Validation of age determination using otoliths of the European anchovy (Engraulis encrasicolus L.) in the Bay of Biscay

Validation of the age determination procedure using otoliths of European anchovy in the Bay of Biscay was achieved by monitoring very strong year-classes in successive spring catches and surveys, as well as the seasonal occurrence of edge types. Historical corroboration of the ageing method was obtained by cross-correlation between successive age groups by year-classes in catches and surveys (1987–2013). Summary annual growth in length is also presented. Yearly annuli consist of a hyaline zone (either single or composite) and a wide opaque zone, disrupted occasionally by some typical checks (mainly at age-0 and age-1 at peak spawning time). Age determination, given a date of capture, requires knowledge of the typical annual growth pattern of otoliths, their seasonal edge formation by ages and the most typical checks. Most opaque growth occurs in summer and is minimal (translucent) in winter. Opaque zone formation begins earlier in younger fish (in spring), and this helps distinguish age-1 from age-2þ.Versión del edito

Validation of age determination from Otoliths for Bay of Biscay anchovy

Comprehension of the annual pattern of annulus formation throughout the anchovy life span was first achieved from the observations of the strong 1982 year class which showed a neat annual progression of modal lengths passing through the fishery until the exceptional age of 5. Validation of the proposed method was subsequently obtained through monitoring of the progression of the strong 1987, 1989 and 1991 year-classes, both by spring annual surveys and by continuous sampling of the commercial catches, coupled to the monitoring of the seasonal marginal edge formation of the otoliths. Since then Age validation has been confirmed by the correlation between the pulses of recruitments (at age 1), as reflected in their relative occurrence in the population in Spring, and the abundance of those recruitments according to surveys. Typically, annual growth of anchovy otoliths of the one and two years old diminish to about 2/3-1/2 and 1/3 of that occurring in their previous ages respectively. Growth of older ages (three and four) are rather similar as, or slightly lesser than, at age 2. Maximum growth (white band formation) occurs in summer and growth detentions (with translucent annulus formation) in winter time. However the opaque edge formation begins sooner at the age of 1 (around February-March) than at older ages (May or June). During the first winter several translucent rings are occasionally formed resulting in a composite annulus formation. In addition during June/July, at peak spawning, a check is formed in many of the one year old anchovies. However, not all year classes, neither all anchovies lay down the same amount of checks and many of them may not show any. As such age determination requires the knowledge of the typical annual growth pattern of otoliths, of their seasonal edge formation by ages and of the most typical checks

Born small, die young: Intrinsic, size-selective mortality in marine larval fish

Mortality during the early stages is a major cause of the natural variations in the size and recruitment strength of marine fish populations. In this study, the relation between the size-at-hatch and early survival was assessed using laboratory experiments and on field-caught larvae of the European sardine (Sardina pilchardus). Larval size-at-hatch was not related to the egg size but was significantly, positively related to the diameter of the otolith-at-hatch. Otolith diameter-at-hatch was also significantly correlated with survival-at-age in fed and unfed larvae in the laboratory. For sardine larvae collected in the Bay of Biscay during the spring of 2008, otolith radius-at-hatch was also significantly related to viability. Larval mortality has frequently been related to adverse environmental conditions and intrinsic factors affecting feeding ability and vulnerability to predators. Our study offers evidence indicating that a significant portion of fish mortality occurs during the endogenous (yolk) and mixed (yolk /prey) feeding period in the absence of predators, revealing that marine fish with high fecundity, such as small pelagics, can spawn a relatively large amount of eggs resulting in small larvae with no chances to survive. Our findings help to better understand the mass mortalities occurring at early stages of marine fish.info:eu-repo/semantics/publishedVersio

Response of Benthic Foraminifera to organic matter quantity and quality and bioavailable concentrations of metals in Aveiro Lagoon (Portugal)

This work analyses the distribution of living benthic foraminiferal assemblages of surface sediments in different intertidal areas of Ria de Aveiro (Portugal), a polihaline and anthropized coastal lagoon. The relationships among foraminiferal assemblages in association with environmental parameters (temperature, salinity, Eh and pH), grain size, the quantity and quality of organic matter (enrichment in carbohydrates, proteins and lipids), pollution caused by metals, and mineralogical data are studied in an attempt to identify indicators of adaptability to environmental stress. In particular, concentrations of selected metals in the surficial sediment are investigated to assess environmental pollution levels that are further synthetically parameterised by the Pollution Load Index (PLI). The PLI variations allowed the identification of five main polluted areas. Concentrations of metals were also analysed in three extracted phases to evaluate their possible mobility, bioavailability and toxicity in the surficial sediment. Polluted sediment in the form of both organic matter and metals can be found in the most confined zones. Whereas enrichment in organic matter and related biopolymers causes an increase in foraminifera density, pollution by metals leads to a decline in foraminiferal abundance and diversity in those zones. The first situation may be justified by the existence of opportunistic species (with high reproduction rate) that can live in low oxic conditions. The second is explained by the sensitivity of some species to pressure caused by metals. The quality of the organic matter found in these places and the option of a different food source should also explain the tolerance of several species to pollution caused by metals, despite their low reproductive rate in the most polluted areas. In this study, species that are sensitive and tolerant to organic matter and metal enrichment are identified, as is the differential sensitivity/tolerance of some species to metals enrichment.CNPq [401803/2010-4]; [PEst-OE/CTE/UI4035/2014]info:eu-repo/semantics/publishedVersio

Growth and movement patterns of early juvenile European anchovy (Engraulis encrasicolus L.) in the Bay of Biscay based on otolith microstructure and chemistry

Various hypotheses have been put forward to explain the mechanisms in the Bay of Biscay that result in a good recruitment of European anchovy. Anchovy larvae from the spawning area in the Gironde River plume are advected towards off-shelf waters, where juveniles are commonly observed. Otolith microstructural and chemical analysis were combined to assess the importance of this off-shelf transport and to determine the relative contribution of these areas for anchovy survival. Chemical analysis of otoliths showed that anchovy juveniles in the Bay of Biscay can be divided into two groups: a group that drifts towards off-shelf waters early in their life and returns later, and a group that remains in the low salinity waters of the coastal area. The first group presents significantly faster growth rates (0.88 mm day-1) than those remaining in the coastal waters (0.32 mm day-1). This may be due to off-shelf waters being warmer in spring/summer, and to the fact that the lower food concentration is compensated for by higher prey visibility. Furthermore, the group of juveniles that drifted off the spawning area and had faster growth rates represents 99% of the juvenile population. These findings support the hypothesis that anchovy in the Bay of Biscay may use off-shelf waters as a spatio-temporal loophole, suggesting that transport off the shelf may be favourable for recruitment. \ua9 2010 Blackwell Publishing Ltd

Egg production of the copepod Acartia bifilosa in two contrasting European estuaries in relation to seston composition

The egg production of the copepod Acartia bifilosa was measured and related to environmental variables and food availability in two estuaries located in the same biogeographic region (Bay of Biscay) but showing very strong differences in abiotic and biotic features: the Gironde estuary (France) and the estuary of Mundaka (Spain). The study was conducted during the spring-summer-autumn period of 1994, Food availability was evaluated by analysing the chlorophyll a (Chi a), the particulate organic carbon (POC) and the easily extractable macromolecular compounds such as proteins, carbohydrates and lipids of the seston. The egg production of copepods was estimated from field incubations with natural water, and phytoplankton feeding of adult females was estimated by means of the gut fluorescence method. The nutritional environment of the Gironde was characterised by high amounts of suspended particulate matter (SPM) with low food value, emphasising the mainly detrital origin of the organic matter (OM). In Mundaka, the higher contribution of phytoplankton to the seston led to marked increase, in particulate food value accounting for up to 35% of organic matter. The weight-specific egg production was found to be sharply higher in Mundaka (ranging from 0.2 to 0.63 x 10(-3) day(-1)) than in the Gironde (ranging from 0 to 0.13 x 10(-3) day(-1)), but the seasonal trend of variations was similar, the highest weight-specific egg production rates occurring in early summer and the lowest in autumn in both estuaries. Egg production was not correlated linearly with temperature since maximal egg production occurred at intermediate temperatures. In Mundaka, the egg production showed a significant positive con-elation with the chlorophyll and the Chl/SPM and the POC/SPM ratios. This coupled with higher values of algal food availability (Chi a/SPM: 10 to 1870 mug g(-1)) and gut fluorescence (between 0, 12 and 0,38 ng Chi a Eq ind(-1)) indicate that a herbivorous diet could cover the energy requirements of A. bifilosa and support egg production. In the Gironde, the algal food availability and the gut fluorescence were lower (Chi a/SPM: 10 to 80 mug g(-1) GF: 0.09 and 0.25 ng Chi a Eq ind(-1)), and the egg production showed significant positive correlation with the particulate food value, suggesting that other sources of carbon rather than phytoplankton ere responsible for the observed changes in egg production, Results indicate that the particular seston properties of each system may be responsible for the noticeable differences in A. bifilosa fertility among estuaries. (C) 2002 Elsevier Science B.V All rights reserved

Life-cycle spatial patterns of small pelagic fish in the Northeast Atlantic: Bay of Biscay anchovy

Publicad