IMPACT ASSESSMENT MODEL FOR CLEAR WATER FISHES EXPOSED TO EXCESSIVELY CLOUDY WATER¹

Abstract

A new type of empirical model described here enables real time assessment of impacts caused by excessive water cloudiness as a function of (a) reduced visual clarity (excessive cloudiness) and (b) duration of exposure to cloudy conditions, in fisheries or fish life stages adapted to life in clear water ecosystems. This model takes the familiar form used in earlier suspended sediment dose effect models where z is severity of ill effect (SEV), x is duration of exposure (h), y is black disk sighting range (y BD, m)—a measure of water clarity, a is the intercept, and b and c are slope coefficients. As calibrated in this study the model is Severity of ill effect is ranked on a 15‐step scale that ranges from 0 to 14, where zero represents nil effect and 14 represents 100 percent mortality. This model, based on peer consultation and limited meta analysis of peer reviewed reports, accomplishes the following: (a) identifies the threshold of the onset of ill effects among clear water fishes; (b) postulates the rate at which serious ill effects are likely to escalate as a function of reduced visual clarity and persistence; (c) provides a context (the “visual clarity” matrix, with its cell coordinates) to share and compare information about impacts as a function of visual clarity “climate” (d) demonstrates changes in predator prey interactions at exposures greater than and less than the threshold of direct ill effects; (e) calibrates trout reactive distance (cm) as function of water clarity in the form where y represents reactive distance (cm) and x represents visual clarity (black disk sighting range, cm), and where a and b are intercept and slope respectively, such that (f) identifies black disk sighting range, in meters, and its reciprocal, beam attenuation, as preferred monitoring variables; and (g) provides two additional optical quality variables (Secchi disk extinction distance and turbidity) which, suitably calibrated as they have been in this study, expand the range of monitoring options in situations in which the preferred technology—beam attenuation equipment or black disk sighting equipment—is unavailable or impractical to use. This new model demonstrates the efficacy of peer collaboration and defines new research horizons for its refinement.

Logging and turbidity in the coastal watersheds of northern California

“…Salmonids in particular may be adversely affected at several life stages in freshwater (Newcombe and MacDonald, 1991;Newcombe and Jensen, 1996;Henley et al, 2000;Newcombe, 2003), although White and Harvey (2007) found that in some cases, adaptive feeding strategies used by trout may overcome difficulties in finding food in turbid conditions. Klein et al (2008, Part B) detailed the linkages between harvest rates, elevated chronic turbidity, reduced growth of juvenile salmonids, and impaired spawning escapement.…”

Exposure of cod Gadus morhua to resuspended sediment: an experimental study of the impact of bottom trawling

“…The presence of a zone of high turbidity near the bottom (nepheloid zone) forced by tides, currents, waves and bioturbation (Cacchione & Drake 1986, Graf & Rosenberg 1997, Pilskaln et al 1998, Palanques et al 2001) may have adapted fish to elevated suspensoid loads, but under such conditions concentrations will usually be much lower than those recorded immediately after trawling. Models have been developed for assessing ill-effects related to sediment doses for lotic, lentic and estuarine species (Newcombe & MacDonald 1991, Newcombe & Jensen 1996, Newcombe 2003. However, the predicted responses had a poor fit to the responses registered in our data.…”

Lethal concentrations of suspended solids for common native fish species that are rare in New Zealand rivers with high suspended solids loads

“…It was also well below that for most other fish species reviewed by Newcombe & MacDonald (1991) but not other genera of smelt. Newcombe (2000) produced an index that combines both the concentration and duration of SS that kill fish. The high value for North American smelt (Osmeridae, 11.3) indicates that both the Osmeridae and Retropinnidae are more sensitive to high levels of suspended solids than other fish taxa.…”