MEPS prepress abstract  -  doi: 10.3354/meps07407

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. Here, 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 (1978–2004) 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 about 22ºC. In contrast, sardine and mackerel exhibited steeply peaked patterns with a marked peak at about 16ºC and 18°C, respectively. On the contrary, jack mackerel showed a very similar spawning temperature pattern with anchovy. These relationships were consistent with their flourish and collapse in the 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.