Introduced perch and algae in New Zealand

This video from New Zealand is called Common Bully nesting.

From the New Zealand Herald:

Cull of pest fish could give clue to beating algal bloom

Friday February 16, 2007

Waikato University scientists who have spent much of the past week killing thousands of pest fish at Wellington’s Karori Wildlife Sanctuary hope the cull will provide clues to controlling algal blooms.

Red-finned European perch have been living in the sanctuary’s lower lake for nearly 130 years and are so numerous that the young perch eat most of the microscopic animals – zooplankton – which would normally control blue-green algae blooms that turn the lake into a thick algal soup.

The lower lake has had toxic algal blooms most summers in the past decade.

In 2004 experiments by a Victoria University student, Kirsty Smith, revealed perch were a bigger part of the problem than the usual suspects, nitrogen and phosphates leaching into the waterway.

Perch are now so dominant in the lower lake that they have effectively created a single-species ecosystem, excluding native fish such as kokopu and bullies, according to Karori Wildlife Sanctuary Trust chief executive Nancy McIntosh-Ward. …

Some of its lake management specialists have been in Wellington since last week using the nation’s only purpose-built electric fishing boat to stun thousands of the perch.

The 1000-volt charges delivered by the boat stunned 2000 perch in just the first two days – and an eel and a trout.

Pest proof fences in New Zealand: here.