The main changes include a lower population mean age, earlier maturity and a prolonged spawning season ( Lin et al., 2006 Ji et al., 2019). Despite its relatively high biomass, population structure and biology have changed. Although the biomass has fluctuated, total landings have remained at a high level ( Wang et al., 2011 Xu and Chen, 2015). In late 1990s the catch increased to nearly 1 million tonnes ( Wang et al., 2011 Xu and Chen, 2015). Since the introduction of a regulation to protect spawning stock in inshore waters in 1989 ( Xu et al., 1994), the stock has recovered considerably. This decline was mainly associated with increasing fishing pressure on spawning stock. In the 1970s the hairtail stock in the East China Sea was fully exploited with an average annual catch of 0.4 million tonnes, but subsequently dropped to around 0.3 million tonnes by the end of the 1980s. Being a demersal species, it is mainly caught by bottom trawling. China lands 70–80% of the global hairtail catch ( Ling et al., 2005 Xu and Chen, 2015), in which the East China Sea stock makes up of 70% of the total catch. Some small local stocks are found in the South China Sea and the coastal waters of southern Fujian and Guangdong Provinces ( Chen, 1999). There are two major stocks of the hairtail: one in the Bohai and Yellow Seas (called the Yellow Sea stock) and the other in the East China Sea. It is the most abundant and important demersal fish species in China where it is distributed in the Bohai, Yellow, East China and South China Seas ( Du et al., 2020 Kwok and Ni, 2000). The hairtail Trichiurus lepturus is widely distributed throughout tropical and temperate waters around the world including northwest Pacific, Indian and Atlantic Oceans ( Froese and Pauly, 1996 Sun et al., 2020). Concurrent pressures of overfishing and climate change have caused considerable decreases in the quality as well as quantity of catches in some important fisheries regions including the East China Sea ( Mi, 1997 Chen et al., 2004 Liu et al., 2004 Wang et al., 2011). Not least of these is climate change, which can lead to large fluctuations in the abundance of fish populations and is contributing to declines in biomass of an increasing number of fish stocks (e.g. The development of the DEB-IBM provides a predictive tool to inform management decisions for sustainable exploitation of the hairtail stock in the East China Sea.įisheries stocks are in decline, and ocean ecosystems are under stress in many parts of the world due to overfishing and destructive anthropogenic forces. The model predicts that increasing fishing mortality by 10% will cause 5.3% decline of the population biomass, whereas decrease of fishing mortality by 10% will result in 6.8% increase of the biomass. These scenario simulations have shown that the population biomass under SSP1-1.9, SSP2-4.5 and SSP5-8.5 would decline by 7.5%, 16.6% and 30.1%, respectively, in 2100. It was also used to explore population responses to changing fishing mortalities. The model was then implemented to simulate the effect of climate change on the population performance under greenhouse gas emission scenarios projected for 2100. The model successfully reproduced these observations of interannual variations in the population dynamics. In addition, the population average age showed a trend of slight decrease. The stock recovered from early 1990s, which coincided with introduction of fishing moratorium on spawning stocks in inshore waters and substantial decrease of fishing efforts from large fisheries companies. High fishing pressure was largely responsible for the dramatic decline of the stock in middle 1980s. The DEB-IBM was validated with histological data for a period of 38 years. The parameter estimation of DEB model shows an acceptable goodness of fit. To investigate energetics of individuals and population dynamics of the species in responses to environmental variations and fishing efforts, we have developed a DEB-IBM by coupling a dynamic energy budget (DEB) model to an individual-based model (IBM). The stock has fluctuated in the past few decades and this variation has been attributed to human pressures and climate change. The hairtail Trichiurus lepturus supports the largest fisheries in the East China Sea.
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