Vulnerability of the Spotted Sea Trout to cold, Trout Stun Events and Trout Kills Along the Crystal Coast. By Dr. Bogus (Updated 2/18/15)
Trout kills (cold stun events) are normal and not as infrequent as you might imagine and have an important impact on natural mortality of spotted sea trout. In the fall and winter trout move south and then reenter the backwater deep creeks for food and shelter against the winter temperatures. If the water temperature falls, as a cold front moves in, sometimes after a snow event, the trout can seek deeper waters for protection. If the temperature drops too quickly they may or may not have time to seek deeper warmer waters. Remember, trout, as are most fish (there are exceptions), are cold blooded and their body temperature is the same as the water around them. As they get colder their body metabolism slows and their speed of movement and feeding and digestion slow considerably. Remember when you trout fish in the winter, the idea is to move your bait, slow, slower and slowest to get a hit, or “bump” from a lethargic trout.
There is always a debate on what the “cold stun” temperature for a trout is, that is the temperature where they lose swimming control and float to the surface upside-down (they have swim bladders) where they may freeze and die. That temperature is somewhere around 39 to 41 degrees or so, but the stunning of the fish it is not instantaneous, it takes some sustained time at or around a critical stun temperature to incapacitate the fish and it may also somewhat depend on the fish’s age as well. So just rapid drops in water temperature of a short duration will not be cause a major trout kill, but would mainly impact fish in very shallow waters like the North River. Also many fish may feel the drop in temperature and have enough time to escape into deeper water in time to protect themselves. Where major trout kills occur, the temperature drops rapidly, often preceded by snowfall, which (the snow and sinking cold-water runoff) also will contribute to rapid water cooling, and then followed by an extended cold air and water temperatures, with water temperatures holding in the 30s for a week or more.
We have seen a number of these events over the years. The first major one I witnessed was the devastating trout stun event of January 2003. I was not in North Carolina during the snow storm and frigid cold of 1989, so I don’t remember that event, but by all accounts it was also epic. More recently we have had a rapid succession of stun events in January 2010, December 2010 and January 2011 which led to the total closure of trout harvest both recreationally and commercially, by NCDMF. It also lead to dropping the bag limit, eventually to 4-fish/day and raised the minimum length to 14-inches to ensure the fish have at least one year to spawn before they are subject to harvest. I’m sure there were other trout kills during my 20-plus years in North Carolina and Emerald Isle that I haven’t documented.
As you may know, I routinely keep ocean surf and Bogue Sound water temperatures on a nearly daily basis. I have some data going back to 1995 and daily data date since 1999, when I moved to my Emerald Isle home permanently. For the stun events that I mentioned above I have the following Bogue Sound and ocean surf water temperature data.
January 22-28, 2003: In the aftermath of a snow storm, Bogue Sound temperatures dropped and remained in the 30s and as low at 30-degrees in a salty slush for the entire week. Many of the creeks were frozen over. Ocean surf at Bogue Pier went as low as 36-degrees, which is about the lowest I’ve ever measured in the surf.
January 3-13, 2010: Bogue Sound remained in the 30s or very low 40s during that entire week and a half, with a low of 35-degrees. Ocean temperature bottomed out during that time at 43-degrees during that week.
December 19-30, 2010: Again after another snow storm (It doesn’t snow in Emerald Isle, does it?), Bogue Sound temperatures rapidly plunged into the 30s with a low of 33-degrees. It should also be noted that almost the entire month was unusually cold with an average of only 41-degrees for the month! The surf reached a minimum of 42-degrees during that period.
January 9-15, 2011: Right after the frigid December 2010 and trout kill, temperatures, already primed for disaster, dropped again into the 30s (low of 33-degrees) for another trout kill event for basically the third event in a little more than a year. This was the final event that precipitated the dramatic closure of the trout harvest and restructuring bag and size limits.
This year (2014) we have seen a rapid drop in temperatures caused by the so-called Arctic Polar Vortex, setting record low temperatures here in eastern North Carolina and around much of the nation. Surf temperatures dropped to 47-degrees around Bogue Pier and I’ve measured Bogue Sound temperatures at a very cold 35 and 34-degrees. We have not had a snow storm prior to this drop in temperatures and the Polar Vortex has weakened and rapidly receded, to whence it belongs (the Arctic!) after just a couple of days. The water was cold but has rebounded to near normal for mid-January and although we have seen skim ice on the creeks, even that has receded as well. It appears that the short duration of the freeze this year minimized the deleterious effects on our beloved trout. In fact, I haven’t heard of any reports of stunned trout. I was out fishing the creeks during this period, no, I didn’t catch any trout but I didn’t see any floating fish either, but I did land many drag stretching slot sized red drum from our local creeks.
UPDATE: By the end of January 2014 we had another attack of the Vortex preceded by a snow and ice storm, resulting in some trout kills. The result was a harvest closure for both recreational and commercial fishermen. Now in mid February 2015 we have had some sustained cold again preceded by a wintery mix of ice and snow resulting in reported trout kills this winter as well. I’ve seen photos of stunned and dead fish from Slocum Creek (Fin Chaser’s Charters). And as of 2/18/15, the frigid cold continues with forecast of teens and single digit temperatures before moderating over the weekend.