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Advanced Taiwan Ocean Prediction System

Tseng, Tsu-Lun - ALL News | 2018-02-22 | Count:333


Title: The possible influence of climate variability and fishing activity on the annual fishing conditions of Grey mullet (Mugil cephalus L.) in the Taiwan Strait


The Grey mullet (Mugil cephalus L.) is a cosmopolitan species that is distributed in tropical and temperate zones at latitudes 42°N–42°S (Thomson 1963). It is one of the most important commercial species of fish in the coastal fisheries of Taiwan. A cohort analysis was performed to estimate the population number and instantaneous rate of fishing mortality by age of Grey mullet in the Taiwan Strait (TS) in 1958–2004. Since 1986, annual catches considerably dropped and continually remained at an extremely low level during the period despite the high fishing intensity. The population number of Grey mullet aged > 4 y has declined since 1986 and decreased to 20 000 individuals in 2004, constituting only 0.01% of the maximum level in 1981. The Grey mullet stock probably lost the reproductive potential because of severe recruitment overfishing since 1960s. Overexploitation of the Grey mullet stock reduced its spawning biomass to age 3–4-y groups, and environmental changes during the past 2 decades have likely driven the stock to consecutive years of poor recruitment and its current low level in the TS.  

The long-term unique long-term (1967–2009) records of catch per unit effort (CPUE) of Grey mullet in the TS was further used to investigate the influences of multi-timescale climatic indices on the annual catch of grey mullet. The CPUE of Grey mullet showed fairly good correspondence with the annual PDO index (R2=0.82, p<0.01). The PDO may play a role in affecting the migration of grey mullet, but increases in SSTs may be a main reason for the decreased catches after 1980. Mean SSTs increased 1.01 °C at the Chang-Yuen Rise in the TS from 1984 to 2009. The 20 °C isotherms in the TS in the winter also shifted from 23–24°N in 1958–1978 to north of 25°N after 1998. The fishing grounds of grey mullet also shifted to the north following changes in the 20 °C isotherm in the TS.

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