whan my dad goes fishing he needs to take a scale to give to the river biologist. they see how old they are. how do

Question: whan my dad goes fishing he needs to take a scale to give to the river biologist. they see how old they are. how do they do this ?
- Keywords:
  age,
  fish,
  river biologist,
  scale
Asked by Ella to Deborah, Euan, Maheen, Rob on 22 Jun 2016.
- Rob Stanley answered on 22 Jun 2016:
  
  From your message in the chat, I think you are asking about salmon in particular.
  
  They look at the growth of the scales a bit like they use tree-rings to age a tree. As the scales of the salmon grow they lay down rings at regular intervals. In the summer months, when there’s lots of food and the salmon can grow quickly, these rings are far apart. And in the winter there is less food, so the rings are closer together.
  
  By looking at how many cycles of large and small distances between the rings there are they can figure out how many years the fish has lived.
  
  Brilliant question by the way, I’ve even learnt something new by looking this up!

Question: whan my dad goes fishing he needs to take a scale to give to the river biologist. they see how old they are. how do they do this ?