Low target strength fish in mixed species assemblages: the case of orange roughy

Abstract Ryan, T. E., Kloser, R. J., and Macaulay, G. J. 2009. Measurement and visual verification of fish target strength using an acoustic-optical system attached to a trawlnet. – ICES Journal of Marine Science, 66: 1238–1244. It is difficult to make acoustic target-strength (TS) measurements of fish behaving naturally in deep-water habitats. The fish may avoid the acoustic instrumentation, and, if measured, there is uncertainty about their species and their orientation relative to the incident sound. To address these issues, a novel acoustic-optical system (AOS) has been developed, which combines a battery-powered, dual-frequency, split-beam acoustic system with a low-light video camera. The AOS attaches to the headline of a commercial deep-water demersal trawlnet that herds fish past the AOS and to the codend. This paper describes initial trials of the AOS to measure calibrated TS of New Zealand orange roughy, validated with video images. The fish species were visually identified, and their behaviour and orientation were approximated. The trawl catch provided associated samples for species identification and measurements of their length and other biological metrics. The combination of acoustics and optics in a net-mountable system constitutes a powerful sampling tool with broader applications in fishery research and ecosystem investigations.

Download Full-text

Industry-collected target strength of high seas orange roughy in the Indian Ocean

ICES Journal of Marine Science ◽

10.1093/icesjms/fsaa101 ◽

2020 ◽

Author(s):

Ben Scoulding ◽

Rudy Kloser

Keyword(s):

Indian Ocean ◽

Cost Effective ◽

Measurement Range ◽

Target Strength ◽

Orange Roughy ◽

Cost Effective Method ◽

The Indian Ocean ◽

State Of The Science ◽

High Seas

Abstract Visually verified in situ target strengths (TS) are the state of the science for determining the conversion from acoustic echo-integration surveys to biomass. Here, we show how these measurements can be made by high seas fisheries during normal operations using a net-attached acoustic optical system (AOS) without specialized personnel on board. In situ TS were collected from ∼45 cm standard length (SL) orange roughy (Hoplostethus atlanticus) in the southern Indian Ocean at 38 and 120 kHz. We use a multiple lines of evidence approach to demonstrate that the previous TS–SL equation developed for ∼10 cm smaller fish in Australia and New Zealand is not suitable for the larger orange roughy and instead propose new TS–SL equations. Our findings show that biomass estimates at 38 kHz will be reduced by ∼58% when using this new TS–SL compared to the existing TS–SL for smaller fish. This highlights the error of extrapolating TS–SL equations outside the measurement range. For this high sea region, the net-attached AOS represented a practical cost-effective method to obtain measurements and provide a result that could be used to inform the management of the stocks. We suggest that this method would be useful in all deep-water fisheries to monitor the TS of the fish for a range of environmental and ontogenetic conditions.

Download Full-text

Acoustic assessment of the biomass of a spawning aggregation of orange roughy (Hoplostethus atlanticus, Collett) off south-eastern Australia, 1990-93

Marine and Freshwater Research ◽

10.1071/mf9961015 ◽

1996 ◽

Vol 47 (8) ◽

pp. 1015 ◽

Cited By ~ 23

Author(s):

RJ Kloser ◽

JA Koslow ◽

A Williams

Keyword(s):

Management Strategy ◽

Sampling Error ◽

Target Strength ◽

Acoustic Beam ◽

Orange Roughy ◽

Eastern Australia ◽

Acoustic Surveys ◽

Surface Bubble ◽

Hoplostethus Atlanticus

Orange roughy, which spawn in an aggregation around a seamount off north-eastem Tasmania, were surveyed acoustically with vessel-mounted and deep-tow transducers from 1990 to 1993. Orange roughy dominated at 700-900 m (95% of individuals) and were less numerous both shallower and deeper. Echo integration estimates from the vessel-mounted transducer were consistently lower than those from the deep-tow transducer by a factor of ~1.8, owing to surface bubble attenuation, vessel movement and acoustic beam thresholding among other factors. The absolute estimate from the deep-towed transducer of the prefishery orange roughy biomass (98200 t ; coefficient of variation, 6.7%) compared well with estimates from stock reduction analysis (95000 to 110000 t) and an egg survey (96900 t; CV, 47%). The acoustic surveys had lower sampling error (CV, 7-15%) than that of the egg survey and required less survey time. The present results support the use of initial absolute acoustic biomass estimates to set a management strategy for the fishery. Stock reduction analysis based on the relative acoustic estimates and catch over the four years indicated that orange roughy target strength was -50 dB � 3 dB, which is consistent with results from models of target strength and from measurements in situ and on dead specimens.

Download Full-text

Morph Composition Matters in the Gouldian Finch (Chloebia gouldiae): Involvement of Red-Headed Birds Increases Vigilance

Birds ◽

10.3390/birds2040030 ◽

2021 ◽

Vol 2 (4) ◽

pp. 404-414

Author(s):

Claudia Mettke-Hofmann

Keyword(s):

Predation Risk ◽

Group Composition ◽

Predation Pressure ◽

Head Movements ◽

Species Assemblages ◽

Same Sex ◽

Mixed Species ◽

Polymorphic Species ◽

Gouldian Finch ◽

Tracking Strategy

Animals invest in costly vigilance to detect threats. Joining groups reduces these costs, which can be further reduced in mixed-species assemblages. In colour-polymorphic species, morphs often experience different predation pressure and vary in a variety of traits. However, little is known about differences in vigilance or how group composition affects vigilance. The aim was to investigate whether higher conspicuousness increased vigilance and whether vigilance was reduced in mixed-morph groups like in mixed-species assemblages. I tested vigilance in the colour-polymorphic Gouldian Finch (Chloebia gouldiae). Same sex pairs of different age and of either pure (red-red or black-black) or mixed head colour were exposed to three contexts (familiar, changed and novel environment) and head movements were recorded. All birds reduced the frequency of head movements with increasing novelty, indicating different vigilance strategies (switching from a searching to a tracking strategy) depending on the situation. While vigilance did not differ between morphs, morph composition mattered. Black-headed pairs made fewer head movements than mixed-head colour pairs. Results indicated that conspicuousness did not affect vigilance, possibly due to existing adaptations to reduce predation risk. However, whenever red-headed birds were involved, vigilance increased either because of higher group conspicuousness or prevalence of aggression.

Download Full-text

In situ measurements of orange roughy (Hoplostethus atlanticus) target strength

ICES Journal of Marine Science ◽

10.1093/icesjms/fsm084 ◽

2007 ◽

Vol 64 (6) ◽

pp. 1220-1234 ◽

Cited By ~ 3

Author(s):

Roger F. Coombs ◽

Richard Barr

Keyword(s):

New Zealand ◽

Standard Length ◽

In Situ Measurements ◽

Rate Of Change ◽

Target Strength ◽

Commercial Fisheries ◽

Orange Roughy ◽

Wide Range ◽

Hoplostethus Atlanticus

Abstract Coombs, R. F., and Barr, R. 2007. In situ measurements of orange roughy (Hoplostethus atlanticus) target strength. – ICES Journal of Marine Science, 64: 1220–1234. Orange roughy (Hoplostethus atlanticus) support one of New Zealand's most valuable commercial fisheries, and its assessment poses many problems. Acoustic estimation using echo integration has become one of the main sources of biomass information, and for this an estimate of orange roughy target strength (TS) is needed. Its schooling characteristics together with patterns in the rate of change of phase vs. TS plots are used to identify ensembles of orange roughy targets from in situ TS data collected from a wide range of fishing areas off eastern New Zealand. The results suggest a TS of −49.3 dB for an orange roughy of 35 cm standard length.

Download Full-text

Cultural learning of predator recognition in mixed-species assemblages of frogs: the effect of tutor-to-observer ratio

Animal Behaviour ◽

10.1016/j.anbehav.2007.10.037 ◽

2008 ◽

Vol 75 (6) ◽

pp. 1921-1925 ◽

Cited By ~ 42

Author(s):

Maud C.O. Ferrari ◽

Douglas P. Chivers

Keyword(s):

Predator Recognition ◽

Species Assemblages ◽

Cultural Learning ◽

Mixed Species

Download Full-text

Assessing introduction risk using species’ rank-abundance distributions

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2014.1517 ◽

2015 ◽

Vol 282 (1799) ◽

pp. 20141517 ◽

Cited By ~ 12

Author(s):

Farrah T. Chan ◽

Johanna Bradie ◽

Elizabeta Briski ◽

Sarah A. Bailey ◽

Nathalie Simard ◽

...

Keyword(s):

Ballast Water ◽

Lower Risk ◽

Water Exchange ◽

Propagule Pressure ◽

Species Assemblages ◽

Total Abundance ◽

Mixed Species ◽

Colonization Pressure ◽

Rank Abundance

Mixed-species assemblages are often unintentionally introduced into new ecosystems. Analysing how assemblage structure varies during transport may provide insights into how introduction risk changes before propagules are released. Characterization of introduction risk is typically based on assessments of colonization pressure (CP, the number of species transported) and total propagule pressure (total PP, the total abundance of propagules released) associated with an invasion vector. Generally, invasion potential following introduction increases with greater CP or total PP. Here, we extend these assessments using rank-abundance distributions to examine how CP : total PP relationships change temporally in ballast water of ocean-going ships. Rank-abundance distributions and CP : total PP patterns varied widely between trans-Atlantic and trans-Pacific voyages, with the latter appearing to pose a much lower risk than the former. Responses also differed by taxonomic group, with invertebrates experiencing losses mainly in total PP, while diatoms and dinoflagellates sustained losses mainly in CP. In certain cases, open-ocean ballast water exchange appeared to increase introduction risk by uptake of new species or supplementation of existing ones. Our study demonstrates that rank-abundance distributions provide new insights into the utility of CP and PP in characterizing introduction risk.

Download Full-text