| Under the influence of high-intensity fishing and marine environmental pressure,the fishery resources of traditional economically important species such as Larimichthys crocea,Larimichthys polyact and Trichiurus haumela in the East China Sea region have been significantly degraded,and the structure of some fish populations has been miniaturized,under-aged and sexually matured earlier.The structure of fishery resources in the East China Sea region has been greatly changed.Branchiostegus,as the mainstay of deep-water drift-net fisheries off the East China Sea,has a high economic value,and its catch has been stable and the fishery has developed rapidly in recent years,with a large resource potential.There are four species of Branchiostegus distributed in Chinese sea area,namely,Branchiostegus japonicus,Branchiostegus albus,Branchiostegus auratus and Branchiostegus argentatus.In the East China Sea area,27°00′～34°00′N and west of 128°00′E,the main species are Branchiostegus japonicus and Branchiostegus albus.The study on the biology and spatial and temporal distribution of the resources of two species of Branchiostegus is conducive to the rational assessment and sustainable utilization of their resources,and has a practical significance that cannot be ignored.In this study,the effective group identification of Branchiostegus japonicus and Branchiostegus albus was conducted based on the samples collected from August to October 2021,aiming to enrich the basic biological information of Branchiostegus;the reproductive biology of the two species of Branchiostegus was studied based on the samples obtained from March to June and August to December 2021;the main environmental factors affecting the distribution of the two species of Branchiostegus and their suitable distribution range were analyzed based on the data of deep-water driftnets operating in the East China Sea from January to April and August to December 2022.The main environmental factors influencing the distribution of the two species of Branchiostegus and their suitable distribution range were analyzed based on the fishing logbook data of deep-water drift-net vessels operating in the East China Sea from January to April and August to December 2022.The main research results are as follows.1.Discrimination of two species of Branchiostegus:399 samples of Branchiostegus,including 187 Branchiostegus japonicus and 212 Branchiostegus albus,were obtained from 27°30′～31°00′N and 122°30′～127°30′E in August-October 2021,and 28 measurable traits of otolith morphology and 55 measurable traits of fish body morphology were measured by framing method,and The analysis of variance and stepwise discriminant analysis were conducted.The results of the difference analysis showed that the otolith morphology of the two square-headed fish differed in the anterior,posterior,ventral and dorsal sides,and the fish body morphology differed in the head,carapace and tail of the fish;the results of the stepwise discrimination analysis showed that the correct discrimination rate based on otolith and fish body morphological parameters were 85.1%and 94.0%,respectively,while the combined discrimination rate based on the two morphological parameters reached 98.0%.The results showed that both otoliths and morphological parameters could be used to effectively discriminate between the two species of Branchiostegus,and the combination of multiple morphological parameters would further improve the accuracy of discrimination.2.Reproductive biology of two species of Branchiostegus:461 samples of Branchiostegus japonicus and 431 samples of Branchiostegus albus were collected from March-June and August-December 2021 in the sea area of 27°00′～31°00′N and 122°30′～127°30′E.The range of body length was 144-359 mm,with a mean body length of 233.0±37.8 mm,and the dominant group was 180-300 mm;the range of body mass was 52.6-982.7 g,with a mean body mass of 275.4±165.8 g,and the dominant group was 100-440 g.The relationship between body mass and body length was W= 0.000014 L3.160563.The absolute fecundity was 8795-137513 grains,and the absolute fecundity was linearly related to body length,body mass and gonadal mass;the analysis concluded that the peak spawning period of Branchiostegus japonicus in the East China Sea was June to October,and the spawning type was once a year.The range of body length of Branchiostegus albus was 186-361 mm,with a mean body length of 242.0±29.4 mm,and the dominant group was 200-300 mm;the range of body mass was 129.2-918.8 g,with a mean body mass of 280.5±114.9 g,and the dominant group was 120-420 g.The relationship between body mass and body length was W=0.000041 L3.053037.The absolute fecundity was 18310-127879 grains,and the absolute fecundity was linearly related to body length and gonadal mass,but the correlation with body mass was low;it was assumed that the peak spawning period of Branchiostegus albus in the East China Sea was April-May,and the spawning type was once a year.3.Spatial and temporal distribution characteristics of the two Branchiostegus:Based on the fishing logs of a deep-water drift-net vessel operating in the East China Sea from January to April and from August to December 2022,the temporal and spatial distribution characteristics of two species of Branchiostegus CPUE in this area are analyzed,and the generalized additive model GAM is used to investigate the environmental factors affecting their temporal and spatial distribution.The results show that the main factors affecting the spatial and temporal distribution of Branchiostegus japonicus resources in this area are month and depth,and the cumulative interpretation deviation rate is 77.7%.The water depth was the main factor affecting the fish,and the cumulative interpretation deviation rate was 32.2%.Branchiostegus japonicus mainly distributed in the range of 60～75 m water depth,23～28℃ sea surface temperature and 0.3～0.7 mg/m3 chlorophyll a concentration.Branchiostegus albus distributed in 80～95 m water depth,20～25℃ sea surface temperature,0.2～1 mg/m3 chlorophyll a concentration range.According to the current production situation of Branchiostegus,it is suggested to manage the Branchiostegus from the following aspects:strengthening the resource dynamic monitoring of the other Branchiostegus,controlling the fishing intensity of Branchiostegus,establish catchable specifications,reducing the use of triple gill nets,standardiizing the nets,determining the minimum mesh size,etc,so as to promote the sustainable conservation and utilization of the two species of Branchiostegus resources in the East China Sea. |
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