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Northeast Fisheries Science Center Reference Document 09-04

Mortality and Serious Injury Determinations for Baleen Whale Stocks along the United States Eastern Seaboard and Adjacent Canadian Maritimes, 2003-2007 (2nd Edition)

Allison H. Glass, Timothy V.N. Cole, and Mendy Garron
NOAA National Marine Fisheries Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole MA 02543

Web version posted May 15, 2009

Citation: Glass AH, Cole TVN, Garron M. 2009. Mortality and serious injury determinations for baleen whale stocks along the United States eastern seaboard and adjacent Canadian Maritimes, 2003-2007 (2nd Edition). US Dep Commer, Northeast Fish Sci Cent Ref Doc. 09-04; 19 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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NEFSC revised/corrected the values of the Mean Annual Mortality & SI Rate and the Annual Entanglement Rate for the Western North Atlantic right whale, and the PBR rates for the Western North Atlantic fin whale, Canadian East Coast minke whale, and the Western North Atlantic Bryde's whale.

Complete previous edition available in PDF here
Revised Table 3 with changes from May 15, 2009 and January 24, 2012 highlighted here


The Northeast Fisheries Science Center (NEFSC) has developed criteria to evaluate reports of human-caused injury and mortality to large whales.  The criteria minimize the identification of false positive human-caused mortalities and serious injuries, and therefore provide a minimum value of human impact to whale stocks.  Serious injury is defined as an injury that is likely to lead to death.  This report describes determinations made for reports received from 2003 through 2007 involving right (Eubalaena glacialis), humpback (Megaptera novaeangliae), fin (Balaenoptera physalus), sei (B. borealis), blue (B. musculus), minke (B. acutorostrata) and Bryde’s (B. edeni) whales observed along the eastern seaboard of the United States and adjacent Canadian Maritimes.  A total of 537 unique large whale events were verified during the period, including carcasses (both beached and at-sea) and live whales. We confirmed 153 unique entanglement, 52 ship strike, and 349 mortality events.  Twenty-one (14%) of the entanglements and 30 (58%) of the ship strikes were fatal.  Serious injury was sustained in 16 (10%) of the entanglement events and in 2 (4%) of the confirmed ship strikes.  Twenty-four (16%) of the entanglements and five (10%) of the ship strike events did not have adequate documentation to determine if serious injury occurred.  Seventy-six (50%) of the entanglement events and 13 (25%) of the ship strike events did not cause serious injury or death.  Of the 349 confirmed mortalities, 280 (80%) lacked sufficient evidence to determine cause of death.  Minke whales had the greatest number of entanglement mortalities (n=9); humpback whales had the highest number of serious injury events resulting from entanglements (n=10); and right whales had the greatest number of ship strike mortalities (n=9) and serious injuries (n=2) from ship strikes.  These mortality and serious injury numbers are minimum counts due to poor detection probabilities and inadequate documentation.  Thus, the true level of human impact to these stocks is assumed to be greater than that reported here, however the amount greater is unknown.


As part of the 1994 amendments to the Marine Mammal Protection Act (MMPA), the NOAA National Marine Fisheries Service (NMFS) is mandated to establish monitoring programs to estimate incidental mortality and serious injury of marine mammals taken during commercial fishing operations.  The Agency is also charged with developing Take Reduction Plans (TRPs) such that within six months of the implementation of the TRP, commercial takes of strategic stocks of marine mammals are reduced to levels below the Potential Biological Removal (PBR) level of the stocks.  The longer-term goal of all the TRPs is to reduce--within 5 years of implementation--commercial takes of marine mammals to insignificant levels approaching zero mortality and serious injury rates, which has been defined as 10% of PBR (69 FR 43338; July 20, 2004). 

The most current five years’ average rate of human-caused serious injury and mortality is reported for each species in the annual marine mammal stock assessment reports (SAR).  This rate when compared to a population’s PBR can be used as an index of the success of a recovery plan.  The PBR is defined as the maximum number of animals, not including natural mortalities, which may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population (Wade and Angliss 1997). The PBR is the product of the following factors:

  1. The minimum population estimate of the stock;
  2. One-half the maximum theoretical or estimated net productivity rate of the stock at a small population size; and
  3. A recovery factor of between 0.1 and 1.0.
This report presents the protocols and determinations for events involving right (Eubalaena glacialis), humpback (Megaptera novaeangliae), fin (Balaenoptera physalus), sei (B. borealis), blue (B. musculus), minke (B. acutorostrata) and Bryde’s (B. edeni) whale stocks along the US eastern seaboard for the period 2003 through 2007.

Members of the National Stranding Network, large whale disentanglement teams, the US Coast Guard, and civilians recorded and submitted marine mammal strandings and human-induced interaction reports to the NMFS Northeast Regional Office (NERO) and Southeast Regional Office (SERO).  The Regional Offices obtained all available information for each report (photos, necropsy reports, etc.), which was then reviewed by NEFSC, NERO, and Northeast Fisheries Observer Program (NEFOP) staff members.  Confirmed reports were designated “events” and the species involved was verified, duplicate records identified and relevant information from each source consolidated into a single record.  Information from additional sightings of a previously documented event was added to the existing record.  If an identified whale was involved in a second interaction, a new event record was assigned.  NEFSC staff 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 in the application of determination criteria within and across years.  Criteria indicated by an asterisk (*) are new this year and were applied to the 2007 events only.  Application of the revised criteria to events prior to 2007 will be completed in a separate document.

Confirmation Criteria for Species and Event (listed in order of certainty)

Species/Event was considered confirmed if it met one of the following criteria:

  1. Photographs or video allowed identification;
  2. Marine mammal expert reported as certain;
  3. Reported by trained observer or member of the Disentanglement Network verified via interview by NMFS, disentanglement or stranding network staff; or
  4. A fisherman reported a whale entangled in gear or a shipper reported colliding with a whale.

Species/Event was considered confirmed in the following less certain cases:

  1. Photographs or video allowed probable identification;
  2. Marine mammal expert reported as possible;
  3. Inexperienced observer’s report allowed probable identification; or
  4. Inexperienced observer’s report verified via interview by NMFS, disentanglement or stranding network staff.

Species/Event was considered unconfirmed if:

  1. Photographs or video were of insufficient quality to verify; 
  2. Inexperienced observer report lacked photographs or video and/or detail to confirm;
  3. Incomplete examination for identification; or
  4. Carcass too decomposed to identify.
Human-Induced Mortality Determinations

Events were categorized as entanglement mortalities if one of the following indications were confirmed to be present during gross inspection or necropsy of the carcass:

  1. Fishing line constricted any body part and subdermal hemorrhaging or extensive necrosis was present at point of attachment;
  2. Extensive entanglement evident*;
  3. Entanglement prevented feeding*; or
  4. A code 2 (fresh dead) whale was pulled up during fishing operations*.

Events were categorized as ship strike mortalities if one of the following indications was 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 one of the following indications was confirmed on a living whale:

  1. Fishing line constricted 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 decline in appearance following entanglement, including skin discoloration, lesions near the nares, fat loss, or increased cyamid loads;
  4. Entanglement prevented feeding*;
  5. Whale was anchored; or
  6. Entanglement was extensive*.

Criteria indicated by an asterisk (*) are new and were applied to the 2007 events only.  Application of the revised criteria to events prior to 2007 will be completed in a separate document. 

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 decline in appearance, including skin discoloration, lesions near the nares, fat loss, or increased cyamid loads.

Injuries that affected the whale’s locomotion or feeding were not considered serious injuries unless they inhibited these functions to the point of likely being 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 entanglement or collisions with vessels).


A total of 537 unique events occurred during 2003 - 2007, involving both live and dead whales (Table 1).  Of these, we confirmed 153 entanglement events and 52 ship strike events.  We were able to verify 349 mortalities, of which 21 were due to entanglements and 30 were the result of ship strikes.  The cause of death could not be confirmed for 280 (80%) of the mortalities.   Entanglement caused serious injury in 16 events, and 2 ship strike events resulted in serious injury.  There were 76 entanglement events which were not serious injuries (this includes cases where the animal was freed by a disentanglement team or shed gear on its own), and 24 which lacked sufficient evidence to determine if a serious injury had occurred.  Thirteen ship strike events occurred which did not result in serious injury, and five events lacked sufficient evidence to make a determination.  Table 2 presents a summary of mortalities attributed to causes other than entanglement or ship strike, confirmed entanglement and ship strike events not resulting in serious injury or mortality, and confirmed events for which insufficient information was available for determination.  Annual human-caused mortality and serious injury rates for 2003 - 2007 are presented for each large whale stock in Table 3.  Tables 4 to 9 (linked below) provide details of each confirmed serious injury or mortality event.  

Over the five-year period, right whales had the highest proportion of entanglements and ship strikes relative to the number of events for a species: of 58 events involving right whales, 20 were confirmed entanglements and 17 were confirmed ship strikes (Table 1).  Of the 20 verified right whale mortalities, 3 were due to entanglements, 9 due to ship strikes, and the cause of the remaining 12 could not be determined.  Serious injury was documented for one entanglement event and two ship strikes (details in Table 4).

Humpbacks were involved in 198 events, were the most commonly observed entangled whale species, and the most commonly observed dead whale (109 confirmed mortalities; Table 1). Of the 76 confirmed entanglements, four resulted in mortality and ten in serious injury.  Ship strikes were relatively uncommon with only eleven verified events, eight of which were fatal (Table 5).  We assumed all humpback events were from the Gulf of Maine stock unless a whale was confirmed to be from another stock.  At the time of this writing, all available information indicated the humpbacks were from the Gulf of Maine stock (Table 3). 

Few fin whales had documented entanglements.  Of 61 fin whale events, 13 were confirmed entanglements; three of these were fatal and three resulted in serious injury.  Eleven ship strike events were documented and eight proved fatal (Table 6).

Mortalities accounted for seven of the eight sei whale events.  Three of these mortalities were attributed to ship strike. In one additional ship strike event, it could not be determined whether the strike occurred pre or post-mortem.  There was one confirmed entanglement event which resulted in serious injury (Table 7). 

Minke whales were involved in 115 events, of which 32 were confirmed entanglements.  Nine of the entanglement events were fatal, the highest percentage for any of the whale species.  There were only two verified ship strike events, both of which resulted in mortality (Table 8).

Bryde’s whales had the lowest number of events--two.  One was a confirmed entanglement which resulted in the death of the whale (Table 9). 

There were no events involving blue whales.

In 95 of the 537 large whale events during 2003 - 2007, positive species identification was not possible.  In 13 of the 95 events, the similarity in body shape and size between fin and sei whales prevented us from distinguishing which of these two species were involved.  In another 21 events, the whales could only be identified as balaenopterids based on the presence of ventral pleats.  The taxonomic identity of the whales involved in the remaining 61 events could not be assigned with any certainty.  Entanglement was confirmed in 11 of these 95 events.  Seventy-three of the 95 events involving unidentified whales were confirmed mortalities (see Table 1).


The criteria employed in this report evolved from recommendations of serious injury workshops (see Andersen et al. 2008 and Angliss and DeMaster 1998) and our experience examining large whale reports since 1990.  The criteria attempt to encompass all event scenarios and minimize the identification of false positive human-caused mortalities and serious injuries.  The resulting values provide a minimum value of human impact to whale stocks.

Differentiating causal injuries from pre-existing ones or post-mortem damage is problematic, but can be accomplished through examination of necropsy data or parsimonious evaluation of available evidence.  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.  Vessel collisions frequently lack external evidence, and may not be detected unless a necropsy is conducted; necropsies frequently identified subdermal hemorrhaging or hematomas, indicating that blood was still circulating at the time of injury.  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; floating carcasses would be pushed aside by the ship’s bow wave (Knowlton et al. 1995).

Our assessment of serious injury was guided by regulation 50 CFR 229.2, which defines serious injury as "any injury that will likely result in mortality."  Evidence of the whale’s deteriorating health was used as confirmation of 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 or hydrodynamic forces) compromises the ability of an animal to fight other infections.  External indications of poor health, including skin discoloration, lesions near the nares, fat loss, or increased cyamid loads are part of a cascade of immunological disorders.  Cases of constricting entanglements invariably follow this sequence. 

Removal of constricting gear typically reversed the decline in appearance, and disentanglement was generally considered to prevent serious injury.  Whales only loosely entangled in line typically did not have external indications of poor health; some whales carried loose wraps for years. 

Over the five-year period, 280 of 349 confirmed mortalities (80%) lacked sufficient evidence to determine cause of death (Table 2).  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.  Likewise, insufficient documentation precluded determination in 24 of 153 confirmed entanglement events (16%) and 5 of 52 ship strike events (10%).

However, perhaps of greater concern is the number of animals never observed.  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, and positively buoyant species, such as right whales, may become negatively buoyant if an injury precludes effective feeding for an extended period (Moore et al. 2004).  The numbers in this report therefore represent the minimum values for human-caused serious injury and mortality to large whale stocks along the U.S. eastern seaboard.


We are especially grateful to the East Coast stranding and entanglement networks, whose members searched for and examined whales both alive and dead.  It is a difficult and smelly job that deserves special recognition.  The United States Coast Guard was instrumental in conveying sightings reported by mariners, investigating carcasses at sea and assisting in disentanglement efforts.  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, Northeast Fisheries Observers and many others for providing the sightings that have allowed this work to be conducted.  Betty Lentell, Misty Nelson, Liz Pomfret-Wiley, Amy Whittingham Chase, Brenda Rone 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 RP, DeMaster DP. 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.  US Dep Commer, NOAA Tech Memo NMFS-OPR-13, 48 p.

Andersen MS, Forney KA, Cole TVN, Eagle T, Angliss RP, Long K, Barre L, Van Atta L, Borggaard D, Rowles T, Norberg B, Whaley J, Engleby L. 2008. Differentiating Serious and Non-Serious Injury of Marine Mammals: Report of the Serious Injury Technical Workshop, 10-13 September 2007, Seattle, Washington. US Dep Commer, NOAA Tech Memo NMFS-OPR-39. 94 p.

Knowlton AR, Korsmeyer FT, Kerwin JE, Wu H, Hynes B.  1995.  The hydrodynamic effects of large vessels on right whales.  Final report to NOAA Fisheries for Contract No. 40EANFF400534, 81 p.

Kraus SD.  1990.  Rates and potential causes of mortality in North Atlantic right whales (Eubalaena glacialis).  Mar Mamm Sci. 6(4): 278-291.

Moore MJ, Knowlton AR, Kraus SD, McLellan WA, Bonde RK.  2004.  Morphometry, gross morphology and available histopathology in North Atlantic right whale (Eubalaena glacialis) mortalities (1970–2002). J Cetacean Res Manage. 6(3):199-214. 

Robbins J, Mattila DK. 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, Mattila DK. 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 p.

Wade PR, Angliss RP.  1997.  Guidelines for assessing marine mammal stocks: Report of the GAMMS Workshop, April 3-5, 1996, Seattle, Washington.  US Dept Commer, NOAA Tech Memo NMFS-OPR-12., 93 p.
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