Threadfin shad, Dorosoma petenense Günther, mortality: causes and ecological implications in a South‐eastern United States reservoir

Abstract

Cold stress was identified as an important factor influencing both reservoir-wide mortality and impingement of threadfin shad, Dorosorna perenense, during the period October 1976 to April 1977 in Watts Bar Reservoir, Tennessee. Relative numbers and size frequency of impinged threadfin shad were similar to the relative numbers and size frequency of shad preyed upon by sauger, Sfizosredion canadense, and skipjack herring, AIosa chrysochloris. This relationship implies that the factor mainly responsible for impingement, low temperature, also influences prey vulnerability. Threadfin shad made up 99% of the combined diet of sauger and skipjack herring from November until the threadfin shad disappeared in January. These predators did not readily switch to alternative prey in the short term, but by the next autumn 25-100% of the diet was alternative prey. Reappearance of threadfin shad the year following mass mortality and ability of the predators to vary their diet emphasize the resilient nature of some predator-prey systems.

Causes and consequences of winter mortality in fishes

“…These observations (and trawl catches) suggested that at low temperatures, sole are sluggish and do not exhibit the normal behaviour of burrowing during the day, making them more vulnerable to cod predation. Similarly, McLean et al (1985) suggested that the reduced schooling behaviour of threadfin shad Dorosoma petenense (Günther) below 12° C increases vulnerability to predation by sauger Stizostedion canadense (Smith) and skipjack herring Alosa chrysochloris (Rafinesque). As low temperatures increase the metabolic requirements of endothermic avian and mammalian predators, they may represent a substantial, but unevaluated, risk to some overwintering fishes (Winship et al , 2002).…”

“…Increased predation pressure could be caused by changes in distribution associated with seasonal migration of the predator, prey or an alternative prey (Murawski, 1993;Cooney et al, 2001). Changes in behaviour and swimming performance at low temperatures may also result in increased vulnerability to predators (Woodhead, 1964a;McLean et al, 1985). In addition to enhanced field sampling to describe diets and distributions, this field would benefit from better characterization of behavioural responses of fish to low temperatures (Lemons and Crawshaw, 1985;Hurst & Duffy, 2005;Hurst, 2007).…”

An updated review of cold shock and cold stress in fish

“…Equilibrium loss and reflex impairment are often thought of as symptoms of chemical anaesthesia (Summerfelt & Smith, 1990) and also can occur following cold stress or other debilitating stressors such as toxicity (McKim et al ., 1987). Equilibrium loss in wild fish has obvious implications for failure to avoid predators ( e.g ., Danylchuk et al ., 2007) or impingement against hydroelectric facility structures (McLean et al ., 1985). Hassan et al .…”