The seedling emergence method has been used in the restoration work of submerged plants at Lake Izunuma-Uchinuma since 2011. Najas ancistrocarpa, an endangered submerged plant in Miyagi Prefecture, was discovered in the sediments of the lake. For the restoration of N. ancistrocapra, it is necessary to collect a soil seedbank of N. ancistrocarpa before its extinction, and improve water quality and sediment quality in Lake Izunuma-Uchinuma.
In shallow lakes, macrophytes may improve water quality by keeping phytoplankton at low densities. In the southern part of Lake Biwa, a rare occurrence of severe drought in 1994 dropped the water level maximally down to -123 cm below the standard level. This drought event improved transparency and light condition of lake water, resulting in the excessive flourish of macrophytes. Massive amount of floating macropyhtes drifted against the lake shore and spoiled, giving off a bad smell and entangled boat screws. Since 2011 the local government started a macrophyte reaping project. To examine the efficacy of the project our research group tracked concentration of macrophytes using a fish finder in 2010 (before the reaping), 2012 and 2013 (after the reaping). We set 10 census lines, separated by 1,600 m across the southern part of Lake Biwa. We recorded the macrophyte community height, depth and type (Hydrilla verticillata, Potamogeton maackianus and mixed community) every 40 meters on the fish finder charts. We estimated the biomass for each point and calculated the biomass of an 800 meter area based on the average biomass of three types of dominant species and made a biomass map GIS. In addition, we calculated the PVI (percent volume infested by macrophytes) in the vertical water column by factoring in the water depth and community height. The estimated total biomass and the mean PVI were 11,850 t and 32.8%, 4,236 t and 17.1%, and 7,873 t and 25.7% in 2010, 2012 and 2013, respectively. These results showed that both biomass and PVI dropped greatly from 2010 to 2012, but recovered to some extent by 2013.The big drop in biomass observed in 2012 and the resultant recovery in 2013 may be explained by the reaping treatment and phytoplankton density, the latter of which was high in 2012 and low in 2013 in terms of chlorophyll A concentration. This suggests that reaping is effective to suppress excessive macrophyte growth specifically when phytoplankton density is higher than a threshold value.
We carried out qualitative observations of adult Odonata fauna at Lake Izunuma-Uchinuma and the surrounding area, Miyagi Prefecture, Japan, in 2014. We observed a total of 10 families and 37 species including 3 species which newly were recorded. Previous studies have recorded a total of 10 families and 44 species in this area. 7 out of 10 species which were not found in this study were designated as an endangered species by Red List of Miyagi Prefecture and/or Red Data Book in Japan. These results indicate that Lake Izunuma-Uchinuma and the surrounding areas are available for over 30 odonate species as habitat, but not for endangered odonate species.
To examine easier methods for captive spawning of the fluvial eight-barbel loach, Lefua sp.1, six pairs of a male and a female were introduced in separate experimental tanks on March 1 in which water temperature was allowed to naturally rise and illumination conditions remained constant. Before the experiment, they had been reared together in the stock tank under conditions of 12 hr/day illumination by a 20-W fluorescent lamp from May in the previous year and water temperature of ca. 8℃ from December in the previous year. In the result, the six pairs all began to spawn in March. Each pair spawned for 3-13 days with intervals of 2-20 days over an entire spawning periods of 9-72 days. Water temperatures both at the first and the last spawning days of each pair were 15.1-16.5℃ and 15.5-22.1℃, respectively. The number of eggs spawned per spawning day and the total number of eggs spawned during spawning periods of each pair were 2-184 and 147-683, respectively. These results denoted the same tendency as found in the previous report in which the loach spawned under water temperature conditions of ca. 15℃ after being artificially increased from ca. 8℃.
We sequenced mitochondrial control region from 32 individuals of an endangered bitterling Acheilognathus typus captured from July through December, 2015 in Lake Izunuma-Uchinuma and its catchment. There had been no record of A. typus since at least 2000 in Lake Izunuma-Uchinuma as it was nearly driven to extinction by predation of introduced largemouth bass Micropterus salmoides in 1990s. Specimens examined were characteristic in that they do not have widely distributed haplotype but that they have haplotypes characteristic to waters in and around Lake Izunuma-Uchinuma. There is no stock with this particular haplotype composition in other known habitats in the Izunuma-Uchinuma area. Individuals examined in this study would be derived from Izunuma-Uchinuma catchment with this characteristic haplotype composition. The largemouth bass eradication efforts by people nearby reduced the bass stock in the lake and cyprinid fishes are now recovering. Our report gives useful information for the prospective restoration process of the endangered bitterling in Lake Izunuma-Uchinuma from a genetic perspective. DDBJ/GenBank entries of sequences given in this report are LC158077-LC158108.
Distribution of freshwater shrimp was investigated in rivers, drains, and reservoirs from 2014 to 2015 in northern Miyagi Prefecture. We collected prawns which closely resembled the native freshwater prawn, Palaemon paucidens, from the two stations. As a result of morphological examination, it was identified to be the alien freshwater prawn, Palaemonetes sinensis. This was the first report that P. sinensis is established in Miyagi prefecture.
Extermination methods of the invasive and alien plant species, the cutleaf coneflower (Rudbeckia iaciniata), were studied in national wild land protection areas of Lake Izunuma-Uchinuma. We focused on two elimination methods (pull up and weeding), and combined both methods in the elimination activity from 2013 to 2015. As a result of the extermination project, the number of cutleaf coneflowers in the two communities decreased from 689 and 421 to 42 (6.1%) and 13 (3.1%), respectively. Also, the elimination effort decreased over the three years. These results suggest the possibility that the communities of cutleaf coneflower could be controlled by the elimination activity.
In this report I discuss the first documented predation of a red-eared slider Trachemys scripta elegans by the largemouth bass. One red-eared slider (45 mm in straight carapace length, 21 g in wet weight) was found in the stomach of a male largemouth bass (388 mm in standard body length) caught by electrofishing in Akanoi bay, Lake Biwa.