Short-term effects of bottom trawling and a storm event on soft-bottom benthos in the eastern Bering Sea

Abstract

A Before–After Control–Impact (BACI) experiment was conducted to investigate the effects of a commercial bottom trawl on benthic invertebrates in a sandy and previously untrawled area of the eastern Bering Sea. Six pairs of experimental and control corridors were sampled with a research trawl before and after four consecutive tows with the commercial otter trawl. A major storm event occurred during the experiment, and it was possible to differentiate its effect from that of the trawling using the BACI model. Species composition changed very little; Asterias amurensis and Paralithodes camtschaticus comprised over 80% of the total invertebrate biomass (kg ha−1) during each year of the study. In general, the commercial trawl did not significantly affect the biomass of the benthic invertebrate populations. The trawling effect after 4–14 d was statistically significant in three of the 24 taxa that were analysed, which was, as expected, because of nothing more than random variation with α = 0.10. Biomass immediately after the trawling disturbance was lower for 15 of the taxa and higher for the other nine, with a median change of −14.2%. Similarly, the effect of trawling on invertebrate biomass after one year was not statistically significant for any of the taxonomic groups (p ≥ 0.23), indicating no evidence of a delayed response to the commercial-trawl disturbance. Further analysis suggests that storms have an overall greater effect on the benthos than do bottom trawls at this location. Both the numbers of taxa significantly affected by trawling and the storm (3 vs. 12), as well as the median sizes of these effects −14.2% vs. −22.0%), were greater for the storm event. Results from this study are combined with those from a related investigation of chronic trawling effects to propose an adaptive management strategy for the study region, including rotating area closures to mitigate for temporary trawling effects.

Response of benthic fauna to experimental bottom fishing: A global meta‐analysis

“…For these species, recovery largely depends on recruitment, settlement and growth in impacted areas and the extent of substrate modification following the fishing event. For example, many sessile invertebrates such as anemones, tunicates and soft corals in sandy disturbed areas of the Bering Sea depend on empty shells for attachment, and trawling can bury these shells and hamper their recovery (McConnaughey & Syrjala, ).…”

Prioritization of knowledge‐needs to achieve best practices for bottom trawling in relation to seabed habitats

“…Sciberras et al . ; McConnaughey and Syrjala ). Understanding which combination of habitat variables predicts recovery would facilitate the development of broad scale predictive maps of habitat sensitivity that could be used for management purposes (see Hiddink et al .…”

“…the winter when many benthic biota are senescent (Van Denderen et al 2015). McConnaughey and Syrjala (2014) suggested that the benthic habitat in their Bering Sea study area is affected more by natural storm events than trawl disturbance. If we are to assess change in seabed habitats and their biota in relation to fishing this implies that we understand the status of those habitats prior to the commencement of fishing.…”

“…The effects of disturbance from fishing gear can be relatively minor and short‐lived in some habitats (e.g. McConnaughey and Syrjala ; Sciberras et al . ; Stokesbury and Harris ), and in others, severe and long‐lasting, especially in habitats formed by living organisms (e.g.…”

“…The effects of disturbance from fishing gear can be relatively minor and short-lived in some habitats (e.g. McConnaughey and Syrjala 2014;Sciberras et al 2013;Stokesbury and Harris 2006), and in others, severe and long-lasting, especially in habitats formed by living organisms (e.g. Beukema 1995;Turner et al 1999;Hall-Spencer and Moore 2000;Koslow et al 2001;Cook et al 2013;Clark et al 2015).…”