Happening now is one of the greatest wildlife viewing spectacles in this part of our province. The eulachon run usually takes place on the Skeena and Nass Rivers in late February and early March.
This is the annual migration of the eulachon (oolichan, (h)ooligan, or candle-fish) upstream with the incoming tides to deposit their eggs and sperm on sand and silt in the pools and backwaters of the river. The Eulachon are very small, weak swimming fish that rely on the incoming tidal waters to help them move upstream against the river currents as far as the tidal limit where the eggs survive the lower salinity better.
These abundant, nutrient-rich fish attract thousands of gulls, many bald eagles, seals, sea-lions and bears (and humans) among others to join in a huge harvesting and feeding orgy. There are so many gulls screaming and flying around that it looks like a wild winter snow storm. Our kids were always excited to see how many bald eagles we could count.
Most exciting to see and hear their breathing “whoomphs” are the sea-lions, marine creatures that spend most of their life in salt-water, but do not appear to be bothered by chasing the eulachon for quite lengthy periods of time in freshwater rivers and lakes.
In fact, you might remember a sea-lion that twice ended up sitting on the Pacific Rim Highway to Tofino in later December. It is thought that it had been hunting up to the end of the adjacent large, fresh-water, Kennedy Lake, quite a distance from the ocean, and it could not figure out how to get back to the ocean. So, it asked for help – twice!
It seems that sea-lions are not particularly affected by changes in salinity and can easily adjust their internal body fluids to cope with their external environment. However other marine organisms, especially anadromous fish such as salmon species, must actively regulate their internal body fluids as they move from salt to freshwater to reproduce and vice-versa.
If the fish were not able to adjust to freshwater after living for several years in the sea, the laws of osmosis mean that their bodies would rapidly fill up with water, dilute all their body fluids and basically incapacitate all their enzymatic activities. I suppose they would ultimately burst. To avoid this dilemma, they actively take up salts and excrete large volumes of dilute urine when in freshwater.
Consequently, anadromous fish including the eulachon, need a period of adjustment when moving from salt to freshwater and vice-versa. How long they need varies with the species, but the adjustment usually takes place in estuaries where the two water types meet and mix. Hence estuaries are extremely important for their survival.
Despite these differences, the goal of osmoregulation remains the same: to maintain an internal environment where cellular functions can proceed optimally. By doing so, organisms can adapt to varying environmental conditions, ensuring survival and overall health.
