NOAA Technical Memorandum NMFS-AFSC-150


Eastern North Pacific Gray Whale 

(Eschrichtius robustus) Unusual 

Mortality Event, 1999-2000 

by 

F. M. D. Gulland, H. Pérez-Cortés M., J. Urbán R.,

L. Rojas-Bracho, G. Ylitalo, J. Weir, S. A. Norman,

M. M. Muto, D. J. Rugh, C. Kreuder, and T. Rowles

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Alaska Fisheries Science Center 

March 2005 
NOAA Technical Memorandum NMFS 

The National Marine Fisheries Service's Alaska Fisheries Science Center 

uses the NOAA Technical Memorandum series to issue informal scientific and 

technical publications when complete formal review and editorial processing 

are not appropriate or feasible. Documents within this series reflect sound 

professional work and may be referenced in the formal scientific and technical 

literature. 

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries 

Science Center continues the NMFS-F/NWC series established in 1970 by the 

Northwest Fisheries Center. The NMFS-NWFSC series is currently used by 

the Northwest Fisheries Science Center. 

This document should be cited as follows: 

Gulland, F. M. D., H. Pérez-Cortés M., J. Urbán R., L. Rojas-Bracho, 

G. Ylitalo, J. Weir, S. A. Norman, M. M. Muto, D. J. Rugh, C. Kreuder, 

and T. Rowles. 2005. Eastern North Pacific gray whale (Eschrichtius 

robustus) unusual mortality event, 1999-2000. U. S. Dep. Commer., 

NOAA Tech. Memo. NMFS-AFSC-150, 33 p. 

Reference in this document to trade names does not imply endorsement by 

the National Marine Fisheries Service, NOAA. 
NOAA Technical Memorandum NMFS-AFSC-150


Eastern North Pacific Gray Whale 

(Eschrichtius robustus) Unusual 

Mortality Event, 1999-2000 

by

 F. M. D. Gulland1, H. Pérez-Cortés M.2, J. Urbán R.3, 

L. Rojas-Bracho4

, G. Ylitalo5, J. Weir6, S. A. Norman7, 

M. M. Muto8

, D. J. Rugh8, C. Kreuder9, and T. Rowles6 

1

The Marine Mammal Center 2Programa Nacional de Mamíferos Marinos 

1065 Fort Cronkhite Instituto Nacional de Ecología, SEMARNAT 

Sausalito, CA 94965 M. Ocampo 1045, Centro 

La Paz, BCS 23020, Mexico 

3

Departamento de Biología Marina


Universidad Autónoma de Baja California Sur


Km. 5.5 Carretera al Sur


La Paz, BCS 23081, Mexico


4

Programa Nacional de Mamíferos Marinos 

Instituto Nacional de Ecología c/o CICESE 

Km. 107 Carretera Ensenada - Tijuana 

Ensenada, BC 22860, Mexico 

5

Northwest Fisheries Science Center


National Marine Fisheries Service


2725 Montlake Boulevard East


Seattle, WA 98112-2097


6

Office of Protected Resources 

National Marine Fisheries Service 

1315 East West Highway 

Silver Spring, MD 20910-3282 

7

Protected Resources Division 8National Marine Mammal Laboratory 

National Marine Fisheries Service Alaska Fisheries Science Center 

7600 Sand Point Way NE National Marine Fisheries Service 

Seattle, WA 98115-6349 7600 Sand Point Way NE 

Seattle, WA 98115-6349 9

Wildlife Health Center


School of Veterinary Medicine


University of California


One Shields Avenue


Davis, CA 95616


U.S. DEPARTMENT OF COMMERCE

Carlos M. Gutierrez, Secretary 

National Oceanic and Atmospheric Administration 

Vice Admiral Conrad C. Lautenbacher, Jr., U.S. Navy (ret.), Under Secretary and Administrator 

National Marine Fisheries Service 

William T. Hogarth, Assistant Administrator for Fisheries 

March 2005 
This document is available to the public through: 

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

www.ntis.gov 
Notice to Users of this Document 

This document is being made available in .PDF format for the convenience of users; however, the 

accuracy and correctness of the document can only be certified as was presented in the original hard 

copy format. 

ABSTRACT


In 1999, the number of gray whale (Eschrichtius robustus) strandings documented along 

the west coast of North America increased to approximately seven times the annual mean of 

41 animals reported between 1995 and 1998. The unusually high number (283) of stranded 

whales in 1999 prompted the National Marine Fisheries Service to consult the Working 

Group on Marine Mammal Unusual Mortality Events in July 1999. The Working Group then 

formally designated the strandings as an “unusual mortality event.” The number of stranded 

animals remained high in 2000, with 368 carcasses reported (a nine-fold increase over the 

1995-98 average). In 2001 and 2002, however, total strandings decreased to 21 and 26 

animals, respectively. Most of the strandings in 1999 and 2000 occurred in Mexican waters 

during the winter season. Increases in all regions except Oregon were significant. The 

greatest proportionate increases occurred in Alaska, resulting in part from an increase in 

survey effort. Only three (0.5%) of the 651 animals that stranded in 1999 and 2000 were 

examined thoroughly to determine cause of death. In 1999 and 2000, more adults and 

subadults stranded compared to 1996-98, when calf strandings were more common. Lipid 

content of blubber was low in stranded animals, but lipid composition was altered by degree 

of carcass decomposition. Several factors have been considered as possible causes for the 

high number of gray whale strandings reported in 1999 and 2000, including starvation, 

chemical contaminants, biotoxins, infectious diseases, parasites, fisheries interactions and 

ship strikes, variability in detection effort and reporting, and affects of winds and currents on 

carcass deposition. While the emaciated condition of many of the stranded whales supports 

the idea that starvation could be a significant contributing factor in these mortalities, the 

underlying cause of starvation during this event is unknown. As some animals were in good 

iii 
to fair nutritional condition, not all strandings can logically be linked to food resource 

limitation and starvation. 

iv

CONTENTS


Page


ABSTRACT............................................................................................................................. iii 


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


METHODS ................................................................................................................................3 


Evaluation of Stranding Detection Effort ..............................................................................3 


Determination of Age ............................................................................................................5

Blubber Analyses ...................................................................................................................5 


Cause of Death .......................................................................................................................5 


Statistical Analyses ................................................................................................................6 


RESULTS ..................................................................................................................................6 


Temporal Changes in Stranding Numbers .............................................................................6 


Spatial Changes in Stranding Numbers .................................................................................7 


Sex of Stranded Whales .........................................................................................................7 


Age Class of Stranded Whales...............................................................................................8 


Blubber Analyses ...................................................................................................................8 


Cause of Death .......................................................................................................................9 


DISCUSSION ..........................................................................................................................11 


RECOMMENDATIONS FOR FUTURE ACTIONS .............................................................17 


ACKNOWLEDGEMENTS .....................................................................................................19 


CITATIONS ............................................................................................................................21 


v 

INTRODUCTION 

Eastern North Pacific gray whales (Eschrichtius robustus) migrate annually along the 

west coast of North America. Wintering areas extend from the Southern California Bight to 

the lagoons of Baja California, Mexico, whereas, the primary summering areas are in the 

Bering and Chukchi Seas (Berzin 1984; Moore et al. 1986, 2000; Swartz 1986). The 

southbound migration begins in October (Rugh et al. 2001) and is led by large whales, many 

of them pregnant females, while juvenile whales are most common late in the migration 

(Perryman and Lynn 2002). The northbound migration is also segregated by sex and age 

class, beginning with whales without calves (February-March), followed by cow/calf pairs 

(April-May) (Poole 1984). Some animals do not undertake the full migration but remain in 

coastal waters from Kodiak Island, Alaska, to northern California through the summer 

(Darling 1984, Darling et al. 1998, Calambokidis and Quan 1999, Dunham and Duffus 2001), 

although this may vary from year to year (Rugh et al. 2002). 

Gray whale abundance estimates and calf production have been monitored for many 

years. The population was increasing at 2.5% per year between the winters of 1967/1968 and 

1995/1996 (Buckland and Breiwick 2002), but the growth rate may have slowed in the 1980s 

(Wade 2002). Rugh et al. (2002) reported that abundance estimates decreased from 

approximately 30,000 in 1997/1998 to under 20,000 in 2000/2001 and 2001/2002. From 

1994 to 1998, the calf index, determined via northern migration surveys in California, ranged 

from 2.7% to 5.8% but dropped to 1.7% in 1999, was still lower in 2000 at 1.1% (Perryman 

 et al. 2002), and continued to decline in 2001 (Perryman et al. 2004). However, the calf 

index recovered in 2002 and 2003 and was at the highest recorded level (9%) in 2004 

(Perryman et al. 2004). Fluctuations in calf production have been positively correlated with 

the length of time that feeding habitat in the northern Bering Sea was free of pack ice during 

the previous year (Perryman et al. 2004). 
Stranding records on gray whales have been maintained for decades and show spatial and 

temporal patterns that reflect the migration along the west coast of North America (e.g., 

Heyning and Dahlheim 1990, Sanchez Pacheco 1998). The number of gray whales that 

strand each year along the migration route is small relative to the expected annual mortality 

(< 5%: Wade and DeMaster 1996). Reported causes of mortality in these animals include 

ship strikes and entanglements in fishing gear (Heyning and Dahleim 1990, Baird et al. 

2002). Several reports have described the increase in gray whale strandings that began in the 

1999 winter season in Mexico (Pérez-Cortés et al. 1999; LeBouef et al. 2000; Norman et al. 

2000; Krahn et al. 2001; Moore et al. 2001, 2003). This report summarizes the National 

Marine Fisheries Service’s (NMFS) investigation of the unusual number of gray whale 

mortalities reported during 1999 and 2000. 

In 1999, an unusually large number of dead gray whales stranded along the coast of North 

America from Baja California Sur, Mexico, to Alaska. In response to these reports, NMFS 

consulted the Working Group on Marine Mammal Unusual Mortality Events in July of 1999. 

The Working Group deemed the strandings an “unusual mortality event” based on the fact 

that the animals were stranding throughout their range, stranding rates had increased 

precipitously, animal behavior and body condition were different from those reported 

previously, and animals were stranding in areas where strandings had not been historically 

noted. In addition to recommending that the mortalities be deemed an unusual event, the 

Working Group also recommended: 1) increasing evaluations and examinations of carcasses; 

2) providing a small group of people to summarize the available information for the working 

group; and 3) coordinating and exchanging information between the four countries (Mexico, 

the United States, Canada, and Russia) in which this stock occurs. 

2

Coordination between the stranding networks was increased after the event was declared 

unusual. A provisional report was prepared for the Working Group in 2000 (Norman 

et al. 2000) and preliminary findings were presented to the Scientific Committee of the 

International Whaling Commission (Pérez-Cortés et al. 1999). To enhance coordination of 

gray whale stranding responses, two workshops were held in Mexico: one in La Paz (March 

2000) and one in Guerrero Negro (March 2001). A protocol for minimal data collection from 

stranded gray whales was developed and distributed to network participants, and a centralized 

real-time reporting mechanism was established. 

METHODS 

Gray whale stranding reports from 1995 to 2002 were examined and verified, and 

positions and descriptions were evaluated in an effort to decrease duplicate reports of the 

same animal. If two animals were reported in the same location, were the same size, and had 

no obvious distinguishing marks (or if the decomposition state was consistent with the 

interval between reports), the animals were considered duplicates. In California, most whales 

were towed out to sea after minimal examination. The stranding network marked these 

animals with either tail notches or body slices to increase the chances of properly identifying 

re-stranded carcasses, and the towing operator often left line attached to the tail flukes. Many 

of these whales re-stranded on the outer coast and were noted as previously documented 

mortalities. 

Evaluation of Stranding Detection Effort 

Stranding detection effort varied significantly both geographically and temporally. 

Because of reports of high stranding rates, an increased emphasis on more-timely reporting 

3

was initiated in April 1999 and continued through 2002 to allow real-time analysis of trends. 

The wintering lagoons in Mexico have been consistently surveyed for stranded whales in the 

recent past, and the effort in 1999 and 2000 was comparable with that of previous years. 

Additional aerial surveys in 1999 and 2000 covered the areas outside the lagoons. Records of 

gray whales that stranded outside their normal winter range were obtained opportunistically. 

The stranding detection and reporting effort in California, Oregon, and Washington (except 

for remote areas of the Olympic Peninsula) was fairly consistent from 1995 to 2002, with 

strandings reported by the U.S. Coast Guard, private vessels, private beachgoers, researchers, 

and stranding-network participants. Stranding reports from British Columbia have been 

opportunistic, as it is impractical to provide thorough coverage of the complex coastline with 

its many islands, shoals, and inland seas. In Alaska, detection effort and area of geographic 

coverage have differed significantly from year to year. No directed survey effort for gray 

whale mortalities occurred from 1995 to 1998. Reports of gray whale mortalities during 

those years were compiled from opportunistic reports that were often relayed to the regional 

stranding coordinator months after the observation. Dedicated survey effort occurred in some 

areas of the Alaska coast in 1999-2001. The following areas were consistently surveyed 

during the same month, between May and August, in each survey year: the coastal regions of 

the northern part of Southeast Alaska in 2000-2001; Yakutat to Cordova in 2000-2001; and 

the Kodiak Archipelago, the north side of the Alaska Peninsula, and Bristol Bay in 1999­

2001. Additional areas were surveyed opportunistically in some years; that is, the south side 

of the Alaska Peninsula and the Gulf of Alaska coast west of Cordova were surveyed in 2001, 

and parts of the northwest coastline north of Bristol Bay were surveyed in 2000. Reports 

from the northern parts of Alaska and Russia have generally been opportunistic. 

4

Determination of Age 

Several sources describe the classification of age based on body length (Rice and 

Wolman 1971, Jones and Swartz 1984, Sanchez Pacheco 1998). Four age classes were 

defined for the purposes of this report, as described in Norman et al. (2000), and reported 

lengths were converted to age class based on the following criteria: calves were less than 

8 m; yearlings were 8.0-8.9 m; juveniles and subadults were 9.0-11.9 m; and adults were 

more than 12 m. 

Blubber Analyses 

Blubber-thickness measurements were not taken at standard morphological sites on 

stranded whales in 1999, and inclusion of the epidermis and hypodermis in the measurements 

was not standardized until 2000. Standardization was attempted in 2000 and 2001, when 

blubber was measured dorsally, laterally, and ventrally along the axillary girth. Blubberthickness measurements were not provided in many stranding reports due to inaccessibility of 

the carcass, danger to stranding-network participants, or decomposition of the carcass. The 

total lipids and lipid classes in blubber samples were analyzed by the methods described in 

Krahn et al. (2001). 

Cause of Death 

Although each stranding was examined as thoroughly as was practical, only three animals 

were examined fully enough to determine their health status and to detect any pre-existing 

diseases. These three whales (two male juveniles and one male yearling) stranded alive and 

were humanely euthanized due to their poor prognosis for survival. Each animal received 

midazolam, intramuscularly at 0.02 mg/kg, as a sedative and then pentothal sodium, 

intravenously into the superficial caudal peduncle veins, to effect (i.e., cessation of 

5

respiration and no detectable heart beat). Necropsies were performed according to Geraci 

and Lounsbury (1993), and tissues were collected for histopathology, toxicology, 

parasitology, and microbiology analyses. 

Statistical Analyses 

The two-sided chi-square test of independence was used to evaluate age-class and sex 

distributions by year and location. Animals that could not be categorized by age class or sex 

were included in the summary tables (as “unknowns”) but excluded from the analyses. 

RESULTS 

Temporal Changes in Stranding Numbers 

Increased numbers of gray whales stranded along most of their migration route in 1999 

and 2000, compared to the previous four years, with the highest numbers reported in Mexico 

and Alaska (Table 1, Fig. 1). Prior to 1999, gray whale stranding rates averaged 41 animals 

per year. Stranding rates increased to 283 whales in 1999 and 368 whales in 2000. These 

high stranding rates were followed by lower than average rates in 2001 and 2002, when the 

number of strandings decreased to 21 and 26 whales, respectively. There are too few 

consistent coast-wide stranding records prior to 1999 to determine changes in temporal 

patterns during the mortality event. However, most strandings occurred when whales were 

expected to be in an area based on their migration cycle (Table 1). 

6

Spatial Changes in Stranding Numbers 

Based on the distribution of strandings throughout all areas, and the inter-annual variation 

in overall number of carcasses retrieved, there was a noticeably higher number of reports than 

expected in 1999 and 2000, particularly in Alaska and Mexico (Table 2). 

In Mexico, 100% of the strandings reported on the outer beaches of the Baja California 

Peninsula were noted first by aerial survey in 1999 and 2000. The greatest number of 

strandings occurred in Laguna Ojo de Liebre (34% in 1999 and 31% in 2000). Some whales 

were found in locations with historically low numbers of strandings; however, an increase in 

search effort in the southernmost lagoons in recent years may have resulted in an increase in 

reported strandings. Particularly during 1999, strandings were recorded in locations outside 

the normal winter range of the gray whale, such as Banderas Bay, Nayarit (Puerto Vallarta 

area), and the coast of Sonora in the Gulf of California. In California, two clusters of 

strandings noted in 1999 and 2000 (in southern California and San Francisco Bay) differed 

from historical stranding locations. Stranding locations in Alaska differed between 1999 and 

2000, possibly reflecting differences in search effort between the two years. 

Sex of Stranded Whales 

Gender was reported for less than half (46%) of the stranded gray whales. In stranding 

reports for all years except 1996, 2000, and 2002, the number of animals of “unknown” sex 

was higher than the number where sex was determined (Table 3). There was an apparent 

increase in the number of adult females that stranded in 1999, particularly in Mexico. 

However, there is a detection bias for males, especially in decomposed or bloated carcasses 

because the penis often protrudes making it easier to identify males. This bias and the high 

number of animals of unknown sex confound any interpretation of the results. 

7

Age Class of Stranded Whales 

In general, about one-third of the known-age strandings were adults, one-third were 

subadults, and the remainder were about equally yearlings and calves (Table 4). However, 

the age-class distribution of carcasses differed significantly by year (p < 0.001). Calf 

strandings were unusually high in 1997 and 1998, while adult strandings were unusually high 

in 1999 and 2000. Although the numbers of calves that stranded in 1999 and 2000 were also 

high, the percentage of the total number of strandings comprised by calves in each of those 

years was much lower than usual (9.0% and 5.6%, respectively). The distribution of age 

classes of stranded animals also differed by region (Table 5), with most adults and subadults 

stranding in Mexico and most calves stranding in California (p < 0.001). In 1996-98, an 

expected higher proportion of calves stranded at the wintering lagoons in Mexico; during 

1999 and 2000, however, the numbers of adults and subadults that stranded surpassed the 

number of calves. 

Blubber Analyses

 Blubber-thickness measurements were not recorded in many stranding reports due to the 

inaccessibility or decomposition of most carcasses. The reported blubber thickness of 64 

samples ranged from 2 cm to 13 cm. However, these results are difficult to interpret since 

measurements were not standardized. 

Blubber samples from carcasses in various stages of decomposition were evaluated from 

the 1999-2000 stranding event (Table 6). Lipid content of blubber from stranded whales was 

low compared to published values from subsistence-harvested whales (Krahn et al. 2001); in 

part, the samples from stranded animals were influenced by degree of carcass decomposition. 

The blubber samples from carcasses that were in moderate or advanced stages of 

8

decomposition contained relatively low lipid concentrations (< 10%) and lower proportions 

of triglycerides, but higher cholesterol and phospholipid levels, in comparison to the blubber 

from carcasses that were classified as “fresh.” 

Cause of Death 

Each of the three stranded whales that were euthanized had different proximate factors 

that contributed to their death. The first animal was a juvenile male that live-stranded in 

Monterey, California, on 11 May 1999. On gross examination, the animal was deemed 

severely emaciated based on the protrusion of the vertebrae along the dorsal midline and the 

absence of the nuchal fat pad. Ulcers were present along the leading edges of the pectoral 

fins, and there was a dense infestation of lice and barnacles over the entire body. Other 

findings included 500 cc of clear fluid in the pericardial sac and pleural cavity and red fluid 

in the stomach. The blood vessels of the meninges were distended and some swelling of the 

brain cortex was apparent. Histopathology showed evidence of a neurotropic encephalitis, 

suggestive of a viral etiology. Serology from this whale, performed by U.S. Department of 

Agriculture (USDA) scientists at the National Veterinary Services Laboratory in Ames, Iowa, 

revealed a haemagglutination inhibition titer to Western equine encephalitis (WEE) of 1/320, 

to Eastern equine encephalitis (EEE) of 1/160, and to Venezuelan equine encephalitis (VEE) 

of 1/180. The serum neutralization titer was 1/100 for EEE, thereby confirming antibodies to 

an encephalitis virus but not specifically identifying the EEE virus. Virus isolation was 

negative for all tissues examined later; however, this may have been a result of culture 

conditions. In comparison, two “control” blood samples (collected in the 1998 season from 

two gray whale neonates with no milk in their stomachs) had no detectable titers to these 

viruses. A third control blood sample (from a gray whale which, based on maternal antibody 

testing results, had suckled prior to stranding and collection) showed a haemaglutination 

9

inhibition titer to WEE and EEE of 1/100 but none with serum neutralization. The USDA 

scientists believe that the positive titers from the whales were a cross reactivity to a related 

but unknown virus (Gulland and Rowles, unpubl. data). 

A second necropsied whale was a yearling male that stranded in Marin County, 

California, on 26 June 1999 (Dailey et al. 2000). The blubber thickness at the mid-lateral 

flank was 8 cm. The most notable gross lesions were granulomas, associated with the 

parasite Bolbosoma balanae, in the first 75 m of the ileum. The stomach was distended with 

anisakid parasites (Anisakis simplex) and food material, and massive numbers of trematode 

parasites (Ogmogaster spp.) were found along the entire intestinal tract. Cachexia, 

congestion and edema of the lungs, whale lice associated with multifocal ulcerative 

dermatitis, and mild interstitial myocarditis were also noted (Dailey et al. 2000). 

A third juvenile whale that stranded in Santa Cruz County, California, on 8 April 2000, 

had a ventral blubber thickness of 7 cm, mild colitis and proctitis associated with trematode 

parasites (Ogmogaster spp.), zymogen depletion in the pancreas (which is consistent with 

fasting or starvation), an ulcerative glossitis of the tongue, and dark neuronal change in the 

frontal cortex and the hippocampus of the brain. Domoic acid was detected in the serum, 

urine, and feces of this whale by receptor assay and was confirmed in the urine and feces by 

HPLC-MS/MS with levels of 1.6 and 0.528 μg domoic acid/ml substrate, respectively. 

In both years of the unusual mortality event, there were reports of gray whale mortalities 

due to fisheries interactions; 7 mortalities were reported in 1999 and 8 were reported in 2000, 

compared to an average of 4.5 fisheries-caused mortalities per year reported between 1995 

and 1998 (Angliss and Lodge 2002). 

One gray whale mortality due to a ship strike was also reported in each of the event years, 

which was similar to the average number of ship-strike mortalities per year (1.25) reported in 

1995-98 (Angliss and Lodge 2002). Two additional gray whale mortalities in 1999-2000 

10

may have been due to ship strikes. In 1999, the vertebra (atlas) of an animal that stranded at 

Olele Point, Washington, was determined to have fractures caused by ante-mortem trauma, 

which may have been due to a ship strike1. In 2000, one whale that stranded in the San 

Francisco Bay area had parallel cuts of equal length in the dorsal blubber that were typical of 

propeller injuries, but this whale was not necropsied fully to determine the extent of the 

damage. It is likely that these wounds were ante-mortem, as dead whales usually float with 

the ventral abdomen facing up and are, thus, more likely to be struck by propellers along the 

ventral, rather than the dorsal, surface. External gross evidence of a ship strike is usually 

limited to the effects of propeller injury. Often, animals that have been struck by the bow of 

a ship show few external signs and must be examined internally before a ship strike can be 

confirmed. Since most of the animals were not examined, the actual number of ship strikes is 

unknown. Due to logistic difficulties, the majority of dead whales observed in San Francisco 

Bay in 2000 were not examined to determine cause of death. Since many of these animals 

were within the main shipping channels when first observed as dead, some of them might 

have been killed by ship strikes. 

DISCUSSION 

The proximate cause of death was determined for only 3 of 651 stranded animals and 

each presented unique etiologies (viral, parasitic, biotoxin). Equine encephalitis, detected in 

the first whale, has not previously been reported in stranded whales and, although typically 

transmitted by insects, its mode of transmission to a marine mammal is unclear. The 

parasites reported in the second necropsied whale are not uncommon in baleen whales. 

However, the intensity of infection and severity of associated lesions were unusual. The third 

1

 P. Gearin, National Marine Mammal Laboratory, Alaska Fisheries Science Center, NMFS, 7600 Sand Point 

Way NE, Seattle, WA 98115. Pers. commun., March 2000. 

11

whale likely was intoxicated with domoic acid, as this neurotoxin (produced by the diatom 

Pseudonitzschia australis) caused the deaths of hundreds of California sea lions (Zalophus 

californianus) in the same region in 2000 (Gulland et al. 2002). Although the levels of 

domoic acid detected in this necropsied whale would indicate acute toxicosis in a laboratory 

primate, toxic doses for cetacea have not been established (Truelove and Iverson 1994). Each 

of the necropsied animals was emaciated, which may have been a cause or consequence of 

their diseases. For instance, malnourished animals might feed in unusual sites and, thus, 

acquire parasites or biotoxins, or immunosuppression caused by malnutrition could increase 

their susceptibility to infectious disease. However, as few whales were examined thoroughly, 

no evidence is available for the actual cause of death of most of the animals involved in this 

event. The emaciated condition of many stranded and living whales suggests that starvation 

may have been a predisposing cause for many of the mortalities observed in 1999 and 2000 

(LeBouef et al. 2000, Moore et al. 2001). Starvation could be primary (resulting from a 

decrease in the availability of prey) or secondary (due to disease and the inability of sick 

whales to feed). However, no reliable quantitative measure of nutritional status is available 

from the stranded whales and not all the stranded whales were visibly emaciated. 

Measurements of blubber thickness have been the most common way to qualitatively 

assess body condition and degree of starvation of cetaceans in the field. Measurements of 

blubber thickness are affected by the state of carcass decomposition, the site measured, and 

the sampling technique. Lipid content of blubber has also been used to assess nutritional 

status. In gray whales, blubber lipid content varies according to season, sex, age, and 

reproductive status (Rice and Wolman 1971). In other mysticetes, blubber lipid composition 

is not uniform throughout the blubber depth or across the body (Willetto et al. 2002; Ylitalo, 

unpubl. data), so this is also likely to be the case in gray whales. Decomposition has dramatic 

effects on blubber lipid composition (Krahn et al. 2001). The decreased proportions of 

12

triglycerides in the blubber of the stranded animals, compared to lipid levels in the blubber of 

gray whales taken in the Russian subsistence harvest, may be due to decomposition and to the 

leaching of these compounds from the blubber, resulting in higher proportions of polar 

compounds. The 43% lipid content of blubber samples from subsistence-harvested whales 

(Krahn et al. 2001) was considerably higher than the 12% lipid content of blubber samples 

from stranded whales classified as “fresh” in 1999 and 2000 (Table 6). Samples from the 

Russian subsistence harvest were expected to have relatively high lipid concentrations 

because the whales were harvested at the end of their feeding season and the samples were 

fresh. In contrast, most of the stranded whales had been migrating north and were fasting 

prior to stranding and samples from these animals, although classified as “fresh,” were likely 

more decomposed since tissues deteriorate rapidly after death. Thus, the low lipid content of 

blubber from stranded whales may be due to poor nutritional condition, decomposition, or 

sampling differences. Decomposition studies are necessary to determine how changes in 

lipid-class profiles will affect the recovery of blubber lipids and the assessment of 

contaminant burdens in stranded animals. 

Investigations of any mortality event proceed under the assumption that many factors are 

involved in the increased number of mortalities and that it is unlikely that a single factor or 

cause is responsible for all of the strandings within the event. Often the proximate cause(s) 

of death is varied and the ultimate cause(s) of death is elusive and difficult to define. Factors 

which may have contributed to the increased number of mortalities observed in 1999 and 

2000 include: 1) adverse nutritional stress; 2) chemical contaminants; 3) biotoxins; 

4) disease or parasites, in which animals are either directly affected or are incapacitated and 

unable to feed, migrate, or reproduce; 5) direct anthropogenic factors (i.e., fishery 

interactions or ship strikes); 6) increased survey/report effort; and 7) affects of wind and 

currents on carcass deposition. The amount of detail contained in the examination and 

13

necropsy reports varied depending on the examiner and the accessibility and condition of the 

carcass. In most cases, the data needed to fully characterize this event were very limited. 

Winds and ocean currents likely influence the number of whale carcasses that actually 

wash ashore in a particular region. Onshore winds will bring more floating carcasses ashore 

than will offshore winds and the degree of decomposition will affect flotation, thereby, 

altering the influence of ocean currents or wind. However, there are too many variables to 

determine whether a whale will float ashore. Winds and ocean currents in 1999 and 2000 did 

not appear to differ enough from previous years to account for an increase in detection or 

deposition of carcasses2

. 

The mean concentrations of organochlorines in the blubber of gray whales that stranded 

in 1999 were previously reported by Krahn et al. (2001). Reported levels were well below 

those observed in apparently healthy gray whales that were harvested in Russia (Tilbury et al. 

2002), suggesting that acute organochlorine toxicity was unlikely to be an important factor in 

this mortality event. Ruelas-Inzunza et al. (2003) found lower levels of total mercury and 

methylmercury in the muscle, kidney, and liver tissues of four gray whales that stranded in 

the Gulf of California during 1999 than has been reported for other marine mammals. 

However, it should be noted that sampling differences and the effect of decomposition on 

blubber lipids may alter the results of the chemical analysis. Overall, no contaminant was 

found that would be the proximate cause for acute mortality of this magnitude. 

Too few carcasses were adequately sampled to assess the importance of fisheries 

interactions, ship strikes, disease, parasites, and biotoxins as factors in this mortality event. 

Viruses, parasites, and domoic acid were determined to have played a role in the death of the 

2

G. Watabayashi, National Ocean Service, NOAA, 7600 Sand Point Way NE, Seattle, WA 98115. Pers. 

commun., January 2000. 

14

three animals that were sufficiently examined to determine the cause of death. The 

significance of these factors in the 1999-2000 mortality event and their interactions with 

nutritional status cannot be determined from the available data. However, the magnitude and 

the wide temporal and spatial distribution of the strandings suggest that a common factor was 

involved, so it is unlikely that a single infectious disease, parasite, or biotoxin was 

responsible for the entire die-off. Although direct evidence of starvation in stranded whales 

is limited, it remains the most likely dominant factor in precipitating this unusual mortality 

event. 

The reason for such a large-scale starvation is unclear. Perryman et al. (2002) showed 

that seasonal changes in ice distribution in the Bering and Chukchi Seas might influence the 

duration of whale feeding (and, thus, nutritional status prior to the southbound migration). 

They documented a correlation between time of ice retreat in the spring and calf production 

the following year. Alternatively, environmental changes such as an El Niño event could 

have resulted in shifts or losses in prey availability in the summer feeding grounds (LeBoeuf 

et al. 2000; Moore et al. 2001, 2003). Nutritional stress can have a significant impact on 

survival through several mechanisms, resulting in different proximate causes of death. In 

addition, nutritional stress may affect reproduction via several mechanisms and at different 

stages. A decrease in food availability in 1998 might have led to increased nutritional stress 

on females that were pregnant in 1998 and lactating in 1999, possibly increasing the mortality 

of lactating adult females in 1999. Unfortunately, the available data do not allow further 

discrimination of which reproductive or life stages might have been affected most nor do they 

elucidate the pathophysiology of the mortalities. 

If food limitation was a result of high population density, then this mortality event could 

be a dramatic example of a density-dependent effect on whale survival (Moore et al. 2001, 

2003). It has been hypothesized that the mechanism that regulates populations of long-lived 

15

mammals, such as cetaceans, would follow a sequence as a population increased, with density 

dependence first affecting the survival rate of immature animals, then the age of sexual 

maturity and the birth rate, and finally the adult survival rate (Eberhardt 1977). This 

hypothesis partially follows from the recognition that a long-lived species that reaches sexual 

maturity slowly and has a low intrinsic rate of increase must maximize adult survival in order 

to persist. Adult females of long-lived species may be able to forgo reproduction to 

maximize individual survival when conditions are poor. Substantial evidence of densitydependent responses in life-history traits in marine mammals, including cetaceans, has been 

reported, particularly in reproductive traits such as pregnancy rates and age of sexual maturity 

(Fowler 1984, 1987). For example, the age of sexual maturity apparently became younger 

for fin and sei whales in the Antarctic as their populations were depleted by commercial 

harvest (Fowler 1987). The lack of much evidence for density dependence in adult survival 

is likely due to the difficulties in estimating survival rates of cetaceans. 

There are no data on the interactions between population dynamics and food limitation in 

large whales, but some data are available on the interactions between resource limitations and 

population dynamics in studies of ungulate populations. In both red deer (Cervus elaphus) 

and Soay sheep (Ovis aries), increasing population density decreases survival of males more 

than females and decreases calf over-winter survival more than that of adults (Clutton-Brock 

et al. 1985, Gulland 1992). The higher mortality of adult female whales in this mortality 

event differs from the pattern of differential survival observed in ungulates. The lactating 

females would likely be most vulnerable to nutritional stress towards the end of lactation, 

which should correspond with food abundance for these whales. However, in years that have 

summer feeding restrictions, these post-lactational females would be most vulnerable to 

disease, starvation, and other mortality factors and may represent a high-risk cohort similar to 

that of neonates and calves. 

16

Populations of cetaceans that are near carrying capacity are likely to be more vulnerable 

to environmental variability. Detecting responses of cetacean populations to environmental 

change is difficult, but there is evidence of nutritional stress in the teeth of dusky dolphins off 

Peru during the 1982-83 El Niño event (Manzanilla 1989). Calf production was low in the 

Eastern North Pacific gray whale population in 1999, 2000, and 2001, and it appears to be 

correlated with environmental conditions (Perryman et al. 2002). While this could be due 

solely to a dramatic environmental change, it could also be due, in part, to the population 

being close to carrying capacity. The higher number of strandings, combined with the greater 

proportion of subadult and adult gray whales that stranded in 1999 and 2000, suggests that 

survival rates of all age classes were lower in these years. The poor calf production in these 

years (Perryman et al. 2002) would also lead to the likelihood of a higher proportion of older 

animals that stranded. That situation was particularly evident within the Mexican lagoons 

where normally (except in 1999 and 2000) there are higher numbers of dead calves than 

adults (Sanchez Pacheco 1998). Taken together, these events could be indicative of a 

population near carrying capacity that experienced substantial nutritional stress during poor 

environmental conditions, which was translated into lower reproduction and higher mortality. 

Although these effects have been seen only in recent years, a new analysis fitting a densitydependent model to the population-trend data suggests the Eastern North Pacific gray whale 

population is no longer increasing and has been relatively stable since the late 1980s or early 

1990s; therefore, it may be close to or already at carrying capacity (Wade 2002). 

RECOMMENDATIONS FOR FUTURE ACTIONS 

Future monitoring of gray whale population parameters, life-history and health 

parameters (including characterization of normal animals), and prey distribution and 

17

abundance is essential for determining the underlying cause(s) of mortalities. Detailed data 

on gray whale body condition during future mortality events and in “normal” mortality years 

are needed. Because gray whales migrate close to shore, their carcasses are often accessible 

to scientists and the public; however, difficult access and regulations dealing with stranded 

marine mammals often prevent examination of carcasses. To better understand the health of 

this population, international stranding networks are needed and stranding response teams 

need more support, particularly in facilitating necropsies. Individuals, organizations, and 

agencies involved in stranding responses should share ideas and recommendations with 

similar groups in other regions or countries (e.g., Geraci and Lounsbury 1993, Tougaard and 

Kinze 1999). It is critical to standardize collection of all data to make analyses comparable 

from one region to another. Whenever possible, carcasses should be marked to avoid 

recounts during successive surveys and to avoid confusion when different teams are 

processing animals in close proximity. Cause of death should be determined by complete 

necropsy of animals whenever possible. Improved methods of assessing nutritional status in 

carcasses and live animals should be developed. 

Due to the net decrease in calf numbers in Mexican lagoons in 1999 (Urbán et al. 2003a, 

2003b), it may also be worthwhile to increase examination of calf or neonate carcasses and to 

collect calf blood samples to screen for diseases (e.g., brucellosis) known to cause abortions 

and early death in several species of mammals (Williams 1982, Ewalt et al. 1994). Efforts to 

monitor and characterize the behavior, reproduction, and health of these animals in the 

lagoons should be continued. Lipid, disease, contaminant, and biotoxin analyses should be 

continued; expansion of nutrition, health, and reproduction research should be initiated; and 

further research on prey availability should be initiated in order to investigate relationships 

between physical, biological, and chemical environmental parameters and gray whale 

mortalities or overall health. Joint international stranding response teams should be formed, 

18

and health assessment protocols should be shared between researchers in Mexico, the United 

States, Canada, and Russia. 

ACKNOWLEDGEMENTS 

The authors thank Joe Cordaro, Brent Norberg, Kaja Brix, Peggy Krahn, Jonna Mazet, 

John Calambokidis, Sue Moore, D. Ann Pabst, Vicki Stegall, and Alejandro Gómez-Gallardo 

for their contributions to this investigation. Brian Tracy and Amy Sloan contributed a great 

deal to this report by validating all the stranding reports received from 1995 to 2001 and 

entering all the data into a database for evaluation. Linda Lowenstine and the pathology 

residents at the University of California - Davis performed histopathology on tissues from 

dead whales. We thank Peggy Krahn, Paul Wade, and Carla Willetto for their comments on 

the manuscript and Todd O’Hara and Sue Moore for reviewing it. Funding for investigations 

was provided by the NMFS/Marine Mammal Health and Stranding Response Program, 

individual stranding network participants, the Marine Biotoxin Laboratory of the National 

Ocean Service, and the Comapañía Exportadora de Sal S.A. The investigation could not be 

undertaken nor completed to the extent it was without the hard work of the volunteer 

stranding network within the United States, Mexico, and Canada. Cooperative stranding 

workshops held in Mexico in 2000 and 2001 were made possible through funding from the 

National Fish and Wildlife Foundation, NMFS, the Ocean Conservancy, and the Wildlife 

Trust. Carcasses were examined and specimens were collected under the U.S. Marine 

Mammal Protection Act (MMPA) permits of the respective NOAA Regional Offices. The 

investigation in Mexico was under the permit of The Secretaría de Medio Ambiente y 

Recursos Naturales (SEMARNAT). 

19

 

CITATIONS


Angliss, R. P., and K. L. Lodge. 2002. Alaska marine mammal stock assessments, 2002. 

U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-133, 224 p. 

Baird, R. W., P. J. Stacey, D. A. Duffus, and K. M. Langelier. 2002. An evaluation of gray 

whale (Eschrichtius robustus) mortality incidental to fishing operations in British 

Columbia, Canada. J. Cetacean Res. Manage. 4(3):289-296. 

Berzin, A. A. 1984. Soviet studies on the distribution and numbers of the gray whale in the 

Bering and Chukchi Seas from 1968 to 1982, p. 409-419. In M. L. Jones, S. L. Swartz, 

and S. Leatherwood (editors), The gray whale, Eschrichtius robustus. Academic Press, 

Inc., Orlando. 600 p. 

Buckland, S. T., and J. M. Breiwick. 	2002. Estimated trends in abundance of eastern Pacific 

gray whales from shore counts (1967/68 to 1995/96). J. Cetacean Res. Manage. 4(1):41-

48. 

Calambokidis, J., and J. Quan. 1999. Photographic identification research on seasonal 

resident whales in Washington State, p. 55-56. In D. J. Rugh, M. M. Muto, S. E. Moore, 

and D. P. DeMaster (editors), Status review of the Eastern North Pacific stock of gray 

whales. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-103, 96 p. 

Clutton-Brock, T. H., M. Major, and F. E. Guinness. 1985. Population regulation in male 

and female red deer. J. Anim. Ecol. 54(3):831-846. 

Dailey, M. D., F. M. D. Gulland, L. J. Lowenstine, P. Silvagni, and D. Howard. 	2000. Prey, 

parasites and pathology associated with the mortality of a juvenile gray whale 

(Eschrichtius robustus) stranded along the northern California coast. Dis. Aquat. Org. 

42:111-117. 

21

Darling, J. D. 1984. Gray whales off Vancouver Island, British Columbia, p. 267-287. In 

M. L. Jones, S. L. Swartz, and S. Leatherwood (editors), The gray whale, Eschrichtius 

robustus. Academic Press, Inc., Orlando. 600 p. 

Darling, J. D., K. E. Keogh, and T. E. Steeves. 1998. Gray whale (Eschrichtius robustus) 

habitat utilization and prey species off Vancouver Island, B.C. Mar. Mammal Sci. 

14(4):692-720. 

Dunham, J. S., and D. A. Duffus. 	2001. Foraging patterns of gray whales in central 

Clayoquot Sound, British Columbia, Canada. Mar. Ecol. Prog. Ser. 223:299-310. 

Eberhardt, L. L. 1977. Optimal policies for conservation of large mammals, with special 

reference to marine ecosystems. Environ. Conserv. 4(3):205-212. 

Ewalt, D. R., J. B. Payeur, B. M. Martin, D. R. Cummins, and W. G. Miller. 1994. 

Characteristics of a Brucella species from a bottlenose dolphin (Tursiops truncatus). 

J. Vet. Diagn. Invest. 6(4):448-452. 

Fowler, C. W. 1984. Density dependence in cetacean populations. Rep. Int. Whaling 

Comm. (Special Issue 6):373-379. 

Fowler, C. W. 1987. A review of density dependence in populations of large mammals, 

p. 401-441. In H. H. Genoways (editor), Current mammalogy. Volume 1. Plenum Press, 

New York. 519 p. 

Geraci, J. R., and V. J. Lounsbury. 1993. Marine mammals ashore: A field guide for 

strandings. Texas A&M University Sea Grant College Program, Galveston, TX. 305 p. 

Gulland, F. M. D. 1992. The role of nematode parasites in Soay sheep (Ovis aries L.) 

mortality during a population crash. Parasitology 105(3):493-503. 

Gulland, F. M. D., M. Haulena, D. Fauquier, G. Langlois, M. E. Lander, T. Zabka, and 

R. Duerr. 2002. Domoic acid toxicity in Californian sea lions (Zalophus californianus): 

Clinical signs, treatment and survival. Vet. Rec. 150(15):475-480. 

22

Heyning, J. E., and M. E. Dahlheim. 1990. Strandings and incidental takes of gray whales. 

Unpubl. doc. SC/A90/G2 presented to the IWC Scientific Committee Special Meeting on 

the Assessment of Gray Whales, April 1990, Seattle. 16 p. [Available from International 

Whaling Commission, The Red House, 135 Station Road, Impington, Cambridge, 

CB4 9NP, UK.] 

Jones, M. L., and S. L. Swartz. 1984. Demography and phenology of gray whales and 

evaluation of whale-watching activities in Laguna San Ignacio, Baja California Sur, 

Mexico, p. 309-374. In M. L. Jones, S. L. Swartz, and S. Leatherwood (editors), The 

gray whale, Eschrichtius robustus. Academic Press, Inc., Orlando. 600 p. 

Krahn, M. M., G. M. Ylitalo, D. G. Burrows, J. Calambokidis, S. E. Moore, M. Gosho, 

P. Gearin, P. D. Plesha, R. L. Brownell Jr., S. A. Blokhin, K. L. Tilbury, T. Rowles, and 

J. E. Stein. 2001. Organochlorine contaminant concentrations and lipid profiles in 

eastern North Pacific gray whales (Eschrichtius robustus). J. Cetacean Res. Manage. 

3(1):19-29. 

Le Boeuf, B. J., H. Pérez-Cortés M., J. Urbán R., B. R. Mate, and F. Ollervides U. 2000. 

High gray whale mortality and low recruitment in 1999: Potential causes and 

implications. J. Cetacean Res. Manage. 2(2):85-99. 

Manzanilla, S. R. 1989. The 1982-1983 El Niño event recorded in dentinal growth layers in 

teeth of Peruvian dusky dolphins (Lagenorhynchus obscurus). Can. J. Zool. 67(9):2120-

2125. 

Moore, S. E., D. K. Ljungblad, and D. R. Van Schoik. 1986. Annual patterns of gray whale 

(Eschrichtius robustus) distribution, abundance and behavior in the northern Bering and 

eastern Chukchi Seas, July 1980-83. Rep. Int. Whaling Comm. (Special Issue 8):231-

242. 

23

Moore, S. E., D. P. DeMaster, and P. K. Dayton. 2000. Cetacean habitat selection in the 

Alaskan Arctic during summer and autumn. Arctic 53(4):432-447. 

Moore, S. E., J. Urbán R., W. L. Perryman, F. Gulland, H. Perez-Cortes M., P. R. Wade, 

L. Rojas-Bracho, and T. Rowles. 2001. Are gray whales hitting “K” hard? Mar. 


Mammal Sci. 17(4):954-958. 


Moore, S. E., J. M. Grebmeier, and J. R. Davies. 2003. Gray whale distribution relative to 

forage habitat in the northern Bering Sea: Current conditions and retrospective summary. 

Can. J. Zool. 81(4):734-742. 

Norman, S. A., M. M. Muto, D. J. Rugh, and S. E. Moore. 2000. Gray whale strandings in 

1999 and a review of stranding records in 1995-1998. Unpubl. doc. SC/52/AS5 presented 

to the IWC Scientific Committee, June 2000, Adelaide. 36 p. [Available from 

International Whaling Commission, The Red House, 135 Station Road, Impington, 

Cambridge, CB4 9NP, UK.] 

Pérez-Cortés M., H., J. Urbán-Ramírez, F. Ollervides, V. Sánchez S., J. Pettis, P. Loreto C., 

and M. A. Palmeros. 1999. A preliminary note on the gray whale, Eschrichtius robustus, 

strandings at Baja California Sur, México during the winter 1998/99. Unpubl. doc. 

SC/51/AS30 presented to the IWC Scientific Committee, May 1999, Grenada. 8 p. 

[Available from International Whaling Commission, The Red House, 135 Station Road, 

Impington, Cambridge, CB4 9NP, UK.] 

Perryman, W. L., and M. S. Lynn. 2002. Evaluation of nutritive condition and reproductive 

status of migrating gray whales (Eschrichtius robustus) based on analysis of 

photogrammetric data. J. Cetacean Res. Manage. 4(2):155-164. 

Perryman, W. L., M. A. Donahue, P. C. Perkins, and S. B. Reilly.	 2002. Gray whale calf 

production 1994-2000: Are observed fluctuations related to changes in seasonal ice 

cover? Mar. Mammal Sci. 18(1):121-144. 

24

Perryman, W. L., G. M. Watters, L. K. Swartz, and R. A. Rowlett. 2004. Preliminary results 

from shore-based surveys of northbound gray whale calves in 2003 and 2004, with a 

comparison to predicted numbers based on the distribution of seasonal ice. Unpubl. doc. 

SC/56/BRG43 presented to the IWC Scientific Committee, June 2004, Sorrento. 7 p. 

[Available from International Whaling Commission, The Red House, 135 Station Road, 

Impington, Cambridge, CB4 9NP, UK.] 

Poole, M. M. 1984. Migration corridors of gray whales along the central California coast, 

1980-1982, p. 389-407. In M. L. Jones, S. L. Swartz, and S. Leatherwood (editors), The 

gray whale, Eschrichtius robustus. Academic Press, Inc., Orlando. 600 p. 

Rice, D. W., and A. A. Wolman. 1971. The life history and ecology of the gray whale 

(Eschrichtius robustus). American Society of Mammalogists Special Publication No. 3, 

Stillwater, OK. 142 p. 

Ruelas-Inzunza, J. R., M. Horvat, H. Pérez-Cortés, and F. Páez-Osuna. 2003. 

Methylmercury and total mercury distribution in tissues of gray whales (Eschrichtius 

robustus) and spinner dolphins (Stenella longirostris) stranded along the lower Gulf of 

California, México. Ciencias Marinas 29(1):1-8. 

Rugh, D. J., K. E. W. Shelden, and A. Schulman-Janiger. 2001. Timing of the gray whale 

southbound migration. J. Cetacean Res. Manage. 3(1):31-39. 

Rugh, D. J., J. M. Breiwick, R. C. Hobbs, and J. A. Lerczak. 2002. A preliminary estimate 

of abundance of the eastern North Pacific stock of gray whales in 2000/01 and 2001/02. 

Unpubl. doc. SC/54/BRG6 presented to the IWC Scientific Committee, April 2002, 

Shimonoseki. 14 p. [Available from International Whaling Commission, The Red 

House, 135 Station Road, Impington, Cambridge, CB4 9NP, UK.] 

Sanchez Pacheco, J. A. 1998. Gray whale mortality at Ojo de Liebre and Guerrero Negro 

lagoons, Baja California Sur, Mexico: 1984-1995. Mar. Mammal Sci. 14(1):149-155. 

25

Swartz, S. L. 1986. Gray whale migratory, social and breeding behavior. Rep. Int. Whaling 

Comm. (Special Issue 8):207-229. 

Tilbury, K. L., J. E. Stein, C. A. Krone, R. L. Brownell Jr., S. A. Blokhin, J. L. Bolton, and 

D. W. Ernest. 2002. Chemical contaminants in juvenile gray whales (Eschrichtius 

robustus) from a subsistence harvest in Arctic feeding grounds. Chemosphere 47(6):555-

564. 

Tougaard, S., and C. C. Kinze (editors). 1999. Proceedings from the workshop on sperm 

whale strandings in the North Sea: The event – the action – the aftermath, Rømø, 

Denmark, 26-27 May 1998. Esbjerg, Fiskeri- og Søfartsmuseets [Fisheries and Maritime 

Museum] Forlag, Esbjerg, Denmark. 50 p. 

Truelove J., and F. Iverson. 1994. Serum domoic acid clearance and clinical observations in 

the cynomolgus monkey and Sprague-Dawley rat following a single IV dose. Bull. 

Environ. Contam. Toxicol. 52(4):479-486. 

Urbán R., J., A. Gómez-Gallardo U., and S. Ludwig. 2003a. Abundance and mortality of 

gray whales at Laguna San Ignacio, Mexico, during the 1997-98 El Niño and the 1998-99 

La Niña. Geofísica Internacional 42(3):439-446. 

Urbán R., J., L. Rojas-Bracho, H. Pérez-Cortés, A. Gómez-Gallardo, S. L. Swartz, S. Ludwig, 

and R. L. Brownell Jr. 2003b. A review of gray whales (Eschrichtius robustus) on their 

wintering grounds in Mexican waters. J. Cetacean Res. Manage. 5(3):281-295. 

Wade, P. R. 2002. A Bayesian stock assessment of the eastern Pacific gray whale using 

abundance and harvest data from 1967-1996. J. Cetacean Res. Manage. 4(1):85-98. 

Wade, P. R., and D. P. DeMaster. 	1996. A Bayesian analysis of eastern Pacific gray whale 

population dynamics. Unpubl. doc. SC/48/AS3 presented to the IWC Scientific 

Committee, June 1996, Aberdeen. 21 p. [Available from International Whaling 

Commission, The Red House, 135 Station Road, Impington, Cambridge, CB4 9NP, UK.] 

26

Willetto, C., T. O’Hara, and T. Rowles. 2002. Bowhead whale health and physiology 

workshop 2001: Summary for the International Whaling Commission (IWC) Scientific 

Committee. Unpubl. doc. SC/54/BRG1 presented to the IWC Scientific Committee, 

April 2002, Shimonoseki. 14 p. [Available from International Whaling Commission, 

The Red House, 135 Station Road, Impington, Cambridge, CB4 9NP, UK.] 

Williams, E. 1982. Brucellosis. Practitioner 226(1371):1507-1517. 

27 
Table 1.--Gray whale stranding reports by month and region, 1995-2002. 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Unknown Total 

1995 Mexico California Oregon Washington Canada Alaska Total 1996 Mexico California Oregon Washington Canada Alaska Total 1997 Mexico California Oregon Washington Canada Alaska Total 1998 Mexico California Oregon Washington Canada Alaska Total 

1 

1 

2 

1 

2 

1 

4 

4 

4 

2 

12 

14 

1 

1 

1 

1 

2 

6 

1 

7 

1 

2 

3 

4 

2 

6 

1 

1 

2 

1 

3 

4 

3 

1 

4 

3 

1 

1 

5 

3 

1 

4 

2 

2 

1 

1 

6 

6 

1 

7 

1 

2 

1 

4 

4 

1 

1 

6 

1 

1 

2 

2 

2 

1 

5 

0 

1 

1 

1 

1 

2 

1 

1 

1 

1 

2 

0 

0 

1


1


1 

1 

0 

1 

1 

2 

1 

1 

1 

1 

1 

3 

0 

1 

1 

1 

1 

1 

0 	1 

1 

0 	1 

1 1 

1 1 

2 

0 	2 

13 

1 

1 13 

1 

1 0 

15 

1 

1 15 

2 12 

2 

1 

5 12 

13 

12 

4 

7 

2 

1 

39 

3 

13 

3 

2 

0 

0 

21 

22 

10 

3 

3 

5 

3 

46 

17 

30 

0 

4 

2 

3 

56 

28

 Table 1.--Continued. 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Unknown Total 

1999 Mexico California Oregon Washington Canada Alaska Total 2000 Mexico California Oregon Washington Canada Alaska Total 2001 Mexico California Oregon Washington Canada Alaska Total 2002 Mexico California Oregon Washington Canada Alaska Total 

6 

4 

1 

11 

18 

1 

19 

1 

1 

0 

33 

2 

1 

36 

41 

2 

43 

1 

1 

2 

3 

2 

1 

6 

69 

5 

74 

57 

6 

63 

0 

4 

1 

5


3 

10 

1 

8 

5 

27 

6 

22 

1 

6 

1 

36 

0 

1 

2 

3 

1 

9 

1 

7 

2 

7 

27 

14 

8 

14 

36 

1 

1 

2 

2 

5 

4 

13 

22 

9 

1 

7 

10 

27 

1 

1 

3 

5 

0


2 

6 

5 

13 

3 

1 

15 

19 

1 

1 

0


2 

1 

1 

47 

51 

1 

5 

6 

0 

1 

1 

6 6 

2 1 3 

1 

2 

1 

4 1 1 9 7 

85 

1 1 

1 

1 1 0 

22 

9 

1 116 

10 

1 

0 0 0 1 10 

8 

1 

0 1 0 0 8 

124 

45 

3 

28 

10 

73 

283 

207 

59 

2 

23 

22 

55 

368 

10 

5 

0 

1 

0 

5 

21 

15 

7 

3 

1 

0 

0 

26 

29

Table 2.--Proportionate increase in gray whale stranding reports by region in 1999 and 2000 compared to 1995-98. 

 Mexico California Oregon Washington Canada Alaska 

Mean number of strandings, 1995-98 Proportionate increase in 1999 Proportionate increase in 2000 

13.75 16.25 2.50 4.00 2.25 1.75 

9.02 2.77 1.20 7.00 4.44 41.71 

15.05 3.63 0.80 5.75 9.78 31.43 

Table 3.--Sex of stranded gray whales by year, 1995-2002. 

Year Male Female Percent female* Unknown Total 

1995 1996 1997 1998 1999 2000 2001 2002 Total 

7 5 9 6 

41 

135 

3 6 

212 

6 6 7 

16 

79 

59 

1 9 

183 

46.2% 54.5% 43.8% 72.7% 

65.8% 

30.4% 

25.0% 60.0% 

46.3% 

26 10 30 34 

163 

174 

17 11 

465 

39 21 46 56 

283 

368 

21 26 

860 

*Percent of animals of known sex. 

30 
Table 4.--Age class of stranded gray whales by year, 1995-2002. 

Adult Subadult Yearling Calf 

Year Number Percent* Number Percent* Number Percent* Number Percent* Unknown Total 

1995 1996 1997 1998 1999 2000 2001 2002 Total 

4 1 3 5 

45 

105 

0 

13 

176 

20.0% 

7.1% 

15.0% 13.5% 

33.8% 

49.3% 

0.0% 

52.0% 

37.5% 

7 

4 

3 4 

50 

81 

3 

4 

156 

35.0% 

28.6% 

15.0% 10.8% 

37.6% 

38.0% 

42.9% 

16.0% 

33.3% 

5 

3 

0 5 

26 

15 

2 

3 

59 

25.0% 

21.4% 

0.0% 

13.5% 

19.5% 

7.0% 

28.6% 

12.0% 

12.6% 

4 

6 

14 

23 

12 12 

2 

5 

78 

20.0% 19 39 

42.9% 7 21 

70.0% 26 46 

62.2% 19 56 

9.0% 150 283 5.6% 155 368 

28.6% 14 21 

20.0% 1 26 

16.6% 391 860 

*Percent of animals of known age. 

Table 5.--Age class of stranded gray whales by region, 1995-2002. 

Area Adult Subadult Yearling Calf Unknown Total 

Mexico California Oregon Washington Canada Alaska Total 

95 

46 

5 

23 

0 

7 

176 

59 

54 

3 

25 

0 

15 

156 

20 

20 

3 

12 

0 

4 

59 

24 

44 

5 

4 

0 

1 

78 

213 

17 

2 

5 

41 

113 

391 

411 

181 

18 

69 

41 

140 

860 

31

Table 6.--Lipid composition of stranded gray whales by degree of carcass decomposition, 1999-2000 

(mean ± standard error; n = sample size). 

Percent lipid composition 

Carcass condition 

Total lipids Wax esters Triglycerides Free fatty acids Cholesterol Phospholipids 

Fresh (n = 22) Slightly decomposed (n = 8) 

Moderately decomposed (n = 26) 

Advanced decomposition (n = 8) 

12 ± 2.8 0.35 ± 0.2 77.4 ± 7.2 5.3 ± 3.6 5.1 ± 2.7 12.3 ± 4.9 

0.58 ± 0.3 3.17± 1.6 83.4 ± 4.3 0.32 ± 0.26 6.7 ± 1.9 6.26 ± 2.9 

8.4 ± 2.2 8.6 ± 3.8 54 ± 7.3 11.3 ± 3.8 6.1 ± 1.4 20.1 ± 4.3 

2.8 ± 1.1 3.2 ± 1.9 16.7 ± 12 39.3 ± 11.3 12.3 ± 4.7 28.4 ± 9.4 

32 
Figure 1.--Annual trends in reports of gray whale strandings by region, 1995-2002. 

0

50 

1999 

Mexico CA OR WA AK 

200 150 100 

1995 1996 1997 1998 2000 2001 2002 

N umb er o f re port ed str and in gs 

Canada 

33

RECENT TECHNICAL MEMORANDUMS


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AFSC149 RUGH, D. J., K. E. W. SHELDEN, C. L. SIMS, B. A. MAHONEY, B. K. SMITH, L. K. LITZKY, and R. C. 

HOBBS. 2005. Aerial surveys of belugas in Cook Inlet, Alaska, June 2001, 2002, 2003, and 2004, 71 p. 

NTIS number pending. 

148 EILER, J. H., T. R. SPENCER, J. J. PELLA, M. M. MASUDA, and R. R. HOLDER. 2004. Distribution and 

movement patterns of chinook salmon returning to the Yukon River basin in 2000-2002, 99 p. NTIS No. 

PB2005-100707. 

147 MCELDERRY, H., J. SCHRADER, D. MCCULLOUGH, J. ILLINGWORTH, S. FITZGERALD, and S. 

DAVIS. 2004. Electronic monitoring of seabird interactions with trawl third-wire cables on trawl vessels -

a pilot study, 39 p. NTIS No. PB2005-100243. 

146 WING, B. L., and D. R. BARNARD. 2004. A field guide to Alaskan corals, 67 p. NTIS No. PB2005-100429. 

145 RUGH, D. J., B. A. MAHONEY, and B. K. SMITH. 2004. Aerial surveys of beulga whales in Cook Inlet, 

Alaska, between June 2001 and June 2002, 26 p. NTIS No. PB2004-106479. 

144 ANGLISS, R. A., and K. L. LODGE. 2004. Alaska marine mammal stock assessments, 2003, 224 p. 

NTIS No. PB2005-100248. 

143 ZENGER, H. H. JR. 2004. Data report: 2002 Aleutian Islands bottom trawl survey, 247 p. NTIS No. 

PB2004-105068. 

142 STEVENSON, D. E. 2004. Identification of skates, sculpins, and smelts by observers in North Pacific 

groundfish fisheries (2002-2003), 67 p. NTIS No. PB2004-105817. 

141 HOFF, G. R., and L. L. BRITT. 2003. The 2002 eastern Bering Sea upper continental slope survey of 

groundfish and invertebrate resources, 261 p. NTIS No. PB2004-101668. 

140 STONE, R. P., and M. M. MASUDA. 2003. Characteristics of benthic sediments from areas open and 

closed to bottom trawling in the Gulf of Alaska., 40 p. + Appendices (111 p.). NTIS No. PB2004-100650 

139 JOHNSON, S. W., M. L. MURPHY, D. J. CSEPP, P. M. HARRIS, and J. F. THEDINGA. 2003. A survey 

of fish assemblages in eelgrass and kelp habitats of southeastern Alaska, 39 p. NTIS No. PB2004-

100139. 

138 PEREZ, M. A. 2003. Compilation of marine mammal incidental take data from the domestic and joint 

venture groundfish fisheries in the U.S. EEZ of the North Pacific, 1989-2001, 145 p. NTIS No. PB2004-

100649 

137 MASELKO, J. M., A. C. WERTHEIMER, and J. F. THEDINGA. 2003. Selection and application of a markand-recapture technique for estimating pink salmon escapements, 44 p. NTIS No. PB2003-107101. 

136 BARBEAUX, S. J., and M. W. DORN. 2003. Spatial and temporal analysis of eastern Bering Sea echo 

integration-trawl survey and catch data of walleye pollock, Theragra chalcogramma, for 2001 and 2002, 

34 p. NTIS No. PB2003-106479. 

135 DIETER, B. E., D. A. WION, and R. A. MCCONNAUGHEY. 2003. Mobile fishing gear effects on benthic 

habitats: A bibliography (second edition), 207 p. NTIS No. PB2003-105080.