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Comparison of Bottomless Lift Nets and Breder Traps for Sampling Salt-Marsh Nekton
Citation:
Raposa, K. AND M. Chintala. Comparison of Bottomless Lift Nets and Breder Traps for Sampling Salt-Marsh Nekton. TRANSACTIONS OF THE AMERICAN FISHERIES SOCIETY. American Fisheries Society, Bethesda, MD, 145(1):163-172, (2016).
Impact/Purpose:
Vegetated salt marsh surfaces provide refuge, forage, and spawning habitat for estuarine nekton, yet are increasingly threatened by accelerating rates of sea-level rise in southern New England and elsewhere. The goal of this study is to evaluate the effectiveness of different gear for monitoring nekton in emergent salt marsh vegetation by comparing nekton metrics between Breder traps and bottomless lift nets and between Breder traps made from different materials. Regardless of the gear that is used, the relative difficulty associated with sampling nekton in marsh surface habitats likely contributes to the omission of this sampling strategy within regional and national monitoring programs that are designed to quantify and track marsh structure and condition. Based on our data and on results from previous studies, we recommend against the use of Breder traps in quantitative marsh surface nekton surveys and monitoring programs even though they are inexpensive and easy to use. Instead, we reiterate the recommendations of Rozas and Minello (1997) that lift nets or similar enclosure traps should be used when it is economically and logistically feasible and that Breder and minnow traps are more suited to collecting, rather than sampling, nekton. However, if Breder traps, minnow traps, or other similar passive gears are to be used, the resultant data must be interpreted cautiously in light of the biases inherent to these gear types and comparisons should not be made with data that were collected with lift nets or other enclosure traps. Over time, the use of lift nets or other similar quantitative enclosure traps will build upon existing nekton datasets and allow for more comprehensive assessments of nekton use of marsh surface habitats at multiple spatial scales. It will also help researchers and resource managers better understand how sea-level rise and other stressors affect the ability of salt marshes to provide essential habitat for nekton over time.
Description:
Vegetated salt-marsh surfaces provide refuge, forage, and spawning habitat for estuarine nekton, yet are threatened by accelerating rates of sea-level rise in southern New England and elsewhere. Nekton responses to ongoing marsh surface changes need to be evaluated with effective and quantitative nekton sampling gear. The goal of this study was to evaluate the effectiveness of different gear for monitoring nekton in emergent salt-marsh vegetation by comparing nekton parameters between Breder traps and bottomless lift nets and between Breder traps made from different materials. Breder traps collected a significantly different nekton community, fewer species, and larger-sized Mummichogs Fundulus heteroclitus than did lift nets. Nekton community composition, richness, and the size of green crabs Carcinus maenas also differed significantly between Breder traps constructed from acrylic and wire mesh. These results show that it is not appropriate to directly compare nekton data between Breder traps and lift nets, nor between Breder traps made from different materials. Our lift-net data correspond well to other data collected with enclosure traps in southern New England. We recommend lift nets or similar enclosure traps for sampling nekton in emergent marsh vegetation and caution against using Breder traps in monitoring and assessment programs.
