scholarly journals Feeding of Plankton in a Turbulent Environment: A Comparison of Analytical and Observational Results Covering Also Strong Turbulence

Fluids ◽  
2020 ◽  
Vol 5 (1) ◽  
pp. 37
Author(s):  
Hans L. Pécseli ◽  
Jan K. Trulsen ◽  
Jan Erik Stiansen ◽  
Svein Sundby
Keyword(s):  
Gadus Morhua ◽  
Capture Rate ◽  
Energy Dissipation Rate ◽  
Shallow Waters ◽  
Gut Content ◽  
Predator Prey ◽  
Turbulent Environments ◽  
Analytical Results ◽  
Probability Densities ◽  
Ambush Predators

The present studies address feeding of plankton in turbulent environments, discussed by a comparison of analytical results and field data. Various models for predator-prey encounters and capture probabilities are reviewed. Generalized forms for encounter rates and capture probabilities in turbulent environments are proposed. The analysis emphasizes ambush predators, exemplified by cod larvae Gadus morhua L. in the start-feeding phase (stage 7 larvae) collected in shallow waters near Lofoten, Norway. During this campaign, data were obtained at four sites with strongly turbulent conditions induced by tidal currents and long-wave swells, and one site where the turbulence had a lower level in comparison. The guts of the selected cod larvae were examined in order to determine the number of nauplii ingested. Analytically obtained probability densities for the gut content were compared with observations and the results used for estimating the rate of capture of the nauplii. This capture rate was then compared with analytical results using also data for the surroundings, such as measured prey densities and turbulence conditions, as quantified by the specific energy dissipation rate. Different from earlier studies, the presented data include conditions where the turbulence exceeds the level for optimal larval encounter-capture rates.

Use of Oceanographic Forecasts and Echosounders to Guide and Enhance an Inshore Gillnet Fishery for Atlantic Cod (Gadus morhua)

1993 ◽  
Vol 50 (10) ◽  
pp. 2129-2136 ◽  
Author(s):  
G. A. Rose ◽  
W.C. Leggett
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Effort ◽  
Shallow Waters ◽  
Gill Nets ◽  
Rule Of Thumb ◽  
Combined Use ◽  
Catch Rates ◽  
Depth Ranges ◽  
High Fish

Vessels fishing with gill nets for Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence in 1985 and 1986 concentrated their fishing effort in shallow waters (<50 m) where cod densities were highest (to 0.5/m3). In both years, seasonal trends (June–August) in mean daily deployment depths of gill nets were positively correlated with mean depths at which cod were surveyed (1985, r = 0.71; 1986, r = 0.51, Ps < 0.05). Daily catch rate variability of individual vessels was accounted for by fish "flux" adjacent to nets (44%), vessel operator skill (19%), and "flux"–skill interaction (8%; total R2 = 0.71). A guided vessel directed to fish at sites predicted to have high fish flux (located down-current from high-density cod aggregations identified by echosounding within depth ranges forecast to be favorable to cod by "rule of thumb" wind-based oceanographic models) had higher catch rates (mean 1.3 t/d) than the fleet average and its own average fishing without guidance (means 0.4 t/d, P's < 0.05). Directed searches were of shorter duration (mean 0.5 h) than searches conducted at random (1.5 h). Combined use of echosounders and air–sea-based forecasts of cod distribution could help stabilize catch rates, especially at times of poor fish availability inshore.

Depth-dependent variation in condition and length-at-age of Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence

2002 ◽  
Vol 59 (9) ◽  
pp. 1451-1459 ◽  
Author(s):  
G A Chouinard ◽  
D P Swain
Keyword(s):  
Deep Water ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
High Abundance ◽  
Shallow Waters ◽  
Depth Range ◽  
Deep Waters ◽  
Feeding Grounds

We describe depth-dependent variation in the condition and length-at-age of southern Gulf of St. Lawrence cod (Gadus morhua) on their feeding grounds in September 1971–2000. Bathymetric variation in condition appears to be linked to abundance. In periods of low abundance, condition was relatively uniform over shallow and intermediate depths (<100–125 m). During periods of high abundance, condition was highest in the shallowest waters and declined steadily as depth increased to 100 m. In all periods, condition was low in deep water. Bathymetric trends in length-at-age contrasted with those in condition. Length-at-age was high in the deep waters where condition was low. Length-at-age also tended to increase from minimum values at intermediate depths to high values in shallow waters. This tendency was most striking in the 1990s, a period when condition was uniform over this depth range. We discuss the ecological, bioenergetic, and sampling implications of these patterns.

scholarly journals Predator-prey encounter and capture rates in turbulent environments

2014 ◽  
Vol 4 (1) ◽  
pp. 85-105 ◽  
Author(s):  
H. L. Pécseli ◽  
J. K. Trulsen ◽  
Ø. Fiksen
Keyword(s):  
Predator Prey ◽  
Turbulent Environments ◽  
Capture Rates

Sealworm (Pseudoterranova decipiens) infections in demersal fish from two areas in Norway

1994 ◽  
Vol 72 (4) ◽  
pp. 598-608 ◽  
Author(s):  
Tor Jensen ◽  
Karin Andersen ◽  
Sophie des Clers
Keyword(s):  
Gadus Morhua ◽  
Demersal Fish ◽  
Phoca Vitulina ◽  
Halichoerus Grypus ◽  
Shallow Waters ◽  
Benthic Fish ◽  
Pseudoterranova Decipiens ◽  
Average Abundance ◽  
Myoxocephalus Scorpius ◽  
Southern Norway

Fish from Torbjørnskjær, in the outer Oslofjord in southern Norway, and from Vega in Nordland in central Norway were examined for infections of the larval nematode Pseudoterranova decipiens transmitted by seals. Three sites were sampled between 1990 and 1992, two (S1 and S2) in Torbjørnskjær and one (S3) in Vega, and 3361 fish were examined in total. In Torbjørnskjær, fish were collected from shallow waters (S1) near skerries where a colony of common seals (Phoca vitulina) regularly haul out, and from deeper waters outside these skerries (S2). In Vega, an extensive zone of rocks and shallow water is inhabited by a colony of grey seals (Halichoerus grypus) and some common seals. In Vega, fish were caught from the littoral zone to 40–50 m depth, except for cusk (Brosme brosme), which were caught in deeper waters. Only demersal and benthic fish were infected in both areas, infection levels being highest in shallow waters close to the rocks (sites S1 and S3). Sculpins (Myoxocephalus scorpius) had the highest infection levels (an average abundance of 36 and 23 worms per fish, respectively), with cod (Gadus morhua) and cusk also heavily infected; the latter species was found only at Vega. Two somewhat different transmission routes to seals are suggested for the two areas.

Energy dissipation rate surrogates in incompressible Navier–Stokes turbulence

2012 ◽  
Vol 697 ◽  
pp. 204-236 ◽  
Author(s):  
Saba Almalkie ◽  
Stephen M. de Bruyn Kops
Keyword(s):  
Energy Dissipation ◽  
Strain Rate ◽  
Dissipation Rate ◽  
Reynolds Numbers ◽  
Energy Dissipation Rate ◽  
Navier Stokes ◽  
Strain Rate Tensor ◽  
One Dimensional ◽  
Probability Densities ◽  
The One

AbstractHigh-resolution direct numerical simulations of isotropic homogeneous turbulence are used to understand the differences between the effects of spatial intermittency on the energy dissipation rate and on surrogates for the dissipation rate that are based on measurements of a subset of the strain rate tensor. In particular, the one-dimensional longitudinal and transverse surrogates, as well as a surrogate based on the asymmetric part of the strain rate tensor, are considered. The instantaneous surrogates are studied locally, locally averaged in space and conditionally averaged to see what statistics of the dissipation rate might accurately be inferred given measurements of the surrogates. The simulations with the Reynolds numbers based on the Taylor microscale of 102–235 are highly resolved for accurate evaluation of higher-order statistics. The probability densities of the local and locally averaged surrogates are significantly different from the corresponding statistics for the dissipation rate itself. All of the surrogates are more intermittent than the dissipation rate, the transverse surrogate is more intermittent than the longitudinal and these trends are still prominent even when the fields are spatially averaged at length scales close to the integral length scale. As a consequence, the intermittency exponent computed from the moments of the locally averaged longitudinal and transverse surrogates is approximately 1.5 and 2.2 times higher, respectively, than that computed by the same method from the dissipation rate field. In addition, while different methods of computing intermittency exponent from the dissipation rate field yield the same result, different methods applied to a surrogate are inconsistent.

scholarly journals Barents Sea cod (Gadus morhua) diet composition: long-term interannual, seasonal, and ontogenetic patterns

2019 ◽  
Vol 76 (6) ◽  
pp. 1641-1652 ◽  
Author(s):  
Rebecca E Holt ◽  
Bjarte Bogstad ◽  
Joël M Durant ◽  
Andrey V Dolgov ◽  
Geir Ottersen
Keyword(s):  
Gadus Morhua ◽  
Trophic Ecology ◽  
Barents Sea ◽  
Atlantic Cod ◽  
Prey Size ◽  
Ecosystem Dynamics ◽  
Polar Cod ◽  
Important Species ◽  
Predator Prey ◽  
The North

Abstract Atlantic cod (Gadus morhua) is an ecologically and commercially important species in the North-Atlantic region. Cod is a top predator and information on its trophic ecology is integral for understanding predator–prey relationships and food-web dynamics. We present an analysis of the trophic patterns of Barents Sea (BS) cod using a unique 33-year time-series of stomach-content data from 1984 to 2016. We assessed patterns in diet (prey) composition across years, between seasons, as well as ontogenetic trends in diet, including predator–prey size relationships. Ontogenetic shifts in diet were observed, with fish becoming more important prey with increasing cod size. A very early onset of piscivory was found in &lt;20 cm cod. Cannibalism was found in cod &gt; 20 cm and increased with size. Juvenile cod exhibit a tendency towards consuming prey up to 33% of their body length, whereas larger cod feed on all prey sizes, resulting in asymmetric predator–prey size distributions. Diet varied significantly during 1984–2016, consistent with changes in both prey, cod abundance, and distribution. Seasonal differences were observed; capelin dominated the winter diet, whereas cod, polar cod, and other fish species were prevalent in summer/autumn months. This work represents an important step towards understanding trophic linkages that determine BS ecosystem dynamics.

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