Distribución y abundancia de los primeros estadios de desarrollo de Sardina pilchardus en el golfo de Túnez (Mediterráneo central) en relación con los factores ambientales

Four seasonal surveys were carried out in the Gulf of Tunis between summer 2002 and spring 2003 to study the abundance and distribution of Sardina pilchardus eggs and larvae in relation to environmental parameters. In the Gulf of Tunis, Sardina pilchardus begins spawning in autumn (23 eggs/10 m²) and attains its peak in winter (257 eggs/10 m²) when the mean SST is lowest (13.4°C). Sardine reproduction seems to be triggered by the decrease in the SST. In winter, the main spawning areas were located to the south of Zembra Island and the north of Cape Bon. Larvae were more abundant in winter (38 larvae/10 m²), while lower densities were collected in autumn and spring (1 larva/10 m²). The highest abundance of larvae (288 larvae/10 m²) was recorded southwest of Zembra Island. Eggs and larvae were mainly concentrated in the relatively warmer and saltier waters with high zooplankton abundance and, inversely, with a low concentration of nitrate and chlorophyll a and a low diatom abundance.Se llevaron a cabo cuatro campañas en el golfo de Túnez, entre verano del 2002 y primavera del 2003, con el objetivo de estudiar la abundancia y distribución de los huevos y larvas de Sardina pilchardus en relación con parámetros ambientales. En el golfo de Túnez Sardina pilchardus inicia la freza en otoño (23 huevos/10 m²), alcanzando el pico de puesta en invierno (257 huevos/10 m²), cuando la temperatura superficial media (SST) es mínima (13.4°C). La reproducción de la sardina se dispara al parecer por el descenso de la SST. En invierno, las principales áreas de puesta se localizaron al sur de la isla de Zembra y en el norte del Cabo Bon. Las larvas fueron más abundantes en invierno (38 larvas/10 m²); mientras que se recogieron menores densidades en otoño y primavera (1 larva/10 m²). La mayor abundancia larvaria (288 larvas/10 m²) fue observada en el suroeste de la isla de Zembra. Los huevos y larvas se concentraron principalmente en las aguas relativamente más cálidas y salinas, con altas abundancias de zooplancton, e inversamente bajas concentraciones de nitrato, clorofila a y abundancia de diatomeas

Áreas de puesta y distribución larvaria de anchoa Engraulis encrasicolus en relación con las condiciones ambientales en el Golfo de Túnez (Mediterráneo Central)

Early life stages of anchovy were investigated in the Gulf of Tunis by means of four seasonal surveys carried out from summer 2002 to spring 2003. Anchovy eggs and larvae were found all year round, but they were much more abundant in spring and summer. In spring, the main spawning area was located in the north of the Gulf, to the west and southwest of Zembra Island. In summer, higher egg and larva abundances were also observed to the southwest of Zembra Island, but secondary spawning grounds were detected in the vicinity of the mouths of the Rivers Majreda and Meliane. No direct correlations between sea surface temperature (SST), salinity (SSS) and chlorophyll a and the horizontal distribution of eggs and larvae were observed. However, egg distributions in all seasons and larval distributions in summer and autumn were significantly related to depth. The temporal variation of temperature seems to control the spawning intensity and the beginning of spawning seems to be triggered by the increase in SST.Se estudiaron los huevos y larvas de anchoa en el Golfo de Túnez por medio de cuatro campañas estacionales llevadas a cabo entre verano del 2002 y primavera del 2003. Los huevos y larvas de anchoa se encontraron a lo largo de todo el año; pero fueron mucho más abundantes en primavera y verano. En primavera, la principal área de puesta se localizó en el norte del Golfo, al oeste y suroeste de la isla de Zembra. En verano, las mayores concentraciones de huevos y larvas también se encontraron en el suroeste de la isla de Zembra; pero se detectaron áreas de puesta secundarias cerca de las desembocaduras de los ríos Majreda y Meliane. No se encontraron correlaciones directas entre la temperatura superficial (SST), la salinidad (SSS) y la clorofila a y la distribución horizontal de huevos y larvas de anchoa. Sin embargo, la distribución de huevos, durante todo el año, y las distribuciones larvarias, en verano y otoño, se relacionaron de forma significativa con la profundidad. La variación temporal de la temperatura parece controlar la intensidad de la puesta y el inicio de la freza parece dispararse por el incremento de la SST

Linking surface hydrodynamics to planktonic ecosystem: the case study of the ichthyoplanktonic assemblages in the Central Mediterranean Sea

Oceanographic processes play a key role in influencing the structure of the marine planktonic ecosystems. Taking advantage of the quasi-simulta-neous collection of a large ichthyoplanktonic dataset in different regions of the Central Mediterranean Sea (Italian/Maltese, Tunisian and Libyan waters), this study aimed at the identification of the main environ-mental drivers that control the structure of the larval fish assemblages. Spatial distribution and taxa com-position were related to physical forcings (geostrophic currents and wind stress) and environmental condi-tions (bottom depth, temperature, salinity, chlorophyll-a concentration). ANOSIM and SIMPER identified contribution of fish taxa to the average Bray–Curtis dissimilarity among regions. In Italian and Libyan waters, two assemblages (neritic and oceanic) were identified, while a mixed assemblage characterized only some stations. Two neritic and one oceanic assemblages were discriminated in Tunisian waters. Random Forest classification model high-lighted the essential role of the bathymetry, while Lagrangian simulations evidenced the action of the hydrodynamics in mixing neritic and oceanic assem-blages in the Italian/Maltese and partially in Libyan waters. These findings highlighted the importance of the multidisciplinary approach and shed light on the potential value of the ichthyoplanktonic surveys for the assessment of the state of the marine ecosystem and the conservation of the fishery resources

Neki biološki parametri trlje blatarice Mullus barbatus L., 1758, u tuniskom zaljevu

The red mullet, Mullus barbatus L. 1758 is one of the main target species of the trawl fishing industry along the continental shelf off the Tunisian Gulf. The reproductive biology of this species has been studied based on statistical sampling conducted between February 2003 and January 2004. Length frequency distribution according to sex revealed that the females were highly represantative in the majority of size classes. Monthly variations in the gonadosomatic index (GSI) showed that males spawn from April to July, whereas the reproductive activity of the females occurs in the late spring and summer (May and July). The estimated lengths at maturity (Lm50) were 13.87 cm for males and 13.94 cm for females. According to the length-weight relationship, positive allometry was confirmed for males, females and pooled sexes.Trlja blatarica, Mullus barbatus L. 1758 je jedna od najvažnijih komercijalnih vrsta koćarskog ribarenja duž obale tuniskog zaljeva. Reprodukcija ove vrste je istraživana na ulovljenim primjercima tijekom uzorkovanja od veljače 2003. do siječnja 2004. Ustanovljena učestalost prema duljini i spolu ukazuje da su ženke rasprostranjenije i u većini u svim razredima. Mjesečna kolebanja gonadosomatskog indeksa (GSI) pokazuju da se mužjaci mrijeste od travnja do srpnja, dok su ženke reproduktivno aktivne u kasno proljeće i ljeto (svibanj, lipanj i srpanj). Duljina pri spolnoj zrelosti (Lm50) iznosila je 13.87 cm za mužjake i 13.94 cm za ženke. Prema duljinsko-masenom odnosu, pozitivna alometrija je ustanovljena za mužjake, ženke i ukupni uzorak

Engraulis encrasicolus (Linnaeus, 1758)egg and larval distribution in the eastern coast of Tunisia in relation to environmental characteristics

An ichthyoplankton survey was conducted on the eastern coast of Tunisia from the 10th to 18th August 2004 with the investigation of 68 stations. The sampling period corresponded to stratified summer conditions, with average SST 26.97°C. The thermocline was found between 25 and 50 m depth. The eastern coast of Tunisia was influenced by the water exchanges between the eastern and western Mediterranean. Anchovy eggs and larvae were a major component of the ichthyoplankton, representing 26 and 19% of the total mean fish egg and larval abundances, respectively. Their mean abundances were 108 eggs.10 m-2 and 112 larvae.10 m-2. The spawning areas were mainly located off the 100 m isobaths, with the maximum abundance occurring near the shelf break, as opposed to the inshore waters where anchovy eggs and larvae were practically absent. Depth was the main factor controlling the distribution of anchovy eggs and larvae. Larval transport from the spawning areas is made evident following southward to south-eastward directionsPublicado

Larval fish community composition and distribution of the central-southern Mediterranean under summer and winter conditions

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

Distribution of tuna larvae in Tunisian east coasts and its environmental scenario

Early life stages of tuna species were investigated along the Tunisian east coast during the summer of 2008 by means of a larval survey conducted on board the R/V HANNIBAL. In this study we define the spawning grounds of tuna fishes in Tunisian waters and relate the tuna larvae spatial distribution to the hydrographic features and other environmental parameters. A total of 282 larvae of Atlantic bluefin tuna (Thunnus thynnus, Linnaeus, 1758), 902 of bullet tuna (Auxis rochei, Risso, 1810) and 19 of little tuna (Euthynnus alletteratus, Raf, 1810), were identified. High larval concentrations of bluefin tuna were located offshore (mean = 200 ± 18 m), at sea surface temperatures ranging between 23.7 to 25.3°C, whereas the highest concentrations of bullet and little tuna were located in shallower waters (mean = 135 ± 75 m), at sea surface temperature ranging between 25.1 to 25.9°C. According to their preference for waters with surface salinities ranging between 37.1 and 37.8, spawning of these species seems to occur mainly in mixed waters. Stations where tuna larvae were collected showed oxygen concentrations between 6.55 and 6.85 mg l-1, as well as low turbidity and chlorophyll a values, from 0.2 to 0.5 NTU a d less than 1 mg m-3, respectively. These three environmental factors were weakly correlated with tuna larvae abundancePublicado

Influence of summer conditions on the larval fish assemblage in the eastern coast of Tunisia (Ionian Sea, Southern Mediterranean)

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