Variability of coastal cephalopods in overexploited China Seas under climate change with implications on fisheries management

Cephalopods (squids, cuttlefish and octopus) have increased globally over the past decades, which may be attributed to their strong phenotypic plasticity, allowing them to adapt quickly to a changing ocean environment. The global proliferation of cephalopods may yield important ecosystem effects worldwide. However, information on cephalopods variability in Chinese waters is still scant. Coastal cephalopods, in spite of chronic overexploitation, form a vital component of the catch composition in China Seas. In this paper, we review the status and trends of coastal cephalopods in China Seas and explore their responses to environmental variability. We focus on four commercially-important coastal cephalopod species, including golden cuttlefish (Sepia esculenta Hoyle), Japanese loligo squid (Loligo japonica Steenstrup), common Chinese cuttlefish (Sepiella maindroni de Rochebrune) and swordtip squid (Uroteuthis edulis Hoyle). Even though spatial distributions of these four species partially overlap, their differing life history strategies with respect to factors such as growth, distribution, migration, and spawning patterns, have led to differing population responses to environmental variability. As a result, an overall increasing trend in cephalopod production has been apparent since the 1990s, accompanied by major changes in species composition. Catch trends of the four species show either decadal patterns of significant decline or increase in the late 1980s to mid-1990s. Statistical analysis indicates different responses to environmental warming, with Japanese loligo squid and swordtip squid seeming to benefit from warmer environment while golden cuttlefish and common Chinese cuttlefish seeming to respond negatively. Our study has allowed us to explore the impacts of environmental changes on Chinese coastal cephalopods in the overexploited ecosystems of the China Seas and to conclude that fluctuations of coastal cephalopods are mainly driven by large scale environmental variations associated with climate change and/or marine ecosystem regime shifts.