长江靖江段刀鲚捕捞量的时间变化及相关环境因子分析

江苏靖江段位于长江近口段,是长江刀鲚渔汛最集中的水域。调查了靖江段2008、2009、2012~2015年6个渔汛期的捕捞数据,采用广义可加模型(GAM模型)分析了刀鲚捕捞量与靖江段表层水温、潮差、气压、降水量、浑浊度、CODMn等环境因子之间的相关性。调查显示,靖江段每年发放刀鲚专项渔业捕捞证84~95本,平均年作业天数28~43 d,2012~2015年的作业天数比2008~2009年明显下降。6个渔汛期刀鲚的年捕捞量变幅为3.71~17.38万尾和3.61~18.26 t,除2013年外,年捕捞量总体上仍呈下降趋势。采用GAM模型对10艘持证渔船的刀鲚日捕捞量与环境因子之间的相关性分析显示,日捕捞量随水温的升高而递增,汛期78.8%的产量在15~23.2℃水温范围获得。而当水温低于10℃时,空网率上升,仅获得5.7%的汛期产量。表明当水温不足10℃时,刀鲚可暂时停止其生殖洄游过程。分析还显示,69.1%的汛期产量在2.0 m以上的大潮差期获得,表明潮汐亦是影响刀鲚日捕捞量的重要因子。低浊度及气压、降水量、CODMn等对刀鲚的日捕捞量无显著性影响,但当浊度大于100 NTU时,日捕捞量迅速降低。可见,水温、潮差和高浑浊度是影响长江靖江段汛期刀鲚捕捞量的关键环境因子。

TEMPORAL VARIATIONS OF COILIA NASUS CATCHES AT JINGJIANG SECTION OF THE YANGTZE RIVER IN FISHING SEASON IN RELATION TO ENVIRONMENTAL FACTORS

The Japanese grenadier anchovy Coilia nasus (Clupeiformesis) is a highly commercial and valuable anadromous fish species in China. Jingjiang section of the Yangtze River, as an important area for fishery resource conservation and reproduction of Japanese grenadier anchovy, is located at the connected region of lower reaches and estuary of the Yangtze River. In our study, we investigated C. nasus catches of fishing seasons from 2008-2009 and 2012-2015 and analyzed its environmental factors such as tidal range, water temperature, pressure, precipitation, turbidity and COD_Mn, and reported its upstream migration. According to fishing license recorded, the fishing period extended from 5 March to 10 May, fishing license numbers per year were between 84-95 and fishing days were 28-43 during the entire fishing period in the Yangtze Jingjiang section from 2008, 2009, 2012-2015. Anchovy numbers ranged from about 3.71 to 17.38 ×10⁴ individuals and the annual weight ranged between 3.61 to 18.26 ton respectively. In general, anchovy total annual catch showed a declining trend except for explosive growth during 2013 fishing period. Fishing intensity parameters decreased significantly during 2012-2015 compared to 2008-2009 fishing periods. Generalized additive models indicated that temperature significantly affected catch. Similar variation trend was also found in all fishing periods, and the daily catch increased with increasing water temperature. 78.8% of total catch number were recorded at a temperature between 15-23.2℃ and few individuals were recorded below 10℃.Our result suggested that a temperature<10℃ may inhibit anchovy upstream migration. Tidal range was also an important factor, and daily catch increased with increasing tidal range. 69.1% of total catch number were recorded at tidal above 2.0 m. This may be because upstream migration of anchovy relies on the tidal currents via selective tidal stream transport limiting the energy cost. Turbidity showed a non-linear negative relationship with the daily catch. Sharply declined daily catch were associated with turbidity above 100 NTU. Low turbidity, pressure, precipitation and COD_Mn did not affect daily catch significantly (P>0.05). Therefore, our findings suggested that tidal range, temperature, and high turbidity significantly affected the catch of C. nasus and accounted for the majority of the daily variation in catch level. Overall, this study is expected to benefit sustainable management of fishery resources and conservation of this species.