Use of a Quadrat Rotenone Technique and Bioenergetics Modeling to Evaluate Prey Availability to Stocked Piscivores

Abstract

Abstract.-Young-of-year gizzard shad Dorosoma cepedianum. the primary prey for piscivores in Ohio impoundments, are difficult to sample by conventional techniques. We developed a technique for sampling littoral zone quadrats with rotenone and compared this method to other gear. To sample, we isolated 0.15-hectare shoreline areas (N = 28 quadrats) with a plastic barrier, which confined the rotenone and even small fish, and applied rotenone at concentrations of 2-3 mg/L. To quantify densities of dead fish that sank, about 18% of the bottom within quadrats was covered with netting. These nets eliminated the need for species-specific recovery rates, which typically are highly variable. Tucker trawls and seines provided lower density and size estimates of gizzard shad than did our quadrat method. Despite difficulties associated with the quadrat rotenone technique such as site selection, variability, and personnel requirements, this method provided the best estimate of size structure and density of gizzard shad populations. To determine if prey size or density influenced stocking success of age-0 piscivores, we used our estimates of gizzard shad biomass and growth to calculate total production of prey (71.3 kg/hectare) during its first growing season. Five taxa of piscivorous fish were stocked and their growth and survival were monitored in conjunction with regular estimates of gizzard shad. Total consumption of prey by all predators, calculated from observed growth by bioenergetics models, was 14.5 kg/hectare, or only about 20% of total young-of-year gizzard shad production. Apparently, factors other than summer prey production, such as spatial and temporal overlap of predators and prey, the gizzard shad: predator size ratio at time of stocking, or availability of gizzard shad in winter, limited first-year growth and survival of stocked predators.

Seasonal Consumptive Demand and Prey Use by Stocked Saugeyes in Ohio Reservoirs

“…Relative to traditional gear (e.g., quadrat rotenone: Johnson et al 1988b, Schaus et al 1997gill nets: Gido and Matthews 2000;electrofishing: Irwin et al 2003a), acoustic surveys allow researchers to sample reservoirwide fish populations with less time and effort. Gear limitations in shallow water could potentially underestimate gizzard shad population size, while the complexities of estimating fish length distributions from target strength could potentially cause overestimation of prey availability (MacLennan and Simmonds 1992; Thomas et al 2002).…”

“…This seasonal consumption matched consumption by saugeyes in Kokosing Lake, Ohio, during JuneSeptember 1984 (Johnson et al 1988b). By varying saugeye survival and growth within a range of documented field values, we determined the consumptive potential of stocked saugeyes.…”

“…Other piscivores, such as largemouth bass Johnson et al 1988b), crappies, white bass, catfishes, and muskellunge Esox masquinongy probably consume gizzard shad, adding to the predatory demand on gizzard shad populations. In Kokosing Lake, the combined consumptive demand during summer by age-0 stocked predators (percids and esocids) and resident largemouth bass was 14.5 kg/ha, only about 20% of the total standing stock of age-0 gizzard shad, allowing a surplus in gizzard shad biomass to persist (Johnson et al 1988b).…”

Valores de DL50 em peixes e no rato tratados com pó de raízes de Derris spp e suas implicações ecotoxicológicas

“…Com base nesses fatos, propusemo-nos a avaliar os efeitos tóxicos produzidos pelos princípios ativos extraídos de plantas do gênero Derris, popularmente conhecidas como timbós verdadeiros (Pires 1973). Este estudo foi programado com o objetivo de definir a sensibilidade de diferentes espécies de peixes de diferentes ní-veis filogenéticos e de interesse zootécnico pelos rotenoides (Howard 1988), afim de se estabelecerem as bases para uma aplicação adequada no controle químico de organismos aquáticos predadores e/ou parasitas das referidas espécies (Johnson et al 1988). Para tanto determinamos as DL 50 em três espécies de peixes filogeneticamente diferenciadas, duas das quais autóctones e conhecidas popularmente como cascudo (Plecostomus sp) e tambaqui (Colossoma macropomum) e uma terceira espécie a tilápia (Oreochromis niloticus) já perfeitamente aclimatada à região neotropical.…”

“…O emprego destes princípios ativos no manejo controlador em aquicultura está bastante difundido na Europa, Estados Unidos e Austrália, onde as interações ecotoxicológicas decorrentes das suas aplicações foram amplamente estudadas (Balcavage & Matoon 1967, Scarnecchia 1988, Matlock et al 1982, Reinertaen et al 1987, Johnson et al 1988.…”