senoritafish | Little fishy ear bones, or art vs. science

Spent the morning reading mackerel otoliths. Otoliths are the ear bones of fish, and are often used to determine the age of the fish. In a Pacific mackerel, they are about the size and shape of fingernail clippings. Reading otoliths is really more of an art than a science. You see, they have rings on them like a tree. During the summer, when the fish has warm water to grow in and lots of available food, an opaque, white layer is laid down. In winter, when water temperatures are cold, and food may not be available, a transparent layer is formed. We look at them under a microscope and count the rings (we call a ring an annulus, plural annuli) to determine the age of the fish. This information is used along with a lot of data from other sources to determine how much of the population is of breeding age, how much spawning is occurring every year, and ultimately, how much biomass of that species exists.

The thing is, on a mackerel, the annuli are not nearly as clear as a tree. Fish are subject to changing environmental conditions as they move from place to place, and physiological changes as they spawn. Any kind of stress on the fish's body can cause a transparent area to be laid down which is not really an annulus. And sometimes transparent zones between annuli are not all that transparent - they look more like a dent on the surface, like on a Ruffles potato chip. So sometimes checks can be obvious and an annulus is hard to see. They are assigned an arbitrary birthday on July 1, so any fish caught on that date or later are called a year older than a fish caught in June which may look exactly the same. Sometimes the annulus for the summer appears in April, so you can't count it yet, and sometimes it hasn't appeared yet in July or August, so you count it before you can really see it.

This is why reading otoliths is called an art, rather than a science.

Most of the biologists roped into doing this hate it with a passion; they feel like it's wasting their valuable time. I don't mind it, however. I know it's important, I'm fairly good at it, being one of only two biologists in the department, and maybe on the West Coast, that knows how to do it for this species. Not that it's hard to learn, it's just tedious. However, tedium has its place. Occasionally, it's nice to be able to sit in darkened room, hum along to the radio, and debate with myself whether that's real or just a check, whether the edge is opaque or transparent, and a separate track of my mind thinks about what other nonsense I can dredge up to put in this journal