Whales sustain fisheries: Blue whales stimulate primary production in the Southern Ocean

Abstract

It has previously been asserted that baleen whales compete with fisheries by consuming potentially harvestable marine resources. The regularly applied "surplusyield model" suggests that whale prey becomes available to fisheries if whales are removed, and has been presented as a justification for whaling. However, recent findings indicate that whales enhance ecosystem productivity by defecating iron that stimulates primary productivity in iron-limited waters. While juvenile whales and whales that are pregnant or lactating retain iron for growth and milk production, nonbreeding adult whales defecate most of the iron they consume. Here, we modify the surplus-yield model to incorporate iron defecation. After modeling a simplistic trajectory of blue whale recovery to historical abundances, the traditional surplusyield model predicts that 10 11 kg of carbon yr -1 would become unavailable to fisheries. However, this ignores the nutrient recycling role of whales. Our model suggests the population of blue whales would defecate 3 9 10 6 kg of iron yr -1 , which would stimulate primary production equivalent to that required to support prey consumption by the blue whale population. Thus, modifying the surplus-yield model to include iron defecation indicates that blue whales do not render marine resources unavailable to fisheries. By defecating iron-rich feces, blue whales promote Southern Ocean productivity, rather than reducing fishery yields.

Seabirds and marine mammals redistribute bioavailable iron in the Southern Ocean

“…At present, both seabird and marine mammal population densities in the Southern Ocean are at historical lows, suggesting scope for a potentially much larger role of both groups as nutrient vectors (e.g. Nicol et al 2010, Lavery et al 2014.…”

Whales as marine ecosystem engineers

“…2012). Rather than reducing fishery yields, the presence of some species, such as blue whales in the Southern Ocean, promotes productivity through the defecation of nutrient‐rich feces (Lavery et al . 2014).…”

Validating the reliability of passive acoustic localisation: a novel method for encountering rare and remote Antarctic blue whales

“…Resources for Antarctic research are diminishing, yet there is the continuing improvement of methods to monitor cetaceans and a strong desire for whale population data from many sources, including the IWC (Anonymous 2010), Antarctic resource managers (CCAMLR; Anonymous 2009a, Lavery et al 2014 and the wider public. In light of this, the IWC Southern Ocean Research Partnership (IWC-SORP) commenced the Antarctic Blue Whale Project (ABWP) in 2009 (Anonymous 2009b).…”