4.3 Management implication
In China, approximately 50% of China’s fish stocks have been overexploited or collapsed (Cao et al. 2017). Our approach can provide insight in anticipation of stock enhancement and management that may facilitate conservation and re-stocking. While our results highlight that, as well as the previously described ‘lack of timely, effective or sufficient management, combined with heavy fishing pressure, particularly at spawning and overwintering grounds were major factors responsible for croaker stock declines’ (Liu and de Mitcheson 2008), climate change-induced overwintering habitat is another potential reason for the stock depletion. This is highly worrying because long-lived migratory fish like L.corcea decline even faster where both heavily fishing and climate-induced habitat suitability synergies (Färber et al. 2018).
The severe situation has led to an urgent need to re-evaluate fishery management and calls for a species-specific or life-history-based approach to stock enhancement (Young et al. 2006, Lotze et al. 2011, Pinsky et al. 2018, Dubik et al. 2019). First, regarding the fishing-caused size truncation effects, the deficiencies in China’s input control allow fishers to conduct indiscriminate intense fishing on large individuals of long-lived species after seasonal closure, and consequently alter the dynamics of the harvested species and the ecosystem(Shen and Heino 2014, Su et al. 2020). Hence, if capture fishery activities are not fully regulated in a scientific and deliberate way, restocking of long-lived migratory fish will be difficult. Here, we suggest establishing stricter input controls on fishery, including reducing the fishing capacity and efforts, eliminating unregistered/illegal fishing vessels, increasing the minimum mesh-size standard and adopting output controls, especially for single-species total allowable catch (TAC) or/and ecosystem TAC ofL. crocea -like species. Secondly, regarding the climate-induced overwintering habitat, we recommend designing seasonal special reserve zones and more targeted regulations in crucial L. croceahabitats, which should be managed like MPAs. Ultimately, our application of HSI model illuminates the mechanisms of fishing-induced life-history variation and climate change-caused ‘mismatch’ impacts on long-lived migratory species (Wilson et al. 2008). Also, fishery managers often deploy hatchery release to address the recruitment bottleneck of species’ restocking (Myers et al. 2004, Taylor et al. 2017, Kitada 2018). Because L. crocea ’s suitable overwintering habitats have shifted towards offshore areas, to tackle both recruitment and habitat bottleneck, we recommend that stakeholders choose larger juveniles, even mega-spawner for hatchery release to keep pace with the shifting of suitable habitats caused by climate change.