Mosquito nets intended to prevent malaria are finding an unanticipated use as fishing nets all across the tropics, according to a new study.
These fine-meshed nets scoop up fish of all types and sizes indiscriminately. Experts are worried they are draining fish populations.
But the study's authors say poverty is the main reason why the practice persists, and efforts to limit mosquito net fishing may end up hurting people who are just trying to get by.
'Pretty much everywhere'
Insecticide-treated bed nets have been an extremely successful tool against malaria. Widespread distribution of these mosquito nets are a major reason why 60 percent fewer people died of the disease in 2015 than did in 2000, according to the World Health Organization. In 2015, health officials delivered more than 150 million nets to countries where malaria is found. Nets are usually given away free or subsidized.
Working on fisheries management in northern Mozambique, Imperial College London graduate student Rebecca Short saw people using them to fish.
"To the naked eye, it did seem to be going on a lot, in a lot of different places there," she said.
Fishing this way takes little skill. And since the nets are often free, it takes no capital. Experts are concerned that it could increase the number of people catching the limited supply of fish.
Other development workers have seen mosquito net fishing elsewhere. But it wasn't clear how common it was.
According to a new study in the journal PLOS ONE, it's very common.
Short and colleagues took a "first quick-and-dirty look" at the scale of the issue with an online survey aimed at conservation, health and development workers worldwide.
Nearly 100 respondents, from Senegal to Samoa, reported seeing mosquito net fishing.
"I don't think even we expected to get the result that we did," Short said. "Pretty much everywhere that malaria's a risk, there's people fishing with these nets."
Some of it was small scale — "a couple people dragging a net through the water," Short said. That's "probably nothing to worry about, especially given the benefits." Small-scale fishing can be a good source of scarce protein and a bit of income, she added, especially for women, who are typically excluded from more profitable work.
On the other hand, there were cases like in Bangladesh, where fishermen blocked off entire rivers with mosquito nets. "Obviously, absolutely nothing gets through in those scenarios," Short added.
Fishing with mosquito nets is illegal in many places, out of concern for the sustainability of the fishery. But Short isn't sure that's the best approach.
She says outlawing mosquito net fishing does nothing to address the reason it happens: poverty.
"There's huge issues with enforcement," she added. "Do you put a mother who's trying to feed her kids in prison for three years just for using a mosquito net to fish with?"
But reef ecologist Tim McClanahan with the Wildlife Conservation Society questioned the benefits mosquito net fishers are gaining.
"There is an assumption that because the poor and women are doing it, it is improving their food security or incomes," he said. According to his research, "This is not always the case."
While many fisheries management approaches focus on catching larger, mature fish that have had time to reproduce, Short's study discusses a controversial view known as balanced harvest. In that approach, fishers aim to catch fish of all sizes, proportional to their numbers in the population. Since mosquito nets catch everything, the authors note, they actually may be helping.
"This assumption is somewhere between wrong and dangerous," he said. The harvest from mosquito nets is not balanced. It's indiscriminate."
Short acknowledges that the issue needs a lot more study, including what actual impact mosquito net fishing is having on fish populations, and better local understanding of why people are doing it.