Recent studies in streams and ponds have demonstrated that the distribution and biomass of aquatic organisms can be estimated by detection and quantification of environmental DNA (eDNA). In more open systems such as seas, it is not evident whether eDNA can represent the distribution and biomass of aquatic organisms because various environmental factors (e.g., water flow) are expected to affect eDNA distribution and concentration. To test the relationships between the distribution of fish and eDNA, we conducted a grid survey in Maizuru Bay, Sea of Japan, and sampled surface and bottom waters while monitoring biomass of the Japanese jack mackerel (Trachurus japonicus) using echo sounder technology. A linear model showed a high R2 value (0.665) without outlier data points, and the association between estimated eDNA concentrations from the surface water samples and echo intensity was significantly positive, suggesting that the estimated spatial variation in eDNA concentration can reflect the local biomass of the jack mackerel. We also found that a best-fit model included echo intensity obtained within 10–150 m from water sampling sites, indicating that the estimated eDNA concentration most likely reflects fish biomass within 150 m in the bay. Although eDNA from a wholesale fish market partially affected eDNA concentration, we conclude that eDNA generally provides a ‘snapshot’ of fish distribution and biomass in a large area. Further studies in which dynamics of eDNA under field conditions (e.g., patterns of release, degradation, and diffusion of eDNA) are taken into account will provide a better estimate of fish distribution and biomass based on eDNA.
We propose a general framework of abundance estimation based on spatially replicated quantitative measurements of environmental DNA in which production, transport, and degradation of DNA are explicitly accounted for. Application to a Japanese jack mackerel (Trachurus japonicus) population in Maizuru Bay revealed that the method gives an estimate of population abundance comparable to that of a quantitative echo sounder method. These findings indicate the ability of environmental DNA to reliably reflect population abundance of aquatic macroorganisms and may offer a new avenue for population monitoring based on the fast, cost-effective, and non-invasive sampling of genetic information.Knowledge on the distribution and abundance of species is crucial for ecology and related applied fields such as wildlife management and fisheries. The detection and quantification of environmental DNA (eDNA) is an emerging methodology for ecological studies and could enhance the ability of investigators to infer occurrence and abundance of species. This approach has been applied, especially but not limited to, to aquatic species such as fish and amphibians and has been identified as a powerful and yet cost-effective tool for species detection (Bohmann et al. 2014, Rees
N. 2004. Direct measurement of the swimming speed, tailbeat, and body angle of Japanese flounder (Paralichthys olivaceus). e ICES Journal of Marine Science, 61: 1080e1087.It is well known that flatfish species such as plaice can utilize the selective tidal stream to conduct vertical movements. However, detailed description of actual swimming behaviour is lacking, principally as a result of the difficulties encountered in monitoring the behaviour of flatfish in the open sea. The present study describes the use of a newly developed datalogger in obtaining simultaneous recordings of the swimming speed, depth, tailbeat, and body angle of free-ranging Japanese flounder (Paralichthys olivaceus) in the open sea. Our data indicate that Japanese flounders adopt a tailbeat-and-glide behaviour. They are found to glide downward without tailbeats for propulsion, and only during the ascent phase are tailbeats conducted. Flounders move horizontally at speeds of 0.59e1.23 km d ÿ1 and at a maximum speed of 0.70e0.82 km h ÿ1 in the open sea. Modal flounder swimming speeds are 30e40 cm s ÿ1 (0.57e0.76 and 0.58e0.77 BL s ÿ1 ), i.e. sometimes lower than the threshold of the speed sensor. In most cases, however, tailbeat oscillations occur at frequencies of 1.2e1.4 Hz. Moreover, flounders travel at a significantly steeper angle during the ascent phase than during the descent phase. In both cases it is believed that flounder optimize the energetic costs of migration, as has been shown for tuna, sharks, and seals.
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