Showing papers on "Pelagic zone published in 1977"

Standard techniques for pelagic fish egg and larva surveys

Abstract: Standard techniques for pelagic fish egg and larve surveys , Standard techniques for pelagic fish egg and larve surveys , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Structure of Pelagic Food Chain and Relationship Between Plankton and Fish Production

Abstract: Further observations on the standing stocks of pelagic organisms confirm the occurrence of approximately equal biomass over logarithmically equal size ranges. A simple theoretical framework is developed that shows that the structural elements of the pelagic ecosystem can be described in terms of the sizes of predator and prey and of the efficiencies of their interactions. In practice this means that if the standing stock at any size range is known, the standing stock at any other size can be estimated, and if the growth rate at this size is known, the production can be estimated. The theory is tested on three fisheries. For the Gulf of Maine and the North Sea, phytoplankton production is estimated from fishery production. For the area off Peru the fishery production is estimated from the plankton production. Key words: pelagic ecosystem, predator–prey relationships, plankton production, marine fisheries, Peru, North Sea, Gulf of Maine

Interstitial Nitrate Profiles and Oxidation of Sedimentary Organic Matter in the Eastern Equatorial Atlantic

Abstract: Pore-water nitrate concentrations in six pelagic eastern equatorial Atlantic cores increase from bottom water values (22 micromolar) to 40 micromolar at a depth of about 5 centimeters, then decrease to undetectable levels at depths as shallow as 40 centimeters. These nitrate concentrations and concentration gradients reflect zones of oxygen reduction, nitrate reduction, and sulfate reduction in the sediments. The estimated benthic flux of nitrate to the ocean from our data is much less than the total globalflux of nitrate to deep waters, even though these equatorial sediments underlie a productive upwelling zone. The estimated denitrification rate in our study area suggests that pelagic sediments may be important sites of marine denitrification.

Photosynthesis and fish production: Hypothetical effects of climatic change and pollution

Abstract: Overall comparisons of marine pelagic productions in different systems are speculative to a high degree. Yet they often bring to our attention processes which have not been sufficiently investigated. One such process may be the decrease of fish production due to the change in the diatom/flagellate ratio. The following hypothesis is discussed in the light of recent investigations: An increasing development of flagellates caused by some types of pollution or climatic changes not only may increase the number of trophic levels and thereby, decrease fish production, but also may cause a change in the flow of biomass from fish to ctenophores and other planktonic predators, thereby again decreasing the harvest available for human consumption.

Ecological studies on the deep-water pelagic community of Korsfjorden, western Norway

Abstract: As part of a project aimed at assessing the available energy in a pelagic system and the efficiency of its transfer, monthly biomass estimates of the 23 main macroplanktonic and mesoplanktonic species have been made in Korsfjorden (Norway). Sampling was carried out over approximately 3 years (1971–1974) and results are presented as mg dry weight in a 690 m3 water column. The total annual stocks of the various species were not constant in the 3 years of sampling. Principal components analyses of the monthly stocks in each of the 3 years show striking differences in the correlation matrices from year to year. On the basis of known and supposed feeding habits, the species have been classified as herbivores, omnivores, or carnivores. The monthly biomass estimates of these groups show a consistent pattern from year to year. This, in contrast to the variable correlations between individual species, indicates that there can be considerable flexibility in the specific composition of a planktonic community without correspondingly marked effects on its trophic structure.

The reproduction of some littoral molluscs from Macquarie Island (Sub-Antarctic)

Abstract: The reproduction of 9 species of littoral molluscs from the sub-Antarctic Macquarie Island was examined. The mode of larval development is reported for all species, and the reproductive patterns for 7 are described from collections taken monthly over a period of 1 year. Two species release gametes for external fertilization, whereas the other 7 have non-pelagic development via brooding or the laying of egg cases; some of these findings were deducted from examination of gonads rather than by direct observation. Features of reproduction important in any correlation between a littoral animal's reproduction and its habitat are discussed, and relationships between pelagic and non-pelagic development of the Macquarie molluscs and (a) distribution in the local environment and (b) habitat are drawn. The widely recognised correlation between species having a non-pelagic development and small number and large size of eggs is considered as a method for predicting the type of larval development (in terms of pelagic versus non-pelagic) from an examination of the ovary. It is suggested that further data on modes of development could be obtained from specimens of marine invertebrates collected throughout southern latitudes and that such data would enhance zoogeographical interpretations.

The integumental sensilla and glands of pelagic Crustacea

Abstract: The pelagic environment can be divided into five gross regions. These are the intertidal and estuarine, the neritic and the oceanic epipelagic, mesopelagic and bathypelagic regions. Each of these regions has an endemic crustacean fauna but many species inhabit more than one region. The ranges and rates of fluctuations of environmental characteristics vary from the extremes encountered in the intertidal and estuarine region to the relative constancy of those in the bathypelagic region.

Distribution and duration of pelagic life of larvae of dover sole, Microstomus pacificus; rex sole, Glyptocephalus zachirus; and petrale sole, Eopsetta jordani, in waters off Oregon

Abstract: Dover and rex sole larvae attain an exceptionally large size and have a long pelagic life. Dover sole larvae (9-65 mm standard length) were collected in mid-water trawls and plankton nets during all months of the year. Judging from growth of larvae and occurrence in bottom trawls of recently metamorphosedjuveniles, Dover sole are pelagic duringtheir first year oflife. Large larvae (50-65 mm standard length) are probably pelagic for over a year and few apparently are recruited to benthic populations. Dover sole larvae were most common in oceanic waters beyond the continental slope and in the upper 50 m of the water column. The rex sole larvae captured were 5-89 mm long. Average size and stage of development oflarvae increased from March through February, andjuveniles were common on the bottom during winter on the outer shelf. Thus the pelagic phase usually lasts about a year. Both rex and Doyer sole may utilize the outer continental shelf-upper slope region for a nursery during early benthic life. Petrale sole larvae (10-22 mm standard length) were rare. They were collected only from March to June and appear to have a pelagic life ofabout 6 mo. Age-group Ojuveniles, uncommon in bottom trawl collections, were only captured on the inner continental shelf in the fall.

DISTRIBUTION, SIZE, AND ABUNDANCE OF MICROCOPEPODS IN THE CALIFORNIA CURRENT SYSTEM AND THEIR POSSIBLE INFLUENCE ON SURVIVAL OF MARINE TELEOST LARVAE l

Abstract: The California Current system can be divided into onshore and offshore faunal zones by a copepod indicator species, Mecynoceraclausii. Near the outer edge ofthe onshore zone copepod nauplii densities were higher than usual. There were about 3 times as many microcopepodids and 12 times as many nauplii on the average throughout the onshore as in the offshore zone. Feeding habits of larvae of sardines, anchovies, and jack mackerel may be adapted to the usual naupliar and copepodid concen­ trations of the zone in which they were spawned. The usual concentration of 56-l"m and wider nauplii in the onshore zone was about 3/liter with 17/liter the highest observed which indicates that for nauplii of al1 sizes there were usual1y about 36/liter and with the highest density of 195/liter. These concentrations are lower than has usual1y been reported to be required for rearing larval fish in laboratories. Numbers ofnauplii decreased exponential1y with increasing size but a naupliar biomass maximum was found to occur at about the 70 I.tffi width. Nauplii of this size are ingested at first feeding by Pacific sardine, northern anchovy, and jack mackerel larvae. It is suggested that larval feeding habits of these fish have evolved to utilize this important food resource at their first feeding. Copepods form the bulk ofmostzooplankton hauls from the sea and are important because they are the main convertors of phytoplankton into food suitable for higher organisms (Marshall 1973). Copepods are especially important as food for planktonic larvae of pelagic marine teleosts. Food of the larvae of commercially important marine fishes has been widely reported as being primarily eggs, nauplii, and copepodid stages of small cope­ pods. Yokota et al. (1961) found that food occur­ ring in the feeding larvae of all the 57 species taken in their primarily coastal samples was almost entirely small copepods, especially nauplii. Duka and Gordina (1973) investigated the food of larvae of 26 species of teleosts from the Medi­ terranean and adjacent areas of the Atlantic and reported that copepod nauplii composed 90% of all items eaten by small larvae (2.3 to 5.0 mm). Stomach content analyses of fish larvae are also corroborated by population dynamic studies of plankton organisms. Fish (1936) noted that in the Gulf of Maine a small copepod, genus Pseudo­ calanus, suffers a much higher predation rate

The importance of physical and biotic scaling to the experimental simulation of a coastal marine ecosystem

Abstract: A marine microcosm, consisting of a pelagic phase interacting with a benthic phase, is described. Variations in water turnover, turbulence, incident radiation and ratio of pelagic volume to benthic surface area are shown to have significant effects on the behavior of these microcosms. It is argued that the inclusion and accurate simulation of appropriate levels of these variables is important in microcosm studies designed to study the dynamics of natural systems.

Approaches to estimating fish biomass and potential yield in Lake Tanganyika

Abstract: The annual fish yield of 73 000 tonnes (22.5 kg/ha) from Lake Tanganyika consists primarily of two planktivorous clupeids Stolothrissa tanganicae (Stdr.) and Limnothrissa miodon (Blgr.) and their centropomid predators, three Lates species (Nile perch) and Luciolates stappersii (Blgr.). At the north and south ends of the lake, the Lates spp. have been fished-up by purse-seines, and the clupeids and young L. stappersii predominate there. Estimates of pelagic fish biomass may employ (i) catch and fishing effort data (ii) abiotic variables (iii) echo-sounding surveys (iv) tropho-dynamic relationships.

The Pelagic - Sargassum Ichthyofauna of the Eastern Gulf of Mexico

Abstract: A total of 2857 fishes comprising 15 families and 40 species was collected at 621ocalities in the eastern Gulf of Mexico between 1971 and 1976. The fauna was dominated by the Carangidae, Balistidae, and Syngnathidae. Monacanthus hispidus was the most abundant species and comprised 84.5% of the total fauna. Species diversity (H') was variable within the Gulf and low in comparison with the western Atlantic Sargassum -associated ichthyofauna. "Index of Affinity" was high within the Gulf due to the abundance of M. hispidus. Perhaps conditions associated with community dispersal, for which M. hispidus is better adapted, permit this species to dominate this community. Additionally, species diversity differences may be due to substrate area or "clumpsize". Floating pelagic Sargassum (or "Gulf weed") and its associated fauna have long held the fascination of biologists and physical oceanographers. Early studies examined the distribution and life history of the weed (see Dooley, 1972 for a review). The faunal communities associated with Sargassum have also been examined and two recent treatments of the subject by Fine (1970) and Dooley (1972) have added considerably to our knowledge of this floating community. The relatively short residence time of most species implies that the Sargassum associated fauna may not represent an ecological community in the usual sense. Nevertheless, it does represent an important biocenosis and demands the attention of ecologists. Virtually all of the previously published work deals with Sargassum associates of the western Atlantic or western Pacific Oceans. There have, 60 however, been few published works ort this fauna from the Gulf of Mexico. Caldwell (1959), Dawson (1962) and Hastings and Bartone (1976) described the range extension of several species' to the northern Gulf of Mexico and attributed the distribution to the species' association with floating Sargassum. There are other references to fishes associated with Sargassum in the Gulf, but these generally apply to systematicbiological studies of specific groups (e.g., Adams, 1960, Histrio histrio; Berry and Vogele, 1961, Monacanthidae; Berry, 1959, Caranx; Moore, 1967, Balistidae) and are not concerned with the entire ichthyofauna. During a series of teaching-research cruises in the eastern Gulf of Mexico from 1971-1976 floating Sargassum was dipneted. While the collection sites and dates were not organized into a systematic sampling pattern, we feel composite examination 1 Bortone et al.: The Pelagic Sargassum Ichthyofauna of the Eastern Gulf of Mexic Published by The Aquila Digital Community, 1977 of the faunal data will add to our knowledge of eastern Gulf of Mexico ichthyofauna. The purpose of this paper is to describe the Sargassum ichthyofaunal associates in the eastern Gulf of Mexico. We examine this community with regard to distribution affinites and relative abundance. Comparisons are made with other Sargassum community studies. MATERIALS AND METHODS A total of 62 collecting stations (Fig. 1) was occupied at irregular intervals from May 1971 to August 1976. One collection was made in January, the remaining from May through October. Collections were obtained from floating Sargassum with a dipnet (6.5 mm stretched mesh), or on a few occasions, with a neuston net towed through clumps of Sargassum. Collecting stations were occupied for 30 min. to 2 hours. Only specimens which were actually shaken from the Sargassum are considered in this report. Our concern was with fish which used the weed as a 88' 87' 86' PelagicSargassum ichthyofauna 61 substrate. Excluded from this analysis were larval fishes, flying fishes (Exocoetidae) and sardines and herring fishes (Clupeidae). Specimens once removed from the weed were fixed in 10% formalin and stored in 40% isopropyl or 70% ethyl alcohol. Later, specimens were identified, measured to the nearest mm for standard length (SL) and deposited in the University of West Florida fish collection (UWF). Biomass and species composition of the weed were not recorded. To compare potential faunal regionalization, inshore/ offshore zones were designated: depths le~s than 20 fathoms (37 m) were placed in zone A; 20100 fathoms (37-183 m) in zone B; and samples from water deeper than 100 fathoms (183 m) in zone C. To examine possible NW to SE changes in community composition along the Florida shelf the northernmost area was designated zone I; the intermediate area zone II; and the southernmost area zone III (Fig. 1).

Studies on portunid crabs from the Eastern Pacific. I. Zonation along environmental stress gradients from the Coast of Colombia

Abstract: East Pacific swimming crabs are poorly known ecologically We trawled samples along 4 estuarine-continental shelf transects to provide information on the population structure and species composition of portunids along environmental stress gradients Portunids comprised almost 99% of the benthic crabs Callinectes toxotes dominates the freshest estuarine areas, but is replaced by C arcuatus in estuary mouth and shallow-shelf samples Deeper shelf samples are dominated by Euphylax robustus and Portunus sper Great numbers of E dovii, a pelagic species, were taken on the shelf; their size distribution implies intraspecific competition Evidence is given that differences in salinity tolerance account for differential landward limits, but competition, predation by fishes, increased fouling and decreased available food exclude eurytopic species from physicochemically equable shelf waters

Do Rotifers show "avoidance of the shore"?

Abstract: The term "avoidance of shore" was used in literature to describe the observation that pelagic crustacea are in general absent near the shore. Experiments in the field show, that Rotifers-which form, together with crustaceans, the main mass of zooplankton-can also be divided not only by morphological criteria but also as a result of their horizontal distribution into inhabitants of either the littoral or the pelagic zone of a lake.These differences of horizontal distribution can be explained by a typical behavioral difference between the littoral rotifer Euchlanis dilatata and the pelagic Asplanchna priodonta: when exposed in the shore zone, Asplanchna wanders in the direction of the pelagic zone, while Euchlanis on the contrary does not prefer any particular direction under the same conditions. Experiments at different lakes with other pelagic rotifers confirm that the "avoidance of shore" shown by Asplanchna is a general phenomenon.The influence of the analyzed behavior on the horizontal distribution patterns of rotifers and the factors which cause and determine the direction of the migration are discussed.

Density, Distribution, and Movement of Nipigon Bay Fishes in Relation to a Pulp and Paper Mill Effluent

Abstract: Density of pelagic fish in accessible portions of Nipigon Bay was lower offshore, less than 100 fish/10,000 m3, and greater nearshore, less than 1800 fish/10,000 m3. Conditions at Red Rock caused intense aggregation there and caused species dominance to shift to sucker at the mill discharge from yellow perch elsewhere. Plume shape and direction did not alter the localized pattern of distribution. Two typical responses to plume concentrations were found using suckers fitted with ultrasonic transmitters. Fish released in high discharge concentrations (>15% dilution by volume) became disoriented for as much as several hours, then appeared to search for "background" conditions. Fish released in low discharge concentrations (<15%) immediately initiated an avoidance reaction. Although individuals tended to avoid areas of altered water quality, the community aggregated at Red Rock in response to, perhaps, increased production of benthic macroinvertebrates. However, telemetry indicated that residence time was sho...

Raising pelagic game fish

Abstract: Pelagic species of game fish, such as marlin and tuna, are raised from an embryonic, or larval, stage to a juvenile stage by a process and apparatus employing a biologically closed, physically open system. The system is kept biologically closed by first filtering and sterilizing sea water and then growing nutrients for the fish therein. The system is kept physically open by flowing a constant fresh source of sea water through the system to carry nutrient to the fish and to carry waste products out.

Aspects of the distribution and ecology of the Myctophidae from the Western and Northern Arabian Sea

Abstract: Indian Ocean Fishery and Development Programme : Pelagic Fish Assessment Survey North Arabian Sea

Resources of horse mackerel off the south west coast of India

Abstract: The resources surveys conducted by the research vessels Sardinella and Rastrelliger of the Pelagic Fishery Project for the past four years from Ratnagiri to Gulf of Mannar have not only enhanced our knowledge of the magnitude, seasonal distribu- tion and abundance of the pelagic fish resources but also of the efficient methods of harvesting the resources.

Zooplankton studies in the Indian Ocean. 1. From Bay of Bengal during south-west monsoon period

Abstract: Zooplankton abundance in the Bay of Bengal during the south-west monsoon period showed that areas close to the land are rich in zooplankton production. Biomass values were low for the northern most stations and gradually increased from north to south indicating the possibility of environmental factors influencing production in this area. Aggregates of different groups of zooplankton evidently contributed to higher biomass values towards the southern part. South-east coast was richest for decapod larvae, fish eggs and fish larvae. Decapod larvae were more abundant nearer to the coast and their density gradually decreased towards the open ocean. Zooplankton stratification in relation to thermocline suggested a preference for zooplankton to congregate above the discontinuity layer

A technique for determining the distribution of pelagic fish larvae

Abstract: A technique is described for studying small scale distributional patterns of fish larvae in the pelagic region. A plankton net is mounted beneath the bows of a small boat, the contents of the net are emptied continually by a suction pump. This system has advantages over previous techniques as it allows a large number of small discrete samples to be taken over a wide area in a short space of time. Preliminary results showed the population of perch larvae in Llyn Tegid is extremely clumped and the overall abundance of the larvae decreases as samples are taken progressively further away from the south-west end of the lake.