"They only breed once in their lives, at the end of it, in sub tropical waters.
"Consequently, their population is determined by those returning to the sub tropics to breed, having survived life in New Zealand.
"Humans, dams and perched culverts, habitat loss and water quality have caused their decline.
"I can't tell whether someone killed these four deliberately or accidentally by something like cement wash entering the waterways."
Mr Bell said long finned eels are classified as 'at risk — declining' and only live in New Zealand, while short finned eels are not threatened and also live in other Pacific countries.
"We are lucky in Kāpiti.
"We can still look from a bridge and see whitebait.
"We can hear morepork at night, see reasonably rare birds such as bellbirds and grey warblers, fern birds and even New Zealand dotterels.
"Our native birds, fish, wetlands, estuaries and forests are part of what attracts many of us to the Kāpiti Coast.
"Eels are also part of our heritage and our taonga.
"We need to be mindful of the effects our actions have on the natural world surrounding us."
