3. CONCLUSION GÉNÉRALE
3.4. Perspectives de gestion et de conservation
La situation de l’anguille d’Amérique dans le système du Saint-Laurent et du lac Ontario est plus qu’inquiétante (Casselman 2003, COSEWIC 2012). Le recrutement d’anguilles jaunes en montaison vers les zones amont du système ainsi que la dévalaison d’anguilles argentées ne représentent qu’un faible pourcentage de valeurs observées au début des années 1980. L’espèce
37
a ainsi été classée comme espèce menacée par le COSWEIC (2012). Encore plus inquiétant est le fait que l’importance relative des facteurs à l'origine de ce le déclin catastrophique est méconnu. Il est clair que d’importantes mesures de gestion sont nécessaires afin de pouvoir rétablir le stock d’anguilles dans le Saint-Laurent. Cela requiert une bonne connaissance et compréhension des différentes causes de mortalité de l’espèce durant sa phase de croissance dans le système. Les mouvements et déplacements durant cette phase pourraient augmenter la probabilité de traverser les zones de pêches commerciales ainsi que les multiples barrages hydro-électriques. Jusqu’à maintenant, les mouvements de l’anguille dans le Saint-Laurent étaient peu connus. La présente étude a permis de démontrer que les anguilles du Saint-Laurent effectuent des mouvements d’au moins 100 à 200 km durant la phase de croissance. De plus, nous avons mis en évidence une exploitation de milieux estuariens et l'existence de différentes tactiques qui pourraient, quant à elles, correspondre à différents écotypes. Pour conclure, des futurs travaux devront approfondir les informations apportées par la présente étude afin de mieux caractériser les mouvements en eau douce ainsi que la présence ou l'absence d’anguilles dans l’estuaire. La gestion et la conservation de l’espèce dans le Saint-Laurent dépend de la capacité à élucider les informations écologiques de l’espèce durant l’ensemble de son cycle vital et durant toutes ses phases
39
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ANNEXE
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Figure 1 The Saint Lawrence River Lake Ontario system including Lake Champlain. Dashed red lines mark the limits of fluvial estuary. The river lies upstream from the upper limit while the brackish estuary begins downstream from the lower limit. Yellow dots indicate capture locations for eels collected between September 2010 and October 2011. Note that eels listed as being from Lake Ontario were in fact captured in the brackish estuary.
Figure 2 : Image of a stained eel otolith sectioned and polished in the transverse plane. Red dots indicate growth rings and represent one year’s worth of growth. The age estimate for this individual is 9 years.
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Table 1 : Mean concentrations in ppm (µg. g-1) and standard deviations for Sr, Ba, Mn and Mg with respect to each of the three habitats formed in the first cluster analysis.
Table 2 : Mean concentrations in ppm (µg. g-1) and standard deviations for Sr, Ba, Mn and Mg with respect to each of the six habitats formed in the second cluster analysis Group (±SD) (ppm) Mean [Sr] (±SD) (ppm) Mean [Ba] (±SD) (ppm) Mean [Mn] (±SD) (ppm) Mean [Mg]
1 1876 (±423.6) 1.65 (±0.93) 6.25 (±1.60) 28.1 (±7.36)
2 661.8 (±126.1) 5.59 (±0.19) 10.30 (±1.25) 35.5 (±5.06)
3 625.2 (±119.9) 2.84 (±0.21) 6.05 (±3.90) 28.3 (±5.57)
Group Mean [Sr] (ppm) Mean [Ba] (ppm) Mean [Mn] (ppm) Mean [Mg] (ppm)
1 1876 (±424) 1.65 (±0.93) 6.25 (±1.60) 28.1 (±7.36) 2 717 (±122) 3.53 (±1.37) 5.64 (±0.90) 27.7 (±4.13) 3 596 (±94) 2.77 (±0.87) 7.42 (±0.97) 33.0 (±3.75) 4 553 (±90) 2.18 (±0.74) 5.37 (±1.83) 25.2 (±4.02) 5 566 (±70) 4.02 (±1.11) 13.9 (±4.49) 35.4 (±4.57) 6 710 (±110) 6.37 (±2.20) 8.51 (±1.81) 35.6 (±4.03)
53
Figure 3 : Cluster Analysis performed on concentrations of 4 elements within each section: A) Dendrogram illustrating the three clusters B) PC scores for each section plotted in multivariate space ( group 1; group 2; group 3). Ba, Mn and Mg are all strongly negatively correlated with PC1 while Sr shows a strong positive correlation with PC2. PC1 and PC2 combine to