Microchemical analyses were carried out in order to estimate the Strontium:Calcium (Sr:Ca) ratio in the otolith of the white mullet, Mugil curema, in the Pernambuco (at the Santa Cruz channel, Brazil) in order to determine its connectivity between the estuary and ocean. Variation in the otolith Sr:Ca ratio was directly related to salinity, with greater salinity denoting a higher otolith Sr:Ca value. Data on the otolith Sr:Ca ratio demonstrates that the individuals analyzed are born in areas of salinity that are characteristic of the estuary, where they develop until approximately one year of age, at which point they migrate to areas of greater salinity until reaching sexual maturity (3 years of age) in the sea. Spawning occurs in the ocean, after which M. curema individuals may either remain or return to the estuary until the next spawning. Differences in estuarine salinity were found for young-of-year individuals and may be related to the season when spawning took place, since M. curema females are found spawning throughout the year. The hypothesis is that higher salinity in the dry season leads to a greater otolith Sr:Ca signature among individuals spawned in this season from birth until one year of life. On the other hand, the lower salinity in the rainy season leads to a lower otolith Sr:Ca signature among individuals spawned in this season. These information are important for the adequate management of the white mullet stock in northeastern Brazil.

*Corresponding author: Dr. Kadri Hasna, Laboratory of Biodiversity and Biotechnology of the Sea. National Institute of Science and Technology of the Sea of Sfax (Tunisia).National Institute of Science and Technology of the Sea, Sfax, B.P. 1035, Sfax 3018. Tunisia. Tel: +21697058272 E-mail: hasnakadri@yahoo.fr Foundation Project: Supported by the National Institute of Science and Technology of the Sea of Sfax (Tunisia).

The Age, growth, mortality, longevity and reproductive parameters were studied for Rostroraja alba from the Gulf of Gabes (Southern Tunisia, central Mediterranean Sea), collected monthly during 2007 from commercial fisheries. 43.75% of the composition was females and 56.25% males. A total of 140 females (44.5 - 160 cm TL) and 180 males (39.5 - 150 cm TL) were examined to study the reproductive cycle. A subsample of 115 specimens (65 females and 50 males, ranging from 39.5 to 160 cm TL) was used for age and growth estimation derived from vertebral centra. The oldest female was 35 years and 160 cm TL, whereas the oldest male was 32 years and 150 cm TL. The von Bertalanffy growth parameters were L∞= 177.6±3.61 cm, k= 0.06 ±3.08 year-1 and t0= -1.28±1.97 10-1 year for females and L∞= 199.6±3.66 cm, k= 0.04± 1.9610-3 year-1 and t0= -1.47±0.35 10-1 year for males. Growth was not significantly different between sexes. The maturity size (TL 50%) was 119.3 cm (94.20 cm DW) for males and 129.4 cm (95.77 cm DW) for females. The maturity age (A50%) was estimated to 19.69 and 23.47 years respectively for males and females. Size and age maturity were not significantly different between sexes.

The age, growth, longevity, mortality and reproductive parameters were estimated for Dipturus oxyrinchus from the Gulf of Gabès (Southern Tunisia, central Mediterranean Sea), collected monthly during 2007 from commercial fisheries. The present study provides the first data on age and growth of this species in Tunisian waters, as well as additional data on its reproduction. A total of 240 females (16.5–105 cm total length (TL)) and 280 males (15.5–95 cm TL) were examined to study the reproductive cycle. A subsample of 285 specimens (175 females and 110 males, ranging from 15.5 to 105 cm TL) were analysed to study the age and growth. The oldest female in this study was 25 yr and 105 cm TL, whereas the oldest male was 22 yr and 95 cm. The annual deposition of growth bands was verified by marginal increment and edge analysis. The von Bertalanffy growth parameters were L∞ = 123.9 ± 2.56 cm, K = 0.08 ± 0.004 yr−1 and t0 = −1.26 ± 0.04 10−1 yr for females and L∞ = 102.1 ± 3.23 cm, K = 0.12 ± 0.007 10−3 yr−1 and t0 = −1.18 ± 0.03 10−1 yr for males. Growth was not significantly different between sexes. The maturity size was 72.05 cm for males and 82.1 cm for females. The maturity age was estimated to be 11.95 and 13.96 years, respectively, for males and females. Size and age at maturity were not significantly different between sexes. The estimated longevity was 26.18 and 38.84 yr for males and females, respectively. Based on life history parameters, natural mortality was estimated at 0.53 yr−1 for females and 0.41 yr−1 for males.

Sardina pilchardus and Engraulis encrasicolus are of great economic importance in Tunisia. However, little is known about their stock structure. Otolith chemistry was used to assess the feasibility of using this natural tag to discriminate populations of sardine and anchovy in the open sea and the coastal area of the Gulf of Gabes. The chemical composition of whole otoliths was analyzed using solution-based inductively coupled plasma mass spectrometry (ICPMS). Linear discriminant analysis classified fish into open sea and inshore groups with close to 97% accuracy for the anchovy and to 94% for the sardine. Respectively, the discrimination was based on P, Fe, Zn, Sc and Sr for the anchovy and P, Sr and B for the sardine. In addition, when we pool together the two species data in each area (inshore/open sea), the discrimination was also accurate reaching 88% of well classification based on P, Fe, Li and Mg. The results reveal a clear discreteness of the open sea and inshore small pelagic groups. Such information will have major implications for fisheries management of sardine and anchovy in Tunisia.

Age estimates, typically determined by counting periodic growth increments in calcified structures of vertebrates, are the basis of population dynamics models used for managing exploited or threatened species. In fisheries research, the use of otolith growth rings as an indicator of fish age has increased considerably in recent decades. However, otolith readings include various sources of uncertainty. Current ageing methods, which converts an average count of rings into age, only provide periodic age estimates in which the range of uncertainty is fully ignored. In this study, we describe a hierarchical model for estimating individual ages from repeated otolith readings. The model was developed within a Bayesian framework to explicitly represent the sources of uncertainty associated with age estimation, to allow for individual variations and to include knowledge on parameters from expertise. The performance of the proposed model was examined through simulations, and then it was coupled to a two-stanza somatic growth model to evaluate the impact of the age estimation method on the age composition of commercial fisheries catches. We illustrate our approach using the saggital otoliths of yellowfin tuna of the Indian Ocean collected through large-scale mark-recapture experiments. The simulation performance suggested that the ageing error model was able to estimate the ageing biases and provide accurate age estimates, regardless of the age of the fish. Coupled with the growth model, this approach appeared suitable for modeling the growth of Indian Ocean yellowfin and is consistent with findings of previous studies. The simulations showed that the choice of the ageing method can strongly affect growth estimates with subsequent implications for age-structured data used as inputs for population models. Finally, our modeling approach revealed particularly useful to reflect uncertainty around age estimates into the process of growth estimation and it can be applied to any study relying on age estimation.

Abstract The thornback ray Raja clavata is one of the most abundant bycatch species of trawl fishing in the waters of the Gulf of Gabès, but little is known about its life history in this area. The present study provides the first data on age and growth of this species in Tunisian waters, as well as additional data on its reproduction. The age of individuals was estimated by counting growth bands on central vertebral sections. Marginal increment and edge analysis supported the hypothesis of annual deposition of growth bands, with the opaque band formed during autumn. The parameters estimated from von Bertalanffy and Gompertz growth functions showed differences between sexes. The oldest thornback ray female was aged 15 years (104 cm TL), whereas the oldest male was 12 years (89 cm TL). Variations in the gonadosomatic and hepatosomatic indices of both sexes and the presence of vitellogenic activity in mature females during the year indicated that the species cannot be considered to be a continuous spawner. Males were found to mature between 55 and 75 cm TL, whereas females matured between 72.4 and 85 cm TL. The TL at which 50% of the population reached maturity was 67.44 and 81.42 cm for males and females, respectively. Males and female thornback rays mature, respectively, at approximately 5.3 and 7 years old.

This paper studies the age and the growth of male and female of the Tunisian blue mackerel Scomber scombrus during 2004–2006. The age was determined by interpreting and counting daily increments on the otoliths sagitta of 320 individuals sampled from landings caught by different gears specially by purse seine. The parameters of the Von Bertalanffy growth curve were estimated for sexes combined: Lf = 31.46(1 − e−0.228 (t+3.034)) (L∞ = 31.46 cm, k = 0.228 per year, t0 = −3.034 years); for male Lf = 27.43(1 − e−0.422 (t+1.747)) (L∞ = 27.43 cm, k = 0.422 per year, t0 = −1.747 years) and for female Lf = 31.70(1 − e−0.227 (t+2.196)) (L∞ = 31.70 cm, k = 0.227 per year, t0 = −2.916 years) for the whole study period. The difference between the growth of male and female is not significant. The relationship between length and weight shows a length growth faster than of the weight with parameters of the equation Wt = a*Lb; a = 9.89*10−5 and b = 2.37 for the sexes combined.

Age and growth of the brown ray, Raja miraletus, was estimated from ring counts on vertebral sections from 95 females (13.5-56.0 cm total length (TL)) and 85 males (13.5-58.0 cm TL) collected from the Gulf of Gabes (Central Mediterranean, Tunisia) during 2007. Marginal increment and edge analyses suggest annual band pair formation. The oldest female and male brown rays were 9 and 7 years old, respectively. Von Bertalanffy growth parameters are L8 = 69.20 cm TL, k = 0.18 year(-1) and t(0) = -0.11 years for females, and L8 = 67 cm TL, k = 0.22 year(-1) and t(0) = -1.01 years for males. Longevity estimates were 19.25 and 15.75 years for females and males, respectively. Based on life history parameters, natural mortality estimation M was in the range 0.37-0.47 for females and 0.60-0.61 for males. Males were found to mature between 28 and 43 cm TL and L-50% was estimated at 34.31 cm TL (21.91 cm DW). Females mature between 33 and 48 cm TL and reached L-50% at 41.8 cm (27.10 cm DW). Age at sexual maturity (A(50%)) was estimated at 2.7 years for males and 4.41 years for females. Females and males have an annual reproductive cycle. Mating occurred mostly through spring and summer.

Age, growth, longevity, natural mortality and size and age at maturity of the longnose spurdog, Squalus blainvillei, in the Gulf of Gabes (Tunisia, Central Mediterranean Sea) are reported. Marginal increment suggested annual band formation. Age estimates ranged from 3 to 15 and 4 to 19 years for males and females, respectively. Von Bertalanffy growth parameters derived from length at age data were: L-infinity = 105.7 cm, K = 0.11year(-1), t(0) = -1.12 year for females and L-infinity = 91.1 cm, K = 0.14 year(-1), t(0) = -1.42 year for males. Males and females reached maturity at 52.3 cm and 62.5 cm TL corresponding to 4.97 and 7.44 years, respectively. Longevity estimates were 24.75 and 31.50 years for males and females, respectively. Based on life history parameters, natural mortality estimation M ranged from 0.16 to 0.33.

Age and growth studies on the white mullet Mugil curema present (Valenciennes, 1836) dissimilarities with regard to the parameters estimated. It is therefore necessary to undertake a growth analysis based on micro- and macrostructures of otoliths from the species in order to reveal the cause of such dissimilarities. Microstructures were validated through otolith marking by balneation in alizarine complexone and demonstrated daily periodicity. Daily microstructures were observed in individuals up to 15.7 cm in fork length and exhibited 5 distinct growth zones. Zones I, II and III (62 d) composed the first macrostructure and Zone IV (223 d) composed the second. It was not possible to see microstructures in Zone V and, beginning with this zone, macrostructures were considered annual, based on the analysis of mean monthly marginal increments. Using daily microstructures and annual macrostructures, the von Bertalanffy function provided the following parameters: L∞ = 34.4 cm, K = 0.365 and t0 = 0.311 yr. The following factors caused the dissimilarities between curves for white mullet: (1) absence of samples for ages 0+ and 1 yr, which caused a high value of mean lengths for these age classes and a diminished K-value; (2) the tendency toward overestimation at the age of 1 yr when estimated from macrostructures; (3) identification of the first 2 macrostructures as annual; and (4) absence of young-of-the-year specimens, causing t0 to be significantly different from 0. These factors lead to the underestimation of the parameters, which makes growth estimates imprecise.

Pomadasys argenteus (Forsskal, 1775) est une espece d'interet majeur pour la peche commerciale et de subsistance sur l'ensemble de son aire de repartition (Afrique de l'Est a Fidji), mais peu d'information est disponible actuellement sur sa biologie et ecologie. Notre etude porte sur les principaux traits biologiques et ecologiques de cette espece en Nouvelle Caledonie, sur la marge est de son aire de repartition. Cette espece a ete observee surtout en mangrove et a moindre degre sur les fonds meubles adjacents. La plupart des poissons ont ete trouves dans peu d'eau (< 5 m), la capture la plus profonde ayant eu lieu par 28m. L'abondance a varie au sein des habitats au cours de l'annee, les poissons devenant plus abondants sur les fonds meubles durant la reproduction entre Juillet et Decembre. Le plus grand poisson mesurait 42 cm (LF) et pesait 1150 g. Les femelles etaient plus abondantes (73% des echantillons sexes) et plus grandes que les mâles, ces derniers n'excedant pas 34 cm LF. Les deux sexes deviennent mâtures a la meme taille (16-18 cm). Une proportion plus importante de femelles a ete observee dans les mangroves comparees aux fonds meubles. La proportion de mâles et de femelles mâtures etait cependant similaire dans les deux habitats. Les aliments etaient peu diversifies, se composant surtout de crabes et de facon moindre de crevettes, bivalves et annelides. Les relations longueur-poids varient en fonction du sexe, les mâles etant plus lourds que les femelles a taille egale. La croissance a ete estimee en analysant les accroissements journaliers et saisonniers des otolithes. Ces methodes ont ete validees par un ensemble de methodes. Une courbe de croissance asymptotique a ete ajustee aux donnees: Taille (mm LF) = 420 * (1―e -0.346*(âge-0.161) ), ou l'âge est donne en annees. La croissance est plus lente que dans la plupart des autres etudes disponibles, sauf au Koweit. Aucune difference de croissance entre les sexes n'a pu etre decelee.

The adaptive mechanisms on the early life stages of fishes to hypersaline stress are still poorly understood and probably determine the resistance of a population to disruption, compared with other less plastic species. The Casamance River in Senegal is an ideal location to test the adaptation to salinity as a dam was built in 1998 to exclude saline water intrusion. This lowered the salinity from 70 to 5 upstream and 60 downstream. The salinity influence on the growth in the early life of three West African fish species (Ethmalosa fimbriata, Sarotherodon melanotheron, and Tilapia guineensis) was studied using the width of microstructures in the otoliths and the individual migratory behaviour analysed from strontium (Sr) to calcium (Ca) ratios in the otoliths. The Sr:Ca ratio was quantified along individual transects measured from the posterior edge of the otolith to the core. The fishes were sampled on both sides of the dam that separated water with low salinity upstream from metahaline and hyperhaline water downstream.The results showed that salinity has different influence on the growth of each species. Ethmalosa fimbriata has the highest growth during the first 180 days in the freshwaters, indicating growth inhibition in the hyperhaline areas. For the two other species no growth difference were found. The Sr/Ca ratio varied widely, in Tilapia and Sarotherodon from below the dam. Individual life histories were more heterogeneous than upstream and showed a crossing of the dam for some individuals which could reach half of the fishes analysed. On the contrary in E. fimbriata, despite the large range of salinity, identical Sr/Ca profiles were found both upstream and downstream. This indicated that Sr/Ca ratio was not appropriate to evaluate life history patterns linked to salinity for this specie. (C) 2009 Elsevier Ltd. All rights reserved.

The shape of sagittal otoliths from the dolphin fish (Coryphaena hippurus) was studied to test the hypothesis that two stocks exist off the northeast coast of Brazil. In all, 82 sagittal otoliths were collected from fish caught by the artisanal fleet in two coastal regions of northeastern Brazil in December 2003 and April/May 2004. Several shape descriptors were determined [area, perimeter, rectangularity, circularity, eccentricity, fractal dimension (FD), and Fourier coefficients (FCs)] to evaluate the degree of similarity in the otoliths between regions. A three-morphotype pattern was revealed through cluster and principal component analyses based on FCs of the 30th harmonics. Apparently, this pattern is not influenced by clinal factors. Despite the great variability between otolith shapes, separation of the samples from two regions was suggested using multivariate and univariate analyses of variance for all shape descriptors and using canonical discriminant analysis. The methods successfully classified 57.1 and 69.6% of otoliths from the Maranhao and Rio Grande do Norte regions, respectively. The FD was a powerful descriptor in discriminating the two stocks. Differences in the shapes of sagittal otoliths may be related to different growth rates of the species and lend credence to the belief that there are two stocks along the Brazilian coast.

We investigated the oxygen isotope composition (δ18O) of shell striae from juvenile Comptopallium radula (Mollusca; Pectinidae) specimens collected live in New Caledonia. Bottom-water temperature and salinity were monitored in-situ throughout the study period. External shell striae form with a 2-day periodicity in this scallop, making it possible to estimate the date of precipitation for each calcite sample collected along a growth transect. The oxygen isotope composition of shell calcite (δ18Oshell calcite) measured at almost weekly resolution on calcite accreted between August 2002 and July 2003 accurately tracks bottom-water temperatures. A new empirical paleotemperature equation for this scallop species relates temperature and δ18Oshell calcite:t(°C)=20.00(±0.61)-3.66(±0.39)×(δ18Oshell calcite VPDB-δ18Owater VSMOW)The mean absolute accuracy of temperature estimated using this equation is 1.0 °C at temperatures between 20 and 30 °C. Uncertainties regarding the precise timing of CaCO3 deposition and the actual variations in δ18Owater at our study sites probably contribute to this error. Comparison with a previously published empirical paleotemperature equation indicates that C. radula calcite is enriched in 18O by ∼0.7‰ relative to equilibrium. Given the direction of this offset and the lack of correlation between shell growth rate and δ18Oshell calcite, this disequilibrium is unlikely to be related to kinetic isotope effects. We suggest that this enrichment reflects (1) a relatively low pH in the scallop's marginal extrapallial fluid (EPF), (2) an isotopic signature of the EPF different from that of seawater, or (3) Rayleigh fractionation during the biocalcification process. Relative changes in δ18Oshell calcite reflect seawater temperature variability at this location and we suggest that the shell of C. radula may be useful as an archive of past seawater temperatures.

The periodicity of striae formation in the tropical scallop Comptopallium radula (Indo-West Pacific Ocean) was investigated with an in situ marking technique, using the calcein fluorochrome. To minimize scallop stress caused by excessive handling, in situ benthic chambers were used for marking experiments. Once marked, scallops (shell height range: 38.4–75.8 mm) remained on site in a large benthic enclosure and were collected at regular time intervals to count new striae formed after marking, over a period of 3 months. A 3-h exposure period with calcein (150 mg l −1 ) was sufficiently long to create a detectable mark in nearly all shells. It was, however, impossible to count the striae in 48.2% of the shells (mainly large specimens) because of a very small growth after marking. Lack of significant mortality during the experiments indicated that tested calcein concentrations were not lethal. A decrease in shell growth rate was observed after marking but the respective impacts of calcein toxicity and changes in environmental conditions could not be discriminated. Our results suggest that in situ calcein marking inside benthic chambers is suitable for shell growth studies of scallops, provided the latter are not too old. After marking, the juvenile C. radula formed an average of one stria every 2.1 days in summer. Reports of 2-day periodicity in biological rhythms are rare. Striae formation in C. radula may be controlled by an endogenous oscillator, synchronized by an environmental cue acting as a zeitgeber, such as seawater temperature or sea level pressure, both of which exhibit 2-day variations in the Pacific Ocean. As in many other scallop species, C. radula forms striae periodically under natural conditions, but this study shows that in pectinid juveniles, this periodicity can deviate from a daily cycle. These results suggest that C. radula shells have tremendous potential for recording environmental conditions during periods ranging from months to a few years and with a resolution of 2 days.