Dive Dry with Dr. Bill

119: Baby Boom

This has been a very interesting fall season for diving. A number of diver friends have asked me about the increased numbers of "baby" fish we are seeing throughout the southland. It appears that a baby boom is exploding in the undersea world this year.

At times the reefs, and even the sandy bottom in some areas, seem covered with the bright blue and red-orange of baby blue-banded gobies. The adults of this species are already fairly small, reaching a world record length of only 2 1/2 inches (although I've seen ones that seem to be larger than that). Given my eyesight, I can barely resolve the much smaller young. If it weren't for their brilliant colors, I might easily overlook them even though they seem to be everywhere.

There also appears to be a bumper "crop" of two wrasse species, the rock wrasse and the senorita. I've seen more this year than at any other time in recent memory. The babies of their relative, the sheephead, do not seem to be much more abundant than normal. Blacksmith, relatives of the garibaldi, always seem to produce large numbers of young. Of course since these young often form schools in open water, they may be more apparent than the bottom dwelling fish species.

It may be my imagination (or my current celibacy), but it also seems that a lot more fish are mating this year. The surfperches are quite active. I've recently filmed male's performing their courtship dances in many species. These include the kelp surfperch, shiner surfperch, black perch and rubberlip seaperch. I know females of our species often complain that their potential mates all seem to have two left feet on the dance floor. Females in this fish family must be quite pleased with the wide range of "moves" their potential lovers exhibit (and they don't even have one left foot)!

So why all this sex (er, reproduction) this year? One hypothesis that seems to make sense relates to the poor summer visibility we divers complained about a year ago. No, it hasn't brought the male and female fish closer together so they can see one another. The poor visibility last year was due to an abundance of nutrients in the water, apparently caused by strong "upwelling" south of Pt. Conception. Colder, nutrient rich waters were brought to the surface as unusually persistent north winds blew the surface waters offshore. The winds then helped carry this nutrient-rich water further south than usual. With persistent high nutrient levels, plankton bloomed and plankton eaters including blue whales appeared in our area. Many algae also responded to the higher nutrient levels.

The increased food supply provided by the plankton and algae undoubtedly resulted in healthier fish, and probably faster than "normal" growth rates. Well-fed and healthy fish may reach sexual maturity earlier than during "normal" periods when food is less abundant. And when those hormones start flowing, there's no stopping most species!

Blue-banded gobies usually live less than 20 months. Therefore they begin breeding within a year. It would be expected that this fish might respond quickly to the enhanced diet of 2003. Senoritas also mature within a year. However rock wrasse and blacksmith normally become reproductive at two years. An abundant food supply might allow them to mature earlier, and this could explain the high numbers of their offspring now. On the other hand sheephead, which are all female at birth, don't start "messing around" until they are about four years old. Young sheephead would not begin to reflect the ideal conditions of last year. Those sheephead which were already reproducing when the abundant food supply occurred would probably produce more young this year as a result.

So other species also exhibit pulses in reproduction based on prevailing environmental conditions. The time lag between abundant food and the reproductive pulse depends to a degree on how quickly each species begins reproducing. Of course these baby boomers won't have the same effect on "social security" as the boomers of our species. In fact, they will ensure the "social security" of their predators by making certain that plenty of food is available! Good thing we are the apex or top predators on Earth (well, most of the time at least). Just hope the aliens from the planet Xanadu don't suddenly appear to solve our "social security" dilemma.

Speaking of apex predators- as you read this, I will be down off Guadalupe Island (Mexico) filming great white sharks (from the safety of a shark cage, hopefully). With any luck I'll return next week with plenty of footage and some great stories to relate in future columns!

© 2004 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.

Schools of young blacksmith intersect, baby rock wrasse, courting black perch,
baby blue-banded goby on sea urchin test (can you find it?).

This document maintained by Dr. Bill Bushing.
Material © 2004 Star Thrower Educational Multimedia