Dolphins & Porpoises: Male vs Female?

Telling the difference between sexes in dolphins & porpoises can be a tricky task, especially since males and females look very similar. We have 3 types of dolphins and porpoises* that are regularly sighted on our tours near Campbell River, BC:

  • Pacific white-sided dolphins
  • Harbour porpoises
  • Dall’s porpoises

 

So how do you know if a dolphin or porpoise is male or female? We’ve got a few tips and tricks to help you out.

REPRODUCTIVE ANATOMY

The only sure-fire way to determine sex is by catching a glimpse or photo of the underside of the animal. Luckily, reproductive anatomy remains consistent with dolphins & porpoises. The underside of a dolphin or porpoise is the best way to tell the difference between male & female. However, this requires actually getting a glimpse at their underside, which can be a tricky thing to accomplish.

When you’ve got a playful, highly acrobatic species like the Pacific white-sided dolphin, catching a glimpse of their bellies can be easier than their more elusive relatives. We often see them jumping, somersaulting, and spinning in the air. If you manage to get a clear photo of their underside, you’ll likely be tell if it’s a male or female!

MALES: From birth, male dolphins & porpoises have their umbilical scar (belly button) plus 2 slits down their belly:

  • Genital Slit
  • Anal Slit

 

Note that these two slits are separate. Some say these two slits looks like an exclamation point.

male pacific white-sided dolphin

Male Pacific white-sided dolphin. Photo by Jenn Libotte.

FEMALES: From birth, female dolphins & porpoises have their umbilical scar (belly button) plus three slits:

  • Genital slit
  • Two mammary slits

 

Females have one long genital slit that contains both the vagina and anus, differing from the males who have two separate slits. There is one small mammary slit on either side of the genital slit. Some say these 3 slits look like a divide sign.

female pacific white-sided dolphin

Female Pacific white-sided dolphin. Photo by Jenn Libotte.

A FEW OTHER SIGNS

SIZE: Mature male dolphins and porpoises tend to be larger than mature females, except in harbour porpoises where mature females are generally larger. However, when you take into consideration juvenile males who will be smaller than females, this can be a tricky way to determine sex in dolphins & porpoises, and sometimes isn’t accurate.

PHYSICAL DIFFERENCES: In Dall’s porpoises, mature males tend to have a more pronounced hump in front of the fluke.

Dall's Porpoise Campbell River

Dall’s porpoise tail stock. Photo by Andy Scheffler.

Dorsal fins of mature male Pacific white-sided dolphins tend to be more stocky and have more nicks and scratches. Again, these can be inaccurate for determining sex. Take with a grain of salt!

Pacific white-sided dolphin with unique dorsal fin

Pacific white-sided dolphin with a unique dorsal fin, many nicks and scratches. Photo by Andy Scheffler.

PRESENCE OF A CALF: Calves tend to stick close to their mothers’ side. They remain under her watchful eye for up to 2 years as she teaches it to hunt, navigate, and avoid danger. If a calf is small and closely associating with the larger individual, chances are high that it’s a female. However, this is a tricky situation again because, especially if a calf is larger, it could be travelling or associating with a larger, unrelated individual.

*Note: excluding killer whales, who are just really big dolphins

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