Spatial density distributions of fish, a balance between environmental and physiological limitation

Data (trawl, acoustic, CTD) from four scientific survey series , i.e. along the Norwegian coast, in the North Sea, and in the Barents Sea summer and winter, are used to describe and discuss the spatial density distributions of blue whiting, cod, haddock, redfish, saithe, capelin, and herring, in banks and shelf sea of depth mainly < 500 m, in relation to environmental conditions (depth, change of pressure, temperature, salinity, daylight, and physiological limitations). For cod, also information from data storage tags (DST) is used. For the demersal physoclists the relative vertical profiles are defined in terms of relative pressure reduction with reference to the pressure at the bottom. Thus vertical profiles with different bottom depth can be expressed in terms of free vertical range (FVR) and compared on a physiological basis. This restriction to rapid vertical movement is evident in the studied physoclist species. The acoustic sA-values show that blue whiting, haddock, saithe, cod, and redfish are mainly distributed within the bottom half of the water column, but also that they adapt to pelagic living. Haddock and blue whiting are more often found to distribute higher into the water column than saithe, cod, and redfish. Pelagic living is seen especially in areas with high acoustic sA-values and where the bottom is deeper than 200m. Day and night vertical profiles in terms of FVR are corrected for unequal day and night losses in the bottom acoustic dead zone. In most years, evidence of diurnal vertical migration for all seven species are found when day and night are clearly distinguishable. In many cases of demersal fish there is higher relative acoustic density in the mid-range of the bottom half of the water column at daytime than nighttime. At nighttime there is a degree of separation, one group of fish descends to aggregate near the seabed and another ascends

Multivariate bilinear time series : alternative models in population dynamics

A bivariate bilinear time series model is introduced as a stochastic discrete time version of the deterministic Lotka-Volterra prey-predator model. It allows a discussion of how stochastic environmental variables effect the populations. Moreover, with time series methods the parameters of the model can be estimated directly from the population time series data. NORSK SAMMENDRAG: Det introduseres en bivariat bilineær tidsrekkemodell som er en stokastisk versjon av bytte-jeger-modellen til Lotka og Volterra. Den tillater en drøfting av hvorledes stokastiske miljøvariabler påvirker populasjonene. Med tidsrekkemetoder kan man dessuten estimere modellens parametre direkte fra tidsrekkedata for populasjonene

Spatial distributions of variables in marine environmental and fisheries research. Part 1: Geostatistics and autocorrelated environmental and fisheries data

The geographical information very often is lost during calculation of indices for the abundance from surveys. Isoplet diagrams showing the distribution of both fish abundance and temperature/salinity are usually produced by hand by skilled personnel. In order to find an objective approach we explored a new stochastic method for abundance calculation and isoplet diagram drawing, using the geostatistics presented in this paper. The potential of geostatistical methods is to analyse the structural pattern of spatially dependent variables, model it and use it to estimate the unknown values at the unsampled locations. Moreover it gives the variance of the estimation error at a location and the variance of the global estimated value which other methods do not give. At each location we can store the estimated values of different spatial dependent variables for the purpose of studying the relationship among them and presenting graphic plots showing the geographic distribution pattem of each variable. Furthermore the structural pattem of each variable can be used to detect the interrelationship among them. This presentation demonstrates these points with the following data: Temperature, salinity, bottom depth, and 0-group cod density in the Barents sea

Spatial distribution of variables in marine environmental and fisheries research Part II: Distribution and length of 0-group fish in relation to environmental factors

Each year in August-September joint Norwegian-Russian 0-group surveys are carried out in the Barents Sea and adjacent waters. Based on data from these surveys, the ambient temperature and salinity for several species were calculated for the Barents Sea and the Svalbard waters as well as the total area. Estimates of mean length were made for each interval in the environmental variables in order to study the variation in 0-group length with temperature and salinity. Differences within and between years in mean lengths were discussed in relation to spatial distribution and overall abundance

Fish migration in oscillating stratified water masses

Abstract Time series records from data storage tag (DST) attached on Northeast Arctic cod (Gadus morhua L.) and Greenland halibut (Reinhardtius hippoglossoides) are investigated in connection with hydrodynamic and hydrographic features at specific locations to obtain spatial and temporal variation on fish migration patterns, which may change the availability of fish to survey gears. From spring to autumn, some Greenland halibut, at 500-800 m depth, were exposed to a persistent diurnal fluctuation of temperature between subzero and 5.5±C. Tidally induced topographic trapped waves with diurnal (K1) frequency were indicated in some region along the Barents Sea escarpment, where the transition zone between warm Atlantic water (AW) and cold Norwegian Sea Arctic Intermediate Water (NAIW) is at 500-700 m. An asymmetry in the temperature diurnal pattern showed a gradual increase followed by a rapid drop. This event may be related to the displacement mechanism of stratified water masses together with the fish diurnal migration pattern in synchrony with tidal motion. The pattern indicates that fish migrated seawards off the slope and was pelagic part of the day, thus unavailable to bottom trawl. Up to three weeks in April, some tagged cod had low vertical activity at a depth exposed to semidiurnal tidal fluctuations of the transition layer between 100-200 m, where cold coastal waters flow on top of warm Atlantic waters. Along the southern coast of the Barents Sea, strong semidiurnal tides can generate baroclinic coastal Kelvin waves causing vertical motion of the pycnocline, thus semidiurnal fluctuation of temperature was observed. Keywords: bottom trapped waves, data storage tag, diurnal vertical migration, Kelvin waves, NE Artic cod, NE Arctic Greenland halibut, spawning activity, temperature gradient

Behavioural rhythm of cod during migration in the Barents Sea

To assess fish abundance by direct methods and to understand and model species interaction, it is important to have proper knowledge about behavioural patterns. Patterns in vertical distribution might strongly affect accessibility of the fish to survey methods and are of importance for modelling within and between species interaction and competition. Such information can be obtained on individual basis by using data storage tags DST). In this paper time series from 19 DSTs attached to adult Northeast Arctic cod are analysed. Depth (pressure) and temperature were recorded with 2-hour intervals. The main purpose is to develop a statistical approach to extract information about rhythmic behaviour (diurnal, semi-diurnal), and to discuss possible ecological impacts of such behaviour of adult cod in the Barents Sea. This includes vertical migration, temperature distribution, and spatialtemporal interrelation caused by fish behaviour. To identify the dynamics in behaviour when fish penetrate stratified water masses, an approach using the rate of change of temperature in relation to change of depth was chosen. The results show that rhythmic behaviour occurred temporarily in 12 of the tags. Spectral density distributions of depth and temperature time series show that rhythms within 24 hour are most common. In 11 out of 12 tags where diel vertical migration (DVM) was detected, this occurred during summer and autumn. In 7 out of 8 tags where semi-diurnal tidal cycles were detected in the temperature series, this occurred during April-May. In some tags diurnal or semi-diurnal cycles appeared in both depth and temperature series. Diurnal rhythms are periodically important for adult cod, but the results are not consistent for all tags and therefore no firm and general principle for such behaviour can presently be concluded

Behavioural rhythm of cod during migration in the Barents Sea

To assess fish abundance by direct methods and to understand and model species interaction, it is important to have proper knowledge about behavioural patterns. Patterns in vertical distribution might strongly affect accessibility of the fish to survey methods and are of importance for modelling within and between species interaction and competition. Such information can be obtained on individual basis by using data storage tags DST). In this paper time series from 19 DSTs attached to adult Northeast Arctic cod are analysed. Depth (pressure) and temperature were recorded with 2-hour intervals. The main purpose is to develop a statistical approach to extract information about rhythmic behaviour (diurnal, semi-diurnal), and to discuss possible ecological impacts of such behaviour of adult cod in the Barents Sea. This includes vertical migration, temperature distribution, and spatialtemporal interrelation caused by fish behaviour. To identify the dynamics in behaviour when fish penetrate stratified water masses, an approach using the rate of change of temperature in relation to change of depth was chosen. The results show that rhythmic behaviour occurred temporarily in 12 of the tags. Spectral density distributions of depth and temperature time series show that rhythms within 24 hour are most common. In 11 out of 12 tags where diel vertical migration (DVM) was detected, this occurred during summer and autumn. In 7 out of 8 tags where semi-diurnal tidal cycles were detected in the temperature series, this occurred during April-May. In some tags diurnal or semi-diurnal cycles appeared in both depth and temperature series. Diurnal rhythms are periodically important for adult cod, but the results are not consistent for all tags and therefore no firm and general principle for such behaviour can presently be concluded

Vertical distribution of cod, haddock and redfish; Impact on bottom trawl and acoustic surveys in the Barents Sea

At a selected location in the Barents Sea acoustic observations, bottom- and pelagic trawl catch data were collected over a 10 day period. A large proportion of the fish were in the acoustic dead zone during the sampling period. Only during a few hours in the daytime high acoustic values were obtained. According to the pelagic trawl hauls these recordings consisted of large haddock ascending from the bottom, while small haddock and small redfish dominated the acoustic recordings at night. The bottom trawl catches showed higher variability and higher average catch rates during the day than at night, but the diurnal variations were relatively less than those of the acoustic recordings. The largest reduction in catch rates from day to night was observed for small haddock and redfish. This is consistent with the observation that these were found pelagicly during night. The acoustic observations and the bottom trawl catch rates were found to be correlated with diurnal cycles in observed light level and semidiurnal cycles in current speed. The results are interpreted in terms of variable catchability of the bottom trawl and variable availability for the echo sounder