Dive behaviour impacts the ability of heart rate to predict oxygen consumption in Steller sea lions (Eumetopias jubatus) foraging at depth

The predictive relationship between heart rate ( f H) and oxygen consumption (![Graphic][1] ) has been derived for several species of marine mammals swimming horizontally or diving in tanks to shallow depths. However, it is unclear how dive activity affects the ![Graphic][2] relationship and whether the existing equations apply to animals diving to deeper depths. We investigated these questions by simultaneously measuring the f H and ![Graphic][3] of Steller sea lions ( Eumetopias jubatus ) under different activity states (surface resting or diving), types of dives (single dives or dive bouts), and depths (10 or 40 m). We examined the relationship over dives only and also over dive cycles (dive + surface interval). We found that f H could only predict ![Graphic][4] over a complete single dive cycle or dive bout cycle (i.e. surface intervals had to be included). The predictive equation derived for sea lions resting on the surface did not differ from that for single dive cycles. However, the equation derived over dive bout cycles (multiple dives + surface intervals) differed from those for single dive cycles or surface resting, with similar f H for multiple dive bout equations yielding higher predicted ![Graphic][5] than that for single dive bout cycles (or resting). The ![Graphic][6] relationships were not significantly affected by dive duration, dive depth, water temperature or cumulative food consumed under the conditions tested. Ultimately, our results demonstrate that f H can be used to predict activity-specific metabolic rates of diving Steller sea lions, but only over complete dive cycles that include a post-dive surface recovery period. * AMR : average metabolic rate (![Graphic][7] ) averaged over the dive cycle (dive + T MRs) DLW : doubly labelled water DMR : diving metabolic rate (![Graphic][8] ) averaged over dive f H : heart rate (beats min–1) f H,inst : instantaneous heart rate (beats min–1) MRs : ![Graphic][9] resting at the surface in open water (pre-dive) ODBA : overall dynamic body acceleration RMR : resting metabolic rate (MRs + resting swim mill trials) ([Young et al., 2010][10]) SI : post-dive surface interval (min) T MRs : SI until returned to ±2% of pre-dive ![Graphic][11] level (MRs) TDR : time-depth recorder ![Graphic][12] : oxygen consumption rate (l O2 min–1) [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif [5]: /embed/inline-graphic-5.gif [6]: /embed/inline-graphic-6.gif [7]: /embed/inline-graphic-73.gif [8]: /embed/inline-graphic-74.gif [9]: /embed/inline-graphic-75.gif [10]: #ref-55 [11]: /embed/inline-graphic-76.gif [12]: /embed/inline-graphic-77.gif