Gender ID - Pinnipeds

He or She? Sometimes gender is easy to distinguish even at a distance and sometimes you have to get up close and examine the animal. In many pinnipeds there are a number of features that often make gender ID fairly straightforward even when the animal is rather decomposed. For example, adult male California sea lions have a bony ridge called a sagittal crest which gives them a very prominent forehead. This secondary sexual characteristic is only found in adult males and thus, can help you determine both age and sex at a distance.

Pinnipeds, like dogs, also have a bone in their penis called a baculum (see above image). Even when all you find is a code 5 skeleton, presence of a baculum can help you definitively determine the sex. Be careful though! Just because there is no baculum present in a decomposed animal does not mean that it is a female. Scavengers can sometimes fly/walk/swim off with smaller bones.

When examining the genital area of a pinniped there are two features which can help you determine sex. First, between the rear flippers, females will have two separate openings – a vaginal and anal opening - which can be seen by pulling the rear flippers apart. In males, there will only be one opening and there will be an additional small PREPEUTIAL opening (for the penis) usually about one third of the way up the ventral abdomen depending on the species and size of the individual. Both males and females will of course also have an umbilical scar (belly button) so be sure to distinguish between this and the PREPEUTIAL opening for the penis in the male.


 Below you will find helpful hints on gender identification in pinnipeds.  CLICK on an image to see an enlarged view.

Gender ID 01 A side view of the head of a MATURE MALE sea lion. Note the prominent, raised bony CREST over the eyes. 
Gender ID 02 This is the skull of a MATURE MALE sea lion, showing the large, raised boney CREST that develops with age and serves as a point of attachment for the muscles on top of the head. Females lack this prominent crest.
Gender ID 03 Side view of the head of a MATURE FEMALE sea lion showing the absence of a crest. Adult females also have the typically lighter coat shown here.
Gender ID 04 YOUNG MALE sea lions will also LACK the CREST, which develops as males become sexually mature. The eyes have been scavenged postmortem.
05-gender-id Side-by-side comparison of an ADULT MALE (left) and ADULT FEMALE (right) STELLER'S SEA LION. Notice the LARGER SIZE and larger BONEY RIDGE on the back of the MALE Steller sea lion skull. Note the ABSENCE OF A TALL BONEY CREST as COMPARED TO a male CALIFORNIA SEA LION. A species identification tip - Remember that Steller sea lions have a diastema (a space) between the last two upper back teeth.
Gender ID 06 Side-by-side comparison of jawbones from a male and female California sea lion, showing the more robust male jawbone with larger teeth, especially the canine teeth.
Gender ID 07 This MALE CALIFORNIA SEA LION skull shows a moderately developed crest, substantial canine tooth tip wear, and a broken upper incisor.
08-gender-id This is how the perineal area and ventral abdomen look for a MALE CALIFORNIA SEA LION. Males only have one opening in the PERINEAL area, the ANUS, and also a second, PREPEUTIAL opening on the ventral abdomen. This second opening contains the PENIS.
09-gender-id This is how the PERINEAL AREA looks for a FEMALE CALIFORNIA SEA LION. Females have two holes in the perineal area (ANUS and VAGINA, which also contains the opening of the URETHRA) and LACK a PREPUCE on the ventral abdomen.