The Environment Adaptability And Conservation Strategy Of Eriocheir Sinensis In Estuarine Life Stages

Chinese mitten crab,Eriocheir sinensis(Decapoda,Brachyura)is an important economic species in China.The estuarine life stages of E.sinensis which composed of the breeding season(mating,spawning,berrying and hatching)and larval development stages(zoeae I-V and megalopae),is the most sensitive to environmental changes,is also the key stage of the population resource.In this study,E.sinensis in beeeding season and larval development stages were studied based on the investigations in the Yangtze Estuary from 2013 to 2015.The spatial and temporal law of E.sinensis spawning was analysed,including the requirements of water temperature and salinity.The horizontal and vertical activity pattern of the ovigerous E.sinensis was forecasted based on the spatio-temporal distribution changes.In the following,the activity pattern of the ovigerous E.sinensis was verified using the ultrasonic telemetry.Meanwhile,the environment adaptability of the ovigerous E.sinensis was explored using a GAM model(generalized additive model)based on the abundance of the ovigerous E.sinensis and environmental factors.The occurring and spatio-temporal distribution law of E.sinensis zoeae and megalopae were expounded,then the environment adaptability of each stage larvae were separately analysed using the GAM models.Ultimately,the conservation strategy of E.sinensis in the Yangtze Estuary was proposed after the environmental adaptability was revealed.These results will provide theoretical basis for the rational utilization and protection of the Chinese mitten crab,also enrich the basic theory of the life history and environment adaptability of E.sinensis.Key results are as follows:1.The spawning laws and water temperature and salinity requirements of female E.sinensis in the Yangtze Estuary.The spawning time of E.sinensis mainly focused after December 25 th,and the habitats were mainly located in the south of Jiuduansha Wetland(121°55?-122°03? E,31°05?-31°10? N),Deep Water Channel of the north channel(121°58?-122°07? E,31°15? N)and the area between Hengsha Shoal and Chongming Shoal(122°00?-122°10? E,31°21?-31°25? N).Meanwhile,the appropriate temperature(°C)and salinity(‰)of female spawning were separately 8-11 and 6-14.2.Activity law and environment adaptability of the ovigerous E.sinensis in in the Yangtze Estuary.The peak time of the ovigerous E.sinensis was from late February to late April,the habitats were located downstream the spawning area,mainly distrbuted in the east of Hengsha Shoal and the waters in Deep Water Channel which located in the south of Hengsha Shoal.During the embryogenesis,the ovigerous E.sinensis mainly inhabited depth 11 m with lower activity level;In the peak time of hatching from late April to early May,the ovigerous E.sinensis mainly inhabited depth 6 m with higher activity level;After the hatching,the original ovigerous E.sinensis would migrate downstream.The ovigerous E.sinensis preferred habitats with salinity 5-15,flow velocity 0.6-1.2 m/s and transparency below 6 cm.3.Spatio-temporal distribution and environment adaptability of the early development stages E.sinensis in in the Yangtze Estuary.After a different hatching period(16-56 d),zoeae I of E.sinensis were hatched from middle March to late May,with a peak from late April to early May.And zoeae V subsequently metamorphosed into megalopae from early May to middle June,with a peak in middle and late May.Zoeae I of E.sinensis were mainly located in the waters with the flow velocity below 0.7 m/s and salinity 6-20 near the mouth of the north branch and southeast Jiuduansha Wetland.With the development of zoeae,the zoeae in the mouth of the north branch stayed,whereas zoeae II-V in the southeast of Jiuduansha Wetland migrated gradually to the southeast and the northeast.And zoeae II-V preferred the waters with the flow velocity below 0.7 m/s,transparency 5-50 m and salinity above 13.Magalopae were occurred in the mouth of the north branch,the east of Hengsha Shoal and the east of Nanhui Shoal.Unlike the zoeae,the flow velocity,transparency and salinity were not important to the megalopae.Megalopae preferred the habitats with water temprature above 16.5 °C,dissolved oxygen above 8.5 mg/l and depth below 7 m.4.The conservation strategy of E.sinensis in the Yangtze Estuary.Based on the environment adaptability of E.sinensis in estuarine life stages,a series of countermeasures were drafted.Fishing plan: the fishing time and location of adult E.sinensis were limited before December 25 th,and in the waters west 122° E;A ban on fishing megalopae.Artificial propagation and releasing: releasing the adult E.sinensis with carapace length above 60 mm in the spawning ground in late December,with a sex ratio 1:1.Establishing the key habitat reserves: based on the reproductive law of E.sinensis,creating a Yangtze Estuary Reserve for breeding stages E.sinensis in Hengsha Shoal from February 15 to May 1.Befor the land reclamation in Hengsha Shoal,finishing the replacement habitat construction of the breeding ground of E.sinensis near the waters.the time of sand exclusion activity in Deep Water Channel should be deplayed to June-October.Reestablishing the breeding ground of E.sinensis using the replacement habitat construction in Nanhui Shoal.