Dynamics of Icefish (Salangidae) Stocks in Nanyi Lake, Eastern China: Degradation and Overfishing

Abstract

There are two genera and four species of icefishes in Nanyi Lake, which have been commercially exploited in the past two decades. As result, icefish yield decreased over the years, from the peak of 260 metric tons to 15 metric tons, and this change was highly correlated (t =-3.95, df = 1, p = 0.001) with increased fishing effort. Meanwhile, the size composition of the icefish assemblage dramatically changed, with significantly increased relative abundance of the small icefish category (from 0.06 to 0.91). Furthermore, sampling during the 2001 fishing season was characterized by a progressive decrease in CPUE (by 3.14 times) and an increase in relative abundance (from 0.83 to 0.97) of the smallest icefish, giving direct evidence of the stocks decline and size diminution of icefishes in relation to the commercial fishing effort. Both the historical records and the 200 1 seasonal changes of the icefish stocks indicated that this resource in Nanyi Lake has been overfished and illustrated that small fishes can also be overfished to degradation when they are commercially exploited.

Degradation of icefishes (Salangidae) in the Yangtze River basin of China: threats and strategies

“…The medium species included Neosalanx taihuensis, with SL over 70 mm. Neosalanx oligodontis was the small species with SL less than 50 mm (Chen 1956;Wang et al 2004). When the proportion of larger body-sized species is reduced, the body-size composition changed and icefish catch devalued, which was defined as size reduction of target assemblage by Cao et al (1991).…”

“…Stocks decline and yields reduction of wild icefish resources in both the freshwaters and estuaries have already been reported (Sun 1982;Zhu 1985), but few papers have focused on the spatial dynamics and diversity change of icefish assemblages so far (Wang et al 2004). …”

“…In the Yangtze River basin, icefishes have been commercially fished since early 1900s in the mid-lower reaches (from the estuary to Gezhouba Reservoir near Yichang City), and icefish fishery was virtually an essential component of historical fisheries in this river basin (Zhu 1985;Wang et al 2002).…”

“…As annual fishes, icefishes reproduce in discrete annual pulses with parental individuals dying shortly after spawning (Wang et al 2002). So, in feeding seasons, the sampled icefish individuals in our investigation were the same cohort at the same age, and this provided a great convenience for our population dynamics study.…”

“…So, in feeding seasons, the sampled icefish individuals in our investigation were the same cohort at the same age, and this provided a great convenience for our population dynamics study. Moreover, the short life span and simple life history allow the rapid response of population size to environmental changes, and thus icefish species are very sensitive to habitat degradation and environmental changes (Wang et al 2004(Wang et al , 2005Islam et al 2006).…”