Limits...
Spatial structure and distribution of small pelagic fish in the northwestern Mediterranean Sea.

Saraux C, Fromentin JM, Bigot JL, Bourdeix JH, Morfin M, Roos D, Van Beveren E, Bez N - PLoS ONE (2014)

Bottom Line: Our results show that sardines and sprats were more coastal than anchovies.Support for the McCall's basin hypothesis (covariation of both population density and presence area with biomass) was found only in sprats, the most variable of the three species.Persistent favourable areas were finally detected, but their environmental characteristics remain to be determined.

View Article: PubMed Central - PubMed

Affiliation: IFREMER (Institut Français de Recherche pour l'Exploitation de la MER), Research Unit EME (UMR 212), Sète, France.

ABSTRACT
Understanding the ecological and anthropogenic drivers of population dynamics requires detailed studies on habitat selection and spatial distribution. Although small pelagic fish aggregate in large shoals and usually exhibit important spatial structure, their dynamics in time and space remain unpredictable and challenging. In the Gulf of Lions (north-western Mediterranean), sardine and anchovy biomasses have declined over the past 5 years causing an important fishery crisis while sprat abundance rose. Applying geostatistical tools on scientific acoustic surveys conducted in the Gulf of Lions, we investigated anchovy, sardine and sprat spatial distributions and structures over 10 years. Our results show that sardines and sprats were more coastal than anchovies. The spatial structure of the three species was fairly stable over time according to variogram outputs, while year-to-year variations in kriged maps highlighted substantial changes in their location. Support for the McCall's basin hypothesis (covariation of both population density and presence area with biomass) was found only in sprats, the most variable of the three species. An innovative method to investigate species collocation at different scales revealed that globally the three species strongly overlap. Although species often co-occurred in terms of presence/absence, their biomass density differed at local scale, suggesting potential interspecific avoidance or different sensitivity to local environmental characteristics. Persistent favourable areas were finally detected, but their environmental characteristics remain to be determined.

Show MeSH

Related in: MedlinePlus

Annual (black) and mean (red) modelled variograms of anchovies, sardines and sprats.The red dotted lines correspond to the 95% confidence interval of the mean variogram deduced from 500 simulations.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4222880&req=5

pone-0111211-g002: Annual (black) and mean (red) modelled variograms of anchovies, sardines and sprats.The red dotted lines correspond to the 95% confidence interval of the mean variogram deduced from 500 simulations.

Mentions: Mean variograms of log biomass exhibited spatial structure for the three species in both directions (i.e, increasing variance when the distance between sampling points increased before levelling off; Figure 2), meaning that the spatial distribution was not random and that two close points had a higher probability to have similar values than distant points. While sardine and anchovy variograms shared similar main characteristics, sprat mean variogram differed slightly. In particular, it differed in the range at which variance stabilized (Figure 2). Variance stabilized rapidly in sprats (range = 4 and 12 nm respectively for the first and second spherical component), while the first structure appeared around 15 nm for sardines and anchovies and the second was not apparent at the scale of our study, i.e. variance did not stabilize completely within the 50 nm limit that we fixed. Further, the mean structure seemed similar between the two perpendicular directions in sprats, while it differed slightly in anchovies and sardines, though the mean variogram of each direction was mostly included in the confidence interval around the mean variogram of the other direction.


Spatial structure and distribution of small pelagic fish in the northwestern Mediterranean Sea.

Saraux C, Fromentin JM, Bigot JL, Bourdeix JH, Morfin M, Roos D, Van Beveren E, Bez N - PLoS ONE (2014)

Annual (black) and mean (red) modelled variograms of anchovies, sardines and sprats.The red dotted lines correspond to the 95% confidence interval of the mean variogram deduced from 500 simulations.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4222880&req=5

pone-0111211-g002: Annual (black) and mean (red) modelled variograms of anchovies, sardines and sprats.The red dotted lines correspond to the 95% confidence interval of the mean variogram deduced from 500 simulations.
Mentions: Mean variograms of log biomass exhibited spatial structure for the three species in both directions (i.e, increasing variance when the distance between sampling points increased before levelling off; Figure 2), meaning that the spatial distribution was not random and that two close points had a higher probability to have similar values than distant points. While sardine and anchovy variograms shared similar main characteristics, sprat mean variogram differed slightly. In particular, it differed in the range at which variance stabilized (Figure 2). Variance stabilized rapidly in sprats (range = 4 and 12 nm respectively for the first and second spherical component), while the first structure appeared around 15 nm for sardines and anchovies and the second was not apparent at the scale of our study, i.e. variance did not stabilize completely within the 50 nm limit that we fixed. Further, the mean structure seemed similar between the two perpendicular directions in sprats, while it differed slightly in anchovies and sardines, though the mean variogram of each direction was mostly included in the confidence interval around the mean variogram of the other direction.

Bottom Line: Our results show that sardines and sprats were more coastal than anchovies.Support for the McCall's basin hypothesis (covariation of both population density and presence area with biomass) was found only in sprats, the most variable of the three species.Persistent favourable areas were finally detected, but their environmental characteristics remain to be determined.

View Article: PubMed Central - PubMed

Affiliation: IFREMER (Institut Français de Recherche pour l'Exploitation de la MER), Research Unit EME (UMR 212), Sète, France.

ABSTRACT
Understanding the ecological and anthropogenic drivers of population dynamics requires detailed studies on habitat selection and spatial distribution. Although small pelagic fish aggregate in large shoals and usually exhibit important spatial structure, their dynamics in time and space remain unpredictable and challenging. In the Gulf of Lions (north-western Mediterranean), sardine and anchovy biomasses have declined over the past 5 years causing an important fishery crisis while sprat abundance rose. Applying geostatistical tools on scientific acoustic surveys conducted in the Gulf of Lions, we investigated anchovy, sardine and sprat spatial distributions and structures over 10 years. Our results show that sardines and sprats were more coastal than anchovies. The spatial structure of the three species was fairly stable over time according to variogram outputs, while year-to-year variations in kriged maps highlighted substantial changes in their location. Support for the McCall's basin hypothesis (covariation of both population density and presence area with biomass) was found only in sprats, the most variable of the three species. An innovative method to investigate species collocation at different scales revealed that globally the three species strongly overlap. Although species often co-occurred in terms of presence/absence, their biomass density differed at local scale, suggesting potential interspecific avoidance or different sensitivity to local environmental characteristics. Persistent favourable areas were finally detected, but their environmental characteristics remain to be determined.

Show MeSH
Related in: MedlinePlus