Spawning Can Take Its Toll On Wild Brook Trout

This radio-tagge brook trout is preparing to spawn in Socatean Stream. The white radio antenna is visible behind the ventral fin. (Photo courtesy of Bill Hansen

By Tim Obrey, IFW Fisheries Biologist

As my grandfather, the incredible Mr. Henry “Limpet” Obrey used to say: “Never judge a fish until you swim a mile in his fins.”  Well… I might have that a little mixed up, but the point I would like to make is that it’s tough to be a wild brook trout.

Think about it, a good meal is a bunch of worms, it’s always wet out, if you’re lucky, you live to the ripe old age of six, and strange people you’ve never met chase you around all day just to take a selfie with you…or worse <gulp!>. The news doesn’t get any better when it comes to spawning and post-spawning mortality.

Back in 1958, Fisheries Biologist Roger AuClair conducted a tagging study on wild brook trout originating in Moosehead Lake.  Roger constructed a wooden fish weir on Socatean Stream and captured the fish during their spawning migration. Roger’s study was one of the first of its kind in Maine.  Roger found that 65% of the male brook trout in his study died soon after spawning.

We duplicated Roger’s work in 2009 on Socatean Stream.  There is still a good run of wild trout in the stream. We were able to use more modern equipment such as radio telemetry and passive integrated transponder (PIT) tags for our study, but the results were remarkably similar.  We estimated 57-60% of the male brook trout perished as a result of spawning stress in our recent study.

We packed up our toys and moved over to the Roach River in 2010 and 2011 to determine if brook trout mortality rates would be different on a larger river.  In fact, they were quite comparable: 51%-57% on the Roach River.  This also correlated well with a study we conducted on Chamberlain Lake in 2006 which found that 51% of mature male brook trout did not survive the spawning run. The data are pretty consistent.  We can expect 50-65% of wild mature male brook trout to succumb in the fall during after spawning.

Our radio telemetry studies enabled us to locate the dead or dying fish and determine the cause of death.  Most of the tags we recovered were in places that indicated predators play a major role in their demise. Otters, mink, great blue herons, eagles, and ospreys take their toll as the tired and stressed brook trout can no longer elude them.  In Socatean Stream, some of the trout actually entered the stream in August but didn’t spawn until October.  That’s a long time to play hide and seek with foraging furbearers and avian assassins. The actual act of spawning is rigorous as well. It’s not all flirting and buying chocolates.  Male brook trout are constantly chasing and fighting other male trout during the courting process.  There is non-stop action for weeks, but successful spawning is essential to maintain the population.

Weirs such as this one on the Roach River allow water to flow through but are a barrier to fish.

It’s a grim picture but it is worth painting.  We are frequently asked about extending the fishing season on wild brook trout (and salmon) in the Moosehead Lake Region into October and November while they are spawning.  Think of the additional stress of hooking and releasing wild fish during the time of year when they are the most vulnerable.  What happens when an angler hooks and plays a female fish that is ready to deposit her egg?  I know I have handled many gravid fish in my career and even when they are anesthetized, many drop their eggs and milt.  And what about freshly deposited eggs in the gravel as anglers wade up and down the streams and rivers in pursuit of the catch? These issues must be carefully considered for the long-term protection of the resource.

Maine is the last place on the eastern seaboard with significant numbers of intact wild and native brook trout populations.  To address public interest in fall fishing, we extended the fishing season several years ago on all waters where the fishery is maintained entirely through stocking.  Successful reproduction is not a concern in these waters.  The hatchery truck comes every year. These are great places to provide additional fishing opportunities in the fall months.   Maine has done an outstanding job protecting its heritage fish, while providing a diversity of year round fishing opportunities.


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