The Impact Of Spatio-temporal And Environmental Factors On The Mauritanian Horse Mackerel Fishing Ground Based GAM

Mauritania horse mackerel mainly conclude Atlantic horse mackerel(Trachurus trachurus) and short-term horse mackerel(Trachurus Cadengat). Atlantic horse mackerel along the African coast distributes from the Strait of Gibraltar to the south of the Senegal coast offshore 300 meters and inhabits hundreds meters above the continental shelf. The highest fish density will be around 18~20 ° N in Mauritanian coast. Short-term horse mackerel inhabits the middle layer of water that also is schooling species. Shoal usually occurs at the bottom area whose depth near 20~100m with temperature 15~22 ℃, sometimes also be active in the middle and upper layer, and even near the surface. They mainly feed on small crustaceans, shrimp and small fish.Mauritania faces west by the Atlantic Ocean with long coastline, from Cape Brown to St. Louis, whose total length is about 700 km, the total continental shelf is 34000Km2, and the exclusive economic zone is 195 000 Km2. The cold currents from the north of Canary mixes the warm water from the southern Guinea, forming a strong upwelling where contains a lot of plankton, which is particularly suitable for the habitat for fisheries resources. That is the reason why Mauritanian could be the one of the world-famous fishing grounds."Kai-shun vessel coming from Shanghai Fisheries(Group) Corporation, captured fish from January 12, 2012 to August 29, 2012 in Mauritanian area, with a 9372 tons harvest that jack mackerel contributed to 4073 tons. Fishing net is a four single-sac trawl for 1440 × 472.25 m.Generalized additive model has a significant advantage of a highly nonlinear and non-monotonic relationship between the response variable is described based on the data and forecast data model determine the response variables and to predict the relationship between. Generalized additive model for the different variables, choose a different program mode, for some factors linear fit and join other factors, the use of smooth function fitting, therefore generalized additive model is sometimes called semiparametric models. For this reason, the generalized additive model is very flexible, and can effectively show the implied ecological relationship of data, improve the understanding of our ecological system.Using the fishery data measured on the sea: yield, fishing time, position, web depth, the water temperature of the target water layer. The SST, SSH and Chl-a data are downloaded from the Oceanwatch, the resolution is 0.5 ° x 0.5 °, the time interval is one week. Calculate the CPUE from the fishery data and draw the distribution graph of CPUE. And then analyze the CPUE and the different factors statistically, including the correlation analysis of different factors, analyze the weight of the influence of different factors to CPUE by using GAM model.The result of environment factors impact on the time and space distribution of horse mackerel in the water of Mauritania as follows:(1)Distribution of fishing ground.In Mauritania waters(20.5 ~ 20.5 ° N, 16.5~ 18 ° W), the range of CPUE’s value is 13.91 kg/h ~ 78750 kg/h, the mean value is 2947.66kg/h. The higher value of CPUE appeared in the east of the fishing ground: 18 ~ 19 ° N, 16 ~ 17 ° W. By processing the depth data of fishing in the EEZ of Mauritania, we divided the water into 6 layers: 0~20 m, 20~ 40 m, 40~60 m, 60~80 m, 80~100 m and 100 above. And analyze the depth of trawling by frequency distribution. The most frequent fishing layer is 0~20 m, reached 54%, while the total frequency of fishing under the 60 m is only 12%.(2) The relationship between space and time factor and Mauritania horse mackerel fishing ground.In the water of Mauritania, the best abundance of the horse mackerel resource is from January to April, the abundance decrease from May. In January and February, central fishing grounds is in 18 ~ 19 ° N, 16.5 ~ 17 ° W, and it moved to the south from March and April, and it moved to northwest after June, in the area of 19.5 ° N, 17.5 ° W.(3) The influence of environment factors to CPUEWe get the conclusion from the GAM model, on the horizontal direction, the different factors on the influence weight of CPUE is SST, fishing time, longitude, SSH, latitude and Chl-a. On the vertical direction, the depth of the net impact the CPUE more than the fish population depth.(4) The influence of the variety of SST and SSHAccording to the overlay chart of CPUE and SST, SSH data, the range of SST in Mauritania’s EEZ is 16~28 ℃. Bigger CPUE mainly distributed within the area of 16~20℃. The range of SSH is-47~-9 mm, the bigger CPUE mainly distributed in the area of-47~-25 mm.In Mauritania fishing ground, through analysis, the optimum space and time environment factors as follows: the best fishing time is around 00:00, fishing area is between 18~19°N,16~17°W, the depth of the net is 0~50m, the temperature of the fishing layer is 15~18℃,SST is within 16~20℃,Fishing vessel towed faster than 4.5kn/hour.