My
rod twitched slightly, and then I could feel the fish gently pick up the
bait. I waited for the fish to take the bait, and then set the hook. Some
minor headshakes were felt and then slack line. Here it comes, it’s going to
jump. The huge twelve and a half foot fish leaped straight out of the water
all the way to its dorsal fin and rolled over like a humpback whale. The
waves from the landing lapped at the side of the boat. After a sweaty,
see-saw battle, we surfed the great fish to shore and pulled out the hook.
Now it was
time to work. Three lengths and one girth measurement, a DNA sample, one
pectoral fin ray clip for aging, one floy tag and a single PIT tag later,
and the fish was ready for surgery. All we had to do was roll the fish over,
which seems to have a calming effect for sturgeon. As they lay upside down,
even the large fish remain docile and still. For Alexis, this was going to
be her biggest fish surgery ever, and probably the largest ever done on a
British Columbia sturgeon. The sturgeon’s belly was like working on a big
white operating table. It looked like it had just swallowed two 45 gallon
drums! The quick surgery reveals this fish to be a pre-spawning female,
holding possibly hundreds of thousands and maybe even a million or more
eggs! Alexis studies the ovaries, and, judging by their size and color,
determines that it won’t spawn right away, but probably in two years. This
fish is not in any rush to spawn as it has been slowly developing this brood
of eggs for 6 or 8 years already! Being in the neighborhood of a centurion
in age, and probably even older, this upcoming spawning event may be her
fifth time. If all goes right during that time, she could very well live to
do it again.
Lets fast
track to 1998. It’s July and it is scorching hot outside. We’ve been
tracking radio-tagged, pre-spawning male sturgeon all over the Fraser,
searching for their elusive spawning grounds., We haven’t had much luck, as
the fish are scattered everywhere, leaving us no clues to pinpoint the
search. For the last month we had been placing substrate mats and D-ring
collection nets throughout the middle and upper river in the areas where
these tagged fish were located and holding, and in any places that looked
similar to these areas even if no tagged fish were located there. Substrate
mats are 50 x 100 cm angle iron frames with furnace filter sides. The mat is
designed to be placed on the river bottom just below suspected spawning
areas and is usually done in pairs. The mat’s job is to collect any sturgeon
eggs rolling downriver before they fall into any one of the little cracks
(known as interstitial spaces) between the boulders and cobbles where the
eggs will incubate. D-rings are d-shaped frames with 3 meter long, tapered,
fine mesh netting with a small collection cup on the end. It looks somewhat
like a small trawl net. The objective here is to anchor below spawning
areas, hang the net out the back of the boat with 5-8 meters of rope and try
to catch hatching sturgeon larvae that are drifting downriver. It may sound
like searching for a needle in a haystack. And in reality, that’s because it
is. However, we’ve learned a thing or two about working the gear and the
river to increase the odds in our favour. And, after some pretty decent
successes here and there, we were due to find the "motherlode".
Pulling
mats is not an easy job. In fact, it can be downright dangerous due to the
amount of debris on the river’s bottom that snags our gear, and the sheer
speed of the current where mats are placed. There is no room for error and
no time for letting your guard down, even for a second. A simple oversight
could mean overboard and, underwater! After pulling a pair of mats out of a
real jungle of wood, where the water was only 15 feet deep and really
moving, and laying them on the deck of the boat, the usual inspection took
place. Our eyes scoured both sides of the frame, looking for something dark
grey or black with a diameter of less than 4 mm (smaller than a green pea).
The egg could look like a lot of the debris that gets caught in the mat. The
mat surface is covered with weeds, insects, the odd eel and loads of fine
gravel and sand. When will we find one, and will we ever see it in all this
gravel? There! There’s one! Up high in the corner between the frame and the
filter, lies "black gold". One single, solitary sturgeon egg. The first
sturgeon egg ever found on the Fraser river. And then Dave hollers he has
one on his mat too! Two needles found in this huge haystack!
The
reproductive cycle of the Fraser’s white sturgeon is not fully known. The
following data will make you appreciate the current regulations on the white
sturgeon. Female sturgeon spawn for the first time when they are
approximately 11-34 years old and males spawn first between 11-22 years of
age (Semakula and Larkin 1968). Subsequent spawning will occur every 4-9
years! Just think back not too long ago when it was legal to keep a fish up
to 2 meters in length. That fish would’ve been a prime reproducing fish as
old as 30 years. The sturgeon population, would suffer quickly as a result
since it appears that sturgeon are likely to stay in their areas, acting
somewhat like "homebodies". If you were to keep that 30 year old sturgeon,
it would take 30 years to replace that same sized fish in that area! And
anglers were keeping these fish at a rate of one per day! It wasn’t until
the mysterious deaths of large adult sturgeon in 1993 and 1994 that sturgeon
regulations were changed to catch and release only.
The actual
spawning event of the white sturgeon in the Fraser is also unknown. There
are suggestions that more than one male will spawn with one female. I think
it would be pretty difficult to prove this in the Fraser given the river’s
turbidity, but some simple observations from working with sturgeon on the
river play into this train of thought. For example, while spending 4 years
of tagging on the river, only one ripe pre-spawning female has been found.
We have a couple of female fish that will spawn in a few years or more, and
even some that had spawned just a month or two before surgery. However, only
one technical pre-spawning female that will spawn the following spring has
been captured and identified. However, the number of pre spawning males, and
males captured in general, is substantially higher. In fact, it seemed that
of the first 20 fish checked during the tagging phase, 19 were male; a very
high "buck to doe ratio". Many males to one female during a spawning event
would provide extensive genetic mixing, keeping the population very healthy,
and could assist in ensuring a higher percentage of eggs being fertilized.
Finding such a lop-sided ratio seems to imply that either the sturgeon
population is very heavily male skewed, that the females are somewhere else
in the river system, or, that they just do not feed as aggressively as the
males. Yet, one would think that to nurture a million eggs, a fish would
have to be feeding excessively!
When spring
freshet arrives, it sends a signal to spawning fish that its time to move to
that magical location. Documentation indicates this area to be a deep, fast
moving reach of river that would obviously have large boulders and cobbles
as well as bedrock due to the scouring effect of such high velocities. This
idea has been proven in the Columbia river, where sturgeon spawning has been
observed in the scoured tailraces of hydro-electric dams. This idea was
somewhat accepted as what the sturgeon would prefer in the Fraser. However,
as it turns out, this is an incorrect assumption as the Fraser is not a
dammed river like the Columbia. The Fraser has a natural freshet and is not
held back by dams. The Fraser experiences natural flows that creates the
development of gravel bars, side-channels, backwaters and the natural
composition of a normal river substrate (bottom). The unaltered flows allow
subsequent seasonal temperature fluctuations, and accounts for the turbidity
changes. There are many different factors in the Fraser that can cause
different spawning behavior and spawning habitat preferences than that of
the Columbia.
After the
freshet peaks and starts to fall, and the water temperatures reach 10-17
degrees Celsius (PSMFC 1992), the sturgeon are thought to begin spawning.
The optimum temperature is thought to be around 15 degrees C. This would
occur sometime in late June through July on the lower Fraser river. The
female, after finding a suitable location, and somehow finding a mate, or
perhaps they find her, will release her eggs, possibly in stages, while a
male or more than one male, will release his milt. River current will allow
sufficient mixing of the eggs and milt for fertilization to occur. The
fertilized egg will fall to the river bottom, and because of the adhesive
nature of the egg’s outer membrane created by fertilization, will cling to
the river substrate in one of the many small pockets between the boulders
and cobbles. The egg will then develop, or incubate. The egg’s hatching time
depends upon the temperature of the water. Sturgeon eggs will hatch in 100
Accumulated Thermal Units (ATU). One ATU is equivalent to 1 degree Celsius
per 24 hours. Therefore, if the river is 15 degrees C., a sturgeon egg will
hatch in about 6.5 days, give or take. This may sound insignificant until
you compare sturgeon to another fish; steelhead for example. In comparison,
a steelhead egg will require 320 ATU from fertilization to alevin, a similar
stage as that of the sturgeon larvae. Salmon are very similar to steelhead
incubation times as well. The grey colored 10 mm. long sturgeon larvae will
hatch out, complete with a yolk sac, but with no mouth, eyes and virtually
no fins. It will drift helplessly with the strong river current, swimming
much like a chironomid, wiggling up and falling down in the water column
until it comes to rest in a slow, quiet backwater. The larvae will soon
become photophobic, that is, it will not like strong light, and will bury
itself in the river substrate or the weedy, grassy littoral zone. From
there, the larvae will survive by feeding off its yolk sac. It will fully
develop its mouth, eyes, fins and scutes (that sharp armor plate sturgeon
are famous for), and within 3 weeks start swimming on its own. It is at this
time that it begins searching out and feeding on small insects found in the
weedy backwater. At this critical young stage, one would think that this is
their most vulnerable time to predation by sculpins and squawfish.
Now, armed
with this little bit of information, we are back to the hunt for the great
spawning grounds. After finding the eggs on the mats, we could concentrate
on working the same area on the day we thought the eggs were expected to
hatch. Sure enough, with a little math, and as usual, lots of luck, we hit
the jackpot. We collected nearly two dozen larvae in our d-rings that
afternoon. We would work the d-rings for an hour and find a larvae or two in
nearly every set.
Some of
these larvae were alive! It was incomprehensible when I thought back to
catching by rod and reel the giant sturgeon, the fish that has been around
before WW I, the man on the moon and the world wide web. And now, here is
this little sturgeon, looking like a tadpole, wiggling up to the surface and
helplessly falling down to the bottom. Was I looking at the next 12 foot
sturgeon? Where will we be when this fish is a giant, and will we have
preserved our surroundings to give this incredible fish that very
opportunity to become a legendary fish? It was an awe-inspiring feeling to
have seen the incredibly opposing life stages of a truly unique British
Columbian fish.
Work in
July and August of 1999 has revealed even more secrets about the white
sturgeon and their mysterious spawning habits. Part II of the story will be
available soon! ML.
