Body length-dependent diel vertical migration of Antarctic krill in relation to food availability and predator avoidance in winter at South Georgia
| Autor: | Makoto Okazaki, Taro Ichii, Tomonari Hayashi, Takehiro Okuda, Kedarnath Mahapatra, Yoshihisa Mori, Philip N. Trathan |
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| Rok vydání: | 2020 |
| Předmět: |
0106 biological sciences
010504 meteorology & atmospheric sciences Ecology biology Food availability 010604 marine biology & hydrobiology Aquatic Science biology.organism_classification Trade-off 01 natural sciences Antarctic krill Environmental science Predator avoidance Diel vertical migration Ecology Evolution Behavior and Systematics Overwintering 0105 earth and related environmental sciences |
| Zdroj: | Marine Ecology Progress Series. 654:53-66 |
| ISSN: | 1616-1599 0171-8630 |
| Popis: | We analyzed diel vertical migration (DVM) of overwintering Antarctic krill at South Georgia, a region that remains ice-free during the austral winter. We considered DVM in relation to krill body length, based on Japanese krill fishery data (1990-2012), and examined DVM in relation to food availability and predator (Antarctic fur seal) avoidance. We report that diel changes in median trawling depth (a proxy for krill vertical distribution) showed significant interannual variation; the overall trend was such that during both daytime and nighttime, the larger the average size of krill, the deeper their median depth. Consistent with the literature, this size-dependent DVM relates to food availability and size-dependent diet; that is, with increasing body length, krill tend to rely less on phytoplankton (which are available in surface layers) as a winter food source. Concerning predator avoidance, and based on analyses using an optimal foraging dive model for fur seals, DVM showed close agreement with size-dependent predation risk; that is, larger krill remained deeper, thereby reducing mortality from fur seals. Therefore, DVM of overwintering krill appears to reflect a compromise between adequate feeding conditions and minimizing predation risk. There was, however, an exception that krill occurred at a shallow depth in winter 2006 when phytoplankton abundance was particularly low and krill density was very high. This supports the hypothesis that physiological demands (i.e. hunger) may become a more important factor affecting DVM than predator avoidance under conditions of insufficient food availability. |
| Databáze: | OpenAIRE |
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