Study suggests we're losing
quality summer trout habitat|
By BRIAN MEDEL
Hunting / Fishing
A VERY interesting study is underway in Nova Scotia,
delving into the amount of suitable cold-water brook trout
habitat that's available in our lakes during the heat of
And it appears that there's a lot less than there was 25
Acadia University professor Mike Brylinsky is working on
the project. He's the director of the Acadia Centre for
Estuarine Research. This work is being prepared for the
provincial fisheries department.
Brylinsky is looking for lakes with cold bottom water
temperatures for summer trout retreats.
Twenty lakes from all over the province were checked 20 to
25 years ago and the same lakes were re-evaluated in 2001.
The preliminary results?
Almost all of the lakes are worse off than they were in the
late 1970s and early 80s.
Although there was little difference in the water
temperatures at the lower levels of these lakes, the
differences in dissolved oxygen levels were significant.
Almost all of the survey lakes had less oxygen at the
bottom of them in the 2001 summertime studies than they did
two decades before.
Most lakes classified as good back then were reclassified
as poor in 2001.
Only one lake originally classified as poor was found to be
By the way, good cold water trout habitat - in a lake - is
defined as a water temperature of 15 degrees Celsius or less
with dissolved oxygen levels of 50 per cent or more.
Brylinsky says these lake troubles are possibly due to
longer growing seasons (in the actual lakes). Algae will grow
in a lake's productive upper levels where sunlight is most
abundant. When it dies and sinks during an extended growth
season, the oxygen at the lake bottom is depleted and trout
that have gone down to escape the heat are in trouble.
The longer growing seasons could be due to global warming.
The start of a growing season in any lake comes with ice-out,
say those who study such things.
Brylinsky says he wants to see if a trend is developing and
is seeking ice-out and ice-in data from anyone who has been
keeping regular notes on a favourite lake for a few years.
You can contact him through Acadia University's Centre for
Interestingly, algae growth may also be attributed to
shoreline development. Urban sprawl, residential expansions
and even cottage country building projects may all be part of
This is because phosphorous enters the water where people
congregate, whether its from a faulty septic system or lawn
fertilizer or erosion.
There are two kinds of lakes in Nova Scotia.
The first group can be called the brown water lakes. These
stratify, or separate into warm upper and cooler lower layers,
at about three metres down from the surface.
The second, clear water lake group usually separates at
about six metres.
The research results are surprising in that very few of the
lakes selected for study actually have suitable cold water
habitat for trout during the summer.
The research team asks a couple of questions. What has
caused this loss of cold water habitat and is this typical of
all Nova Scotia lakes?
One of the selection criteria used to decide which lakes to
survey was accessibility by road. Roads are also needed for
But a lake that can be reached by road is also susceptible
to shoreline development.
Many of the lakes surveyed have summer cottages or
permanent homes on them.
If development is responsible for the observed changes,
then it underscores the importance of identifying lakes that
currently do contain summertime cold water habitat so we can
act to make sure they're not lost to encroaching human
It's also important to identify and protect cold water
streams that are associated with the lakes, says Brylinsky.
It should be noted that these lakes were tested during
either July or August.
During July some of the lakes surveyed had water
temperatures of less than 20 degrees Celsius with dissolved
oxygen levels at more than 50 per cent. Lakes like these could
have provided limited refuge for brook trout. Because of their
intermediate position they would have fallen somewhere between
poor and good, having some suitable cold water during the
Incidentally, the two lakes during the summer of 2001 that
had the best cold water habitat were French Clearwater Lake in
Yarmouth County and Millet Lake in Lunenburg County.
These two lakes were also the deepest.
It would be premature, based on the results of this study,
says Brylinsky, to conclude that few lakes in Nova Scotia
contain habitat suitable for cold water species.
But there's more to learn and this important study will
Brian Medel is an avid angler and hunter living in Yarmouth
County. His column appears every Thursday.