| Crocodile Shark,Pseudocarcharias kamoharai,is a common by-catch species in the tuna longline fishery.It is at the top of the marine ecosystem,which plays a very important role in the stability and diversity of the marine ecosystem.However,because of its low commercial value,after catch is often discarded,its biological data and research are relatively lacking.At present,the species is affected by fishery activities,and its resource status is worrying.According to the total of 1561 Crocodile Sharks biological data collected by Chinese national tuna fisheries observers in the tropical Atlantic from 2019 to 2015(6.38°S~15.17°N,42.02°W~18.53°W)and total of 114 vertebrae samples of Crocodile Shark were collected.The content and results of this paper are as follows:1.Biological characteristics of Pseudocarcharias kamoharai from the tropical Atlantic OceanAccording to the data of 1426 ind Crocodile Sharks,the biological characteristics were studied and compared according to different gender.There are significant difference in the average fork length,dominant fork length and the relationships between fork length and round weight of male and females of Pseudocarcharias kamoharai(P<0.05).The average fork length of female samples was significantly larger than that of male samples(P<0.01).The female-male ratio was 1:1.71,and the chi-square test did not accord with 1:1 distribution(P>0.05).The feeding level of Pseudocarcharias kamoharai in the two ocean areas was mainly 0 and I,separately.There was no significant difference in feeding level between male and female(P>0.05).Tropical Atlantic male Hepatosomatic indices(HSI)were 7.47~42.63,with an average value of 20.04 ± 3.9.The HSI of female individuals ranged from 7.94 to36.36 with an average of 18.33 ± 5.0.The HSI of Male and female was significantly different.Female was significantly greater tha n male(P<0.05).The pups of Pseudocarcharias kamoharai were in the range of 1~6ind(of which 5 were not found),and the number of pups was 4 which accounted for 81% and the female-male ratio of pups is 1:1.Pregnant female’s fork length range of 77~99cm;total weight range of 4.2~8.0kg and for the pups from the same female,there is 50 percent probability to make the female-male ratio of these pups becomes 1:1.The average number of pups for each pregnant female was 3.72 and the ratio accords with 1:1(P>0.05).2.Age and growth of Pseudocarcharias kamoharai from the tropical Atlantic OceanAccording to the total of 114 Crocodile Sharks(54.0–101.0 cm,fork length,LF)vertebrae samples((male 54,female 60))and related data,which were collected from the tropical Atlantic Ocean(6.31°S~12.15°N,18.32°W~36.47°W)by Chinese Tuna Fishery Scientific Observer from November 2012 to January 2016.Age verification consists of 4 common elasmobranchs age verification methods,there are the alizarin red S staining method,cobalt nitrate and ammonium sulfide staining method embedded in polyester resin,polished slide method and X-ray photography method.This research selected a proper age verification method towards Crocodile Shark based on the test results,and analyzed the relationship between its age and length.The results show that: In this study,the method that used 0.01% alizarin red S solution to vertebral bone staining could reach the best results;through the observation of Vertebrae Ring,female group’s age range is from 2 to 10 years whereas male’s is from 2 to 11 years.The mean absolute percentage error(MAPE)is 9.41%,so the accuracy of verification is relatively high.The relationship between Fork length(LF)and vertebrae radius(VR)as follows: LF=111.07VR+345.37,R2=0.567,and the growth parameters of the cone-shaped shark were estimated as follows: t0=-1.82,K=0.252,LF∞=107.74 cm,t∞=11.9a.There were no significant differences in the relationship between LF and VR and the relationship between fork length and age(P> 0.05).3.Preliminary analysis of Pseudocarcharias kamoharai resources dynamic and spatial distribution in the tropical Atlantic OceanThe resource dynamics and spatial distribution of 1561 tailed shark data were analyzed.The results were summarized as follows: In the study area(6.33°S~17.43°N,18.25°W~42.03°W),the highest concentration of the CPUE area was in the zone 5°N~10°N,20°W~30°W;The CPUE value was in the range: 0.00-3.94 and the average were 0.83.From 2010 to 2015,CPUE showed a variation trend,but the upward trend was not significant.The Chondrichthyes accounted for the total proportion of the catch decrease;the total number of Crocodile Sharks accounted for 5.8% of total number of fish caught,accounting for 22.5% of the total number of Chondrichthyes bycatch.The higher average CPUE values of the Tropical Atlantic Crocodile Shark were recorded in December,and January to March.The largest fork length class(fork length range of 85-90cm)of the Crocodile Shark were distributed in the regions 5°N~7.5°N,27.5°W~37.5°W and 5°N~0°,25°W~30°W.Crocodile Shark hook depth ranges between 140-313 m,the average observed depth was 221 m.The frequency of 1-3 hooks(140-212m)is the largest,accounting for 55.59% of the total catch rate.There was no significant difference in the hook position of the Crocodile Shark in different months from October to April.Crocodile Shark was obviously distributed in the shallow water layer during pregnancy.There was no significant difference between feeding level and hook position of Crocodile Shark.4.Relationship between environmental factors and the CPUE(catch per unit effort)of the Pseudocarcharias kamoharai in tropical Atlantic Ocean based on the Tweedie-GAM model.The research on the relationship between the CPUE(Catch per unit effort)and environmental factors can provide basic data for resource protection and management of this important species.Based on the Tweedie distribution theory,and the data of 1085 Crocodile Sharks collected by the national observers of longline fishery from 2009 to 2015 in the tropical Atlantic Ocean(6.38°S~14.92°N,42.03°~18.53°W),the Tweedie-GAM model was established,and the temporal and spatial effects of CPUE as well as the relationship with environmental factors were analyzed.The results showed the explained cumulative deviance of the Crocodile Shark’s CPUE to be 40.2%.The spatio-temporal factors(year,month,longitude,latitude)all had significant effects(P<0.05)on the Crocodile Shark CPUE.environmental factors such as: sea surface height(SSH),chlorophyll-a concentration(C HL),weather code(WC),sea surface salinity(SSS)and sea level pressure(SLP)all had significant effects on CPUE(P<0.05).However,the Beaufo rt wind force and lunar scales did not have significant effects on the CPUE(P>0.05).Significant correlation(P<0.05)was observed indifferent latitudes and months between the sea surface temperature.The standardized CPUE of the Crocodile Shark in 2009-2015 showed an increasing fluctuation tendency. |
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