Hélène de Pontual

A pilot tagging experiment on European hake (Merluccius merluccius): methodology and preliminary results

European hake (Merluccius merluccius) were caught alive in the northern Bay of Biscay in June/July 2002, using a codend specially designed to avoid crushing fish and also to retain water while hauling the trawl. In all, 1307 fish were tagged with anchor T-bar tags, injected with tetracycline, then released. The length range of the tagged and marked fish varied from 13 to 58 cm, and the modal size was 28 cm, at which length they were assumed to be 2-3 years old. A mean survival rate of 68.2% was estimated. Mortality was mainly caused by stress of capture and physical damage, and depended on the size of the catch and the depth of trawling. By the end of March 2003, 32 fish and three tags had been returned to the laboratory (a 2.7% return rate), the recapture data indicating that the probability of survival after release does not depend on catch depth or depth at location of release. For combined sexes, the somatic growth rate was estimated at 0.033 ± 0.019 cm day −1 (n=15). Males and females did not differ significantly in somatic growth rate, which were, respectively, 0.028±0.018 (n=6) and 0.033 ± 0.012 cm day −1 (n=6). This pilot experiment represents the first recorded mass tagging of European hake, which is known to be a very fragile species. The preliminary results indicate that it would be possible to carry out a large-scale tagging experiment of the European stocks in order to improve assessment and subsequent management decisions.

Influence of ontogenetic and environmental changes in the otolith microchemistry of juvenile sole (Solea solea)

We analysed otolith composition, specifically Sr/Ca ratios, with the aim of determining whether metamorphosis and the transition to benthic life of Bay of Biscay sole occur in marine or estuarine conditions. Otoliths of wild juveniles (0-group) collected in two estuarine nurseries showed characteristic Sr/Ca chronologies, with a significant decrease of the Sr/Ca ratio from the core to the accessory growth centres. As the otolith Sr/Ca ratio decreases in respect of the ambient salinity, this could suggest a relative synchronism in the timing of estuarine nursery entrance. In order to validate this hypothesis, hatchery-produced larvae were reared in a tidal marsh mesocosm until they completed metamorphosis (around 1 month post-hatching) and settled on the bottom. The otoliths from these juveniles exhibited a similar Sr/Ca pattern, which could not be explained as a result of habitat changes, and especially salinity variations, but rather reflected an ontogenetic signal. Since both wild and reared soles achieved high growth rates during metamorphosis, this suggests a link between a high metabolic rate and the observed Sr/Ca drop. In addition, ontogenetic changes during this transitional phase could involve the setting of functional mechanisms, responsible for the regulation of free Sr 2+ in either plasma or endolymph or both. Nevertheless, this common trend appeared to be modulated by environmental cues: Sr/Ca ratios were significantly higher for reared fish compared to wild fish during the larval period. A possible explanation is that experienced temperatures were much higher in the incubator than in the field. Furthermore, Sr/Ca values obtained in the otolith juvenile area, with the lowest ratios for soles from the Loire nursery, suggest that the salinity regime of estuarine nurseries could exert an environmental control on otolith Sr/Ca ratios, thus providing ecological records of up-estuary migration after metamorphosis.

Chemical composition of saccular endolymph and otolith in fish inner ear: lack of spatial uniformity

Fish otoliths provide a record of age, growth, and environmental influences. In both trout and turbot, spatial chemical investigation of the endolymph surrounding the otolith (sagitta) showed a lack of uniformity. Proteins, PO(3-)(4), and Mg(2+) were significantly more concentrated in the proximal (facing the macula) than distal zone, whereas the opposite was observed for K(+) and total CO(2) (totCO(2)). Na(+) concentration ([Na(+)]) was 20% higher in the proximal zone in trout but not in turbot. Total Ca and Cl(-) contents were uniformly distributed in both species. We propose that the endolymphatic gradients of protein and totCO(2) concentration within the endolymph are involved in the otolithic biocalcification process. Microchemical analyses of otolith sections by wavelength dispersive spectrometry showed a lack of spatial uniformity in the K/Ca and Na/Ca ratios, whereas the Sr/Ca ratio was uniform. There is a clear relationship between endolymph and otolith [K(+)], but the interpretation of the results for [Na(+)] needs further investigation. Thus the lack of uniformity in the otolith composition must be taken into account when investigating otolith microchemistry.Fish otoliths provide a record of age, growth, and environmental influences. In both trout and turbot, spatial chemical investigation of the endolymph surrounding the otolith (sagitta) showed a lack of uniformity. Proteins, [Formula: see text], and Mg2+ were significantly more concentrated in the proximal (facing the macula) than distal zone, whereas the opposite was observed for K+ and total CO2(totCO2). Na+ concentration ([Na+]) was 20% higher in the proximal zone in trout but not in turbot. Total Ca and Cl- contents were uniformly distributed in both species. We propose that the endolymphatic gradients of protein and totCO2 concentration within the endolymph are involved in the otolithic biocalcification process. Microchemical analyses of otolith sections by wavelength dispersive spectrometry showed a lack of spatial uniformity in the K/Ca and Na/Ca ratios, whereas the Sr/Ca ratio was uniform. There is a clear relationship between endolymph and otolith [K+], but the interpretation of the results for [Na+] needs further investigation. Thus the lack of uniformity in the otolith composition must be taken into account when investigating otolith microchemistry.

Shedding light on fish otolith biomineralization using a bioenergetic approach.

Otoliths are biocalcified bodies connected to the sensory system in the inner ears of fish. Their layered, biorhythm-following formation provides individual records of the age, the individual history and the natural environment of extinct and living fish species. Such data are critical for ecosystem and fisheries monitoring. They however often lack validation and the poor understanding of biomineralization mechanisms has led to striking examples of misinterpretations and subsequent erroneous conclusions in fish ecology and fisheries management. Here we develop and validate a numerical model of otolith biomineralization. Based on a general bioenergetic theory, it disentangles the complex interplay between metabolic and temperature effects on biomineralization. This model resolves controversial issues and explains poorly understood observations of otolith formation. It represents a unique simulation tool to improve otolith interpretation and applications, and, beyond, to address the effects of both climate change and ocean acidification on other biomineralizing organisms such as corals and bivalves.

Otoliths imprinting of sole (Solea solea) from the Bay of Biscay: a tool to discriminate individuals from nursery origins?

Sole nurseries are located in the main bays and estuaries of the Bay of Biscay, where juveniles from the same stock concentrate and constitute temporarily isolated groups. This context being favourable for elemental analyses of juvenile otoliths, this study has been initiated with the aim of obtaining environmental imprints of the main nurseries of origin of juveniles recruiting to the adult stock, and of evaluating the relative contribution of these nurseries to the stock. The objectives were to compare (i) the otolith elemental imprints obtained by sampling juveniles in the Loire and the Gironde nurseries, and (ii) two multi-elemental analysis techniques: laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and solution-based ICPMS (SB-ICPMS) adapted to small volumes. Depending on the fish origin, differences in Sr and Rb concentrations were shown using LA-ICPMS. Comparisons between the antero-dorsal and postero-ventral sites from where otolith material was ablated also suggested a spatial heterogeneity in otolith composition at least for some metals. From linear discriminant analyses, 73 % and 79 % of individuals (bootstrap estimations) were correctly classified with respect to their origin from the composition of the antero-dorsal and postero-ventral areas, respectively. The SB-ICPMS analysis was more powerful, which resulted in an 89 % rate of correct classification from a 2-variable model (Mg and Cd), whereas a 5-variable model (Li, Mg, Rb, Cd, Th) resulted in a 91 % rate of correct classification (bootstrap estimations). These results confirm that sole juveniles from the main estuaries of the French Atlantic coast could be discriminated by the elemental fingerprints of their otoliths.

Effects of T-bar and DST Tagging on Survival and Growth of European Hake

Controlled experiments were conducted to assess the effects of T-bar and DST tagging on post-release survival and growth of European hake. In this study, two groups of each 30 hake were considered: small fish (SF, average total length: 29.9 cm ± 2.2 cm) and large fish (LF, average total length: 36.4 cm ± 2.5 cm). Within each size group, fish were randomly assigned to one of 3 treatment groups: control (C), T-bar tagging referred as conventional tagging (CT) and DST tagging (DST) with dummy tags. After 4 months, the overall survival rate was 35%. Smaller fish were less impacted by the stress induced by handling, anaesthesia and tagging and in the SF group, the survival rates were similar (30%) for CT or DST. Specific growth rates were highly variable and no significant difference could be observed between control and tagged fish. Our results demonstrate that (1) conventional tagging affects fish survival rates and (2) DST tagging is feasible in the field on “small fish” with expected survival rate and recapture probability close to that of conventional tagging.

Preparation techniques alter the mineral and organic fractions of fish otoliths: insights using Raman micro-spectrometry

The high spatial resolution analysis of the mineral and organic composition of otoliths using Raman micro-spectrometry involves rigorous protocols for sample preparation previously established for microchemistry and trace elements analyses. These protocols often include otolith embedding in chemically neutral resin (i.e., resins which do not contain, in detectable concentration, elements usually sought in the otoliths). Such embedding may however induce organic contamination. In this paper, Raman micro-spectrometry reveals the presence of organic contamination onto the surface obtained from the use of epoxy resin, specifically Araldite. This contamination level varies depending on otolith structures. Core and checks, known as structural discontinuities, exhibit the most important level of contaminations. Our results suggest that otolith embedding with resin affects the organic matrix of the otolith, probably through an infiltration of the resin in the crystalline structure. The interpretation of chemical otolith signatures, especially Raman otolith signatures, and stable isotope analyses should then be revised in light of these results. In this respect, we propose a method for the correction of Raman otolith signatures for contamination effects.

New insights into behavioural ecology of European seabass off the West Coast of France: implications at local and population scales

&NA; From 2010 to 2012, 246 data storage tags were deployed on European seabass in the Iroise Natural Marine Park, a marine protected area (MPA) off west Brittany, France. A return rate of 14.6% associated with long time series of data provided new information on fish ecology (e.g. maximum experienced depth greater than 225 m, temperature range 6.80–21.87°C). Depth and temperature series were used to infer individual migration using an innovative hidden Markov model (HMM) especially developed for seabass geolocation. Reconstructed fish tracks revealed that seabass is a partially migratory species, as individuals exhibited either long‐distance migrations towards the Bay of Biscay or the Celtic Sea, or residency behaviour in the Iroise Sea. Fidelity to summer feeding areas and to winter spawing areas was demonstrated. These results suggest that the population is spatially structured. The Iroise Sea is likely a mixing zone for different stocks or sub‐populations, and may also shelter a resident population. At the population scale, such findings may impact ICES stock assessment and the resulting decisions from EU managers. At the local scale, conservation action could be taken by MPA managers. Besides, this study demonstrates the high potential of archival tags for investigating multi‐year behavioural patterns such as site fidelity to offshore spawning areas.

Coupling spectral analysis and hidden Markov models for the segmentation of behavioural patterns

BackgroundMovement pattern variations are reflective of behavioural switches, likely associated with different life history traits in response to the animals’ abiotic and biotic environment. Detecting these can provide rich information on the underlying processes driving animal movement patterns. However, extracting these signals from movement time series, requires tools that objectively extract, describe and quantify these behaviours. The inference of behavioural modes from movement patterns has been mainly addressed through hidden Markov models. Until now, the metrics implemented in these models did not allow to characterize cyclic patterns directly from the raw time series. To address these challenges, we developed an approach to i) extract new metrics of cyclic behaviours and activity levels from a time-frequency analysis of movement time series, ii) implement the spectral signatures of these cyclic patterns and activity levels into a HMM framework to identify and classify latent behavioural states.ResultsTo illustrate our approach, we applied it to 40 high-resolution European sea bass depth time series. Our results showed that the fish had different activity regimes, which were also associated (or not) with the spectral signature of different environmental cycles. Tidal rhythms were observed when animals tended to be less active and dived shallower. Conversely, animals exhibited a diurnal behaviour when more active and deeper in the water column. The different behaviours were well defined and occurred at similar periods throughout the annual cycle amongst individuals, suggesting these behaviours are likely related to seasonal functional behaviours (e.g. feeding, migrating and spawning).ConclusionsThe innovative aspects of our method lie within the combined use of powerful, but generic, mathematical tools (spectral analysis and hidden Markov Models) to extract complex behaviours from 1-D movement time series. It is fully automated which makes it suitable for analyzing large datasets. HMMs also offer the flexibility to include any additional variable in the segmentation process (e.g. environmental features, location coordinates). Thus, our method could be widely applied in the bio-logging community and contribute to prime issues in movement ecology (e.g. habitat requirements and selection, site fidelity and dispersal) that are crucial to inform mitigation, management and conservation strategies.