existing gas sampler is deficient in regard to its efficiency, handling and ability. In order to solve these problems, a new gas sampler was developed and its function was investigated. The sampler is a vessel made of aluminium and contains a polyester bag inside the vessel. The vacuum method is employed for taking the gas. The maximum capacity of the gas volume that can be taken is about 15 liters and sampling time can be from 15 sec to 10 min per sample. In addition, many odor surveys were carried out and the practicality of the new sampler was investigated. It was concluded that the new sampler was easy to handle and was more efficient than the existing gas sampler.     

Traitement des récoltes micronectoniques

This paper deals with some mechanical treatments of micronektonic samples which enable easier sorting into taxa. At sea, it is only possible to hose the net intensively before being brought on board ship; organisms are then washed into a bucket, the bucket emptied, and the samples preserved in a 10% buffered formaldehyde solution. A laboratory method for sorting gelatinous organisms based on differential specific gravity is described. The sorter consists of a cylinder 1.60 m high, supplied with running water. The remaining fraction is then sorted into 3 size groups. The device consists of a set of grills made from equidistant glass rods, through which organisms are sieved by the reciprocating motion of the grills into a large jar filled with running water. As this method results in higher sorting efficiency, it is recommended that further research be made in this direction.     

Fast Ferry Traffic as a Qualitatively New Forcing Factor of Environmental Processes in Non-Tidal Sea Areas: A Case Study in Tallinn Bay,Baltic Sea

The impact of wake wash from high-speed ferries on the coastal environment in non-tidal seas is analysed in terms of wave energy and power, and properties of the largest waves. Shown is that hydrodynamic loads caused by heavy high-speed traffic may play a decisive role not only in low-energy coasts but also in certain areas with high wind wave activity. For example, ship-generated waves form, at least, about 5–8% from the total wave energy and about 18–35% from the wave power in the coastal areas of Tallinn Bay exposed to dominating winds. The periods of wake waves from high-speed ships frequently are much larger than dominating periods of wind waves. The leading waves typically have a height of about 1 m and a period of 10–15 s. Such waves extremely seldom occur in natural conditions in many regions of semi-enclosed seas. They cause unusually high hydrodynamic loads in the deeper part of the nearshore. The fast ferry traffic thus is a qualitatively new forcing component of vital impact on the local ecosystem. It is demonstrated that wakes from high-speed ferries may trigger considerable changes of the existing balance of coastal processes. Owing to their low decay rates combined with their exceptional compactness after crossing many kilometres of the sea surface, such wakes may cause considerable remote impact of the ship traffic. This feature has to be addressed in the analysis of the impact of harbours and associated ship traffic in the neighbourhood of vulnerable areas.     

A Bayesian approach for understanding the role of ship speed in whale-ship encounters

Mandatory or voluntary reductions in ship speed are a common management strategy for reducing deleterious encounters between large ships and large whales. This has produced strong resistance from shipping and marine transportation entities, in part because very few studies have empirically demonstrated whether or to what degree ship speed influences ship-whale encounters. Here we present the results of four years of humpback whale sightings made by observers aboard cruise ships in Alaska, representing 380 cruises and 891 ship-whale encounters. Encounters occurred at distances from 21 m to 1000 m (x = 567 m) with 61 encounters (7%) occurring between 200 m and 100 m, and 19 encounters (2%) within 100 m. Encounters were spatially aggregated and highly variable across all ship speeds. Nevertheless a Bayesian change-point model found that the relationship between whale distance and ship speed changed at 11.8 knots (6.1 m/s) with whales encountering ships, on average, 114 m closer when ship speeds were above 11.8 knots. Binning encounter distances by 1-knot speed increments revealed a clear decrease in encounter distance with increasing ship speed over the range of 7-17 knots (3.6-8.7 m/s). Our results are the first to demonstrate that speed influences the encounter distance between large ships and large whales. Assuming that the closer ships come to whales the more likely they are to be struck, our results suggest that reduced ship speed may be an effective management action in reducing the probability of a collision.     

Food size spectra,ingestion and growth of the copepodAcartia tonsa during development: Implications for determination of copepod production

Clearance rates on different sizes of spherically shaped algae were determined in uni-algal experiments for all developmental stages (NII through adult) of the copepodAcartia tonsa, and used to construct food size spectra. Growth and developmental rates were determined at 7 food levels (0 to 1 500 g C l^-1 ofRhodomonas baltica). The lower size limit for particle capture was between 2 and 4 m for all developmental stages. Optimum particle size and upper size limit increased during development from 7 m and 10 to 14 m for NII to NIII to 14 to 70 m and 250 m for adults, respectively. When food size spectra were normalized (percent of maximum clearance in a particular stage versus particle diameter/prosome length) they resembled log-normal distributions with near constant width (variance). Optimum, relative particle sizes corresponded to 2 to 5% of prosome length independent of developmental stage. Since the biomass of particulate matter is approximately constant in equal logarithmic size classes in the sea, food availability may be similar for all developmental stages in the average marine environment. Juvenile specific growth rate was exponential and increased hyperbolically with food concentration. It equaled specific female egg-production rate at all food concentrations. The efficiency by which ingested carbon in excess of maintenance requirements was converted into body carbon was 0.44, very similar to the corresponding efficiency of egg-production in females. On the assumptions that food availability is similar for all developmental stages, and that juvenile and female specific growth/egg-production rates are equal, female egg-production rates are representative of turnover rates (production/biomass) of the entireA. tonsa population and probably in other copepod species as well. Therefore, in situ estimates of female fecundity may be used for a rapid time- and site-specific field estimate of copepod production. This approach is shown to be fairly robust to even large deviations from the assumptions.     

Ein fotoschlitten für biologische und geologische kartierungen des meeresbodens

A photosledge is described; it is 4 m long and 2 m wide and can be used also on an uneven sea bottom. In its foremost part a camera is mounted in a pressure sphere which has been tested for water depths down to 6,000 m. The camera system can hold 90 m of film; with an exposure size of 24x24 mm this accounts for 3,600 exposures. The time between 2 exposures may be varied from 1 to 10 sec and this allows to cover a distance of 2 to 20 nautical miles at a speed of 2 knots within 1 single mission. The photographic angle may be changed from vertical to horizontal. Best results have been obtained with angles of 30 and 45 degrees from the vertical. The electronic flash, with a power of 60 Wsec, is mounted below the camera. Successful work has been conducted in the North Sea and the Baltic Sea at depths between 40 and 50 m, on the continental slope off Portugal between depths of 140 and 240m, and on top of Great Meteor Seamount at depths between 280 and 350 m.     

Early-life nutritional environment and spatial navigation in the water shrew, Sorex palustris (Insectivora)

Studies were conducted to study the effects of early-life nutritional environment on spatial navigation ability in the water shrew (Sorex palustris), as well as to provide information on life history traits and husbandry. The mean longevity of males and females in captivity was 652.3 +/- 33.8 SD and 616.2 +/- 22.5 days, respectively. Litter sizes ranged from 5 to 8 and neonatal mass ranged from 0.71 to 0.83 g. Spatial navigation was examined by use of the Morris water apparatus, where animals were required to locate the position of an escape platform in a circular tank of water. The platform was visible (proximal cue version of the task) in some tests. In other tests it was hidden beneath the surface (distal cue version) by making the water opaque using a non-toxic white dye. The tank was divided into 4 quadrants and the position of the plafform in any quadrant could be fixed for any subject or varied between subjects. Early-life under-nutrition was achieved by maintaining some shrews on a restricted diet (received half the amount of food as did controls). Under-nutrition was found to have an adverse effect on spatial navigation. Regardless of nutritional status, shrews were able to locate a hidden plafform that was placed at the center of a given quadrant more rapidly (escape latency) when it was visible (44 to 69 sec) than when it was hidden (83 to 164 sec). Results also showed that these shrews utilize both proximal and distal cues in this spatial task. Control subjects spent more time at a location where the platform had been in a previous test (69% of the trial period) than their undernourished counterparts (45 to 51%). This is the first experimental analysis of spatial navigation and the effects of early-life under-nutrition on this task, for S. palustris.     

A submerged membrane filter apparatus for microbiological sampling

The sampler is operated by hydrostatic pressure and consists of a stainless steel cylinder to which is attached a membrane filter holder. A glass inlet tube is broken by a messenger and a predetermined volume of water is filtered. Valves protect the membrane from flow-back and release the pressure as the sampler returns to the surface. The sampler works satisfactorily at 15 m and is strong enough to be used down to 6000 m. The filling rate is controlled by a jet behind the filter holder.     

A sampler for the aseptic collection of water samples in the sea

A sampler is described which can be used for the collection of microbiological, phytoplanktological, and chemical sea-water samples. The sampler consist of a polyvinylchloride (PVC) frame on which a sterile silicone-rubber container (500 ml) is assembled. The sampler is fitted with a couple of reversing thermometers. All materials used, including the hydrographic cable and the messenger, have been tested for toxicity. The container, actuated by the messenger, fills and then is closed by a stop-cock to prevent any contamination with upper-level sea water during hauling aboard. The reversing thermometers reverse only when the sample has been taken properly. Thus, the thermometers guarantee good functioning of the sampler and supply also information on the exact depth at which the sample was collected. The device can operate at any depth and several devices can be operated in one cast. During normal operation, contamination due to microorganisms attached to the frame and container is negligible.This work was performed under the association contract Euratom-CNEN.     

A laboratory study of behavioral interactions of the Antarctic keystone sea star Odontaster validus with three sympatric predatory sea stars

The circumpolar sea star Odontaster validus is ubiquitous in the nearshore marine benthos of Antarctica. Despite its ecological importance, little is known of its behavioral interactions with other common sympatric sea stars. To examine these interactions we employed time-lapse video analyses conducted in a large laboratory tank (1.8 m diameter circular tank, 1,629 L). In each experimental trial, 34 adult O. validus were placed in a tight circular grouping on one side of the tank, and one adult individual of one of three common sympatric species of predatory sea star (Labidiaster annulatus, Diplasterias brandti, or Perknaster aurorae) was placed on the opposite side of the tank. Digital images of sea star movements were then captured at one min intervals over a 24 h period and aspects of sea star movements subsequently analyzed. Each 24 h treatment was replicated three times, as was a control treatment consisting only of O. validus. O. validus had significantly elevated levels of activity in the presence of P. aurorae when compared with the other two sea stars (potential chemically mediated response), and displayed a distinct “flight response” (change in direction and twofold to sixfold increase of speed) upon tactile contact with this species. Moreover, an “alarm response” was detected when individuals of O. validus that encountered a fleeing conspecific also fled the vicinity. In contrast, our results indicated that O. validus displays virtually no chemical or tactile behavioral responses to the large multi-armed L. annulatus and only weak tactile responses to D. brandti.     

Bayesian hierarchical spatio-temporal modelling of trends and future projections in the ocean wave climate with a \text{ CO }_2 regression component

Bad weather and rough seas continue to be a major cause for ship losses and is thus a significant contributor to the risk to maritime transportation. This stresses the importance of taking severe sea state conditions adequately into account, with due treatment of the uncertainties involved, in ship design and operation in order to enhance safety. Hence, there is a need for appropriate stochastic models describing the variability of sea states. These should also incorporate realistic projections of future return levels of extreme sea states, taking into account long-term trends related to climate change and inherent uncertainties. The stochastic ocean wave model presented in this paper exploits the flexible framework of Bayesian hierarchical space-time models. It allows modelling of complex dependence structures in space and time and incorporation of physical features and prior knowledge, yet at the same time remains intuitive and easily interpreted. Furthermore, by taking a Bayesian approach, the uncertainties of the model parameters are also taken into account. A regression component with $\text{ CO }_2$ as an explanatory variable has been introduced in order to extract long-term trends in the data. The model has been fitted by monthly maximum significant wave height data for an area in the North Atlantic ocean. The different components of the model will be outlined in the paper, and the results will be discussed. Furthermore, a discussion of possible extensions to the model will be given.     

Effect of light intensity on activity and food-searching of larval herring,Clupea harengus: a laboratory study

Larvae of Clupea harengus were reared from spawning herring caught in March 1982 and 1983 in the Firth of Clyde, Scotland. An infra0red observation technique was used to record the behaviour of larval herring both in shallow dishes using a top view and in a tank 2 m deep using a side view. The amount of time larvae spent swimming, which was minimum in complete darkness, increased with increasing light intensity and as the larvae grew. Maximum swimming speeds of feeding larvae were recorded at light intensities between 10 and 100 lux. The presence of food organisms (Artemia sp., Brazilian strain) at light intensities below the feeding threshold (0.1 lux) caused an increase in the proportion of time spent active, but light intensities above the threshold had different effects, depending on developmental stage: larvae of 12 mm increased swimming speed, but 21 mm larvae decreased speed. In the 2 m deep tank in darkness, larvae displayed inactive periods wherein they sank head first, interspersed with periods of upward swimming. As light intensity increased, vertical swimming was replaced by horizontal swimming. These results are discussed with reference to food searching and vertical migration of larval herring in the sea.     

Ferric Oxide Incrustations on Cell Walls of the Green Alga Cladophora rupestris Growing near an Iron Ore Unloading Terminal

Cladophora rupestris plants growing near an iron ore unloading terminal bore red-brown cell wall incrustations. These were shown to be of ferric oxide by histochemical tests. Iron-free Cladophora plants transplanted to this same location developed Fe₂O₃ incrustations after 3-4 weeks. Similar crustose deposits of smaller sizes were observed on Cladophora plants growing near rusty chains in a harbour at some distance from the ore terminal. Cladophora would seem to be a useful factor monitoring organism for iron ore dust spillage in the sea.     

Application to the Port of Sines of a new tool for risk assessment in port navigation

This paper describes a first approach on the risk assessment in port navigation using GUIOMAR, an integrated system for port and coastal engineering modelling developed at the National Civil Engineering Laboratory (LNEC), Portugal, using a GIS software environment. A set of automatic procedures was designed to include a new methodology based on the amplitude of the wave-induced vertical movement of a ship along its trajectory. In this methodology, the risk in port navigation is assessed on the basis of a combination of the probability of exceedance of a pre-set threshold for the ship??s vertical movements and its consequences. To test the new procedures, a set of sea wave records obtained at the Sines wave-buoy from 1988 to 2002 was transferred into Sines Port using two numerical models of sea wave propagation and deformation (SWAN and DREAMS), included in the GUIOMAR system. The numerical model WAMIT was used for estimating the wave-induced ship??s vertical movements inside the port. By applying the new procedures, automatic generation of risk maps was carried out for navigation in the vicinity of the West breakwater of the Port of Sines. The recent developments contribute towards a more versatile and efficient GUIOMAR system, which results in a more adequate tool to support decision-making processes in port and coastal management.     

Patterns of abundance, population size structure and microhabitat usage of Paracentrotus lividus (Echinodermata: Echinoidea) in SW Portugal and NW Italy

In coastal habitats, wave exposure influences several aspects of the life history of marine organisms. Here, we assess how hydrodynamic conditions can generate variation in density, size structure and microhabitat usage of Paracentrotus lividus and whether these effects are consistent between regions that are markedly different for oceanic climate, such as the coasts of SW Portugal and NW Italy. The abundance of P. lividus was ~4 times higher in SW Portugal than in NW Italy, but within each region, there was no effect of wave exposure. In SW Portugal, higher urchin abundances were found at shallower depths, while no effect of depth on urchin abundance emerged in NW Italy. Most of the variation in urchin abundance occurred at small spatial scales (metres), and our results suggest that habitat complexity, that is, the presence of cracks and crevices, is an important determinant of patterns of distribution of this species. The population in NW Italy was characterized by a unimodal size distribution, with a higher proportion of medium-sized individuals. In contrast, in SW Portugal, smaller individuals represented a large proportion of the populations. Size structure varied between exposed and sheltered habitats in SW Portugal, suggesting that the proportion of individuals from different size cohorts may vary along wave-exposure gradients as a result of direct or indirect effects of hydrodynamic forces. In SW Portugal, most urchins occurred in burrows, while in NW Italy, urchins were mainly observed in crevices. These results suggest that creating/occupying burrows might be an adaptive behaviour that allows sea urchins to better withstand stressful hydrodynamic conditions and, therefore, are more common on exposed Atlantic coasts. Overall, our study suggests that the effects of hydrodynamic forces on sea urchin populations are context dependent and vary according to background oceanic climate.