Trends In Fishery Activities And Fishery Resources In The Pearl River Estuary

The Pearl River Estuary,as a typical estuarine ecosystem,is well-known for its moderate salinity and temperature,sufficient dissolved oxygen,abundant organic matter,and fast growth of planktonic organisms.The Pearl River estuary was once one of the famous fishing grounds in China,with rich fishery resources and complex swimming animal community structure.In recent decades,factors such as over-exploitation,land-based discharges and changes in the natural environment have led to a serious decline in fishery resources,with the proportion of high-quality,economic species showing a declining trend and low-quality,non-economic species becoming the dominant species for fishing.The decline of fishery resources can have serious ecological and socio-economic impacts,but effective fisheries management can restore declining resources and achieve sustainable exploitation of fishery resources.Therefore,this study aims to investigate the current status of fishery production and the changing characteristics of fish community composition and trophic structure in the Pearl River Estuary,and then comprehensively analyse the risks and challenges faced by the fishery in the Pearl River Estuary,and make recommendations for optimisation,so as to provide a basis for fishery managers to grasp the development status of the fishery in the Pearl River Estuary,with a view to providing reference for the sustainable development of fishery resources in the Pearl River Estuary.The main findings of this study are as follows:（1）Current status of mixed fishery production in the Pearl River Estuary.Based on the Guangdong Agricultural Statistical Yearbook（missing 1996）for a total of 27 years during 1994-2021,historical literature,and social survey data,quantitative and qualitative analyses were conducted on the number of marine fishing motorized fishing vessels in the Pearl River Estuary,their total power,total catch,sub-production of different types of motorized fishing vessels,and the overall status of fishery production in the Pearl River Estuary.The results show that since 2003,when the Ministry of Agriculture formulated the"Opinions on the Implementation of the Marine Fishing Vessel Control System from2003 to 2010",the implementation of the"double control"system for fishing vessels has been effective,and the rising pattern of the number and total power of motorized fishing vessels in the Pearl River Estuary has been controlled.During 2004-2020,the overall number and power of fishing vessels in the Pearl River Estuary showed a decreasing trend,but the average single-boat power of motorized fishing vessels has increased rapidly again in recent years,indicating that the fishing intensity in the Pearl River Estuary remains too high.Among them,trawlers and gillnet motorized fishing vessels dominate,with an average power of 199 k W of fishermen’s vessels participating in the social survey.The total fishing production in the Pearl River Estuary began to show a decreasing trend from1997（356,000 t）.The single-vessel fishing power increases rapidly from 2016 to 2020,while the catch from 2010 to 2020 basically remains between 174,000 t and 223,000 t.Among them,during 1993-2020,the overall decreasing trend of fish catch production ratio,while the overall increasing trend of shrimp,crab and shellfish catch production ratio;the average value of the year-by-year production ratio of trawl and gillnet,which have great destructive power to fishery resources and ecological environment,reaches70.53%.In addition,the fishermen and managers who participated in the social survey showed that the fishery resources and the proportion of economic species in the Pearl River Estuary waters have declined seriously,and the fishing catch is mainly miscellaneous fish.Studies have shown that the fishing intensity in the Pearl River Estuary is still too high and the fishery resources are in an over-utilized state.The economic fish with long life cycle,slow reproduction rate and large individuals in the catch are gradually replaced by fish with short life cycle,fast reproduction rate and small individuals（miscellaneous fish）.（2）Problems faced by fishery resources and mixed fisheries in the Pearl River Estuary and suggestions for optimization.By comparing and summarizing the current status of mixed fishery production and the changing characteristics of fish community composition and trophic structure in the Pearl River Estuary,the existing problems and challenges faced by the fishery resources and mixed fisheries in the Pearl River Estuary were clarified,and suggestions for optimization were made.Studies have shown that the sustainable exploitation of fishery resources in the Pearl River Estuary is facing great challenges.The fisheries in the Pearl River Estuary suffer from low employability of fishermen,defective production data statistics,still excessive fishing intensity,unreasonable operation structure,and construction of marine protected areas.Therefore,it is recommended to organize fishermen to carry out training in fishery skills and other vocational skills,encourage switching to other industries,establish a sound statistical system for fishing catches,reduce the fishing intensity in the waters of the Pearl River Estuary,stabilize the fishery in the waters off the South China Sea,and at the same time strengthen scientific research on fishery resources,continuously optimize the structure of fishing operations,and implement augmentation and release during the fishing moratorium.（3）Characteristics changes in fish community composition and trophic structure in the Pearl River Estuary.The changes in community composition and trophic structure,such as fish stock,dominant species composition,mean trophic level（MTL）and fishing-in-balance（Fi B）index were comprehensively analyzed using data from 14 fishery bottom trawl surveys in the Pearl River Estuary in 1973—1975,1986—1987,1991,1998—1999,2006—2007,2012 and 2020—2021.The results showed that the stock density of fishery resources decreased from 665.65 kg·km^-2 in 1973-1975 to 376.92 kg·km^-2 in 2020-2021,with an overall downward trend.From 1973-1975 to 2020-2020,the dominant species composition changed dramatically,and showed a shift from high-trophic-level fishes to low-trophic-level fishes.Meanwhile,the number of dominant species and the proportion of total catch of high-trophic-level fishes also showed a downward trend.The mean trophic level of fish community decreased overall,falling from 3.74 in 1973-1975 to 3.22in 2020-2021 at a rate of 0.11 of a trophic level per decade.Since the implementation of marine fisheries management measures,such as a summer moratorium in 1999,the number of dominant species and the proportion of total catch of high-trophic-level fishes increased during 2006-2007,resulting in a significant rebound in the mean trophic level of fish community,followed by a progressive decrease.The fishing-in-balance index showed an overall wavelike decreasing trend and was closely related to the changes of the mean trophic level of fish community and the fishery resources.The fishing-in-balance index decreased with the decline of the mean trophic level and stock density of the fish community in 1986-1987,2012,and 2020-2021,and vice versa in 1991 and 2006-2007.In addition,the mean trophic level of fish community increased significantly in1998-1999,while the fishing-in-balance index and stock density decreased significantly,possibly as a result of the interference of extreme El Ni?o event in 1997-1998 and heavy oil spill event in 1999.The study suggested that fish resources in the Pearl River Estuary have been overfished and that the marine fisheries are largely shifting from large,long-lived,high-trophic level fish to small,short-lived,low trophic level fish.