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Northeast Fisheries Science Center Reference Document 05-08

Mortality and Serious Injury Determinations for Large Whale Stocks Along the Eastern Seaboard of the United States, 1999-2003 (2nd Edition)

Timothy V.N. Cole, Dana L. Hartley, and Richard L. Merrick
National Marine Fisheries Serv., Woods Hole Lab., 166 Water St., Woods Hole, MA 02543

Web version posted December 5, 2005

Citation: Cole TVN, Hartley DL, Merrick RL. 2005. Mortality and serious injury determinations for large whale stocks along the eastern seaboard of the United States, 1999-2003. US Dep Commer, Northeast Fish Sci Cent Ref Doc. 05-08; 18 p.

Information Quality Act Compliance: In accordance with section 515 of Public Law 106-554, the Northeast Fisheries Science Center completed both technical and policy reviews for this report. These predissemination reviews are on file at the NEFSC Editorial Office.

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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.  A serious injury has been defined as “any injury that will likely result in mortality”.  Using guidelines recommended by NMFS’s 1997 Serious Injury Workshop, the Northeast Fisheries Science Center developed protocols for determining large whale serious injuries and human-caused mortalities.  We describe the protocols used and report on the determinations made for right, humpback, fin, sei, blue, minke and Brydes whale events that occurred from 1999 through 2003 along the eastern seaboard of the United States.  A total of 408 unique large whale events were reported during the period, including both strandings and sightings at sea.  These included 173 entanglement reports and 37 reports of ship strikes.  We were able to verify 146 entanglement events, 25 ship strikes, and 267 mortalities.  Entanglements were identified as the cause of 29 whale deaths and ship strikes the cause of 18.  Entanglements were determined to have caused serious injury in 18 events.  Minke whales had the greatest number of entanglement mortalities (15).  Humpback whales had the highest number of serious injury events resulting from entanglements (12) and the most incidents of ship strike mortalities (6).  Right whales and fin whales each had five mortalities from ship strikes.  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.


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 Plan 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. 

Mortalities are relatively easy to assess, but assessments of serious injuries are more problematic. NOAA has defined an ‘injury’ under 50 CFR 229.2 as:

“... a wound or other physical harm. Signs of injury to a marine mammal include, but are not limited to, visible blood flow, loss of or damage to an appendage or jaw, inability to use one or more appendages, asymmetry in the shape of the body or body position, noticeable swelling or hemorrhage, laceration, puncture or rupture of eyeball, listless appearance or inability to defend itself, inability to swim or dive upon release from fishing gear, or signs of equilibrium imbalance. Any animal that ingests fishing gear, or any animal that is released with fishing gear entangling, trailing or perforating any part of the body will be considered injured regardless of the absence of any wound or other evidence of an injury.”

A serious injury has been defined as “any injury that will likely result in mortality”.

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).  Specifically, the Atlantic SRG (ASRG) at its April 1999 meeting recommended that

“…the draft serious injury guidelines be followed whenever possible and applied in all fisheries. Those serious injury observations should be added to the observed mortalities and extrapolated to the population for status determination.”

 The ASRG was specifically concerned about serious injuries to small cetaceans in the Atlantic pelagic longline fishery and large cetaceans in Northwest Atlantic Ocean pot and gillnet gear.

Subsequently, the Northeast (NEFSC) and Southeast Fisheries Science Centers (SEFSC) prepared serious injury determinations for the SARs and presented these to the ASRG in autumn 1999.  The SEFSC implemented the Serious Injury Workshop recommendations for small cetaceans taken in the longline fishery, while the NEFSC implemented the Workshop’s large cetacean recommendations for right, humpback, fin, sei, blue, minke and Brydes whales interacting with gillnet and pot gear.  At this and subsequent meetings, the ASRG spent considerable time discussing the protocols in general, and the analyses conducted for specific species (especially right whales). 

Serious injury determinations continue to be prepared annually by the NEFSC and SEFSC. However, the actual criteria used in these determinations have never been formalized in manuscript form.  In this document, we formally describe these protocols and report on the determinations made from 1999 through 2003.


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:

  1. The event was observed by a trained marine mammal observer who was certain of the species or event;
  2. 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;
  3. The observer was inexperienced, but the report was accompanied by photographs or videotape of sufficient quality to positively verify the species or event;
  4. A fisherman reported a whale entangled in his/her gear or a shipper reported colliding with a whale;
  5. Gear was retrieved from a whale.
Events and the species involved were considered confirmed in the following less certain cases:
  1. The observer was experienced and was fairly certain, but not positive, of the species or event;
  2. The observer was inexperienced, but was interviewed and the account was descriptive enough that the species or event was probable but not certain;
  3. 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:

  1. 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;
  2. 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;
  3. The event was photographed or video taped, but staff reviewing the images could not identify species or the event’s occurrence;
  4. 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:

  1. Fishing line constricted any body part;
  2. 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:

  1. Large linear lacerations (anywhere on body, as opposed to just dorsally as in Kraus 1990);
  2. Large areas of subdermal hemorrhaging, hematoma or edema;
  3. Extensive skeletal fracturing; or
  4. 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:

  1. Fishing line constricted on any body part, or was likely to become constricting as the whale grew;
  2. It was uncertain if the line was constricting, but appendages near the entanglement’s point of attachment were discolored and likely compromised;
  3. The whale showed a marked changed in appearance following entanglement, including skin discoloration, lesions near the nares, fat loss, or increased cyamid loads;
  4. Gear was ingested;
  5. 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).


A total of 408 events was reported during 1999-2003, involving both live and dead whales (Table 1).  There were 173 reports of entanglement and 37 of ship strike.  From these, we confirmed 146 entanglement events and 25 ship strike events.   We were able to verify 267 mortalities, and determine that 29 mortalities were due to entanglements and 18 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 1999-2003 are presented by stock in Table 2Tables 3 to 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 50 reports involving right whales, 31 were confirmed entanglements and 8 were confirmed ship strikes.   Over the five-year period, there were 18 verified right whale mortalities (Table 1).   Three of these mortalities were due to entanglements, and five were due to ship strikes.  Serious injury was documented for five entanglement events involving right whales.

Humpbacks were involved in 169 reported events (Table 1). Of these, 74 of the 82 reported entanglements could be confirmed, as could 10 of the 14 reported ship strikes.   Humpbacks were the most commonly observed entangled whale species and the most commonly observed dead whale (92 confirmed mortalities).  Entanglements accounted for eight mortalities and 12 serious injuries.  Ship strikes were relatively uncommon, with only 10 confirmed events, six of which were fatal. Whales identified as members of the Gulf of Maine stock accounted for five of the entanglement mortalities, nine of the entanglement serious injuries and three of the ship strike mortalities (Table 2).

Fin whales had a low proportion of entanglements; of 40 reported events, only 7 were of entanglements (all confirmed), two of which were fatal (Table 1).  Ten ship strikes were reported, five of which were confirmed and proved fatal.  No serious injury events involving fin whales were reported.

Only four events were reported for sei whales, all of which were confirmed mortalities.  Two of the mortalities were determined to have resulted from ship strikes.

Minke whales were reported in 82 events.  Entanglements accounted for 35 of these events, but only 27 could be confirmed (Table 1).   Fifteen 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, but neither of these could be confirmed.

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 in the Gulf of Mexico, which resulted in the death of the whale. 

In 61 of the 408 large whale events reported during 1999-2003, positive species identification was not possible (Table 1).  In five stranding events, the similarity in body shape and size between fin and sei whales prevented positive species identification.  In another 14 strandings, the whales could only be identified as balaenopteriids based on the presence of ventral pleats.   In 42 other events, the taxonomic identity of the whales could not be assigned with certainty.  Entanglement was reported in 12 of these cases, five of which were considered confirmed.  Twenty eight of the 42 reported events involving unidentified whales were confirmed mortalities.


Sufficient experience with serious injury determinations has been gained since 1999 to now comment on the efficacy of the recommendations from the 1997 Workshop for assessing large whale serious injuries.

First and foremost, determinations of human-caused mortality and serious injury must be made on a case-by-case basis.  The guidelines provided in the Workshop report tend to be overly general, so it is important that individual users clearly define a priori how the guidelines are to be used and then apply them in a consistent fashion.   The process might best be conducted using the same personnel to ensure consistency.  All available data should be carefully examined before determinations are made.   Frequently determinations are made in a rush in response to decision makers’ requests, when in fact a measured approach will likely provide a more accurate evaluation.  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 2003 were made in late summer 2004 for the 2005 SAR).

Secondly, for dead animals, it is essential that the carcass be recovered and necropsied by a competent biologist with an attending veterinarian or pathologist present.  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.

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 in our serious injury work was the number of animals we never saw!  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). But 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.  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.  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.


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 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, Mendy Garron and Misty Niemeyer verified records. 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.


Angliss, R.P., and D.P. DeMaster. 1998. Differentiating serious and non-serious injury of marine mammals taken incidental to commercial fishing operations: Report of the Serious Injury Workshop, 1-2 April 1997, Silver Spring, Maryland.U.S. Dep. Commer., NOAA Tech Memo. NMFS-OPR-13, 48 p.

Barco, S.G., W.A. McLellan, J.M. Allen, R.A. Asmutis-Silvia, R. Mallon-Day, E.M. Meagher, D.A. Pabst, J. Robbins, R.E. Seton, W.M. Swingle, M.T. Weinrich, and P.J. Clapham. 2002. Population identity of humpback whales (Megaptera novaeangliae) in the waters of the US mid-Atlantic states. Journal of Cetacean Research and Management 4(2): 135-141.

Hamilton, P.K., M.K. Marx, and S.D. Kraus. 1998. Scarification analysis of North Atlantic right whales (Eubalaena glacialis) as a method of assessing human impacts. Paper SC/M98/RW28 presented to the IWC Special Meeting of the Scientific Committee towards a Comprehensive Assessment of Right Whales Worldwide, 16-25 March 1998, Cape Town, South Africa.

Knowlton, A.R., and S.D. Kraus. 2001. Mortality and serious injury of northern right whales (Eubalaena glacialis) in the western North Atlantic Ocean. Journal of Cetacean Research and Management (Special Issue 2): 193-201

Kraus, S.D. 1990. Rates and potential causes of mortality in North Atlantic right whales (Eubalaena glacialis). Marine Mammal Science 6(4):278-291.

Mattila, D.K., and J. Robbins. 1998. Monitoring of entanglement scars on the caudal peduncle of humpback whales in Gulf of Maine. Center for Coastal Studies. Order number 40EMNF700232 pp.

McLellan, W.A., Rommel, S.A., Moore, M., Pabst, D.A. 2004. Right whale necropsy protocol. Final report to NOAA Fisheries for contract #40AANF11252551pp.

Moore, M.J., A.R. Knowlton, S.D. Kraus, W.A. McLellan, R.K. Bonde. 2004. Morphometry, gross morphology and available histopathology in North Atlantic right whale (Eubalaena glacialis) mortalities (1970–2002). Journal of Cetacean Research and Management 6(3):199-214.

Robbins, J., and D.K. Mattila. 1999. Monitoring entanglement scars on Gulf of Maine humpback whales. Center for Coastal Studies. Order number 40ENNF800288.

Robbins, J., and D.K. Mattila. 2000. Monitoring entanglement scars on the caudal peduncle of Gulf of Maine humpback whales: 1997-1999. Center for Coastal Studies. Order number 40ENNF900253. 24 p.

Robbins, J., and D.K. Mattila. 2001a. Monitoring entanglements of humpback whales (Megaptera novaeangliae) in the Gulf of Maine on the basis of caudal peduncle scarring. Unpublished report to the Scientific Committee of the International Whaling Commission: SC/53/NAH, 25 p.

Robbins, J., and D.K. Mattila. 2001b. Gulf of Maine humpback whale entanglement scar monitoring results, 2000. Center for Coastal Studies. Order number 40ENNF030121.

Robbins, J., and D.K. Mattila. 2003. Gulf of Maine humpback whale entanglement scar monitoring results, 2001. Report to the National Marine Fisheries Service. Order number 40ENNF030121.

Robbins, J., and D.K. Mattila. 2004. Estimating humpback whale (Megaptera novaeangliae) entanglement rates on the basis of scar evidence. Report to the National Marine Fisheries Service.Order number 43ENNF030121, 22 pp.

Robbins, J.D., W. McKay, and M.L. Sheridan. 2004. Gulf of Maine humpback whale, Megaptera novaeangliae, vital rates inferred from blubber progesterone concentrations. Report to the National Marine Fisheries Service, Order number EA133F03SE0293, 25 pp.

Wiley, D.N., R.A. Asmutis, T.D. Pitchford, and D.P. Gannon. 1995. Stranding and mortality of humpback whales, Megaptera novaeangliae, in the mid-Atlantic and southeast United States, 1985-1992. Fishery Bulletin 93 [1]: 196-205.
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