The flux of nitrogen in the Gulf of Maine (a) at present and (b) before commercial hunting.

<p>Point-source pollution, industrial emissions of nitrogen, and allochthonous sources from Townsend <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013255#pone.0013255-Townsend1" target="_blank">[18]</a>. The range of historical estimates are adapted from Lotze <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013255#pone.0013255-Lotze2" target="_blank">[66]</a>. Sources that are not expected to be influenced by anthropogenic change, such as offshore transport from Scotian Shelf water, are not included in this graph.</p

A conceptual model of the whale pump.

<p>In the common concept of the biological pump, zooplankton feed in the euphotic zone and export nutrients via sinking fecal pellets, and vertical migration. Fish typically release nutrients at the same depth at which they feed. Excretion for marine mammals, tethered to the surface for respiration, is expected to be shallower in the water column than where they feed.</p

Contemporary nitrogen flux in the Gulf of Maine.

<p>Influx and loss from Townsend <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013255#pone.0013255-Townsend1" target="_blank">[18]</a>.</p><p>Coastal point sources from Sowles <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013255#pone.0013255-Sowles1" target="_blank">[20]</a>.</p

The role of cetaceans in the nitrogen cycle by season.

<p>Seasonal estimates based on the percentage of total consumption in the Gulf of Maine <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013255#pone.0013255-Kenney1" target="_blank">[24]</a>.</p

Shipboard incubation time-course experiments on Humpback whale samples collected on Stellwagen Bank, Gulf of Maine.

<p>(<b>a</b>) Net NH₄⁺ production vs. fecal PON concentration in time course incubations of material collected in whale fecal plumes. Samples 1 and 2 had the highest initial NH₄⁺ concentrations, yet their rates of NH₄⁺ production ranged from the second lowest to the highest in the entire data set. (<b>b</b>) NH₄⁺ concentration vs. incubation time.</p

Effect of common and historically important marine mammals on the nitrogen cycle in the Gulf of Maine ecosystem.

<p>Total annual nitrogen released is 365 x N excreted day⁻¹ for resident toothed whales and pinnipeds; for baleen whales, which migrate seasonally out of the study area, the total nitrogen released is expected to be 83% of annual excretion <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013255#pone.0013255-Lockyer1" target="_blank">[48]</a>.</p

Body mass and consumption rates for cetaceans and seals in the Gulf of Maine.

<p>Body mass and consumption rates for cetaceans and seals in the Gulf of Maine.</p

Time courses for NH₄⁺ concentration in fecal suspensions from the Bay of Fundy right whale.

<p>Time courses for NH₄⁺ concentration in fecal suspensions from the Bay of Fundy right whale.</p

Uptake experiment using natural ¹⁵NH₄⁺ tracer obtained from right whale fecal matter suspension filtrates.

<p>Change in NH₄⁺ concentration over incubation time (a); change in PON (b); change in Chl <i>a</i> (c), changes in δ¹⁵N for NH₄⁺ and PON (d).</p

N analyses on frozen archived samples provided by colleagues from the New England Aquarium (NEA), and the University of Alaska, Sitka (UAS).

<p>BOF is Bay of Fundy; SeC Seymour Canal, AK; SiS Sitka Sound, AK;</p