Acoustic surveys have been undertaken in different parts of the waters around Europe. In this pap... more Acoustic surveys have been undertaken in different parts of the waters around Europe. In this paper we consider those taking place in NE Atlantic waters-off the NE Scottish coast, the Bay of Biscay and off the Spanish Atlantic coast-and in the Mediterranean Sea-the Catalonian Sea, the Gulf of Lion and the Aegean Sea. Retained school variables were: corrected school length (m), school height (m), school area (m 2), school perimeter (m), school energy (Nautical area scattering coefficent, S A), school density (energy vs. area), school depth (m) and bottom-depth-under-school (m). STATIS (Structuration de Tableux à Trois Indices de la Statisque), a multi-table analysis based on the Principal Component Analysis was used to analyse the correlation in different schools, parameters and intra-and interstock relationships. In all stocks, the first three axes extracted explained between 86.89% (Sete) and 91.84% (Aberdeen) of the total variance, because the annual variability present in the correlation structure of each stock is not widely dispersed. In all stocks, the first factorial axis was typified by the morphological variables (school length, school height, school area and school perimeter), which showed a very clear pattern with all of them being closely related. There were major differences between all stocks in regard to the general correlation relationship of the energetic variables analysed i.e. school energy and school density. Energy and density showed less variability than the morphological variables in all stocks with the exception of one survey. There were some differences between stocks in relation to the correlation of bathymetric variables. In all cases, school density and, to a lesser extent, school energy were opposed to the bathymetric variables, so that schools with higher densities would be located near the surface and in shallower areas. A complete analysis of all the surveys of each stock showed a homogeneous pattern which was very similar to most of the stocks considered separately. All morphological variables are well grouped and show a strong positive correlation. In general, therefore, all the schools analysed increased and decreased equally in all their dimensions. Both bathymetric variables are strongly correlated.
Not to be cited without prior reference to the author Identifying the potential habitat of anchov... more Not to be cited without prior reference to the author Identifying the potential habitat of anchovy Engraulis encrasicolus at different life
Importance de la zone côtière dans les évaluations des stocks de petits poissons pélagiques: Anal... more Importance de la zone côtière dans les évaluations des stocks de petits poissons pélagiques: Analyse d'une série de campagnes acoustiques et d'une expérimentation en zone côtière
Information integrated from different parts of the Mediterranean was used in order to model the s... more Information integrated from different parts of the Mediterranean was used in order to model the spatial and temporal variability of the distribution grounds of anchovy at different life stages. Acoustic data from the Aegean Sea (Eastern Mediterranean), the Adriatic Sea and the Sicily Channel (Central Mediterranean), the Spanish waters and the Gulf of Lions (Western Mediterranean) have been analyzed along with satellite environmental and bathymetry data to model the spatial distribution of adult anchovy during summer and early autumn and the spatial distribution of juvenile anchovy during late autumn and winter. Similarly, egg distribution data from summer surveys were used to model the potential spawning habitat of anchovy in June and July. Generalized Additive Models were applied in a presence/absence approach. Selected models were used to produce potential habitat maps for the entire Mediterranean basin for each year and period, indicating areas presenting the highest probability of supporting the presence of anchovy adults, juveniles and spawning grounds. The temporal stability of these areas was examined. Bottom depth and productivity were 1 the most important parameters found in all models. An expansion of anchovy adult habitat area was observed from summer to early autumn in all study regions. Potential juvenile grounds were identified within the continental shelf in association to high productivity waters, presenting a more extended distribution towards deeper waters in late autumn and moving to more inshore waters in winter. Potential spawning grounds presented a high degree of overlapping between June and July, being more extended compared to the adult grounds in summer.
Small pelagic fish are known to aggregate into schools and clusters of schools. It is commonly as... more Small pelagic fish are known to aggregate into schools and clusters of schools. It is commonly assumed that the number of such schools and clusters, as well as their size and densities, will vary with the stock abundance. We have carried out a PCA based meta-analysis, using series of acoustic survey data from five different locations in Europe to examine this assumption. The study concluded that there was no discernible relationship between stock abundance and the number of schools seen, or on the clustering of those schools. The study also showed that the number and structure of the school clusters was strongly correlated with the number of schools seen. An increased number of schools in an area tended to be linked with denser clusters (more schools per kilometre) and a higher occupation of the survey area by those clusters. There was also a weaker tendency to find more clusters. It is not clear whether these relationships and the absence of a link to abundance are due to density independence in aggregation patterns or whether such density dependence is only functional at relatively low stock abundance levels. 2001 International Council for the Exploration of the Sea
Studies of small pelagic fish biomass are limited by the fact that research vessels and fishing b... more Studies of small pelagic fish biomass are limited by the fact that research vessels and fishing boats are usually restricted to working areas with a bottom depth >20 m. Consequently, "unsampled" areas can represent a large proportion of the continental shelf, and the biomass in those areas can be important and must be taken into account in assessment methods in order to avoid misleading interpretations in population dynamics. A time-series ten years long has been compiled from acoustic-assessment surveys of small pelagic fish stocks, and the results show an overall increase in the acoustic fish density towards the coast, where values were the highest. Additional experiments on transects covering shallow-water areas (5-20 m) were conducted from 2001 to 2003 with small boats and a research vessel to evaluate the acoustic fish density in those areas. The results confirmed that the fish biomass in shallow water is significant, sometimes very large, and should be evaluated to avoid underestimation. Therefore, surveys should be conducted in shallow water, if at all possible, as well as at greater depths when carrying out surveys destined to support assessment exercises.
Small pelagic fish are known to aggregate into schools and clusters of schools. It is commonly as... more Small pelagic fish are known to aggregate into schools and clusters of schools. It is commonly assumed that the number of such schools and clusters, as well as their size and densities, will vary with the stock abundance. We have carried out a PCA based meta-analysis, using series of acoustic survey data from five different locations in Europe to examine this assumption. The study concluded that there was no discernible relationship between stock abundance and the number of schools seen, or on the clustering of those schools. The study also showed that the number and structure of the school clusters was strongly correlated with the number of schools seen. An increased number of schools in an area tended to be linked with denser clusters (more schools per kilometre) and a higher occupation of the survey area by those clusters. There was also a weaker tendency to find more clusters. It is not clear whether these relationships and the absence of a link to abundance are due to density independence in aggregation patterns or whether such density dependence is only functional at relatively low stock abundance levels. 2001 International Council for the Exploration of the Sea
Identification of potential juvenile grounds of short-lived species such as European sardine (Sar... more Identification of potential juvenile grounds of short-lived species such as European sardine (Sardina pilchardus) in relation to the environment is a crucial issue for effective management. In the current work, habitat suitability modelling was applied to acoustic data derived from both the western and eastern part of the Mediterranean Sea. Early summer acoustic data of sardine juveniles were modelled using generalized additive models along with satellite environmental and bathymetry data. Selected models were used to construct maps that exhibit the probability of presence in the study areas, as well as throughout the entire Mediterranean basin, as a measure of habitat adequacy. Areas with high probability of supporting sardine juvenile presence persistently within the study period were identified throughout the Mediterranean Sea. Furthermore, within the study period, a positive relationship was found between suitable habitat extent and the changes in abundance of sardine juveniles in each study area.
Acoustic surveys have been undertaken in different parts of the waters around Europe. In this pap... more Acoustic surveys have been undertaken in different parts of the waters around Europe. In this paper we consider those taking place in NE Atlantic waters-off the NE Scottish coast, the Bay of Biscay and off the Spanish Atlantic coast-and in the Mediterranean Sea-the Catalonian Sea, the Gulf of Lion and the Aegean Sea. Retained school variables were: corrected school length (m), school height (m), school area (m 2), school perimeter (m), school energy (Nautical area scattering coefficent, S A), school density (energy vs. area), school depth (m) and bottom-depth-under-school (m). STATIS (Structuration de Tableux à Trois Indices de la Statisque), a multi-table analysis based on the Principal Component Analysis was used to analyse the correlation in different schools, parameters and intra-and interstock relationships. In all stocks, the first three axes extracted explained between 86.89% (Sete) and 91.84% (Aberdeen) of the total variance, because the annual variability present in the correlation structure of each stock is not widely dispersed. In all stocks, the first factorial axis was typified by the morphological variables (school length, school height, school area and school perimeter), which showed a very clear pattern with all of them being closely related. There were major differences between all stocks in regard to the general correlation relationship of the energetic variables analysed i.e. school energy and school density. Energy and density showed less variability than the morphological variables in all stocks with the exception of one survey. There were some differences between stocks in relation to the correlation of bathymetric variables. In all cases, school density and, to a lesser extent, school energy were opposed to the bathymetric variables, so that schools with higher densities would be located near the surface and in shallower areas. A complete analysis of all the surveys of each stock showed a homogeneous pattern which was very similar to most of the stocks considered separately. All morphological variables are well grouped and show a strong positive correlation. In general, therefore, all the schools analysed increased and decreased equally in all their dimensions. Both bathymetric variables are strongly correlated.
Not to be cited without prior reference to the author Identifying the potential habitat of anchov... more Not to be cited without prior reference to the author Identifying the potential habitat of anchovy Engraulis encrasicolus at different life
Importance de la zone côtière dans les évaluations des stocks de petits poissons pélagiques: Anal... more Importance de la zone côtière dans les évaluations des stocks de petits poissons pélagiques: Analyse d'une série de campagnes acoustiques et d'une expérimentation en zone côtière
Information integrated from different parts of the Mediterranean was used in order to model the s... more Information integrated from different parts of the Mediterranean was used in order to model the spatial and temporal variability of the distribution grounds of anchovy at different life stages. Acoustic data from the Aegean Sea (Eastern Mediterranean), the Adriatic Sea and the Sicily Channel (Central Mediterranean), the Spanish waters and the Gulf of Lions (Western Mediterranean) have been analyzed along with satellite environmental and bathymetry data to model the spatial distribution of adult anchovy during summer and early autumn and the spatial distribution of juvenile anchovy during late autumn and winter. Similarly, egg distribution data from summer surveys were used to model the potential spawning habitat of anchovy in June and July. Generalized Additive Models were applied in a presence/absence approach. Selected models were used to produce potential habitat maps for the entire Mediterranean basin for each year and period, indicating areas presenting the highest probability of supporting the presence of anchovy adults, juveniles and spawning grounds. The temporal stability of these areas was examined. Bottom depth and productivity were 1 the most important parameters found in all models. An expansion of anchovy adult habitat area was observed from summer to early autumn in all study regions. Potential juvenile grounds were identified within the continental shelf in association to high productivity waters, presenting a more extended distribution towards deeper waters in late autumn and moving to more inshore waters in winter. Potential spawning grounds presented a high degree of overlapping between June and July, being more extended compared to the adult grounds in summer.
Small pelagic fish are known to aggregate into schools and clusters of schools. It is commonly as... more Small pelagic fish are known to aggregate into schools and clusters of schools. It is commonly assumed that the number of such schools and clusters, as well as their size and densities, will vary with the stock abundance. We have carried out a PCA based meta-analysis, using series of acoustic survey data from five different locations in Europe to examine this assumption. The study concluded that there was no discernible relationship between stock abundance and the number of schools seen, or on the clustering of those schools. The study also showed that the number and structure of the school clusters was strongly correlated with the number of schools seen. An increased number of schools in an area tended to be linked with denser clusters (more schools per kilometre) and a higher occupation of the survey area by those clusters. There was also a weaker tendency to find more clusters. It is not clear whether these relationships and the absence of a link to abundance are due to density independence in aggregation patterns or whether such density dependence is only functional at relatively low stock abundance levels. 2001 International Council for the Exploration of the Sea
Studies of small pelagic fish biomass are limited by the fact that research vessels and fishing b... more Studies of small pelagic fish biomass are limited by the fact that research vessels and fishing boats are usually restricted to working areas with a bottom depth >20 m. Consequently, "unsampled" areas can represent a large proportion of the continental shelf, and the biomass in those areas can be important and must be taken into account in assessment methods in order to avoid misleading interpretations in population dynamics. A time-series ten years long has been compiled from acoustic-assessment surveys of small pelagic fish stocks, and the results show an overall increase in the acoustic fish density towards the coast, where values were the highest. Additional experiments on transects covering shallow-water areas (5-20 m) were conducted from 2001 to 2003 with small boats and a research vessel to evaluate the acoustic fish density in those areas. The results confirmed that the fish biomass in shallow water is significant, sometimes very large, and should be evaluated to avoid underestimation. Therefore, surveys should be conducted in shallow water, if at all possible, as well as at greater depths when carrying out surveys destined to support assessment exercises.
Small pelagic fish are known to aggregate into schools and clusters of schools. It is commonly as... more Small pelagic fish are known to aggregate into schools and clusters of schools. It is commonly assumed that the number of such schools and clusters, as well as their size and densities, will vary with the stock abundance. We have carried out a PCA based meta-analysis, using series of acoustic survey data from five different locations in Europe to examine this assumption. The study concluded that there was no discernible relationship between stock abundance and the number of schools seen, or on the clustering of those schools. The study also showed that the number and structure of the school clusters was strongly correlated with the number of schools seen. An increased number of schools in an area tended to be linked with denser clusters (more schools per kilometre) and a higher occupation of the survey area by those clusters. There was also a weaker tendency to find more clusters. It is not clear whether these relationships and the absence of a link to abundance are due to density independence in aggregation patterns or whether such density dependence is only functional at relatively low stock abundance levels. 2001 International Council for the Exploration of the Sea
Identification of potential juvenile grounds of short-lived species such as European sardine (Sar... more Identification of potential juvenile grounds of short-lived species such as European sardine (Sardina pilchardus) in relation to the environment is a crucial issue for effective management. In the current work, habitat suitability modelling was applied to acoustic data derived from both the western and eastern part of the Mediterranean Sea. Early summer acoustic data of sardine juveniles were modelled using generalized additive models along with satellite environmental and bathymetry data. Selected models were used to construct maps that exhibit the probability of presence in the study areas, as well as throughout the entire Mediterranean basin, as a measure of habitat adequacy. Areas with high probability of supporting sardine juvenile presence persistently within the study period were identified throughout the Mediterranean Sea. Furthermore, within the study period, a positive relationship was found between suitable habitat extent and the changes in abundance of sardine juveniles in each study area.
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