Kélig Mahé

Institut Français de Recherche pour l'Exploitation de la Mer | Ifremer · Department of Fisheries Resources - Channel/North Sea

The otolith is a calcified structure located in the inner ear of fish, commonly used to estimate their age. Its shape can be utilized to differentiate between fish populations. Otoliths from 22 different species have been collected in the English Channel and North Sea regions. By employing 3D images of otoliths, it has become possible to identify t...

Although otoliths are widely used as archives to infer life history traits and habitat use in fishes, their biomineralization process remains poorly understood. This lack of knowledge is problematic as it can lead to misinterpretation of the different types of signals (e.g. optical or chemical) that provide basic data for research in fish ecology,...

Brackish habitats are considered important for the facultatively catadromous European eel, but knowledge of eel habitat use strategies and the consequences on their condition, particularly in the estuaries areas, is limited and yet necessary for understanding some features such as growth and maturation in the different habitats that eel inhabit dur...

Knowledge of the spatial structuring of stocks is essential to study the dynamics of fish populations, and thus to manage fisheries. In this study, sagittal otolith shape was used to understand the stock structures of populations of the main commercial species caught around la réunion island. A total of 1091 individuals, belonging to nine species o...

Fisheries management is generally based on age structure models. Thus, fish ageing data are collected by experts who analyze and interpret calcified structures (scales, vertebrae, fin rays, otoliths, etc.) according to a visual process. The otolith, in the inner ear of the fish, is the most commonly used calcified structure because it is metabolica...

PFASs are ubiquitous in the global environment due to their wide use, persistence and bioaccumulation, and are of concern for human health. This study investigated the levels of PFASs in seafood with a view to provide knowledge on the occurrence of PFASs in marine resources and to evaluate seafood safety and human health risk via dietary exposure t...

Sagittal otolith shape analysis is one of the most widespread techniques worldwide to discriminate fish stock units, as this proxy integrates both environmental and genetic factors. All previous otolith shape studies have been carried out using two-dimensional (2D) images, a partial representation of the whole shape of the otolith. However, prior t...

Among all human-induced pressures, ocean warming is expected to be one of the major drivers of change in marine ecosystems. Fish species are particularly vulnerable during embryogenesis. Here, the impact of temperature was assessed on embryonic stages of Atlantic herring (Clupea harengus), a species of high socio-economic interest, with a particula...

Dans le cadre du suivi des espèces commerciales ciblées par la pêche dans les RUP (régions ultrapériphériques), l’Ifremer a élaboré le projet Accobiom (ACquisition de COnnaissances sur les paramètres Biologiques des ressources marines exploitées en Outre-Mer) afin de renforcer les connaissances sur les stocks halieutiques en Outre-mer. A l’avenir,...

This poster presents the reproductive cycle during the 12 months of the year (with the fish proportions : during peak reproduction, able to reproduce and the sexual rest). Total length and Age at the first sexual maturity of the main demersal species exploited around Reunion Island (Indian Ocean) are identified. These data were carried out and anal...

This poster presents the growth of the main demersal species exploited around Reunion Island based on the relationships established between total length, total weight, age and first sexual maturity. These data were carried out and analysed during the European research project IPERDMX (2019-2022) which aims to specify the state of the exploited popu...

This poster presents the sagittal otoliths of the main demersal species exploited around Reunion Island. These calcified structures in inner-ear are used to estimate the fih ageing and others biological parameters. The otolith shape is an efficient tool to discriminate the stock unit (or management unit) of these species. These data were carried ou...

Otoliths are very useful biomarkers especially for fish growth. Climate change with the associated global changes in warming and acidification could affect the calcification and the shape of otoliths during the crucial larval period in teleost fish. To evaluate this predicted combined effect of temperature and CO2, Atlantic herring (Clupea harengus...

The groupers (Epinephelidae family) are demersal species that are a vulnerable resource due to increasing fishing pressure around Reunion Island. Five species of groupers are among the main species exploited by commercial and recreational fisheries around La Réunion Island: blacktip grouper ( Epinephelus fasciatus; Forsskål 1775), oblique-banded gr...

The European hake Merluccius merluccius is the third most valuable species for the North-East Atlantic and the Mediterranean fisheries. European hake has been rated as overexploited in the Mediterranean, thus careful management is advisable. Mediterranean hake is well-differentiated from Atlantic hake, but sub-population structure within the Medite...

Abundance and growth of the European eel from six small northern French estuaries during their growth phase were examined to explore variations according to the local habitat characteristics. The length–weight relationships and growth models fitted to length-at-age back-calculated otolith growth increments were used to compare the growth. Higher ab...

Otoliths, calcified structures in the inner ears, are used to estimate fish age, and their shape is an efficient fish stock identification tool. Otoliths are thus very important for the management and assessment of commercial stocks. However, most studies have used left or right otoliths, chosen arbitrarily without evaluation of the difference betw...

Body length–weight (L–W) relationships of 123 fish species (122 Actinopterygii and 1 Elasmobranchii) were studied from 10 218 individuals caught around Réunion Island from 2000 to 2021. All species, except for 4 with a very small number of individuals and limited length range, showed a significant relationship between total length and total weight....

The workshop aimed to collate information on existing ageing protocols and the used calcified pieces to better standardize the interpretation of annual growth rings and then the ageing of the European sea bass (Dicentrarchus labrax).

Otolith morphology analysis is one of the main tools used for fish or fish stock identification. Moreover, otolith shape can also be used in animal dietary studies (stomach content) for the identification of prey fishes and their size according to the relationship between fish and otolith sizes. In the present study, the relationship between fish l...

Telomeres protect the coding sequence of chromosome ends and Telomere Length (TL) has been proposed as a biomarker of cellular aging, cumulative stress exposure and life-span in humans. With the aim to propose new biomarkers, a q-PCR protocol was adapted for the measurement of TL in the European flounder Platichthys flesus. The protocol was then ap...

Sclerochronology is a method used to estimate the season of death (season of capture) of archaeological individuals based on a modern growth model. This method has been increasingly accepted in South America and has mainly been applied to coastal archaeological sites (on the Atlantic and Pacific Oceans). This is the first time that this method has...

The otolith, found in both inner ears of bony fish, has mainly been used to estimate fish age. Another application that has been developing significantly in recent years, however, is the use of otolith shape as a tool for stock identification. Often, studies have directly used the shape asymmetry between the right and left otoliths. We tested the m...

The extant coelacanth was discovered in 1938;¹ its biology and ecology remain poorly known due to the low number of specimens collected. Only two previous studies¹,² have attempted to determine its age and growth. They suggested a maximum lifespan of 20 years, placing the coelacanth among the fastest growing marine fish. These findings are at odds...

Otolith morphology analysis is one of the main tools used for fish or fish stock identification. Moreover, otolith shape can also be used in fish dietary studies (stomach content) for the identification of prey fishes and their size according to the relationship between fish and otolith sizes. In the present study, the relationship between fish len...

Despite the high commercial value of the striped seabream Lithognathus mormyrus (Linnaeus, 1758) in the Gulf of Tunis, biological data on its age, growth and exploitation rate are lacking. With the aim of estimating growth parameters, 516 individuals, ranging from 6–27.5 cm total length and from 3.5–293.5 g total weight, were collected from the art...

Arcachon Bay, in the southern Bay of Biscay, is the first French production area of Manila clam (Ruditapes philippinarum) with an annual commercial fisheries production around 400 tons in recent years. This bivalve mollusc was introduced into the bay in the 1980s for aquaculture purpose and quickly succeeded in natural settlement so that its high m...

Marine organisms show population structure at a relatively fine spatial scale, even in open habitats. The tools commonly used to assess subtle patterns of connectivity have diverse levels of resolution and can complement each other to inform on population structure. We assessed and compared the discriminatory power of genetic markers and otolith sh...

We describe sclerochronological analyses of tadpole codling (Salilota australis) vertebrae as a proxy for the seasonal timing of fishing activities at one Middle Holocene (6500 BP) and three Late–Middle Holocene (3500–2500 years BP) archaeological sites located in Seno Otway and in the central zone of the Strait of Magellan, Chile. These data provi...

The age and growth of the haffara seabream, Rhabdosargus haffara (Forsskål, 1775) from Hurghada fishing area, Red sea, Egypt, were investigated using a sample of 466 specimens. The fish length varied between 12.7 and 27.2 cm and the weight from 38.1 to 293.2 g. Samples were collected from the artisanal fisheries during the fishing season from Augus...

The assessment and management of fish populations is based on the use of management units called fish stocks. The shape of otoliths, calcified structures of the fish's inner ear, can be used to discriminate these stocks. First, this thesis focuses on the study of the spatio-temporal variability of the otolith's shape for three fish species with dif...

L’évaluation et la gestion des populations de poissons se basent sur l'utilisation d’unités de gestion appelées « stocks halieutiques ». Pour discriminer ces stocks, la forme des otolithes, pièces calcifiées de l’oreille interne des poissons, peut être utilisée. Dans ce contexte, cette thèse s'est consacrée premièrement à l’étude de la variabilité...

The uncertainty in age estimation by otolith reading may be at the root of the large variability in red mullet (Mullus barbatus) growth models in the Mediterranean. In the MEDITS survey, red mullet age data are produced following the same sampling protocol and otolith reading methodology. However, ageing is assigned using different interpretation s...

While otolith shape analysis can provide a valuable tool for discriminating between fish populations, factors which may influence otolith shape, such as the effect of size, directional asymmetry in growth, and local environmental conditions, are often unknown. Here, we analyzed differences in otolith shape across three size classes of age-0 common...

Otolith shape is an efficient tool for fish stock discrimination. Therefore, it is crucial to identify the environmental parameters that could influence otolith morphogenesis and growth. Current global ocean warming negatively affects the production of polyunsaturated fatty acids (EPA and DHA) by phytoplankton and thus their availability in marine...

This study aimed to determine uranium (U) pollution over time using otoliths as a marker of fish U contamination. Experiments were performed in field contamination (~20 μg L⁻¹: encaged fish: 15d, 50d and collected wild fish) and in laboratory exposure conditions (20 and 250 μg L⁻¹, 20d). We reported the U seasonal concentrations in field waterborne...

Age, growth and mortality of the Starry weever Trachinus radiatus were studied for the first time from 214 individuals collected in the Gulf of Tunis between February 2014 and January 2016. The significant relationship between length-weight was observed for males (a = 0.011, b = 2.992, R 2 = 0.981, n = 77) and females (a = 0.010, b = 3.036, R² = 0....

Otolith shape analysis is an efficient fish stock identification tool. However, most applications used left and right otoliths or only one of them arbitrarily chosen without testing for biases resulting from potential directional bilateral asymmetry (DA) in otolith shape, i.e., a unimodal population-level deviation form bilateral symmetry between r...

Background. Striped seabream, Lithognathus mormyrus (Linnaeus, 1758), is a bony fish, which has a high economic value on the Algerian coast. Because of the increasing fishing pressure, however, a close monitoring is recommended. The information about the biology of this species, occurring in the south-western Mediterranean Sea and especially in the...

European anchovy, Engraulis encrasicolus, is a small pelagic coastal marine fish largely spread from the North Sea to central Africa, including the entire Mediterranean and the Black and Azov Seas. The aim of this study is to identify the potential different populations of European anchovies and their relationship between the Northeast Atlantic, th...

La structure démographique de deux des plus abondantes espèces de Trachinidae des côtes tunisiennes : Trachinus draco Linnaeus, 1758 (la grande vive) et Trachinus radiatus Cuvier, 1829 (la vive à tête rayonnée) a été établie à travers l’étude de la sex-ratio, de la distribution de fréquence en taille et en âge, de la détermination des paramètres de...

The growth and mortality of the brown meagre, Sciaena umbra from the Gulf of Tunis, were investigated using a sample of 276 specimens, ranging from 15.3 to 49.2 cm total length and from 43 to 1565 g total weight. Specimens were collected from artisanal fisheries between October 2008 and September 2011. Otoliths were extracted, thin cross-sections w...

Summary: The growth and mortality of the brown meagre, Sciaena umbra from the Gulf of Tunis, were investigated using a sample of 276 specimens, ranging from 15.3 to 49.2 cm total length and from 43 to 1565 g total weight. Specimens were collected from artisanal fisheries between October 2008 and September 2011. Otoliths were extracted, thin cross-s...

The growth and mortality of the brown meagre, Sciaena umbra from the Gulf of Tunis, were investigated using a sample of 276 specimens, ranging from 15.3 to 49.2 cm total length and from 43 to 1565 g total weight. Specimens were collected from artisanal fisheries between October 2008 and September 2011. Otoliths were extracted, thin cross-sections w...

This study presents analyses about weight-length relationships, condition factor and form factor of Trachinus draco in the Gulf of Tunis. The fish samples were collected monthly from commercial landings of the soecues in the Gulf of Tunis between February 2014 to January 2015. The weight-length relationships of males, females and combined sexes exh...

Background Life in the darkness of caves is accompanied, throughout phyla, by striking phenotypic changes including the loss or severe reduction in eyes and pigmentation. On the other hand, cave animals have undergone constructive changes, thought to be adaptive, to survive in this extreme environment. The present study addresses the question of th...

Otolith shape analysis was examined to determine its utility for stock identification of the bogue Boops boops (L.) along the Algerian coast. The outlines of 179 otoliths collected in three locations (Oran, Bejaia and Annaba) between 2013 and 2016 were digitised and analysed for shape variation by elliptical Fourier analysis. Potential confounding...

Evaluating fish larval condition in terms of nutrition and growth is essential as it will influence their development and survival capacity. The present study aims to investigate larval condition of Downs herring (Clupea harengus L.) during winter in the Eastern English Channel and Southern Bight of the North Sea. Four condition indices including i...

Stock structure of whiting (Merlangius merlangus) in the North East Atlantic is unclear. This study uses mixed effects models to analyse growth variability as a way to investigate stock identification. Growth trajectories for 634 individuals and length-at-age data for 78,686 individuals were analysed for spatial coherence and temporal synchrony in...

Otoliths are paired calcified structures located in the inner ear of the teleost fishes. Fisheries scientists have been using the otoliths for a variety of applications as fish ageing, species identification and also species interaction. The symmetry between left and right otoliths is considered species dependent. The application of analysis techni...

The ornate jobfish Pristipomoides argyrogrammicus Valenciennes 1832 occurs in the Indo-West Pacific Ocean, where it is harvested by small-scale coastal fisheries. Management of this species is hindered by lack of adequate biological data. We sampled a total of 113 individuals from the landings of local artisanal fishers on the island of Réunion (so...

The fish remains sampled from archaeological sites are generally the result of human food refuse; therefore, the study of retrieved fish scales may provide reliable information on the season of capture and on paleoclimate and paleoenvironmental changes. Among Western European freshwater fishes, the grayling, Thymallus thymallus¸ has the most easily...

Weight–Body Length relationships (WLR) of 45 fish species (37 Actinopterygii and eight Elasmobranchii) were investigated. A total of 31,167 individuals were caught and their biological parameters measured during the four quarters from 2013 to 2015, on five scientific surveys sampling the North-eastern Atlantic Ocean from the North Sea to the Bay of...

Swordfish Xiphias gladius is an oceanic-pelagic species. Its population structure in the Western Indian Ocean was studied from the shape of the sagittal otoliths of 391 individuals collected from 2009 to 2014. Normalised elliptical Fourier descriptors (EFDs) were extracted automatically using TNPC software. Principal components analysis (PCA) condu...

Previous studies have shown that the amount of food influences fish otolith structure, opacity and shape and that diet composition has an effect on otolith chemical composition. This study investigated the potential correlation between diet and otolith shape in 5 wild marine fish species by addressing 4 complementary questions. First, is there a gl...