Streaked Shearwater Calonectris leucomelas rearing chicks in the central Sea of Japan did not switch diet at the 2013/2014 regime shift

抄録

Climate-driven changes in the abundance, distribution, and migration patterns of forage fish affect the diet composition of seabirds. Decadal climate changes, known as regime shifts, have occurred several times in the Sea of Japan, influencing the food web and leading to shifts in the diet of diving seabird species. To examine whether a long-range surface-feeding species, Streaked Shearwater Calonectris leucomelas, switched diet in response to the 2013/2014 regime shift, we sampled 826 stomach contents from individuals at Awashima Island between 2008 and 2020. They fed mainly on Japanese Anchovy Engraulis japonicus and Bullet Mackerel Auxis rochei, with benthic fish as minor prey, both during the negative and positive phases of the Pacific Decadal Oscillation (PDO) before and after the 2013/2014 regime shift, thus showing no evidence of prey switching. Although fisheries landings of Japanese Anchovy and Bullet Mackerel showed decreasing trends after the 2013/2014 regime shift, with a rise in cold-water Japanese Sardine (Sardinops melanostictus) dominance, this change was not reflected in the shearwater diet. Streaked Shearwater, a highly mobile and adaptable seabird species with an extensive foraging range, maintained a relatively stable diet, even under unpredictable environmental conditions including climate shifts.