Spatiotemporal Distribution And Its Relationship With Environmental Factors In Different Fish Farms

Cephalopods are considered to be one of the three underutilized fishery resources in the world and an important source of protein for human beings in the future.According to the estimation of related scholars,the catchable amount of cephalopods in the world is 0.1 billion to100 million tons.Therefore,the development prospect of cephalopod resources is very wide,especially the Marine Ommastrephidae resources.As one of the important fishing targets of China’s ocean squid fishery,the annual fluctuation of its resources often leads to overinvestment in fishing.Understanding and grasping the distribution and changes of its fishery resources and fishing grounds combined with biological characteristics will play an extremely important role in the sustainable development of China’s ocean squid fishery.Based on the fishing log data of Dosidicus gigas in the Eastern Pacific,Illex argentinus Castellanos in the Southwest Atlantic,Sthenoteuthis oualaniensis in the Indian Ocean and Ommastraphes bartramii in the North Pacific Ocean,including vessel name,operation time,operation location(latitude and longitude),daily output,etc.,the fishing log data of Dosidicus gigas in the Eastern Pacific,Illex argentinus Castellanos in the Southwest Atlantic,Sthenoteuthis oualaniensis in the Indian Ocean and Ommastraphes bartramii in the North Pacific are collected.Combined with the corresponding sea surface temperature(SST),chlorophyll-a concentration(Chl-a)data,fisheries in production center of gravity method is used to study the location changes,and then using Arcgis 10.0 software visualization soft time and space distribution of fish farms,using the generalized additive model fitting relationship between CPUE and the impact factor and drawing,the final comparison soft fish farms mechanism differences between different sea area.The research results of this paper areas follows:(1)The results of the study on the changes of catch and CPUE of different species showed that the monthly catch of Dosidicus gigas in the Eastern Pacific increased firstly and then decreased from December 2019 to April 2020,and the highest catch was found in February.Except for the increase in February,the CPUE curve showed a general downward trend.For Illex argentinus Castellanos in the Southwest Atlantic,the annual catch showed a trend of decreasing first and then increasing,and the highest catch was in 2018.The CPUE curve was high in 2014,but showed a slow fluctuation trend in other years.Except for 2014,the monthly catch increased first and then decreased in other years,and the peak value of catch was mostly concentrated in February and March.CPUE also showed a trend of increasing first and then decreasing,with high CPUE usually distributed in February and March.The monthly catch of Sthenoteuthis oualaniensis in the Indian Ocean decreased first and then increased,and the high catch was concentrated from September to November in 2017.CPUE increased first and then decreased,with the highest value in August.Except for June,the catch of Ommastraphes bartramii in the North Pacific was firstly increased and then decreased in 2019,and the highest catch was in June.The overall CPUE curve showed an upward trend firstly and then a downward trend,and high CPUE was distributed in June,July,September,October and November.(2)The distribution of different kinds of squid farms and the research results show that the SST,Chl-a squid stem fisheries center of gravity concentration distribution in 0°～3°S、105°W～114°W area,different fisheries center of gravity by the changes are apparent in warp direction.GAM model showed that the optimal SST range was 24.5～25.5 °C and the optimal Chl-a range was 0.16～0.20 mg/m~3 in the Eastern Pacific.The center of gravity of Illex argentinus Castellanos in the Southwest Atlantic is distributed in the sea area of 45°S～47°S and59°W～61°W.Except for 2014,the distribution of the center of gravity of production in each month from 2016 to 2018 is relatively concentrated.According to the GAM model,the optimal SST range in the Southwest Atlantic is 12～14 °C.The optimal range of Chl-a is 0.1～2.0 mg/m~3.The center of gravity of Sthenoteuthis oualaniensis in the Indian Ocean is distributed in12°N～16°N and 58°E～63°E sea areas.The center of gravity of Sthenoteuthis oualaniensis first advances to the southwest and then retracts to the northeast.GAM model showed that the optimal SST range was 26.0～27.5 °C,and the optimal Chl-a range was 0.2～0.4 mg/m~3.The fisheries center of gravity Ommastraphes bartramii in the North Pacific Ocean is distributed in38°N～45.5°N,173°W～176°W,38°N～ 45.5°N,160°E～165°E sea area,GAM model shows that the optimal SST range in the North Pacific is 14～19 °C,the optimal range of Chl-a is 0.1～2.0mg/m~3 after.According to the results of this study and related literature,it is concluded that during this period,the population of the Eastern Pacific is small group,the population of the Southwest Atlantic is mainly summer spawning,the population of the Indian Ocean is large group,and the population of the North Pacific is mainly winter and spring spawning.Changes in the distribution of different kinds of squids CPUE were related to biological characteristics,fishing routes and Marine environment changes.The CPUE decreased gradually from December to April of the following year because the spawning period of Dosidicus gigas was from October to January of the next year,and the individuals died after spawning.In addition,the migration of Dosidicus gigas after reaching maturity length of equator led to the disperse location of the fish,which was also the reason for the difference in the yield of each month;The high overlap between the spawning ground and the working area of the main catch from January to March is one of the reasons for the high CPUE distribution in the Southwest Atlantic;the Indian Ocean squid in each season resources exist differences lead to the change of CPUE;The North Pacific CPUE is different because fishing boats switch,there are different fishing objects in different sea areas.Compared with single environmental factor and space factor,time factor has a more significant impact on CPUE,because the influence mechanism is complex.Except for the factors studied in this paper,other environmental factors have not been comprehensively considered,and other factors can be added for comprehensive consideration in the future.