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Fishes / Acipenser fulvescens / Lake sturgeon
McQUINN, I.H., P. NELLIS, 2007. An acoustic-trawl survey of middle St. Lawrence Estuary demersal fishes to investigate the effects of dredged sediment disposal on atlantic sturgeon and lake sturgeon distribution. Pages 257-271 in J. Munro(ed.), D. Hatin, K. McKown, J. Hightower, K.J. Sulak, A.W. Kahnle & F. Caron(co-ed.). Anadromous sturgeons : habitats, threats, and management. American Fisheries Society (Am. Fish. Soc. Symp., 56).
Atlantic sturgeon Acipenser oxyrinchus and lake sturgeon A. fulvescens in the middle St. Lawrence estuary are under consideration for designation as "endangered" or "vulnerable" species. A potential threat to these species is the disposal of dredged sediments in an area where young-of-the-year and juvenile Atlantic sturgeon concentrate. The objectives of this study were (1) to study the short-term and cumulative impacts, if any, of the dumped sediments on the abundance, distribution, and movements of the two sturgeon species downstream of the disposal area, and (2) to investigate the usefulness of acoustic surveys for assessing sturgeon density and distribution. A two-phase, combined acoustic-trawl survey was conducted to describe sturgeon distributions and produce concurrent acoustic and trawl estimates of the relative abundance of demersal fish within the area (lake sturgeon and Atlantic sturgeon were presumed to dominate the acoustic echoes). This series of surveys was the first known attempt to quantify sturgeon abundance and distribution with a vertically deployed echo sounder. The results showed good correspondence between the two methods. Replicated sampling also showed the repeatability of the acoustic technique and stability in demersal fish distribution on a scale of days. The acoustic surveys indicated that the spatial distribution of demersal fishes was dependent on substrate, as these fishes avoided areas of dredged sediment dumping and associated sand dunes. Our study showed that under certain conditions, acoustic-trawl surveys can reliably assess sturgeon density and distribution.©2007 American Fisheries Society
NELLIS, P., J. MUNRO, D. HATIN, G. DESROSIERS, R.D. SIMONS, F. GUILBARD, 2007. Macrobenthos assemblages in the St. Lawrence estuarine transition zone and their potential as food for Atlantic sturgeon and lake sturgeon. Pages 105-128 in J. Munro(ed.), D. Hatin, K. McKown, J. Hightower, K.J. Sulak, A.W. Kahnle & F. Caron(co-ed.). Anadromous sturgeons : habitats, threats, and management. American Fisheries Society (Am. Fish. Soc. Symp., 56).
The St. Lawrence estuarine transition zone (ETZ) harbors the only known concentrations of age-0 and early juveniles of the St. Lawrence Atlantic sturgeon and lake sturgeon populations. Past dredging and disposal operations conducted in the ETZ to deepen the navigation channel resulted in the creation of an extensive sand dune biotope near the juvenile sturgeon concentration areas. In order to characterize the dune biotope within a diversified set of biotopes in the ETZ, nine areas were selected for study, including two areas to cover the sand dune complex. The study objectives were (1) to identify the benthos assemblages of the ETZ and the main physical factors controlling them, (2) to measure the sampling areas' biological characteristics and feeding potential for sturgeon, and (3) to compare the dune areas' feeding potential with selected control areas. In 1999-2001, grab sampling was conducted at 141 stations to determine macrobenthos composition and sediment parameters. Depth, slope, and slope orientation were measured from multibeam sonar echosoundings. Salinity, current velocity, and tidal amplitude were provided by a hydrodynamic model of the ETZ. Benthos assemblages were determined using cluster analysis on taxon biomass. Four major assemblages were identified, all having Tubificidae as the dominant or subdominant taxon : zebra mussel Dreissena polymorpha, Gammarus tigrinus, Tubificidae, and Capitella sp. assemblages. A succession of the major assemblages was observed from the freshwater front to the upper mesohaline waters. Three minor assemblages, the Chironomidae, Physidae, and Cumacea, were concentrated in the upper oligohaline zone. Taxonomic richness was highest in areas with the lowest maximum salinity (0.0-0.5), and diversity was highest in areas with intermediate maximum salinities (0.5-2.0). The largest biomass values were found in areas with maximum salinities less than 0.5, in the zebra mussel assemblage. Controls and dune areas had similar macrobenthos richness and diversity, but dune areas had significantly lower densities and biomasses. Feeding potential for a given sturgeon life stage was measured as the sum of taxa biomasses standardized using the prey proportions in that life stage's feeding regime. For age-0 Atlantic sturgeon and for all lake sturgeon lige stages, all of which feed mostly on gammarids, the feeding potential of control and dune areas were not significantly different. For juvenile and subadult Atlantic sturgeon, which feed mostly on tubificids, the dune areas had a significantly lower feeding potential than the control areas. The lower feeding potential of the sand dune areas created by dredged sediment deposition is considered an important issue for the management of the St. Lawrence Atlantic sturgeon population.©2007 American Fisheries Society
GUILBARD, F., J. MUNRO, P. DUMONT, D. HATIN, R. FORTIN, 2007. Feeding ecology of Atlantic sturgeon and lake sturgeon co-occurring in the St. Lawrence estuarine transition zone. Pages 85-104 in J. Munro(ed.), D. Hatin, K. McKown, J. Hightower, K.J. Sulak, A.W. Kahnle & F. Caron(co-ed.). Anadromous sturgeons : habitats, threats, and management. American Fisheries Society (Am. Fish. Soc. Symp., 56) .
Atlantic sturgeon Acipenser oxyrinchus and lake sturgeon A. fulvescens live in sympathy in the St. Lawrence estuarine transition zone (ETZ). To describe their feeding ecology and compare their diets in this zone, sturgeons were sampled during the summer and fall of 2000 by trawling in the main channel and by gill netting in the shallower nearshore habitat. Stomach contents were sampled by gastric lavage of live specimens (trawling) and by digestive tract sampling (gill netting). Relative importance by taxonomic group was based on percent occurrence and percentage of the diet by number and weight for three sturgeon size-classes that corresponded to age-0, juvenile, and subadult stages. Spatial, seasonal, and life stage variations were observed in the diet composition of both sturgeon species. Age-0 fish of both species fed mainly on gammarids. Juveniles and subadults from both species fed mainly on oligochaetes and gammarids, but in opposite proportions : gammarids were the dominant prey for lake sturgeon and oligochaetes for Atlantic sturgeon. Subadult Atlantic sturgeon also fed on fish in the summer and on insects and mollusks in the nearshore habitat in fall. Vegetal matter was frequent and abundant in the stomach contents of Atlantic sturgeon subadults, especially in the nearshore habitat, and vegetal mass in the diet was correlated with gammarid biomass. In addition to gammarids, the lake sturgeon diet was correlated with gammarid biomass. In addition to gammarids, the lake sturgeon diet included insects, oligochaetes, and mollusks, whose proportions increased with sturgeon size-class. The proportion of amphipods decreased with size-class during both summer and fall. In the St. Lawrence ETZ, Atlantic sturgeon appear to be specialist feeders while lake sturgeon appear to be more often generalists. Diet diversity was higher in lage sturgeon, which fed on all of the 15 taxa identified in the macrobenthos of the ETZ; the diet of Atlantic sturgeon consisted of 10 taxa. In the main channel in fall, dietary overlap between Atlantic sturgeon and lake sturgeon was low for the juvenile and subadult life stages. The strong dependence of Atlantic sturgeon and lake sturgeon on oligochaetes and gammarids suggests that the areas where these benthic assemblages are found, near the freshwater-saltwater limit, are important feeding habitats for the age-0, juvenile, and subadult stages of both sturgeon species.©2007 American Fisheries Society
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