Research on seabird
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Seabirds feed on small fish and other prey while ranging across the ocean. By learning more about seabird ecology, we can monitor large-scale changes in marine ecosystems. They biomagnified pollutants through the food web and also often ingest marine plastics. We are also able to monitor the status of these anthropogenic stresses and their impact by working with seabirds. Through these studies, we hope to contribute to SDG 14 (LIFE BELOW WATER).
The United Nations has designated the decade starting in 2021 as the "Decade of Ocean Science," with the aim of contributing to SDGs.
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Prey and distribution of seabirds can be a useful indicator of climate-driven marine ecosystem change in areas where conventional boat surveys are difficult. How does the decrease of sea ice in the Arctic and Antarctic Seas affect the marine ecosystem and how do seabirds respond? We found that the short-tailed shearwaters moved into the Chukchi Sea through the Bering Strait in late summer. Thus the Chukchi Sea could be a key area to store energy before 2 weeks of migration to the south. A study by Oshoromaru under the ArCS project showed that the krill, the main diet of this seabird species, was smaller in summer but grew in autumn to be the suitable size as prey of this seabird species.
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Seabirds can be a good indicator of the changes in global marine ecosystems. Surveys of seabirds are easier and they cost much less than boat surveys. Seabirds are marine top predators ranging widely and thus can be an integrated and useful indicator of a broad range of ecosystems. Rhinoceros Auklet is a species that breeds at mid-and high latitudes in the North Pacific, burrowing and nesting on isolated islands, diving to 70 m depth, and feeding on a variety of forage fish. Parents return to the islands at night. We have monitored food and chick growth for more than 30 years on Teuri Island located in the Sea of Japan in Hokkaido. We found that the chicks grew better when they were fed with sardines and sand lance in the cold period in the 1980s and anchovy during the warm period in the 1990s. However, after 2014, juvenile greenling was the main prey species, and the chick growth and fledging success were poor. These timings of prey-switching have been associated with decadal-scale climate change, i.e. regime shifts. After 2018, the birds began to eat the sand lance again: indicating the start of the cold regime or may be not. Thus our study indicates that marine birds may signal a major shift in marine ecosystems in advance.
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About 400 million tons of plastic are produced each year and nearly 10 million tons are discharged into the ocean. The incidence of plastics in the stomach of seabirds has increased year by year since it was reported in the 1960s. The incidence in the Northern Fulmar increased between the 1970s and the 2000s in the North Atlantic and between the early 2000 and 2008 in the Arctic. Most individuals of this species now have plastics in their stomachs. The effect of plastics ingested by seabirds is not well understood. A review of previous studies on the effects of plastic indicates that the effects are likely if the mass of ingested plastic is 0.25% or more of body weight. We are conducting a plastic feeding experiment using seabird chicks in a semi-natural condition.
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