Age and growth comparisons of Hovsgol grayling (Thymallus nigrescensDorogostaisky, 1923), Baikal grayling (T. baicalensisDybowski, 1874), and lenok (Brachymystax lenokPallas, 1773) in lentic and lotic habitats of Northern Mongolia

Abstract

Despite concern over the conservation status of many Mongolian salmonids and the importance of their ecological role in Mongolia's aquatic ecosystems, little is known about their basic biology. Hovsgol grayling (Thymallus nigrescens) is endemic to Lake Hovsgol, Mongolia and listed as endangered on the Mongolian Red List. Baikal grayling (T. baicalensis) and lenok (Brachymystax lenok) are found in lakes and rivers throughout the Selenge drainage. A detailed study of the age and growth of these three salmonids was conducted based on 1,682 samples collected from July 2006 to July 2013 in Lake Hovsgol, its outlet the Eg River, and one of the Eg's largest tributaries, the Uur River.Our results suggest that Hovsgol grayling in particular can reach a much older maximum age (17 years in our samples) than previously believed based on aging from scales. Female Hovsgol grayling were heavier at a given length than their male counterparts. Lenok had a greater average length-at-age in Lake Hovsgol compared to the rivers and greater weight-at-length in the warmer Uur River than in the Eg; female lenok from the rivers had a greater average length-at-age than their male counterparts. This study provides critical new information for the management and conservation of these threatened salmonid species in Mongolia. Present Address

Fish conservation in the land of steppe and sky: Evolutionarily significant units of threatened salmonid species in Mongolia mirror major river basins

“…This unique B. lenok phylogroup is genetically distinct and thus highly valuable in the context of genetic conservation for the species. Incidentally, this group has also been the focus of increased scientific research on B. lenok including studies on their feeding ecology (Olson, Jensen, & Hrabik, ), thermal tolerances (Hartman & Jensen, ), lotic and lentic growth comparisons (Tsogtsaikhan et al, ), and seasonal movements (Kaus, Büttner, Karthe, Schäffer, & Borchardt, ).…”

“…The lack of genetic distinction detected by the mtDNA marker analysis suggests there is either a significant amount of contemporary gene flow between Lake Hovsgol and Selenge basin inhabitants via the Eg‐Uur River or else it has ceased only recently. The morphological differences displayed by individuals that inhabit Lake Hovsgol, including significant differences in the length–weight and age–length relationships compared to T. baicalensis sampled from riverine environments (Tsogtsaikhan et al, ), are likely due to the high ecological flexibility and phenotypic plasticity of this genus, which has previously caused confusion between intraspecific forms in Lake Baikal (i.e., black and white Baikal graylings, Knizhin et al, ). However, the contrib analysis and the pairwise F ST values still indicated that individuals sampled from Lake Hovsgol, while not a separate species, displayed genetic differentiation from each other, which justifies the Lake Hovsgol population as a priority within the T. baicalensis ESU.…”

Pelagic–littoral resource polymorphism in Hovsgol grayling Thymallus nigrescens from Lake Hovsgol, Mongolia

“…Saggital otoliths were collected opportunistically from 21 Hovsgol grayling and aged following the methods of Tsogtsaikhan et al (2017). Thin transverse sections of otoliths were examined under a compound microscope (50× magnification) using transmitted light, and age determination was made by one experienced reader.…”

Migration and movement profiles of a potadromous fish (Brachymystax lenok Pallas 1773) in a highly connected river system (Mongolia)

“…This salmonid inhabits the rivers and lakes of Siberia and northern Asia, including Mongolia, where it has been listed on the country's Red List of Fishes as vulnerable due to widespread population declines that have resulted from increased water pollution, habitat destruction, climate change and fishing activities (Dulmaa, 1999;Kottelat, 2006;Ocock et al, 2006). While fish capture and consumption have traditionally not been a major part of the local culture in Mongolia, this is changing rapidly (Chandra, Gilroy, Purevdorj, & Erdenebat, 2005;Bailey, 2012;Hogan & Jensen, 2013;Tsogtsaikhan et al, 2017) and thus the current widespread unregulated and illegal fishing operations that occur throughout the country has now been considered as the primary driver of B. lenok population declines. In response, authorities now need to adapt more comprehensive protection measures and improve management strategies to conserve and maintain robust B. lenok stocks in Mongolia.…”

“…Previous research on B. lenok has focused on phylogenetic origins of conspecifics (Froufe, Alekseyev, Alexandrino, & Weiss, 2008;Froufe, Alekseyev, Knizhin, Alexandrino, & Weiss, 2003;Shed'ko et al, 1996), spawning behaviour (Esteve & McLennan, 2008), feeding and diet (Chandra et al, 2005), thermal ecology (Hartman & Jensen, 2017) and biometric comparisons between lotic and lentic populations (Tsogtsaikhan et al, 2017). However, a detailed knowledge of this species' spatial ecology remains largely unknown, with only a single study being conducted on the re-described Brachymystax tsinlingensis Li 1966 (Xing et al, 2015) reported as B. lenok tsinlingensis in the Nakdong River, South Korea.…”