Diagnostic tools for unbiased in situ target strength estimation
In situ target strength (TS) is theoretically the optimal measure to scale echo-integration values to fish density. In practice, in situ TS is often biased. The number of fish per sample volume (N v ) has been used to set a threshold density to reduce the bias attributable to multiple targets. Howev...
| Published in: | Canadian Journal of Fisheries and Aquatic Sciences |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Canadian Science Publishing
2001
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1139/f01-152 http://www.nrcresearchpress.com/doi/pdf/10.1139/f01-152 |
| Summary: | In situ target strength (TS) is theoretically the optimal measure to scale echo-integration values to fish density. In practice, in situ TS is often biased. The number of fish per sample volume (N v ) has been used to set a threshold density to reduce the bias attributable to multiple targets. However, order of magnitude differences in the N v threshold have been reported within the theoretical range 0 < N v [Formula: see text] 1. To investigate the use and scale-dependence of the N v index, with the objective of achieving unbiased estimates of in situ TS, redfish (Sebastes spp.) aggregations were measured in Newfoundland waters. When averaged over large horizontal distances (large scale), TS was biased upwards if N v exceeded 0.04. However, TS could be estimated at higher densities without bias using smaller measurement scales. To deal with these scale-dependent variations, we develop diagnostic tools based on N v and an echo-count index (T v ), which enable unbiased estimates of the N v threshold and in situ TS. |
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