Inside a laboratory at Nanaimo's Pacific Biological Station, researchers examine specimens of about 30 different species of fish to gauge their ages – including a 147-year-old rougheye rockfish.
The station's sclerochronology lab, sarted in 1977, is one of several around the world with researchers working full-time to identify the ages to determine the health of species population.
At first, fish aging labs were used to identify the ages that various fish species reached sexual maturity, but now the labs are used to monitor overall health.
Audrey Ty, lab manager, said stock assessors will arrange for samples from recreational fisheries, sport fisheries, commercial fisheries and research fisheries, preferably at different times of the year, in Canadian waters along the Pacific coast.
If a population has an increase in young, it means the adults are able to reach maturity and reproduce effectively, which bodes well for a population. If the population has entirely an elderly population, experts know there is something of concern. The data is then given to Fisheries and Oceans Canada stock assessors and other researchers.
To read the samples, Ty compared fish to trees, as both have age rings – but for fish it's on their scales and bones.
"Unlike a tree, there's not just one ring per year," she said. "So we look for where the rings are condensed and closer together which means the growth is slowing."
The fish grow the most during spring and summer, resulting in rings with spaces farther apart. By using that metric, researchers are able to determine an exact age. To make the seasons stand out more, the bone may be heated up, which makes the winter and fall lines darker and easier to differentiate.
"There's often little puzzles, like trying to figure out, 'is this [ring] strong enough to count? Does it go all the way around?'"
Ty started at the lab in 2008 as a casual worker preparing lingcod fin-rays – a bone in the fin researches use to age lingcod and Pacific cod. While she personally carries a degree in biology, sge said many of the positions don't require a college-level education, as it is a technician role focusing on pattern recognition and attention to detail.
"I do enjoy the fact I'm providing something that's needed," she told the News Bulletin. "A good stock assessment to know the health of a population does need ages, it does need to know if more young are coming in, if there is enough old, it needs to know if the size of that age is changing, if the fish are getting smaller at a certain age – sometimes that means the fishing pressure is too much."
A big part of the job for the seven technicians employed at the Nanaimo aging lab is studying rockfish. Some of most common rockfish at the lab include Pacific ocean perch, yellowtail and quillback, with researchers measuring them based on an otoliths bone from the inner ear.
"They're the ones the stock assessors have to do most frequent assessments on, I think they're the major fisheries or sometimes they're species that are recovering or they need to check on them more frequently," Ty said. "When we give them the ages its like a snapshot in time of how many young fish, how many middle-age fish, how many fish in the range that have lots of babies, how many males, how many females."
When it comes to rockfish, many of the genus don't reach sexual maturity until they're about a decade old. If they get caught before then, they never get the chance to reproduce. The record for the oldest rougheye rockfish aged at the lab was 147.
"They're a long-lived species and for some of the rockfish, really their ability to have young successfully only happens to, they call them, BOFFFs – big old fat fecund females."
Aside from rockfish, there are seasonal fish such as hake in the fall and herring in the spring. Salmon are also regularly studied, with scales being the choice cut for examination.
"Scales are used for fish who have younger lifetimes because as fish gets older the years would pile up on the scale and we wouldn't be able to count them, but salmon are usually less than eight years old so on the scale you can see how the lines get finer and closer together and they go all the way around."
Shelled bivalves, like geoducks, can also be aged, sometimes reaching hundreds of years old – although they need to be done a little different with researchers taking the hinge of the shell and pressing in clear craft film before putting the impression in a slide.
"Fish can get quite old, and it's kind of fascinating you can get an idea of how old they are from their scales and their ear bones," Ty said. "It just helps get information about the life history of fish and the health of fish populations."
