Successful ecosystem-based management of Antarctic krill should address uncertainties in krill recruitment, behaviour and ecological adaptation

Abstract

Antarctic krill, Euphausia superba, supports a valuable commercial fishery in the Southwest Atlantic, which holds the highest krill densities and is warming rapidly. The krill catch is increasing, is concentrated in a small area, and has shifted seasonally from summer to autumn/winter. The fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources, with the main goal of safeguarding the large populations of krill-dependent predators. Here we show that, because of the restricted distribution of successfully spawning krill and high inter-annual variability in their biomass, the risk of direct fishery impacts on the krill stock itself might be higher than previously thought. We show how management benefits could be achieved by incorporating uncertainty surrounding key aspects of krill ecology into management decisions, and how knowledge can be improved in these key areas. This improved information may be supplied, in part, by the fishery itself.

Antarctic krill Euphausia superba: spatial distribution, abundance, and management of fisheries in a changing climate

“…Catch reports from the commercial krill fisheries, required by CCAMLR on a haul-by-haul basis at gradually finer spatiotemporal scales, are the main sources of data on the distribution of harvesting operations. Several factors, including the patchiness of these operations compared to the distribution of the stock and the scarce knowledge held on the mechanisms and patterns of krill flux (movement), limits the use of catches per unit effort for stock-assessment purposes (SC-CAMLR 1989, Santa Cruz et al 2018, so abundance estimates derive mostly from standardized net and acoustic surveys (Meyer et al 2020). For cost reasons, large, area-scale surveys have been rare events -for the Southwest Atlantic sector, they were only conducted in 2000 and 2019.…”

“…Ecosystem-based risk assessment of the krill fisheries therefore requires data on fisheries, on krill abundance at various scales (to account for flux), and on local predator requirements in fisheries hotspots -all collected and analyzed in ways that allow evaluation of functional relationships (Kawaguchi & Nicol 2020, Meyer et al 2020. When examining advances in the ecosystem risk assessment underlying Scientific Committee advice on krill, it is instructive to focus on a few particularly important decisions by the Commission:…”

“…(5) The most recent substantive update of Conservation Measures related to krill fishing (CM 51-07-2009;CCAMLR 2009b) allocated the trigger level among 4 subareas (48.1−4) in the Southwest Atlantic, again largely based on survey-derived estimates of the standing krill stock (CCAMLR 2009a). Driving the subdivision was advice by the Scientific Committee, based on improved modeling of functional relationships among fisheries, krill, and spatially restricted predators which indicated that even the relatively low trigger-based catch limit might not suffice to protect predators should the fishery become more concentrated near foraging areas (SC-CAMLR 2009, Meyer et al 2020. The Conservation Measure subdividing the trigger level was time limited and has been renewed several times: that currently in force expires in November 2021 (CM 51-07-2016;CCAMLR 2016b).…”

“…A dynamic, whole-ecosystem, data-driven procedure that can support adaptive management of krill is still a work in progress (Kawaguchi & Nicol 2020, Meyer et al 2020), yet 3 moves by the Scientific Committee since the latest regulatory update deserve attention. In 2013, it consolidated a staged approach envisaging catch limits above the trigger level advised based on information that incorporates a steadily broader range of observation series, including multiple-scaled krill surveys and CEMPbased quantification of predator demand (SC-CAMLR 2013).…”

Detecting Climate Signals in Southern Ocean Krill Growth Habitat

“…Currently, krill are managed with catch limits that are deemed to be precautionary, however, these limits are set using a stock assessment that does not account for environmental variability or climate change impacts (Constable and Kawaguchi, 2018;Watters et al, 2020). Fisheries compete with natural predators for krill biomass, making coordinated management critical for sustaining the Antarctic marine ecosystem (Meyer et al, 2020;Watters et al, 2020). Variation in climate, however, independently affects krill productivity, yielding bottom-up fluctuations in krill biomass (Atkinson et al, 2019).…”