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1990. Estimation of submergent plant bed biovolume using acoustic range information. Can. J. Fish. Aquat. Sci. 47: 805-81 2.Acoustic nieasurements of the distance between the water surface, top of the aquatic plants, and bottom of the water column were made using chart recording echosounders. The vertical cross sectional area (m2), height (m), biovolume (rn3), of aquatic plant beds and variances were computed for three surveys of Devils Lake, Oregon, in May, July, and September, 1986 when coefficients of variation for the plant bed biovolume estimates were 0.1 8, 0.05, and 0.06, respectively (n = 14). Coefficients of variation for plant biomass estimates (g/m2) computed from SCUBA quadrat samples collected concurrently with the acoustic surveys, were 0.98 (n =48), 0.81 (n = go), and 1.05 (n = 901, respectively. The higher precision of the biovolume estimates allow for a 5-to 18-fold greater capability to detect a change in the mean. -the lower costs of the biovolume estimates allow for a 10-to 33-fold greater precision-for-cost. The plant bed biovolume variable contains ecologically different information than the biomass variable in that it provides a direct estimate of the amount of aquatic habitat in a lake that is influenced by plants; it should prove useful for evaluating plant control practices and possibly for studying plant-fish interactions.Des mesures acoustiques de la distance separant la surface de I'eau et le sorr~met des plantes aquatiques, et le fond de la colonne d'eau ont ete effectuees 2 I'aide d'echosondeurs graphiques. La superficie de la section verticale (m2), la hauteur (m), le volume de vegetaux (m3) et les variations ont ete calcules en mai, juillet et septembre 1986 dans le lac Devils en Oregon, lorsque les coefficients de variation du volume vegetal etaient estimes respectivement 2 0,18, 0,05 et 0,06 (n = 14). Les coefficients de variation des estimations de la biomasse vegetale (g/m2) calcules A partir des echantillons SCUBA de quadrats preleves en meme temps que les releves acoustiques s'elevaient respectivement A 0,98 (n = 48), 2 0,81 (n = 90) et A 1,05 (n = 90) pour les trois releves. La precision plus 6levee de I'estimation du volume vegetal augmente de 5 A 18 fois la capacite de detection d'un changement dans la moyenne. Le coGt inferieur de ces estimations permet d'obtenir un rapport coGt-precision de 10 i 33 fois superieur. La variable du biovolume vegetal donne des informations ecologiques differentes de celles de la variable de la biomasse en ce qu'elle donne une estimation quantitative directe de I'habitat aquatique d'un lac qui est influence par la vegetation; cela devrait se reveler utile pour I'evaluation des methodes de contrale des vegetaux et, eventuellement pour I'etude des interactions vegetaux-poissons.

Previous research has documented two main migratory routes of juvenile sockeye salmon (Oncorhynchus nerka) through the Strait of Georgia, British Columbia, Canada, and large interannual variability in marine survival rates of the Chilko Lake stock. Simulation models were used to explore the influence of surface currents on the migratory route of juvenile sockeye salmon (smolts) through the Strait of Georgia. We used a model of downstream migration to generate daily numbers of Chilko Lake sockeye salmon smolts entering the Strait of Georgia, based on daily counts of smolts leaving the rearing lake. A numerical hydrodynamic model (driven by surface wind, tide, and Fraser River discharge) hindcasted surface currents in the Strait of Georgia on a 2 km × 2 km grid. A smolt migration model simulated fish moving through the Strait with different compass‐oriented migratory behaviours (i.e. swimming speed and directional orientation) within the time‐varying surface advection field. Results showed that surface currents within the Strait of Georgia can affect the migratory route of sockeye salmon smolts in spite of their large size (8 cm). Wind is the forcing mechanism primarily responsible for determining which migratory route would be used. Under prevailing wind conditions (i.e. toward the north‐west), most sockeye salmon smolts would use the eastern migratory route; however, relatively brief south‐eastward wind events (lasting about 2 days) would force most smolts into the western migratory route. Given the heterogeneity of food for salmon within the Strait, we hypothesize that wind‐driven variability in the annual proportion of smolts that use the western and eastern migratory routes in the Strait of Georgia affects early marine survival rates of Fraser River sockeye salmon.

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