According to the PA Game Commission.

After comparing harvest data from the 80's to those of recent years the pgc
has found that the reproductive rates have not changed.

What has changed is that fewer juvenile muskrats are surviving to become
reproductively viable adults.

Muskrats are currently being captured and equipped with radio transmitters
so they can try to figure out why the juvenile rats are not surviving.

What could be killing off most of / mainly juveniles?

It will be interesting to see what they come up with.


This is from the 2018 PGC annual report.
(I think they started this in 2017 so maybe they will have some results in the near future.)

Understanding Changes in Muskrat Populations
Muskrat populations have been declining throughout the Northeastern states for decades and
Pennsylvania is leading the charge with recent initiatives to determine the cause.
In Pennsylvania, trappers harvested 300,000 to 450,000 muskrats annually throughout the
1970s and early 1980s. During the 2017-18 trapping season, trappers harvested just under 25,000
muskrats, the lowest harvest ever produced in the Commonwealth. The Game Commission has
initiated an integrated approach to investigate these trends.
Comparisons of muskrat harvest data from the 1980s to those from recent years suggest that
reproductive rates have not changed, but that fewer juvenile muskrats are surviving to become
reproductively viable adults. Muskrats are currently being captured and equipped with radio
transmitters to assess movements, survival rates, and cause-specific mortality factors. The Game
Commission has increased disease surveillance and initiated toxicology and contaminant assessments
to better understand potential environmental impacts on muskrat populations. Pennsylvania
trappers will be providing biological samples this fall and winter to bolster these investigations.
The agency is replicating trapper surveys that were conducted in the 1980s to assess changes in
trappers’ perceptions of muskrat population trends as well as potential causes for declines. These
surveys will allow a comparison of muskrat harvests from various wetland habitat types in the
1980s to those from recent seasons and could provide valuable insights for the management of this
wetland furbearer.

GREAT BLUE HERONS - This is the reason for the muskrat decline in my area. I have spent time watching the rat dens as the young start to come out and the herons clean the litters up within days. It doesn't take a college education and lots of grant money to figure these things out ,but I'm sure this is what they will determine in their study.

This will be interesting.

This will definitely be interesting, Thanks for posting this.

Eaven if they find hard evidence that it is birds of prey they will not release those findings . They will deny that it can be predators . They will blame it on fracking or some other politically correct boogyman . Studies all across the country absolutely ignore that the reduction in common prey species may be from predators . They realy dont want to admit birds of prey have any impact on anything .

Let's see, Roundup sprayed everywhere
Deicing stuff they spray on the roads
Otter population growing
Mink population growing
And of course, all the birds.
In 1980 we had a harvest of 800,000
2010 we harvested 80,000
I will not hold my breath waiting for their report

New York had the same studies around 10 years ago.

I submitted around 200 to 300 carcasses of female rats
over the course of 3 years.

Findings indicated an average of 13 young per year
per capita (determined via placental scar count).

Initial production of young was NOT declining,
but recruitment of yoy to adult size age was
NOT occurring.

To my knowledge,
we were never informed what was definitively
causing the mortality of yoy muskrat.

Certainly, no one cause was determined.

w

lack of oxygen to the brain gets em every time.

The river I'm on has Herons, Otter and Eagles, things you didn't see when the Muskrat population was good. Also a lot more Mink than years past.

The Bass population has also dropped to the point it's catch and release now. I don't know the answer but steps need to be taken.

What river Hipster ?

i live on one of the headwaters of the Allegany--the Oswayo--and the eagles are crazy here.

It's hawks and owls. Back In the day we could legally shoot them and DDT took It's toll.

The biggest factor Is lack of habitat. We use to have 100s of small marshes around here know they are gone.

Turtles, floods, mink, coyotes, fox, coons, Hawks. Possibly in that order.

Juniata river.

I also travel 25 miles and trap/fish the Susquehanna river.

Are they still using the water is too clean theory?