珠江东塔产卵场鳙繁殖的生态水文需求

鳙(Aristichthys nobilis(Richardson)),我国著名的四大家鱼之一,是一种重要的大型淡水经济鱼类。然而近年来由于各种原因,我国鳙种群数量急剧下降。依据2006—2013年珠江中下游长时间序列仔鱼数据和日平均流量数据,分析了研究水域鳙的繁殖生态,包括仔鱼出现的时间分布特征和早期资源周年变化规律,同时采用交互小波光谱分析方法 (cross wavelet analysis),分析了径流量与鳙仔鱼多度的关系。发现珠江水系鳙早期资源发生主要在5至8月,2006—2011年早期补充资源量逐渐减少,2012—2013年间呈明显著增加;鳙早期资源年度出现的时间呈缩减趋势,其中最大繁殖量出现的时间逐年提前。交互小波光谱分析结果表明:径流量的改变与鳙仔鱼的多度显著正相关,当径流量大于5×103m3/s,且持续2d以上,是珠江水系鳙大量繁殖的基础,将对受梯级水坝控制的鳙产卵场的繁殖生态水文保障具有指导意义。

Analysis of the ecohydrological demands of bighead carp breeding in the Dongta spawning grounds of the Pearl River, via cross-wavelet analysis

Bighead carp, Aristichthys nobilis (Cyprinidae, Hypophthalmichthys), is one of the four big traditional domestic carp species (along with black carp, grass carp, and silver carp). It is a large fish of high commercial importance because of its palatability and popularity with Chinese consumers. The size of the bighead carp population in China has decreased significantly in recent years, because of various environmental stressors and habitat losses due to dam construction, pollution, and overfishing. In this study, we investigated the ecology of bighead carp breeding in the Pearl River, which is a large subtropical river and the longest river in southern China. This study was based on a dataset generated by sampling at a fixed station (23° 2'' 40" N, 112° 27'' 5" E) every 2 d, from 2006 to 2013. The earliest bighead carp larvae were captured on April 13, 2008, and the latest were found on October 7, 2006. The breeding season primarily lasted from May to August and accounted for 99% of all annual spawning. The total number of larvae found decreased gradually from 2006 to 2011, and then increased significantly in 2011. The date of the earliest recorded spawning did not change over the years, but the date of the latest spawning day occurred earlier each year, indicating that the length of the spawning period (interval between the first and last spawning days of the year) has decreased over time. Our results also show that peak spawning occurs earlier each year. We used cross-wavelet analysis with phase angle and coherency parameters to analyze the relationship between the abundance of bighead carp larvae and the local hydrological conditions. Simulation studies have shown that the spectral signature produced by the cross-wavelet method is a useful approach to developing an objective and quantitative understanding of how river discharge affects the population size of bighead carp larvae. Discharge was positively correlated with the abundance of bighead carp larvae, though larval occurrence always lagged behind discharge. That is, water discharge acted as a trigger for the spawning of bighead carp. Simulation studies have shown that an increase in water discharge >5×10³ m³/s and lasting at least 2 d is a prerequisite for the bloom spawning of bighead carp in the Pearl River. This study was undertaken as part of a long-term investigation of the Pearl River''s wild fisheries resources, and our results will help guide their protection and management. The wavelet approach is a particularly promising method of analyzing ecological data such as the relationship between hydrological conditions and fish larva occurrence. Our results will help pave the way for the quantitative analysis of the impact of the environment on an organism. We propose that frequency and scale domain methods, in the form of wavelet transforms, can serve as useful probes during preliminary investigations of fisheries data, in order to elucidate the mechanisms underlying changes in fish diversity and abundance. We conclude with a discussion about the role wavelet analysis could play in appropriately guiding flexible probabilistic models linking fisheries with environmental covariates.