Andrew S. Brierley

Fish do not avoid survey vessels.

The precarious condition of the worlds fisheries is making ever-greater demands of the scientific assessment of fish stocks. Traditional assessments that rely on commercial catch statistics can have major shortcomings (as shown, for example, by the collapse of Canadas northern cod stock), increasing the need for more fishery-independent data. Acoustic surveys can provide such information, but ocean-going research vessels have high operating costs, and there is also widespread concern that fish avoid these vessels because of the noise they make, thereby biasing abundance estimates. Here we present new data gathered by an autonomous underwater vehicle (AUV) showing that vessel avoidance is not a significant source of bias. Our investigation also heralds the arrival of AUVs as effective survey platforms.

Oceanography: Fish do not avoid survey vessels

The precarious condition of the worlds fisheries is making ever-greater demands of the scientific assessment of fish stocks. Traditional assessments that rely on commercial catch statistics can have major shortcomings (as shown, for example, by the collapse of Canadas northern cod stock), increasing the need for more fishery-independent data. Acoustic surveys can provide such information, but ocean-going research vessels have high operating costs, and there is also widespread concern that fish avoid these vessels because of the noise they make, thereby biasing abundance estimates. Here we present new data gathered by an autonomous underwater vehicle (AUV) showing that vessel avoidance is not a significant source of bias. Our investigation also heralds the arrival of AUVs as effective survey platforms.

Observations on the distribution and relative abundance of the scyphomedusan Chrysaora hysoscella (Linné, 1766) and the hydrozoan Aequorea aequorea (Forskål, 1775) in the northern Benguela ecosystem

Observations on the abundance of medusae at the surface were conducted in the northern Benguela ecosystem, over the period August 1997–June 1998. The results suggest that Chrysaora hysoscella is found inshore, whereas Aequorea aequorea tends to be found offshore. Although these relative observations are subject to bias caused by seasonal changes in the survey area, they are generally supported by the results of correlation analyses, and by the results of a more quantitative, cross-shelf trawl survey. Both species of medusae display marked patchiness, and can be very abundant. They appear to have mostly non-overlapping patterns of distribution in the upper layers of the water column, and so are able exert a consistent predation pressure across the width of the continental shelf. The estimates of biomass obtained are used as input variables to existing models of energy flow within the ecosystem.

An investigation of avoidance by Antarctic krill of RRS James Clark Ross using the Autosub-2 autonomous underwater vehicle

Abstract The autonomous underwater vehicle (AUV) Autosub-2 was deployed on eight missions ahead of RRS James Clark Ross in the northern Weddell Sea and in the Bransfield Strait, Southern Ocean, to assess avoidance of the research vessel by Antarctic krill Euphausia superba . The AUV was equipped with the same type of scientific echosounder as the research vessel (Simrad EK500 operating at 38 and 120xa0kHz) and measured the density of krill along transect acoustically (gxa0m −2 wet mass) prior to the ship’s arrival. We hypothesised that if krill avoided the ship, perhaps in response to radiated noise, then the ship should detect less krill than the AUV which is known to have much lower noise levels than the ship. We were unable to detect any significant difference between the density of krill detected by the ship or the AUV, either at the transect level or at finer scales within transects. We conclude, therefore, that avoidance by krill of RRS James Clark Ross will not significantly bias acoustic estimates of krill abundance by this vessel.

Addendum: Fish do not avoid survey vessels

This corrects the article DOI: 35003648

Fish do not avoid survey vessels (addendum)

This corrects the article DOI: 35003648

A comparison of Antarctic euphausiids sampled by net and from geothermally heated waters: insights into sampling bias

Abstract The Antarctic euphausiids Euphausia superba and E. crystallorophias were sampled using an 8u2009m2 rectangular midwater trawl inside the caldera of Deception Island. Specimens of the same species were collected on the same day from the strandline and sublittoral fringe within the caldera at a bay where these euphausiids had been incapacitated by high temperature geothermally heated waters. Differences between length frequency distributions of samples obtained by both methods were investigated once net-caught specimens had been subject to the simulated effects of geothermally heated waters. Differences between maturity stage/sex ratios for E. superba samples were also assessed. No significant differences between sizes of net-caught or beach-sampled E. crystallorophias were detected, but significant differences were found between both the sizes and sex/maturity stages for E. superba samples. Possible explanations for these differences are discussed.

Fish do not avoid survey vessels: Oceanography

The precarious condition of the worlds fisheries is making ever-greater demands of the scientific assessment of fish stocks. Traditional assessments that rely on commercial catch statistics can have major shortcomings (as shown, for example, by the collapse of Canadas northern cod stock), increasing the need for more fishery-independent data. Acoustic surveys can provide such information, but ocean-going research vessels have high operating costs, and there is also widespread concern that fish avoid these vessels because of the noise they make, thereby biasing abundance estimates. Here we present new data gathered by an autonomous underwater vehicle (AUV) showing that vessel avoidance is not a significant source of bias. Our investigation also heralds the arrival of AUVs as effective survey platforms.