Ask a scientist: What’s the deal with sea lice?

The Question:

“Fishermen have told me there are more sea lice in the Sound than there have been in the past. This has resulted in having to haul groundfish sets in less than 12 hours or else the sea lice will have eaten your fish off the hooks and all the bait. What is the lifecycle of sea lice? How do crab, halibut, etc. compete with them for food? I cannot imagine how anything else can live in an environment infested with these things as they seem to be able to pick the bones clean of any meat in a matter of hours. How do fish and other creatures manage with all the lice on them?”


The Answer:

Sea Lice are of the family Caligidae. They are one-centimeter-long parasites that feed on the mucus, blood, and skin of host fish – preferring areas of their head, back and caudal region. Sea lice are crustaceans and go through a series of molts. As juveniles, they are non-parasitic and non-motile. They float around feeding on an internal egg-yolk. In this stage, they are planktonic. After about two days, they become free swimming and parasitic. Once this happens, they are able to attach to fish via antennae. After they attach to live fish, they mature into adults. As the sea lice mature into adults, their grazing becomes more lethal, as they can cause enough skin damage to kill the fish. Sea lice live around two months and require a live fish as a host.

Zeke, it is possible that the creatures eating your bait and groundfish are actually sand fleas. Sand fleas are of the family Talitridae. They are a smaller crustacean than sea lice. Sand fleas are usually found eating bait or halibut if left on the ocean floor for too long. Unlike sea lice, they do not have a planktonic stage or require live fish as hosts. Their life cycle is longer than that of sea lice; they live approximately one year. There has not been much research into how live fish defend themselves from sand fleas. Dr. Benjamin Americus suspects it is through increasing mucus production and shaking off fleas like a dog.


Unfortunately, there is also not a lot of research on the changes in populations of sea lice or sand fleas in Alaska, nor their competition with fishes for food. If fishermen are reporting more of either, that is worth looking into more. Generally, Alaska has not had the same problems with fish pathogens as the Lower 48 thanks to cooler temperatures.

Thank you, Dr. Benjamin Americus of Alaska Sea Grant, for consulting with us to answer this question. We are currently seeking out more Ask a Scientist questions. Whether you are out in the Sound or out the road, if you have a question, please email it to [email protected].