AMJ 2001 Quarterly Rpt. AMJ 2001 sidebar
|
(Quarterly
Report for April-May-June 2001)
Figure 1. Cruise track for the Steller sea
lion research cruise aboard the chartered fishing
vessel Big Valley, 19-29 May 2001.
Cruise
Continues Effort to Estimate Steller Sea Lion
Survival and Study Food Habits
Personnel from the National Marine Mammal Laboratory
(NMML) conducted a Steller sea lion (Eumetopias
jubatus) research cruise in the Gulf of Alaska
from 19 to 29 May 2001. The primary cruise
objective was to search for sea lions marked and
tagged as pups to improve estimates of survival,
with a secondary objective to collect scats for food
habits studies. Each of the 29 known rookery
and haul-out sites in the Kodiak Archipelago,
Shelikof Strait, and Kenai Peninsula areas were
visited (Figure 1 above). Nine of the sites
were occupied by 100 or more sea lions, 13 were
occupied by 10-100 sea lions, and 7 were unoccupied.
We resighted 39 of the 258 pups branded at
Sugarloaf Island and Marmot Island rookeries in July
2000, and 6 of 12 young-of-the-year and juvenile sea
lions that had been captured at Long and Sea Otter
Islands near Kodiak in March 2001. We also observed
three animals with plastic flipper tags. One
observed at the Ushagat (southwest) haulout in the
Barren Islands had been tagged as a pup on Atkins
Island, 325 nautical miles (nmi) (600 km) to
the southwest, on 28 June 2000. Another at
Shakun Rocks in northern Shelikof Strait had been
tagged as a pup on Chirikof Island, approximately
185 nmi (340 km) to the southwest, on 29 June 2000.
A total of 71 scats were also collected for
food habits analysis. Other marine mammal sightings
during the cruise included about six fin whales at
Uyak Bay on the west side of Kodiak Island; three
fin whales off the southwest side of Takli Island in
Shelikof Strait, hundreds of humpback whales on the
morning of 24 May off the Barren Islands; and
hundreds of unidentified large whales off the east
side of Kodiak Island, especially between Cape
Chiniak and Cape Barnabas. Also, four killer whales
were observed at the Cape Sitkinak sea lion haul-out
site. The whales cruised past the haulout
several times, but with no apparent interest or
interaction between sea lions and whales.
By John Sease and Brian Fadely.
Aleutians Passes Cruise:
Killer Whale Component
Introduction
The decline of Steller sea lions in the central and
western areas of the North Pacific Ocean and the
Bering Sea has precipitated a number of research
projects seeking to investigate possible causal
factors. One of these, the Aleutians Passes
Project, has two fundamental goals: 1) examination
of productivity near sea lion rookeries and haulouts
and 2) documentation of the number and ecotype of
killer whales (Orcinus orca) in waters
between Unimak and Seguam Passes in the central
Aleutian Islands chain. This project combines
a suite of oceanographic and biologic measures to
examine productivity. Standard hydrographic
measurements (conductivity-temperature- depth (CTD)
and sea surface temperature (SST)), nutrient
availability and primary production, zooplankton
prey field assessment (acoustic and prey capture),
and spatial pattern and relative abundance of
seabirds and marine mammals are all used to
determine specific and relative productivity within
the study area. The number and ecotype of
killer whales are investigated using standard
photoidentification methods and the collection of
biopsy tissue samples for isotopic analysis. Preliminary
results of the first field season of killer whale
observations are presented here.
Methods
Marine mammal surveys were conducted from 4 to 24
June 2001, beginning and ending in Seward, Alaska.
The study focuses on the relative
productivity and occurrence of killer whales at four
Aleutian Islands passes: Seguam, Amukta,
Akutan and Unimak. The passes border Steller
sea lion rookeries and haulouts where populations
are either in decline or holding steady. The
surveys focused on transect lines along and across
the passes (Figure 1 below).
The four passes are distinctly different in
physiography: Seguam—narrow and deep; Amukta—
broad and deep; Akutan—narrow and shallow; Unimak—broad
and shallow. Thus, the four passes provide
a baseline for a suite of comparisons of hydrography
and productivity at dynamic centers of seawater
exchange between the North Pacific Ocean and the
Bering Sea.
Two primary marine mammal observers maintained a
watch from port and starboard sides of the bridge of
the University of Alaska research vessel Alpha
Helix for 12 to 16 hours each day when
conditions were suitable for survey (i.e., Beaufort
<05; visibility > 1 km). Observers at
port and starboard stations searched with naked eye
and binoculars (7X or higher) with reticles. Observers
scanned for 1 hour at each station, followed by a
1-hour break. The two primary observers were
assisted in sighting marine mammals by University of
California at Irvine seabird researchers conducting
surveys from either the port or starboard side
(depending on glare) and by the ship’s crew.
Data were recorded by the starboard observer
using WinCruz software on a laptop computer
interfaced to the ship’s Global Positioning System
(GPS). Positions along the cruise track were
updated at 2-minute intervals. When marine mammals
were seen, bearing and reticle to the sighting,
species, group size (best/high/low estimates) and
the animals’course and speed were recorded. During
transit to the study area, only killer whales were
approached for photographs. All other sightings were
recorded in passing mode. After reaching the
study area, other cetaceans were sometimes
approached for positive identification.
When killer whales were seen within the study area,
the marine mammal team moved to the bow of the Alpha
Helix to photograph whales as the ship
maneuvered as close to the whales as possible.
During calm sea conditions, a rigid hull inflatable
boat (RHIB) was deployed to provide close access to
whales for high-quality photographs and biopsy
attempts. Whales were approached from behind on
their left sides to obtain standard identification
photographs of their dorsal fins and saddle patches.
On two occasions, close approaches were made from
the RHIB to obtain biopsy tissue samples using a
crossbow to deliver a hollow-tipped dart. A
tissue sample was obtained on the first occasion; on
the second occasion the whales proved elusive.
Attempts were made to biopsy individuals that were
distinctive, but this was not accomplished due to
the tight spacing of the whales. The tissue biopsy
was split into two samples: a skin sample, stored in
DMSO for DNA and isotopic analysis; and a blubber
sample, frozen for analysis of contaminants. Attempts
to biopsy whales were limited by several factors. At
times when oceanographic work was not under way, sea
conditions limited work from the RHIB to two
occasions. Also, emphasis was placed on obtaining
identification-quality photographs prior to biopsy
attempts, which were made at the end of encounters
when whales were more difficult to approach closely.
Figure 1. Map of killer whale sightings during
Aleutian Passes cruise, 4-24 June 2001.
Provisional Results
A total of 265 hours of survey for marine mammals
was completed, including transit to (81.5 h) and
survey in (183.5 h) the study area. Viewing
conditions were usually good to excellent, with
little disruption to surveys by rain or fog. Ten
marine mammal species were seen, with Steller sea
lions the most common pinniped seen when animals
hauled out on land were included. Dalls porpoise (Phocoenoides
dalli) were the cetaceans most often seen.
Fin whales (Balaenoptera physalus) were
seen during transits to and from the study area, but
not in the study area. Regions of high fin
whale sighting rates included waters near the Semidi
Islands on the outbound leg and at the Shumagin
Islands on the return passage. Fin whales
usually were seen in groups of 2-10 whales and were
often near humpback whales (Megaptera novangliae),
although the two species did not appear to interact.
Although seen with fin whales, humpbacks were
also seen as singletons and pairs, often along the
coast or near islands. Minke whales were seen
as singletons throughout the cruise, with two to
three animals that seemed resident in Akutan Pass.
Although ubiquitous, Dalls porpoise were
particularly common near Samalga Pass, where counts
were an order of magnitude higher than in any other
region. Surprisingly, sperm whales (Physeter
macrocephalus) were common north of Seguam
Island and in Seguam Pass, but were not seen
elsewhere.
Killer Whale Encounters and
Sightings
Twenty sightings were made of a total of 295 killer
whales over the course of the cruise (Figure
1 above). Fifty killer whales were
seen as the ship was departing Seward with the
remaining 245 whales seen in the study area. Overall,
when best and high estimates of group size were
tallied, the number of killer whales seen ranged
from 295 to 332 for the cruise and from 245 to 276
whales for the study area. These provisional
counts likely under-represent the total number of
animals because the counts made in transit are
probably low. There was a hiatus of sightings
between the Kenai Peninsula and Unimak Pass, both
going to and returning from the study area.
There were 10 encounters with killer whales when the
cruise schedule permitted approach and focused
efforts to obtain identification photographs, and 10
sightings where counts-only were obtained while the
ship was in transit (Table
1 below). Fifty-five rolls of black and
white film and three 90-minute digital video tapes
were shot during the 10 encounters. Each
encounter usually began with the sighting of a
comparatively small group of animals (two to five
whales, often including one adult male), but after
approach of the first identified animals additional
whales were usually seen. The first two
encounters occurred as the ship was leaving Seward
and likely were whales in the area known and
photographed by Alaskan researchers during the past
10-15 years. The remaining eight encounters occurred
in the study area at locations ranging from Seguam
to Unimak Passes.
Killer whales were often seen in regions where they
were photographed during surveys conducted in 1992
and 1993, including Makushin Bay along the north
coast of Unalaska Island, where the largest group
was encountered. Waters southwest of Unimak
Pass and north of Seguam Island also appeared to be
areas of concentration for killer whales. While
there was no concerted attempt to cross-match killer
whales seen to those photographed in the study area
in 1992 and 1993, at least four whales (AK 160-163)
appeared to be individuals photographed during the
earlier surveys. In addition, several males
had very distinctive dorsal fins that should aid in
group identification on surveys scheduled later this
summer.
Table
1. Aleutians Passes Cruise: Killer
Whale Encounters and Sightings. (DES =
digital echosounder, * =
encounter truncated) |
Date |
Encounter
Number |
Location |
Number
Whales |
Number
Photos |
4
June |
1 |
Resurrection
Bay |
12-14 |
1
roll + |
4
June |
2 |
Gore
Pt/S. Kenai Penin. |
38-42 |
6
rolls |
7
June |
Sighting |
Kres
#1 - Kres #2 DES tow |
1
B male |
None |
7
June |
3 |
Krenitzin
Island |
42-46 |
15
rolls |
9
June |
4 |
NW
Seguam Island |
34-38 |
8
rolls |
10
June |
Sighting |
Seguam
Pass/CTD line |
8 |
None |
11
June |
5 |
NW
Seguam Island |
4 |
2
rolls |
11
June |
6 |
Seguam
Pass |
7 |
1
roll |
11
June |
Sighting |
Seguam
Pass/DES tow |
2 |
None |
13
June |
*7 |
Seguam
Pass |
22-25 |
4
rolls |
13
June |
*8 |
NW
Umnak Island |
5-6 |
2
rolls |
13
June |
Sighting |
N.
Umnak Island/DES tow |
10-12
(min) |
None |
14
June |
Sighting |
N.
Akutan Pass/CTD line |
4 |
None |
14
June |
Sighting |
Akutan
Pass/CTD line |
1
male |
None |
15
June |
Sighting |
N.
Akutan Pass/CTD line |
5 |
None |
15
June |
9 |
Unalaska
Bay B Dutch |
18-22 |
4
rolls |
17
June |
10 |
Unalaska/Makushin
Bay |
50-55 |
12
rolls |
17
June |
Sighting |
N.
Akutan Island |
15-18 |
None |
18
June |
Sighting |
Unimak
Pass/CTD line |
12-15 |
None |
18
June |
Sighting |
Unimak
Pass/CTD line |
5-7 |
6
frames |
Total
|
10
Encounters |
295-322 |
55
rolls+ |
10
Sightings |
245-276 |
6
frames |
Killer
Whale Predation
We witnessed no attacks by killer whales on marine
mammals, nor did we see killer whales near Steller
sea lion haulouts. We did see killer whales
swimming near Dalls porpoise on two occasions, and
on one instance a large male made a lunging leap
that seemed directed at the porpoise. On both
occasions we were in passing mode and did not watch
the encounter in detail. Thus, no conclusions should
be drawn from these observations other than killer
whales may have been pursuing Dalls porpoise. In
Unimak Pass, three humpback whales near Akun Island
were seen repetitively flipper-slapping as a killer
whale group passed them and one male turned back for
a closer approach. Again, no attack was
witnessed. While fish eating by killer whales could
not be determined with certainty, whales encountered
north of Seguam Island (Encounter 3 or 4) (Table 1
above) appeared to be feeding on fish, as determined
by the ship’s echosounder.
By Sue Moore.
Cook Inlet Beluga Whales,
June 2001
Beluga whales in Cook Inlet, Alaska, have been the
center of scientific, management, and media
attention for several years (see AFSC
Quarterly Report, Oct-Dec 2000 issue).
The NMFS has conducted systematic aerial
surveys of all coastal areas within the inlet and
tracklines across the inlet each June or July since
1993. Data from these surveys have shown a gradual
decline in distribution, with fewer sightings in the
southern part of Cook Inlet and a drop in abundance
(from 653 animals in 1994 to 347 in 1998) until
1999, when Native Alaskan groups stopped hunting
belugas, based on concerns for the population.
Since then, abundance has been estimated to be
367 animals in 1999 and 435 in 2000, suggesting that
the decline has halted or reversed.
The number of whales taken by Native hunters was
well correlated to the evident decline in abundance.
NMFS considered this sufficient evidence such
that, in May 2000, the small, isolated stock was
designated as Depleted under the Marine Mammal
Protection Act, providing a legal mechanism for NMFS
to regulate the harvest. Habitat degradation
in Cook Inlet was also considered, because Anchorage
(the biggest city in Alaska), several military
bases, petroleum extraction, and sewage outfall
occur in northern areas of the inlet. However,
NMFS found little evidence to support loss of
habitat as a mechanism of decline in this case, thus
habitat protection through the Endangered Species
Act was not considered necessary to the recovery of
the Cook Inlet stock at the time.
Figure 1. Aerial survey effort and beluga
groups seen in Cook Inlet during flights conducted
5-12 June 2001. All but two whales (found near
Homer) were near river mouths or in shallow coastal
waters of the northern part of the inlet. The
survey covered all coastal areas and 1,186 km of
offshore waters. The northern part of the
inlet was surveyed six times, but only one
representative trackline is shown here.
Continuing the annual surveys of
Cook Inlet is a major priority of the NMML beluga
project. NMFS conducted aerial surveys from 5 to 12
June 2001 (55 flight hours) including six passes
covering coastal areas of the northern part of Cook
Inlet, where almost all belugas have been found in
recent years, as well as the southern part of the
inlet and 1,186 km of offshore transects (Figure 1
above). The project used the same aircraft (an
Aero Commander), research protocol, and observers as
used in most of the past 9 years. Viewing
conditions were generally good to excellent. Except
for two beluga whales observed near Homer (the first
for this project since 1994), all whales were found
in a few primary areas in bays or near river mouths
around the northernmost parts of the inlet
(especially the Susitna Delta, Knik Arm, and
Chickaloon Bay/Turnagain Arm). This distribution is
consistent with distributions documented
across the past three decades. The index
count, based on medians of multiple counts of the
groups encountered, was 211 in June 2001. This
is below index counts for years prior to 1998 (305
in 1993, 281 in 1994, 324 in 1995, 307 in 1996, and
264 in 1997), but the 2001 count is essentially the
same as counts made during the past 3 years (193 in
1998, 217 in 1999, and 184 in 2000) (Figure 2
below). Abundance estimates—corrected for missed
groups, whales below the surface, and surfacings not
seen—are typically 1½ to 2½ times the index
counts: 653 (CV = 0.43), 491 (CV = 0.44), 594
(CV = 0.28), 440 (CV = 0.14), 347 (CV = 0.29), 367
(CV = 0.14), 435 (CV = 0.23) in 1994-2000,
respectively.
Figure 2. Median and maximum counts of belugas
in Cook Inlet, Alaska, made during aerial surveys
each June/July 1993-2001. These index counts
are not corrected for missed whales, but they do
indicate a decline in numbers until 1999 when the
subsistence hunt stopped.
By Dave Rugh and Rod Hobbs.
Calculating the Haul-out
Proportion of Alaska Harbor Seals
The proportion of harbor seals that are hauled out
and, thus, available to be counted during aerial
surveys varies as a function of environmental
covariates, such as date, time of day, tidal state,
and weather. In recent studies we estimated
the number of harbor seals that would have been
counted during an aerial survey of the Gulf of
Alaska in 1996, if all sites had been surveyed under
ideal conditions. We conducted a separate analysis
of harbor seal haul-out behavior to estimate the
proportion of seals that would have been at sea
under ideal conditions (and, therefore, not
available to be counted). We monitored the
haul-out behavior of 112 radio-tagged harbor seals
from radio signals recorded remotely at four Alaskan
haul-out sites (Grand Island in 1994, Cordova in
1995, Pedersen Glacier in 1998, and Cape Peirce in
2000). For each site, we created a statistical
model of the proportion of seals hauled out as a
function of environmental covariates. Using
these models, we identified the environmental
conditions that would result in the greatest
proportion of seals hauled out. Although those
ideal conditions differed between sites, the
proportion of seals predicted to be hauled out under
those conditions was consistent (84%) at the two
sites we believed to have representative data, Grand
Island and Cape Peirce. We are drafting a
manuscript which describes the haul-out behavior
models, combines the results from adjusting survey
counts and haul-out proportions to ideal
environmental conditions, and estimates the
population size of harbor seals in the Gulf of
Alaska in 1996.
By Mike Simpkins.
Harbor Seal Haul-out
Behavior and Movements in Tidewater Glacial Fjords
Biologists from NMML and the Alaska Department of
Fish and Game (ADF&G) continued a study on the
haul-out behavior and movement of harbor seals using
tidewater glacial fjords in Southeast Alaska. Because
tidewater glaciers attract some of the highest
concentrations of harbor seals recorded in Alaska,
an initiative is under way to more fully understand
the ecology and site fidelity of seals that use the
floating ice during their annual cycle. Data
collected on daily haul-out patterns and habitat use
will provide biologists greater confidence in
estimating seal abundance and will also provide
insight into why seals aggregate in such large
numbers on glacial ice. As in 1999, the study
focused on two fjords–Tracy and Endicott
Arms–located approximately 80 km south of Juneau.
Seal captures and instrument deployments were
completed in two phases: 19-30 April from the NOAA
ship John N. Cobb and 26-31 May from the U.S.
Fish and Wildlife Service vessel Curlew and
the John N. Cobb. Of the 20 animals
captured, 15 were fitted with both VHF head tags and
time-depth recorders (TDRs) and 5 with VHF flipper
tags. The head tags and TDRs will fall off
during the seals’ annual molt, which begins in
early August. The TDRs were equipped with radio
beacons and will be recovered using aerial and boat
reconnaissance. In contrast to 1999, when all
instruments were deployed in Tracy Arm, 16 of 20
instruments this year were deployed in Endicott Arm.
Radio monitoring stations were deployed near
the glaciers at both Tracy and Endicott Arms and
near the fjords’ shared mouth to record when seals
were hauled out on the floating ice and to track
movements in and out of the fjords. These
stations are being serviced regularly and will
continue collecting data until the end of the
molting season. The NMML and ADF&G also
collaborated with the University of Alaska in Juneau
(UAS) to conduct direct observations of seals from a
land-based camp in Tracy Arm. The camp was
occupied for about 6 weeks from late May to early
July. The primary goal of the study was to test
several methodologies for quantifying potential
interactions between seals and tour vessels, which
make daily excursions through the ice field at Tracy
Arm to view the glacier.
By John Jansen, Dave Withrow, and Jack
Cesarone.
Harbor Seal and Cruise Ship
Interactions
Plans are being made to study the potential
disturbance of harbor seals using glacial ice
habitats in Disenchantment Bay, Alaska (40 km north
of Yakutat), in a collaborative effort by NMML, the
ADF&G, and the Yakutat Tlingit Tribal Council.
The 2-3 year study will be supported by the
Northwest Cruise Association (NWCA) through an
agreement with the Yakutat Tlingit Tribal Council.
There is concern about possible impacts of
vessel traffic on harbor seals, particularly during
the pupping period, which coincides with the onset
of the tour vessel season. An average 1-2 NWCA
vessels enter the bay daily between mid-May and mid-
September; the frequency of smaller boat traffic,
such as charters, appears to be negligible, with two
or fewer visits per week. To aid in the study
design, a NMML biologist visited Yakutat in mid-June
to learn about the area and concerns from the tribal
elders, to evaluate ideas for potential study
designs, and to develop the logistical
considerations for implementing field work next year
such as seal and ice distributions, ship- or
land-based observation points, and vessel traffic
corridors. A study proposal will be completed
by December 2001, with the study anticipated to
begin early spring 2002.
By John Jansen, Dave Withrow, and John Bengtson.
Up
|