Opinions, musings, ideas, pearls of wisdom
Old Friends
By Dougald Scott
Old Friends
By Dougald Scott
The other day Elaine Cook reminded me of some old friends I hadn't thought of in a long while. It seems that she and John were checking out the Aptos Creek lagoon and encountered several biologists who were surveying the fish population in the lagoon with a beach seine. Of immediate interest to Elaine and John were the juvenile steelhead, which the biologists reported were averaging around ten per net pull (a reassuring number for all of us concerned about the welfare of steelhead in Aptos Creek). What really caught my attention though, was her observation that there were large numbers of tiny little fish called "sticklebacks," my old friends.
Since sticklebacks are only 2-3 inches in length, most anglers are not familiar with them, but just about every biologist has encountered them at some point in their career. Here is how R.J. Wootton describes them in the introduction to his book, The Biology of Sticklebacks:
"The three-spined stickleback has received more attention from zoologists than almost any other species of fishÉ Studies on the three-spined stickleback have made important contributions to ethology [the study of animal behavior], evolutionary biology, vertebrate physiology and ecology."
I captured my first three-spined stickleback in Corcoran Lagoon (the one with the radio towers in it) back in my grade school days. I remember proudly identifying it with my little Golden Nature Guide to Fishes. Later, in my career as a biologist, I had many encounters with sticklebacks. While surveying salmonid populations in local streams, I learned that these little fish occur in all of the creeks, rivers, and coastal lagoons of Santa Cruz County (in fact, they populate just about every body of fresh, brackish, water from 35¡-70¡ in the Northern Hemisphere; they also occur in the near shore ocean environments of these latitudes). They proved to be wonderful subjects for student projects in genetics, animal behavior and parasitology (they carry some very interesting parasites).
Sticklebacks are found in fresh and salt water because they are anadromous; that is they typically spend part of their life in the sea, but return to fresh water to reproduce. Unlike most salmonids, sticklebacks do not have to rigidly adhere to this life cycle. They can spawn in brackish water; in fact, the Corcoran Lagoon population was observed spawning when the lagoon's salinity was the same as seawater. On the other hand, many populations are landlocked, successfully spawning without spending any time in saltwater. In our local waters, sticklebacks that are not landlocked spend the winter months in the ocean and return to their streams and lagoons for spawning in the spring and summer.
During their reproductive season, male sticklebacks develop a red throat and fore-belly, and their eyes become bright blue. The males build elaborate little nests with an entry at one end and an exit at the other. Once their nest is assembled, they fiercely guard their territory from other males, but perform showy zig-zag dances to entice females into their nest. When a female enters the nest, she deposits her eggs and swims out the exit. The male follows her through and fertilizes the eggs and then drives the female away. Males usually repeat this process with up to seven females.
Once spawning is complete, the male tends the nest by fanning which keeps a flow of oxygenated water on the developing eggs. When the eggs hatch, he tears the nest apart to form a cleared nest pit. Then for a few days he guards the young in the nest pit. If a young offspring strays from the nest, he sucks them into his mouth and carries them back to the nest pit where he spits them out. At the end of the breeding season, when the young have matured and are on their own, many, and in some populations, all of the adults die, leaving the new generation to carry on.
Landmark studies were carried out on sticklebacks in the 1930s and 40s. Biologists presented male sticklebacks that were tending their nests with little wooden models of different shapes and colors. They found the males would attack just about any shape, so long as it was painted red on the underside. Models that were identical in size and shape to a live stickleback, but without the red underside, did not elicit a response. Similarly, the red underside turned out to be the main attractor for the females. These studies formed an important part of the "releaser" theory in animal behavior (this is the notion that certain environmental cues will trigger an innate behavioral response in the subject).
On another front, sticklebacks play an important roll in screening for water pollution. Since they are easy to capture in large numbers and easy to maintain in laboratory aquaria, they provide a cost effective way to screen for a wide range of pollutants. In addition to being sensitive to heavy metals and other well-known toxins, sticklebacks have proved useful in testing for more subtle, hard to detect pollutants which mimic natural hormones such as estrogen and testosterone. Most effluent from industry and municipalities in California is routinely screened using sticklebacks. These are just a few of the areas where sticklebacks are making important contributions to science.
So, the next time you are visiting one of our creeks, ponds, or coastal lagoons, look for the sticklebacks and make friends.