Evaluation of plankton surface pushnets and oblique tows for comparing the catch of diadromous larval fish |
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| Institution: | 1. Department of Biology, East Carolina University, Greenville, NC 27858, United States;2. Institute for Coastal and Marine Resources, and Department of Biology, Greenville, NC 27858, United States;1. Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai 608 502, India;2. Department of Zoology, Khadir Mohideen College, Adirampattinam 614 701, India;1. Soil and Water Lab, Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY, USA;2. Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA;3. Gerencia de Ambiente e Hidrología, Empresa Pública de Agua Potable y Saneamiento EPMAPS, Quito, Ecuador;4. Institut de Recherche pour le Développement, Centre d''Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul Valéry Montpellier, EPHE, IRD, Montpellier, France;1. State Key Laboratory for Environment-friendly Energy Materials, Southwest University of Science and Technology, Mianyang, 621010, China;2. State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology, Chengdu, 610054, China;3. Laboratory for Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, 621900, China;4. College of Communication Engineering, Chengdu University of Information Technology, Chengdu, 610225, China |
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| Abstract: | A bow-mounted surface pushnet and an obliquely towed plankton net were compared to evaluate gear efficiency and effectiveness in collecting larval fishes under daytime and nighttime conditions. The diadromous species targeted were striped bass Morone saxatilis, white perch, Morone americana, and river herring Alosa sp. We sampled the lower Roanoke River, North Carolina, from March through June of 2002 and 2003. Striped bass, white perch and river herring represented over 90% of the larvae collected during the study period. Mean larval densities (number/100 m3) were 63.4 for striped bass, 26.4 for river herring, and 17.7 for white perch. Striped bass larval densities were significantly higher in the surface pushnet for both years (P ≤ 0.05). In 2002, white perch mean larval density was significantly higher at night in the surface pushnet samples, but in 2003 there were no differences between day and night samples. River herring mean densities were significantly higher in the surface pushnets for both years, but showed no clear patterns between day and night samples. Larger larvae were consistently collected in the surface pushnets for all species. Overall, the surface pushnet was easier to operate. The pushnet was mounted on the bow of a small jon boat and required less specialized gear and fewer personnel than oblique sampling. The method also allows for sampling in shallow water or vegetated habitats. Because larvae were significantly larger in the surface samples, using surface pushnets may not allow for detection of the smaller-sized larvae therefore underestimating the abundance of smaller fish. Depending on the question being asked, we recommend that sampling programs should use both gear types to reduce any gear biases. |
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