(Perccottus Glehni) in the Delta of the Selenga River, Buryatia, Russia

J. Great Lakes Res. 22(2):370-378 Internat. Assoc. Great Lakes Res., 1996 Biology of Amur Sleeper (Perccottus glehni) in the Delta of the Selenga River, Buryatia, Russia Alexander G. Litvinov1 & Robert O'Gorman2 1Buryat Institute of Biology Siberian Branch, Russian Academy of Sciences 6 Sakhyanova Street Ulan-Ude, Buryatia, Russia 670042 2National Biological Service Great Lakes Science Center Lake Ontario Biological Station 17 Lake Street Oswego, New York 13126 ABSTRACT We determined the fecundity, growth, diet, and density of the Amur sleeper (Perccottus glehni) in the Se- lenga River Delta on Lake Baikal during 1986-1991 to better understand how this invading exotic will affect Baikal's endemic fishes. We also compared the Amur sleeper's diet with that of other fishes living in the delta. The largest Amur sleepers were about 200 mm long and weighed 200 g; the oldest were age 7. All females were mature at age 2. Fecundity ranged from 884 eggs at age 1 to 37,056 eggs at age 7. Highest densities of Amur sleepers were found in oxbow lakes where densities sometimes exceeded 4,000 fish per ha. The bulk of the diet of amur sleeper age 2 and older was chironomids, fish, and fish eggs. Chironomids were also important in the diet of the commercially valuable Siberian roach (Rutilus rutilus lacustris) and Siberian dace (Leuciscus leuciscus baicalensis). Thus the Amur sleeper may cause population declines of these important endemic fishes through resource competition and predation on their juvenile life stages. However, Amur sleepers were the species of fish most frequently eaten by Eurasian perch (Perca fluviatilis) and northern pike (Esox lucius). So, maintaining vigorous populations of these two predators may well be an effective strategy for limiting the size of Amur sleeper populations. Index words: Amur sleeper, Lake Baikal, Selenga River, exotics INTRODUCTION Amur sleepers (Perccottus glehni) are native to the Amur River drainage in northeastern Asia but they have been widely introduced across central and western Russia (Pronin 1982, Elovenko 1985). In 1969, Amur sleepers were accidently introduced into Lake Gusinoe in the Lake Baikal watershed during an intentional release of eastern carp (Cyprinus carpio haematopterus) from the ponds of the Khabarov Fish Hatchery (Pronin 1982). Lake Gusinoe is connected to the Selenga River by a channel, 20-25 km long, which enters the main river about 200 km upstream from the river's discharge into Lake Baikal. The Khabarov Fish Hatchery is located in southeastern Siberia, near the Amur River. During the early 1980s, Amur sleepers spread from Lake Gusinoe down the Selenga River to the delta on Lake Baikal, and by 1985-1986, they were present in many of the numerous oxbow lakes in the southern portion of the delta. In 1987-1989, single specimens of Amur sleeper were caught at widely scattered locations along Lake Baikal's eastern shore - Proval Bay (just north of the delta), Posol'skoe Bay (about 30 km south of the delta), in Lake Baikal off the mouth of the delta, and in the Turka River (about 120 km north of the delta). By 1994, Amur sleepers had spread to the west shore of Lake Baikal near the head of the Angara River (about 120 km to the southwest of the delta). Colonization of large lakes throughout the world by non-native fishes has resulted in severe disruption of the endemic fish communities: Nile perch (Lates niloticus) in Lake Victoria, Africa (Barel and Witte 1986, Ribbink 1986, Goldschmidt et al. 1993); peacock cichlid (Cichla ocellaris) in Gatun Lake, Central America (Zaret 1979); and sea lamprey (Petromyzon marinus) and alewife (Alosa pseudoharengus) in the Laurentian Great Lakes, North America (Christie 1974; Smith 1968, 1970; Eck and Wells 1987). Assessing how, or if, the Amur sleeper will affect the Lake Baikal fish community and developing mana- gement strategies to ameliorate any effect, requires knowledge of the sleeper's biology in its new envi- ronment and of the sleeper's interaction with the endemic fish community. Consequently, we determined the fecundity, growth rate, food habits, and density of the Amur sleeper in the Selenga River Delta during 1986-91. We also compared their diet with that of other fishes living in the same areas of the delta. DESCRIPTION OF STUDY AREA The Selenga River empties into eastern Lake Baikal through a 600-km2 delta (Fig. 1). The river is highly braided in the delta; much of the area is flooded during periods of high flow and when the waters recede, numerous small waterbodies are either isolated from the river, or connected to it only by narrow channels. METHODS We sampled fish at 8 stations in the Selenga River Delta with gillnets, seines, and a tow-net during May- September 1986-1989 and also during October 1988. The gillnets were of nine mesh sizes, from 18- to 50-mm mesh (stretch measure) and were set on bottom overnight to capture fishes other than Amur sleeper for diet analysis. The seine, which was used to collect Amur sleepers, was 30-m long and 2-m deep. It was constructed of 6- and 10-mm mesh (stretch measure) and was equipped with a bag of 5-mm mesh (stretch measure). The seine was tied to 25-m-long ropes, deployed from a boat, and retrieved, by hand, from the shore by pulling on the ropes. The tow net was 0.7- by 0.8-m square and of standard number 15 netting (15 meshes per cm). It was pulled behind a motor boat to collect juvenile fishes. Fecundity of Amur sleepers was determined from fish seined from the Selenga River delta in May and June 1988. Fish were measured (total length, nearest mm) and weighed (nearest g, single beam balance) immediately after collection. Ovaries were removed and weighed (nearest g, single beam balance), and a 1-g sample was removed from each ovary and preserved in a 4% formalin solution. If one ovary weighed less than 1 g then both ovaries were weighed together. Eggs in the 1-g subsample from each ovary were counted under a microscope in the laboratory and the total number of eggs in the ovary was calculated by direct proportion. The ovaries contained eggs of two distinct sizes, and we counted each size group separately. Amur sleepers spawn twice each year in the Selenga Delta, once in late May and again in late June. The larger eggs were deposited in the first spawning and the smaller eggs, after furt- her development, were deposited in the second. Ages of the female Amur sleepers were determined from scales, opercula, and otoliths which were removed from the fish in the field (see below). To calculate growth and determine longevity, Amur sleepers collected during June-August were aged, mainly from otoliths. If age was difficult to determine from the otoliths, scales and opercula were examined. The fish were measured (total length, nearest mm) and weighed (nearest g, single beam balance) in the field. Sex of the fish was determined by visual inspection of the gonads. Otoliths, scales, and opercula were examined, and the annuli counted, under a binocular microscope at 56X to 140X. Scales were placed between glass slides for viewing. Numbers of Amur sleepers at eight sampling sites in the delta were estimated, mostly during late July, from seine catches and the area swept by the seine after correcting for efficiency of the seine. The efficiency of the seine was determined at each site by first catching, marking (by clipping a fin), and releasing Amur sleepers. Then, after 1 to 2 hours, the seine was hauled three times at the release site (with about 30 min between hauls) and the mean of the proportion of marked fish recaptured in each of the three seine hauls was considered the efficiency of the seine at that sampling site. Recaptured, marked fish were removed from the water so for each seine haul the proportion of marked fish recaptured was R/(M-C) where R = number of marked fish recaptured, M = number of fish marked, and С = number of marked fish caught by previous seine hauls. Our estimate of efficiency would be biased downward by marked fish emigrating from the area prior to making the seine hauls to recapture them. However, Amur sleepers are relatively sedentary during midday (A.G. Litvinov, personal observation), and we conducted all trials of seine efficiency between noon and 3 PM. So we assume that any such bias was small. Diet of the Amur sleeper and the fishes associated with it in the delta of the Selenga River was determined from fish collected at all sites during May-October, 1988. Fish for food habits were preserved whole immediately after collection in 4% formalin solution except that only the stomachs of the largest individuals were preserved. In the laboratory, the preserved fish were measured and the stomachs were removed. Ages were determined from scales (northern pike Esox lucius, Siberian dace Leuciscus leuciscus baicalensis, Siberian roach Rutilus rutilus lacustris, wild goldfish Carassius auratus gibelio, and ide Leuciscus idus); otoliths (Amur sleeper, lake minnow Phoxinus perenurus, common minnow Phoxinus phoxinus, and spiny loach Cobitus taenia sibirica); and opercula (Eurasian perch Perca fluviatilis). Contents of the stomach were identified and counted with the aid of binocular and monocular microscopes. Intact food items were weighed, large specimens with a teacup balance (nearest g) and smaller specimens with a spring scale (nearest 0.5 mg). The weights of microscopic (i.e., zooplankton) or partially digested food items, were determined from lengths of characteristic body parts (measured with an ocular micrometer) and length- weight regressions derived from either fresh specimens or published regressions (Ruttner-Kolisko 1977, Balushkina and Vinberg 1979).

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