Abstract
Antarctic krill (Euphausia superba) is harvested using different design midwater trawls. Knowing the selective properties between trawls is crucial information for the management of the krill resources. This study compared the catch patterns between different commercial krill trawls at similar times and overlapping fishing grounds based on scientific data collected by scientific observers onboard commercial trawlers Long Teng (LT) and Fu Rong Hai (FRH). The results showed significant differences in the length-dependent catch densities and cumulative catch densities of krill between the two trawls. The krill length range in catches from LT's trawl was wider than that of FRH's trawl. Furthermore, the catch would consist of a larger proportion of smaller krill in the LT's trawl. The LT's trawl caught significantly higher proportions of krill below 38 mm than FRH's trawl. Even, the LT's trawl caught substantial numbers of krill <30 mm, whereas the FRH's trawl caught very few of them. The main factors causing the difference between trawls in catch pattern were inferred to be related to gear design including differences in mesh sizes used. The results of this study enhance the quality of comparative analysis of scientific data from commercial trawls and the understanding of gear selectivity of different configuration trawls used for harvesting krill.
Highlights
Since 1993, the krill trawl fishery has concentrated on subareas 48.1, 48.2, and 48.3 of FAO area 48, west of the South Atlantic (CCAMLR, 2020a)
The scientific survey of fisheries is an important supplement to large-scale scientific investigations and assessments of krill resources
Commercial trawlers involved in krill fishery use different trawl designs, such as trawl structure, net dimensions, mesh sizes, and operations that affect the selectivity of trawls and result in sampling bias between different trawls (Zimarev et al, 1990; Kasatkina, 1997)
Summary
Since 1993, the krill trawl fishery has concentrated on subareas 48.1, 48.2, and 48.3 of FAO area 48, west of the South Atlantic (CCAMLR, 2020a). Those scientific data collected by scientific observers onboard commercial trawlers provide important information for the management of krill resources and the ecosystem of the Antarctic Ocean (Okuda and Kiyota, 2012) One such information is the length composition of krill in catches used to better understand the population structure of krill resources, assess fishing gear selectivity, and formulate feedback management (FBM) indicators. It is integral information for the acoustic study of krill distribution based on acoustic measurements onboard commercial trawlers (CCAMLR, 2011; Kasatkina, 2017). The selectivity properties of trawls need to be considered to analyze the krill length data collected from commercial fisheries, including a comparison of the length composition of krill from different trawls (Kasatkina, 1997)
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