Subsampling multi-species trawl catches from tropical northern Australia:: Does it matter which part of the catch is sampled?

• Published in: Fisheries research Vol. 48; no. 2; pp. 117 - 126
• Main Authors: Heales, D.S, Brewer, D.T, Wang, Y.-G
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-09-2000; Elsevier
• Subjects: Amusium pleuronectes; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Bycatch; Exploitation and management of natural biological resources (hunting, fishing and exploited populations survey, etc.); Fundamental and applied biological sciences. Psychology; Leiognathus moretoniensis; Marine; Northern Prawn Fishery; Prawn trawling; Shrimp trawling; Subsampling; Tropical; Australia; Oceania; Bycatch; Tropical; Prawn trawling; Shrimp trawling; Subsampling; Northern Prawn Fishery; Generalized linear model; Estimation; Spatial variation; By-catches; Marine environment; Species diversity; Capture rate; Vertebrata; Fishery; Animal community; Pisces; Sampling; Invertebrata; Ecological abundance
• ISSN: 0165-7836; 1872-6763
• DOI: 10.1016/S0165-7836(00)00182-X

Subsampling is a common method for estimating the abundance of species in trawl catches. However, the accuracy of subsampling in representing the total catch has not been assessed. To estimate one possible source of bias due to subsampling, we tested whether the position on trawler sorting trays from which subsamples were taken affected their ability to represent species in catches. This was done by sorting catches into 10
kg subsamples and comparing subsamples taken from different positions on the sorting tray. Comparisons were made after species were grouped into three categories of abundance, either ‘rare’, ‘common’ or ‘abundant’.
A generalised linear model analysis showed that taking subsamples from different positions on the sorting tray had no major effect on estimating the total numbers or weights of fish or invertebrates, or the total number of fish or invertebrate taxa, recorded in each position. Some individual taxa showed differences between positions on the sorting tray (11.5% of taxa in a three-position design; 25% in a five-position design). But consistent and meaningful patterns in the position of these taxa on the sorting tray could only be seen for the pony fish
Leiognathus
moretoniensis and the saucer scallop
Amusium
pleuronectes. Because most bycatch taxa are well mixed throughout the catch, subsamples can be taken from any position on trawler sorting trays without introducing bias.