North Atlantic Right Whales- Evaluating 

Their Recovery Challenges in 2018

US DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Northeast Fisheries Science Center

Woods Hole, Massachusetts

September 2018

NOAA Technical Memorandum NMFS-NE-247
North Atlantic Right Whales - Evaluating 

Their Recovery Challenges in 2018

Sean A. Hayes1, Susan Gardner1, Lance Garrison2, 

Allison Henry1, Luis Leandro1

1 NOAA Fisheries, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543

2 NOAA Fisheries, Southeast Fisheries Science Center 75 Virginia Beach Drive Miami, Fl 33149

US DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Northeast Fisheries Science Center

Woods Hole, Massachusetts

September 2018

NOAA Technical Memorandum NMFS-NE-247

This series represents a secondary level of scientific publishing. All issues employ thorough internal 

scientific review; some issues employ external scientific review. Reviews are transparent collegial 

reviews, not anonymous peer reviews. All issues may be cited in formal scientific communications.
iii

Table of Contents

ABSTRACT .................................................................................................................................... 1

INTRODUCTION .......................................................................................................................... 1

Signs of Trouble .......................................................................................................................... 1

Demographic Effects .................................................................................................................. 2

Distribution Change .................................................................................................................... 3

Increased Mortality ..................................................................................................................... 3

POTENTIAL CAUSES OF THE DECLINE ................................................................................. 4

Ecosystem Dynamics .................................................................................................................. 4

Whales and Fisheries Are On the Move ................................................................................. 4

Prey Availability Drives Reproductive Success ..................................................................... 4

Right Whales Follow Prey in a Changing Ocean ................................................................... 6

Reproduction Requires Robust Females ................................................................................. 6

Anthropogenic Stressors ............................................................................................................. 7

Ship Strikes ............................................................................................................................. 7

Entanglement .......................................................................................................................... 8

Increase in Entanglement Risk ................................................................................................ 8

Sublethal Challenges- Skinny Whales and Few Calves ........................................................... 11

Biological Cost of Stressors .................................................................................................. 11

Biological Demands of Right Whale Pregnancy .................................................................. 12

HOW LONG DO NORTH ATLANTIC RIGHT WHALES HAVE?.......................................... 13

A Long-Lived Animal............................................................................................................... 13

An Illustration of Potential Decline, 2017-2067 ....................................................................... 14
iv

A Matrix Model .................................................................................................................... 14

Results ................................................................................................................................... 14

INDICATORS OF SUCCESSFUL MANAGEMENT MEASURES .......................................... 16

ACKNOWLEDGMENTS ............................................................................................................ 17

REFERENCES CITED ................................................................................................................. 17

APPENDIX 1 Data Sources for Figure 4 ..................................................................................... 22

APPENDIX 2 Model Inputs and Methods used for Population Projection .................................. 22

Figures and Tables 

Figure 1 North Atlantic right whale serious injury/mortality rates 2000-2017 .......................... 2 

Figure 2 American lobster landings in Maine ............................................................................ 5 

Figure 3 Timeline of significant management actions focused on reducing fishing 

entanglement ................................................................................................................ 9 

Figure 4 Index of fishing effort, US and Canada ..................................................................... 10 

Figure 5 Right whale entanglements from 1997 through 2017 with set location .................... 11 

Figure 6 Cumulative annual probability of no entanglement ................................................... 13 

Figure 7 Matrix population projection model output of North Atlantic right whale 

female population trend under current population conditions ................................... 15 

Table Matrix projection model output of female North Atlantic population trends 

for 5-year intervals, 2017-2067 .................................................................................. 15 
1 

ABSTRACT

The North Atlantic right whale (Eubalaena glacialis) population has been in decline for 8 years 

due to increased mortality and sublethal effects from multiple factors. Together these have 

contributed to a decrease in calving. Shifting ecosystem conditions have also changed North 

Atlantic right whale behavior and fishing patterns. For example: 

• North Atlantic right whales have expanded their distribution farther into northern waters,

and are visiting different foraging areas.

• Calanoid copepod distributions appear to be in a similar state of change and this may be

affecting available forage for North Atlantic right whales

• The whales’ range expansion has exposed them to vessel traffic and fisheries in Canadian

waters, which did not have protections for right whales in place until late last summer

(2017).

• American lobster (Homarus americanus) populations are also changing distribution,

moving north and into deeper, cooler waters of the Gulf of Maine. The US fisheries are

moving farther offshore to capitalize on this, increasing the overlap between their fishing

activity and North Atlantic right whale foraging areas and migration corridors.

The net result of these events is that severe entanglements have increased among North Atlantic 

right whales. Animals are in poor body condition likely from a combination of repeated 

entanglement stress, potentially limited forage and increased migratory costs- all contributing to 

a decrease in female calving rate. Ship strikes are still a real threat to the population. At the 

current rate of decline, all recovery achieved in the population over the past three decades will be 

lost by 2029. 

INTRODUCTION 

Signs of Trouble

After several decades of recovery and years of collaboration among stakeholders, the North 

Atlantic right whale (Eubalaena glacialis), hereafter referred to as the right whale, began to 

decline (Pace et al. 2017). This trend was subtle at first, initially signaled by fewer sightings in

traditional survey areas, but other warning signs began to emerge (Kraus et al. 2016). The 

number of documented mortalities increased markedly in 2016 and 2017 (Hayes et al. 2018; 

Hayes et al. 2017) and an improved way of modeling the population’s numbers (Pace et al. 2017) 

revealed a clearer picture of the population size and decline in numbers. Concern further 

escalated throughout 2017 and 2018 when only 5 calves were born and there were 19 confirmed 

mortalities through August.

Taken together these signs meant that risks posed to right whales and associated management 

measures needed to be revisited for multiple US fisheries on the Atlantic coast. This occurs

through the biological opinion process under the federal Endangered Species Act, which was 

reinitiated in October 2017, and through the take reduction team process under the federal 

Marine Mammal Protection Act. 
2 

Demographic Effects 

Increased mortality rates and decreased calving have moved the population into a decline that 

has continued for at least the last 8 years. At present, right whale deaths attributable to human 

activity are mostly caused by ship strikes and entanglement in pot/trap and anchored gillnet 

fishing gear. An encounter with fishing gear is the most frequent cause of documented right 

whale serious injuries and deaths in recent years. The odds of an entanglement event are now 

increasing by 6.3% per year, while ship strikes events remain flat (Fig. 1). At the current rate of 

decline, the population will have returned to its 1990 numbers, likely with comparatively 

reduced genetic diversity, and could decline past a point of no return in just a few decades.

Fig. 1 North Atlantic right whale serious injury/mortality rates from known sources 2000-2017 

(Henry et al 2017; 2016 & 2017 values preliminary). Models are simple logistic regressions 

fit using maximum likelihood-based estimation procedures available in R. The right whale 

population trend is overlaid and referenced to right y-axis (Hayes et al, 2018). 
3 

Distribution Change

Historically, right whales have returned to habitats in specific geographic locations annually, 

ensuring that a large portion of the population could be seen in each year. Therefore annual 

population estimates were conducted by simply sighting and counting as many animals as 

possible each year. Resulting estimates also assumed that an animal had died if it were not seen 

for 6 consecutive years. 

Changes in this distribution pattern began around 2010 when the population peaked at 481 

individuals. The whales were no longer using some of their established habitat areas in as great a 

number, and not staying within them for as long. This meant a new method was needed to 

account for animals, even those not sighted in a year. Once developed, this more advanced 

assessment tool, based upon mark recapture methods, enabled rapid assessment of the population 

with increased precision within one calendar year, much faster than the five or so years required 

to get good confidence on an annual estimate using the previous method. It also provided 

precise population estimates with greater resolution on the number of whales that likely died in 

any given year. Estimates made using the new method confirmed that in recent years, many 

deaths (around 10 to 20/yr) were going undetected annually and that by the end of 2016, the right 

whale population had declined to 451 individuals. A revised population estimate accounting for 

the many deaths and few births of 2017 is being developed and will be available later this year. 

Increased Mortality 

The large number of observed right whale mortalities in 2017 triggered an unusual mortality 

event (UME) to investigate the causes. The National Marine Fisheries Service (NMFS) is 

authorized to declare UMEs under the federal Marine Mammal Protection Act when an 

unanticipated significant die-off occurs in a marine mammal population, requiring an immediate 

response. Two other UMEs were declared that year due to 80 humpback whale and 40 minke 

whale deaths. Ongoing investigations for these two species have preliminarily identified causes 

of death that include entanglements, ship strikes, and disease. 

In contrast to other large whale species, the problems of right whales are often more apparent 

because they are monitored more intensely and their coastal distribution means more 

opportunity for overlap with human activities, leading to it being nicknamed ‘the Urban Whale’ 

(Kraus et al. 2007). 

While perhaps more attention is paid to the right whale given their more dire population status, it 

can be an indicator of more chronic problems that need addressing, not just for the sake of right 

whales but also for other populations of large whales. By example, although Gulf of Maine 

humpback whale status has improved, entanglement mortalities still remain high for this stock

(Hayes et al. 2018). 

There is considerable urgency to address the issues of mortalities that stem from human 

activities. Large whales, including right whales, are long-lived and can breed multiple times 

during their lives. This means these species can be resilient and able to recover after periods of 
4 

poor reproduction. However, recovery for any species cannot take place if the number of deaths 

is more than the number of births in the population. 

POTENTIAL CAUSES OF THE DECLINE

Ecosystem Dynamics 

One of the constant challenges of resource management is that things change. While it is much 

easier to make management decisions if conditions are static, ecosystems are inherently dynamic 

and will change over time in response to a variety of influences. This is the case for the 

emerging story for right whales. 

Sometime around 2010, ecosystem shifts occurred within their habitat that changed right whale 

movements and fishing practices in a way that has increased interaction between whales and 

fishing gear, and that potentially presents other environmental challenges. 

Currently the Gulf of Maine is warming faster than 99.9% of all other ocean regions on the 

planet (Pershing et al. 2015). This is having dramatic impacts across the food web, from the 

middle and upper trophic level organisms such as American lobster (Homarus americanus), 

Atlantic cod (Gadus morhua) and right whales (Greene 2016); to the zooplankton at the base of 

the food web such as calanoid copepods (Grieve et al. 2017; NEFSC 2018). 

Whales and Fisheries Are On the Move

American lobster are experiencing strong population fluxes and redistributions with temperature 

warming. The southern New England lobster fishery has been severely limited by epizootic shell 

disease, which lobsters become susceptible to at warmer temperatures. In the Gulf of Maine,

coastal waters remain cool enough and offshore, deeper waters have warmed enough for lobsters, 

and lobster fishing, to expand farther offshore. As a result, Maine lobster landings have 

increased steadily for the past 30 years, with an increasing portion of this caught 3 or more miles 

offshore over the past 10 years (Fig. 2). Note that Maine lobster landings did downturn sharply 

in 2017, and future trends are uncertain. 

Prey Availability Drives Reproductive Success

It is essential to also recognize that environmental factors and lower trophic level dynamics also 

contribute to right whale birth and mortality rates. Changes in prey availability influence right 

whale health and reproduction. In particular, abundance of the copepod Calanus finmarchicus in 

the Gulf of Maine is a strong predictor of right whale reproductive success (Greene and Pershing 

2004; Meyer-Gutbrod and Greene 2014; Meyer-Gutbrod et al. 2015). 
5 

Fig 2. American lobster landings in Maine: a) total annual landings b) relative proportion of 

landing by distance from shore c) increase in landings from 3-12 and >12 miles 

offshore from Maine’s 10% harvester reporting, no VTR data included. 

https://www.maine.gov/dmr/commercial-fishing/landings/

Meyer-Gutbrod and Greene (2018) followed individual whales over the past three decades to 

evaluate the relationship of calving and mortality rates to prey availability. They found that prey 

availability is a driver of decadal differences in the right whale population’s recovery. Periods of 
6 

low prey availability coincided with reduced birth rates (Meyer‐Gutbrod and Greene 2018) and 

the interval between births has been observed to lengthen during periods when prey availability 

is low (Meyer-Gutbrod et al. 2015). 

Similarly, years with few births contribute to years of decline or stagnation in population growth, 

indicating the pronounced effect of reproductive variability on species viability (Pace et al. 

2017). That said, Meyer-Gutbrod and Greene (2018) modeled population growth rates under 

scenarios of high and low prey availability and found that the population should continue to 

grow even with poor prey availability and only fails to do so when whale mortalities reach 8 to 

10 per year. It is worth noting natural mortality seems to be very rare in adult right whales: there 

has been no confirmed case of natural mortality in adult right whales in the past several decades 

(Corkeron et al. Accepted with revision; Henry et al. 2017; van der Hoop et al. 2013). 

Right Whales Follow Prey in a Changing Ocean

The copepod C. finmarchicus has shifted in distribution and abundance in recent years due to 

unprecedented warming in the Gulf of Maine, and this is likely to impact the right whale 

population (Greene 2016; Mills et al. 2013; Reygondeau and Beaugrand 2011). It appears that in 

the last decade (~2005-2015), that there has been a general decline in C. finmarchicus in the Gulf 

of Maine (2009-2014, but 2015 was average abundance) and on Georges Bank (below average 

abundance since 2008) (NEFSC 2018) as well as the Scotian Shelf (Johnson et al. 2017). 

Changes in plankton forage species abundance likely played a role in the changing movement 

patterns of right whales that began sometime in the past 10 years. There have been decreases in 

both acoustic detections and physical observations of right whales in the northern Gulf of Maine 

and the Bay of Fundy, and a concurrent increase in sightings of many of the same animals in the

Canadian Gulf of St. Lawrence (Daoust et al. 2018; Davis et al. 2017; Meyer-Gutbrod et al. 

2018; Meyer‐Gutbrod and Greene 2018). 

During winter, whales are spending more time offshore in the mid-Atlantic, and less time on the 

coastal calving grounds just off the southeastern U.S., where in 2017 and 2018 calving has been 

quite poor. 

Reproduction Requires Robust Females

Reproduction depends on adequate adult female health and body condition. Reproductive 

females are particularly vulnerable to prey reductions because pregnancy and lactation increases 

caloric demand and they have less access to prey during migration to calving grounds (Fortune et 

al. 2013; Miller et al. 2012; Rolland et al. 2016). 

Several of the ecosystem shifts mentioned earlier are likely to have negative consequences for 

reproduction in right whales. First, a reduction in prey will have energetics costs for females. 

Northward shifts in the right whales’ feeding grounds, as a result of changes in prey availability, 

will increase energetic cost of the calving migrations from the southern calving grounds off the 

coast of Florida and Georgia, particularly if animals do not adapt to also calve farther north. 
7 

The cost of entanglement has also been shown to have direct and indirect consequences for right 

whales (van der Hoop et al. 2017b; van der Hoop et al. 2017c). This will be detailed next, but in 

the Gulf of Maine where ecosystem shifts are occurring more trap fishing is also occurring 

offshore, increasing the overlap with right whale foraging areas. 

Whales have also expanded their range, foraging into the Gulf of St. Lawrence. This increased 

the whales’ exposure to risk from fixed gear fisheries. Some of this risk has reduced by strong 

protections put in place by the Canadian government during the spring of 2018 (DFO/TC Canada 

2018; DFO Canada 2018). 

Anthropogenic Stressors

In a review of mortality sources for all large whales, entanglement in fishing gear was the 

number one cause, followed by natural causes and then vessel strikes. An exception to this is 

the right whale for which there is very little evidence of natural mortality in adult whales, likely 

due to shortened life spans associated with anthropogenic causes (Corkeron et al. Accepted with 

revision), as all confirmed causes of adult mortality and serious injury since 1970 have been due 

to fishing gear and vessel strike (Henry et al. 2017; van der Hoop et al. 2013). 

The relative contribution from these two causes was approximately equal through the year 2000 

(van der Hoop et al. 2013), but entanglement events resulting in death or serious injury have 

increased steadily since then, while ship strike frequency has remained lower with no specific 

trend (Fig. 1). For the recent 19 known right whale mortalities (17 in 2017 and 2 to date in 

2018), the cause of death could be determined for 10. Ship strikes are implicated in five blunt 

force trauma cases and entanglement in the remaining five. In 2017, seven other entangled 

whales were observed: three were disentangled, three shed the gear, and one was not seen again. 

Ship Strikes 

Reducing Risk

Ship strikes are currently the second most frequently documented cause of mortality in right 

whales. The per capita mortality frequency has not varied much, hovering around 0.34% deaths 

or serious injury events per year (Fig. 1). Several management actions were implemented in U.S. 

and Canadian waters beginning in 2008 to reduce the risk of collisions between right whales and 

large vessels. Major actions include:

● Voluntary two-way routes for commercial vessels off the Southeast U.S. and in Cape

Cod Bay

● Modification of the Boston, Massachusetts Traffic Separation Scheme

● Canada and the International Maritime Organization established the voluntary Area To

Be Avoided concept in the Roseway Basin

● Seasonal Management Areas in habitats off of Massachusetts, ports along the MidAtlantic coast, and the southeastern U.S. where vessels are required to slow to speeds less

than 10 knots during transits for vessels 65 ft in length or longer
8 

● Intermittent implementation of voluntary speed restrictions in Dynamic Management 

Areas within which right whale aggregations are observed outside the boundaries of the 

Seasonal Management Areas

Several analyses have been conducted to evaluate the effectiveness of these management efforts 

(Conn and Silber 2013; Lagueux et al. 2011; Silber et al. 2014; van der Hoop et al. 2012). In 

general, while these analyses were based on a short time-series of available data, collectively 

they suggest that after ship-strike rules put in place, a reduction in right whale mortality from 

ship strikes followed, and in general were at the lowest on record per capita from 2010 through 

2016. 

Responding to Changing Risk

In 2017, right whale deaths by ship strike increased when 5 ship-strike mortalities were 

confirmed, 1 in U.S. and 4 in Canadian waters (Fig. 1), likely caused in part when right whales 

began to spend more time in new areas with high vessel traffic and no speed restrictions. 

Increased survey effort in these areas also made it more likely that these events would be 

observed and reported. 

Entanglement

Reducing Risk

Management efforts to reduce entanglement risks in U.S. waters have focused on gear 

technology to make entanglements less likely to harm or kill whales, restricting where and when 

gear that poses a threat can be used when whales are likely to be present, and reducing the 

amount of gear in the water column (Fig 3). Measures are recommended through a take reduction 

team, as mandated under the federal Marine Mammal Protection Act. Each team comprises a 

variety of experts and stakeholders, who assist NOAA Fisheries in developing a take reduction 

plan when necessary. 

Since 1997, a series of rules have been implemented based on the take reduction plan (Fig. 3). 

These include the sinking groundline (2009) and vertical line (2015) rules. While there appears 

to have been a subsequent reduction in entanglements caused by groundline (Morin et al. 2018), 

which moved 27,000 miles of line from the water column to the bottom (NMFS, 2014), absolute 

entanglement rates appear to be on the rise (Fig 1).

Increase in Entanglement Risk 

Fewer but Stronger Lines in US Waters

There may also have been unintended consequences of the 2015 vertical line rule. The rule 

required ‘trawling up’ (using more traps per trawl) in some regions. While this reduced the 

number of lines, it also meant that lines had to be stronger to accommodate the increased load of 

multiple traps. This natural adaptation, and the fact that stronger rope was available, contributed 

to an increase in the severity of entanglements as found by Knowlton et al. (2016), who observed 

very little evidence of entanglement with ropes weaker than 7.56 kN (1700 lbsf). 
9 

Fig 3. Timeline of significant management actions focused on reducing fishing entanglement

Entanglement Trends Upward

Knowlton et al.(2012) showed that nearly 85% of right whales have been entangled in fishing 

gear at least once, 59% at least twice, and 26% of the regularly seen animals are entangled 

annually. These findings represent a continued increase in the percentage of whales encountering 

and entangling in gear, which grew from to 61.5% in 1995 (Hamilton et al. 1998), to 75.6% in 

2002 (Knowlton et al. 2005), confirming further the growing severity of the problem. 

More Vertical Line in Right Whale Habitat

Rough estimates are that approximately 622,000 vertical lines are deployed from fishing gear in 

U.S. waters from Georgia to the Gulf of Maine. Notably until spring of 2018, very few 

protections for right whales were in place in Canadian waters. In comparison to recent decades, 

more right whales now spend significantly more time in more northern waters and swim through 

extensive pot fishery zones around Nova Scotia and into the Canadian Gulf of St. Lawrence

(Daoust et al. 2018). 

Taken together, these fisheries exceed an estimated 1 million vertical lines (100,000 km) 

deployed throughout right whale migratory routes, calving, and foraging areas. Figure 4 

illustrates the scale of the challenge by providing fishery statistics for the various regions (data 

sources provided in Appendix 1).
10 

Fig 4. Index of fishing effort. a) The change in number of vertical lines in US waters from 2011 to 

2016, b.) The approximate number of traps in USA Northeastern states and Canadian 

provinces. Data sources in Appendix 1. 

Closures Are Effective, But May Not be Enough 

A great deal of effort has been put into identifying entanglement ‘hot-spots’: relatively small 

areas where focused management measures can have minimal impact to fishing while providing 

great benefit to whales. Clear examples of this approach include the seasonal closure of Cape 

Cod Bay, and now the static closure within the Area 12 fishing zone of the Canadian Gulf of St. 

Lawrence. Both are relatively small areas where a significant portion (30 to 50+ %) of the right 

whale population has reliably occurred for several weeks to months over the past few years. 

Management actions have a population level benefit with impacts restricted to very local 

portions of fisheries. While still difficult choices, this has been the preferred management 

approach. 

However, these closures, while likely very effective regionally, may not be enough. Each vertical 

line out there has some potential to cause an entanglement. With a 26% annual entanglement rate 

in a population of just over 400 animals, this translates to about 100 entanglements per year, 

which is significant for such a small population. But from the perspective of an individual fixed 

gear fisherman, they may never encounter a right whale. With more than 1 million lines out 

there, any single line has perhaps a 1 in 10,000 chance of entangling a whale in any one-year

period. This can vary somewhat from regions with high to low densities of lines and/or whales. 

However, in general, this means a fisherman and his or her descendants could go several 

generations without ever entangling of a right whale. Given this, it’s easy to believe that ‘all 

these entanglements are happening somewhere else’ regardless of where one fishes. Being able 

to directly link an entanglement with specific gear deployed at a specific place in time is rare, but 

by mapping known locations of gear that led to the entanglement of a right whale, one can see 

that there is no place within the fished area along the East Coast of North America for which 

entanglement risk is zero (Fig 5).
11 

Fig 5. Right whale entanglements from 1997 through 2017 for which the set location and type of 

gear are known, and gear was recovered from a whale. 

Sublethal Challenges- Skinny Whales and Few Calves 

Fundamentally, a population increases when there are more births than deaths. Much attention 

has been paid to direct mortality caused by ship strikes and entanglement, but less focus has been 

put on the secondary effects of these and other variables where animals survive but fail to thrive 

because of the harm done. This is particularly evident in calving among mature females. 

Biological Cost of Stressors

The abundance of photographs of known individual right whales taken over several decades have 

been used to develop health indicators associated with natural and human-caused stressors 

(Schick et al. 2013). This has been refined into a quantitative health score, including a predictive 

threshold below which females seem incapable of having a calf (Miller et al. 2012; Rolland et al. 

2016). 
12 

We understand that right whales are exposed to numerous sublethal stressors, including 

fluctuating food resources (Meyer-Gutbrod and Greene 2014) and even underwater noise 

(Rolland et al. 2012). Several recent studies have also focused on sublethal effects of 

entanglement, the first of which includes increased swimming energy costs from dragging gear

(van der Hoop et al. 2016). Even if disentangled, there are several injuries that can have costs 

lasting long after disentanglement. These include trauma wounds from rope cuts that may or 

may not eventually heal, and damage to baleen plates that can prevent efficient filter feeding for 

many years since these plates grow slowly. 

Recent studies have also shown that even without accounting for injury, the drag from carrying 

rope and other gear for long periods of time can be energetically more expensive for a female 

than the migratory and developmental costs of a pregnancy (van der Hoop et al. 2017a; van der 

Hoop et al. 2017b; van der Hoop et al. 2017c). 

Biological Demands of Right Whale Pregnancy

While serious injuries represent 1.2% of all entanglements, there are often sublethal costs to less 

severe entanglements. Should an entanglement occur but the female somehow disentangles and 

recovers, it still has the potential to reset the clock for this “capital” breeder. She now has to 

spend several years acquiring sufficient resources to get pregnant and carry a calf to term, the 

probability of a subsequent entanglement is fairly high, and this will create a negative feedback 

loop over time, where the interval between calving becomes longer. This is certainly a 

contributing factor in the longer calving interval for females, which has now grown from 4 to 10 

years (Pettis et al. 2017). 

Figure 6 demonstrates a simple model for estimating the probability that an animal will NOT 

become entangled over time. Similar to asking what are the odds of NOT getting ‘heads’ in 10 

coin tosses, this model simply asks what are the odds of not getting entangled over time if there 

is a 74% chance of not getting entangled each year (Knowlton et al. 2012). Historically the

median calving interval of a female right whale is 3 to 4 years (Pettis et al. 2017). The model 

estimates that animals have a about a 30 to 40% chance of not getting entangled during that 

period, or, conversely, a 60 to 70% chance of getting entangled. 

With the calving interval now nearly twice as long as in the past, half as many calves are being 

born. So while entanglements often do not kill an animal, they may have a large impact by 

reducing or preventing births in the population. There is an additional variable, stress, which is 

much harder to quantify but known to have costs in mammals that are foraging in an 

environment with some mortality threat (Hernández and Laundré 2005). 

It is difficult to tease out the relative effects of poor foraging conditions and the energetic costs 

of entanglement on the increased frequency of thin whales and the subsequent decrease in 

calving. Both are likely having some influence. While there are dozens of documented cases of 
13 

ship strikes and entanglement linked to right whale mortality, to date there is no confirmed 

observation of a right whale starving to death from poor forage. 

Fig 6. Cumulative annual probability of no entanglement (annual rate = 74%)

HOW LONG DO NORTH ATLANTIC RIGHT WHALES HAVE?

A Long-Lived Animal 

Right whales have the potential to be a very long-lived species. In the southern hemisphere 

where shipping and fishing pressures are much lower, there is little evidence of human activities 

causing right whale mortality. There is also little evidence of natural mortality in adult animals 

(Corkeron et al. Accepted with revision). Since the ban on commercial whaling of Southern right 

whales in 1935 (Gambell 1993) these animals have not yet lived long enough to die of natural 

causes. 

Meyer-Gutbrod and Greene (2018) demonstrated that even under poor foraging conditions, right 

whales should be able to recover if annual human-caused mortality is kept somewhere below 8-

10 deaths per year. This means that in the absence of human-caused mortalities, right whales 

could potentially endure several decades under poor foraging conditions and still recover once 

environmental conditions improve. However, in the current situation in the northern hemisphere, 
14 

where animals are living much shorter lives, there is great cause for concern that the risk of 

extinction is much higher than in the southern hemisphere, where animals are not regularly 

subject to human caused mortality. 

An Illustration of Potential Decline, 2017-2067 

A Matrix Model 

In order to measure current population trends, we used a three-stage (calf, juvenile, adult) matrix 

population projection model (Caswell 2006) for female right whales, derived from Corkeron et 

al. (Accepted with revision), to project the future abundance of right whales. Survival values used 

for input into the population projection model were calculated using a Cormack-Jolly-Seber 

(Pace et al. 2017) variant of a mark-resight model (see Appendix 2 for details) and determined 

the population is declining at 2.33% per year. 

We started the model estimating an abundance of 160 females alive at the end of 2017. With 

approximately 1.5 males per female (Pace et al. 2017), 160 females would result in an overall 

species abundance of about 400. It is possible that this abundance estimate may be marginally 

low, but since the model overestimates calving success, we assumed that these biases should 

cancel each other out. 

Using the stage derived from the matrix model, we assumed that the 2017 starting population of 

160 females was composed of 10 calves, 60 juveniles, and 90 adults. We ran 1000 stochastic 

projections forward 50 years (Fig. 7).We then extracted median and 95% quantile estimates of 

projected abundance from those projections, and estimates of the number of adult females 

remaining, for 5, 10, 15, 20, 25 and 50 years. Results are shown in the Table.

Results

The model projects that in 2067, 50 years from 2017, there would be 49 female North Atlantic 

right whales remaining, of which only 32 would be adults. In 20 to 25 years (2037-2042) there 

would be fewer than 50 adult females. In the near term, at the current rate of decline, all recovery

in the population over the past 3 decades will be lost by 2029, with the population returning to 

the 1990 estimate of 123 females. 

Notably, the model does not adjust for varying environmental conditions, which are known to 

fluctuate on a decadal time scale for North Atlantic Ecosystems (Nye et al. 2014) and are 

presently unfavorable. This approach may overestimate the rate of population decline but not the 

overall trajectory. 
15 

Fig. 7 Matrix population projection model output of North Atlantic right whale female population 

trend under current population conditions.

Table of matrix projection model output of female North Atlantic population trends for 5-year 

intervals, 2017-2067

Years from 2017 Number of females Cis Number of adult females

5 144 126 to 161 75

10 129 107 to 150 67

15 114 91 to 141 59

20 102 77 to 130 53

25 90 66 to 119 47

50 49 27 to 76 32
16 

The threshold for functional extinction is very hard to define and likely varies by species. If the 

population declines to the 1990 level, there is a new threat: a repeated genetic bottleneck. 

Genetic bottlenecks happen when a population is so small that the genetic make-up of remaining 

group is not the same as that of the initial population. The effect of repeated bottlenecks is likely 

to mean that if the population returned to the 1990 level, that group would have less genetic 

diversity than the group that existed in1990. This can lead to reduced resilience and contribute to 

increased risk of extinction (Amos and Harwood 1998; Melbourne and Hastings 2008). 

INDICATORS OF SUCCESSFUL MANAGEMENT MEASURES 

Determining the management actions necessary to reverse the current population trend is beyond 

the scope of this document. However, the scale of the actions will need to be quite significant to 

be successful. Entanglement has increased dramatically and ship strikes continue to occur. 

The population decline began in 2010 (Fig. 1), when entanglement was occurring at a rate of 

26% among sited animals per year (Knowlton et al. 2012). Since then, the right whale range 

expansion has put them in the path of more shipping and more fishing gear – encountering 

almost twice the amount of gear owing to expansion of more fishing farther offshore in US 

waters and northward into Canadian waters (Fig. 4). 

It is logical to conclude that to reverse the right whale decline, it may be necessary to reduce the 

impacts of entanglements and other harmful human interactions with right whales across their 

expanded range to pre-2010 levels. For recovery it may be necessary to go further, considering

more modifications to fishing and shipping practices to compensate for potentially reduced 

forage opportunity and increased migratory costs. 

Several biological indicators can be recommended for monitoring the short- and long-term

effectiveness of any management actions that might be put in place to reduce the rate of both 

ship strikes and fishing gear entanglement. 

Short-term indicators include fewer observed numbers of ship strikes and entanglements. These 

could be noticeable within 6 months to 1 year, but there is considerable variation around 

detectability of these events and the results will initially have a great deal of uncertainty. It takes 

approximately 1 year to conduct a population assessment and determine any changes in 

abundance. The assessment will alleviate some the uncertainty in detecting mortality risks that 

that might be mitigated by management actions. It should be noted that number of mortalities is 

the bluntest indicator of management success. 

However, teasing the relative effects of management actions and natural variability on 

population size and condition will take several years of data and analysis. Metrics such as the 

frequency of scarring, improvements in body condition, and overall health scores could be 

detectable under stable environmental conditions in 2 to 3 years. Similarly, if environmental 

conditions are adequate for females to accumulate enough resources to calve, it will likely take at 

least 2 to 4 years to separate the impact of management action that reduced the frequency of, say, 

costly entanglements from the impact of natural variability. Ultimately, confidence in any 

estimate of population trajectory will emerge over 5 to 10 years.
17 

In an ideal situation, evidence of human-caused injuries and mortality decreases, body condition 

improves, and the birth rate exceeds the death rate, resulting in more North Atlantic right whales.

ACKNOWLEDGMENTS 

The authors want to thank Peter Corkeron and Richard Pace for multiple contributions made in 

the form of contributed analysis, repeated discussions, figures, and critiques of the document. 

We would also like to thank National Marine Fisheries Service colleagues at the Greater Atlantic

Regional Fisheries Office, the Northeast Fisheries Science Center, and the Office of Protected

Resources for constructive feedback that improved the content, with special thanks to Teri Frady. 

Finally, little of the content is new here. Rather, we have pieced together a larger picture from

existing work and many informed discussions with stakeholders from all sides of this issue over 

the past several years- thank you for the opportunity to have those discussions. 

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22 

 APPENDIX 1 Data Sources for Figure 4 

Several data sources were used to construct Fig 4. All vertical line estimates in 4A were provided 

by Industrial Economics. Trap counts provided in 4B were acquired from a variety of sources. 

Raw trap counts were provided for Maine and Massachusetts. Trap counts for New Hampshire 

and all Canadian provinces were generated by multiplying license counts by trap limits. These 

were quite variable across regions, in which case the multiplier used is reported in the Table in 

the report. 

APPENDIX 2 Model Inputs and Methods used for Population 

Projection

In order to determine current rate of population decline we used a simple, three-stage matrix 

population projection model (Caswell 2006) for female right whales, derived from Corkeron et 
23 

al. (Accepted with revision), to project the future abundance of North Atlantic right whales. The 

model’s three stages are: calf, juvenile and adult. Survival values used for input into the 

population projection model are derived from survival estimates calculated using a CormackJolly-Seber (as opposed to the published Jolly-Seber, Pace et al 2017) variant of a mark-resight 

model (see Appendix 1 for details). We used the lower 95% credibility intervals of the median 

estimates of survival for 2011-2015 from the model. These were: calves: 0.86137, juveniles: 

0.92684, and adult females: 0.92684. The matrix projections also assume: a calving interval of 

4.75 years (the mean of median inter-calf intervals for calving females 2011-2017, from the 2017 

North Atlantic Right Whale Report Card (Pettis et al. 2017), ; females maturing at 11; and a 

current maximum longevity of 50. With no calves born this year, this calving estimate is 

arguably optimistic, but the inter-calf interval estimate for 2018 would be undefined, and so is 

unusable. Survival and transition probabilities for stages were calculated as described in 

Corkeron et al. (Accepted with revision).The model was run in R 3.4.3 (R_Core_Team 2017), 

using the libraries diagram (Soetaert 2017), popbio (Stubben and Milligan 2007) and popdemo 

(Stott et al. 2016). 

The matrix used for analyses is:

 calf immat adlt

calf 0.00000 0.00000 0.10526

immat 0.86137 0.86254 0.00000

adlt 0.00000 0.06430 0.92443

This gives an intrinsic rate of increase of 0.9767, or a decline of 2.33% per year. 

To develop a stochastic projection from this model, we took a starting abundance estimate of 160 

females alive at the end of 2017, as the unusually high observed mortality of right whales that 

year (Meyer‐Gutbrod and Greene 2018) meant that starting earlier would not capture one 

important recent anthropogenic impact on this species. With approximately 1.5 males per female 

North Atlantic right whale now (Pace et al. 2017), 160 females would give an overall species 

abundance of ~400. It is possible that this abundance estimate may prove to be marginally low, 

but as the model overestimates calving success, we assume that these biases should cancel each 

other out. When an abundance estimate for 2017 is available (by October-November 2018) the 

model can be revised.

APPENDICES REFERENCES CITED

Corkeron P, Hamilton P, Bannister J, Best P, Charlton C, Groch KR, Findlay K, Rowntree V, 

Vermeulen E, III, Pace RM. In review. The recovery of North Atlantic right whales, Eubalaena 

glacialis, has been constrained by human-caused mortality. 

Pace RM, Corkeron PJ, Kraus SD. 2017. State–space mark–recapture estimates reveal a recent 

decline in abundance of North Atlantic right whales. Ecol Evol 7(21):8730-8741. 

Pettis HM, Pace RM, Schick RS, Hamilton PK. 2017. North Atlantic Right Whale Consortium 

2017 annual report card. Boston MA: North Atlantic Right Whale Consortium. [accessed 8-26-
24

2018] Report to the North Atlantic Right Whale Consortium, October 2017, amended 8-18-2018. 

https://www.narwc.org/report-cards.html.

R_Core_Team. 2017. R: A language and environment for statistical computing. Vienna, Austria: 

R Foundation for Statistical Computing. https://www.gbif.org/tool/81287/r-a-language-andenvironment-for-statistical-computing.

Soetaert K. 2017. diagram: Functions for Visualizing Simple Graphs (Networks), Plotting Flow 

Diagrams. R package version 1.6.4. https://CRAN.R-project.org/package=diagram.

Stott I, Hodgson D, Townley T. 2016. popdemo: Demographic Modelling Using Projection 

Matrices. R package version 0.2-3. https://CRAN.R-project.org/package=popdemo.

Stubben C, Milligan B. 2007. Estimating and Analyzing Demographic Models Using the popbio 

Package in R. J Stat Soft 22(11).
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