[MARMAM] MMS report available - sperm whale study

Dagmar Fertl dfertl at geo-marine.com
Fri May 25 19:42:46 PDT 2007


The following is recently released by the Minerals Management Service and
might be of interest to listserve subscribers. 

 

Palka, D. and M. Johnson, eds. 2007. Cooperative research to study dive
patterns of sperm whales in the Atlantic Ocean.  OCS Study MMS 2007-033. New
Orleans, Louisiana: Gulf of Mexico Region, Minerals Management Service.

 

It can be downloaded (3 mb) for free at:

 

http://www.gomr.mms.gov/PI/PDFImages/ESPIS/4/4247.pdf

 

Executive Summary:

 

The National Marine Fisheries Service (NMFS) is required to produce stock
assessments for all marine mammal stocks within the U.S. Exclusive Economic
Zone. The Minerals Management Service (MMS) is evaluating potential
environmental impacts of offshore oil and gas activities on marine mammals.
Both agencies have a need for similar information on sperm whales and this
is the basis for the cooperative research outlined here. This study,
conducted in July 2003, has started a baseline of line transect,
photo-identification, oceanographic and genetic data for the Atlantic sperm
whale. Compared with the Delta region in the Gulf of Mexico, parts of the
Atlantic Ocean may serve as a control population of sperm whales with little
exposure to sounds of oil and gas related activities. A total of 12 sperm
whales were tagged during the four-week, July 2003 cruise yielding a
substantial data set spanning both deep foraging and socializing from 9 of
the 12 tagged animals. These tag recordings represent the first acquisition
of sound and movement data from sperm whales in the North Atlantic. Visual
and acoustic surveys were performed whenever weather permitted throughout
the cruise and visual focal follows were made when tags were deployed.
Complimentary data products included physical oceanographic measurements and
skin and fecal samples from tagged and neighboring whales. The tag data set
from the cruise has been examined using techniques developed on the Sperm
Whale Seismic Study (SWSS) program to parameterize foraging and social
behaviors. The data set has also been integrated into a combined data set
covering the Gulf of Mexico, North Atlantic and Mediterranean seas to enable
comparative analyses. We found that the North Atlantic whales follow a
foraging and socializing cycle similar to the Gulf of Mexico whales but dive
significantly deeper to forage. Foraging largely occurs at 500-1,100 m but a
small amount of food may be taken in water as shallow as 300 m. A wide range
of codas was produced but even fairly closely located groups appeared to
prefer distinct codas.

 

An unusually high rate of breaching, possibly associated with tag
attachment, limited the longevity of the tag attachment. The maximum
attachment duration of six hours in this Atlantic Ocean study compares
unfavorably with 16 hours in the Gulf of Mexico and Mediterranean. The
unknown reason for why there were few long attachments may reduce the number
of future successful tagging events from whales in the Atlantic. Breaching,
possibly associated with tag attachment, has been observed in other areas,
and those breaching rates varied from year to year. So, perhaps this first
year in the Atlantic is just on the high side of the inter-annual
variability. Further work is needed to address this. In addition, there are
areas in the Atlantic, such as off Virginia, where there are, at times, a
substantial amount of low frequency impulsive sounds from underwater
explosions in Navy test ranges. Such times and areas should not be
considered as a future controlled exposure study area. Acoustic data could
potentially be used in two ways to improve the sperm whale abundance
estimates. One way is to utilize both visual and passive acoustic detections
to estimate the abundance. A new project to advance development of such
methods was recently funded. The visual and acoustic data collected during
the Search Mode in this cruise will be used as a test case. Another way
acoustic data could be used to improve visual line-transect abundance
estimates is to use the dive time pattern data collected on the acoustic tag
(DTAG) in surfacing-based line-transect analysis methods. If we assume the
tagged animals are representative of the dive patterns of the Atlantic
population, then there is a 27% (CV=0.46) chance that a single sperm whale
is at the surface to be able to be detected by a visual sighting team. A
simple implementation of using these dive data is to estimate total
abundance of sperm whales as a function of (i) the abundance using standard
visual line-transect methods, assuming this is an abundance estimate of
surface animals and (ii) the percentage of time whales are at the surface
using the tag data. Using this over-simplified method the dive time
corrected total abundance of sperm whales would then be 14,922 (CV=0.60),
which is about 3.5 times greater than the standard visual abundance
estimate. However, this abundance estimate is biased upwards due to the
facts that the standard abundance estimate is based on detection of groups
of whales, where groups are usually greater than one, while the probability
of a whale being at the surface using the tag data is based on singleton
whales, and individual sperm whales do not dive totally independent of the
other animals in its group. Thus, surface-based, not group-based,
line-transect analysis methods are required to properly account for the
confounding facts. These methods are explained in this report and are under
development, thus results are not currently available. Another objective of
this and the SWSS cruises is to address the question "Do sperm whales have
preferred habitats that can be defined physiologically and/or with
oceanographically?" One way to address this is to model the distribution and
abundance of the sperm whales with respect to physical and biological
parameters, such as water depth, bottom slope, sea-surface temperature,
salinity at the surface, mixed layer depth, surface color (primary
productivity), and distribution and abundance of other trophic levels (such
as that obtained from bongo samples). Such a model can also include nuisance
variables, such as Beaufort sea state, which affects the sightability of the
whales, but probably does not affect the actual distribution of the whales.
To start this process, five-day composites from the middle of the cruise of
sea surface temperature (SST) and chlorophyll-a (chl-a) using satellite
pictures were produced and the sightings were overlaid. Interestingly, sperm
whales appear to be present in more diverse combinations of SST and chl-a
than many of the other cetacean species detected during this cruise. This
could imply that sperm whales are not cueing in on these two parameters,
like some other species do. Or, sperm whales are generalists and so can
utilize a variety of habitats or perhaps sperm whales are not cueing in
ocean surface factors but are cueing on ocean bottom factors. More data are
needed to address this. Because this cruise concentrated on putting tags on
sperm whales and not investigating many type of potential habitats, this
cruise surveyed a limited number of types of potential habitats. However,
the NEFSC conducted a large scale line transect abundance survey in 1998 and
is currently conducting one during the summer of 2004. The plan is to merge
the line transect data of the 1998, 2003, and 2004 surveys to investigate
habitat preferences of sperm whales in the Atlantic. Stepwise selection of
Generalized Additive Models (GAM) will be used to define a model that uses
physical and biological parameters to describe the sperm whale habitat. To
start this modeling exercise, the 1998 data were used to model the
distribution and abundance of sperm whales in five nautical mile sections of
the track line. The stepwise GAM determined depth and an interaction between
two groups of plankton species (groups 2 and 3) were the best predictors for
sperm whale distribution and abundance, where depth was the most influential
factor. Sperm whales were inversely related to Plankton group 3, which are
species generally associated with warm core rings. Sperm whales were
positively related to Plankton group 2, which are species most often
associated with cooler waters, such as those on the outside edge of a ring
or in between warm core rings. Thus, these GAM results can be interpreted as
Atlantic sperm whales are most commonly found in waters approximately 2000
meters deep, when those waters are cool, like those found on the outside or
in between warm core rings.

******************

 

Dagmar Fertl

Geo-Marine, Inc.

2201 Avenue K, Suite A2

Plano, Texas 75074 USA

972-423-5480

FAX 972-422-2736

dfertl at geo-marine.com

http://www.geo-marine.com

 

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