Fish kills and bottom-water hypoxia in the Neuse River and Estuary: reply to Burkholder et al.

Burkholder et al. (1999) authored a comment in Manne Ecology Progress Series (MEPS) that selectively criticizes elements of our findings that appeared earlier in the Same journal (Paerl et al. 1998). For the benefit of the readership of MEPS, it would have been useful to have had both their comment and our reply in the Same volume. Unfortunately, we were not informed of their comment pnor to its publication. The lengthy cornment by Burkholder et al. is focused on the relationship between hypoxia/anoxia and the occurrence of fish kills in the Neuse River Estuary. While the main criticisms by Burkholder et al. are addressed separately in this response, we must emphasize that our paper specifically examined the effects of organic matter loading on the oxygen dynamics of this estuary, and not the relationship between fish kills and hypoxia/anoxia as Burkholder et al. imply. The comment by Burkholder et al. revolves around one ancillary aspect of our paper, namely our conclusion that many of the 'reported fish kills appeared to reflect the magnitudes, areal coverage and duration of hypoxia and anoxia events' (Paerl et al. 1998). Burkholder et al. present 5 specific criticisms and provide what they consider to be evidence to support their arguments. First, they contend that we 'lack depth profiles of dissolved oxygen data to support any of [our] conclusions about kills of surface schooiing fish'. We do not lack these data; however we felt that the vertical profiles of dissolved oxygen (DO) concentrations for specific dates, tirnes, and locations were not necessary to illustrate the overall spatiotemporal distribution of bottomwater hypoxia in the estuary, and therefore, these data were not included in the manuscnpt. Vertical profile data for D 0 and other physical Parameters are collected by our laboratory and by colleagues, and have been published biweekly since 1994 in a graphical format on our web site (http://www.marine.unc.edu/neuse/modmon/). Second, Burkholder et al. assert that we have used 'unrecorded' or 'nonexistent' fish kill data and 'misconveying' data in the State of North Carolina's Department of Environment and Natural Resources (Division of Water Quality) data base. We believe this is a very serious ailegation and one that is blatantly false. The data on fish kills in the Neuse River Estuary were obtained from official State records of documented events at the time our paper was submitted for publication (15 August 1997). In this regard, it is inappropnate and unfair for Burkholder et al. to present undocumented and unvenfied data that neither we nor State officials were aware of at the time of manuscript publication. To the best of our knowledge, the data that 'we failed to cite' have not been available to scientific coiieagues and are not Part of the official fish kill data archived by the State. A recent (June 1999) reexamination of the State's official fish kill data (North Carolina Department of Environment, Division of Water Quality; http://esb.ehnr.state.nc.us/FishkilL/fishkill99.htm) indicates that data on the numbers and locations of fish kills which were referred to in our study (Paerl et al. 1998) have not been altered or adjusted since the appearance of our paper. We accordingly stand by both our own and the State's data, which show spatial overlap between penods of bottom water hypoxia, anoxia and State-investigated fish hlis. Third, Burkholder et al. argue that our conclusion concerning the conditions conducive to fish kills is not supported because, in their opinion, we lack an understanding about the behavior of the resident fish populations. We strongly refute this point. Widespread mortality of resident fauna is one of many consequences of oxygen depletion in this System. Fish kdls are inherently unpredictable because motile fauna usually vacate stressful conditions such as hypoxia and anoxia in stratified bottom waters before suffenng mortality (Renaud 1986, Pihl et