| West African waters are one of the world’s first-class cephalopod fisheries,and since the large-scale industrial development began in the 1970 s,the rising production has brought huge economic benefits to the local area and attracted global fishery practitioners to go there.However,since the 21 st century,the exploitation of cephalopod resources in West Africa has tended to be saturated,and it is difficult to reach new heights,and some species have been in decline.In this context,both the management level of local governments and the fishing efficiency of fishing enterprises have raised higher requirements,and it is especially important to further understand and master the cephalopod fishery.To further understand and grasp the relationship between cephalopods and spatial and temporal and environmental factors,in order to provide reference significance for rational planning of commercial fishing,scientific fishery management of production,and enhanced conservation of fishery resources.This paper is based on fishing data from selected vessels in the main commercial cephalopod(cuttlefish,octopus,squid)fisheries in Morocco and Mauritania and environmental data(SST,SSS,Chl-a,SSHA,etc.)in West African waters from 2019 to 2021 from Shanghai Dier Deepsea Fisheries Co.,Ltd.We analyzed the spatial and temporal distribution of the West African cephalopod bottom trawl fishery and analyzed the CPUE of the main West African cephalopod species in relation to spatial and temporal factors and major environmental factors using GAM.The results showed that:(1)The closed season of Morocco is generally from April to June and October to December,and the cephalopod production shows a decreasing trend from the beginning of the fishing season to the closed season.The main producing species in Morocco is cuttlefish,which accounts for about 60% of the total cephalopod production,followed by octopus at about 30% and squid at only 10%.The production of cuttlefish is relatively stable throughout the year,while octopus has higher production in July and August than other months,and squid has lower production throughout the year.The spatial distribution of Moroccan fishing grounds showed a large operating range in the first two months of fishing,generally within the coastal range of 21°N to 25°N,and higher yields,and then gradually contracted as the yield decreased.Cuttlefish are mainly concentrated between23°20′N and 23°40′N in the first half of the year,and move slightly north in the second half of the year compared to the first half,between 24°N and 24°20′N.The center of gravity of the octopus fishery is more similar to the cuttlefish,the overall concentration,between 23°30′N and 24°N.The fishing grounds of squid were more dispersed,and the production was very low.The overall trend of the center of gravity of the fishery showed that the first half of the fishery was located in the southwest direction,and the second half of the fishery was shifted to the northeast.Mauritania is slightly different from Morocco in terms of closed season policy,Mauritania has two closed seasons from May to July and October to November,and the cephalopod production also shows a decreasing trend from the beginning of fishing to closed season,and the cephalopod production also shows a decreasing trend from the beginning of fishing to closed season.The cephalopod resource is dominated by octopus,which accounts for more than 50% of the total catch,and squid and cuttlefish are less productive,with octopus having higher production in July and August,cuttlefish having higher production in the first half of the year than in the second half,and squid showing a gradual decrease in production within a single fishing cycle.Spatially,the range of fishing grounds in Mauritania is very small,with most months in the range of 20°N～21°N,17°W～18°W.The distribution of the center of gravity of octopus and cuttlefish fishing grounds is relatively similar,while the squid fishing grounds are relatively scattered,but they are basically between 20°N ～20.7°N,17°E～17.5°E.The overall characteristics of the center of gravity of the winter fishery is south,and the center of gravity of the summer fishery is north.(2)The GAM model results showed that month had a significant effect on CPUE for all three species,with high values for cuttlefish and squid at the beginning and middle of the year and at the end of the year,while high values for octopus were mainly distributed at the beginning and at the end of the year;month had a significant effect on both full and new moons for cuttlefish and octopus,while squid only had a significant effect on new moons;high values were found in 22°N～26°N,15°W～17°W for cuttlefish,20°N～26°N,15°W～17°W for octopus,and 20°N～26°N,15°W～17°W for squid.The effect of chlorophyll concentration was positively correlated with cuttlefish and squid,but not with octopus;SST was positively correlated with octopus and negatively correlated with cuttlefish and squid;SSS had a significant effect on all three species,but fluctuated with a small range;offshore distance was negatively correlated with cuttlefish and squid,but the octopus is suitable for the offshore distance of 0.3 ° ～ 0.4 ° range.The sea surface height anomaly was-0.1m～0.2m as the optimum range for cuttlefish,-0.1m～0.1m as the optimum range for squid,and negative correlation with octopus;bottom depth was not significant for cuttlefish and octopus,and weakly significant for squid,but the variation was not significant.Cephalopods are extremely sensitive to the environment because of their short life cycle,and in the future,cephalopods have great prospects for exploitation in terms of both their resources and market demand,so it is important to study the relationship between their fishing grounds and various environmental factors.The results of this study can provide a scientific basis for the assessment of fishery abundance,scientific fishery management,and conservation of fishery resources in West African cephalopod fisheries. |
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