Population size,growth and movements of Anguilla australis in a small lake |
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Authors: | D. J. Jellyman S. K. Crow |
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Affiliation: | National Institute of Water and Atmospheric Research Limited, Christchurch, New Zealand |
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Abstract: | To study growth rates, movements and estimate population size of shortfin eels Anguilla australis in a small lake (2·5 ha) near Christchurch, New Zealand, 617 A. australis were tagged with PIT tags. Tag retention was high (95%) and over the seven recapture events spread over 2 years, 55% of tagged A. australis were recaptured. Growth of recaptured A. australis averaged 13·1 mm year?1 and declined slightly with increasing total length. Distance moved from original capture site increased with increasing time at large. Population estimates of A. australis > 400 mm (susceptible to capture by fyke net) from recaptures of individuals averaged 1451 A. australis, with a biomass of 170 kg ha?1. An average of 6·6% of the estimated total population matured as male silver A. australis each year. Results from radio‐tracking of four A. australis gave an average nightly foraging area of 2780 m2, and there was no apparent preference for inshore movement (within 5–6 m of the shoreline) or offshore movement. Fyke‐net efficiency (total catch relative to the estimated total population available to each net) measured over four consecutive nights fishing was 88%. The lack of precision of the shoreline triangulation system used, ±10 m, meant that the positional data were considered too coarse to be used in a proposed novel population estimation technique based on determining population size within foraging areas. |
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Keywords: | foraging area freshwater eels mark– recapture New Zealand PIT tags population estimates |
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