Biologists care A LOT about otoliths. Why? It all boils down to protecting the fish stocks targeted by fisherman. Every time someone catches a fish, stock is removed from the population. Nothing to feel bad about if you follow fishing regulations! The regulations are put in place to protect fish stocks… so if you hate that you can only take home 2 Red Snapper per trip, it’s not personal. Try to change your mindset to the bigger picture. Regulations are trying to ensure that you can catch Red Snapper for the long run.
So, back to otoliths. How do we know anything about fish populations? Well, what do you want to know? How old are they? How old are they when they spawn? Two very good questions! That is where otoliths come in… each fish has technically 6 otoliths, but we only care about two of them (the sagittae). They are made of calcium carbonate and a few other trace minerals and lie just behind the fish’s brain. These bones grow with the fish and produce growth rings, similar to rings on a tree! If we collect these bones, take a thin slice of them and observe them under the microscope, then we can age the fish quite accurately. The main purpose of these bones is not just so we can age the fish, obviously – their day job is to provide balance and orientation (also sound detection). Otherwise, the fish wouldn’t know which way was up or down. The size and shape of otoliths are very unique to the fish. A fast, quick fish like a tuna will have very tiny otoliths, whereas a slow mover like a Red Drum will have big, bulky otoliths. Here is a side by side pair of otoliths: Atlantic Croaker on the left, Red Snapper on the right.
The key to knowing age structure of a fish population is getting samples. If I had a group of people and only asked a few of them their age, that wouldn’t be a very representative look at the group as a whole. Same with fish. So the more fish we age, the better! Unfortunately, it is very expensive to send researchers out to catch these fish, so biologists rely heavily on the general public. There is a program funded by NOAA called MRIP. This program funds state biologists to regularly man marinas and get basic data on the fisherman but also collect otoliths and other data from the fish he catches. The fillets are not touched though, I promise! So if a biologist comes up to you after a day of fishing, it may be a little annoying to stop what you are doing and fill out a survey and temporarily surrender your fish, but please consider it. It’s like investing into your fishing future!