Salmon smolt falling prey to bass

CBC News - Nova Scotia

Salmon smolt falling prey to bass as they leave Miramichi River
New study shows up to 18 per cent of young salmon get eaten by striped bass

By Paul Withers, CBC News Posted: Jan 19, 2018 5:00 AM AT

 A newly published three-year study says large numbers of Atlantic salmon smolt are being eaten by striped bass as the smolts leave New Brunswick's Miramichi River and enter the Gulf of St. Lawrence for open ocean.

The report, published this week in the Canadian Journal of Fisheries and Aquatic Sciences, estimates striped bass are eating two to 18 per cent of salmon smolts. Smolts are young salmon that are ready to go to sea.

"I would say it's quite significant," said Jason Daniels, a biologist with the Atlantic Salmon Federation who co-authored the study.

The highest levels of predation were in the northwest branch of the Miramichi, where striped bass go to spawn. There, smolt predation ranged from seven to 18 per cent.

The estimated consumption rate comes as the population of striped bass in the Gulf of St. Lawrence explodes. Anglers reported seeing them from Cape Breton to Labrador, according to the federation.

Smolt survival down twofold since 2000s

In 2016 there were an estimated 318,000 striped bass in the Gulf, up from 5,000 in the mid-1990s.

"There's 300,000-plus fish moving into one 10-kilometre section of river; that's a lot of fish to pack in there," said Daniels.

The report says salmon smolt survival in the Miramichi estuary is estimated to have fallen twofold since the mid-2000s.

Daniels said it's the first study to quantify the degree of predation of smolts in the Miramichi by striped bass.

Between 2013 and 2016, the Atlantic Salmon Federation inserted miniature acoustic transmitters into 514 Atlantic salmon smolts in the Miramichi River. Dozens of receivers were placed in the river and estuary.

At the same time, staff from the Department of Fisheries and Oceans and the province of Quebec tagged 110 striped bass.

Transmitters differentiate between species

Receivers confirmed both species were in the same place at the same time, with unfortunate results for the salmon smolts.

"The more time they are hanging out together, the more likely predation is to occur," said Daniels.

Most importantly, the transmitters were specially coded to differentiate each species, allowing scientists to understand how each moved in the water.

"If we saw any smolt tags behaving more like striped bass, then we interpreted that as a smolt had been predated," said Daniels.

The study indicates large numbers of smolts are being taken by stripers, but notes there are other threats in the Miramichi estuary, including the physiological stress associated with migration, and human causes like pollution.

The impact on adult salmon who eventually return to the Miramichi is not directly correlated. Daniels said the bass could be killing the weak who were doomed to die anyway.

"That said, 20 per cent of a population is certainly not helping anything."