Abstract
Based on length frequency data of miter squid (Uroteuthis chinensis) collected in the northeastern South China Sea in 1975–1977, 1997–1999, and 2018–2019, asymptotic length, optimal length at first capture, relative mortality, and relative biomass of the stock were estimated using length-based Bayesian biomass estimation (LBB). The LBB-estimated asymptotic length for 2018–2019 was smaller. Optimal lengths at first capture for the later far exceeded average lengths in catches because of a major increase in fishing intensity. Between 1975 and 1977, relative total mortality (Z/K) was low, but it increased in the latter two periods, while relative natural mortality (M/K) showed a downward trend. Relative biomasses (B/B0 and B/Bmsy) indicated that the stock was close to unexploited between 1975 and 1977, but they declined to the levels of 6% and 4% in the later periods, which correspond to growth in fishing horsepower. Indeed, by 2018, fishing horsepower increased by nearly four times the optimal level. The analysis suggests that the stock of miter squid has been overfished since the mid-1980s and is now under heavy fishing pressure. To recover the stock, it is imperative to reduce fishing intensity and enforce size-at-first-capture regulations.
Highlights
Fishing activity dates back many centuries in coastal waters, but the exploitation of virtually all coastal stocks started to occur around 1990 (Brander, 2013)
Data for 2018–2019 were collected during the implementation of a fishery improvement project (FIP), and the squid samples from commercial catches were supplied by a fish processing factory as coordinated by the China Blue Sustainability Institute; these samples were collected from trawl fishing
The mean length (Lmean; Figure 2A) and relative biomass (B/B0; Figure 2H) of the squid were above the levels of moderate exploitation in the period of 1975–1977, which indicated that the squid was underexploited
Summary
Fishing activity dates back many centuries in coastal waters, but the exploitation of virtually all coastal stocks started to occur around 1990 (Brander, 2013). Increased fishing intensity affects the life histories of fishes and marine invertebrates (: fish), leading to rapid declines in fish stocks, and it impacts entire marine ecosystems (Vincent and Hall, 1996; Pauly et al, 1998; Hutchings, 2000; Kuparinen and Merilä, 2007). Due to the over-exploitation of fish stocks, many governments and non-government organizations (NGOs) agree there is a need for science-based management. Science-based fishery management requires evaluation of sustainable fishery catches based on the existing yield, survey, or life history data of target fish (Dick and MacCall, 2011; Costello et al, 2012; Thorson et al, 2013; Froese et al, 2017). Most fishery stock assessment methods require numerous parameters to be input for estimation, which limits their broad application. Fishery stock assessment methods that require inputs
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