Differences in Size Selectivity and Catch Composition Between Two Bottom Trawls Used in High-Arctic Surveys of Bottom Fishes, Crabs and Other Demersal Macrofauna

Long-term monitoring of the high-Arctic marine biota is needed to understand how the ecosystem is changing in response to climate change, diminishing sea-ice, and increasing anthropogenic activity. Since 1959, bottom trawls (BT) have been a primary research tool for investigating fishes, crabs and other demersal macrofauna in the high-Arctic. However, sampling gears, methodologies, and the overall survey designs used have generally lacked consistency and/or have had limited spatial coverage. This has restricted the ability of scientists and managers to effectively use existing BT survey data for investigating historical trends and zoogeographic changes in high-Arctic marine populations. Two different BTs currently being used for surveying the high-Arctic are: 1) a small-mesh 3-m plumb-staff beam trawl (PSBT), and 2) a large-mesh 83-112 Eastern bottom trawl (EBT). A paired comparison study was conducted in 2012 to compare catch composition and the sampling characteristics of the two different trawl gears, and a size selectivity ratio statistic was used to investigate how the probability of fish and crab retention differs between the EBT and PBST. Obvious contrasting characteristics of the PSBT and EBT were mesh size, area-swept, tow speed, and vertical opening. The finer mesh and harder bottom-tending characteristics of the PSBT retained juvenile fishes and other smaller macroinvertebrates and it was also more efficient catching benthic infauna that were just below the surface. The EBT had a larger net opening with greater tow duration at a higher speed that covered a potentially wider range of benthic habitats during a single tow, and it was more efficient at capturing larger and more mobile organisms, as well as organisms that were further off bottom. The ratio statistic indicated large differences in size selectivity between the two gears for both fish and crab. Results from this investigation will provide a framework for scientists and mangers to better understand how to interpret and compare data from existing PBST and EBT surveys in the high-Arctic, and the results provide information on factors worth considering in choosing what BT gear to use for a standardized long-term BT sampling program to monitor fishes, crabs and other demersal macrofauna in the high-Arctic.