Eric Rochard

Biological characteristics of European Atlantic sturgeon, Acipenser sturio, as the basis for a restoration program in France

The European Atlantic Sturgeon, Acipenser sturio, has received increased attention in France because of population declines due to overfishing and deterioration of spawning grounds. Conservation of this species requires many actions, including publicizing the necessity to protect this fish and its habitats, investigations on catches and probable spawning grounds, and on artificial reproduction, which is still in an experimental stage. During its sea life, European Atlantic sturgeon occur from the Bay of Biscay to the Bristol Channel and North Sea. Presently, the number of young fish in the Gironde Estuary during summertime is low and the population has a unimodal age structure. At the time this paper was written, the last recorded reproduction of sturgeon in the Gironde system occurred in 1988 (new evidence of reproduction was discovered in 1995). Growth of young fish from the 1988 cohort was faster than that previously determined for others cohorts. Over our study period (1980–1994), the availability of wild broodfish declined. Successful artificial reproduction of wild-caught females requires an optimal physiological state; any delay decreases their reproductive potential. Acclimatiza tion of wild-caught juveniles to fresh water was most successful when fish were transported and held upon arrival in low salinity water. For such wild-caught juveniles, the first food intake usually occurs several months after capture, but remains irregular. These findings will be used to improve ongoing efforts to restore A. sturio.

Structure of the Gironde estuarine fish assemblages: a comparison of European estuaries perspective

An estuary is an ecotone. It plays various vital roles in the functioning of the different fish species encountered. Each estuary has its own geographical, hydraulic, sedimentological and biological characteristics. These specific features influence the makeup and structure of the fish assemblages and the dynamics of the fish populations. The Gironde estuary is the biggest estuary in France and one of the largest in Europe. It is considered to be relatively unspoilt. The aim of this study is to provide an initial reference document on the specific composition of its fish assemblage. This study establishes a list of the fish species sampled by two different and complementary methods which have been regularly undertaken since 1979. A typology is recognized according to a series of ecological criteria. The relative proportion of fish species that spend all their life cycle in the Gironde estuary is very small. Moreover, the Gironde would appear to be the European estuary with the largest migratory amphihaline fish assemblage. Considering the study made by Elliott and Dewailly (1995), the Gironde estuarine fish population can be compared to those of 17 other European estuaries. The classification we obtained, raised a number of questions on the particularities of estuarine environment, with regard to ecological diagnostics and comparisons. Important points include the need for an inter-calibration of sampling practices, the relevance of taking into account the physical dimension of the environment (tidal range, upstream limit of saline intrusion, etc.), the degree of anthropogenic influence and its evolution.

Downstream migration of juvenile European sturgeon Acipenser sturio L. in the Gironde estuary

The European sturgeon (Acipenser sturio) is an endangered diadromous fish species that spawns in the rivers in late spring and early summer. The juveniles spend their first years in the brackish waters (5‰ to 25‰) of the estuary zone before moving out to sea. This study describes the downstream migration pattern of juvenile sturgeon, belonging to the 1994 cohort, the only one born naturally in the Gironde basin, France since the end of the 1980s. During October 1994 to December 1996 the inland section of the Gironde estuary was sampled monthly by trawl (n=818 tows) and all European sturgeon caught (n=381) were marked and released. The first sturgeon of the 1994 cohort (TL=27 cm) were caught in early March 1995 in the zones furthest upstream. During their second fall of life, juveniles gradually acclimatized, and spread over a wide range of salinity conditions. A first incursion into marine water was also observed (at least for a few fish) by the end of the second winter. During this second period, sturgeon showed preference for two particular zones situated at 18 and 38 km, respectively, from the mouth of the estuary. These zones, belonging to two different salinity sectors of the estuary, did not appear to be any different to their neighbors with regards to depth and type of substrate. There were no significant size differences among estuarine zones. Seasonal movements of sturgeon seem to be motivated by a search for warmer temperatures. After a period of early acclimatization of 15 months, juvenile European sturgeon appear to be highly tolerant of salinity variations.

Evaluation of a Gastric Lavage Method for Sturgeons

Abstract Because of their threatened status, sturgeons (Acipenseridae) can no longer be sacrificed for stomach content analysis. We tested a nonlethal method of gastric lavage on Siberian sturgeon Acipenser baeri. The efficiency and harmlessness of the method were tested with four different volumes of food (10, 20, 30, and 40 cm3), each composed of brown shrimp Crangon crangon, Chironomidae, earthworm Lumbriscus terrestris, and sand goby Pomatoschistus minutus. The Siberian sturgeons were force-fed before the gastric lavage was performed. Some prey were recovered from all the sturgeons, and the average food item recovery rate from stomach contents was 67.5%; recovery of brown shrimp and sand goby (78.2%) was greater than that of vermiform items (51.4%). The volume of food had no significant influence on the prey recovery rate. No mortality resulted from the gastric lavage. However, the method is not totally benign because the fish that had undergone gastric lavage averaged significantly greater weight los...

The Combined Use of Correlative and Mechanistic Species Distribution Models Benefits Low Conservation Status Species.

Species can respond to climate change by tracking appropriate environmental conditions in space, resulting in a range shift. Species Distribution Models (SDMs) can help forecast such range shift responses. For few species, both correlative and mechanistic SDMs were built, but allis shad (Alosa alosa), an endangered anadromous fish species, is one of them. The main purpose of this study was to provide a framework for joint analyses of correlative and mechanistic SDMs projections in order to strengthen conservation measures for species of conservation concern. Guidelines for joint representation and subsequent interpretation of models outputs were defined and applied. The present joint analysis was based on the novel mechanistic model GR3D (Global Repositioning Dynamics of Diadromous fish Distribution) which was parameterized on allis shad and then used to predict its future distribution along the European Atlantic coast under different climate change scenarios (RCP 4.5 and RCP 8.5). We then used a correlative SDM for this species to forecast its distribution across the same geographic area and under the same climate change scenarios. First, projections from correlative and mechanistic models provided congruent trends in probability of habitat suitability and population dynamics. This agreement was preferentially interpreted as referring to the species vulnerability to climate change. Climate change could not be accordingly listed as a major threat for allis shad. The congruence in predicted range limits between SDMs projections was the next point of interest. The difference, when noticed, required to deepen our understanding of the niche modelled by each approach. In this respect, the relative position of the northern range limit between the two methods strongly suggested here that a key biological process related to intraspecific variability was potentially lacking in the mechanistic SDM. Based on our knowledge, we hypothesized that local adaptations to cold temperatures deserved more attention in terms of modelling, but further in conservation planning as well.

Post-release Monitoring Techniques

This section deals with the monitoring techniques that have been tested and used in the context of the Gironde population dynamic survey. Very recent methods and results are presented as well as earlier data. Monitoring is currently used mainly to estimate the efficiency of stocking (survival and growth parameters) and spatial and temporal distribution, in order to localize the essential habitat of the fish.

What Is the Future for the European Sturgeon

The present book appears 20 years after the peer-reviewed proceedings of “Acipenser”, the first International Symposium on sturgeon (ISSI) (Williot 1991) where two preliminary investigations on the European sturgeon were presented (Castelnaud et al. 1991; Rochard et al. 1991).

Tagging European and Atlantic Sturgeons in Europe

Tagging is a widespread method used to acquire data on fish populations. Successive steps to obtain a practical tagging method for European sturgeon are detailed, and a list of different tags used in Acipenser sturio and Acipenser oxyrinchus in Europe is drawn up. The need to bring together tagging information at the European level is pointed out.

Modelling the Future of Stocked Fish

Stocking with juvenile sturgeon is a key point of the action plans described below for A. sturio. It is essential to assess the expected effects of these stocking measures in order to improve practises. Using a few parameters of population dynamics assessed from monitoring some cohorts, we simulated the survival of the stocked fish. Simulations are obviously highly sensitive to the mortality rate. Based on simulations using the best range of available parameters for the Gironde population, the number of females on spawning grounds constitutes a bottleneck for the dynamic of this population.

Age Assessment in European Sturgeon

Age determination is a key tool in population dynamics for acquiring data on age structure and cohort strength. In the case of a protected species, the method is required to have no adverse effects on the fish. A method using a thin section of the first pectoral fin ray has been set up on Acipenser sturio according to these prerequisites, and has been validated. The main limitations concerning old fish or fish held in captivity are discussed.