Can better salmon habitats also curtail mosquitoes?

You can kill mosquitoes without harming salmon. And you can also help salmon without helping mosquitoes.

That’s a key takeaway from a presentation by the Fraser Valley’s chief mosquito killer following one of the worst mosquito seasons on record.

Mosquitoes and salmon

Locals paid for last year’s high water—and the moquitoes that followed—with both their blood and money. The Fraser Valley Regional District’s mosquito hotline logged one of its highest call loads ever, and local governments spent $130,000 more than planned, The Current recently reported.

To keep the mosquitoes in check, the regional district employs a local company, Morrow Bioscience, which deploys a larvicide in certain hotspots.

The larvicide doesn’t have any impact on salmon or other beneficial species. And Morrow owner Dirk Lewis recently told local politicians that killing mosquitoes also doesn’t indirectly hurt salmon by removing the bugs from their food supply.Salmon are opportunistic eaters, but asked about the food chain connection of fish and mosquitoes, Lewis noted that the two types of animals prefer very different habitats.

“Mosquitoes like warmer water and low oxygen: those are the triggers for the larvae to hatch,” he said. “Salmon love cooler water and high oxygen content.”

Lewis pointed to local salmon habitat projects as evidence that improving fish-friendly wetlands doesn’t have to mean dealing with more mosquito bites.

“We found that if you enhance habitat with salmon in mind you will very rarely get annoyance/floodwater mosquitoes coming from those areas,” Lewis said. “The salmon-mosquito larva interface for these ones is not that tight.”

Lewis pointed to a salmon enhancement project on Brae Island, near Fort Langley, where an area was improved in a way that bolstered fish while reducing the number of mosquitoes.

“If you get an area that is going to produce mosquitoes, the salmon are keen enough to get the heck out of there,” he said.

The mosquitoes do become food for many animals, from the non-discriminating salmon, to sticklebacks (another common type of fish) and water beetles and dragonflys. But Lewis noted that mosquitoes are generally not all that useful as a food source for local animals.

That’s because of the very short period in which the mosquitoes and their larvae are active. If an animal depended on them as a food source, he said, “they’d be very hungry within 10 days.”