Comparison of Push Nets and Tow Nets for Sampling Larval Fish with Implications for Assessing Littoral Habitat Utilization

Abstract

Understanding sampling effectiveness is critical to gear selection and the determination of larval fish dynamics. We evaluated bow-mounted push nets for collecting larval fish across reservoirs and habitats and compared them with traditional tow nets. By means of a pushed 0.5-m-diameter conical net and towed 0.5-m-diameter and 0.75-m-diameter conical nets, ichthyoplankton samples were taken during daylight hours from May to July on 21 reservoirs that varied in morphological and environmental characteristics. The push net had higher catches than the same-diameter tow net. However, the push net was not as efficient as the larger-sized tow net in July, when larvae are larger. For pelagic habitats, bow-mounted push nets or large tow nets will sample the larval fish community more efficiently than traditional 0.5-m-diameter conical tow nets. We also assessed push nets for sampling nearshore littoral habitats (<1.0 m in depth). Across reservoirs the littoral areas had much higher catch rates than did the offshore pelagic zone; estimates of peak larval fish densities were four times as high in the littoral zone. Deriving estimates of larval fish abundance from pelagic habitats only will probably lead to underestimation of total larval fish densities. The versatility of the push net in sampling littoral habitats is an important consideration when designing surveys to estimate larval fish communities. Bow-mounted push nets can be used to effectively sample both pelagic and littoral larval fish communities, whereas traditional tow nets are only suited for pelagic habitats.