Status of the FIBEX Acoustic Data from the West Atlantic

Summary

A re-analysis of FIBEX (First International BIOMASS Experiment) acoustic survey data from the West Atlantic region found good agreement between four research vessels (Itzumi, Dr Eduardo L. Holmberg, Odissey, Walther Herwig) despite using different sound frequencies for krill detection. The combined dataset estimated total West Atlantic krill biomass at 32.7 million tonnes across the surveyed areas. The Walther Herwig survey contributed approximately 80% of the krill biomass estimate for fishing area 48.1 due to detecting a massive krill concentration near Elephant Island. Data from the Professor Siedlecki survey showed inconsistent results compared to other vessels, with no clear explanation for the differences. The frequency differences between 50 kHz and 120 kHz acoustic systems did not significantly affect biomass estimates. The study confirms FIBEX as the most reliable comprehensive krill survey available for the region.

This 3D plot shows krill density measurements across the Bransfield Strait and South Shetland Islands region. Vertical bars represent density values at each sampling location, with taller spikes indicating higher krill concentrations. The data reveals highly patchy krill distribution, with several dramatic density peaks in specific areas while most of the surveyed region shows much lower concentrations.

Key Findings

Four out of five research vessels showed good agreement in their krill population estimates.

The total estimated krill biomass was 32.7 million tonnes across the surveyed West Atlantic areas.

The Walther Herwig survey detected a massive krill concentration that contributed approximately 80% of the biomass estimate for fishing area 48.1.

The difference in acoustic frequencies (50 kHz versus 120 kHz) did not significantly affect biomass estimates.

Data from the Professor Siedlecki survey was inconsistent with other surveys, with no clear explanation for the differences.

Krill distribution was extremely uneven and concentrated in patches throughout the survey area.

Abstract

Data from the FIBEX acoustic survey in the West Atlantic sector have been re-examined to check the consistency of krill abundance estimates derived from different survey vessels. There is a good level of consistency between the results from four of the vessels, Itzumi, Dr Eduardo L. Holmberg, Odissey and Walther Herwig. While there is an error factor due to the combination of data collected at 50 kHz (Walther Herwig survey) with data collected at 120 kHz (all other vessels), it is concluded that this does not materially affect the estimated biomass. The data from the Professor Siedlecki survey do not provide estimates that are consistent with the other surveys. The authors can find no explanation for this difference.

Published in

CCAMLR Science

1994

Authors

Trathan, P.N., Everson, I.

Institutions

British Antarctic Survey

Methods

AcousticDataField

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