[MARMAM] New paper on mesopelagic prey abundance and distribution for northern elephant seals

Yoko Mitani yo_mitani at fsc.hokudai.ac.jp
Tue Dec 6 20:57:09 PST 2016

Dear All,

My coauthors and I are pleased to announce the publication of our
paper titled “Linking mesopelagic prey abundance and distribution to
the foraging behavior of a deep-diving predator, the northern elephant
seal” published in Deep Sea Research Part II.

Saijo, D., Mitani, Y., Abe, T., Sasaki, H., Goetsch, C., Costa, D. P.,
& Miyashita, K. (2016). Linking mesopelagic prey abundance and
distribution to the foraging behavior of a deep-diving predator, the
northern elephant seal. Deep Sea Research Part II: Topical Studies in

The Transition Zone in the eastern North Pacific is important foraging
habitat for many marine predators. Further, the mesopelagic depths
(200–1000 m) host an abundant prey resource known as the deep
scattering layer that supports deep diving predators, such as northern
elephant seals, beaked whales, and sperm whales. Female northern
elephant seals (Mirounga angustirostris) undertake biannual foraging
migrations to this region where they feed on mesopelagic fish and
squid; however, in situ measurements of prey distribution and
abundance, as well as the subsurface oceanographic features in the
mesopelagic Transition Zone are limited. While concurrently tracking
female elephant seals during their post-molt migration, we conducted a
ship-based oceanographic and hydroacoustic survey and used mesopelagic
mid-water trawls to sample the deep scattering layer. We found that
the abundance of mesopelagic fish at 400–600 m depth zone was the
highest in the 43 °N zone, the primary foraging area of female seals.
We identified twenty-nine families of fishes from the mid-water
trawls, with energy-rich myctophid fishes dominating by species
number, individual number, and wet weight. Biomass of mesopelagic
fishes is positively correlated to annual net primary productivity;
however, at the temporal and spatial scale of our study, we found no
relationship between satellite derived surface primary production and
prey density. Instead, we found that the subsurface chlorophyll
maximum correlated with the primary elephant seal foraging regions,
indicating a stronger linkage between mesopelagic ecosystem dynamics
and subsurface features rather than the surface features measured with
satellites. Our study not only provides insights on prey distribution
in a little-studied deep ocean ecosystem, but shows that northern
elephant seals are targeting the dense, species-diverse mesopelagic
ecosystem at the gyre-gyre boundary that was previously inferred from
their diving behavior.


Yoko Mitani

Laboratory of Marine Ecosystem Change Analysis
Hakodate Marine Station, Field Science Center for
Northern Biosphere, Hokkaido University
Hakodate Research Center for Fisheries and Oceans
20-5 Benten-cho, Hakodate, Hokkaido 040-0051, JAPAN
TEL: +81-138-85-6558; FAX: +81-138-85-6625
E-mail: yo_mitani at fsc.hokudai.ac.jp

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