Determining age by studying calcified structures is a discipline called sclerochronology, and it is extremely valuable since stock assessment models depend on age-structured data.

In theory, you can count annual rings on otoliths just like you can count tree rings to age them. But it's often more complicated than that, and errors can have big consequences on how well a fish population is managed. For example, rockfish used to be greatly under-aged, leading scientists to believe that they were fast-growing and could sustain much more intensive fisheries than in reality, which caused their collapse in Canadian waters.

The Baltic Sea, with its fluctuating salinity levels, can confuse things even further by creating false rings and "noise" in the main underlying pattern. There are still many aspects we don't understand about reading otoliths from Baltic Sea plaice, especially patterns deposited in early life -- in fact, one of the studies that inspired this project is an unpublished paper aiming to confirm the position of the first true annual ring.

The main goals of this professional practice were to: 1) Standardize an approach to taking measurement on juvenile plaice otoliths. 2) Create categories to differentiate otoliths based on general patterns. 3) Guide future research to validate age determination.

I barely grazed the tip of the iceberg during my internship, but luckily there are exciting horizons ahead! This summer, an undergraduate student will be continuing the data collecting process I initiated, to increase our sample size, and next academic year another student will be conducting their Bachelor's thesis on similar questions but with flounder. Here are some of the next steps to be taken, taking into consideration what we learned from my experience: