I was intrigued by Blainsville's Beaked Whales after I learned about them in an online class on Marine Megafauna. That interest inspired me to explore how the whales and the seals that all hunt at great depth live. Whether these animals ever cross paths is unknown. So little is known about beaked whales at all. Certainly this particular group, in the Canary Islands, is no where near Northern Elephant Seals in the north Pacific, but the habitat of other beaked whales overlaps with them.
The paper I wrote follows. Unfortunately, the blog wouldn't allow me to post the illustrative figures.
Deep
sea predators hunt in a three-dimensional world that is dark and has few
landmarks. Large marine mammals have senses and strategies that allow them to
hunt successfully and share the deep ocean. Food isn't evenly spread around,
but is concentrated in predictable ways. The deep scattering layer, the benthic
boundary layer, and the oxygen minimum layer – these terms will be defined
below - all describe zones that attract or aggregate various organisms. Those
organisms attract predators that feed on them, and on up the food chain to the
top predators.
Down
1,000 feet and deeper, northern elephant seals are only one of the 20 or so
mammals feeding in a dark, cold world. Blainville’s beaked whales are one of
the others that dive deep to hunt. As cetaceans, they are very different from
seals, but the deep ocean is one of the largest ecosystems on earth and offers
many ecological niches. Different diving and foraging strategies allow them to
exploit various prey.
Although
you are familiar with the northern elephant seal, Blainville’s beaked whale is
less well known. This paper will introduce
you to Blainville’s beaked whale and compare the foraging behaviors of these
two deep diving mammals.
Blainville’s beaked whale: These small whales are 15 to 20
feet long, weigh 1,800 to 2,300 lbs., and are dark gray or brownish blue, with
a small dorsal fin. The males grow tusk-like teeth that point forward. Not
much research has been done on these whales, as their small population ranges
across oceans where they are hidden from human view. They live in small social
groups, three to seven or perhaps as many as twelve individuals. Cookie-cutter
sharks often scar adults. Males often have long scratch scars, suggesting
violent competitive courtship, but no one knows
for
sure. They are usually sighted in waters 1,600 to 3,300 feet deep near deeper
chasms. They use echolocation to find
their prey.
Beaked
whales, although considered toothed whales in contrast to baleen whales, have
hardly any teeth. Little is known about them. Most research is based on rare
examples of carcasses that wash up on beaches.
All
deep divers have to balance the amount of energy it takes to dive down and find
prey against the amount of nourishment they get from the dive. Prey species in
shallow water have a good oxygen supply, move fast and can escape. Species that
live deep, in the dark, with less oxygen, move more slowly and are easier to
catch.
Blainville’s beaked whales forage on
tropical and sub-tropical continental slopes associated with oceanic islands,
submarine canyons and seamounts. They are one of 22 species of beaked whales,
several of which reside or migrate along our central California coastline. For
this paper,1 the researchers looked at the resident population of
whales living around El Hiero in the Canary Islands off Africa.
Whales
use echolocation to find their prey in the dark, different from elephant seals that
rely on seeing bioluminescent prey or detecting prey movements in the water
with their whiskers (vibrissae). Blainville’s beaked whales have two
distinctive kinds of clicks to help them succeed: search clicks while they are
foraging and buzz clicks in the final stage of capturing the deep-water squid,
crustaceans and fish that are their prey.2
To
gather information about how the whales hunt, the researchers used tags that
recorded the sounds the whales made as they hunted, as well as the time and
depth of the dives.
Foraging
dives for these whales are as deep as 1,600 to 4,400 feet (mean 2,700 feet), and
as long
as 23
to 65 minutes (mean 48 minutes). They produce distinct clicks while searching
for prey, and change to buzzing as they attempt to capture prey and eat. They
dive silently down about 1 to 11 minutes (mean 4 minutes), reaching a depth of 550
to 2,900 feet (mean 1,400 feet) before they start clicking to look for prey.
They spend 9 to 38 minutes hunting (mean 24 minutes), buzzing to catch
prey 4 to 53 (mean 27) times and then silently swim back to the surface, taking
9 to 35 minutes to get there (mean 19 minutes).
If the
observed dives are typical, these whales are able to catch a days’ worth of
food in eight hours of foraging. They spend a third of their lives
performing foraging dives, and only half of that time is spent actually hunting
and catching prey. While the hunting phase of the whale’s dive is distinctly
marked by its clicks, for the elephant seal it is the horizontal motion, or rapid
up and down motion, after a long descent that separates the transit phase of a
dive from the hunting phase.
Northern
elephant seals range farther and dive deeper in different habitat. They are not
considered resident in any part of their range across the northeast Pacific
Ocean. Their dives are separated into four types (Figure 5): active-bottom,
especially around the deep scattering layer; flat-bottom (ocean floor
foraging); drift dives (food-processing/rest), and v-shaped (transit) dives.
Transit dives are used to get the seal to and from foraging areas, or between
those areas. Elephant seal dives
typically last 20-30 minutes. Dives up
to 2 hours have been recorded. 3
There are three major ocean zones
that are of interest when studying Blainville’s beaked whale.
1.) The Deep Scattering Layer (DSL)
is a layer of living organisms, fish and zooplankton so dense that it
scatters sound waves used to detect the ocean bottom. These organisms migrate
vertically up toward the surface at night and sink down during the day,
creating a shifting
depth
of what early researchers thought was the ocean bottom. During the day the DSL
is a discrete and dense layer, consisting mostly of small (1-6 inches long)
organisms, located at depths between 1,300 and 2,600 ft., while at night the
more active species in the DSL disperse upwards to forage. The dives of female elephant seals are
observed to follow the elevation of the DSL.
2.) The Benthic Boundary Layer (BBL) extends from the sea floor to some
600 ft. above it. It holds most of the
biomass in abyssal waters (3,300–11,000 ft. depth) and typically comprises
species with low locomotor capacity. Male
elephant seals appear to forage the BBL very near the ocean floor. 3.) The
Oxygen Minimum Layer (OML) is the zone of lowest oxygen, a limiting factor for
aerobic life. The OML is a region usually dominated by organisms with
low metabolic rates as an adaptation to the low oxygen concentration in the
water.
Deducing from the angle they
descend and the depths they hunt, scientists conclude the whales are hunting in
two of these major biological areas: the lower part of the DSL, and the BBL. The whales are able to find prey
in both locations, even on a single dive. They are probably hunting for slow
species associated with the deeper part of the DSL and along the sea floor. They
don't chase their prey far, and are able to catch about 30 per dive. They dive
past the fast-moving prey close to the surface and pick up the slower ones
deeper down.
The
echoes of the sounds they made allowed the researchers to figure out how far
from the bottom the whales were hunting. They begin their echolocation clicking
above the DSL and sometimes continue foraging at moderate depths before heading
down the continental slope around the island. This kind of steep slope is
habitat to rich concentrations of sea floor and open ocean fish and
cephalopods. These resident whales have found a stable and abundant resource
that gives them a secure ecological niche.
Northern
Elephant Seals and Blainville's Beaked Whales are very different critters that
inhabit the depths. Whales hunt with echolocation, seals by sight and
motion. They forage in different parts of the ocean, but both dive deep to
hunt, in a dark, cold environment that is as strange as another planet.
Seals spend much more of their time at sea hunting than do the whales,
but it would be interesting to see how the two would compare if an "hours
hunting per year" calculation were made.
Recent
studies of Cuvier's beaked whales give one of them the record for longest (2
hours 17 minutes) and deepest (almost two miles) mammalian dives.
Although
little is known about species such as the Cuvier's beaked whale, initial
research finds them in every ocean except the polar ones. Perrin's beaked whale
was identified in 2002, and thus far found only along the California coast
between San Diego and Monterey.
NES are
better researched than any of the rare and elusive beaked whales. The limited
research on these whales tends to be in coastal areas, simply because it's more
accessible; research could be biased toward coastal populations. Exactly where
beaked whales live and how they use their range for feeding, mating and other
life cycle activities is largely unknown.
Because they
depend on echolocation for social communication as well as foraging, any
interference with their ability to echolocate has the potential to disrupt
their lives. Increased seismic blasts and sonar use have been associated with
beaked whale stranding. Tagging to learn more about whale and seal lives can
help find ways to protect them.
Elephant
seal docents are experienced ocean and coastal observers. If you find a beaked
whale washed up on the beach, report it to The Marine Mammal Center and file a report with the Beaked Whale Resource.
References:
1.
Arranz P, de Soto
NA, Madsen PT, Brito A, Bordes F, et al. (2011) Following a Foraging
Fish-Finder: Diel Habitat Use of Blainville’s Beaked Whales Revealed by
Echolocation. PLoS ONE 6(12): e28353. doi:10.1371/journal.pone.0028353, http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0028353
2.
Foraging
Blainville's beaked whales (Mesoplodon densirostris) produce distinct click
types matched to different phases of echolocation
3.
Condition and
mass impact oxygen stores and dive duration in adult female northern elephant
seals, J. L. Hassrick, D. E. Crocker, N. M. Teutschel, B. I. McDonald, P. W. Robinson, S. E. Simmons and D. P. Costa, http://jeb.biologists.org/content/213/4/585.full
Cuvier’s beaked whales hold
their breath longer, news story, http://www.bbc.com/news/science-environment-26743090
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