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Dive Dry with Dr. Bill

#478: A Courtin' We Will Go

There is a traditional English folk song, actually originating in Scotland about 1548 AD, that I'm sure my readers all know. It goes like this: "A frog went a-courtin' he did ride." Now I don't remember ever knowing all the verses, so it didn't make a lot of sense to me as a kid. But then, not a lot did at that tender young age. Heck, I thought courtin' meant being on the basketball or tennis court. Thanks to the Internet and Joni Mitchell, I now understand such things... as well as the hysterical (er, historical) story of how the song may have played a role in the courting of England's Queen Elizabeth I by the Duke of Anjou, not to mention appearing in a Tom and Jerry cartoon, and froggie went a courting, riding on a snail, to Miss Mouse's house. So what does that have to do with today's column? Not much as you shall see!

Now that I understand things, I too "go a-courtin'" although rarely with the female of my own species. Don't get me wrong, I'm not into those kinds of behavior. But in my endeavor to present my readers and cable TV show viewers the real story of the kelp forests, I do search out courtship and mating behavior by the residents of the waters surrounding our island. It's part of my mission in life! After all, if most species don't go courting, they doesn't survive.

A while back I was approaching the dive park stairs after enjoying a leisurely dive. I was surrounded by schools of blacksmith, lots of kelp bass, garibaldi, senorita, rock wrasse... you know, the usual cast of characters. My eye detected unusual motion and my brain processed it in a nanosecond causing me to instinctively lift my camcorder and begin filming the two fish that had attracted my attention. I knew them to be kelp rockfish (Sebastes atrovirens), which are usually very sluggish like all their rockfish relatives and just sit on the reef. However, these two were doing a little dance just like the many surfperch species I've observed during "Dancing with the (Star) Fishies." Many species of male fish can dance to the delight of their damsels... unlike most males of the species Homo sapiens (including this author).

These relatively small reef fish (no longer than 17") are found from as far north as Fort Bragg south to central Baja, in relatively shallow water (subtidal to 268.96 feet, but usually above 100 according to that authority on all things fishy, Dr. Love) compared to their deeper water relatives. They are by far the most common of the rockfish seen by divers in the Casino Point Dive Park, in part because they highly favor kelp forest habitats. Their heads bear long spines, especially on the gill covers, showing their resemblance to the scorpionfish with which they are closely related. They have large, lace-like pectoral fins which allow them to glide through the water on those occasions when they aren't stationary on the reef. There you'll see them upright, on their sides or even upside down... they seem unaffected by gravity (or logic). Body color is variable, ranging from whitish to tan or brown to greenish or even reddish and they have dark flecks on the sides and back.

The pair I observed and filmed involved the male cozying up to his potential mate and swimming behind her, often with his mouth partially open. No, they aren't cannibalistic. They feed on zooplankton, small fish, crustaceans (including shrimp, isopods and crabs) and even a little escargot. On rare occasions, I have observed kelp bass (Paralabrax clathratus) performing a very similar mating dance. Female rockfish are sexually mature at three to six years and six to nine inches in length, although some studies differ in their assessment. If the male rockfish is successful, it will mate with the female, inseminating her. She will store the sperm until it is time to fertilize her eggs. Based on DNA studies, kelp rockfish females are somewhat promiscuous and will mate with more than one male.

The CDF&G states that spawning off southern California begins in March and goes into June. Therefore these two had apparently checked the calendar and got an "early bird" start at the very beginning of the season. A female will produce between 10,000 and 275,000 eggs. Since they are viviparous (live bearing), they release tiny larvae about 1/6" long. These larvae grow, munching on plankton, and settle out into the kelp canopy as an advanced larval stage after one to two months. The juvenile fish begin appearing over the reef, often schooling together before settling down. It is not uncommon to see these schools of miniature rockfish swimming about in the shallows off the Casino groyne (breakwater).

Although adult rockfish may be ambush predators, darting out from their place on the reef to snatch an opportunistic meal during the day, much of their munching occurs at night. At this time they search for prey, probably using their rather large eyes in the dim light. A wise kelp rockfish may live 20-25 years if they are not munched by a cormorant, marine mammal, or other fish including their close relatives. Adults primarily risk death at the "hands" (er, mouths) of sharks, dolphins and pinnipeds. This species was rarely targeted until the 1990s when the live fish trade boomed, although they have been taken by recreational anglers on hook-and-line and by spearos. Heck, they are usually pretty easily approached by divers so there really isn't much challenge in taking them.

Now I'm not one who likes to interfere too much with Mother Nature. If I did so, the critters down under would not allow me to get up close and personal to film their interesting behaviors. However, in this case the poor male rockfish apparently became sheepish when he saw me filming his courtship dance, and left his lady friend out in open water as he ducked into a crevice in the reef. My apologies to this amorous couple, especially the young lad. I hate it when that happens.

© 2012 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM 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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Sequence of courting kelp rockfish in the dive park... at least until I interfered...
and the abandoned female out in the open while her potential mate hides!

This document maintained by Dr. Bill Bushing.
Material and images © 2011 Star Thrower Educational Multimedia