Chiswell Chronicles: June 19, 2017

In the past week at Chiswell, another 23 pups were born, bringing our total to 65 pups! In addition to new pups being born, copulation events are also well underway. Approximately 10 days after birth, females become receptive and mate with males on the colony.

E94 copulated with a female this week

For example, E94 is a 12 year old male that was born on Chiswell in 2005. This was the first year he has held a territory on the rookery, and this week we observed him mating. While males can reach reproductive maturity around the age of 6, it is common for them to be too small to hold a territory until they are 10-12 years-old!

They grow up so fast…



This week we are highlighting two females: Anita and Dee. The interesting thing about these two known females is that neither has a pup this year!

Anita was first seen in 2005. She is identified by two marks: a very large fungal patch on her neck and a scar on her right side.

Anita can be identified by her scar and fungal patch

Anita has not been seen with a pup this year–but has been seen on the island nursing her yearling, E235. “Skipping” a year is fairly common for Steller sea lion moms and approximately 20% of juveniles continue to be nursed by their moms between the ages of 1 and 2. This extended nursing period can have significant impacts on pup survival. From our research on Chiswell, researchers have shown that survival for individuals that are weaned at age 1 is between 40-60%, but survival for individuals that suckle for 2-3 years can be as high as 90%! (Read more about this Here).

This year: Anita did not give birth to a pup but has been observed nursing a yearling

The other female without a pup this year is Dee. She can most easily be identified by a trio of fungal patches and a quartet of scars on her right side.

Dee has been seen on Chiswell since 1999! We spotted her again this year, but without a pup.

First seen in 1999, Dee is one of the sea lions we have known for the longest time! While we’ve seen her for 18 years now, it is possible she was pupping on Chiswell even before our camera system first observed her. Interestingly, while we have seen her on Chiswell every year, she hasn’t had a pup since 2013. This suggests Dee is ‘senescent’, or experiencing age-related declines in reproductive investment.

Ref: Maniscalco, J. M. (2014). The effects of birth weight and maternal care on survival of juvenile Steller sea lions (Eumetopias jubatus). PLoS One, 9(5), e96328.

All photographs and activities conducted under NMFS Permit No. 18438-00

Written by: Dr. Amy Bishop and Pam Parker

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