[MARMAM] New publication - Deep Dives and High Tissue Density Increase Mean Dive Costs in California Sea Lions

Mason Cole masonrcole at gmail.com
Mon Jul 24 07:24:05 PDT 2023

Dear all,

We are excited to share our new publication:

Cole, Mason R., Colin Ware, Elizabeth A. McHuron, Daniel P. Costa, Paul J.
Ponganis, and Birgitte I. McDonald. "Deep dives and high tissue density
increase mean dive costs in California sea lions (Zalophus
californianus)." *Journal
of Experimental Biology* (2023): jeb-246059.
DOI:  https://doi.org/10.1242/jeb.246059

Abstract:  Diving is central to the foraging strategies of many marine
mammals and seabirds. Still, the effect of dive depth on foraging cost
remains elusive because energy expenditure is difficult to measure at fine
temporal scales in wild animals. We used depth and acceleration data from
eight lactating California sea lions (*Zalophus californianus*) to model
body density and investigate the effect of dive depth and tissue density on
rates of energy expenditure. We calculated body density in 5 s intervals
from the rate of gliding descent. We modeled body density across depth in
each dive, revealing high tissue densities and diving lung volumes (DLVs).
DLV increased with dive depth in four individuals. We used the buoyancy
calculated from dive-specific body-density models and drag calculated from
swim speed to estimate metabolic power and cost of transport in 5 s
intervals during descents and ascents. Deeper dives required greater mean
power for round-trip vertical transit, especially in individuals with
higher tissue density. These trends likely follow from increased mean swim
speed and buoyant hinderance that increasingly outweighs buoyant aid in
deeper dives. This suggests that deep diving is either a ‘high-cost,
high-reward’ strategy or an energetically expensive option to access prey
when prey in shallow waters are limited, and that poor body condition may
increase the energetic costs of deep diving. These results add to our
mechanistic understanding of how foraging strategy and body condition
affect energy expenditure in wild breath-hold divers.

Please email me at masonrcole at gmail.com if you have any questions.

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