Declined fitness in larvae born from long-distance migrants of anadromous Coilia nasus in the lower reaches of the Yangtze River, China
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摘要: 洄游性刀鲚是长江中下游在经济和生态上具有重要价值的鱼类。依照亲体-后代的权衡理论认为,长距离洄游消耗的能量由后代增加的适合度补偿,长距离洄游群体后代的生长率和摄食会更好。该研究在刀鲚整个洄游区域设置四个采样点采集鱼类早期资源,通过分析刀鲚的早期生长和摄食揭示长距离和短距离洄游群体后代的适合度。研究结果表明,早期生长率、仔鱼的摄食强度和摄食的高营养饵料比例随着洄游距离的增加而下降,与假设不相符,这可能与由人类活动导致的河流生境改变密切相关。由于过度捕捞,刀鲚种群个体小型化严重,洄游距离明显缩短,再加上江湖阻隔,长距离洄游群体无法到达连通湖泊鄱阳湖和洞庭湖繁殖,只能在生境条件比较差的干流中繁殖。长距离洄游群体的后代又由于在洪水季节出生,遇到高流量带来的低密度饵料,因而摄食强度低,摄食的高营养饵料比例少,生长率就比河口出生的短距离群体后代慢。但这种现象可能因为现在的长江全年禁渔得到缓解,禁渔可使刀鲚长得更大活得更久,最后足以能洄游到连通湖泊的繁殖和产卵,后代在湖泊中育幼,存活率高,对群体的补充强度大。Abstract: Anadromous Coilia nasus is a socioeconomically important species from the middle and lower reaches of the Yangtze River. Here, we compared growth and feeding of C. nasus larvae in four reaches along the full migration corridor of the river (640 km) to determine how fitness varies between progenies of short- and long-distance migrants. Results demonstrated that larvae collected in downstream sections grew faster, exhibited higher feeding intensities, and consumed larger zooplankton (a favored food resource). Our results did not support the parent-offspring trade-off theory, which predicts that the costs and benefits of migration increase with migration distance, and higher parental costs with long migration should be offset by increased offspring fitness. We suggest pervasive human impacts along the river are likely driving the observed ecological patterns. Overfishing has resulted in a truncated body size in migrants, which shortens their migration distance; isolation of floodplain lakes from the river restricts fish spawning and nursing to suboptimal lotic river habitats; and higher discharge experienced by larvae born from long-distance migrants in the upstream river reaches during the later flooding season results in declined feeding intensity and slower growth compared to those produced from short-distance migrants in the earlier season. We predict that a fishing ban in the Yangtze River will allow fish to grow larger and older so they can access floodplain lakes further upstream, which will further enhance recruitment of the C. nasus population.
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Figure 1. Abundance, body length-at-age relationships, and feeding intensity profiles of Coilia nasus larvae at Chongming, Jingjiang, Nanjing, and Anqing in the Yangtze River in 2009 and 2010
A: Map of middle and lower reaches of the Yangtze River, China, showing four sampling sites (●) for C. nasus larvae, including locations of Datong Hydrological Station (//) and Jiujiang Meteorological Station (▲) and a picture of C. nasus. B, C: Temporal fluctuations in abundance of C. nasus larvae at Chongming (red circles), Jingjiang (blue triangles), Nanjing (black triangles), and Anqing (purple rhombus) in 2009 (B) and 2010 (C). D, E: Body length-at-age relationships of C. nasus larvae at Chongming (red circles), Jingjiang (blue triangles), Nanjing (black triangles), and Anqing (purple rhombus) in 2009 (D) and 2010 (E). Regressions were y=0.69x+3.36 (r2=0.97, 2009) and y=0.63x+4.04 (r2=0.98, 2010) at Chongming, y=0.70x+2.92 (r2=0.95, 2009) and y=0.63x+3.85 (r2=0.97, 2010) at Jingjiang, y=0.60x+3.35 (r2=0.99, 2009) and y=0.58x+3.34 (r2=0.98, 2010) at Nanjing, and y=0.58x+3.61 (r2=0.98, 2009) and y=0.57x+3.69 (r2=0.94, 2010) at Anqing, respectively. F, G: Percentage compositions of gut at different fullness levels, i.e., 0 (empty), 1 (≤25% full), 2 (≤50% full), 3 (≤75% full), 4 (full), and 5 (distended with thin stomach wall) for C. nasus larvae at Chongming, Jingjiang, Nanjing, and Anqing in the Yangtze River in 2009 (F) and 2010 (G).
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ZR-2021-423 Supplementary Materials.pdf
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