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ORCA TIMES- Quarterly report: January – March 2019

RESEARCH & MONITORING

Bumper breeding season for Robberg seals?

Between January-March volunteers assisted biologists with six boat-based counts of Cape fur seals that haul out on Robberg Peninsula. Apart from routine counts of adult seals, which have levelled off since 2012 despite seasonal fluctuations in their numbers, our biologists were surprised by the large increase in the number of pups born this year. A minimum estimate of 838 pups revealed almost twice the numbers that were recorded during last season, which was also consistent with a two-fold increase in pup mortality from stranding records. These data suggest that the Robberg seal colony experienced a bumper breeding season, most likely related to an increase in the availability of their preferred prey – small pelagic fish. Previous studies have shown how the quantity and quality of prey affects the body condition of seals, which affects the timing of puberty, implantation of embryos, mortality of foetuses and therefore reproductive rates of females. Continued monitoring of annual fluctuations in the numbers of new born pups may be crucial in studying the importance of seal birth rate as an indicator of changes in the local food-web, especially if linked to results from monthly diet analysis (see section on seal scats).

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