Marty Sharpe writes in the Dominion Post about a study showing that farm runoff (nitrates) going into the Taharua and Mohaka rivers is making trout smaller.
The effect on size is due to the increased algal levels in the water – the rivers’ clarity and food value decrease, meaning smaller trout.
An excerpt: (read in full here)
“Councils could now start implementing nutrient limits in catchments based on scientific fact rather than anecdote. “There have been a lot of studies done on [trout] abundance, but not much has been done on how big they are and how that has changed over time,” Mr Sevicke-Jones said.
“”They [trout] are smaller. They can actually be more abundant. They are just not reaching optimum size any more due to the food available to them. Now this work has been done we can say `OK, all those arguments we’ve been having, we no longer need to have again’.”
“The algae may also affect native species such as eels but this had not been studied yet, he said.”