Title: Interannual variation in the population dynamics of snailfish Liparis tanakae in the Yellow Sea
Abstract: The snailfish,Liparis tanakae,is a cold-water,demersal fish that has become one of the top predators in the Yellow Sea ecosystem because of a decline in the abundance of the commercially targeted species in recent years. We evaluated the interannual variation in relative stock density,distribution,biological and reproductive characteristics of snailfish based on fishery data collected by bottom trawl during winter(1958—2010) in the Yellow Sea. In the northern Yellow Sea,the snailfish was primarily distributed around the Liaodong Peninsula near the 50 m isotherm. In other regions of the Yellow Sea,the species was primarily distributed in the central Yellow Sea in 1959,but had expanded its distribution by 1985. Relative to surveys in 1958—1959 and 1985,the distribution of snailfish moved northward by the 1990s from 34°N to 36°N. In 2005,the species was found in all areas of the Yellow sea and in 2010,it was primarily distributed southeast of Shidao(35.5—36.5°N,123.5 —124.5°E) and off southern Jiangsu province. The relative stock density of snailfish was low in the late 1950s(1.1—4.1 kg / h),then increased in the 1980s and 1990s,peaking at 15.5 kg / h in 1993—1994. The density then decreased to 3.8 kg / h in the late 1990s and has recovered only slightly in the last 10 years. We observed a similar trend in occurrence frequency. In the late 1950s,snailfish only accounted for 12. 0%—26. 5% of the occurrence frequency. However,it peaked at 87. 5% in the 1980s. In other years,the occurrence frequency was relatively large(45. 8%—77.3%),though most notably in thecoldyears such as 1985,2005 and 2010. We observed a significant negative correlation between relative stock density and sea surface temperature in the ten most recent years suggesting that this cold-water species responded rapidly to the changing temperature. Similarly,we observed a negative but insignificant correlation between the occurrence frequency and sea surface temperature. The average body length of snailfish was 35.1 cm in 1985,33.9 cm in 1999—2001,33.8 cm in 2005 and 32.3 cm in 2010,suggesting a tendency towards miniaturization.The average body length of male individuals was significantly larger than for female individuals in all survey years(except1985). The b value for males in 1985,2005 and 2010 were significantly less than 3,consistent with intensely negativeallometric growth of the population whereas the remaining b values were not significantly different. We evaluated the sex ratios(♀: ♂) within five length groups(20,20—30,30—40,40—50,50 cm). There was no significant difference in the sex ratio during the survey years. However,the ratio did differ within body length groups. Within 20 cm group,all fish were female in 1985 and 2010 and male in 2000—2001 and 2005. In the 20—30 cm group,there was no difference in the ratio during four decades,although in 2005,the catch was dominated by female snailfish. In the 30—40 cm group,there was no difference in all survey years. In the 40—50 cm group,males dominated the catch in 2005 whereas the ratio was equal in all other years. Finally,the catch of 50 cm fish consisted exclusively of males in all survey years. In 1985,2000—2001,2005 and 2010,the proportion of sexually mature fish(at stage IV or beyond stage IV) were 51.1,53.8,41. 8 and 23.9%,respectively,while for those at stage III the proportions were 6.7,38.5,48.7 and 71.8%,respectively.Changes in biological characteristics may be the result of overfishing. In addition,a shrift in feeding habits may also have played an important role as the dominant prey categories of snailfish have changed significantly. In summary,the lack of interspecific competition,rapid growth and varied diet likely explain the variation in abundance of snailfish in the Yellow Sea ecosystem.
Publication Year: 2013
Publication Date: 2013-01-01
Language: en
Type: article
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