Why do gull nests get flooded on the Yukon River in Whitehorse at this time of year?

Every year around this time, people notice a few unfortunate Mew Gull nests getting threatened by rising water in the Yukon River in downtown Whitehorse.

Aerial view of the Shipyards Park/Quartz Road area on 9 May 2019. Mew Gulls (20 pairs or so) prefer to nest on the grassy islands adjacent to Quartz Road in the centre right of the photo. Large flocks of Herring Gulls are often seen resting on the gravel bar on the extreme right but few if any nest here — they prefer to nest on the rocks immediately below the Whitehorse Rapids Dam. (photo Jim Hawkings)

Typically these at-risk nests are located on very low and often small gravel islands, for example in the Quartz Road/Shipyards Park area.  I just got an email from a concerned resident who noticed this very thing (see photos). Why do these gull nests get flooded?  Is Yukon Energy responsible for this?

This Mew Gull nest is about to be flooded by the rising water. Mew Gulls nest on islands to be safe from terrestrial predators, but sometimes they make a poor choice by nesting too close to the low water level. (photo Lysane Busque)
The Yukon River adjacent to Quartz Road in the vicinity of Walmart 10 June, 2020. The small dot in the water is a Mew Gull nest about to be submerged by rising water. (photo Lysane Busque)

Well, as it happens, the rising water at this time of year is a natural phenomenon. Natural runoff from snow melt causes this rising water. Yukon Energy operates water control structures (dams) in Whitehorse and at Marsh Lake, but from May through July they just let the River flow without any restriction.  They do regulate the flow of water beginning in August and throughout the winter months to make optimal use of all the storage capacity they are allowed to use upstream of the Marsh Lake dam on Marsh, Tagish, and Bennett Lakes.

Water levels in the Yukon River at Whitehorse, December 2018 to June 11, 2020. Water levels reach a natural minimum each year in May and then begin to rise as the spring runoff hits. Click on the graph to see a larger version. (Real-time hydrometric data from Environment and Climate Change Canada)

If you look at the chart above you will see that the water level on the river in Whitehorse is at a minimum in May, after which it rises rapidly through June, July, and into August due to snow melt and glacial runoff.  At Marsh Lake, which is located upstream of both the Whitehorse Rapids and Marsh Lake dams, the annual minimum water level is also in May and rises in much the same fashion during June and July (see chart below).

Water levels at Marsh Lake, December 2018 to June 11, 2020. Water levels reach a natural minimum each year in May, just as they do in the Yukon River below the Whitehorse Rapids Dam. Click on the graph to see a larger version. (Real-time hydrometric data from Environment and Climate Change Canada)

The differences between these two locations show up during August though April, when Yukon Energy is manipulating flows through both dams to provide electricity generation when it is needed most — during the cold months of winter.

Mew Gulls begin nesting in May when water is at a yearly low pretty much everywhere in Yukon.  They nest on the ground, so they are smart enough to choose islands in order to prevent terrestrial predators such as foxes, coyotes, and the like from eating their eggs and young.  Successful nests are the ones that are placed high enough on these islands to survive the rising water until the eggs hatch.  Once hatched, young gulls are very soon able to swim and can safely leave the nest and move to higher ground where their parents continue to look after and feed them.  Some gulls, perhaps the younger, less experienced ones, gamble by nesting very close to the low water.  In some years this might work – they are safe from predators and win the race against the rising water; in others they get flooded.  Maybe it is a mistake they only make once — we don’t really know.

Should we rescue these nests?  We probably could scoop up some of these nests and place them on the adjacent islands, but would the parents accept this or simply abandon the nests?  Would other gulls nesting nearby take offence and attack the newcomers?

In fact this type of thing (nests getting flooded) happens all the time in nature….birds take risks.  If they are lucky they will live to learn from them.  As long as we are not causing this problem, I don’t really see a reason to intervene in the few instances that are right in front of our noses.  What do you think?