Washington, Feb 3 (IANS) Killer whales closer to menopause seem to be more successful in bringing up their young, whose survival rates were also higher. Eric Ward of Northwest Fisheries Science Centre, Seattle, coordinated a team of researchers who studied killer whales inhabiting the inland and near shore waters of Washington state and British Columbia (Canada).

They used a 30-year dataset collected by the Centre for Whale Research and Canada’s department of fisheries and oceans.

Ward informed that “during annual photographic surveys, nearly every individual in the population has been recorded. Each animal has unique pigmentation, scars, and fin shapes, allowing us to track the survival and reproductive performance of each female over time”.

The authors aimed to investigate what benefits killer whales derive from the menopause.

One theory, termed the “attentive mother hypothesis”, is that giving birth to calves and then losing the ability to reproduce helps the mother to focus on bringing up her offspring, without wasting time and energy on further pregnancies.

The authors’ results support this theory to an extent in that during a calf’s first year of life, having a mother who was nearing menopause increased chances of survival, said a Northwest Fisheries release.

“We found that the oldest mothers may also be the best mothers. Older females may be more successful in raising young because of maternal experience, or they may allocate more effort to their offspring relative to younger females,” said Ward.

Killer whales are extremely long lived, with one female believed to be more than 90 years old. Males rarely live past 50, but female life expectancy is considerably longer. Females can produce their first calf as early as age 10, and continue to produce offspring until their early 40s.

These findings were published in BioMed Central’s open access journal Frontiers in Zoology.