Retrospective and Predictive Investigation of Fish Kill Events

Abstract

Fish kill investigations are critical to understanding threats to aquatic ecosystems and can serve as a measure of environmental disruption as well as an early indicator of emerging disease. The goal of this study was to analyze historical data related to such events among wild fish populations in Minnesota in order to assess the quality and completeness of the data and potential trends in fish kills. After excluding events with incomplete data (e.g., in which the location was not reported), we analyzed 225 unique fish kills from 2003 to 2013 that were recorded in two Minnesota Department of Natural Resources databases. The most reported fish kills occurred during 2007 (n = 41) and during the month of June (n = 81) across all years. Centrarchid species were present in the most fish kills (138), followed by cyprinid and ictalurid species, which were present in 53 and 40 events, respectively. Environmental factors were the most common cause of death reported. Models of environmental factors revealed that the maximum nighttime land surface temperature was the most critical factor in fish mortality, followed by changes in primary productivity and human disturbances. During the course of this study, data gaps were identified, including underreporting, inconsistent

Koi herpesvirus and carp oedema virus: Infections and coinfections during mortality events of wild common carp in the United States

“…All clinically healthy carp collected from Minnesota lakes in 2017 were negative for KHV, CEV and SVCV. There were no reports of mortality events from these lakes during the study period and no previous reports of fish kills according to the University of Minnesota's online fish kill database (http://z.umn.edu/fishkill; Phelps et al, ). These lakes are not directly connected to lakes with mortality events reported in this study, and only one lake was located in the same watershed as an outbreak lake.…”

“…Efforts were made to standardize fish kill investigations and laboratory procedures; however, since fish kills are unpredictable events often initially reported by the public (i.e. http://z.umn.edu/fishkill), the number of fish collected, extent of decomposition of samples, reliability of field observations and response time are often variable (Phelps et al, ). Attempts were made to collect at least five carp with clinical signs representative of the mortality event and to record field observations within 24 hr of the initial report.…”

“…For both KHV and CEV, highly sensitive molecular assays are the most reliable diagnostic methods and several detection protocols have been developed (Adamek et al, 2016;Gilad et al, 2004;Matras et al, 2017). Importantly, molecular methods can be useful for detecting pathogens even when fresh samples are not available, which is often the case with outbreaks of disease in wild fish (La & Cooke, 2011;Phelps et al, 2019).…”

Modelling the probability of detecting mass mortality events

“…Larger values of α represent MMEs that are easily detected by an observer, such as those involving large or abundant species in easily observed locations (e.g., charismatic megafauna in open fields or fishes near shore) whereas small values of α would correspond to MMEs of small, cryptic, or rare species in locations that are difficult to study (e.g., small shrews in dense forests or fossorial caecilians). Similarly, small, soft-bodied taxa that degrade quickly or that are rapidly scavenged or washed out of aquatic systems (e.g., Phelps et al, 2019) would have larger values of λ. While the probability of detecting animal carcasses, and thus MMEs, depends on myriad factors affecting carcass persistence and detectability (e.g., Korner-Nievergelt et al, 2015;Santos et al, 2016), exponential decay accounts for the general trend of declining detection probability as carcasses decay and are removed at a more or less constant rate (e.g., Regester and Whiles, 2006).…”

“…While MMEs can produce spectacular levels of mortality, leaving hundreds to hundreds of thousands of carcasses in their wake, carcasses are scavenged, decompose, sink from view, or otherwise disappear (Santos et al, 2016), making MMEs difficult to detect without frequent surveillance (Santos et al, 2016;Kennedy et al, 2017). This is likely especially important for MMEs invovling soft-bodied species in environments with large numbers of scavengers or rapid rates of decay or flow through (Teixeira et al, 2013;Santos et al, 2016;Kennedy et al, 2017;Phelps et al, 2019). And MMEs involving small, rare, or cryptic species may be difficult to detect even at the peak of an event.…”