Productivity and Change in Fish and Squid in the Southern Ocean

Abstract

Southern Ocean ecosystems are globally important and vulnerable to global drivers of change, yet they remain challenging to study. Fish and squid make up a significant portion of the biomass within the Southern Ocean, filling key roles in food webs from forage to mid-trophic species and top predators. They comprise a diverse array of species uniquely adapted to the extreme habitats of the region. Adaptations such as antifreeze glycoproteins, lipid-retention, extended larval phases, delayed senescence, and energy-conserving life strategies equip Antarctic fish and squid to withstand the dark winters and yearlong subzero temperatures experienced in much of the Southern Ocean. In addition to krill exploitation, the comparatively high commercial value of Antarctic fish, particularly the lucrative toothfish, drives fisheries interests, which has included illegal fishing. Uncertainty about the population dynamics of target species and ecosystem structure and function more broadly has necessitated a precautionary, ecosystem approach to managing these stocks and enabling the recovery of depleted species. Fisheries currently remain the major local driver of change in Southern Ocean fish productivity, but global climate change presents an even greater challenge to assessing future changes. Parts of the Southern Ocean are experiencing ocean-warming, such as the West Antarctic Peninsula, while other areas, such as the Ross Sea shelf, have undergone cooling in recent years. These trends are expected to result in a redistribution of species based on their tolerances to different temperature regimes. Climate variability may impair the migratory response of these species to environmental change, while imposing increased pressures on recruitment. Fisheries and climate change, coupled with related local and global drivers such as pollution and sea ice change, have the potential to produce synergistic impacts that compound the risks to Antarctic fish and squid species. The uncertainty surrounding how different species will respond to these challenges, given their varying life histories, environmental dependencies, and resiliencies, necessitates regular assessment to inform conservation and management decisions. Urgent attention is needed to determine whether the current management strategies are suitably precautionary to achieve conservation objectives in light of the impending changes to the ecosystem.

Global Connectivity of Southern Ocean Ecosystems

“…Spatial movements of organisms associated with ocean currents (and sea ice drift in polar waters) influence their distributions and hence susceptibility to transport into or out of the Southern Ocean. Vertical migrations by a range of zooplankton, fish and cephalopod species (see Caccavo et al, 2021;Johnston et al, unpublished data) involve interactions with water masses that may facilitate north-south exchanges across the APF.…”

“…Mesopelagic fish are ubiquitous in the world's ocean and comprise a substantial source of biomass (Irigoien et al, 2014;Saunders et al, 2019). Of the mesopelagic fish, lanternfish (Family Myctophidae; hereafter myctophids) are the most speciose and biomass-dominant group in most oceanic regions (Gjosaeter and Kawaguchi, 1980;Catul et al, 2011), including the Southern Ocean (Hulley, 1981;Lubimova et al, 1987), where they are important in pelagic food webs and biogeochemical cycles Murphy et al, 2007;Saunders et al, 2017Saunders et al, , 2019Caccavo et al, 2021). In parts of the Southern Ocean the majority of myctophid species either do not reproduce or their young do not recruit in waters south of the APF (Saunders et al, 2017), with the core populations of most myctophid species centered at predominantly sub-Antarctic, or temperate latitudes (Hulley, 1981;McGinnis, 1982;Loeb et al, 1993;Christiansen et al, 2018).…”

“…The effect of enhanced productivity in the Southern Ocean may lead to reductions in total export of nutrients from the Southern Ocean, resulting in the trapping of nutrients (Moore et al, 2018), with a consequent reduction in productivity across the rest of the global ocean affecting global oxygen and carbon budgets and food webs (Holzer and Primeau, 2013;Primeau et al, 2013;Hauck et al, 2015;Bronselaer et al, 2016;Keller et al, 2016). Nutrient biogeochemistry can also be modified by changes in microbial processes or shifts in community composition, abundance, distribution, behavior, and/or trophic interactions of phytoplankton, zooplankton and higher organisms (Azam et al, 1991;Lavery et al, 2010;Maas et al, 2013;Sailley et al, 2013;Ratnarajah et al, 2014;Schmidt et al, 2016;Cavan et al, 2019;Bestley et al, 2020;Henley et al, 2020;Caccavo et al, 2021;Pinkerton et al, 2021;Johnston et al, unpublished data).…”

Southern Ocean Food Web Modelling: Progress, Prognoses, and Future Priorities for Research and Policy Makers

“…Model development Murphy et al, 2012;Fulton and Link, 2014;Melbourne-Thomas et al, 2017;Fulton et al, 2019;Rogers et al, 2019;Geary et al, 2020Biogeochemistry Post et al, 2014Cavan et al, 2019;Henley et al, 2020 Primary producers Alvain and Ovidio, 2014;Deppeler and Davidson, 2017;Pinkerton et al, 2021Zooplankton Atkinson et al, 2012bAngel and Blachowiak-Samolyk, 2014;Hosie et al, 2014;Kouwenberg et al, 2014;Lindsay et al, 2014;Roberts et al, 2014;Swadling, 2014;Zeidler and De Broyer, 2014;Schaafsma et al, 2018;Pinkerton et al, 2020Krill Atkinson et al, 2012aCuzin-Roudy et al, 2014;Siegel, 2016;Meyer et al, 2020 Fish and squid Kock et al, 2012;Duhamel et al, 2014;Rodhouse et al, 2014;Caccavo et al, 2021 Flying birds Ropert-Coudert et al, 2014;Bestley et al, 2020; https://www.acap.aq/ Penguins Ratcliffe and Trathan, 2011;Ropert-Coudert et al, 2014;Borboroglu and Boersma, 2015;Hindell et al, 2020;Bestley et al, 2020 Seals Trites andPauly, 1998;Southwell et al, 2012;Ropert-Coudert et al, 2014;…”

From Data to Marine Ecosystem Assessments of the Southern Ocean: Achievements, Challenges, and Lessons for the Future

“…For CCAMLR's Convention area, all summary catch and fishing effort statistics since 1970 are made publicly available in the annual Statistical Bulletins. In addition, CCAMLR receives data from scientific observers onboard fishing vessels, research survey data, and the CCAMLR Ecosystem Monitoring Program (CEMP; Caccavo et al, 2021). In contrast to the summary statistics, these high-resolution fishery and research data are not made available to those outside of CCAMLR due to commercial confidentiality concerns by fishing members.…”