Analysis Of Biological Characteristics And Resource Status Of Coilia Mystus In Oujiang Estuary

Coilia mystus was one of the main economic fishes in the Oujiang Estuary.It starts to reproduce and migrate upstream from the shallow coastal waters in late April every year.In recent years,due to overfishing and environmental pollution,the resources have been declining.In 2015,2018,2019,and 2020,the study conducted fishery biological resource monitoring and investigation in Oujiang Estuary.11 stations(F01-F11)were set up from Lingkun Island to Qiaoxia Township for survey nets used by the masses.Drift nets and small double trawl nets were surveyed during the breeding and migration season of Coilia mystus from April to August each year.This paper conducts research on the biological characteristics,feeding habits,resource distribution characteristics and environmental factors of Coilia mystus,and the main results were as follows:1.Biology of Coilia mystusIn this study,the age structure of the four generations of Coilia mystus migratory population was relatively similar,that was,age 1,age 2,and age 3 accounted for more than90%,and the number of individuals(above age 3)was relatively small.Body length and weight:The average body length of the four generations of Coilia mystus was162.71±21.04mm,and the average weight was 19.39±8.79g.The average body length and weight of the four generations are relatively similar.The maximum and minimum values appeared in 2015;The difference in body length between the 4 generations was not significant(P>0.05),and the difference in body weight was not significant except in 2015and 2019(P>0.05),and the differences among other generations were significant(P<0.05);5-8,2015 The average body weight of the Coilia mystus gradually becomes smaller.The average value of the length and weight of the Coilia mystus in July 2019 and August 2020was relatively large,and the average value of the other months was relatively small.Fecundity:the average value of absolute fecundity of Coilia mystus was 17711±7817.The absolute fecundity difference between 2018 and 2019 is significant(P<0.05),and the absolute fecundity difference between 2018 and 2020 was significant(P<0.05),the difference in absolute fecundity between 2019 and 2020 was also significant(P<0.05).2.Feeding habits of Coilia mystusBased on the technology of stable carbon and nitrogen isotopes,the feeding habits of Coilia mystus in Oujiang Estuary were studied.The results show that the average value of?¹³C of Coilia mystus in Oujiang Estuary is(-17.09±1.88)‰,and its variation range was-26.80‰-(-15.09‰);the average value of?¹⁵N was(11.69±0.85)‰,and its variation range was 9.59‰-17.14‰.Person correlation analysis showed that the?¹³C value and?¹⁵N value of Coilia mystus were significantly positively correlated with body length.According to the calculation of the?¹⁵N value,the average trophic level of Coilia mystus in Oujiang Estuary was 3.67±0.20,and the trophic level was significantly positively correlated with body length.Fish,crabs,decapods,copepods,mysid shrimps and krill are the food organisms eaten by Coilia mystus in Oujiang Estuary,among which decapods have the highest nutritional contribution rate.The nutrient contribution rate of decapod,mysid shrimp,and copepod to Coilia mystus in the Oujiang estuary was significantly higher than that in the coastal waters,while the contribution rate of krill in the coastal waters was higher.3.Coilia mystus resourcesAccording to the monitoring data of the Coilia mystus flow gillnet in Oujiang Estuary,during the fishing season,the catch of Coilia mystus migratory breeding population was roughly expressed in the waters adjacent to Jiangxin Island(stations F02 and F01,as well as the most downstream station F10).And the most upstream station F03 has very little output).Monthly changes:The trawl survey did not collect Coilia mystus in April,and a small amount of Coilia mystus appeared in May.The catch of Coilia mystus was higher in June and July,and Coilia mystus disappeared in August.The feeding grounds and overwintering grounds for Coilia mystus were mainly distributed in the waters near the mouth of the Oujiang River,and the spawning grounds are mainly distributed in the Jiangxinyu area of the Oujiang River;from the monthly changes of fish eggs,larvae and juveniles,it can be seen that Coilia mystus are in April each year.It began to cluster towards the Oujiang River estuary,and spawning began in the estuary in May.June was the peak period of spawning of Coilia mystus.In July,spawning decreased significantly,and spawning was about to end in August.4.Habitat suitability evaluationOujiang Estuary was one of the main habitats of Coilia mystus,and grasping the temporal and spatial distribution characteristics of its early resources in the Oujiang Estuary can provide a scientific basis for the restoration and management of Coilia mystus resources.The roe,larvae and environmental factors of Coilia mystus were sampled monthly,and the GAM model was used to study the environmental factors that affected the early population distribution.Based on the prediction performance of the area under the receiver operating characteristic curve(AUC)evaluation model,the prediction of the eggs,larvae and juveniles of anchovy from May to July in 2020.The results showed that:May to July was the main breeding period of Coilia mystus in Oujiang Estuary.Surface temperature and surface salt were the main environmental factors affecting the early population of Coilia mystus in Oujiang Estuary.Surface salt has a very significant impact on the distribution of Coilia mystus eggs.The suitable salinity was 0-0.3‰;the suitability of larvae and juveniles to water temperature and water salt was wider than that of fish eggs,and the distribution of resources was greatly affected by surface temperature,and the most suitable surface temperature is 23-25?.The forecast results for 2020 are similar to actual surveys.The low-salt water area near Qidu Island in the upper reaches of the Oujiang River was the main water area where the eggs of Coilia mystus are distributed.The larvae and juveniles of Coilia mystus were distributed in the waters of the Oujiang River.The island's coastal waters and near the entrance to the sea.