Multi-species regime shifts reflected in spawning temperature optima of small pelagic fish in the western North Pacific

Abstract

Small pelagic fish have exhibited cyclic population dynamics in complex marine ecosystems worldwide. These fish regime shifts have been associated with ocean regime shifts; however, the biological mechanisms have remained unresolved and have been considered to depend mainly on multi-step processes through food webs. In the present study, we focus on species-specific temperature optima and show that similarities and differences in spawning temperature optima reflect those in the long-term population dynamics among multi-species pelagic fish in the western North Pacific. Spawning temperature optima were examined for anchovy, sardine, mackerel and jack mackerel, based on the occurrence of eggs and larvae, using a long-term (1978 to 2004) data set of egg and larval surveys off the Pacific coast of Japan. Anchovy exhibited a plateau-like spawning temperature pattern with a peak at ca. 22C. In contrast, sardine and mackerel exhibited steeply peaked patterns with marked peaks at ca. 16 and 18C, respectively. On the contrary, jack mackerel showed a very similar spawning temperature pattern to anchovy. These relationships were consistent with their flourish and collapse in long-term population dynamics. Furthermore, sardine and mackerel with stenothermal spawning patterns showed dramatic fluctuations relative to anchovy and jack mackerel with more eurythermal features. The multi-species comparisons extracted a simple and direct pathway: if viewed at large scales, direct temperature impacts on vital parameters provide a plausible explanation of multi-species regime shifts of small pelagic fish in the western North Pacific.