Fish kills caused by a variety of circumstances
During the course of a given year, people enjoying the outdoors are sometimes alarmed to find significant fish kills.
Sometimes, the cause is easy to explain, with Mother Nature responsible for some and human activities for the others.
Sometimes, fish kills are confined to specific species, such as the outbreak that was seen in 2014 at Indian Lake that appeared to be restricted to white bass.
Last fall, carp began dying on Pymatuning Reservoir on the Ohio-Pennsylvania border. This was suspected to be caused by the koi herpes virus, which is specific to koi, goldfish and carp. It spreads under warm, crowded conditions. Similar outbreaks have occurred in the Sandusky Bay in recent years.
During some years, such as 2011, thousands of stressed walleyes perish and float to the surface of Lake Erie after spawning. A cool, extended spring spawning period was blamed that year.
Yet, even though 10,000-to-20,000 was estimated to be lost, it was only a fraction of the entire population, unlike salmon which all deteriorate and die after spawning.
Tens of thousands of smelt can be seen in the spring when many of the adults, also weakened after spawning, drift through the islands area in large windrows when the wave direction is unfavorable. They are often mistaken for young walleyes by unfamiliar observers.
Currently, there are hundreds of dead gizzard shad washing up on several local shorelines, particularly in the Sandusky Bay area. This species is thought to have invaded the Great Lakes when the Ohio-Erie Canal was connected, which provided a pathway that connected the previously separate watersheds.
Gizzard shad are subject to winter mortality because of Ohio’s water temperatures often falling below the tolerance level of this predominantly southern species.
Each fall, over 90 percent of the population dies off in Lake Erie as water temperatures fall below 40 degrees (Fahrenheit). With an extended cold winter, even adult specimens of the species which have survived through previous winters to reproduce and replenish their population succumb to the elements.
Some may recall years when various Lake Erie fish species were stricken with Viral Hemorrhagic Septicemia (VHS) and wonder if the shad have this disease.
Because of VHS, there are restrictions in the transport of emerald shiners between states, which have led to local shortages during the fall perch fishing season.
Eric Weimer, Ohio Division of Wildlife Sandusky Fisheries Research Unit Supervisor, does not suspect that VHS is in play, but adds that specimens collected from Lake St. Clair this week are being tested for the virus.
A few years ago, there was an early spring outbreak in the Milwaukee Harbor where VHS was confirmed to be the culprit killing their gizzard shad. The Ohio DOW will monitor the kills, but realistically there is nothing that can be done other than let the disease fade away as water temperatures increase.
A second common cause of Mother Nature-related fish winter kill occurs when the aquatic life uses up the available dissolved oxygen under the ice in ponds, reservoirs or small lakes. This typically occurs in years when there is a long period of ice cover and snow also blankets the ice. This combination blocks out sunlight and prevents photosynthetic activity by plants to provide adequate dissolved oxygen levels.
Strong winds can push the poorly-oxygenated bottom water from below the thermocline, known as the dead zone toward the shore as an upwelling, fatally enveloping fish along the Lake Erie shoreline. A turnover such as occurred in East Fork Reservoir in 2015 subjected fish to poorly-oxygenated bottom water from below the thermocline there, too.
Other fish kills can be directly tied to poor manure management or a combination of activities that are made worse by the weather.
Even though Ohio passed legislation in 2015 that prohibited spreading manure whenever one-half inch of precipitation has been forecasted to prevent it from being washed into nearby creeks, there were instances this summer of agricultural operators spreading manure in Northwestern Ohio streams prior to large rain events.
This led to dissolved oxygen depletions that killed tens of thousands of fish in Allen, Hardin and Williams Counties. Another kill in 2016 was traced to the town of Delphos leaking raw sewage into the Auglaize River.
Mining, fracking, pipeline construction and other activities may lead to unexpected pollution harmful to aquatic life, so all observed spills should be reported to the Ohio EPA emergency hotline at 1-800-282-9378. Fish kills should be reported to the Ohio Division of Wildlife at 1-800-7622437.
Originally posted on March 11, 2018 by John Hageman at Sandusky Register
Image courtesy wfmj.com.