We investigated population structure, resource density changes of Larimichthys polyactis and its relationship with environmental factors in spring, based on the survey data of bottom trawl in adjacent sea areas of Zhoushan fishery spawning ground protection area from 2014 to 2019. The results showed that the relationship between body length and body weight of Larimichthys polyactis was W=0.44×10-4×L2.78, and parameter b was less than 3, which indicated that L. polyactis had negative allometric growth in recent years. There was a negative correlation between fullness and body length, with body becoming slender. From 2014 to 2019, body length and weight of L. polyactis were the highest in 2014 and the lowest in 2019. Since 2014, population size of L. polyactis in Zhoushan fishery spawning ground protection area and adjacent sea area had gradually decreased, indicating that the miniaturization of L. polyactis had not altered in recent years. From the perspective of the annual change of resource density, resource density of L. polyactis was higher than that before the establishment of the reserve, indicating that the management and protection of the reserve area played a protective role in the recovery of L. polyactis resources. The fitting results of GAM model showed that water depth and bottom water temperature were the environmental factors closely related to the density distribution of L. polyactis resources. With increasing water depth, the resources showed a fluctuating upward trend and were the highest near the water depth of 60 m. In the range of 12-16 ℃ water temperature, the resources increased with the increases of bottom water temperature. When water temperature was above 16 ℃, resources decreased with the increases of bottom water temperature.
根据2014—2019年舟山渔场产卵场保护区及邻近海域底拖网调查资料,分析了春季小黄鱼的群体结构、资源密度变化及其与环境因子的关系。结果表明: 小黄鱼的体长-体重关系式为: W=0.44×10-4×L2.78,b值<3,说明近年来小黄鱼为负异速生长,肥满度与体长呈负相关,身体趋于细长。2014—2019年小黄鱼的体长和体重均以2014年最高、2019年最低。2014年以来,舟山渔场产卵场保护区及邻近海域小黄鱼的群体规格逐渐减小,说明近年来小黄鱼个体小型化现象并未改善。与产卵场保护区设立前的数据相比,保护区建立后小黄鱼资源密度有所提升,表明保护区管护对小黄鱼的资源恢复起到了一定的保护作用。GAM模型拟合结果显示,与保护区及周边海域小黄鱼资源密度分布关系密切的环境因子主要是水深和底层水温。随着水深的增加,小黄鱼资源量呈波动上升趋势,在水深60 m附近时资源量最高;在12~16 ℃水温范围内,小黄鱼资源量随底层水温升高而增大;当水温>16 ℃时,其资源量随底温的上升而下降。.
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