Search

Background. The Gulf of Gabès supports an important fishery which is characterized by a great diversity of fish species. Despite this importance, there has been no attempt to examine the whole larval fish assemblage in this area. The aim of this study was to investigate the larval fish communities during summer and winter seasons in the Gulf of Gabès. Materials and methods. Two multidisciplinary surveys were carried out aboard the R/V Hannibal in 2009. A total of 80 and 70 stations were sampled during winter and summer surveys, respectively. Stations were arranged in a regular sampling grid of 10 × 10 nautical miles. Ichthyoplankton was sampled by oblique tows with a Bongo net of 60 cm mouth diameter, fitted with 335 µm mesh nets. Zooplankton dry weight was obtained by drying aliquots of the zooplankton sample in an oven at 60ºC, for 72 hours. Results. In summer 34 taxa representing 24 families, were collected, whereas in winter 35 taxa, representing 16 families, were collected. Larval fish communities were dominated by small pelagic species: sardinella and anchovy in summer and sardine in winter. The results also highlight the Gulf of Gabès as an important spawning ground for many large and medium pelagic fishes, both highly migratory (Thunnus thynnus) and resident species (Auxis rochei, Euthynnus alletteratus). The summer/winter differences observed in species composition and abundance of the larval fish communities reflected the seasonality in fish species spawning in the Mediterranean Sea, likely influenced by the highly contrasting environmental conditions between seasons. Thus, the seasonal changes in the hydrographic conditions of the Gulf of Gabès result in different scenarios that provide suitable spawning environments for a variety of fishes, allowing them to share the Gulf as spawning habitat. Conclusion. The Gulf of Gabès is an important fish spawning area for demersal, small pelagic, medium pelagic, and large pelagic (tunas). Larval species composition differed considerably between summer and winter surveys., Sí

Age and growth of the horse mackerel Trachurus trachurus, caught in the two sides of the Strait of Sicily, central Mediterranean Sea (Italy: GSA16 and Tunisia: GSA13), were estimated by length-frequency analysis using FISAT II software. The estimated Von Bertalanffy growth parameters, compared with likelihood ratio test showed significant differences in horse mackerel growth, caught from the two areas. Trachurus trachurus from Tunisia tended to be greater in size than those from Italy. Satellite sea surface temperature revealed a constant higher temperature regime in Tunisian waters, which resulted 1°C warmer than Italian waters. Chlorophyll a concentration showed a higher primary production (+ 12%) in the Italian waters compared to Tunisian waters. Relationships between growth and geographical distribution denote the effect of environmental conditions on growth especially water temperature and primary production, although the role of other factors could not be excluded, among them genetic and/or epigenetic ones.

Age and growth of Blue runner Caranx crysos from the Gulf of Gabes (Tunisia). This work was executed for the research programs carried out for the sustainable management of pelagic resources in Tunisia by estimating exploitable biomasses, establishing biological parameters and analysing the exploitation. The study was based on reading the otoliths of 1238 specimens to determine the age and growth of Caranx crysos from the Gulf of Gabes in Southeastern Mediterranean. Marginal increment analysis showed a single annual minimum during winter (January). Eight age classes, ranging from 0+ to 7+ years, were determined for both sexes. Growth was modelled using standard and generalized von Bertalanffy equations. The relationship between observed total length TL and age «t» was described by the following standard equations : TL = 46.67 (1-e-0.17 (t + 1.92)) for females and TL = 47.66 (1-e-0.17(t + 1.86)) for males. Relationships between body mass (W) and total length (L) showed difference of nature of allometry according to sex. The calculation of the theoretical maximum mass (Mp∞) used the formulas : Mpt = 1244,98 (1-e-0,17 (t + 1, 92))3,01 for females et Mpt = 1372,46 (1-e-0,17 (t + 1,86))3,06 for males. The age at first sexual maturity (t50) was 2.8 years for females and 2.4 years for males. The maximum theoretical age (tmax) or longevity reached 15.5 years and 15.6 years for females and males, respectively., Ce travail entre dans le cadre des programmes de recherche réalisés pour la gestion durable des ressources pélagiques en Tunisie par l’estimation des biomasses exploitables, l’établissement des paramètres biologiques et l’analyse de l’exploitation. L’étude est basée sur la lecture des otolithes de 1238 spécimens pour déterminer l’âge et la croissance de Caranx crysos du golfe de Gabès dans le Sud-Est de la Méditerranée. La croissance en longueur a montré que la formation de l’anneau d’arrêt de croissance est marquée en hiver (janvier). Le comptage des anneaux d’arrêt de croissance révèle huit groupes d’âge pour les deux sexes (0+ à 7+). Les équations de croissance en longueur selon le modèle de von Bertalanffy sont : LT = 46,67 (1-e-0,17 (t + 1,92)) pour les femelles et LT = 47,66 (1-e-0,17 (t+ 1,86)) pour les mâles. La relation taille-masse a montré que la nature de l’allométrie diffère selon le sexe. Le calcul de la masse maximale théorique (Mp∞) s’exprime par les formules suivantes : Mpt = 1244,98 (1-e-0,17 (t + 1, 92))3,01 pour les femelles et Mpt = 1372,46 (1-e-0,17 (t + 1,86))3,06 pour les mâles. L’âge de la première maturité sexuelle (t50) est estimé à 2,8 ans pour les femelles et 2,4 ans pour les mâles. L’âge théorique maximal (tmax) ou longévité atteint 15,5 ans et 15,6 ans pour les femelles et les mâles, respectivement., Sley Ayda,Hajjej Ghailen,Jarboui Othman,Bouaïn Abderrahmen. Âge et croissance de la Carangue coubali Caranx crysos du golfe de Gabès (Tunisie). In: Revue d'Écologie (La Terre et La Vie), tome 73, n°2, 2018. pp. 191-202.

Age and growth of Octopus vulgaris were estimated for the first time by using stylets of 200 specimens (97 males, 103 females) collected from the Tunisian southern coasts (the Gulf of Gabès), between June 2011 and May 2012. Females ranged in age from 215 days (7.5 months) to a maximum of 889 days (29.6 months), corresponding to weights of 380 to 5800 g. Males ranged in age from 102 days (3.4 months) to a maximum of 1251 days (41.7 months), corresponding to weights of 280 to 6350 g. A strong positive relationship between estimated age and both dorsal mantle length and body weight was observed. Our results indicated that under favourable conditions the life cycle of Octopus vulgaris could be extended to 2.5 years for most of the population and exceptionally to 3.5 years for some males in the Tunisian waters. Our data provided also a high growth individual variability and suggest the existence of octopus sub-annual cohorts which hatch through the year. The highest growth rate for both sexes was observed for individuals hatched in summer.

The occurrence of a morphologically altered individual identified as Portunus segnis is reported in this note. An adult male of this species with an additional chela on the left cheliped, which could result in difficulties for reproduction and escape from predators. The cause of the malformation remains unknown, but the result are indicative that is most likely due to errors in morphogenetic processes.

This contribution reports for the first time the occurrence of the brown shrimp Penaeus aztecus Ives, 1891 in the central Mediterranean Sea (Gulf of Gabes, southern Tunisia). This penaeid species was observed in 24 samples landed in Sfax harbour (Southern East of Tunisia). A full description of the species is given with illustrations.

This review reports shell morphometric relationships (height/length and width/length) for the most common and abundant bivalve species found in coastal areas of the Gulf of Gabes (southern Tunisia). Systematic surveys were carried out from May 2012 to August 2014 using quadrants (0.25 m^) and shovels, on soft bottoms in the littoral zone down to 1 m depth. For this particular study, a total of 7641 bivalves were sampled, belonging to 12 species distributed in 8 Families. Almost all regressions (79.2%) were highly significant (P < 0.001), the exceptions being the H/L relationships for four bivalve species (16.6%, p > 0.05) and the W/L relationship for Venerupis decussata (4.2%, 0.01 < P < 0.05). In addition, the results revealed that the shell morphometric relationships indicated negative allometries (H/L = 9 species; W/L = 3 species), positive allometries (W/L = 7 species) and isometries (H/L = 3 species; W/L = 2 species). Data were compared with some morphometric relationships available for the same species in other geographical areas and several ecological hypotheses or explanations were formulated for the distinct types of growth exhibited by different bivalve species. Data here present are essential for management and conservation for these flagship species.

Venerupis decussata represents one of the most common marine mollusc species present in soft bottom infralittoral assemblages in southern Tunisian waters. It is a Mediterranean autochthonous species that in Tunisia is heavily harvested from natural populations. This bivalve represents an important economic issue, especially in terms of employment and the trade balances of the country via its exportation. The status of this species is still poorly known and there is a knowledge gap about its abundance. The present work aimed to investigate the stock assessment, the population structure and to give some biological parameters of V. decussata along the Gabes coastal area. The main results showed a scattered distribution pattern of the species according to location ranging between 0 and 26.6 ind.m -2. A remarkable stock was estimated to be 2405 tons (total fresh weight), with a mean biomass around 52.5 g.m -2 and a total abundance reaching an estimated 908.8 million individuals in the investigated area of 4577 hectares. Shell length of sampled individuals ranged from 4.2 to 41.65 mm, and median size varied by location. The overall sex ratio (F:M) was significantly different from parity (F:M = 1:1.17, χ]-test, P < 0.001). Males were found to mature between 22 and 27 mm shell length (SL), whereas females matured between 22 and 28 mm SL. The size at which 50% of the population reached maturity was 24.08 and 24.76 mm SL for males and females, respectively. Overall, V. decussata proliferates in some portions of the study area.

The striped sea bream Lithognathus mormyrus (Linnaeus, 1758) is a commercially valuable sparid fish frequently caught and landed off the Gulf of Gabes (southern coasts of Tunisia). Age, growth and reproductive aspects of the southeastern Tunisian population were estimated by analyzing 1221 specimens ranging in total length (TL) from 9.7 to 24.1 cm. Ages were estimated by counting growth bands on otoliths and verified by marginal increment analysis, with specimens ranging in age from 1 to 8 years. The von Bertalanffy growth function was selected as the most adequate model to fit this species' growth, with the estimated parameters being L∞ = 31.22 cm TL, k = 0.112 year-1 and t0 = -2.307 years. Gonads were analyzed macroscopically over a one-year period and the spawning season found to occur from September to November. The length at first maturity for males occurs at 13.99 cm TL and 3.4 years while females mature at slightly larger size (14.32 cm TL) and earlier age (3.1 years). The results presented in this study purpose to fill the gaps in knowledge concerning aspects of population dynamics, namely age and growth and reproduction of striped seabream in the Gulf of Gabes.

The stomach contents of 622 little tunny Euthynnus alletteratus, sampled between January 2008 and December 2009, were examined. Fish size ranged from 19.2 to 97.8 cm fork length, and all fish were captured in the coastal areas of Tunisian waters. Among 622 stomachs examined, 287 were empty (%VI = 46.14). There were no significant variations in the vacuity index (%VI) depending on sex. After the stomach contents analysis, 22 prey taxa belonging to 14 families were identified: 15 fish species, 3 crustaceans, 3 mollusks and 1 vegetal species (Posidonia oceanica). This study was based mainly on the evolution of the index of relative importance (IRI) with respect to sex, fish size and season. Little tunny are carnivorous fish that feed opportunistically. Teleosts were found in the majority of stomachs, with a total relative importance (%IRI) of 97.3% and Sardinella aurita was the most important prey species (%IRI = 17.56) followed by Boops boops (%IRI = 0.87) and Sardina pilchardus (%IRI = 0.77). All other prey (crustaceans and molluscs) are secondary or incidental.

Morphometric and meristic characters of the two carangid species, C. crysos and C. rhonchus were studied from Gulf of Gabes, Tunisia, Eastern Mediterranean. Monthly samples of the two species were collected during one year for this study. Eleven morphometric (in percentage of total fish length) and seven meristic characters have been studied. No significant differences were observed between male and female fish. Negative allometric growth of morphometric characters of C. crysos and C. rhonchus were observed.

Le présent travail se propose d’expliquer les stratégies reproductrices adoptées par la dorade coryphène Coryphaena hippurus Linnaeus, 1758, sur la base de données biométriques combinées à l’étude des structures microscopiques ovariennes et testiculaires faites sur des échantillons cumulés sur deux années, et à un suivi périodique et régulier des débarquements. La dorade coryphène est un poisson gonochorique dont le développement ovocytaire est du type asynchrone, puisqu’en période de reproduction la structure ovarienne est quadrimodale avec la présence simultanée de tous les types d’ovocytes : primordiaux, prévitellogéniques, vitellogéniques et ovules. Confirmé par l’évolution de l’indice gonadosomatique et la biométrie ovarienne, ce constat permet de conclure que cette espèce se reproduit bien dans les eaux tunisiennes et qu’elle se caractérise par des pontes répétées et étalées dans le temps, de mai à septembre.

Les contenus stomacaux de 178 individus de Coryphaena hippurus, de longueur à la fourche (LF) comprise entre 18 et 82 cm et de poids individuel compris entre 71 et 5 880 g, pêchés sur les côtes tunisiennes entre juillet et décembre 2010, ont été analysés. Cette espèce pélagique, prédatrice et opportuniste, se nourrit de téléostéens comme proies préférentielles et de crustacés comme proies secondaires ou accessoires. Les juvéniles (< 25 cm LF) s’alimentent d’espèces exclusivement pélagiques, Clupeidae et engraulidae, alors que les moins jeunes (25-50 cm LF) se nourrissent d’espèces épipélagiques, Scombridae et Belonidae. Les espèces benthiques, sparidae, Congridae, Mugilidae et dactylopteridae, sont les proies des sub-adultes (> 50 cm LF). Les crustacés sont représentés essentiellement par les Amphipodes (Hyperiidae) chez les juvéniles de moins de 25 cm LF, par les euphausiacés pour la classe de taille 25-50 cm LF et par les décapodes pour les individus de plus de 50 cm LF. La présence de proies typiquement benthiques, tel que le céphalopode Sepia officinalis, montre les grandes performances de chasse et l’opportunisme de la dorade coryphène, qui est donc capable d’aller chercher ses proies sur les fonds marins.

The spider crab Maja squinado (Herbst, 1788) is an endangered Mediterranean species. Here, we characterized the reproductive biology of M. squinado, from the Gulf of Gabés, since no information on its reproductive parameters in Tunisian waters has been assessed previously. Sex ratio, reproductive cycle and size at first sexual maturity were studied in 770 individuals (292 females and 478 males) caught monthly in shallow and deep waters. The overall samples presented a carapace length (CL) ranging between 22.5 and 87 mm (62.07% males and 37.92% females). Proportions of both sexes varied depending on size and season, the majority of individuals ≤ 52 mm CL were females and the males were predominant in spring and winter. The size at which 50% of the population reached maturity was 52.17 ± 0.79 and 54.31 ± 0.45 mm CL for females and males, respectively. Monthly changes in the gonadosomatic and hepatosomatic indices and seasonal changes in microscopic characteristics of the gonads of both sexes showed that the reproductive activity was greatest in autumn and winter with a peak in November. M. squinado exhibited a short resting phase that occurred simultaneously in females and males from April to September.