Background/Question/Methods The European eel (Anguilla anguilla L., 1758) is facing a dramatic de... more Background/Question/Methods The European eel (Anguilla anguilla L., 1758) is facing a dramatic decline in most of its distributional range and the species is now considered critically endangered according to the IUCN Red list. In 2007 the European Commission issued a Regulation (EU 1100/2007) for eel recovery and the sustainable use of eel stocks. Accordingly, management measures need to be implemented so as to guarantee, for each water basin, the downstream migration of at least 40% of silver eel biomass with respect to the historical baseline. A crucial step of the EU eel management plans is thus to estimate spawner escapement under current and pristine conditions. Although in central and northern Europe the estimation of eel baselines has received considerable study, very little is known about the eel productivity of Mediterranean coastal (MC) lagoons under historical and present conditions. These data are critical to effective management as coastal lagoons are characterized by v...
If a species is bycatch in a fishery targeted at its competitor or predator, it experiences both ... more If a species is bycatch in a fishery targeted at its competitor or predator, it experiences both direct anthropogenic mortality and indirect positive effects through species interactions. If the species involved interact strongly, the release from competition or predation can counteract or exceed the negative effects of bycatch. We used a set of two-and three-species community modules to analyze the relative importance of species interactions when modeling the overall effect of harvest with bycatch on a nontarget species. To measure the trade-off between direct mortality and indirect positive effects, we developed a ''bycatch transition point'' metric to determine, for different scenarios, what levels of bycatch shift overall harvest impact from positive to negative. Under strong direct competition with a targeted competitor, release from competition due to harvest leads to a net increase in abundance even under moderate levels of bycatch. For a three-species model with a shared obligate predator, the release from apparent competition exceeds direct competitive release and outweighs the decrease from bycatch mortality under a wide range of parameters. Therefore, in communities where a shared predator forms a strong link between the target and nontarget species, the effects of indirect interactions on populations can be larger than those of direct interactions. The bycatch transition point metric can be used for tightly linked species to evaluate the relative strengths of positive indirect effects and negative anthropogenic impacts such as bycatch, habitat degradation, and introduction of invasive species.
The European eel Anguilla anguilla is thought to be in a multi-decadal decline across its range. ... more The European eel Anguilla anguilla is thought to be in a multi-decadal decline across its range. Although its northern Atlantic sub-populations are well-studied, little is known about the historical trend and current status of eel stock in the Mediterranean Sea. To fill this gap, we gathered catch data for 86 lagoon fisheries in nine countries across the Mediterranean basin and analysed historical trends and geographical and environmental patterns. We found a region-wide decline in eel catch, beginning in the mid-1970s and exceeding the simultaneous decline in non-eel fisheries, as well as lower productivity in larger lagoons and those in the southern Mediterranean. Additionally, we developed a population dynamics model to provide a preliminary estimate of pristine, potential, and actual escapement of spawning adults (silver eels) across the Mediterranean basin under historical and current conditions. Model results suggest that current escapement is 35% of escapement at pristine bio...
The first signs of sea star wasting disease (SSWD) epidemic occurred in just few months in 2013 a... more The first signs of sea star wasting disease (SSWD) epidemic occurred in just few months in 2013 along the entire North American Pacific coast. Disease dynamics did not manifest as the typical travelling wave of reaction-diffusion epidemiological model, suggesting that other environmental factors might have played some role. To help explore how external factors might trigger disease, we built a coupled oceanographic-epidemiological model and contrasted three hypotheses on the influence of temperature on disease transmission and pathogenicity. Models that linked mortality to sea surface temperature gave patterns more consistent with observed data on sea star wasting disease, which suggests that environmental stress could explain why some marine diseases seem to spread so fast and have region-wide impacts on host populations.
The European eel Anguilla anguilla is thought to be in a multi-decadal decline across its range. ... more The European eel Anguilla anguilla is thought to be in a multi-decadal decline across its range. Although its northern Atlantic sub-populations are well-studied, little is known about the historical trend and current status of eel stock in the Mediterranean Sea. To fill this gap, we gathered catch data for 86 lagoon fisheries in nine countries across the Mediterranean basin and analysed historical trends and geographical and environmental patterns. We found a region-wide decline in eel catch, beginning in the mid-1970s and exceeding the simultaneous decline in non-eel fisheries, as well as lower productivity in larger lagoons and those in the southern Mediterranean. Additionally, we developed a population dynamics model to provide a preliminary estimate of pristine, potential, and actual escapement of spawning adults (silver eels) across the Mediterranean basin under historical and current conditions. Model results suggest that current escapement is 35% of escapement at pristine biomass levels, ,40% target set by EC regulation 1100/2007. Furthermore, we estimate that a complete closure of lagoon fisheries would achieve 57% of pristine escapement under current recruitment levels. Though preliminary, this analysis represents a first step towards a full assessment of the role of the Mediterranean subpopulation in overall eel stock recovery.
Background/Question/Methods The European eel (Anguilla anguilla L., 1758) is facing a dramatic de... more Background/Question/Methods The European eel (Anguilla anguilla L., 1758) is facing a dramatic decline in most of its distributional range and the species is now considered critically endangered according to the IUCN Red list. In 2007 the European Commission issued a Regulation (EU 1100/2007) for eel recovery and the sustainable use of eel stocks. Accordingly, management measures need to be implemented so as to guarantee, for each water basin, the downstream migration of at least 40% of silver eel biomass with respect to the historical baseline. A crucial step of the EU eel management plans is thus to estimate spawner escapement under current and pristine conditions. Although in central and northern Europe the estimation of eel baselines has received considerable study, very little is known about the eel productivity of Mediterranean coastal (MC) lagoons under historical and present conditions. These data are critical to effective management as coastal lagoons are characterized by v...
If a species is bycatch in a fishery targeted at its competitor or predator, it experiences both ... more If a species is bycatch in a fishery targeted at its competitor or predator, it experiences both direct anthropogenic mortality and indirect positive effects through species interactions. If the species involved interact strongly, the release from competition or predation can counteract or exceed the negative effects of bycatch. We used a set of two-and three-species community modules to analyze the relative importance of species interactions when modeling the overall effect of harvest with bycatch on a nontarget species. To measure the trade-off between direct mortality and indirect positive effects, we developed a ''bycatch transition point'' metric to determine, for different scenarios, what levels of bycatch shift overall harvest impact from positive to negative. Under strong direct competition with a targeted competitor, release from competition due to harvest leads to a net increase in abundance even under moderate levels of bycatch. For a three-species model with a shared obligate predator, the release from apparent competition exceeds direct competitive release and outweighs the decrease from bycatch mortality under a wide range of parameters. Therefore, in communities where a shared predator forms a strong link between the target and nontarget species, the effects of indirect interactions on populations can be larger than those of direct interactions. The bycatch transition point metric can be used for tightly linked species to evaluate the relative strengths of positive indirect effects and negative anthropogenic impacts such as bycatch, habitat degradation, and introduction of invasive species.
The European eel Anguilla anguilla is thought to be in a multi-decadal decline across its range. ... more The European eel Anguilla anguilla is thought to be in a multi-decadal decline across its range. Although its northern Atlantic sub-populations are well-studied, little is known about the historical trend and current status of eel stock in the Mediterranean Sea. To fill this gap, we gathered catch data for 86 lagoon fisheries in nine countries across the Mediterranean basin and analysed historical trends and geographical and environmental patterns. We found a region-wide decline in eel catch, beginning in the mid-1970s and exceeding the simultaneous decline in non-eel fisheries, as well as lower productivity in larger lagoons and those in the southern Mediterranean. Additionally, we developed a population dynamics model to provide a preliminary estimate of pristine, potential, and actual escapement of spawning adults (silver eels) across the Mediterranean basin under historical and current conditions. Model results suggest that current escapement is 35% of escapement at pristine bio...
The first signs of sea star wasting disease (SSWD) epidemic occurred in just few months in 2013 a... more The first signs of sea star wasting disease (SSWD) epidemic occurred in just few months in 2013 along the entire North American Pacific coast. Disease dynamics did not manifest as the typical travelling wave of reaction-diffusion epidemiological model, suggesting that other environmental factors might have played some role. To help explore how external factors might trigger disease, we built a coupled oceanographic-epidemiological model and contrasted three hypotheses on the influence of temperature on disease transmission and pathogenicity. Models that linked mortality to sea surface temperature gave patterns more consistent with observed data on sea star wasting disease, which suggests that environmental stress could explain why some marine diseases seem to spread so fast and have region-wide impacts on host populations.
The European eel Anguilla anguilla is thought to be in a multi-decadal decline across its range. ... more The European eel Anguilla anguilla is thought to be in a multi-decadal decline across its range. Although its northern Atlantic sub-populations are well-studied, little is known about the historical trend and current status of eel stock in the Mediterranean Sea. To fill this gap, we gathered catch data for 86 lagoon fisheries in nine countries across the Mediterranean basin and analysed historical trends and geographical and environmental patterns. We found a region-wide decline in eel catch, beginning in the mid-1970s and exceeding the simultaneous decline in non-eel fisheries, as well as lower productivity in larger lagoons and those in the southern Mediterranean. Additionally, we developed a population dynamics model to provide a preliminary estimate of pristine, potential, and actual escapement of spawning adults (silver eels) across the Mediterranean basin under historical and current conditions. Model results suggest that current escapement is 35% of escapement at pristine biomass levels, ,40% target set by EC regulation 1100/2007. Furthermore, we estimate that a complete closure of lagoon fisheries would achieve 57% of pristine escapement under current recruitment levels. Though preliminary, this analysis represents a first step towards a full assessment of the role of the Mediterranean subpopulation in overall eel stock recovery.
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