Further evidence that Antarctic toothfish are important to Weddell seals

• Published in: Antarctic science Vol. 33; no. 1; pp. 17 - 29
• Main Authors: Ainley, David G., Cziko, Paul A., Nur, Nadav, Rotella, Jay J., Eastman, Joseph T., Larue, Michelle, Stirling, Ian, Abrams, Peter A.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.02.2021
• Subjects: Adults; Annual variations; Aquatic mammals; Associated species; Biological Sciences; Biomass; Cameras; Catch per unit effort; Commercial fishing; Continental shelves; Dissostichus mawsoni; Ecosystem management; Ecosystems; Fish; Fisheries; Fisheries management; Fishery management; Fishing; Food chains; Interspecific relationships; Leptonychotes weddellii; Perspective; Predation; Prey; Seals; Seals (animals); Time series; Ross Sea; Southern Ocean; toothfish harvest rules; precautionary catch levels; McMurdo Sound; intraguild predation; Ross Sea; competition; CCAMLR Ecosystem Monitoring Program
• ISSN: 0954-1020; 1365-2079
• DOI: 10.1017/S0954102020000437

Antarctic toothfish Dissostichus mawsoni and Weddell seals Leptonychotes weddellii are important mesopredators in the waters of the Antarctic continental shelf. They compete with each other for prey, yet the seals also prey upon toothfish. Such intraguild predation means that prevalence and respective demographic rates may be negatively correlated, but quantification is lacking. Following a review of their natural histories, we initiate an approach to address this deficiency by analysing scientific fishing catch per unit effort (CPUE; 1975–2011 plus sporadic effort to 2018) in conjunction with an annual index of seal abundance in McMurdo Sound, Ross Sea. We correlated annual variation in scientific CPUE to seal numbers over a 43 year period (1975–2018), complementing an earlier study in the same locality showing CPUE to be negatively correlated with spatial proximity to abundant seals. The observed relationship (more seals with lower CPUE, while controlling for annual trends in each) indicates the importance of toothfish as a dietary item to Weddell seals and highlights the probable importance of intra- and inter-specific competition as well as intraguild predation in seal-toothfish dynamics. Ultimately, it may be necessary to supplement fishery management with targeted ecosystem monitoring to prevent the fishery from having adverse effects on dependent species.