Research On The Associative Characteristics Of Tuna Associated Schools Around Drifting Fish Aggregating Devices Based On Echo-sounder Buoys Data

Tuna purse seine fishing is a fishing operation that uses purse seine nets to catch floating objects associated schools and free schools of tuna that inhabit the surface and mixed layers,Based on drifting fish aggregating devices,DFADs have produced 54% of the total tuna purse seine,DFADs have been deployed and largely equipped with echo-sounder buoys,which provide accurate geographic positioning of DFADs and estimates of tuna aggregation biomass for the tuna purse seine fishery on a remote and continuous basis,thereby effectively reducing the carbon footprint and fleet operating costs associated with searching for fish,and significantly improves the success of the fleet’s catch rate.This paper assesses and analyses the reliability of the acoustic data from DFADs deployed by Chinese purse seine vessels in the western and central Pacific Ocean and investigates the characteristics effect of tuna floating objects associated schools under DFADs.This paper provides scientific support to reveal the aggregation dynamics of tuna floating objects associated schools under DFADs and to assess the impact of DFADs on the marine ecological environment in the Central and Western Pacific Ocean in the future.The first part of this paper is based on the echo-sounder buoys data of DFADs collected by China’s purse seine vessels in the Central and Western Pacific Ocean,combining data from fishing logs,new DFADs deployment data and netting data,and applying a multilayer perceptron classification model to evaluate the accuracy of the DFADs tuna schools detected by echo-sounder buoys.The second part is based on the classification results of the presence or absence of tuna schools around newly deployed DFADs,and the key analysis indicators such as colonization time,colonization rate and continuous residence time of tuna schools around DFADs,which provide data support to explore the process of tuna schooling and cluster dynamics around newly deployed DFADs.The main findings of this paper are as follows.(1)Classification of the presence and absence of floating objects associated schools of tuna under DFADs.The multi-layer perceptron classifier performed well in distinguishing the presence and absence of tuna schools under DFADs,with an accuracy of 84%,and was accurate and effective in detecting tuna aggregations under DFADs(sensitivity of 0.98).The effectiveness of the proposed method in distinguishing the presence or absence of tuna aggregation under DFADs with echo-sounder buoys in the western and central Pacific Ocean.(2)Associative size classification of tuna schools under DFADs.The efficiency of the multilayer perceptron classifier in classifying the size of tuna schools under DFADs was significantly lower than that in classifying the presence or absence of tuna schools under DFADs,and the overall classification and recognition accuracy was low at 48%;the multilayer perceptron classifier was accurate and effective in detecting tuna aggregations under DFADs(sensitivity of 0.98),and did not perform well in identifying the absence of tuna schools.(3)Characteristics of the pelagic distribution of the biomass of the tuna floating objects associated schools.Before and after sunrise,the depths of tuna schools under DFADs inhabited in the western and central Pacific Ocean were in the middle to lower water layers,and tuna species in DFADs schools were more likely to occupy waters deeper than 80 m.The biomass of tuna schools inhabiting deeper water layers was higher than that of tuna schools inhabiting shallow water layers,and the proportion of the distribution of the biomass of tuna schools in DFADs schools in each water layer would increase with the depth.The distribution of DFADs tuna biomass in each water layer will increase with depth.(4)Time and rate of colonization of tuna schools under DFADs.The shortest drift immersion time of newly deployed DFADs at sea was only 9 days,and the longest drift immersion time reached 283 days,and the average drift immersion time of DFADs at sea was 92.09±58.15 days.The fastest colonization time was 2 days after the deployment of newly deployed DFADs,and the slowest colonization time was 22 days after the deployment.The colonization rate of newly deployed DFADs in the Central and Western Pacific was 48.49±21.78%,with the lowest colonization rates of DFADs at 5.56% and the highest at 95%,with most DFADs reaching nearly50%.(5)Daily colonization rates of DFADs.The mean value of the daily colonization rates of tuna attached to DFADs was 43.49% and the maximum value was 67.48%,which was the highest peak of the daily colonization rates on the 25 th day after the deployment of newly deployed DFADs,i.e.from 1 to 140 days,indicating that tuna were attached to DFADs for a longer period of time,further confirming that DFADs have a stronger attraction effect on tuna.This further confirmed the strong attraction and aggregation effect of DFADs on tuna.(6)Continuous stay and absence time of tuna floating objects associated schools under DFADs.The average continuous residence time of tuna floating objects associated schools around DFADs was 11.72 days in the western and central Pacific Ocean,with the longest continuous study residence time of up to 53 days detected by DFADs buoys.Between the two consecutive periods of stay,the DFADs were in a state of no tuna cluster attachment,with a mean continuous absence of 8.83days(standard deviation SD: 10.63 days),of which the longest continuous absence was 76 days.