Netherlands Journal of Sea Research最新文献

Results presented in an earlier paper showed that differences in temperature and salinity could explain approximately 30% of the variability in growth rates of juvenile southern flounder (Paralichthys lethostigma) in different creeks of the Pamlico River estuary. In addition, the maximal growth rate was lower than expected from published laboratory results, suggesting food limitation. In the present paper, the obtained mean and maximal growth rates are related to simultaneously collected data on the amount of food available in the creeks. Thirteen different groups of food items were observed in the stomachs of the flounder. Most of the stomachs of flounder collected outside the cages contained only mysids (65 to 75%). Inside the cages, 25 to 45% of the flounder stomachs contained only mysids, while 85 to 100% of the stomachs contained both mysids and other food categories. Individual growth rates of the founder were only significantly related to the number of mysids in the stomachs, and not to any of the other food categories. Stomachs of other fish species mostly showed food categories other than mysids. This indicates that interspecific competition for food did not occur. The four creeks of the cage experiment showed significant differences in abundance of mysids. However, in only one of the two trials the abundance of mysids was significantly related to the observed growth rates. It can be concluded that mysid abundance does not unequivocally explain the variability in growth rates of juvenile southern flounder in low salinity nursery areas of Pamlico Sound, and that the hypothesis of food limiting maximal growth is not supported by the results of this study.

This paper provides basic information on the general ecology and life history cycles of various flatfish species in the Bohai Sea, China. The species studied are Paralichthys olivaceus (Temminck & Schlegel), Cleisthenes herzensteini (Schmidt), Eopsetta grigorjewi (Herzenstein), Verasper variegatus (Temminck & Schlegel), Pleuronichthys cornutus (Temminck & Schlegel), Pseudopleuronectes yokohamae (Günther), Pseudopleuronectes herzensteini (Jordan & Snyder), Kareius bicoloratus (Basilewsky), Zebrias zebra (Bloch), Cynoglossus semilaevis Günther, Cynoglossus abbreviatus (Gray) and Cynoglossus joyneri Günther. Information on reproduction, eggs and larval distribution, growth and adult abundance is presented. Based on the biology and ecology of these flatfish, artificial enhancement of the commercial species in the Bohai Sea is discussed.

The effect of PCB contamination on the reproduction of female dab was studied under laboratory conditions. Females were contaminated during gonad maturation by multiple oral administration of capsules containing the technical PCB mixture Clophen A40. PCB contamination resulted in increased levels in the eggs, with concentrations of selected PCB congeners of 35 to 86 μg·g⁻¹ lipid for PCB-exposed fish, 10 μg·g⁻¹ lipid for eggs from fish fed with mussel meat and fish fed with shrimp. A statistically significant dose-effect relationship was found between the PCB content of the eggs and the PCB dose ingested by the fish. For eggs from the PCB-treated fish the mean fertilization rate was 61% and mean hatching 45%, compared to 67% fertilization and 59% hatching for eggs from untreated fish. Rate of development and survival of the eggs and mortality of the larvae after hatching were mainly related to incubation temperature. No statistically significant differences between untreated and PCB-treated fish could be found in egg production, egg quality, fertilization rate, hatching rate and survival of larvae.

Juveniles of four species of pleuronectid flatfishes were abundant in bays and nearshore areas around Kodiak Island, Alaska during August 1991. Flatfish nursery areas located in deep water bays such as those surrounding Kodiak Island have not been previously reported. Age-0 rock sole (Pleuronectes bilineatus), flathead sole (Hippoglossoides elassodon), Pacific halibut (Hippoglossus stenolepis) and age-1 yellowfin sole (Pleuronectes asper) were collected close to one another and at first appeared to share nursery areas. Closer examination of associated within-bay distribution, depth, substrate, temperature and salinity data revealed characteristics which limited nursery area overlap. The major concentrations of juveniles of these species could usually be segregated by one or more of the physical parameters investigated. Based on the physical characteristics found to be most important in determining distribution of juveniles for each species, we hypothesize the following relationships. Age-0 rock sole are found predominantly in water depths less than 50 m, on sand or mixed sand substrate outside of or within bays. Age-0 flathead sole are found predominantly in water depths greater than 40 m, on mud or mixed mud substrate throughout bays. Age-0 Pacific halibut are found predominantly in water depths less than 40 m, on mixed sand substrate near or outside mouths of bays. Age-1 yellowfin sole are found predominantly in water depths less than 40 m, on mixed substrates at upper reaches of bays. These hypotheses will be field tested, after which the relationships may be considered for application to broader geographic areas.

Comprehensive ecosystem models involve aspects from each of the biological, chemical and physical sciences. Consequently such models, for example the European Regional Seas Ecosystem Model (ERSEM), are often based on computer code written by a number of different research groups each with a well-defined area of responsibility. To construct a meaningful integrated model capable of combining the expertise from each of these disciplines requires a formalized ecosystem structure that provides a template for model development. Assumptions made at this stage will to a large extent determine the qualities of the resulting model. Essential too is a system of quality management that assures a correct and consistent end product. Such a system, however, requires the flexibility to allow the various contributors the freedom to pursue individual and novel representations of ecosystem function, if the model is to be ground breaking. The system adopted by the ERSEM group, which should have a wider applicability than marine ecosystem modelling, is described here. Finally, the methodology used to gauge the relative merits of alternative ecosystem representations is described.

This paper presents an overview of the concept, structure and implementation of the European Regional Seas Ecosystem Model (ERSEM). The model dynamically simulates the biogeochemical seasonal cycling of carbon, nitrogen, phosphorus and silicon in the pelagic and benthic food webs of the North Sea, and is forced by irradiance, temperature and transport processes.

The model has a coarse spatial resolution into ten boxes, the ICES boxes, of which the five deepest have been resolved into surface (0 to 30 m) and deep (30 m to bottom) boxes.

At the open boundaries, time series are prescribed for dissolved and particulate nutrients. River loads of nutrients for the rivers discharging into the North Sea are prescribed at monthly intervals. A general circulation model has been used to aggregate the exchange volumes across the box boundaries into daily in- and outflows. From these, the horizontal transports of dissolved and suspended constituents are calculated. Vertical transport is in the form of sinking and sedimentation for particulates and in the form of turbulent diffusion for dissolved constituents.

The physical model contains all information specific to the area to be modelled, whereas the biological/chemical submodels have been constructed not to be site-specific.

The biological variables are represented as functional groups expressed in units of organic carbon and the chemical variables as the internal pools in the biological variables and as the dissolved inorganic pools in water and sediment, expressed in units of N, P and Si.

The model runs in a software environment (SESAME) developed for enabling the development of large and complex models in a modular way by a consortium of institutes, each focusing on different. aspects of the ecosystem, translating these into modules within the model. With the exception of fish populations, where size- and age-structure are explicity represented, all the other biological components have been modelled as unstructured populations aggregated into functional groups. This approach is shown to be appropriate for taxa having short generation times in relation to the annual cycle and for taxa which do not span more than one trophic level during their lifetime.