News of a die-off of fish is never a good thing to hear. When it happens to be our beloved striped bass, it is bad. When the majority of the fish involved are small fish that have not yet reached sexual maturity, it is even worse. Unfortunately such was the case this week at a small river located in central Connecticut that dumps into Long Island Sound.
Word of the event began to spread over the weekend as a local news agency ran a brief report on the issue on the evening news, yet no further information could be found at the time. Discussion began to circulate online as to the event and speculation as to the cause, location and validity of the story was varied. Eventually an image popped up and I immediately recognized the location.
So I went down to the river Wednesday afternoon and photographed hundreds of dead bass from little 12-inchers on up to fish of about 24 inches in length. They were everywhere I looked. They were on the bottom of the small open water area kept free of ice by frolicking sea ducks. They were encased in ice along the stretches where flow was slow enough to allow the water to freeze. And then, in what turned out to be the largest collection of fish, they were strewn all throughout the marshland near where the small river feeds into Long Island Sound. At first I thought there was simply a large congregation of sea gulls resting on the shoreline, but as I approached it was obvious that they were in fact not birds. Soon my fears were realized as I began to literally walk on dead bass after dead bass. They were everywhere I looked and with each turn it got worse. I spent about 30 minutes documenting the fish and searching for anything that might have led me to the cause, but I only found more dead bass.
I spoke to several local residents and they report that dead fish are dispersed from roughly a mile upstream to over 3 miles east of the mouth of the river. Likely those dead bass outside the river got their by the tidal movements, but for the fish to be spread out so far from the source shows the scale of the number of fish involved.%pullstart%According to the Connecticut Department of Energy and Environmental Protection, the most likely cause of the die-off is what is known as cold shock.%pullend%
I put a call into Rod MacLeod, Senior Fisheries Biologist at Connecticut Department of Energy and Environmental Protection (DEEP), Marine Fisheries Division in Old Lyme on Thursday morning regarding the issue. When asked for the DEEP’s position on the cause of the die-off, he responded by saying, “The most likely cause of the die-off is what is known as cold shock. While other species like white perch, mummichogs, etc, may be more adapted to such drastic changes in water temperatures such as what was experienced recently, the striped bass is apparently not as resilient. While we did see several blue crabs washed up on the shore, no other species of fish were discovered. Many sea gulls were seen feeding on the fish carcasses and there was even a bald eagle sighted.”
He went on, “The recent heavy snow storm and subsequent drop in water temperatures was also coupled with the extreme tides of the new moon. This further dropped the water levels associated with low tide and likely stranded the striped bass in the deeper basins of the river thereby blocking their escape to the safety of the Sound.”
As we spoke, Rod directed me to several sources relating to the phenomenon of “Cold Shock” which the DEEP has cited as the reason for the event. According to Donaldson, M. R., Cooke, S. J., Patterson, D. A. and Macdonald, J. S. (2008), Cold shock and fish. Journal of Fish Biology, 73: 1491–1530. doi: 10.1111/j.1095-8649.2008.02061.x, “Rapid decreases in water temperature may result in a number of physiological, behavioral and fitness consequences for fishes termed ‘cold shock’. Cold-shock stress occurs when a fish has been acclimated to a specific water temperature or range of temperatures and is subsequently exposed to a rapid decrease in temperature, resulting in a cascade of physiological and behavioral responses and, in some cases, death. Rapid temperature decreases may occur from either natural (e.g. thermocline temperature variation, seiches and storm events) or anthropogenic sources (e.g. varied thermal effluents from power generation and production industries). The magnitude, duration and frequency of the temperature change as well as the initial acclimation temperatures of individuals can influence the extent of the consequences of cold shock on fishes.”
Several people who I spoke to theorized that the fish kill was due to alleged dumping of snow and/or snow-melt from the storm last week. When asked about this, Rod responded by saying, “The magnesium chloride that is used on the roads as snow and ice melt has been tested and determined to be at most an irritant to wildlife in the concentrations used on our local highways and roads. When we first inspected the river there was no discernable discoloration or cloudiness to the water. Further, if this was the cause for the event then there would be widespread cases of these types of events throughout the region. There have been documented cases of striped bass die-offs in the past in this river, including last winter following a very similar set of circumstances, so the most likely cause, again, is cold shock.”
So while striped bass are known to inhabit a great many of our local tidal rivers and harbors throughout the winter months, and while for the most part they have evolved to be able to withstand a wide variety of temperatures and conditions, there is quite obviously a limit to what they can tolerate.
If you happen to witness a similar event such as the one outlined here, be sure to record it and notify your local environmental agency immediately. Drop us a line at The Fisherman Magazine as well so we can assist in getting the word out and documenting such events.