Thermal stratification drives movement of a coastal apex predator

A characterization of the thermal ecology of fishes is needed to better understand changes in ecosystems and species distributions arising from global warming. The movement of wild animals during changing environmental conditions provides essential information to help predict the future thermal response of large marine predators. We used acoustic telemetry to monitor the vertical movement activity of the common dentex (Dentex dentex), a Mediterranean coastal predator, in relation to the oscillations of the seasonal thermocline during two summer periods in the Medes Islands marine reserve (NW Mediterranean Sea). During the summer stratification period, the common dentex presented a clear preference for the warm suprathermoclinal layer, and adjusted their vertical movements following the depth changes of the thermocline. The same preference was also observed during the night, when fish were less active. Due to this behaviour, we hypothesize that inter-annual thermal oscillations and the predicted lengthening of summer conditions will have a significant positive impact on the metabolic efficiency, activity levels, and population dynamics of this species, particularly in its northern limit of distribution. These changes in the dynamics of an ecosystem’s keystone predator might cascade down to lower trophic levels, potentially re-defining the coastal fish communities of the futureVersión del editor2,92

First record of the yellow mouth barracuda Sphyraena viridensis in the Tunisian Northern coast

Au mois d’avril 2007, neuf (9) spécimens de Sphyraena viridensis dont 7 femelles et 2 mâles ont été identifiés pour la première fois dans un lot de Sphyraena sphyraena sur l’étale de vente du marché de Bizerte (Nord de Tunisie). Leur poids variait entre 206g et 936g correspondant à des tailles comprises entre 396mm et 623mm. Selon les informations reçues ces individus ont été capturés au trémail à Ghar el Melh. En mai de la même année, 5 individus femelles de S. viridensis ont été également trouvés et échantillonnés dans la le même port; ils mesuraient entre 421mm et 456mm correspondant à des poids compris entre 258g et 308g. D’après leurs tailles, ils sont adultes. Disséqués, tous les individus étaient matures. L’identification de S. viridensis du Nord de la Tunisie permet d’élargir la répartition géographique et confirmer sa présence en Méditerranée occidentale.نتعرف لأول مرة من خلال هذا العمل علي سمك المغزل(Sphyraena viridensis) بالمياه الشمالية التونسية إذ تم في افريل 2007 اصطياد 9 سمكات من هذا النوع ضمن سمك المغزل المتعارف بالجهة (Sphyraena sphyraena) . وتتمثل هذه الأسماك في 7 إناث و 2 ذكور وقع صيدها بواسطة شباك المبطن بغار الملح وتم جلبها إلي سوق بنزرت حيث عثرنا عليها. تتراوح أوزان هذه السمكات بين 206غ إلي 936غ مما توافق أطوالها بين 396مم و 623مم وفي شهر ماي 2007، عثرنا في نفس الجهة علي 5 إناث من سمك (Sphyraena viridensis) . تتراوح أطوالها بين 421مم و 456مم وزنها بين 258غ و 308غ. وبعد التشريح اتضح أنها ناضجة جنسيا. إن التعرف على هذا النوع من السمك بالمياه الشمالية التونسية من شانه أن يوسع توزيعه الجغرافي ويؤكد وجوده في البحر الأبيض المتوسط.In April 2007, nine (9) individuals of S. viridensis composed of 7 females and 2 males have been identified for the first time mixed with S. viridensis on the stand of fish market in Bizerte (Tunisian Northern region). Their weights were between 206g and 936g, corresponding to the sizes comprised between 396mm and 623mm. According to the received information, these individuals were captured in Ghar el Melh. In May, the same year, 5 female individuals of S. viridensis were also captured in the same area. They measured between 421mm and 453mm and weighted respectively between 258g and 308g. After dissection, the individuals were all mature. The discovery of the S. viridensis in the Tunisia northern waters allows to widen its geographical repartition and to confirm its presence in the occidental Mediterranean.PublishedSphyraenidae; Sphyraena viridi

Reproduction period, sex-ratio and sexual maturity of <Dentex maroccanus> (Teleostei, Sparidae) in Tunisian coasts

The survey of the reproduction period, of age and size of first sexual maturity of has been achieved for the first time on the Tunisian coasts. The reproduction period is limited between July and October for this species of . The sex-ratio of , per season, by size classes and by region, shows a dominance of females. This ratio inverts in favour of males during the reproduction period, generally between June and August and this for the large specimens (more than 18 cm TL). The calculation of the maturity ratio by size classes and by sex, permitted to determine the size and the age of first sexual maturity. The value of L50 (50% of mature) corresponds for the two sexes to 15cm of fish total length and about 2 years old. At the age of 3 years (TL=19.5 cm), 100% of the population are mature. We can note that the smallest mature individuals met during our sampling measured 11 cm of total length (1 year old).L’étude de la période de ponte, de l'âge et de la taille de première maturité sexuelle du Denté a été réalisée pour la première fois sur les côtes tunisiennes. La période de frai pour cette espèce se situe entre juillet et octobre. L'étude de la sex-ratio par saison et par classe de taille montre en général une dominance des femelles par rapport aux mâles qui s’inverse en faveur de ces derniers pendant la période de frai (juin- août) et ceci pour les grandes classes de taille (supérieures à 18 cm). Le calcul du pourcentage des individus matures par classe de taille et par sexe, nous a permis de déterminer la taille de première maturité sexuelle. La valeur estimée de L50 (50% de matures) des deux sexes correspond à une longueur totale de 15cm et à un âge commun estimé à 2 ans environ. A l'âge de 3 ans (LT = 19.5 cm ), 100% de la population sont matures. Notons que le plus petit individus mature rencontré au cours de notre échantillonnage mesure 11 cm de longueur totale (correspondant à un âge de 1 an).Publishe

Predictive distribution models of European hake in the south-central Mediterranean Sea

The effective management and conservation of fishery resources requires knowledge of their spatial distribution and notably of their critical life history stages. Predictive modelling of the European hake (Merluccius merluccius L., 1758) distribution was developed in the south-central Mediterranean Sea by means of historical fisheries-independent databases available in the region. The study area included the international waters of the south-central Mediterranean Sea and the territorial waters of Italy, Malta, Tunisia and Libya. Distribution maps of predicted population abundance index, and probabilistic occurrence of recruits and large adults were obtained by means of generalized additive models using depth and seafloor characteristics as predictors. Presence/absence data of the two life stages was obtained using threshold values applied to the mean weight of the survey catches. Modelling results largely matched previously reported knowledge on habitat preference of the species and its critical life phases. Hake recruits showed an occurrence peak at 200 m depth with preference for soft bottoms. Large adults preferred deeper and harder bottom substrates. Prediction maps allowed to improve our knowledge on the distributional patterns of one of the most important shared stocks in the south-central Mediterranean. This knowledge is essential for an appropriate development of regional-spatial-based management plans