Croissance larvaire et force du recrutement chez le maquereau bleu du sud du golfe du Saint-Laurent
|Advisor:||Fortier, Louis; Castonguay, Martin|
|Abstract:||In marine fish, year-to-year variability in recruitment is tremendous and represents one of the main sources of problems for fisheries management. The central hypotheses in fisheries oceanography relate the variability in recruitment strength to that in larval survival. Fast growth would enhance larval survival by shortening the period of extreme vulnerability to predation. The objective of this study was to test the hypothesis that strong recruitment in Atlantic mackerel from the southern Gulf of St. Lawrence occurs only in years when environmental conditions favour fast growth, and selection for fast growth is weak. Mackerel larvae were captured on the Magdalen Shallows during the summer of four consecutive years (1997-2000) which comprised an exceptionally strong year class (1999) and three years of low recruitment (1997, 1998, 2000). Age and individual growth trajectory of a larval sub-sample was determined by the analysis of sagittal otoliths. Prey selectivity and feeding performance were assessed by the examination of gut content coupled to the quantification of potential prey available at time of capture. Our results show that the 1999 strong year class resulted from the unique combination of high growth potential reflecting optimal environmental conditions, and low selection for fast growth due to predation. The three years which yielded low recruitment were rather characterized by weak growth potential and/or strong selection for fast growth early in life. Mackerel larvae strongly selected for nauplii stages of the copepod Pseudocalanus sp. at first feeding, and for cladocerans and fish larvae during the late larval stage. Feeding performance and growth of first-feeding larvae followed an Ivlev function relative to preferred prey availability and reached a satiation threshold at a Pseudocalanus sp. biomass of 1 µgC L-1. Past the first-feeding stage, growth increased linearly with temperature over the complete thermal range encountered during the four years. Strong year classes would thus emerge in years characterized by high abundance of the preferred prey at the initiation of exogenous feeding, relatively warm temperature following the first-feeding stage, and weak predation pressure through the whole larval stage.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||13 April 2018|
|Collection:||Thèses et mémoires|
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