Whitebait season begins on Monday and the Conservation Department is asking fishers to stick to the rules and not be greedy.
In most of New Zealand, including Whanganui, the season runs from August 15 until November 30.
Whitebait are juveniles of five species of native fish: giant kokopu, banded kokopu, shortjaw kokopu, inanga, and koaro. Those that escape the whitebait net grow into adults ranging from 10 to 60 centimetres long.
Conservation Department (DOC) freshwater scientist Jane Goodman said whitebait are iconic in New Zealand.
"Unfortunately four of the five species are categorised as either threatened or at risk due to declining numbers and habitat. Fishers are encouraged to only take what they need and to think about the sustainability of the fishery for future generations."
She said it was good to see more conservation measures happening, such as planting and fencing off spawning grounds and adult habitat.
"We urge people to contact their local DOC or regional council office if they see overhanging culverts or other barriers that stop whitebait migrating."
Whitebaiting is permitted between 5am and 8pm or between 6 am and 9pm when daylight saving starts on September 28.
DOC will be patrolling whitebaiting sites and talking to whitebaiters throughout the season to ensure people are complying with the regulations.
"We plan several of these trips each season. We also respond to calls from the public reporting breaches in the rules," Whanganui senior partnerships ranger Les Judd said.
DOC administers regulations that cover fishing methods, location, legal fishing times and net size. Illegal whitebaiting carries a maximum fine of $5000 and whitebaiting equipment can be seized.
Common calls DOC receives during the whitebait season involve people with gear taking up more than a third of the width of a stream, unoccupied nets, and people fishing in illegal areas such as within 20m of a culvert or stream confluence.
Pamphlets with the regulations are at local DOC offices and sporting shops and on DOC's website.