黄海中南部黄鮟鱇生物学特征及其资源密度的年际变化

Interannual variations in the biological characteristics,distribution and stock density of anglerfish Lophius litulon in the central and southern Yellow Sea

根据1985年、2000年、2005年和2009年秋季共4个航次的底拖网调查数据,对黄海中南部黄鮟鱇的生物学特征、相对资源密度和群体分布的年际变化进行了研究。结果表明,黄鮟鱇雌性平均体长大于雄性平均体长,从1985年到2009年个体小型化、种群体长结构简单化明显,体长、体重由负异速生长转变为等速生长。种群以雄性为主,除2000年外各年的样品性比均与1差异显著,小于20 cm体长组和40—50 cm体长组的性比变化明显,由雌雄相当分别转变为雄性占优势和全部为雌性。各年样品的性腺成熟度均以II期为主,但2005年和2009年的样品中出现部分性成熟个体。黄鮟鱇分布密集区的水温范围为9.3—10.8℃,盐度范围为32.4—33.2;近年来黄鮟鱇的相对资源密度呈升高趋势,且群体分布向黄海北部扩展,产量与提前2年的海表温度具有极显著相关性(r=0.61,P=0.004),这可能因为海表温度主要对黄鮟鱇生活史初期造成影响从而影响其产量。黄鮟鱇生物学特征、资源分布与种群密度的变化可能与捕捞强度和气候变化有关,是种群对外界压力的适应性响应。

In the Yellow Sea and East China Sea regions, the anglerfish Lophius litulon has become an important fisheries species in recent years. In this paper, we examined interannual variations in the biological characteristics, stock distribution and stock density of this fish based on bottom-trawl survey data collected in the central and southern Yellow Sea during the autumn of 1985, 2000, 2005 and 2009. Results showed that the average body length of the female was larger than that of males in all sampling years, and the differences were significant in 1985 and 2005 （P 〈 0.05）. In addition, average body length in both sexes decreased markedly over the past two decades, with individual miniaturization and the dominant frequency distribution of body length being reduced from double peaks to a single peak, indicating clear simplification of the population structure. The relationship between body length and body weight showed negative allometric growth in 1985 and 2000, and the allometric growth parameter b was significant smaller than 3 （P 〈 0.05） in these two years, while growth became isometric in 2005 and 2009. The sex ratios were significantly smaller than 1 （P 〈 0.05） in the sampling years 1985, 2005 and 2009, and males were dominant in the samples, but was insignificant from 1 （P 〉 0.05） in the 2000 sampling year. Moreover, sex ratios in both the 〈 20 cm and 40-50 cm body-length groups were not significantly different from 1 in both 1985 and 2000 （P 〉 0.05）, but male dominated in the 〈 20 cm body-length group （P 〈 0.05） and all individuals were female in the 40-50 cm body-length group in 2005 and 2009. Gonad development was mainly stage II in all sampling years, while a very small proportion of sexually mature individuals were found in 2005 and 2009. Bottom water temperature within the high density distribution area ranged from 9.3 to 10.8 ℃, with salinity in the range 32.4-33.2. The relative biomass and percentage of anglerfish in the total catch showed a clear increasing trend from 2.94 kg/h, 3.0% （1985） and 1.33 kg/h, 1.2% （2000） to 5.86 kg/h, 10.5% （2005） and 5.62 kg/h, 9.8% （2009）. The stock distribution area shifted towards the northern Yellow Sea over the past two decades. An effective index was the changes in stock density and occurrence frequency in the Yellow Sea above 36° latitude north： the relative stock density and occurrence frequency increased from 0 in 1985 to （1.0±1.4） kg/h and 57.9% in 2000, and then to （6.9±9.8） kg/h and 83.3% in 2009 in the same sea area. Regression analysis showed that the annual catch of anglerfish （Yn） was highly and significantly, positively correlated with sea surface temperature （SST） of the 2 years previously （r=0.61, P=0.004）, which may be due to the influence of SST on the early life history of this species. However, the yields in 1997-2001 and the corresponding SST in 1995-1999 were excluded during the regression process, as the especial high SST in 1995-1999 may have interfered with anglerfish stocks and resulted in abnormally low catches of anglerfish during 1997-2001. Accordingly, the changes in biological characteristics, stock distribution and relative stock density of anglerfish may be related to pressures originating from increased fishing intensity and climate change.