Small-scale fisheries (SSFs) constitute a substantial component of European fisheries and have a ... more Small-scale fisheries (SSFs) constitute a substantial component of European fisheries and have a high socioeconomic importance, especially for remote insular areas. Traps produce catches of high quality and value, associated with limited bycatch and low habitat impact. Long-standing trap SSFs in both the Mediterranean and the Atlantic showcase the potential of such SSFs to support remote fishing communities; however, trap SSFs remain relatively understudied. Here, we investigate the spatial and temporal dynamics of a Greek trap SSF targeting Plesionika narval (Fabricius, 1787) in the eastern Mediterranean, by means of Generalized Additive Models fitted on fishers' logbook data from 2005 to 2014. The dynamics of both catch per unit effort (CPUE) and profits suggest a pronounced seasonality for this fishery, while there are also signs of local overexploitation in the traditional fishing grounds. Additionally, small vessels (\ 12 m) report higher CPUEs than larger vessels. Our results point to management measures that could improve the sustainability of this valuable SSF, such as changes in the spatial and temporal allocation of fishing effort, and in fleet composition. The insights gained from this study are relevant to other localized trap SSFs and illustrate().,-volV) (0123456789().,-volV)
Geostatistical methodology was used to analyse the structure and describe the spatial patterns of... more Geostatistical methodology was used to analyse the structure and describe the spatial patterns of North Sea herring (Clupea harengus L.), using data from the 1992 ICES (Division IVa) acoustic survey. Three different scales of spatial structures were identified: an unresolved small-scale variability, which accounted for 48% of the total variance, and two structure components, the first being a meso-scale of ≈9 nmi (nautical miles) (≈30%) and the second a large-scale of ≈17 nmi (22%). Geostatistical analysis permitted the determination of spatial density gradients as well as patch sizes (range from 9 to 17 nmi). The use of the truncated data and the robust variogram on the raw data provided additional information for the structure. The utilization of this information in the variographic analysis resulted in better estimations. The best unbiased predictor was used to objectively map the herring population distribution by kriging. The kriging estimates were better with interpolation of a large number of points. Herring tended to aggregate mainly in meso-scale patches with a diameter of 9 nmi and to a lesser extent in large-scale patches of 17 nmi diameter. Environmental factors (depth, salinity and temperature) partly explained the spatial distribution of herring, despite the absence of a trend in the variogram structure. The study demonstrates the existence of spatial correlation and an objective way of optimal mapping of the population. Geostatistics provided additional information on herring spatial organization which is important to understand the behaviour of the species and to study its relationship with the environment.
Page 1. Spatial analysis and mapping of acoustic survey data in the presence of high local variab... more Page 1. Spatial analysis and mapping of acoustic survey data in the presence of high local variability: geostatistical application to North Sea herring ...
Small-scale fisheries (SSFs) constitute a substantial component of European fisheries and have a ... more Small-scale fisheries (SSFs) constitute a substantial component of European fisheries and have a high socioeconomic importance, especially for remote insular areas. Traps produce catches of high quality and value, associated with limited bycatch and low habitat impact. Long-standing trap SSFs in both the Mediterranean and the Atlantic showcase the potential of such SSFs to support remote fishing communities; however, trap SSFs remain relatively understudied. Here, we investigate the spatial and temporal dynamics of a Greek trap SSF targeting Plesionika narval (Fabricius, 1787) in the eastern Mediterranean, by means of Generalized Additive Models fitted on fishers' logbook data from 2005 to 2014. The dynamics of both catch per unit effort (CPUE) and profits suggest a pronounced seasonality for this fishery, while there are also signs of local overexploitation in the traditional fishing grounds. Additionally, small vessels (\ 12 m) report higher CPUEs than larger vessels. Our results point to management measures that could improve the sustainability of this valuable SSF, such as changes in the spatial and temporal allocation of fishing effort, and in fleet composition. The insights gained from this study are relevant to other localized trap SSFs and illustrate().,-volV) (0123456789().,-volV)
Geostatistical methodology was used to analyse the structure and describe the spatial patterns of... more Geostatistical methodology was used to analyse the structure and describe the spatial patterns of North Sea herring (Clupea harengus L.), using data from the 1992 ICES (Division IVa) acoustic survey. Three different scales of spatial structures were identified: an unresolved small-scale variability, which accounted for 48% of the total variance, and two structure components, the first being a meso-scale of ≈9 nmi (nautical miles) (≈30%) and the second a large-scale of ≈17 nmi (22%). Geostatistical analysis permitted the determination of spatial density gradients as well as patch sizes (range from 9 to 17 nmi). The use of the truncated data and the robust variogram on the raw data provided additional information for the structure. The utilization of this information in the variographic analysis resulted in better estimations. The best unbiased predictor was used to objectively map the herring population distribution by kriging. The kriging estimates were better with interpolation of a large number of points. Herring tended to aggregate mainly in meso-scale patches with a diameter of 9 nmi and to a lesser extent in large-scale patches of 17 nmi diameter. Environmental factors (depth, salinity and temperature) partly explained the spatial distribution of herring, despite the absence of a trend in the variogram structure. The study demonstrates the existence of spatial correlation and an objective way of optimal mapping of the population. Geostatistics provided additional information on herring spatial organization which is important to understand the behaviour of the species and to study its relationship with the environment.
Page 1. Spatial analysis and mapping of acoustic survey data in the presence of high local variab... more Page 1. Spatial analysis and mapping of acoustic survey data in the presence of high local variability: geostatistical application to North Sea herring ...
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