Changed prevalence, not absence explains toothfish status in McMurdo Sound Grant Ballard and David Ainley [email protected], [email protected]

Antarctic toothfish have been icebergs in the area from 2001- additionally that neither studied in McMurdo Sound, in 2005 altered the ecosystem in iceberg-related changes in the southern , ways that were not favorable to ocean currents nor in primary , for the past 50 toothfish, thus accounting for productivity in McMurdo Sound years. Among many other the decreases in fishing success. would have been sufficient to findings, studies have shown impact toothfish presence. that smaller (<100cm) toothfish We responded to these ideas in lack the fat to attain buoyancy a 2016 article published in the Main Points journal Antarctic Science. Our and thus remain on the ocean  Large Antarctic toothfish response, based on thorough floor. Adding fat as they grow, have disappeared from they can eventually rise above review of all available data, is to shallower depth ranges suggest that numbers of large the bottom to feed primarily on in the southern Ross Sea, (buoyant) toothfish became but can still be found at . markedly reduced where depths >500m. There is ongoing debate over bottom depths are <500 m,  We hypothesize that this is due to a combination the potential ecosystem effects depths that had been of fishing by humans, of the toothfish fishery in the previously targeted by the killer whales, and Ross Sea. We previously toothfish fishery (focused on Weddell seals. reported a dramatic decline in the largest fish), as well as the  We find no evidence the numbers, size, and depth which is regularly supporting a hypothesis condition of toothfish caught attainable by Weddell seals and that large icebergs during a 39-year scientific Ross Sea killer whales – two decreased toothfish numbers. fishing effort. major toothfish predators. We

propose that the combination Ainley, D.G., G. Ballard, J.T. Eastman, Subsequently, other authors of these factors has resulted in C.W. Evans, N. Nur, & C.L. Parkinson. have questioned the relevance 2016. Changed prevalence, not the remaining toothfish now absence explains Antarctic toothfish of those findings because they status in McMurdo Sound. Antarctic being found at greater depths Science. were derived from a single in McMurdo Sound. doi:10.1017/S0954102016000584 location, and a more recent single-year effort was able to We also counter arguments capture toothfish in the vicinity, that toothfish vanished during but at deeper depths than the and following the presence of long-term study. the icebergs. Available analyses reveal that toothfish movement Additionally, it has been into the Sound would not have hypothesized that mega- been significantly affected, and

December 2016, Point Blue Conservation Science visit www.pointblue.org/publication-briefs