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.
Bibliographical noteFunding Information:
Preparation for this work was principally provided by National Science Foundation grant PLR 1543541 to DGA. Weddell seal data collection was most recently supported by NSF grants ANT 1141326 and 1640481 to JJR, R.A. Garrott and D.B. Siniff, and prior NSF Grants to JJR, R.A. Garrott, D.B. Siniff and J.W. Testa. Acquiring toothfish catch data was most recently supported by NSF Awards OPP 1142158 (to C.-H. Christina Cheng and Arthur L. DeVries), OPP 1645087 (to C.-H. Christina Cheng and J. Catchen) and OPP 1644196 (to PAC and Arthur L. DeVries), and prior NSF grants to Arthur L. DeVries and C.-H. Christina Cheng.
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- CCAMLR Ecosystem Monitoring Program
- McMurdo Sound
- Ross Sea
- intraguild predation
- precautionary catch levels
- toothfish harvest rules