Whale Stocks Research Articles

Contemporary sightings of eastern North Pacific right whales, 2006 to 2023

North Pacific right whales Eubalaena japonica once numbered in the 10s of 1000s. Today, the eastern population is one of the most endangered large whale stocks in the world. A lack of dedicated surveys and a population in the 10s of animals have resulted in considerable knowledge gaps. Here, we collate all contemporary sightings of eastern North Pacific right whales (ENPRWs) from 2006 through 2023 to investigate possible migratory routes and elucidate important habitat. Sightings in the northern Bering Sea, Gulf of Alaska, and along the west coast of North America have increased. Of the 99 sightings recorded between 2006 and 2023, 58 occurred during the few dedicated ENPRW surveys with simultaneous aerial and vessel platforms. All animals sighted were non-calves. Opportunistic sightings along the California coast were only reported in spring months (February-May). While this timing would coincide with a northward migration from lower latitudes, poor photo quality prevented matching of these animals, making it difficult to determine migratory patterns. Furthermore, there have been no sightings in Hawai’i or Mexico since 1996, and no sightings in the eastern North Pacific off the continental shelf since the 1970s. To date, only 2 animals have been photographically matched from Alaska to more southerly latitudes, and there have been no photographic matches between the Bering Sea and the Gulf of Alaska. Feeding has been observed throughout their range, suggesting right whales opportunistically feed whenever possible. While their primary migratory destinations remain unknown, these recent sightings provide insight into important ENPRW habitat in Alaska.

Update on the status of gray whales since the 2020 Implementation Review

The International Whaling Commission’s Scientific Committee conducts regular Implementation Reviews (IRs) of the biology, threats and status of whale species subject to aboriginal subsistence whaling. The last IR of plans for hunting eastern North Pacific (ENP) gray whales by the Chukotka Natives of the Russian Federation and the Makah Tribe of the United States of America occurred in 2020. This paper presents a review of new scientific findings on gray whales to assess whether the current status of the stock(s) is within the parameter space tested in the 2020 IR. Updated information on gray whale stock structure hypotheses, abundance and calf productivity, health and strandings, human removals by hunting and non‐hunting sources, population growth rates, immigration into the Pacific Coast Feeding Group, parameterisation of the Makah hunt, and future episodic mortality events (EMEs) were reviewed for this assessment. For almost all factors, it appears that the current dynamics of the ENP gray whale population are within the parameter space evaluated in 2020 IR. The exception is that EMEs affecting whales in the ENP are occurring more frequently and at a greater magnitude than previously evaluated. However, preliminary evaluations suggest that the performances of the Gray Whale Strike Limit Algorithm (SLA) and Makah Management Plan are robust to recent and future EMEs of Northern Feeding Group gray whales and reductions of productivity of the Pacific Coast Feeding Group, at least under the initial parameterisations. We therefore conclude that there is no compelling need for a Special IR prior to the next scheduled IR in 2026, while noting that additional abundance data for 2022/23 and 2023/24 analysed after drafting this paper could strengthen or weaken the evidence for this conclusion.

Utilizing long-term opportunistic sightings records to document spatio-temporal shifts in mysticete presence and use in the Central Salish Sea

The Salish Sea supports several baleen whale species, including humpback (Megaptera novaeangliae), gray (Eschrichtius robustus) and minke whales (Balaenoptera acutorostrata). With the exception of minke whales, these species were decimated by commercial whaling in the 1900s. Because recovery of these populations is monitored on broad spatial scales determined by stocks or populations, their use of the Salish Sea ecosystem is not well documented or understood. We collated 17,436 opportunistic sighting reports to assess patterns in mysticete presence and distribution in the Salish Sea (1976–2019). We used the proportion of sightings for each species and spatial models targeting comparisons between species to limit the influence of spatio-temporal variation in reporting efforts. Humpback whale sightings have increased dramatically since the late 2000s, mirroring population-wide increases and suggesting a renewed use of historically important feeding areas. Gray whale sightings increased most notably at two distinct times (1989, 2017), both of which align with periods of high mortality experienced by the delisted Eastern North Pacific stock of gray whales and may reflect individuals straying from their migration routes. Sightings of minke whales remained relatively stable over this study period and were likely driven by a group of 30–40 individuals that forage off shallow banks and bathymetrically complex habitats around the San Juan Archipelago. Though it can be difficult to separate the bias that accompanies public sightings databases, citizen science efforts are invaluable for monitoring the recovery of rebounding populations and can illuminate longitudinal patterns that would otherwise go unnoticed.

Reproductive parameters of Bering‐Chukchi‐Beaufort Seas bowhead whales

AbstractData from Bering‐Chukchi‐Beaufort Seas bowhead whales (Balaena mysticetus), harvested during 1973–2021 by aboriginal subsistence hunters, were used to estimate reproductive parameters: length at sexual maturity (LSM), age at sexual maturity (ASM), pregnancy rate (PR), and calving interval. Sexual maturity (N = 187 females) was determined from the presence/absence of corpora in the ovaries, or a fetus. Using sampling bias‐corrected logistic regression, LSM was estimated at 13.5 m, 95% CI [13.0, 13.8]. There was a downward trend in LSM over time, statistically significant with one method but marginal with another. A growth model translated this estimate to an ASM estimate of 23.5 years, 95% CI [20.4, 26.7]. Pregnancy rate was determined from mature females (N = 125), and from a subset limited to certain autumn‐caught whales (n = 37) to reduce bias. The PR was estimated at 0.46 globally, 95% CI [0.36, 0.55] and 0.38 for the autumn sample, 95% CI [0.20, 0.51]. Both estimated PRs are consistent with a 3‐year calving interval, because the larger estimate includes two cohorts of pregnant whales harvested in spring, and bowhead whale gestation is longer than 12 months. These analyses represent the most conclusive empirical estimates of ASM, LSM, and PR for this bowhead whale stock from the largest available data sets to date.

Quantification by droplet digital PCR and species identification by metabarcoding of environmental (e)DNA from Blainville's beaked whales, with assisted localization from an acoustic array.

Detection and identification of species, subspecies or stocks of whales, dolphins and porpoises at sea remain challenging, particularly for cryptic or elusive species like beaked whales (Family: Ziphiidae). Here we investigated the potential for using an acoustically assisted sampling design to collect environmental (e)DNA from beaked whales on the U.S. Navy's Atlantic Undersea Test and Evaluation Center (AUTEC) in The Bahamas. During 12 days of August 2019, we conducted 9 small-boat surveys and collected 56 samples of seawater (paired subsamples of 1L each, including controls) using both a spatial collection design in the absence of visual confirmation of whales, and a serial collection design in the proximity of whales at the surface. There were 7 sightings of whales, including 11 Blainville's beaked whales (Mesoplodon densirostris). All whales were located initially with the assistance of information from a bottom-mounted acoustic array available on the AUTEC range. Quantification by droplet digital (dd)PCR from the four spatial design collections showed no samples of eDNA above the threshold of detection and none of these 20 samples yielded amplicons for conventional or next-generation sequencing. Quantification of the 31 samples from four serial collections identified 11 likely positive detections. eDNA barcoding by conventional sequencing and eDNA metabarcoding by next-generation sequencing confirmed species identification for 9 samples from three of the four serial collections. We further resolved five intra-specific variants (i.e., haplotypes), two of which showed an exact match to previously published haplotypes and three that have not been reported previously to the international repository, GenBank. A minimum spanning network of the five eDNA haplotypes, with all other published haplotypes of Blainville's beaked whales, suggested the potential for further resolution of differences between oceanic populations.

An exploratory assessment of the Bering-Chukchi-Beaufort Seas stock of bowhead whales using a stochastic population dynamics model

The stochastic population dynamics model used by Aboriginal Whaling Management Procedure developers is revised to correct weaknesses related to uncertainty parameterisation and replacement yield estimation. Two variants of this model, along with the standard deterministic version, are used to assess the Bering-Chukchi-Beaufort Seas stock of bowhead whales. The variants differ with respect to the magnitude and complexity of the stochastic variation they introduce into natural mortality and birth/calf survival processes. An allowable catch statistic, E (Q0), is defined for appropriate use with stochastic model assessments. Using the same assessment methods, likelihood and priors as IWC (1999a), 5th percentiles of E (Q0) were found to be 117, 106 and 91 for the deterministic, simpler stochastic and extreme stochastic models, respectively. Bayes factor results show that there is no evidence suggesting that either stochastic model should be favoured over any simpler alternative, and the deterministic model yielded the best fit overall. The E (Q0) estimates confirm and strengthen past IWC Scientific Committee inference that under current bowhead subsistence hunting levels the stock should continue to increase towards stabilisation above its maximum sustainable yield level.

Timing of the gray whale southbound migration

The southbound migration of the eastern North Pacific stock of gray whales (Eschrichtius robustus) has been documented by the National Marine Fisheries Service most seasons since 1967 at or near Granite Canyon, in central California, and by the American Cetacean Society’s Los Angeles Chapter every season since 1985 at Point Vicente, southern California. This has provided a rare opportunity to examine cetacean migratory timing data over a relatively long time series. In 1998/99, anecdotal reports indicated a major change had occurred in the timing of the migration, which prompted this study to compare the observed timing relative to expected dates. Although no observers were at Granite Canyon in 1998/99, data collected from this site indicated that prior to 1980, annual median sighting dates ranged from 4-13 January (overall median = 8 January; CI = 1.3), but since then there has been a one-week (6.8 day; CI = 2.0) delay, with median dates now ranging from 12-18 January (overall median = 15 January; CI = 1.7). This delay in timing is better represented as a shift in dates than as a trend, and it occurred shortly after a major oceanographic regime shift in the North Pacific Ocean. The shift in whale sighting dates occurred equally in the onset of the migrations (when the first 10% of the whales passed a site), the median (50%) and end (when 90% of the whales passed). At Granite Canyon, there were no significant trends in these dates prior to 1980 or in dates following the shift. In mid-February (median = 15 February, CI = 1.9, at Point Vicente), few gray whales are still going south and some are already migrating north. Most of the migration (the period between the 10% and 90% sighting dates) occurs across a period of 34 days (CI = 2.0), but the entire southbound migration may take > 70 days to pass a location in any given year. It takes a whale approximately 54 days to migrate from the north central Bering Sea to the lagoons in Baja California (8,000km), but some whales may travel as far as 10,000km. Based on available observations and calculations using a travel rate of 147km/day, current median (peak) sighting dates of the southbound migration should be: 1 December in the north central Bering Sea (here considered the theoretical starting point for the migration); 12 December at Unimak Pass, Alaska; 18 December for Kodiak Island, Alaska; 5 January for Washington State; 7 January for Oregon; 15 January for central California; 18 January in southern California; and 24 January at the northern lagoons in Baja California (considered here to be the terminus of the migration). Although no observations were made at Granite Canyon in 1998/99, sightings made at Yaquina Head, Oregon (median sighting date = 7 January) and at Point Vicente (median = 20 January) indicate that the timing of that migration was consistent with previous years.

Towards an estimate of the Southeastern Pacific humpback whale stock

Between 1991 and 1997 a photo-identification study of Southeastern Pacific humpback whales was carried out on the central coast of Ecuador (1°26’S, 80°50’W), South America. During this period, a total of 219 whales were identified and catalogued by the colouration pattern on the ventral side of their flukes. Naturally marked whales were used to estimate the population through the Petersen’s mark-recapture method as modified by Bailey. With data from the final two seasons (1996-1997), the resultant estimate was 1,922 (95% CI = 77-3,767) whales. Pooling data from the first six years resulted in an estimate of 2,683 (95% CI = 397-4,969) whales. Sources of bias relate to violations of the assumptions of closure and equal catchability conditions. The low inter-yearly resighting rate and a high rate of new discoveries in the last season indicate that only a fraction of the population has so far been identified. Despite the broad confidence interval, these data provide an indication of the current number of whales.

A note on humpback whales off the coast of Ecuador during the 1997 ‘El Niño’ event

The southeastern Pacific humpback whale stock was studied for seven years (1991-1997) on the central coast of Ecuador (1°25’S, 79°55’W) during the breeding season (June-September). Boat trips were conducted from two different sites, Puerto López and Puerto Cayo, following well-defined routes offshore. In 1997, a strong El Niño affected the eastern Pacific area. In order to try and investigate possible climate-induced shifts, results obtained from 1996, a ‘normal’ year, were compared with those obtained in 1997, when water temperature was 4°C above its historical mean. Four factors were considered: whale encounter rate; distribution; group structure; and crude birth rate. The whale encounter rate decreased in 1997 for both sites: 11.2% for Puerto López and 8.7% for Puerto Cayo, although the differences were not statistically significant (p > 0.05). Group distribution in relation to water depth was not significantly different (p > 0.05), nor were the mean distances from sighting sites to port (p > 0.05). Group size was equal in both years for Puerto López, but in Puerto Cayo it was larger in 1997, although not significantly (p > 0.05). Group composition was not significantly different (p > 0.05). No difference in birth rate was found in Puerto López. Results for Puerto Cayo are difficult to interpret. No changes in the investigated parameters were found in the study area during El Niño 1997. Since humpback whales do not feed in tropical waters, they may not be as vulnerable to El Niño events as other marine mammals.

An examination of certain of the assumptions made in the Bayesian approach used to assess the eastern North Pacific stock of gray whales (Eschrichtius robustus)

An assessment of the eastern North Pacific stock of gray whales (Eschrichtius robustus) is conducted using a variant of the Bayesian stock assessment method of Wade (2002). This variant is based on the BALEEN II population dynamics model and uses parameters whose values are more familiar to members of the International Whaling Commission’s Scientific Committee. The sensitivity of the results to changes to some of the specifications used in the assessment is examined. The results are shown to be relatively insensitive to the first year considered in the analysis and the year for which a prior on absolute abundance is specified. An alternative Bayesian assessment method which involves projecting the population forward from pre-exploitation equilibrium in 1600 is also considered. As expected from previous assessments, results from this method are unable to mimic the recent trends in absolute abundance obtained from shore counts and are inconsistent with the fact that the fishery was commercially extinct by the end of the 19th Century. Allowing for underestimation of historical commercial and aboriginal catches provides improved consistency with recent trends in abundance but does not resolve these problems completely. The impact of process error (in the form of temporally correlated fluctuations in calf survival) on the dynamics of the population is found to be largely inconsequential in terms of resolving the inconsistency between historical catches and recent estimates of abundance.

A Bayesian stock assessment of the eastern Pacific gray whale using abundance and harvest data from 1967-1996

Abundance and harvest data since 1966/67 were used to assess the eastern Pacific stock of gray whales. A Bayesian statistical method was used to estimate probability distributions for the parameters of both a simple and an age and sex structured population dynamics model, as well as output quantities of interest. Model comparisons using the Bayes Factor provided conclusive evidence that an additional parameter should be used to account for unexplained variation in the abundance time series. Incorporating the additional variance parameter decreased the precision of the estimates of the other parameters. Point estimates of carrying capacity ranged from 24,640-31,840 for the different models, but the posterior distributions from the selected models were very broad and excluded few values. The current depletion level (population size as a fraction of carrying capacity) was estimated to be about 0.75, with a lower 2.5th percentile of 0.36. The probability that the population was still below one-half of its carrying capacity was estimated to be 0.21, with a corresponding probability of 0.28 that the population was still below its maximum sustainable yield level. Quantities from which catch limits could potentially be calculated were estimated, including current replacement yield, maximum sustainable yield and the quantity Q1 (described in Wade and Givens, 1997).

A framework for evaluating Strike Limit Algorithms for populations reduced to small numbers

A generic framework is outlined within which operating models for populations reduced to low numbers but still subject to exploitation (‘type 3 fisheries’) can be developed. This framework is founded on an individual-based operating model that includes temporally correlated environmental variation in births and survival as well as the possibility of occasional catastrophic reductions in survival. Methods are developed to specify the value of the parameter that determines the productivity of the resource from that for MSYR, to enable simulation trials based on this framework to be parameterised in terms of MSYR. Three potential candidate Strike Limit Algorithms are evaluated using 14 ‘generic’ simulation trials that capture a range of factors pertinent to type 3 fishery situations. The ‘Maximum-likelihood-like’ SLA developed for use in the management of the Bering-Chukchi-Beaufort Seas stock of bowhead whales performs adequately for many of these 14 trials, but not all. In contrast, a variant of the ‘PBR approach’ is shown to perform adequately in terms of achieving conservation objectives for all of the trials. The information needed to specify trials for actual type 3 fishery situations is outlined.

Some analyses on the modern whaling catch history of the western North Pacific stock of gray whales (Eschrichtius robustus), with special reference to the Ulsan whaling ground

This study analysed post-1900 published and unpublished records of gray whales in the western North Pacific. Modern whaling recorded a peak annual catch of 100-200 whales in the 1910s, followed by a rapid decline in the 1920s and 1930s and a continued low level (perhaps 10-20 whales/year) for over 40 years to the l960s. Catches made during the last phase could have been the major factor suppressing recovery until recently. There are reasons to believe that this gray whale stock breeds in Hainan waters.

A Strike Limit Algorithm based on Adaptive Kalman Filtering with an application to aboriginal whaling of bowhead whales

A full and detailed description of a Strike Limit Algorithm (SLA) based on Adaptive Kalman Filtering techniques with an application to the Bering-Chukchi-Beaufort (B-C-B) Seas stock of bowhead whales is presented in this paper. Extended Kalman filters are used to estimate the present stock size and posterior probability distributions for MSY-rate (MSYR) and the pre-exploitation stock size K. A catch control law selected from a one-parameter family of such rules is then used on the conditional estimates of stock size. These conditional strike limits together with the posterior distributions of the various combinations of MSYR and K, give a cumulative distribution function for the strike limit. The eventual strike limit is then determined as a pre-specified percentile of this distribution. The SLA can be tuned to varying degrees of risk by the choice of the parameter characterising the catch control law and the percentile of the distribution for the strike limit. The procedure is tested on the Evaluation Trials set by the Standing Working Group on Aboriginal Whaling Management Procedures.

Empirical estimation of safe aboriginal whaling limits for bowhead whales

This paper provides a complete description of a Strike Limit Algorithm (SLA) considered by the International Whaling Commission (IWC) for the management of hunting of the Bering-Chukchi-Beaufort Seas stock of bowhead whales by native Alaskans to meet their cultural and subsistence needs. The algorithm applies a statistical estimation and optimisation strategy to extract the best features of selected SLAs to form a Bayes rule estimator. It focuses on safely satisfying moderate subsistence need, while favouring stock protection by setting strike limits below what would be required to fully satisfy need in the final portion of this century if need were more than doubled.

A review of bowhead whale (Balaena mysticetus) stock identity

For management purposes, the Scientific Committee of the International Whaling Commission has considered bowhead whales as having five stocks (geographically distinct segments of the population): Spitsbergen, Davis Strait, Hudson Bay, Okhotsk Sea and Bering-Chukchi-Beaufort Seas (B-C-B). These divisions are defined primarily by known distribution and seasonal movements. Historically, bowhead whales had a circumarctic distribution, with several periods of range expansion and contraction depending upon access through Arctic straits. Heavy exploitation by pre-20th century commercial whalers reduced bowhead whale abundance, further segregating stocks. A portion of the B-C-B stock escaped whalers by migrating into the pack ice each spring and summering in the Beaufort Sea. Few bowhead whales are now found in the summer in the Chukchi or Bering Seas. The distribution of this species should be considered labile, affected by sea ice and availability of prey, a factor that improves the likelihood of genetic mixing between stocks. Genetic variability has remained relatively high in spite of the severe depletion of the population, and there is no evidence of any recent genetic bottleneck. Besides geographic distribution and genetics, stock identity may be studied via morphological differences, reidentification of individuals between different stock areas, acoustic signatures, pollutant burdens, parasites and predators, feeding ecology and conception dates. Harpoon heads, research tags and lens racemisation indicate that bowhead whales are long-lived, can travel over large areas and may mix among stocks. Because conception occurs during or near the time of the spring migration, there are opportunities for genetic mixing among whales that might use different summering areas.

Application of a Strike Limit Algorithm based on adaptive Kalman filtering to the eastern North Pacific stock of gray whales

The application of a Strike Limit Algorithm (SLA) based on Adaptive Kalman Filtering techniques to the eastern North Pacific (ENP) stock of gray whales is described. This SLA is a modification of an earlier one which was designed for the Bering-Chukchi-Beaufort Seas stock of bowhead whales. Extended Kalman filters are used to estimate the present stock size and posterior probability distributions for Maximum Sustainable Yield (MSY) and MSY-rate (MSYR). A catch control law selected from a one-parameter family of such rules is then used on the conditional estimates of stock size. These conditional strike limits together with the posterior distributions of the various combinations of MSYR and MSY, give a cumulative distribution function for the strike limit. The eventual strike limit is then determined as a pre-specified percentile of this distribution. The SLA can be tuned to varying degrees of risk by the choice of internal model parameters – so-called tuning parameters. The procedure is tested based on a set of trials specified by the IWC Scientific Committee Standing Working Group on Aboriginal Whaling Management Procedures, designed to test the performance of potential SLAs for the ENP gray whale stock.

An examination of assessment models for the eastern North Pacific gray whale based on inertial dynamics

Bayesian assessments of the eastern North Pacific stock of gray whales are conducted using the standard BALEEN II model and the inertia model developed by Witting (2000; 2001; 2003). The analyses confirm the increase in gray whale population size since 1968, but indicate that catches up to 256 animals per annum will lead to population decline if the inertia model is correct. However, analyses based on the standard BALEEN II model with a starting year of 1930 or 1968 fit the calf count data better than the inertia model, and indicate a population at its (current) equilibrium level and that the current catches are sustainable. The results of both the BALEEN II model and the inertia model are sensitive to the choice of the functional form used to represent density-dependence and those of the inertia model to the starting year for the analyses.

Estimates of abundance of the eastern North Pacific stock of gray whales (Eschrichtius robustus) 1997-2002

The southbound migration of the eastern North Pacific stock of gray whales (Eschrichtius robustus) was documented by the National Marine Fisheries Service from 13 December 1997 to 24 February 1998, 13 December 2000 to 5 March 2001 and from 12 December 2001 to 5 March 2002. Research protocol was essentially identical to that used in previous surveys. This involved single observers independently searching for whales and recording data on effort and sighting time, location, count and direction-headed. In 1997/98, there were 2,346 pods (3,643 whales) counted during 435.0h of standard observational effort when visibility was recorded as fair to excellent. In 2000/01, a total of 1,694 pods (2,754 whales) were counted during 592.4h, and in 2001/02, there were 1,712 pods (2,800 whales) during 531.5h. The southbound migrations in 1997/98 and 2001/02 were normal, beginning in mid-December, centred on mid-January (mean dates=18 January 1998 and 15 January 2002 respectively) and ending by mid-February. However, in 2000/01 (mean date=25 January 2001) the migration was more protracted than any other migration observed in the past 25 years, with many whales still travelling south three weeks after the typical end date. Data analysis procedures were comparable to those used in previous years, with the exception of a new correction factor for nighttime travel rates. Abundance estimates were 29,758 whales in 1997/98 (CV=10.49%; 95% log-normal confidence interval=24,241 to 36,531), 19,448 in 2000/01 (CV=9.67%; 95% log-normal confidence interval=16,096 to 23,498) and 18,178 in 2001/02 (CV=9.79%; 95% log-normal confidence interval=15,010 to 22,015). The abundance in 1997/98 was the highest estimate made since this project began in 1967/68. It was followed by two much lower estimates – probably related to the high mortality rates observed in 1999 and 2000. This whale population appears to be approaching the carrying-capacity of its environment.

Updated 1978-2001 abundance estimates and their correlations for the Bering-Chukchi-Beaufort Seas stock of bowhead whales

The method of Cooke (1996) and Punt and Butterworth (1999) for computing abundance estimates for bowhead whales of the BeringChukchi-Beaufort Seas stock is reviewed. These abundance estimates are computed from estimates N4 of the number of whales that passed within the 4km visual range of the observation ‘perch’ from which the whales are counted, the estimated proportions P4 of the whales that passed within this range and the estimated standard errors (SE) of N4 and P4. Errors discovered while assembling the data used in developing previous estimates were corrected, and new estimated detection probabilities, N4 and P4 values and SEs were computed using the corrected data. The method of Cooke (1996) and Punt and Butterworth (1999) was then applied. The resulting 2001 abundance estimate was 10,545 (95% confidence interval 8,200 to 13,500), extremely close to the 2001 N4/P4 abundance estimate of 10,470 (95% confidence interval 8,100 to 13,500) (George et al., 2004). The estimated rate of increase of this population from 1978 to 2001 was 3.4% per year (95% confidence interval 1.7% to 5%).