| Dolphinfish or mahi-mahi?Coryphaena hippurus?belongs to the order Perciformes,the family Coryphaenidae,the genus Coryphaena,which is a mid-upper ocean migratory fish,widely distributed in the tropical and subtropical seas of all oceans,and in the Yellow Sea,Bohai Sea,East China Sea,South China Sea and adjacent waters around Taiwan.The Northwest Pacific Ocean is a vast ocean that connects the arctic and subarctic seas to the north.The Northwest Pacific is also an active area of heat and material exchange between the equatorial Pacific and the subtropical Pacific,which plays an extremely important role in global climate change.What's more,the confluence of the Pro-tidal cold current and the Kuroshio warm current in the northwest Pacific Ocean provides favorable environmental conditions for marine life,thus forming the fishing ground with the highest catch in the world.As an important economic species and one of the top predators in the food chain of marine ecosystem,it is necessary to study the changes in the resource amount and the response to climate change of Coryphaena hippurus.Based on the survey data during the fall of 2018 in the high seas of the northwestern Pacific?including survey date,latitude and longitude,fish,and field investigation data of temperature?salinity and chlorophyll?combined with the statistical data of FAO,the climate index data,the biological characteristics in the Northwest Pacific,resources distribution and environmental factors,and the relationship between its resources status and mechnisms in response of the climate change are preliminary studied in order to provide theoretical support for the rational exploitatiion and utilization of resources.The results are as follows:?1?Biological characteristics of Coryphaena hippurus of the Northwest Pacific.This paper analyzed the biological characteristics of the species in the Northwest Pacific Ocean,such as fork length,body weight distribution,sexual maturity and feeding habits,by using dolphinfish samples collected from the neckton survey project in the Northwest Pacific in 2018.Coryphaena hippurus's fork length ranged from 40.2to 81.1 cm,with an average fork length of 54.4 cm?SD=4.7?,and the dominant fork length group was 50 to 60 cm.Kruskal-wallis test found no significant difference in fork length between male and female?P>0.05?.The weight of dolphinfish ranged from509.4 to 4823.6g with an average weight of 1475.6g?SD=478.2?,and the dominant weight group ranged from 1000 to 2000 g.Kruskal-wallis test found no significant weight difference between male and female?P>0.05?.Relationship between fork length and body weight:(2=0.01272.9108?n=129,R2=0.7833?.The ratio of male to female of dolphinfish is 1.9.Coryphaena hippurus gonad maturity stage?,?immature individuals.In 129 dolphinfish samples,grade 0 stomach accounted for 3.9%,grade 1stomach accounted for 34.1%,grade 2 stomach accounted for 25.6%,grade 3 stomach accounted for 27.1%,and grade 4 stomach accounted for 9.3%.Coryphaena hippurus stomach contains fish,cephalopods,crustaceans 3 categories,11 species,belonging to9 families,and mainly fish.?2?Relationship between distribution and marine environment of Coryphaena hippurus in Northwest Pacific.A total of 53 sites were surveyed,of which 14 sites where dolphinfish was caught,ranging from 35°N to 41°N and 146°E to 160°E.From the east to west,it is mainly distributed in the eastern survey area,and from the north to south,it is mainly distributed in the southern survey area.In terms of latitude,the area with high abundance of dolphinfish covers a latitude range of 37°N to 39°N.In terms of longitude,the distribution range of longitude in the area with high abundance of dolphin appears at 157°E?158°E.The SST range of investigated sea area was 17.1to 28.6?,and the SST range of Coryphaena hippurus was 22.8 to 27.5?,mainly distributed in the high temperature sea area where the SST was greater than 23.7?.The SSS in the surveyed sea area ranged from 32.3 to 34.4‰,and the SSS in the sea area where Coryphaena hippurus was distributed ranged from 33.3 to 34.4‰,mainly in the high-salt area greater than 33.7‰.The concentration of Chla in the surveyed sea area ranged from 0.10 to 1.28 mg/m3,and the concentration of Chla in the sea area distributed by dolphin ranged from 0.10 to 0.79 mg/m3,mainly distributed in the sea area with low concentration of Chla less than 0.27 mg/m3.?3?A preliminary study on Coryphaena hippurus resources and it response to climate and environmental variability in the Northwest Pacific Ocean.The annual yield of Coryphaena hippurus in the northwest Pacific Ocean fluctuated significantly from1950 to 2017,but in general,the annual yield of Coryphaena hippurus in the Northwest Pacific Ocean increased gradually from 1950 to 2017 and peaked in the 1990s,then fluctuating gradual decline.The data show that the annual production from past 68 year varies from 5500 to 32104 tonnes,with an average annual production of 15035 tonnes?SD=5898?.The STARS method was used to analyze the decadal changes of Coryphaena hippurus yield and climate index?PDO,AOI,SOI?in the Northwest Pacific Ocean from 1950 to 2017.The results showed that the yield of Coryphaena hippurus in the northwest Pacific Ocean transformation in 1956/1957,1976/1977 and2006/2007 respectively.PDO transformation in 1956/1957,1979/1980,1997/1998 and2013/2014.AOI transformation in 1988/1989.SOI transformation in 1990/1991,2007/2008 and 2013/2014.The correlation between PDO,AOI and SOI of Coryphaena hippurus yield in the Northwest Pacific Ocean from 1950 to 2017 was analyzed by using cross correlation function.The results showed that there was a significant positive correlation between the yield of dolphin and PDO?P<0.05?,and the cross-correlation coefficient reached the maximum at one year's lag of PDO,the corresponding cross-correlation coefficient was 0.387,indicating that the lag time of PDO on the abundance of Coryphaena hippurus was one year.There was a significant positive correlation between the yield of Coryphaena hippurus and AOI?P<0.05?.The cross-correlation coefficient of the yield reached the maximum at one year's lag of AOI,and the corresponding cross-correlation coefficient was 0.282,indicating that the lag time of the influence of AOI on the resource abundance of Coryphaena hippurus was one year.There was a significant negative correlation between the yield of dolphin and SOI?P<0.05?,and the cross-correlation coefficient reached the maximum in the year of lagging SOI,with the corresponding cross-correlation coefficient of-0.414,indicating that there was no lag in the effect of SOI on the resource abundance of Coryphaena hippurus. |
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