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Fish Facts Friday - paper on alewife die offs from cold shock


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Suggests the shock from warm to cold changes ion concentrations leading to tremors and loss of equilibrium.

 

These papers and the news articles talk about upwellings as temperature shocks....but swen it was calm and alewife were dying it made me wonder if cold shock also happen when prey avoid surface predators and disturbance as in the picture (from GreatLaker).

 

 

1127959014_DivingAlewife.thumb.jpeg.85d3a502e94f58c92de2145362840e8d.jpeg

Stanley and Colby - 1971 - Effects of Temperature on Electrolyte Balance and .pdf

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I would add this year there was increased competition on the plankton community from the smelt rebound. Probably a combination of factors at play. Some of the anecdotal thoughts running through my head.....


1).  Less kings stocked

2).  More Smelt competition?

3). Another invasive in the plankton community?  I noticed a lot more orange fillets in the past few years ( blood red invasive shrimp effect?)

4). Mild winters but slow to warm up springs

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Interesting paper.  However doesn't explain why the temperature change.  Here's my take on it (from many yrs of fishing Big-O around Rochester.) 

 

Big-O in the Central area is very dynamic.  We all know in late winter to early spring the entire lake is basically 40F - top to bottom. After a while a Thermal Bar sets up & moves off-shore.  (Temp on inside may be 50F and outside may be 39F and only lasts a week or 2.)  We also know that much later in the summer a Thermocline sets up where surface temp may be 65F but a fairly consistent band of 54F water can be found at a certain depth. (We all love to find where 54F hits the bottom.) 

 

However, there's a transition period, typically in mid/late May to mid/late June.  This is when the charters all head off-shore for their fishing.  i.e. 250 FOW plus. Fishing for us recreational fishermen becomes real tough.  Thank Heavens for graduations, little league, Father's day, weddings...(well maybe not weddings)

 

Anyways,  Big-O is very dynamic, and I don't mean just in terms of the changing winds and cloud cover. I'm talking currents.  Some days on a S-N troll, your GPS says 2.5 mph but down speed is 3.7.  15 minutes later they match at 2.5. Then it changes again. Other days I've seen the same thing on an E-W troll. There's generally an easterly current along the south shore but that's not always true.   (Niagara is obviously different than Rochester)

 

I generally troll S-N and a number of years ago I noticed something interesting during Transition on my down temperature probe. Namely, during this "Transition" period, there are drastic temperature changes at depth.  Not smooth at all.  (And yes, I have had the unit checked.) 

 

For example, going N at 2.5 GPS with surface at 60F and probe down 30 feet, down temp reads 60F.  Then a couple minutes later 45F, couple more minutes 58, then 40.  Kind of like the unit goes whacky. Then all of a sudden the temp reading goes steady as I continue north bound and it stays steady. The 1st time this happened, I changed battery, cable, antenna & rewired connections.  Couple days later when I got back out, same thing happened so I pulled the entire unit & sent back to factory.  They returned it saying the unit was fine. 

 

So here's my theory:  During Transition, there's a band of water depths where the temperature is very unstable.  Some years it may be from 70 FOW to 110 FOW, others, like this year it may be 50 to 180FOW.  The lake does not mix or stratify evenly due to currents and heating. Ever notice those perfectly calm surface areas adjacent to a streak where there are some small waves?  I guarantee there's a temperature difference between the two areas. Ever notice, some guys love to fish after a strong south wind - they say the warm inshore water gets blown out to the deep water & helps settle thing down.  Also, ever notice that some guys hate a strong NE wind?  (That really messes with water temps.) 

 

Anyways, this is what I've observed graphically over the years. (I picked temps & FOW just to illustrate irregularity)  the first is a profile of the Thermocline.  Second is the Transition Period.

 

Untitled2.thumb.jpg.87b7c42b8a7e89bc83fde4a289192993.jpg

 

 

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Back to the Alewife:  These irregular temperature changes are below the surface and they appear to be in dynamic motion as the lake mixes and tries to setup due to the various currents. This is the Transition Period.  The cold spot at 50FOW today may be at 30 FOW tomorrow or in a couple hours.  Alewife are not great swimmers and could very easily get caught in rushes of cold water. Alewife spawning just happens to coincide with the Transition Period.  Remember, this is all happening well below the surface.  My advice is to keep going North when you encounter these temperature conditions. (Just like the charter guys who found out that in June, you have to go deep.)    

 

 

 

Luck to all,

Tom B.

(LongLine)
 

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Lakes Erie and Ontario are rivers with strong currents relative to surface winds. At Buffalo the lake surface will rise to plus nine foot but at Toledo ships will anchor off shore due to shallow conditions in the harbor. That is a tremendous volume of water moving distances of hundreds of miles. Offshore winds on the south shore will blow warm surface waters to Ontario and cold waters will upwell near the south shore. Fishing changes with water temperature changes. Surface winds make the lakes like rivers with current and water temperature changes.


Sent from my iPhone using Lake Ontario United

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One of the things that is hard to factor in is that In Lake O especially the currents are not unidirectional they go all over the place and there are many cross currents. Very different than most river current.
 
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Scott - as long as you have them installed correctly - trust your electronics.

 

Just some thoughts:

 

The main driver of river current is the elevation change between upstream & down stream plus how much water is draining into the river.  Also the water in the center is generally moving much faster than along the shore. (however it may be more turbulent along the shore)

 

The main driver is of Big-O mixing current has to be the wind, which goes all over the place, even though we live in the "Prevailing Westerlies".  Check the wind maps. I've seen NW winds at Olcott, and South wind at the Genny at the same time.  I've also seen strong SW winds produce 6 ft white caps off the Oak yet the Genny area be calm due to the Braddocks area acting like a topographical wind barrier.  (i.e. The Genny is in a cove) The degree of mixing has to be different.  (Why do fishermen travel west during mid/late spring? That's where the fish are.  Why are the fish there?  IMO,  water temps are more stable).  Yes, I've seen/experienced multiple "sub-surface" currents.  (I learned long ago not to use pancake weights on Big-O)

 

Big-O has a natural "Double gyre"  i.e typical currents (negating winds).  The 1st starts at Niagara and flows along the S shore. It turns and flows counterclockwise around the Salmon River area.   The 2nd starts at Niagara and flows along the Canadian shore.  However this 2nd one gets about 2/3 of the way to the St Lawrence and then the doubles back in a clockwise direction.  (Meets the 1st current head-on)  Interestingly there is generally a south bound current near the Scotch Bonnet Ridge that generally hits the S shore near Sandy/Hamlin area.  Winds, especially anything out of the east, can mess this up.

 

I believe the lakes' bottom topography can sometimes affect the mixing of temperatures.  I.e. With a strong south wind cold deeper water moves towards the south.  Where the bottom is generally flat (like at Rochester) there's no "barrier" to its movement. (other than the warmer shallows) At the Oak, where you don't have to go nearly as far offshore to find the same depth of water as you do off Rochester, the steeper bottom gradient has to deflect some of that cold water upwards.  (look at how fast the deep water temp gauge changes off Rochester - one day it's 58F & next day can be 44F)

 

I don't know, (and I'm not going to count) but I'd be willing to bet that more little alewife died (per unit of shoreline) along the flat bottom area (say from Braddocks to Ginnea) than anywhere else.  

 

Lastly, currents in winter are much faster in winter than in summer.  Why?  Lake is not getting nearly as much direct sunlight (hence heat) and remember "Gales of November".  i.e Big waves & strong winds.

 

Luck to all,

 

Tom B.

(LongLine)

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