南极大西洋扇区磷虾渔业渔获率突变特征及其致因分析

本研究利用CCARMLR数据库中提取的南极大西洋扇区(含48.1、48.2和48.3亚区)1982-2011年30年间的南极磷虾(Euphausia superba)年平均渔获率数据,运用Mann-Kendall法分析了其时间序列的发展趋势及突变特征.从趋势特征看,48区月均名义CPUE由1982年的5t/h左右,变化至2011年的10t/h左右.CPUE值时间序列呈现显著性周期波动,线性趋势年均增幅为0.221t/h.48.1亚区为主要捕捞区域,其CPUE线性趋势增幅最小,为年均0.088 t/h;而48.2亚区增幅最大,年增幅达0.323 9 t/h; 41.3亚区的年增幅为0.261 t/h.就渔获率突变特征而言,过去30年48区磷虾渔获率变化趋势为先缓后快的逐渐上升过程,渔获率突变点发生在1999年,这个突变在2001年后显著性存在.3个亚区磷虾渔获率均存在“上升突变”突变点.48.1亚区渔获率分别于2001年和2004年出现相交突变点,但均未通过α=0.05的显著线检验.48.2亚区分别于1995-1996年“向下突变”,但未通过α=0.05的显著线检验,1996-1997年出现“向上突变”,2000年通过α=0.05的显著线检验.48.3亚区突变发生在1992年,突变点通过α=0.05的显著线检验.结合海冰面积和捕捞(包括般队、捕捞技术、加工工艺)等因子分析突变的致因时,发现:(1)捕捞技术和加工工艺是最主要的致突变因子;(2)海冰面积在1983-1993年对渔获率突变有明显贡献;(3)空间上,越靠近南大陆,环境因子对突变的发生越容易产生作用.

Mutation characteristics and the effect on catch rates in Antarctic krill fishery in the Atlantic Sector of the Antarctic Ocean

  Antarctic krill (Euphausia superba)(hereafter krill), are one of the most important components of the Antarctic ecosystem food web. Area 48 of the Commission on the Conservation of Antarctic Marine Living Resources (CCAMLR) is in the Atlantic sector of the Southern Ocean, and is the primary fishing ground for commercial krill fishing fleets. We evaluated the changes in catch rate over time in this region using average catch rate data derived from a database which covers CCAMLR subareas 48.1 (50°W−70°W, 60°S−65°S), 48.2 (30°W−50°W, 57°S−64°S), and 48.3 (30°W−50°W, 50°S−57°S) from 1982 to 2011 using the Mann–Kendall(M–K) method. The average nominal CPUE was ~5 t/h in 1982 and increased to 10 t/h by 2011 in Area 48. The standard deviation for these estimates was very large and almost equal to the mean. Nominal CPUE fluctuated periodically, but the linear trend growth per year was 0.221 t/h. Subarea 48.1, the primary fishing area, had a linear trend growth per year of 0.088 t/h. Subarea 48.2 accounted for the biggest proportion of the increase in Area 48, increasing at a rate of 0.323 9 t/h per year. The rate of increase in subarea 48.3 was 0.261 t/h per year. In the past 30 years, the krill catch rate in area 48 increased slowly at first, then rapidly up to 1999, before undergoing a significant change after 2001. After the late 1980s, and concomitant with a decrease in the southwest Atlantic sector krill resource, catch rates followed an upward trend as fishing technology improved. The mutation point in area 48 in 1999 occurred at the same time as the Japanese fleet catch rate increased significantly, accounting for more than 70% of the global catch. The mutation points of catch rate occurred in 2001 and in 2004 in subarea 48.1, though they were not significant. There was retraction of sea ice area from 2001 to 2003 resulting in a rebound in krill populations and a subsequent increase in catch per unit effort (CPUE) in 2004. There were two mutation points of catch rate in subarea 48.2, the first one occurred in 1995–1996, and was a downward change point that did not pass the α=0.05 significance level. The second event occurred in 1996–1997 and passed the α=0.05 significance level in 2000. The mean density of post-larval krill during 1976–2003 in the southwest Atlantic sea was lowest in 1994, resulting in lower harvest during 1995–1996. Recruitment restored normal and the catch rate mutation points in subarea 48.2 appeared in 1996–1997. The mutation points of catch rate occurred in 1992 in subarea 48.3, and passed the α=0.05 significance level in 1996. After the breakup of the former Soviet Union in 1991, the size of the Russian and Ukrainian trawler fleet declined sharply because fuel subsidies were canceled. The catch by the former Soviet Union before 1992 was about 84% of the world total, but after 1992 the global catch was made predominantly by vessels from Japan, which has a CPUE more than twice that of the former Soviet Union’s fleets. At a spatial level, the fishing effect dominates the three subareas, but the impact of sea ice coverage is more significant when closer to the shelf of the Antarctic Peninsula.