CHANGES IN COMPOSITION OF FISH AND DECAPODS CATCHES ALONG SALINITY GRADIENT IN THE RAZDOLNAYA RIVER AND TOP OF THE AMUR BAY IN THE WARM PERIOD OF YEAR

Quantitative samples of fish, crabs and shrimps from the Razdolnaya estuary are analyzed. The area surveyed in May-September of 1990–2014 includes the internal estuary of this largest river of southern Primorye and its external estuary — the top of the Amur Bay with the depth < 13 m. In total, 478 samples were collected: 244 in the external estuary by trawl and 234 in the internal estuary by fry seine. Distribution density and biomass are calculated using the «areal» method with certain coefficients of catchability (1.0 for fry seine). The upper freshwater layer (salinity 0–5 ‰) was observed in the lower stream of the river till sandy bar, the brackish-water cline was traced at the river bottom from the mouth to the distance 10–15 km upstream. The seawater with salinity > 30 ‰ did not penetrate over sand bar to the river. Species diversity of fish and decapods was presented by 108 taxa (fishes — 88, decapods — 20) belonged to 43 families, among them 84 species were caught in the Amur Bay and 41 species in the Razdolnaya, but no more than 67 species were caught in the Amur Bay only and 24 species — in the Razdolnaya only, other 17 species were found in both external and internal estuaries (Acanthogobius flavimanus, Acanthogobius lactipes, Crangon septemspinosa, Crangon spp., Eriocheir japonica, Hypomesus nipponensis, Giporhamphus sajori, Konosirus punctatus, Liopsetta pinnifasciata, Oncorhynchus masou masou, Palaemon sp., Pholis nebulosa, Planiliza haematocheila, Pugettia quadridens, Salangichthys microdon, Syngnathus schlegeli and Tribolodon spp.). Total biomass was higher (9.1 g/m2 ) in the external estuary than in the internal estuary (6.7 g/m2 ) with the mean value 9.0 g/m2 . It was almost uniform over the internal estuary with only slight increasing on the distance about 5 km from the mouth. Simpson index of dominance increases from external to internal estuary but decreases in the river in the order: 0.127 at Peschany Peninsula — 0.168 in the northwestern Amur Bay — from 0.193 to 0.252 in the internal estuary — 0.164 in the river. Six clusters with similar species composition are defined, they change in direction from the sea to the river in the following order of the dominant species: L. pinnifasciata in the sea — prawns gen. Palaemon at the bar (upper part of the external estuary) — P. haematocheila at the river mouth (lower part of the internal estuary) — P. haematocheila and E. japonica in the main part of the internal estuary — Acanthorhodeus chankaensis and Gobio macrocephalus (with the highest biomass up to 22 g/m2 ) in the minor adjoining river stream — G. macrocephalus in the upper part of the internal estuary.

Vertical distribution and diel migration of Crangon septemspinosa Say, 1818 (Decapoda, Caridea) on Georges Bank, northwest Atlantic

We sampled for vertical distribution and possible diel vertical migration (DVM) of Crangon septemspinosa Say, 1818 on and around Georges Bank, Northwest Atlantic, between 1995 and 1999. Both juveniles and adults were found to undergo DVM, being distributed within the lower water column (and perhaps on or in the bottom) during the day, and distributed throughout the water column at night, with higher abundances seen in all depth strata at night. Differences in vertical distribution were also found based on location and chlorophyll concentration for juveniles, but no effects were seen of season, salinity, temperature, lunar periodicity, year, or copepod prey for either juveniles or adults. Variation in vertical distribution and DVM were only moderately well explained (50% of the total variance) by the above factors, suggesting that some other factor(s) not measured by us (e.g., predation) were potentially also controlling the vertical distribution and diel migration of C. septemspinosa on Georges Bank.

Advancing an Ecosystem Approach in the Gulf of Maine

<i>Abstract</i> .—Because of partial recirculation and steep bottom slopes, the Gulf of Maine (GoM) contains steep environmental gradients in both space and time. I focus, in particular, on optical properties associated with both resources and risks. The GoM estuary-shelf systems differ from those whose fine sediments are trapped behind barrier bars; in the GoM, nepheloid layers prevail over a wide range of depths, and onshore-offshore turbidity gradients at a given water depth are also steep. Turbidity reduces predation risk. Three crustacean species that are major fish forages respond to the strong environmental gradients in resources and risks by migrating seasonally both horizontally and vertically. Northern shrimp (also known as pink shrimp) <i>Pandalus borealis</i> , sevenspine bay shrimp <i>Crangon septemspinosa</i> , and the most common mysid shrimp in the GoM, <i>Neomysis americana</i> , share both stalked eyes that appear capable of detecting polarized light and statocysts. This pair of features likely confers sun-compass navigational ability, facilitating use of multiple habitats. All three species converge on a shallow-water bloom at depths <100 m of the western GoM shelf in December–March, well before the basin-wide, climatological spring bloom in April. In addition to reaching abundant food resources, I propose that they are also using optical protection, quantified as the integral of the beam attenuation coefficient from the surface to the depth that they occupy during daylight. Spring immigration into, and fall emigration from, estuaries appear to be common in GoM sevenspine bay shrimp and <i>N. americana</i> , out of phase with their populations south of New England and with turbidity differences a likely cause. Migration studies that include measurements of turbidity are needed, however, to test the strength of the effect of optical protection on habitat use by all three species. Simultaneous sampling of estuaries and the adjacent shelf, together with trace-element tracer studies, would be very useful to resolve timing and extent of mass migrations, which likely are sensitive to turbidity change resulting from climate change. These migrations present special challenges to ecosystem-based management by using so many different habitats.

Variability in the density and sound-speed of coastal zooplankton and nekton

Forman, K. A., and Warren, J. D. 2010. Variability in the density and sound-speed of coastal zooplankton and nekton. – ICES Journal of Marine Science, 67: 10–18. Acoustic sampling techniques provide an advantage over traditional net-sampling by increasing scientist ability to survey a large area in a relatively short period, as well as providing higher-resolution data in the vertical and horizontal dimensions. To convert acoustic data into measures of biological organisms, physics-based scattering models are often used. Such models use several parameters to predict the amount of sound scattered by a fluid-like or weakly scattering animal. Two important input parameters are the density (g) and sound-speed (h) contrasts of the animal and the surrounding seawater. The density and sound-speed contrasts were measured for coastal zooplankton and nekton species including shrimps (Palaemonetes pugio and Crangon septemspinosa), fish (Fundulus majalis and Fundulus heteroclitus), and polychaetes (Nereis succinea and Glycera americana) along with multiple physiological and environmental variables. Factors such as animal size, feeding status, fecundity, gender, and maturity caused variations in g. The variations in g observed for these animals could lead to large differences (or uncertainties) in abundance estimates based on acoustic scattering models and field-collected backscatter data. It may be important to use a range of values for g and h in the acoustic scattering models used to convert acoustic data into estimates of the abundance of marine organisms.

Predation on winter flounder (Pseudopleuronectes americanus) eggs by the sand shrimp (Crangon septemspinosa)

This study estimated rates of sand shrimp (Crangon septemspinosa) predation on winter flounder (Pseudopleuronectes americanus) eggs and examined the effect of temperature on density-dependent mortality of early-stage flounder. In laboratory experiments, shrimp feeding rates on flounder eggs were positively correlated with temperature and shrimp size. Immunological assays of shrimp stomach contents indicated that 7.2% of shrimp collected from the Niantic River (Connecticut) had flounder eggs in their stomachs. Incidence of egg predation was highest in February (20%) and decreased continuously into early April (1.2%). In a deterministic model simulating predator-induced mortality of flounder eggs during a spawning season, shrimp consumed 0.4%–49.7% of the total flounder spawn. Variations in shrimp population abundance and size structure accounted for the greatest variability in egg mortality. Water temperature during the spawning season presumably alters the population dynamics of early-stage flounder. In a long-term survey, the number of yolk-sac flounder larvae in warm years (≥4.3 °C) was depressed at high egg densities, indicating strong compensatory processes that increased egg mortality and limited the abundance of larvae. Failure of flounder to produce strong year-classes of larvae during warm years, possibly resulting from altered trophic dynamics, may explain the inability of stocks to recover from previous overexploitation.