Open the lood­gates

Flood pre­ven­tion on the Fraser could be hurt­ing sal­mon, study inds

Metro Canada (Vancouver) - - FRONT PAGE - Jen St. De­nis

As re­searchers con­tinue to study why sal­mon pop­u­la­tions on the Fraser River have fallen to his­toric lows, two new stud­ies show that flood­gates on the river could be re­duc­ing habi­tat for fish — and there is lit­tle over­sight when it comes to check­ing the eco­log­i­cal im­pact of that in­fra­struc­ture.

“Past re­search in our lab had found that these flood­gates were as­so­ci­ated with low oxy­gen quan­tity in the creeks flow­ing into the Fraser through the flood­gates,” said Re­becca Seifert, the lead au­thor of a study by Si­mon Fraser Univer­sity.

“They were see­ing a dead zone where it was hard for sen­si­tive fish like trout and sal­mon to sur­vive.”

The flood­gates, many of which were in­stalled decades ago, re­duce the flow of wa­ter, mean­ing more al­gae grows around the gates and lowers the oxy­gen level.

Re­searchers have also found more in­va­sive species and fewer na­tive species near flood­gates — and there are over 300 gates be­tween Delta and Hope.

When the gates are closed, ju­ve­nile sal­mon can’t get out of the creeks where they were born to pass down the Fraser River and out to the open ocean, an im­por­tant part of the sal­mon life cy­cle.

Seifert wanted to know just how of­ten the flood­gates were closed, so she in­stalled timelapse cam­eras.

She found that many of the gates, which close when high wa­ter pres­sure pushes them closed, are shut al­most all the time dur­ing the high­wa­ter spring sea­son. That’s also when ju­ve­nile sea­son are try­ing to mi­grate to the Fraser.



A bald ea­gle eats a chi­nook sal­mon along the Har­ri­son River.

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