Effects of variable mean target strength on estimates of abundance: the case of Atlantic mackerel (Scomber scombrus)

Atlantic mackerel Scomber scombrus is a small pelagic, migratory fish which supports commercial fisheries. These fish school and are detectable using echosounders, yet fishery-independent estimates of their abundance in the North East Atlantic do not consider acoustic data. Accurate estimates of mea...

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Bibliographic Details
Published in:ICES Journal of Marine Science
Main Authors: Scoulding, Ben, Gastauer, Sven, Maclennan, David N., Fassler, S.M.M., Copland, Phillip, Fernandes, Paul G.
Format: Article in Journal/Newspaper
Language:English
Published: 2017
Subjects:
Atlantic mackerel
biomass estimation
geostatistics
scattering properties
target strength
North East Atlantic
Online Access:https://research.wur.nl/en/publications/effects-of-variable-mean-target-strength-on-estimates-of-abundanc
https://doi.org/10.1093/icesjms/fsw212
Description
Summary:Atlantic mackerel Scomber scombrus is a small pelagic, migratory fish which supports commercial fisheries. These fish school and are detectable using echosounders, yet fishery-independent estimates of their abundance in the North East Atlantic do not consider acoustic data. Accurate estimates of mean target strength (TS) are presently limiting echo-integration surveys from providing useful estimates of Atlantic mackerel abundance and distribution. This study provides TS estimates for in situ mackerel from multi-frequency split-beam echosounder measurements. TS equals 52.79 dB at 18 kHz, 59.60 dB at 38 kHz, 55.63 dB at 120 kHz, and 53.58 dB at 200 kHz, for a mean mackereltotal length¼33.3 cm. These values differ from those currently assumed for this the sensitivity of acoustically estimated mackerel biomass around the Shetland Islands, Scotland, in 2014, to various estimates of TS. Confidence limits were obtained using geostatistics accounting for coverage and spatial autocorrelation. Stock biomasses, estimated from 38 and 200 kHz data, differed by 10.5%, and stock distributions were similar to each other and to the estimates from an independent stock assessment. Because mackerel backscatter at 38 kHz is dominated by echoes from the flesh and may have similarities to echoes from fish with swimbladders, and backscatter at 200 kHz is dominated by relatively stable echoes from the backbone, we recommend using 200 kHz data forestimates of Atlantic mackerel biomass.

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