Similar to the situation in the Columbia River basin,
sockeye salmon heading to Canada’s Fraser River to spawn might not make it at
all due to lack of snowmelt combined with record-high temperatures.
(See CBB, July 31, 2015, “Warm Water Hitting Returning
Sockeye Hard: NOAA Says Maybe 80 Percent Mortality For Upper Columbia” http://www.cbbulletin.com/434644.aspx)
University of British Columbia biologist Tony Farrell this
week explains what Fraser River sockeye are facing under such conditions:
What are ocean and
river temperatures like for salmon at the moment?
It’s been particularly warm out in the Pacific Ocean this
year, which means there’s a lot of hungry mackerel and tuna waiting to eat baby
salmon as they migrate from the Fraser River to the Pacific in search of food.
The mackerel and the tunas like the water a little warmer than the salmonids,
so when warmer water moves north, as it does periodically, they follow. But
because the Fraser River can’t move, it’s a bit like running the gauntlet for
the salmon smolts.
The Fraser River is at historically low water levels and
high temperatures for this time of the year. With very little snow pack across
the province this year, the normal snowmelt has not happened. We’ve also had
incredibly hot and dry conditions.
It’s low water and it’s hot water. As of July, the level of
the Fraser River was at a 25-year minimum, and reliable records don’t go back
beyond 25 years. The temperature has never reached 20.5 degrees Celsius this
early in the year. On average, it would be four degrees cooler.
What effect do these
factors have on salmon migration?
If you don’t have any water, you can’t swim. Small streams
will be drying up, but we may not be into those sorts of problems for most of
the salmon spawning habitats. Instead, the worry is that it may be too hot for
them to swim upstream to spawn.
Sockeye salmon stocks appear to have tailored their swimming
ability to swim up the Fraser River to a particular summer temperature and
water flow. There’s a temperature at which salmon swim best. If the Fraser
River is five to seven degrees Celsius above that particular temperature, they
will not be able to get enough oxygen to their muscles to even swim.
Diseases also start taking over when the temperature is too
hot. Normally, fish can tolerate a few scratches and cuts on their skin from
predators attacking them or fishermen’s nets. But at high temperatures, fungus
and bacteria proliferate. If fungus clogs the gills, the fish cannot breathe
properly, making matters even worse.
Summer temperature in the Fraser River is so important, so
it’s closely monitored. The Department of Fisheries and Oceans’ Environmental
Watch Program warns that at 18 degrees Celsius, sockeye salmon have a decreased
swimming performance. At 19 degrees they show early signs of stress and slowed
migration. At 20 degrees they have high pre-spawn mortality and disease. And at
21 degrees it’s severe stress and early mortality. Right now, the temperature
is sitting at around 20.5.
Is there a chance the
sockeye won’t migrate at all?
How many sockeye turn up at the river is determined by how
many sockeye salmon went out four years earlier and what their ocean survival
was. The tuna and mackerel are likely affecting survival rates. Whether they
make it up the Fraser River involves a series of separate questions:
-- Have the salmon managed to store enough energy? Sockeye
salmon stock stop feeding weeks before they reach the river and then they
migrate up the river on an empty stomach gradually running down their “gas
tank” of fat stores.
-- Is the temperature right? I have heard that sockeye
salmon are holding in the cooler Alberni Inlet on Vancouver Island because the
temperature of Stamp Falls and Sproat River are in excess of 22 degrees
Celsius. Salmon may be waiting for the temperature to cool down, but they
cannot wait indefinitely, otherwise their “gas tank” will become too low for
Pacific salmon, including sockeye, spawn only once, so a
successful river migration is critical. Typically, a salmon that makes it back
to the river does a very good job of getting to the spawning area unless it’s
captured or the conditions are bad. This year, it looks like the river
temperature conditions are particularly bad for sockeye salmon. Right now the
DFO is talking about the possibility of closing fisheries down to ensure that
at least some salmon make it up to spawn.
Is there any hope on
I think the good news is that nature always has surprises for
us. We second-guess nature and very often we’re wrong. So let’s hope all the
dire predictions are only partially wrong. What we do know is that some stocks
of sockeye salmon tolerate higher temperatures than others. Will these stocks
take over if other stocks fail? We don’t know. But if, as we suspect, there’s a
potential for adaptation within the species, a key question is whether climate
change is happening too fast for adaptational processes to take place. We don’t
know the answer to that either, but UBC scientists are working on it.