Dive Dry with Dr. Bill

#404: Is It a Buoy or a Gull?

It's been some time since I've written a column specifically about sex. I am often astounded by how taboo this subject is since other than breathing, the two most fundamental behaviors of any species (humans included) are "munching" and "mating." Some say love makes the world go 'round. I wouldn't know anything about that four letter word. However, I do know that without "mating," the world as we know it would stop within a generation. The only exception would be all those critters that reproduce asexually, and how boring is that?

Sex is used to sell everything from cigarettes (a real turn off for me if a woman smokes) to men's clothing (check out GQ) to... yes, even dive gear. We are bombarded with it daily through the print media, the Internet and TV. Well, I've eliminated the latter from my life this year. Actually I'm much more inclined towards that four letter word (L-O-V-E) than the three letter word, but you get my drift. We treat it as something dirty, yet are constantly bombarded with it for all sorts of purposes totally unrelated to reproducing our species. Strange behavior.

In my work as a marine biologist and starving dive bum, I often need to tell the "sex" (or, if you prefer, gender) of the critters I encounter. Sometimes this can be very difficult since both genders look the same in many species. Sometimes one can't assign gender to a critter because it is either both (hermaphrodite) or neither (asexual). However, I enjoy the mental challenge... and other divers are often shocked that I can so quickly determine it in some species. Hey, that's what tens of thousands of $$$ and a decade of post-high school education gave me the training to do.

I always go down to the dive park on weekends even if I'm not diving. I prefer the more solitary and interesting dives at night midweek, but enjoy socializing with other divers... especially of a certain gender! As is often the case, I get requests from other divers to look at photos they had taken or listen to their descriptions of critters they observed so I could identify them. Several of the critters on a recent weekend were hermaphrodites (black sea hares and the stunning Hypselodoris nudibranch). I amused several people by talking about the mating habits of the black sea hare... their orgies of a dozen or more individuals lasting for days. I also had questions about sexing horn sharks and identified one crab as a male. "How can you tell?" I was asked. Again, it's the years of training... but I'm going to give you some hints in this week's column.

The wrasses such as the sheephead and rock wrasse are well known members of the dive park community. Since all are born females, I have stunned divers by telling them that the tiny juvenile they photographed was of that persuasion. Then as they mature, the color of the older female sheephead shifts to a less dramatic pink. When they finally grow up and become males, they are banded in black and pink (or red). The rock wrasses also go through different color phases in the male and female versions, and their gender can be readily distinguished by a trained expert like myself (and you if you look closely at the pictures here)!

When a species exhibits identifiable differences between males and females, we refer to this as sexual dimorphism. Dimorphism merely means "two forms..." if you know Greek. Although I didn't learn much of it at Harvard, I spent a month in Greece the summer before I moved to Catalina and could at least sound out the Greek alphabet and those words that were phonetic. My favorite Greek words were ouzo, moussaka, dolmades and souvlaki. Of course they have little to do with marine life, but did make my life there very enjoyable! Back then SCUBA diving was largely forbidden due to the antiquities in Greek waters, so I spent most of my time free diving... or "munching," savoring the tastes found in Athens and on the islands of Spetsai, Rhodes and Crete.

The shark question was even easier to respond to. Male sharks have structures known as claspers located on the underside near their anal fins. These claspers are used to transmit sperm to the female for insemination. It is fairly easy to detect them on horn sharks, although one might need to pick up the real young ones to see them. However, I wouldn't recommend using this technique to try to determine the gender of a great white or a tiger shark! Wouldn't be prudent unless you want to see what it's like to be lower on the food chain.

One example of sexual dimorphism that you can tell at a glance involves the rather tasty rock scallop. This is a species of bivalve in our waters that is related to other shelled molluscs like the mussel or clam. The "buoys" have a very obvious red to orange fringe when the shell is open, while the "gulls" are more grey or green in color. I have no idea why this is so, although it does seem to afford the ladies more camouflage from divers who fancy them. When I first dove Catalina waters in the late 1960s, I was treated to the taste of a raw rock scallop by a more experienced SoCal diver... but I have no recollection of its gender, just the flavor. Yummy!

Kids often "play" with the striped shore crabs that skitter about on the rocks of the Casino groyne (breakwater) and divers come up with tales of "humongous" sheep crabs during late winter and spring. After identifying the species for them, I ask "Do you know if they are boys or girls?" Again comes the cry "How can you tell?" In this case you really have to pick them up and turn them over. Be careful of those claws... the sheep crab can break pencils, and maybe fingers, but I've never conducted a scientific experiment to test that hypothesis. The boys have a triangle shaped telson (tail) while the girls have an oval shaped telson which is used to carry the eggs tucked in between it and the body. And "That's how you tell, son!" Get it?

© 2010 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Female (top) and male (bottom) rock wrasse , well endowed male horn shark, female (top) and male (bottom)
scallops, and telsons of female (left) and male (right) sheep crabs.

This document maintained by Dr. Bill Bushing.
Material and images © 2010 Star Thrower Educational Multimedia