Spatial And Temporal Analysis Of Chilean Jack Mackerel Fishing Ground And Its Migratory Route In The Southeast Pacific

Chilean jack mackerel(Trachurus murphyi)in the southeast Pacific Ocean is an important marine fishing target in the world.Its catch the highest proportion of the global jack mackerel catch,from the exclusive economic zone of Chile,Peru,Ecuador to the sea off New Zealand which whole are distributed in the south Pacific.In 2000,our country entered the southeastern Pacific Ocean off Chile to detect and catch Chilean jack mackerel,and it quickly became the main fishing ground for large-scale trawl fisheries in our country.However,due to the changes in the marine environment in recent years and the wide distribution of its own resources,new changes have taken place in its fishing grounds.In addition,because Chilean mackerel is a highly migratory straddling pelagic fish,it is difficult to grasp its migration route.Therefore,the study of the temporal and spatial distribution and migration route of Chilean mackerel fishing grounds is particularly important.The fishing data and biological data of Chilean jack mackerel with Sea Surface Temperature(SST),Sea Surface Salinity(SSS),chlorophyll concentration(Chl-a)and sea surface temperature anomaly(SSTA)were used in this paper.Hierarchical cluster analysis and neural network and Frequency distribution method were used in this study to analyze the temporal and spatial changes of the fishing grounds and migration route of Chilean jack mackerel.It is expected to provide a scientific basis for the production and scheduling of Chilean jack mackerel fishing boats in our country.The main research conclusions are as follows:(1)Temporal and spatial changes of the center of gravity of the fixed cluster’s center: The distribution range of the center of gravity of the fixed cluster of Chilean mackerel in April to August is 43.4°S-43.7°S,80.5°W-81.3°W sea area,42.4°S-42.7°S,79.8°W-81.3°W sea area,41°S-41.4°S,79.3°W-80.7°W sea area,38°S-38.4°S,78.9°W-79.5°W sea area,28.2°S-31° S,77.4°W-79.3°W sea area.Specifically,the center of gravity of the fixed cluster of fish from April to July moves from south to north in latitude at about 5°,and the longitude moves from west to east at about 1.7°.In August,the fish school continues to move to the northeast,at latitude.It is about 8°,and the longitude is about 1°.(2)The relationship between cluster gravity center and SSTA index: Chilean jack mackerel cluster gravity center is affected by SSTA in both longitude and latitude,and has a significant negative correlation with SSTA value in longitude,and a significant positive correlation in latitude.When the sea surface temperature anomaly rises,the cluster’s center of gravity shifts to the northwest,and when the sea surface temperature anomaly decreases,the cluster’s center of gravity shifts to the southeast(3)The relationship between the age of Chilean jack mackerel and the range of fork length: the range of the second-year harpoon length is 193-268 mm;the range of the third-year harpoon length is 268-317 mm;the fourth-year-old harpoon length is318-349 mm;the fifth-year-old harpoon Length range 350～388 mm;6-year-old harpoon length range is between 388～437 mm,7-year-old harpoon length range is437～463 mm,8-year-old harpoon length range is between 463～483 mm,9-year-old harpoon length is greater than 483 mm.(4)The migratory route of Chilean jack mackerel: The fish school with a dominant fork length of 2-4 years migrated westward from the coastal waters of Chile and Peru.After reaching the sea area near 39.5°S and 78°W in May,the fish school migrated to the northwest for feeding and overwintering.After reaching the sea area near 33°S and 85°W in October,the fish school turned to the southwest for feeding before spawning.From November to next March,they reached the spawning groundthe sea areas near 37°-39°S and 85°-88°W.From next March to April,the fish school migrated from the spawning ground to the southwest.After reaching the sea area near 41°S and 87°W in next May,the fish school turned to the northwest for feeding and overwintering.After reaching the sea area near 36.5°S and 95°W in next October,the fish school turned to the southwest for feeding before spawning.Our research indicated that large Chilean jack mackerel at the same longitude tended to migrate to the south,while large Chilean jack mackerel at the same latitude tended to migrate to the west.The westward migration took an S shape.