Type of Document Master's Thesis Author Knotek, W. Ladd URN etd-02132009-172544 Title Smallmouth bass mortality during parental care :implications for year-class strength Degree Master of Science Department Fisheries and Wildlife Sciences Advisory Committee
Advisor Name Title Orth, Donald J. Committee Chair Angermeier, Paul L. Committee Member Miller, Orson K. Jr. Committee Member Neves, Richard J. Committee Member Keywords
Date of Defense 1995-12-05 Availability restricted Abstract
I tested hypotheses that daily mortality rates (DMR) of smallmouth bass offspring were influenced by life stage, density and growth, parental male attributes, fungus infection (egg stage), and predation during parental care in the North Anna River, Virginia.
In 1994, stream discharge was relatively low and stable during spawning, and nest success was high (64%). Mortality (attrition) averaged 9.5% per day (range 5.2-13.9%) and 94.1% total (range 80.9-99.5%) for broods that survived to dispersal. Mean DMR for the interval from swim-up to larval metamorphosis (14.0%) was higher (p=0.04) than earlier (egg to swim-up, 6.7%) and later (metamorphosis to juvenile, 9.1%) periods.
Persistent factors during parental care (e.g. nest habitat, male attributes) did not strongly influence survival. Brood size and DMR also were unrelated (r<0.34, p>O.07) during each developmental period, suggesting density-dependent regulation was not prominent at the brood scale. Clutch size and nest success were important determinants of juvenile production for mating males. Larger males received more eggs (r=O. 40, p
Fungus (Saprolegnia parasitical infection was a major source of egg mortality. In field and laboratory studies, severity of infection was enhanced on clutches with higher dead egg abundance ("colonization points") and egg densities. Fungus growth rate also was strongly influenced by temperature and level of bacterial contamination. Predation was a primary cause of nest failure (70% of nest loss in 1994) and brood attrition. Diurnal nest predators were generally successful only in the absence of parental males, but American eels (Anguilla rostrata) were common nocturnal predators of larval and juvenile (14-20 mm SL) offspring and contributed to brood losses prior to swim-up.
Brood mortality information (1994) and annual data (1992-94) on nest success, swim-up larvae production, and August juvenile abundance suggest post-larval survival is an important determinant of annual cohort abundance.
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