Fish Assemblage Shift after Japanese Smelt (Hypomesus nipponensis McAllister, 1963) Invasion in Lake Erhai, a Subtropical Plateau Lake in China

The introduction of non-native fish species is known to have adverse effects on aquatic ecosystems, but their effect on plateau lakes is not well studied. In this study, we examined the effect of the Japanese smelt (Hypomesus nipponensis) invasion on the fish assemblage in Lake Erhai, a subtropical plateau lake in southwestern China. Through cluster analysis and non-metric multidimensional scaling (NMDS), we found a significant fish assemblage shift: the population of sharpbelly (Hemiculter leucisculus) fell by 67% in catch per unit effort (CPUE) from 2.262 to 0.741; topmouth gudgeon (Pseudorasbora parva) fell by 52% from 0.61 to 0.29; and icefish (Neosalanx taihuensis) plummeted by 88% from 0.736 to 0.088. Meanwhile, the numbers for crucian carp (Carassius auratus) improved by almost 185% from 1.82 to 3.36. A Pearson correlation analysis showed that these four species significantly correlated with the invasion of the Japanese smelt: sharpbelly (−0.71), topmouth gudgeon (−0.71), icefish (−0.62), and crucian carp (0.81). This study documented the expansion of invasive fish and their effects on native species over time, thus providing a case study of invasive fish as well as a theoretical basis for further research into interspecies interactions.

Coastal fishes in the northwestern Okhotsk Sea (westward from 147o E): fishery and prospects of its development

Fishery at the northwestern Okhotsk Sea coast is analyzed for the period from 2000 to 2019. Pacific herring, saffron cod, pacific cod, capelin, flounders (Limanda aspera, Pleuronectes quadrituberculatus and Platichthys stellatus), and smelts (Hypomesus japonicus and Osmerus mordax) are landed in this area. The spawning herring prevails (95.2 %) in the catch. Almost all spawning herring is caught at the coast of Khabarovsky Krai. Taking into account the area of spawning grounds for herring in the lagoons of the coasta, withdrawal of this species could be increased, though actually it was decreased in the last two decades in 1.8 times, and since 2012 the herring fishery is continued in Okhotsk District only. The fishing strategy changed: offshore harvesting with stationary nets transformed to combined using of stationary and casting nets and expanded to the rivers. The catches delivery changed, as well: the herring catches are processed mostly ashore since 2008. Withdrawal of saffron cod fluctuated from 1.9 % to 186.5 % of the total available catch (TAC) volume for this species, with rapid growth in the last 5 years; its main fishing grounds shifted from the waters of Nikolayevsk District to the waters of Tugur-Chumikan District. Landings of smelt grew since 2009, too: annual catches of rainbow smelt increased from 72.2 t, on average, in 2009–2014 to 119.4 t in the last 5 years (up to 90 % of this volume was caught in Tugur-Chumikan District); landing of japanese smelt grows even faster and now exceeds 50 % of TAC. The stock of capelin was exploited weakly, annual catches of this species changed from 0.7 % to 23.3 % of TAC. Stationary and casting nets were the only fishing gears used for the capelin fishery in 2000s, but recently midwater trawls are also used. Catches of flounders had a growth tendency, though they were rather low and never exceeded 50 % of the recommended volumes. Dynamics of the pacific cod landings became positive when fishermen started to use small boats for this fishery, its annual catches increased in 2014–2019 from 69.7 to 84.8 t, the withdrawal rate achieved 9.3 % of TAC. Available fish resources in the northwestern Okhotsk Sea and technical equipment of local enterprises provide strong potential of fishery industry in this area.

Feeding ecology of the non-indigenous fish Hypomesus nipponensis in Lake Ulungur, China: insight into the relationship between its introduction and the collapse of the native Eurasian perch population

Studies of feeding ecology are essential in gaining an understanding of how established non-indigenous fish species interact with the invaded communities. In the present study, we investigated the composition and seasonal variation in the diet of the introduced Japanese smelt Hypomesus nipponensis, a small planktivorous fish, in Lake Ulungur, China. The objective was to examine the ecological role of this established non-indigenous smelt through the analysis of its diet, which might give more insight into the relationship between its introduction and the collapse of the native Eurasian perch population. Results showed that the Japanese smelt had a broader feeding spectrum than had been previously reported. Of 10 taxonomic or ecological categories of food, cladocerans (54.70%) and rotifers (15.39%) were the most important food items in terms of the index of relative importance (IRI), whereas surface food and chironomid larvae were the most important by weight. Although cladocerans were consistently the most important food, rotifers and copepods, together with surface food and chironomid larvae, substituted when cladocerans were scarcer. Because both rotifers and chironomid larvae are important food of larval and young perch, introduction of Japanese smelt into the lake might be responsible for the collapse of the perch population because of the suppression of rotifers and chironomid larvae in spring through seasonal predation.