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What causes interindividual variation in fitness? Evidence of heritability of latent individual fitness traits has resparked a debate about the causes of variation in life histories in populations: neutralism versus empirical adaptationism. This debate about the processes underlying observed variation pits neutral stochastic demographic processes against evolutionarily relevant differences among individual fitness traits. Advancing this debate requires careful consideration of differences among inference approaches used by proponents of each hypothesis. Here we draw parallels between several disciplines focusing on processes generating variation in individuals' life-course, and we contrast methodologies to disentangle these processes. We draw on other disciplines to clarify terminology, risks of flawed inference, and expand the panel of hypotheses and formalizations of processes generating variation in life histories. Trends Evidence of heritability of individual fitness traits in wild populations has reopened a debate about the relative contribution of neutral, stochastic demographic processes to observed variations in life histories. There are conceptual differences among published studies documenting heterogeneity in life histories; differences so fundamental that they led to misunderstandings between schools of thought. The question of the processes generating heterogeneity in longitudinal trajectories has stimulated a large body of work in econometrics, political, social and biomedical sciences, which have highlighted risks of flawed inference; these risks have been overlooked in biology. Other disciplines offer useful frameworks for future work on life histories in three areas: terminology, the characterization of the diversity of processes underlying variation in life histories, and the methods of statistical inference to disentangle these processes.

For small cetaceans bycatch in fishing gear is one of the largest threats towards their conservation. In order to effectively manage this threat, an estimation of the maximum number of animals that can be killed by anthropogenic activities each year is required. Such calculations rely on species or population specific information on population dynamics, and information on the current state of the population relative to carrying capacity. Here, we calculate the mortality limit for the Belt Sea population of harbour porpoises (Phocoena phocoena) based on a modified potential biological removal (mPBR) method. We estimate that for the population to reach the conservation objective set by ASCOBANS (the population should reach 80% of carrying capacity (assumed here to be 50,000 animals), with the assumption that this is achieved within 100 years with an 80% probability) a maximum of 29 animals can be removed annually. This removal rate applies a recover factor (Fr) of 0.1 that accounts for many uncertainties in population dynamics, abundance estimates, and the current removal rate and depletion level of the population. However, even using the highest possible Fr value (1.0) (which is not recommended for populations with unknown status and does not allow the population to reach the conservation objective), the mPBR limit of the population is 292, which is still significantly lower than the current estimated levels of bycatch in this population (~700 a year). Therefore, urgent action is required in order to ensure that this population is able to reach the conservation objective and achieve good environmental status under a range of European legislation.

International audience ; Effective conservation requires monitoring and pro-active risk assessments.We studied the effects of at-sea mortality events (ASMEs) in marine mammals over two decades (1990–2012) and built a risk-based indicator for the European Union's Marine Strategy Framework Directive. Strandings of harbor porpoises (Phocoena phocoena), short-beaked common dolphins (Delphinus delphis), and striped dolphins (Stenella coeruleoalba) along French coastlines were analyzed using Extreme Value Theory (EVT). EVT operationalizes what is an extreme ASME, and allows the probabilistic forecasting of the expected maximum number of dead animals assuming constant pressures. For the period 2013–2018, we forecast the strandings of 80 harbor porpoises, 860 common dolphins, and 57 striped dolphins in extreme ASMEs. Comparison of these forecasts with observed strandings informs whether pressures are increasing, decreasing, or stable. Applying probabilistic methods to stranding data facilitates the building of risk-based indicators, required under the Marine Strategy Framework Directive, to monitor the effect of pressures on marine mammals.

International audience ; Effective conservation requires monitoring and pro-active risk assessments.We studied the effects of at-sea mortality events (ASMEs) in marine mammals over two decades (1990–2012) and built a risk-based indicator for the European Union's Marine Strategy Framework Directive. Strandings of harbor porpoises (Phocoena phocoena), short-beaked common dolphins (Delphinus delphis), and striped dolphins (Stenella coeruleoalba) along French coastlines were analyzed using Extreme Value Theory (EVT). EVT operationalizes what is an extreme ASME, and allows the probabilistic forecasting of the expected maximum number of dead animals assuming constant pressures. For the period 2013–2018, we forecast the strandings of 80 harbor porpoises, 860 common dolphins, and 57 striped dolphins in extreme ASMEs. Comparison of these forecasts with observed strandings informs whether pressures are increasing, decreasing, or stable. Applying probabilistic methods to stranding data facilitates the building of risk-based indicators, required under the Marine Strategy Framework Directive, to monitor the effect of pressures on marine mammals.

Effective conservation requires monitoring and pro-active risk assessments.We studied the effects of at-sea mortality events (ASMEs) in marine mammals over two decades (1990–2012) and built a risk-based indicator for the European Union's Marine Strategy Framework Directive. Strandings of harbor porpoises (Phocoena phocoena), short-beaked common dolphins (Delphinus delphis), and striped dolphins (Stenella coeruleoalba) along French coastlines were analyzed using Extreme Value Theory (EVT). EVT operationalizes what is an extreme ASME, and allows the probabilistic forecasting of the expected maximum number of dead animals assuming constant pressures. For the period 2013–2018, we forecast the strandings of 80 harbor porpoises, 860 common dolphins, and 57 striped dolphins in extreme ASMEs. Comparison of these forecasts with observed strandings informs whether pressures are increasing, decreasing, or stable. Applying probabilistic methods to stranding data facilitates the building of risk-based indicators, required under the Marine Strategy Framework Directive, to monitor the effect of pressures on marine mammals.

International audience ; Effective conservation requires monitoring and pro-active risk assessments.We studied the effects of at-sea mortality events (ASMEs) in marine mammals over two decades (1990–2012) and built a risk-based indicator for the European Union's Marine Strategy Framework Directive. Strandings of harbor porpoises (Phocoena phocoena), short-beaked common dolphins (Delphinus delphis), and striped dolphins (Stenella coeruleoalba) along French coastlines were analyzed using Extreme Value Theory (EVT). EVT operationalizes what is an extreme ASME, and allows the probabilistic forecasting of the expected maximum number of dead animals assuming constant pressures. For the period 2013–2018, we forecast the strandings of 80 harbor porpoises, 860 common dolphins, and 57 striped dolphins in extreme ASMEs. Comparison of these forecasts with observed strandings informs whether pressures are increasing, decreasing, or stable. Applying probabilistic methods to stranding data facilitates the building of risk-based indicators, required under the Marine Strategy Framework Directive, to monitor the effect of pressures on marine mammals.

International audience ; The first Unusual Mortality Event (UME) related to fishing activity along the Atlantic coast recorded by the French Stranding Network was in 1989: 697 small delphinids, mostly common dolphins, washed ashore, most of them with evidence of having been bycaught. Since then, UMEs of common dolphins have been observed nearly every year in the Bay of Biscay; unprecedented records were broken every year since 2016. The low and unequally distributed observation efforts aboard fishing vessels in the Bay of Biscay, as well as the lack of data on foreign fisheries necessitated the use of complementary data (such as stranding data) to elucidate the involvement of fisheries in dolphin bycatch. The aim of this work was to identify positive spatial and temporal correlations between the likely origins of bycaught stranded common dolphins (estimated from a mechanistic drift model) and fishing effort statistics inferred from Vessel Monitoring System (VMS) data on vessels >12 m long. Fisheries whose effort correlated positively with dolphin mortality areas after 2016 included French midwater trawlers, French Danish seiners, French gillnetters, French trammel netters, Spanish bottom trawlers, and Spanish gillnetters. For the French fleet only, logbook declarations, sales, and surveys carried out by Ifremer were integrated into fishing effort data. Six fleets were active in common dolphin bycatch areas at least twice between 2016 and 2019: gillnetters fishing hake, trammel netters fishing anglerfish, bottom pair trawlers fishing hake, midwater pair trawlers fishing sea bass and hake, and Danish seiners fishing whiting. Except for changes in hake landings in some fisheries, there were no notable changes in total fishing effort practice (gear or target species) based on the data required by the ICES and Council of the European Union that could explain the large increase in stranded common dolphins recorded along the French Atlantic coast after 2016. Small scale or unrecorded changes could have modified ...

International audience ; The first Unusual Mortality Event (UME) related to fishing activity along the Atlantic coast recorded by the French Stranding Network was in 1989: 697 small delphinids, mostly common dolphins, washed ashore, most of them with evidence of having been bycaught. Since then, UMEs of common dolphins have been observed nearly every year in the Bay of Biscay; unprecedented records were broken every year since 2016. The low and unequally distributed observation efforts aboard fishing vessels in the Bay of Biscay, as well as the lack of data on foreign fisheries necessitated the use of complementary data (such as stranding data) to elucidate the involvement of fisheries in dolphin bycatch. The aim of this work was to identify positive spatial and temporal correlations between the likely origins of bycaught stranded common dolphins (estimated from a mechanistic drift model) and fishing effort statistics inferred from Vessel Monitoring System (VMS) data on vessels >12 m long. Fisheries whose effort correlated positively with dolphin mortality areas after 2016 included French midwater trawlers, French Danish seiners, French gillnetters, French trammel netters, Spanish bottom trawlers, and Spanish gillnetters. For the French fleet only, logbook declarations, sales, and surveys carried out by Ifremer were integrated into fishing effort data. Six fleets were active in common dolphin bycatch areas at least twice between 2016 and 2019: gillnetters fishing hake, trammel netters fishing anglerfish, bottom pair trawlers fishing hake, midwater pair trawlers fishing sea bass and hake, and Danish seiners fishing whiting. Except for changes in hake landings in some fisheries, there were no notable changes in total fishing effort practice (gear or target species) based on the data required by the ICES and Council of the European Union that could explain the large increase in stranded common dolphins recorded along the French Atlantic coast after 2016. Small scale or unrecorded changes could have modified ...

International audience ; The first Unusual Mortality Event (UME) related to fishing activity along the Atlantic coast recorded by the French Stranding Network was in 1989: 697 small delphinids, mostly common dolphins, washed ashore, most of them with evidence of having been bycaught. Since then, UMEs of common dolphins have been observed nearly every year in the Bay of Biscay; unprecedented records were broken every year since 2016. The low and unequally distributed observation efforts aboard fishing vessels in the Bay of Biscay, as well as the lack of data on foreign fisheries necessitated the use of complementary data (such as stranding data) to elucidate the involvement of fisheries in dolphin bycatch. The aim of this work was to identify positive spatial and temporal correlations between the likely origins of bycaught stranded common dolphins (estimated from a mechanistic drift model) and fishing effort statistics inferred from Vessel Monitoring System (VMS) data on vessels >12 m long. Fisheries whose effort correlated positively with dolphin mortality areas after 2016 included French midwater trawlers, French Danish seiners, French gillnetters, French trammel netters, Spanish bottom trawlers, and Spanish gillnetters. For the French fleet only, logbook declarations, sales, and surveys carried out by Ifremer were integrated into fishing effort data. Six fleets were active in common dolphin bycatch areas at least twice between 2016 and 2019: gillnetters fishing hake, trammel netters fishing anglerfish, bottom pair trawlers fishing hake, midwater pair trawlers fishing sea bass and hake, and Danish seiners fishing whiting. Except for changes in hake landings in some fisheries, there were no notable changes in total fishing effort practice (gear or target species) based on the data required by the ICES and Council of the European Union that could explain the large increase in stranded common dolphins recorded along the French Atlantic coast after 2016. Small scale or unrecorded changes could have modified ...