Cetaceans – Male or Female? How to Know?

By The Marine Detective on January 27, 2019

The information here on The Marine Detective is, in part, intended to answer important life questions like “How Do Octopuses Poo?“. Right up there as life-enhancing information is the answer to “How can you determine sex in cetaceans?” (Cetaceans are whales, dolphins and porpoises and it is important to use this term because, for example, Orca are actually members of the dolphin family.)

Please know that I am being serious here. This is meant to be anything but giddiness-inducing, whale-porn-perceived content. Further, I believe to my core that the more knowledge we have of our marine neighbours, the more understanding, connection and respect there is for the Ocean and thereby, the better the hopes for our own species.

And, in that regard, I am here to serve.
So here you go.

The following allow determination of sex in cetaceans:

• Presence of a calf beside the mother. BUT this can be difficult to determine unless the calf is really young i.e. it just could be a smaller, unrelated individual travelling with a larger one;
• DNA testing BUT this is not useful to the average person;
• Seeing a male’s penis BUT it is usually concealed inside the body / genital slit where it isn’t creating drag and losing heat;
• There can be behavioural clues BUT you need some pretty good understanding of a species for this; and
• Physical differences between sexes (other than the penis). BUT, with the exception of differences between adult dorsal fins in some cetacean species, these features are on the underside of the animal. This means you don’t often get a chance to see them.

But look!
It’s a female Pacific White-Sided Dolphin!

How do I know? Female cetaceans have mammary slits and the genital slit is larger, containing both the vagina and anus. See below. The mammary slits contain the mammary glands which produce milk for baby.

Note too how all cetaceans have a belly button. All mammals have belly buttons of course as we develop in utero, attached with an umbilical cord to our Mom’s placenta. 🙂

Here is the contrast between a male and female Pacific White-Sided Dolphin.

These difference exist right from birth.

In the case of the really big dolphins – Killer Whales / Orca – not only are there these differences, but the pigmentation pattern in the pelvic area is different in males and females too, right from birth. Males have a larger area of white than the females do. See below.

Of course AFTER the age of puberty, it is really easy to discern a mature male Orca, from a female because the dorsal fin is much larger in mature males. The pectoral fins are larger too and the edges of the tail are often curved downward. Mature males are also larger than females. BUT these physical difference only start developing around the age of thirteen. Many people make the error of presuming an Orca with a smaller dorsal fin is always a female. Nope, the individual with a smaller dorsal fin could be an immature male.

To the trained eye, the dorsal fins of mature male Pacific White-Sided Dolphins are also different from that of females and immature males.

The dorsal fins of the mature males are stockier and often have more nicks and scratches as shown in the photo below.

In Dall’s Porpoises, the mature males’ dorsal fins also look different than that of the females and juvenile males. The angle is different as you can see from the images below. This is very, very difficult to discern while in the field however i.e. I can look at a photo of their dorsal fins and determine sex in mature Dall’s Porpoises but, in real time, I rely on behavioural clues and/or the presence of a calf.

How to discern if a Harbour Porpoise is male or female?

Good luck! The mature females are bigger in this species but that is VERY difficult to discern and I have never seen the underside of a Harbour Porpoise except when a Bigg’s Killer Whale was making an attack. Harbour Porpoises are very cryptic and very rarely are they acrobatic.

BUT males do have a very distinctive behaviour. They always try to mate from the left.

Want to know the detectable sex differences in Humpback Whales?

The genital and mammary slits can be very difficult to see. What is much easier to detect is that, from birth, only females have a bump know as the “hemispherical lobe” (note that nobody knows what this structure is for). However, where in dolphins you can get a clear look at the pelvic area when they leap out of the water, this is not the case with Humpbacks. The way they breach, there is a big “skirt” of water obscuring the pelvic area.

That’s why we researchers get really excited when Humpbacks lie on their backs and tail lob, as in the photos below. THEN there is a chance of seeing the pelvic area. Please see our Marine Education and Research blog at this link for detail on discerning sex in Humpback Whales.

So there you go, armed with more knowledge about our cetacean neighbours. To reiterate, I’ve made the effort to share all this because I believe that the more we see those we share the planet with as individuals and the more understanding we have  . . .  the better we can be. That you for being someone who cared enough to read this.

Since I am feeling quite “teachery” with this blog, how about a test? 🙂 “Oh yes!” (said no one ever).

But if you want to test your knowledge, see the images below. Are these male or female Pacific White-Sided Dolphins? Scroll down after the three images for the answers.

Answers:
The sexes of the Pacific White-Sided Dolphins in the last three images are:
#1 is male
#2 is male
#3 is female. The mammary slits are difficult to see but you can clearly see the larger genital slit and that there isn’t a separate slit for the anus.