Friday, February 3rd, 2023
Friday, February 3rd, 2023

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VHS threatens the fish of Lake Superior

By Tim Spielman

Associate Editor

Duluth, Minn. – Last summer, the threat of a spreading fish
virus forced a federal agency to issue a crackdown on movement of
some fish species in several Great Lakes states. The ban, modified
last November, affected not only private aquaculturists, but also
some state fish-stocking programs.

Recently, the Izaak Walton League of Minnesota hosted an
informational meeting meant to illuminate the citizenry, and
perhaps prevent the spread of viral hemorrhagic septicemia (VHS) to
Lake Superior. To this point, fish die-offs from the disease only
have been reported in the eastern Great Lakes basins.

But several factors make the threat of VHS in Lake Superior
great, according to a panel of speakers at the gathering. Even more
ominous is that the virus is unlike any past ‘exotic’ menace to the
largest Great Lake.

‘Something like this has never happened in the Great Lakes
before – a single pathogen that affects as many species as it does
at a single time,’ said Sue Marcquenski, fish health specialist for
the Wisconsin DNR. Scientists studying dead fish in other Great
Lakes have concluded that the strain of VHS has remained
consistent, she said, which means ‘this has been a single fish kill
persisting over time.’

What could happen to Lake Superior fish species is purely
conjecture right now, experts say. But, they agree, the potential
could be devastating, affecting the food web, predator/prey
relationships, and other lake dynamics. For example, Marcquenski
said if it had a profound effect on a certain native fish species,
that could make it easier for another, non-native species to become
established.

Background

According to the USDA’s Animal Plant and Health Inspection
Service (APHIS), the agency responsible for wild fish health, VHS
‘is an extremely serious pathogen of fresh and saltwater fish, and
is causing an emerging disease in the Great Lakes region of the
United States and Canada Š Due to its high mortality and severe
economic consequences, VHS is classified as a reportable disease by
the World Organization for Animal Health.’

APHIS says the outbreak in the Great Lakes appears to be a new
strain of the virus – different from that which affected fish in
Europe.

The new strain has been responsible for die-offs of muskellunge,
smallmouth bass, northern pike, freshwater drum, gizzard shad,
yellow perch, black crappie, bluegill, rock bass, white bass,
redhorse sucker, bluntnose sucker, round goby, and walleyes,
according to APHIS.

The Michigan DNR has provided information regarding VHS on its
website. That state has been monitoring VHS in its Great Lakes
waters for several years.

According to the Michigan DNR, ‘The earliest confirmed report
(of VHS) is 2003 in a Great Lakes muskellunge from Lake St. Clair
(near Detroit, and between lakes Huron and Erie) so it is likely to
have been introduced (to Michigan waters) in 2002 or 2003.

‘The virus also was confirmed from spring 2005 freshwater drum
samples from Lake Ontario (Bay of Quinte) and from a lake whitefish
from Lake Huron (Cheboygan) from a fall 2005 sample.’

All told, VHS has affected Lake Huron, the St. Clair River, Lake
St. Clair, Lake Erie, the Niagara River, Lake Ontario, and the St.
Lawrence River.

How it arrived

How VHS got to the Great Lakes is open to debate, as is how long
it’s been present, according to APHIS. But groups attempting to
ward off entry to Lake Superior are focusing their efforts on the
ballast water of ships entering Duluth/Superior harbor. Ballast
water – water kept in holds to stabilize cargo-free ships –
frequently has been blamed for bringing foreign species into the
Great Lakes.

Marcquenski said the U.S. Coast Guard and APHIS have begun anew
talks regarding ballast water regulations.

A news release from the Coast Guard says that agency will work
with APHIS to develop ‘new federal regulations on ballast
water-discharge standards.’

Other federal agencies are contributing their expertise to a
rule-making process.

‘The rule-making is intended to spur vessels to use a variety of
ballast water treatment technologies to prevent the introduction
and spread of aquatic nonindigenous species, such as VHS,’ the
press release states.

Current regulations primarily require vessels to exchange their
ballast water with mid-ocean water. However, the effectiveness of
this practice varies and not all vessels are able to conduct the
exchange.

As the rule-making process proceeds, public comment will be
sought, the Coast Guard release states.

Gary Glass, of the Izaak Walton League, said sterilization of
vessels that enter the Duluth/Superior harbor should be standard
procedure.

‘There’s no reason (disinfectant) can’t be used,’ he said. ‘It’s
a viable solution, and it could be in place by the beginning of the
next shipping season.’

Glass said citizens should demand accountability – from the
shipping industry to recreation boaters, to the government agencies
that enforces Great Lakes rules.

‘The present fishery we have would be affected in some way (by
VHS),’ he said. ‘If it’s a disease that kills a lot of fish, people
tend to notice.’

Lake Superior concerns

While state officials hope to ward off the spread of VHS to Lake
Superior, they acknowledge that conditions are ripe for the disease
to spread to the lake, and perhaps flourish there.

While other non-native invaders have found the lake’s cool
nature a deterrent, VHS is fond of cold water. ‘(Fish) mortality is
greatest between 37 and 54 degrees Fahrenheit,’ according to APHIS.
And further, Duluth/Superior is an oft-visited port.

As far as reaching Lake Superior, fish movement is one
possibility, but ‘If fish continue to be the key movement vector,
the virus will likely take a long time to get established in Lake
Superior, as fish movement through the Soo Locks is limited,’
according to the Michigan DNR.

‘We know fish could bring it Š but that would be slower,’
Marcquenski said.

‘The fastest way for it to move, and cause an outbreak, is for a
vessel to take on ballast water amid a fish kill (in infected
waters),’ she said. Concentrated levels of VHS taken on by a ship
could be delivered to Lake Superior within days, she said.

The Michigan DNR states: ‘(The) situation could rapidly change
if the key vector is ballast water exchange. Duluth (Superior)
harbor in western Lake Superior has the second highest ballast
exchange rate in the Great Lakes, and the Chicago area also has a
very high ballast exchange rate. The virus could quickly be spread
by this vector if the virus can remain alive for sufficient time to
be transported by this method.’

Minnesota DNR fisheries supervisor Don Schreiner, of Duluth,
calls the Mississippi River entry (via Chicago), a ‘backdoor’
introduction of the disease to areas of Minnesota and
Wisconsin.

Not only are various fish species susceptible to the disease,
other circumstances make them even more vulnerable, such as when
they experience other stresses, such as spawning or if water
quality is poor, Marcquenski said. She said the state of Wisconsin
is looking into its own set of rules that would limit movement of
the virus. It could affect bait dealers, as well as those who
collect and ship fish species from the Mississippi River to
outstate ethnic markets.

In Superior, all fish would be susceptible to VHS, Schreiner
said.

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