An Integrated, Size-Structured Stock Assessment of Antarctic Krill, Euphausia superba

Abstract

The Antarctic krill (Euphausia superba) fishery is the largest fishery in the Southern Ocean, and it has been operating for over 45 years. In the past decade, the spatial distribution of the krill fishery has focused on the Bransfield Strait off the Antarctic Peninsula (subarea 48.1). However, the high fishing effort and climate change have placed great pressure on krill resources in this region, and conservation concerns have been raised. Because aging krill is difficult and uncertain, we developed an integrated size-structured model to estimate the fishing mortality, recruitment and spawning biomass of krill. The results indicated that in 1992–2011, the average spawning biomass of krill ranged from 1.14 × 106 to 1.45 × 106 tons, the estimated biomass of the maximum sustainable yield (BMSY) ranged from 3.96 × 105 to 4.90 × 105 tons and the estimated average recruitment ranged from 2.3 × 1012 to 5.03 × 1012 individuals in the research area. We explored the effect of different data weighting schemes for the length data on the assessment output. However, our estimates also have uncertainties. In addition, an attempt was made to analyze the correlation between model-estimated recruitment and mature biomass with climate change. Future stock assessments of krill resources should be comprehensive and multimethod, and the management of krill resources should be based on science that considers the demand of fishing communities and ecosystem protection.

Managing for Climate Resilient Fisheries: Applications to the Southern Ocean

“…Adaptive management is a structured approach to decision-making in the face of uncertainty that focuses on monitoring and forecasting environmental outcomes to reduce uncertainty and improve fisheries management (Chavez et al, 2017;McCarthy and Possingham, 2007;Sekadende et al, 2020;Williams et al, 2009). Similarly, adaptive fisheries management requires the regular adjustment of management measures based on ecosystem monitoring indices for stock assessments (Wang et al, 2021). Introducing adaptive management measures towards climate resilience can minimize the negative impacts of climate change on fisheries by aligning management practices with the spatial and temporal effects of climate change, ecosystem change, and socioeconomic responses (Free et al, 2019;Free et al, 2020;Kenny et al, 2018).…”

“…As targeted species continue to shift their distribution under climate change, stock assessments need to innovate towards accounting for environmental change and uncertainty as well as ecosystem dynamics (Funk and Brown, 2009;Karp et al, 2019). A stronger understanding of how environmental variables drive productivity and trophic dynamics can facilitate the development of multispecies and ecosystem-based stock assessments (Thøgersen et al, 2015;Wang et al, 2021). Not only can climate change affect distribution and movement, but it can also lead to changes in recruitment, mortality rate, and productivity (Pankhurst and Munday, 2011;Portner and Peck, 2010).…”

“…While moving towards ecologically informed stock assessments is a goal for many researchers and managers, currently, ecosystem drivers, ecological interactions, and the effects of climate change are rarely accounted for in fishery stock assessments (Skern-Mauritzen et al, 2016;Wang et al, 2021). Only 2% of global fisheries include ecosystem drivers of stock productivity in their management (Skern-Mauritzen et al, 2016), none of which are in the Southern Ocean.…”

“…This is especially problematic because krill recruitment is extremely variable (recruitment cycles can take 5-8 years) and distinctly specific to each region (Loeb, 2007;Ross et al, 2014;Watters et al, 2020). A long term goal of CCAMLR has been to manage krill fisheries based on ecosystem monitoring indices (Wang et al, 2021), as stated in the CEMP. Implementing this would require an integrated and environmentally informed stock assessment, one that considers the environmental factors affecting the life stages of krill populations.…”

“…Current climate change projections predict the Southern Ocean will experience the most pronounced warming at depths of 0-2,000m compared to other ocean bodies (Bindoff et al, 2022;Hoegh-Guldberg, 2018). More specifically, the western Antarctic Peninsula has been identified as being one of the most climatically sensitive regions on earth (Hendry et al, 2018;Meredith et al, 2019;Wang et al, 2021). The general prognosis for Southern Ocean systems is one of overall warming and freshening, increased acidification, strengthening of westerly winds, increase in ocean eddy activity, shifting currents, increased primary production in the water column and less in sea ice, and declines in sea ice extent; all these physical changes will have potentially dramatic impacts on Antarctic marine ecosystems (Bindoff et al, 2022;Chown and Brooks 2019;Collins et al, 2019;Constable et al, 2014;IPCC, 2021;Henley et al, 2020;Karp et al, 2019;Pinkerton et al, 2021;Rintoul et al, 2018;Rogers et al, 2019).…”