Canadian Manuscript Report of Fisheries and Aquatic Sciences No
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Scientific Excellence • Resource Protection & Conservation • Benefits for Canadians Excellence scientifique • Protection et conservation des ressources • Bénéfices aux Canadiens DFO - Library / MPO B bliothèque 1 111111 11111 11111 11111 11111 11111 11111 1 1 I I I 111111111 Results of Rotary Auger Trap Sampling, Lower Stuart River, British Columbia, in April and May 1992 G.C. Taylor and M.J. Bradford Department of Fisheries and Oceans West Vancouver Laboratory 4160 Marine Dr., West Vancouver B.C. V7V 1N6 1993 Canadian Manuscript Report of P,? Fisheries and Aquatic Sciences 2211 // ( Fisheries Pêches 1+1 and Oceans et Océans CanadU Canadian Manuscript Report of Fisheries and Aquatic Sciences Manuscript reports contain scientific and technical information that contributes to existing knowledge but which deals with national or regional problems. Distribu- tion is restricted to institutions or individuals located in particular regions of Canada. 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Les rapports manuscrits sont produits à l'échelon régional, mais numérotés à l'échelon national. Les demandes de rapports seront satisfaites par l'établissement auteur dont le nom figure sur la couverture et la page du titre. Les rapports épuisés seront fournis contre rétribution par des agents commerciaux. g55 Canadian Manuscript Report of Fisheries and Aquatic Sciences 2211 1993 RESULTS OF ROTARY AUGER TRAP SAMPLING, LOWER STUART Riye4 BRITISH COLUMBIA, IN APRIL AND MAY 1992 ,;--,;;;; - -oee\ re,„ (Ye by G.C. Taylor and M.J. Bradford Department of Fisheries and Oceans Biological Sciences Branch West Vancouver Laboratory 4160 Marine Dr. West Vancouver, B.C. V7V 1N6 ii © Minister of Supply and Services Canada 1993 Cat. No. Fs 97-4/2211E ISSN 0706-6473 Correct citation for this publication: Taylor, G.C. and M.J. Bradford. 1993. Results of rotary auger trap sampling, lower Stuart River, British Columbia, in April and May 1992. Can. Manuscr. Rep. Fish. Aquat. Sci. 2211:18p. 111 ABSTRACT Taylor, G.C. and M.J. Bradford. 1993. Results of rotary auger trap sampling, lower Stuart River, British Columbia, in April and May 1992. Can. Manuscr. Rep. Fish. Aquat. Sci. 2211:18p. Rotary auger traps were used in the lower Stuart River to sample migrating juvenile chinook salmon (Oncorhynchus tshawytscha) and sockeye salmon (Oncorhynchus nerka) between 18 April 1992 and 30 May 1992. Peaks in abundance were recorded on May 20 for chinook fry and on April 25 for sockeye smolts. Greater numbers of all salmonids were caught during the nighttime. Most chinook fry were captured migrating close to the shore while sockeye smolts were caught in similar numbers close to the shore and in the main flow of the river. Based on an estimated trapping efficiency of 2.18%, we estimated the population size of migrant chinook fry at 716,000 for the period sampled. Fork lengths for salmonids are also reported as are abundance data for non-salmonid species. RÉSUMÉ Taylor, G.C. and M.J.Bradford. 1993. Results of rotary auger trap sampling, lower Stuart River, British Columbia, in April and May 1992. Can Manuscr. Rep. Fish. Aquat. Sci. 2211:18p. Dans le cours inférieur du Fraser, on a utilisé, entre le 18 avril et le 30 mai 1992, des pièges à vis sans fin pour échantillonner les jeunes saumons quinnats (Oncorhynchus tshaw tscha et rouges (Oncorhynchus nerka en migration. On a observé des pics d'abondance le 20 mai pour les alevins de quinnat et le 25 avril pour les smolts de salmon rouge. C'est pendant la nuit qu'on capturait le plus grand nombre de salmonidés. La plupart des alevins de quinnat étaient pris tandis qu'ils migraient près de la côte, alors que les smolts de saumon rouge étaient pris en nombres similaires près de la côte et dans le courant principal du fleuve. À partir d'une efficacité de capture estimée à 2,18 %, nous avons calculé que l'effectif de la population d'alevins de quinnat en migration serait de 716 000 pour le période d'échantillonnage. Nous notons les longeurs à la fourche des salmonidés ainsi que des données sur l'abondance pour les autres espèces. 1 INTRODUCTION Both chinook salmon (Oncorhynchus tshawytscha) and sockeye salmon (Oncorhynchus nerka) are known to use the Stuart River for juvenile downstream migration (Williams 1969, Lister et al. 1981). While a portion of the chinook salmon population migrates as post-emergent fry in May and June (Lister et al. 1981), some remain to overwinter in the Stuart River and its tributaries (Emmett 1989, Emmett and Convey 1990, Duff et al. 1992). Juvenile sockeye salmon rearing in Stuart and Takla Lakes migrate down the Stuart River in the spring as one year old smolts (Williams 1969). The objective of this study was to obtain information on the timing of migration of juvenile chinook and sockeye salmon in the lower Stuart River during spring 1992, and to estimate the abundance of migrating chinook salmon. The migration of hatchery reared chinook juveniles as well as incidental catches of other species were also recorded. These data are baseline biological information that will assist in the development of habitat management plans for the Stuart-Takla watershed (Langer et al. 1992). STUDY AREA AND MATERIALS AND METHODS The study site was located on the Stuart River near the Chinohchey Creek confluence, approximately 70 km downstream from Stuart Lake and approximately 30 km upstream of the confluence of the Stuart and Nechako Rivers (Fig. 1). Sockeye spawning occurs above Stuart Lake while most chinook spawning takes place in the first 15 km below the lake. This study site was chosen because: 1) it was the first segment of river downstream of the chinook spawning area with adequate velocity to ensure continuous operation of two rotary auger traps, 2) the river was sufficiently narrow for installation of the traps and 3) previous studies on downstream migration of juvenile salmon on the Stuart River used this site (Lister et al. 1981, Duff et al. 1992). Upstream of the site, the river was generally too slow or too wide and shallow for the traps to function properly. The site was also accessible by boat from the end of Sturgeon Point Road (Davidson's Landing), 7 km upstream of the trap site. A private road leading directly to the site from Davidson's Landing was in poor condition and could not be used for this study. Sampling commenced on 18 April 1992 and concluded on 30 May 1992. During trap installation, the river was approximately 50 m wide between banks. However, this distance increased substantially during the study as the river rose due to spring freshet. 2 Two rotary auger traps were used for sampling, both of which were suspended off a 16 mm steel cable that spanned the river. Each trap was attached to the cable with a 13 mm steel cable leader. The ends of the leader were clipped onto the front of each trap pontoon with 10.2 cm carabiners and the leader was looped through a 15.25 cm snatch-block on the main cable.