You know your day is going to be "interesting" when you reach into your fin's foot pocket to pull your dive gloves out, and you feel a sharp pain. I was on the King Neptune preparing to suit up for the first dive of the day, and reacted by shaking my gloves hard. There, clinging to them for dear life, was a good sized centipede which must have lodged itself into the tight protected area while the fins were in my dive bag at home. "Sorry" to say it quickly became fish food!
The dive there at Little Gibraltar was somewhat uneventful... other than the fact I missed the submerged pinnacle on my way down the anchor line. I guess it must have been karma. I doubled back and found it after filming a few critters. I often refer to this site as the "moray condo" because they are usually common here, but I didn't see a single one. Always one to see the silver lining in the darkest of clouds, I just smiled that there would be less video to edit that night, allowing me to get to karaoke.
Captain Bob Kennedy moved the King Neptune to Hen Rock where we did two dives. Now this is not my favorite dive site on the island, but other divers tend to really like it. What have I been missing? However, it does reward me on occasion with some interesting critters and behavior. I did the first dive over the sandy bottom, looking for a favorite fish of mine (at least of the ones not found on my dinner plate). I frequently see the small orangethroat pikeblenny here, and enjoy filming the silly males as they go berserk trying to draw the attention of the ladies. Reminds me of the nights I used to spend at the Chi Chi Club dancing and... trying to draw the attention of the ladies!
For the third dive, I decided to venture out to the deeper, outer reef. I hadn't been there in a while and it is often a good place to film nudibranchs, those beautiful shell-less snails that underwater photographers love to encounter. I wasn't disappointed, but they will be the subject of a future column. As I approached the reef, I noticed one small sheep crab on the bottom at 65 feet. I looked around and saw a larger one moving towards it. Seemed like a good opportunity to film some potential behavior if they interacted, so I put my eye to the viewfinder and my finger to the record button.
It isn't easy looking through the tiny viewfinder, so all I could see was the larger crab approach the smaller one. It then trapped the smaller one within a "cage" created by its eight legs and two claws. Looked like this would be another great opportunity to film sheep crabs "in the act." This is why they enter our shallow waters starting about February. I often see them doing the wild thing with their legs entangled, the male's claws holding the female tight. However, the larger male seemed to hesitate as I filmed. It then quickly released the smaller crab and went on its merry way. The smaller crab exited stage right... in somewhat of a hurry.
Now I thought this unexpected behavior a bit strange. I went over to check both sheep crabs, turning them over. Not entirely to my surprise, I discovered they were both... male! Even a casual diver can discern a crab's gender since the telson, or tail section, of males is thin and pointed while that of females is oval and broad to carry the eggs. I assumed male sheep crabs would have less trouble identifying a female from a male, but this one did seem to be a bit confused... to be anthropomorphic. I'm guessing it realized its mistake when it sensed that no chemical sex pheromones were being released by the other crab. I don't like writing about the same species too frequently, but if you read a recent column, I hypothesized about sheep crabs feeding on sea cucumbers for the same reasons that Asian males do, as an aphrodisiac. Perhaps this male had just finished munching on a cucumber, and was driven by lust.
This encounter reminded me of the years when my Toyon biology students studied our island bison for my Animal Behavior class. Male bison are known to initiate mounting behavior similar to that used in mating when they encounter another male they wish to express dominance over. Perhaps this sheep crab was just showing that it was the alpha male in that neck of the reef. Thinking of bison expressing dominance brought back another memory. When I was at Toyon, Susan Wheeler (the headmaster's wife) was driving our small brown VW bug down the Toyon road. She encountered a large male bison on that narrow road, which forced her to stop. The dominant male came over to the brown VW bug, and mounted it... with Susan inside at the wheel.
Needless to say she was a bit freaked out by this. When she arrived back at the school, she told me the story. I told her the bison was probably doing one of two things. It either wanted to mate with her, which was highly unlikely given the differences in their "biology," or its attention was focused on the VW bug instead of her. She looked at me with a questioning look, and I explained about bison bulls displaying their dominance over other males. Perhaps the bison was confused, and thought the VW was another bison. And with that I end this strange (but true) tale.
© 2008 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 "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass," "Common Fish and Invertebrates of the Sea of Cortez" or the new "Sharks and Rays of Southern California" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!
Male crab (right) approaching "female" crab, trapping it, mounting it... and departing "unfulfilled."
This document maintained by
Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia