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Male southern elephant seals eats selectively

Summary

Southern elephant seals, prominent predators in Antarctica, exhibit selective eating habits, challenging the assumption that they consume a wide variety of prey.

Dietary Preferences of Male Southern Elephant Seals

New research from UNSW Sydney reveals that adult male southern elephant seals exhibit selective eating habits, preferring specific foods. This study, highlighted in the Marine Ecology Progress Series journal, sheds light on the dietary choices of these lesser-studied male seals, despite their substantial size.

Male southern elephant seals

Diet Analysis using whisker samples

Studying the dietary habits of male elephant seals in their natural habitat poses challenges due to their formidable size and aggressive nature. Weighing up to four tonnes, these seals dwarf their female counterparts. Researchers employ a unique approach, analyzing whisker samples in the lab to obtain detailed records of the seals’ activities.

In a study focused on 31 male southern elephant seals from the Western Antarctic Peninsula, scientists utilized whisker samples to infer the seals’ eating habits based on stable isotopes—chemical indicators of their fast food consumption. Each whisker analyzed provided up to a year’s worth of data on the culinary preferences of each seal, enabling the team to compile the most comprehensive picture of the male southern elephant seal diet to date.

The findings revealed that the majority of male southern elephant seals are specialists, exhibiting consistent and limited dietary preferences over time. Many of these can be categorized as extreme specialists, consuming less than 20% of the available food types within their population’s range. Notably, only one seal in the sample displayed a generalist approach, opting for a diverse diet from various food sources.

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Dietary Specialization and Body Size in Male Southern Elephant Seals

The study identified a correlation between individual variation and body size among male southern elephant seals. Larger seals, irrespective of their size, consumed higher on the trophic scale, opting for larger, energy-dense prey like big squid, especially leading up to the breeding season. Interestingly, even smaller seals exhibited extreme specialization, feeding lower on the trophic scale with smaller fish from early adulthood.

While the exact cause of this picky eating behaviour remains uncertain, potential factors include gape size influencing ideal prey size, variations in seasonal and yearly food availability, and the strategic concentration on specific food types, even if subpar, to enhance foraging success rates and enable size gain for competition in breeding rights among males.

Conservation and Climate Threats to Southern Elephant Seals

Despite successful conservation efforts, the southern elephant seal population, once on the brink of extinction due to hunting, has rebounded and is no longer classified as endangered. However, the resurgence faces new challenges posed by climate change. Climate-induced alterations in the Southern Ocean, such as shifts in krill availability, pose a threat to the seals’ preferred food sources higher up the food chain.

Additionally, the Western Antarctic Peninsula, their habitat, is undergoing significant changes due to ocean warming, impacting the entire ecosystem. Professor Rogers emphasizes the need for further research to understand and address the potential consequences of climate change on food resource availability for southern elephant seals in the Southern Ocean.

Journal Link: https://www.int-res.com/abstracts/meps/v725/p185-199/

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