Does the size of subsamples taken from multispecies trawl catches affect estimates of catch composition and abundance?

Heales, D. S., Brewer, D. T., Wang, Y. G. and Jones, P. N. (2003) Does the size of subsamples taken from multispecies trawl catches affect estimates of catch composition and abundance?. Fishery Bulletin, 101 4: 790-799. doi:10.1039/9781847550118-00169


Author Heales, D. S.
Brewer, D. T.
Wang, Y. G.
Jones, P. N.
Title Does the size of subsamples taken from multispecies trawl catches affect estimates of catch composition and abundance?
Journal name Fishery Bulletin   Check publisher's open access policy
ISSN 0090-0656
1937-4518
Publication date 2003-10
Sub-type Article (original research)
DOI 10.1039/9781847550118-00169
Open Access Status DOI
Volume 101
Issue 4
Start page 790
End page 799
Total pages 10
Place of publication Seattle, WA, United States
Publisher U.S. National Marine Fisheries Service
Language eng
Abstract Although subsampling is a common method for describing the composition of large and diverse trawl catches, the accuracy of these techniques is often unknown. We determined the sampling errors generated from estimating the percentage of the total number of species recorded in catches, as well as the abundance of each species, at each increase in the proportion of the sorted catch. We completely partitioned twenty prawn trawl catches from tropical northern Australia into subsamples of about 10 kg each. All subsamples were then sorted, and species numbers recorded. Catch weights ranged from 71 to 445 kg, and the number of fish species in trawls ranged from 60 to 138, and invertebrate species from 18 to 63. Almost 70% of the species recorded in catches were "rare" in subsamples (less than one individual per 10 kg subsample or less than one in every 389 individuals). A matrix was used to show the increase in the total number of species that were recorded in each catch as the percentage of the sorted catch increased. Simulation modelling showed that sorting small subsamples (about 10% of catch weights) identified about 50% of the total number of species caught in a trawl. Larger subsamples (50% of catch weight on average) identified about 80% of the total species caught in a trawl. The accuracy of estimating the abundance of each species also increased with increasing subsample size. For the "rare" species, sampling error was around 80% after sorting 10% of catch weight and was just less than 50% after 40% of catch weight had been sorted. For the "abundant" species (five or more individuals per 10 kg subsample or five or more in every 389 individuals), sampling error was around 25% after sorting 10% of catch weight, but was reduced to around 10% after 40% of catch weight had been sorted.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Mathematics and Physics
 
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Created: Wed, 17 Nov 2010, 13:49:56 EST