Shift towards Opportunistic Life-History of Sleeper in Response to Population Decline over Multi-Decadal Overfishing

Understanding long-term changes in life-history traits is central to assessing and managing freshwater fisheries. In this study, we explored how life-history traits have shifted in association with long-term change in population status for a native fish species (freshwater sleeper, Odontobutis sinensis, a by-catch species of shrimp traps) in the middle Yangtze lakes, China. We assessed the life-history traits of the species from Honghu Lake in 2016, where abundance had been dramatically lower following about 60 years of high fishing pressure, and made comparisons to similar data from Liangzi Lake (1957), when fishing intensity was low and abundance was high, and Bao’an Lake (1993–1994), when about 10 years of intense exploitation had occurred and abundance had greatly declined. Modern Honghu Lake sleeper exhibit life-history traits that are substantially more opportunistic compared to both of the historical populations. Modern fish were larger at age-1 and had significantly faster growth rates, a higher prevalence of sexually mature individuals and increased fecundities. Fish from the historical samples were larger and had higher age class diversity and delayed sexual maturation. Combined, the data suggest that faster growth towards early sexual maturation and reduced body sizes are associated with destabilized populations and ecosystems. Similar life-history patterns are common in other declined fish populations under exploitation. Recovering historic fish life-history dynamics requires conservation management policies aimed at reducing harvest and improving floodplain habitats.

Comparison of photosynthetic fluorescence characteristics of several submerged plants in Honghu Lake, China

Submerged plants are the pioneer species of eutrophic water remediation, and they are important for maintaining the health of aquatic ecosystem, while light is the main limiting factor for the growth of submerged plants. In this study, we measured the maximal quantum yields of photosystemⅡ(Fv/Fm) and rapid light curves (RLCs) of five dominant submerged macrophytes in situ by using pulse-amplitude modulated fluorometer (Diving-PAM). Results revealed that P. crispus L. and M. verticillatum L. had the highest Fv/Fm value, all species’ Fv/Fm are less than 0.8. In addition, the variation trends of Fv'/Fm' and Fv/Fm were same. All species showed statistically significant differences in α, while P. crispus L. and M. verticillatum L. showed the highest α value in the five species. And the variation trends of rETRm and Ek were basically the same. It indicated that P. crispus L. and M. verticillatum L., both of which had high photosynthetic efficiency, had excellent ability to withstand hard light. Compared five species, P. crispus L. and M. verticillatum L. had resistance capacity to hard light as well as faster photosynthetic rate, and V. natans (Lour.) Hara had higher resistance capacity to low light. Thus, when submerged plants are used for water restoration, V. natans (Lour.) Hara could be regarded as a pioneer species in eutrophication water restoration. P. crispus L. and M. verticillatum L. will have better effects when used in shallow water areas.

Water quality evaluation based on the water quality index method in Honghu Lake: one of the largest shallow lakes in the Yangtze River Economic Zone

Honghu Lake is the largest lake-type wetland in Hubei Province, China. It is also one of the largest shallow lakes in the Yangtze River Economic Zone, a key area in the relatively more developed southeast of China. However, the water quality has seen a deterioration tendency in recent decades, mostly owing to unreasonable human activities such as lake enclosure aquaculture following rapid social and economic development. Based on the water quality index (WQI) method, the water quality of Honghu Lake, by the vast amount of data collected from five observation sites monitored over ten years, was analyzed and evaluated. The results show that: (i) the water quality of Honghu Lake is in the ‘General’ grade as a whole with a WQI value of 43.41 ± 6.66; (ii) the water quality has been improving in the recent two years, reversing its decade-long deterioration; (iii) the water quality sampled at the Lantian site is the worst while that of the Guandun site is the best; (iv) the concentration of Pb and Cd are the key parameters to determine the water quality of Honghu Lake. Therefore, it can be concluded that more attention should be paid to investigate heavy metals in Honghu Lake in the future.