Northeast Fisheries Science Center Reference Document 06-04
Mortality and Serious Injury Determinations
for Baleen
Whale Stocks along the Eastern Seaboard
of the United States,
2000-2004
by by Tim Cole1,
Dana Hartley2,
and Mendy Garron2
1National Marine Fisheries Serv.,
166 Water St.,
Woods
Hole, MA 02543
2National Marine Fisheries Serv., Three Heritage Way, Gloucester,
MA 01930
Print
publication date April 2006;
web version posted April 10, 2006
Citation: Cole T, Hartley D, Garron M. 2006. Mortality and Serious Injury Determinations for Baleen Whale
Stocks Along the Eastern Seaboard of the United States, 2000-2004. US Dep Commer, Northeast
Fish Sci Cent Ref Doc. 06-04; 18 p.
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ABSTRACT
The
Northeast Fisheries Science Center has developed protocols for determining
large whale serious injuries and human-caused mortalities. This
report describes determinations made for right, humpback, fin, sei,
blue, minke and Brydes whale events that occurred from 2000 through
2004 along the eastern seaboard of the United States. A total
of 417 unique large whale events were reported during the period, including
both carcasses stranded on beaches and sighted at sea. These
included 171 entanglement reports and 42 reports of ship strikes. We
were able to verify 147 entanglement events, 29 ship strikes, and 276
mortalities. Entanglements were identified as the cause of 27
whale deaths and ship strikes the cause of 21. Entanglements
were determined to have caused serious injury in 18 events. Minke
whales had the greatest number of entanglement mortalities (12). Humpback
whales had the highest number of serious injury events resulting from
entanglements (11) and the most incidents of ship strike mortalities
(7). Right whales had six mortalities from ship strikes and fin
whales had five. No serious injuries resulting from ship strikes
were confirmed for any species. These human-caused mortality
and serious injury rates represent the minimum levels of impact to
these stocks. Procedures and methods for estimating actual serious
injury and mortality rates have yet to be developed.
INTRODUCTION
As part of the 1994 amendments to the Marine Mammal Protection
Act (MMPA), the NOAA National Marine Fisheries Service (NMFS) was mandated
to establish monitoring programs to obtain statistically reliable estimates
of incidental mortality and serious injury of marine mammals taken during
commercial fishing operations. The Agency was also charged with
developing Take Reduction Plans (TRPs) to reduce commercial takes of
strategic stocks of marine mammals below the Potential Biological Removal
(PBR) levels specified in the TRPs within six months after TRP implementation. The
longer-term goal of all the TRPs is to reduce -- within 5 years of implementation
-- commercial takes and serious mortality of marine mammals to insignificant
levels approaching zero mortality and serious injury rates.
In April 1997, NMFS convened a Serious Injury Workshop to develop
a consistent set of guidelines for determining what constitutes a serious
injury (Angliss and DeMaster 1998). Although the Workshop
produced a set of recommendations, implementation of a national serious
injury standard has not yet occurred.
Nonetheless, NOAA Fisheries staff and Scientific Review Group (SRG)
members decided to take account of serious injuries in the annual marine
mammal stock assessment reports (SAR). Subsequently, the Northeast
Fisheries Science Center (NEFSC) implemented the Workshop’s large
cetacean recommendations and prepared serious injury determinations
for the SARs.
This report presents the protocols and determinations for events involving
right, humpback, fin, sei, blue, minke and Brydes whales during 2000 – 2004. Determinations
for these species during 1999 – 2003 are presented in Cole et
al. (2005).
METHODS
Marine
mammal strandings and human-induced interaction events were recorded
and submitted to the NMFS Northeast Regional Office (NERO) and Southeast
Regional Office (SERO) by members of the National Stranding Network,
large whale disentanglement teams, the U.S. Coast Guard and civilian
sources. The Regional Offices identified and obtained all available
information for each event (photos, necropsy reports, etc.) and placed
these in a central folder for each event. Case files were compiled
for all individually identified whales with injuries. Several NEFSC
and NERO staff were involved in reviewing event records, confirming each
event’s occurrence and the species involved, identifying duplicate
records and consolidating unique information from each source into a
single record for each event. Information from additional sightings
of a previously documented event was added to the original event record. If
an identified whale was involved in a second interaction, a new event
record was assigned. The NEFSC staff then reviewed each mortality
event and assigned a cause of death following the confirmation criteria
listed below. Each injury event was similarly examined for indications
of cause, and identified as a serious injury if it was likely to lead
to the whale’s death. One staff member (TVC) reviewed all
determinations each year to ensure consistency within and across years.
Event and Species Confirmation Criteria
Events and the species involved were considered confirmed if they meet
one of the following criteria:
- The event was observed by a trained marine mammal observer who
was certain of the species or event;
- The event was observed by a trained member of the Disentanglement
Network and the species or event was verified via interview by NMFS,
disentanglement or stranding network staff;
- The observer was inexperienced, but the report was accompanied
by photographs or videotape of sufficient quality to positively verify
the species or event;
- A fisherman reported a whale entangled in his/her gear or a shipper
reported colliding with a whale;
- Gear was retrieved from a whale.
Events and the species involved were considered confirmed
in the following less certain cases:
- The observer was experienced and was
fairly certain, but not positive, of the species or event;
- The observer
was inexperienced, but was interviewed and the account was descriptive
enough that the species or event was probable but not certain;
- The report was accompanied by poorer quality photographs
or video, and staff reviewing this material assessed the event as probable
but not certain.
Events or the species involved were considered unconfirmed if:
- The observer was inexperienced
and no photographs or video were taken, and the observer’s
account did not provide sufficient detail to identify the species
or event occurrence;
- The observer
was experienced, but did not see the whale long enough or in good
enough conditions to state the species or event as being probable;
- The
event was photographed or video taped, but staff reviewing the images
could not identify species or the event’s occurrence;
- A carcass
was too decomposed to identify species or to show any indication
of human interaction.
Human-Induced Mortality Determinations
Events were categorized as entanglement mortalities if the following
indications were confirmed to be present during gross inspection or necropsy
of the carcass:
- Fishing line constricted any
body part;
- Subdermal hemorrhaging
or extensive necrosis was present at point of attachment.
Events were categorized as ship strike mortalities if any of the following
indications were confirmed to be present on a carcass:
- Large linear lacerations (anywhere
on body, as opposed to just dorsally as in Kraus 1990);
- Large areas
of subdermal hemorrhaging, hematoma or edema;
- Extensive
skeletal fracturing; or
- A
code 2 (fresh dead) carcass was brought in on the bow of a
ship.
Serious Injury Determinations
Events were categorized as entanglement serious injuries if any of the
following indications were confirmed on a living whale:
- Fishing line constricted any
body part, or was likely to become constricting as the whale grew;
- It
was uncertain if the line was constricting, but appendages near the
entanglement’s point
of attachment were discolored and likely compromised;
- The
whale showed a marked changed in appearance following entanglement,
including skin discoloration, lesions near the nares, fat loss, or
increased cyamid loads;
- Gear
was ingested;
- Whale was anchored.
A whale was typically not considered seriously injured if all constricting
lines were removed or shed.
Events were categorized as ship-strike serious injuries if, following
the appearance of a linear laceration or large gouge, a living whale
exhibited a marked change in skin discoloration, lesions near the nares,
fat loss, or increased cyamid loads.
Injuries that impaired the whale’s locomotion or feeding were
not considered serious injuries unless they were likely to be fatal in
the foreseeable future. No forecasts were made as to how an entanglement
or injury might increase the whale’s susceptibility to further
injury (e.g., from additional entanglements or collisions with vessels).
RESULTS
A
total of 417 events was reported during 2000 - 2004, involving both live
and dead whales (Table 1). There were 171
reports of entanglement and 42 of ship strike. From these, we confirmed
147 entanglement events and 29 ship strike events. We were
able to verify 276 mortalities, and determine that 27 mortalities were
due to entanglements and 21 mortalities were the result of ship strikes. The
cause of death could not be established for the remaining mortalities. Entanglement
was determined to have caused serious injury in 18 events. There
were no records of serious injuries resulting from ship strikes. Annual
human-caused mortality and serious injury rates for 2000 - 2004 are presented
by stock in Table 2. Tables 3-8 provide the details of each
confirmed serious injury or mortality record.
Right whales had the highest proportion of entanglements and ship strikes
relative to the number of reports for a species -- of 54 reports involving
right whales, 29 were confirmed entanglements and 9 were confirmed ship
strikes. Over the five-year period, there were 20 verified
right whale mortalities (Table 1). Three
of these mortalities were due to entanglements, and six were due to ship
strikes. Serious
injury was documented for five entanglement events involving right whales.
Humpbacks were involved in 173 reported events (Table 1). Of these,
74 of the 83 reported entanglements could be confirmed, as could 11 of
the 15 reported ship strikes. Humpbacks were the most commonly
observed entangled whale species and the most commonly observed dead
whale (97 confirmed mortalities). Entanglements accounted for eight
mortalities and 11 serious injuries. Ship strikes were relatively
uncommon, with only 11 confirmed events, seven of which were fatal. Whales
identified as members of the Gulf of Maine stock accounted for five of
the entanglement mortalities, eight of the entanglement serious injuries
and three of the ship strike mortalities (see Table 2, Table 4).
Fin whales had a low proportion of entanglements; of 42 reported events,
nine were of entanglements (all confirmed), three of which were fatal
(Table 1). Eleven ship strikes were reported, five of which were
confirmed and proved fatal. One serious injury resulted from an
entanglement.
Only six events were reported for sei whales, four of which were confirmed
mortalities. Two of the mortalities were determined to have resulted
from ship strikes.
Minke whales were reported in 85 events. Entanglements accounted
for 35 of these events, but only 27 could be confirmed (Table 1). Twelve
of the confirmed entanglement events were fatal, the highest percentage
for any of the whale species. One additional entanglement event
was determined to have caused serious injury. There were only two
ship strike reports, one of which resulted in death.
Blue whales and Brydes whales appeared in only one reported event each. The
blue whale report was a confirmed entanglement in the St. Lawrence River,
Canada, but there was not sufficient information available to confirm
if a serious injury was sustained. The Brydes whale report was
a confirmed entanglement which resulted in the death of the whale.
In 55 of the 417 large whale events reported during 2000 - 2004, positive
species identification was not possible (Table 1). In
seven events, the similarity in body shape and size between fin and sei
whales prevented positive species identification. In another 13,
the whales could only be identified as balaenopteriids based on the presence
of ventral pleats. The taxonomic identity of the whales involved
in the remaining 35 events could not be assigned with any certainty. Entanglement
was reported in 10 of these cases, five of which were considered confirmed. Twenty-six
of the 35 reported events involving unidentified whales were confirmed
mortalities, but the cause of death could not be determined.
DISCUSSION
The
serious injury determinations for Northwest Atlantic baleen whales are
performed annually, immediately prior to completion of the draft Stock
Assessment Report for the next year (i.e., determinations for
animals observed in 2004 were made in late summer 2005 for the 2006 SAR). This
delay helps facilitate careful examination of all available data for
determinations, which are done on a case-by case basis. The same
personnel are used to ensure consistency in the determinations both within
and between years.
Differentiating causal injuries from pre-existing ones or post-mortem
damage is problematic, but can be accomplished through examination of
necropsy data. Necropsies frequently identify subdermal hemorrhaging
or hematomas indicating that blood was still circulating at the time
of injury. McLellan et al. (2004) have provided an excellent
right whale necropsy protocol that should be followed by qualified personnel
when examining carcasses.
In our determinations, fishing line constrictions were considered circumstantial
evidence of pre-mortem entanglement, as these constrictions were likely
the result of force applied by an active animal. Large lacerations
were considered an indication of a pre-mortem vessel collision since
only whales at depth would be exposed to the propellers of a ship.
Events involving constricting entanglements with evidence of the whale’s
deteriorating health were considered confirmed serious injuries. Removal
of constricting gear was generally considered to prevent serious injury. A
whale’s physiological response to tissue damage includes increased
secretion of glucocorticoids, which suppresses lymphocytes and if sustained
(due to chronic destruction of tissue by gear) compromises the ability
of an animal to fight other infections. Therefore, the removal
of gear frees a whale’s immune system resources to combat resident
disease or infection that might otherwise lead to the whale’s death. Loosely
wrapped gear did not appear to elicit as much stress (some whales carried
loose wraps for years), and were not considered serious injuries even
if they impaired the locomotion or feeding of an animal. We also
made no attempt to predict how an entanglement or injury might increase
a whale’s susceptibility to further injury; however, further research
on the fate of individual entangled/injured/impaired animals might provide
information to improve such predictions. Fishing gear interactions may
also generate non-lethal effects, such as impacts to reproduction that
may negatively affect population recovery (Robbins and Mattila 2001a;
Robbins et al. 2004); however, such impacts require further investigation.
However, our greatest concern remains the number of animals we never
saw. There
is currently no reliable method for estimating the number of large whales
that die each year from entanglements, although recovered carcasses provide
minimum values. Scar-based studies suggest that interactions between
whales and fishing gear are common, and that many whales survive those
encounters. Hamilton et
al. (1998) examined photographs of 357 individual right whales and
found that 62% (n = 220) had scars from entanglement, and 124 had been
entangled more than once. Approximately half (48-65%) of Gulf of
Maine humpback whales have been entangled at least once in their life
time, while 8-25% sustain new injuries each year (Mattila and Robbins
1998; Robbins and Mattila 1999, 2000, 2001a, 2001b, 2003, 2004). Although
scar studies generally only provide information on non-lethal encounter
rates, any interaction between a whale and fishing gear has the
potential to be fatal if a constricting entanglement occurs. Humpback
whale scar evidence suggests that only 3-10% of entanglements are witnessed
and reported (Robbins and Mattila 2000, 2004). Thus, whales may
succumb to entanglement before the event can be detected. Negatively
buoyant species are less likely to be detected after death. Right
whales may also become negatively buoyant if an injury precludes effective
feeding for an extended period (Moore et al. 2004).
Vessel collisions frequently lack external evidence, and may not be
detected unless a necropsy is conducted. Knowlton and Kraus (2001)
reported on 45 right whale mortalities from 1970-1999. Of these,
16 (36%) were attributed to ship strikes, 13 (29%) to natural causes,
13 were from unknown causes, and 3 (7%) were the result of entanglements. Of
15 right whales identified as ship strike mortalities, four (27%) showed
no outward appearance of a strike (Hamilton et al. 1998). Wiley
et al. (1995) reported a similar lack of external evidence of vessel
collisions; of 20 large whale carcasses examined from the Carolina, Virginia
and New Jersey coasts, 6 (30%) had major injuries potentially attributable
to ship strikes and two of these showed no external signs of trauma. Carcasses
floating at sea often cannot be examined sufficiently for either internal
or external indications, and generate false negatives if they are not
towed ashore and necropsied. Of the 30 right whales necropsied
during 1970 through 2002, 13 (43%) were confirmed as ship strike mortalities,
four (13%) were confirmed to be the result of entanglement, and one was
due to natural causes (Moore et al. 2004). The causes of
death were not identified for the remaining cases, however, one was possibly
the result of a ship strike. An additional 24 mortalities were
reported during the period, but no internal examination was conducted
(Moore et al. 2004).
The Marine Mammal Commission has indicated that serious injury and mortality
estimates based only on confirmed reports are not precautionary because
these estimates are negatively biased. That is, not all injured
or dead animals are accounted for. Given the low sighting probability
and apparently high rate of interaction of whales with fishing gear and
ships, we concur that any estimate based on observed dead or seriously
injured animals is a very conservative lower bound. Thus, if the observed
mortality and serious injury estimate developed from stranding/floater/entanglement
data is near but below a threshold value (e.g., PBR for a marine
mammal stock), it is reasonable to assume that the true mortality/serious
injury value exceeds the threshold.
ACKNOWLEDGMENTS
We are especially grateful to the East Coast stranding and entanglement
networks, whose members searched for and examined whales both live and
dead. It is a difficult and seemingly thankless job that deserves
special recognition. We are also grateful to the staff of the Provincetown
Center for Coastal Studies and New England Aquarium, NOAA aerial survey
teams, Wildlife Trust, the States of Florida/Georgia and many others
for providing the sightings that have allowed this work to be conducted. Liz
Pomfret-Wiley, Amy Whittingham Chase, Brenda Rone and Misty Niemeyer
verified records. Misty Nelson triple-checked everything. Members
of the Atlantic Scientific Review Group have provided numerous useful
comments on the protocols described here. We also thank the anonymous
reviewers of earlier drafts of this report. Also thanks to Dr.
Richard Merrick, who provided the momentum to put these protocols in
manuscript form.
LITERATURE
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