Age determination and growth of leaping mullet, (Liza saliens R.1810) from the Messolonghi Etoliko lagoon (western Greece)

This study is the first detailed work on the age and growth of the leaping mullet (Liza saliens, Risso 1810) in the central Mediterranean. During the period 1991-1995 the age and growth of leaping mullet from the Messolonghi -Etoliko lagoon system (western Greek coast) were studied. Age and growth determinations were based upon otolith samples taken from 537 fish. Marginal increment analysis was used to validate age determination. Annulus formation took place around November each year. The back-calculated lengths at age estimated from the otoliths showed no differences between sub-areas of the lagoon system and the recorded limited between-years variability showed no persistent temporal pattern. The maximum age of leaping mullet in the Messolonghi - Etoliko lagoon was 5 years for males and 6 years for females. The von Bertalanffy equation (L‡=32.99±1.25 cm, k=0.258 ±0.017 year-1, t0=-0.47±0.04 year) accurately describes the growth of the total length of leaping grey mullet for all life stages (fry, juveniles and adults). A large spread and length overlap characterized the age groups. The estimated Length-Weight relationships were common for the two sexes (W=0.0079L3.01)

Ovarian allometry and the use of the gonosomatic index: a case study in the Mediterranean sardine, Sardina pilchardus.

Abstract The gonosomatic or gonadosomatic index [GSI=(ovary weight/fish weight)·100] has been widely used in fisheries science and experimental reproductive studies as a simple, low-cost measure of reproductive condition. However, its properties have not been fully evaluated, and several pitfalls, such as size-dependence and changes in ovarian allometry, may invalidate its use. In the present study, we examined ovarian allometry and the appropriateness of GSI for assessing ovarian activity in the Mediterranean sardine Sardina pilchardus. The analysis was based on a large sample of histologically scored females collected over an annual cycle in the eastern Mediterranean (Aegean and Ionian Seas). First, we examined GSI dependence on fish size by comparing ovary weight-on-fish weight relationships in different stages of oocyte development. The effects of recent spawning (incidence of postovulatory follicles) and intensity of follicular atresia were also addressed. In a subsequent step of the analysis, we applied generalized linear models (GLMs) to analyze the relationship between GSI and histological stage, taking into account the parallel effects of additional factors related to geographical region, month of capture, fish length and energetic reserves (fat stage, hepatosomatic index-HSI). Ovarian growth was isometric in all stages of oocyte development and states of atresia, but altered to positive allometric at the stage of oocyte hydration. Oocyte growth and intensity of atresia significantly affected GSI. Fish length, geographical region, month of capture, fat stage and HSI did not substantially affect GSI, further strengthening the appropriateness of the index for the Mediterranean sardine. Finally, we provide first evidence, based mainly on available (but yet limited) published information for other fish species, that: (1) the pattern of ovarian allometry may not be altered by fecundity variations and (2) the pattern of ovarian allometry may reflect the pattern of oocyte growth (i.e. isometric vs. allometric ovarian growth could reflect group-synchronous vs. -asynchronous oocyte development). Alternatively, the pattern of ovarian allometry could reflect the presence or absence of size dependency in the relative fecundity (eggs per gram of body weight) and/or egg size. The isometric ovarian growth in the Mediterranean sardine could be attributed to the lack of such size-dependent effects

Rise of oceanographic barriers in continuous populations of a cetacean: the genetic structure of harbour porpoises in Old World waters

<p>Abstract</p> <p>Background</p> <p>Understanding the role of seascape in shaping genetic and demographic population structure is highly challenging for marine pelagic species such as cetaceans for which there is generally little evidence of what could effectively restrict their dispersal. In the present work, we applied a combination of recent individual-based landscape genetic approaches to investigate the population genetic structure of a highly mobile extensive range cetacean, the harbour porpoise in the eastern North Atlantic, with regards to oceanographic characteristics that could constrain its dispersal.</p> <p>Results</p> <p>Analyses of 10 microsatellite loci for 752 individuals revealed that most of the sampled range in the eastern North Atlantic behaves as a 'continuous' population that widely extends over thousands of kilometres with significant isolation by distance (IBD). However, strong barriers to gene flow were detected in the south-eastern part of the range. These barriers coincided with profound changes in environmental characteristics and isolated, on a relatively small scale, porpoises from Iberian waters and on a larger scale porpoises from the Black Sea.</p> <p>Conclusion</p> <p>The presence of these barriers to gene flow that coincide with profound changes in oceanographic features, together with the spatial variation in IBD strength, provide for the first time strong evidence that physical processes have a major impact on the demographic and genetic structure of a cetacean. This genetic pattern further suggests habitat-related fragmentation of the porpoise range that is likely to intensify with predicted surface ocean warming.</p

The great melting pot. Common sole population connectivity assessed by otolith and water fingerprints

Quantifying the scale and importance of individual dispersion between populations and life stages is a key challenge in marine ecology. The common sole (Solea solea), an important commercial flatfish in the North Sea, Atlantic Ocean and the Mediterranean Sea, has a marine pelagic larval stage, a benthic juvenile stage in coastal nurseries (lagoons, estuaries or shallow marine areas) and a benthic adult stage in deeper marine waters on the continental shelf. To date, the ecological connectivity among these life stages has been little assessed in the Mediterranean. Here, such an assessment is provided for the first time for the Gulf of Lions, NW Mediterranean, based on a dataset on otolith microchemistry and stable isotopic composition as indicators of the water masses inhabited by individual fish. Specifically, otolith Ba/Ca and Sr/Ca profiles, and delta C-13 and delta O-18 values of adults collected in four areas of the Gulf of Lions were compared with those of young-of-the-year collected in different coastal nurseries. Results showed that a high proportion of adults (>46%) were influenced by river inputs during their larval stage. Furthermore Sr/Ca ratios and the otolith length at one year of age revealed that most adults (similar to 70%) spent their juvenile stage in nurseries with high salinity, whereas the remainder used brackish environments. In total, data were consistent with the use of six nursery types, three with high salinity (marine areas and two types of highly saline lagoons) and three brackish (coastal areas near river mouths, and two types of brackish environments), all of which contributed to the replenishment of adult populations. These finding implicated panmixia in sole population in the Gulf of Lions and claimed for a habitat integrated management of fisherie

Séminaire d'initiation à la théorie et à la pratique des sondages. Recueil des exposés

Thè present document is a compilation of the topics presented during an introductory course to sampling techniques held in the IFREMER center of Nantes (17-21 October 1988). The purpose of this course was a presentation of some basic elements of the sampling theory followed by a description and practice of the principal sampling techniques. After an introoduction th the sampling theory the floowing sampling techniques were presented : simple Random Sampming, Ratio estimator, Stratified sampling, Cluster Sampling and Multistages Sampling. Two supplments with the basic mathematical and statistical notions used in this document are also included.Ce document présente le contenu des exposés oraux faits à l'occasion d'un séminaire d' initiation aux techniques d'échantillonnage qui s'est déroulé du 17 au 21 Octobre 1988 au centre IFREMER de Nantes. L'objectif étant une sensibilisation aux techniques et à la pratique des sondages, seules les stratégies d'échantillonnage les plus couramment utilisées sont présentées, un certain nombre de développements ne sont que suggérés et plusieurs démonstrations sont éludées. Après une introduction des concepts de base de la théorie des sondages, sont succesisivement abordés l'échantillonnage aléatoire simple, l'estimation par le rapport, les échantillonnages stratifié, par grappe et par niveau (ou degré). Deux annexes de rappels mathématique et statistique devraient apporter une aide au lecteur

Length–girth relations of fishes from a Mediterranean lagoon system

We estimated the relations between total length (TL) and opercular (Gope) and maximum (Gmax) girths, for the eight most representative lagoon fish species in Mesolonghi–Etolikon lagoons within 2015–2017 (June through December). The following species were studied: Chelon saliens (Risso, 1810); Chelon auratus (Risso, 1810); Chelon ramada (Risso, 1827); Mugil cephalus Linnaeus, 1758; Diplodus puntazzo (Walbaum, 1792); Diplodus sargus (Linnaeus, 1758); Sparus aurata Linnaeus, 1758; Dicentrarchus labrax (Linnaeus, 1758). For five of these species (C. saliens, C. auratus, C. ramada, S. aurata, and D. labrax) LGR estimates were not available. Results showed that both Gope and Gmax increased significantly linearly with TL for all studied species with all r2 values being higher than 0.862. When Gmax values were plotted against TL for all species combined, two significant (ANCOVA, P < 0.05) length–girth relations were identified corresponding to different body shapes. The implications of girth measurements for lagoon gear selectivity estimates are also discussed