Approche quantitative de la fonction de nourricerie jouée par les ...

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Chapitre 4 : Impact of vegetation structure dynamics and usage on the nursery function of West European tidal salt-marshes. laboratory until identification to species level. Once identified, the total length in mm (TL), fork length (FL) and fresh weight to the nearest mg (FW) were measured. Measurements were conducted on sub-samples when the samples were too large (there was a pronounced shoaling effect in the juvenile stages of some species). Estimates of the numbers and biomass were then made using the mean weights per size class. Two additional seasonal sampling campaigns (spring and autumn) were conducted at the same time in Mont Saint-Michel bay. They consisted of 7 catches in June and 7 in September using the same sampling methods, and in similar conditions. A comparison in spring and autumn between the two bays was then made to assess any latitudinal differences that could exist between these two salt marshes on the west coast of France. In order to estimate the share of each age group present in our samples, two analyses are carried out in the same time. Firstly, individuals of each species are old near at the year using length frequency diagram. Secondly, a validation is carried out thanks to a scalimetric analysis under binocular magnifying glass. A numerical distribution of each cohort is practised in order to estimate the percentages of each cohort (G0, G1 and G2 & +). Thus, various groups are describe by using the respective percentages of YoY (G0), of G1 and of G2 and +. This classification in guild is related then to these percentages. Four behaviours of colonization of the estuarine complexes can be identified and gathered in colonizing guilds: (i ) Only the first stage is present (Young-of-the-Year or YoY). These species then are qualified young of the year settlers (YoY Salt Marsh Settlers). (%G1 < 10% ; %G2 < 5%). (ii) Secondly, the young-of-the-year and the youthful ones are present in the studied zone. One will then speak about youthful or juvenile settlers (Juvenile Salt Marsh Settlers). (%G1 > 10% ; %G2 < 5%). (iii) Thirdly, when various cohorts are present but that all the ecophases are not indexed, one speaks about opportunist saltmarsh settlers (Opportunistic Salt Marsh Settlers). (%G1 10%; %G2 5%). (iv) Lastly, when all the cohorts are present, in spite of the temporary side of these mediums undergoing marling one will speak about resident settlers (Resident Salt Marsh Settlers). 124
Chapitre 4 : Impact of vegetation structure dynamics and usage on the nursery function of West European tidal salt-marshes. 3.3. Analyses. The Catch Per Unit Effort (CPUE) (number or biomass per min of fishing) was calculated for each species from the numbers and biomasses captured (Laffaille 2000). N Where: ⎛ N ⎞ ⎛ N ⎜ i ⎟ + ⎜ ⎝ t ⎠ ⎝ t 2 i+ 1 ⎞ ⎟ ⎠ i i+ 1 i− i+ 1 = × ti−i+ 1 CPUE • CPUE = Number or biomass of fish per species per minute • ti = Sampling duration in minutes • ti-i+1 = Time in minutes between samples i and i+1 = ∑ N i+ 1 + ∑ ∑ ti+ 1 + ∑ • Ni = Quantity of fish captured per species (in numbers or biomass) during sampling i. • N i-i+1 = Estimate of the quantity of fish per species (in numbers or biomass) having colonised the salt marshes between samplings i and i+1 The temporal variations in the structure of the community were analysed by cluster analysis (Euclidian distance, Ward's method), the CPUE values were log (x+1) transformed as recommended by Field et al. (1982). Species only recorded a single time or in a single sample were excluded from the analysis. An analysis of the size frequency distribution was conducted on the fish populations captured in the salt marshes of the Aiguillon bay. Three size classes were used: young-of-the- year (YoY), juveniles and adults. A cluster analysis was conducted on the percentages of these classes. The values were log (x+1) transformed as recommended by Field et al. (1982). 4. Results. 4.1. Composition of the fish population of the Aiguillon bay : A total of 16 302 fish belonging to 22 species were captured during the samplings (20 genera) with a total biomass of more than 115 kg. More than 60% of the species occurred in both sites. Four different ecological guilds were present (Elie et al. 1990; Laffaille et al. 2000a). Three transient species (amphihaline catadromous) were captured (Eel (Anguilla anguilla L. 1758), Thinlip mullet (Lira ramada, Risso, 1810) and Flounder (Platichthys N t i i 125
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UNIVERSITE DE LA ROCHELLE UFR SCIEN
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Remerciements : Je tiens tout d’a
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(Ciboulette), Aurélien RIDE (Lapin
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Sapere aude (N’aie pas peur de sa
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6. REMERCIEMENTS. .................
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3. RESULTATS. .....................
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Introduction générale et contexte
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dorsal Face ventral Introduction g
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Otolithe d’un juvénile de l’an
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TOME 1 : Première partie. TOME 1 :
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TOME 1 : Première partie. Chapitre
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Chapitre 1 : Structuration du peupl
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Chapitre 2 : Evolution des assembla
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Chapitre 2 : Evolution des assembla
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TOME1 : Conclusion exergue par les
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Introduction. TOME 2 : Introduction
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TOME 2 : Introduction. indiquer la
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1.1. Description du cycle biologiqu
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TOME 2 : Introduction. de répartit
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Efficacité de la nourricerie éval
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Chapitre 1 : Variations régionales
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Chapitre 2 : Les marais salés cont
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15N depleted δ15N‰ 15N enriched
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TOME 2 : Chapitre 3 Chapitre 3 : Di
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Chapitre 3 : Discrimination de quat
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TOME 2 : Chapitre 4 44 : Concentrat
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Chapitre 4 : Reconstitution de l’
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Conclusion générale et perspectiv
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Littérature citée. Bibliographie.
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Bibliographie. Charnov, E. L. et J.
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Bibliographie. Fritsch, M. et Y. Mo
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Bibliographie. Kneib, R. T. (1995).
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Bibliographie. Maitland, P. S. (197
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Bibliographie. Ecobio 6553, Muséum
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Bibliographie. Secor, D. H. (2002).
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Annexes : Annexe 1 : Description de
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Annexe 2 : Curriculum vitae. Emmanu
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Annexes. 2001 Stagiaire: Universit
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Annexes. Parlier E., Duhamel S., Fe
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Résumé Approche quantitative de l
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