'Long lost' population of St. John River striped bass may have been discovered

For more than four decades it was believed native striped bass in the St. John River had been lost forever.

The population crashed over a short period following the opening of the Mactaquac Dam in 1968.

Sporadic searches since then for evidence of "stripers" spawning in the river had brought up nothing.
 
The only fish found were visitors from U.S. rivers or from the Shubenacadie in Nova Scotia.

But a new study by scientists from Canada and the U.S. shows the St. John's native striped bass population has very likely managed to survive.

"It's pretty exciting," said lead author Nathalie LeBlanc of the Canadian Rivers Institute at the University of New Brunswick.

"It would be very exciting if we could some day in the future bring that population up to the numbers that it used to be."

The river's native striped bass were once a major attraction for anglers. A 63-pound striped bass — the all-time Canadian record for striped bass — was captured at Reversing Falls.

The first clues a population of the native fish was hanging on came in a 2008 study that identified not just visiting bass from the U.S. and the Shubenacadie, but also a third group of fish.

The genetics didn't match anything on record.

The fish were tentatively labelled "native" but further research was needed.

That research has just been concluded.

The verdict: There is a unique group of striped bass in the river, and its genetic signature points to a very distinct and long-established population. 

The breakthrough began in 2014 with the discovery of one-year-old stripers in the St. John and Kennebecasis Rivers by the Rivers Institute's Samuel Andrews.  

The fish were captured, clips were taken from the fins, and they were released back into the river.

All the fish dated from the same year, 2013 and are today about 60 centimetres (24 inches) long.

The next step was not so easy.

​LeBlanc, a geneticist and PhD candidate, found there are no known samples from the pre-crash population to compare to.

There are some mounted trophy fish, but LeBlanc learned getting a DNA test from a mounted fish would cost tens of thousands of dollars, while offering only the slightest chance of success.

She nonetheless ground up the new fin clips, extracted DNA, and assembled a panel of several thousand DNA markers to compare the native fish with those from elsewhere, a process of elimination.

The results are conclusive.

"This study firmly establishes that there is also a St. John River striped bass with a unique genetic signature," said Canadian Rivers Institute biologist Scott Pavey of UNB, who oversaw LeBlanc's research.

So where has this native population been hiding all these years?

"The population crash in the St. John River was less than 50 years ago," said LeBlanc.

"Striped bass live about 30 years. So if there were striped bass existing in small numbers in the St. John River, which is very possible because it's a huge river, then theoretically they would only have had to spawn once between 1970 and now in order to keep the population going."

The challenge now is to find ways to ensure this native population survives.

The fish found so far date from just two spawning years. A next step is to determine if there was something unique about water flow timing or volumes through the Mactaquac Dam during those two years.

The area below the Mactaquac Dam had been a traditional spawning ground for striped bass. 

The research team is now recommending steps to protect those St. John River striped bass that spawned in 2013.

Work done in the northeast of the U.S. has shown that allowing anglers to keep only fish that are larger or smaller than the protected population can work.

LeBlanc suggests that could offer a solution here.