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Using barnacle and pigmentation characteristics to identify gray whale calves on their feeding grounds
... It is possible that calves weaned prior to when they were first observed in the study area as cow-calf pairs in the PCFG have been observed separated as early as the beginning of July (Calambokidis et al., 2012). To make an estimate of what proportion of new whales observed in the study area are calves, photographs were analysed following methods developed by Bradford et al. (2011). The analysis was limited to new whales in the study area that were also seen in the PCFG for the first time in that year. ...
... head and postcranial region were used for the analysis. Whales with evidence of only recently attached barnacles, no old barnacle scars, and white pigmentation mottling the postcranial region were recorded as calves (Bradford et al., 2011). The goal of this analysis was to determine how important northwest Washington was as a site for cow-calf pairs and for recently weaned calves. ...
... Some new whales were first observed later in the year (i.e. autumn) than when calves become independent of their mothers (Bradford et al., 2011;Calambokidis et al., 2012). ...
Gray whales (Eschrichtius robustus) in northwest Washington were studied, with the aims to: (1) increase understanding of gray whale use of the study area; (2) document the annual and seasonal fluctuations in the numbers of whales utilising the area; and (3) assess the fidelity of whales to the study area within and between years. Together these goals establish a baseline of gray whale behaviour during summer and autumn in the region of the Makah Tribe's proposed whale hunt. From 1984 to 2011, a total of 225 unique gray whales were observed, with 49% being observed again in a future year. There was significant variability in observation rates of gray whales by month and year. During the feeding season, the observation rate increased to a peak in August in the north research segment in the Pacific Ocean and to a peak in October in research segments in the Strait of Juan de Fuca and in the southern research segment in the Pacific Ocean. Gray whales were most commonly observed at depths of 5-15m over rocky substrates and often near kelp forests, although the locations where they fed were dynamic by both month and year. Some whales habitually returned to northwest Washington, however the average whale in the study area was observed in only 31.6% (SE = 1.6%) of the possible years in which they could have been observed. Gray whales in the study area had an average minimum tenure (residency time) of 24.8 days out of a possible 183 days of the feeding season. A discovery curve analysis did not reach an asymptote over the 27 years of this study showing that there is no population closure to the research area. Based on these findings, it can be concluded that even though northwest Washington is an important feeding area, most Pacific Coast Feeding Group (PCFG) gray whales do not have strong fidelity to this one region within the IWC defined PCFG range. The findings presented in this paper provide a baseline for evaluating the impact of Makah hunting activities on the behaviour of PCFG whales that utilise the Makah's traditional hunting area once hunting activities resume.
... Age class was initially determined based on a combination of length from tip of the snout to the fluke notch (calf <7-8 m, yearling 8-9 m, subadult 9-11.1 m for males and 9-11.7 m for females, adult �11.1 m for males and � 11.7 m for females). This was subsequently modified depending on date and latitude of stranding, baleen plate length, and barnacle size, as calves and subadults in the lower latitudes were often shorter than the previously reported length ranges [3,[37][38][39][40][41]. Yearling and subadult age classes were combined because. ...
... Where the carcass code was scored as between decomposition states (e.g. 2.5 or 3.5), [40], the post-mortem state was assigned to the more advanced decomposition state for tabulation and analysis. ...
Beginning in December 2018, increased numbers of gray whale ( Eschrichtius robustus ) strandings were reported along the west coast of Mexico, the United States, and Canada, prompting declaration of a gray whale Unusual Mortality Event (UME) by the United States National Marine Fisheries Service. Although strandings declined in 2020 and 2021 from a peak in 2019, the UME is still ongoing as of fall 2023. Between 17 December 2018 and 31 December 2021, 503 animals stranded along the west coast of North America, with 226 strandings in Mexico, 71 in California, 12 in Oregon, 56 in Washington, 21 in British Columbia, and 117 in Alaska. These included 187 males, 167 females, and 149 whales of undetermined sex; and 193 adults, 194 subadults, 40 calves, 1 fetus, and 75 whales of undetermined age class. We report on 61 of the 503 carcasses (12%) that had external and internal gross necropsy and/or histopathology data: of these 61 whales, findings that contributed to death were identified in 33 (54%) whales. Sixteen of the 61 (26%) were severely emaciated. Gross lesions of blunt force trauma consistent with vessel strike were identified in 11 of the 61 animals (18%), only two of which were emaciated. Two whales (3%) were entangled at time of death, and one died from entrapment. Signs of killer whale ( Orcinus orca ) interaction were documented in 19 of the 61 animals; five were deemed from recent interactions and three (5%) likely contributed to mortality. A specific cause of death could not be identified in 28 of 61 whales (46%). Additionally, logistical challenges and the advanced state of decomposition of most examined carcasses precluded detection of potential infectious or toxic causes of morbidity or mortality. Up to 2016, the eastern North Pacific population of gray whale population had generally been increasing since the cessation of historic whaling and a prior UME in 1999–2000. However, recent abundance and calf production estimates have declined, a trend that overlaps the current UME. The relative contributions of carrying capacity, environmental change, prey shifts, and infectious, toxic, and other processes to the increased gray whale mortalities have not yet been resolved. Nevertheless, the marked temporal increase in strandings, including findings of malnutrition in some of the whales, along with low calf production, likely represent consequences of complex and dynamic ecological interactions in the ocean impacting the population.
... Where whale barnacle fossils are found, they belong nearly exclusively to the genus Coronula (Fleming, 1959;Zullo, 1969;Beu, 1971;Buckeridge, 1983;Bianucci et al., 2006a, b;Dominici et al., 2011;Collareta et al., 2016;Taylor et al., 2019). The genus Cryptolepas is represented by a single extant species, Cryptolepas rhachianecti, which is a host-specific inhabitant of the skin of gray whales (Eschrichtius robustus Lilljeborg, 1861) (Newman and Ross, 1976;Newman and Abbott, 1980;Seilacher, 2005;Bradford et al., 2011;Hayashi, 2012;Swartz, 2018). Like its host, C. rhachianecti previously has been known only from the Northern Hemisphere, both in the present day and within the fossil record. ...
... The gray whale lineage has a geological and historical presence in much of the North Atlantic, and it is reasonable to expect that C. rhachianecti also once ranged throughout the North Atlantic as well (Bisconti and Varola, 2006;Noakes et al., 2013;Alter et al., 2015;Bosselaers and Collareta, 2016;Hufthammer et al., 2018;Rodrigues et al., 2018). Overharvesting led to the final collapse of this population by sometime in the 18 th century, however, and today C. rhachianecti is found only in the North Pacific, where it is a host-specific symbiont of the gray whale (Newman and Ross, 1976;Newman and Abbott, 1980;Scarff, 1986;Bradford et al., 2011;Hayashi, 2012). Modern gray whales live in two distinct populations in the western and eastern North Pacific, although some interchange between these populations does occur (LeDuc et al., 2002;Cooke et al., 2007;IWC, 2011). ...
We report the finding of two partial specimens of Cryptolepas rhachianecti (Cirripedia, Coronulidae), a coronulid barnacle known only to inhabit the skin of gray whales ( Eschrichtius robustus ), in Pleistocene-aged sediments from the Canoa Basin, Ecuador. While the historical range of gray whales includes the North Pacific and North Atlantic, to our knowledge this is the first inferred evidence of a gray whale population having resided within the South Pacific. We describe the two Cryptolepas rhachianecti fossils, use isotopic analysis to investigate evidence of migration in their host whales, and discuss their implications for our understanding of gray whale evolutionary history.
... Photo-identification is an important methodological technique that provides a means to understand individual spatiotemporal movement patterns of gray whales. The gray whale is a suitable species for photo identification studies as individuals are born with unique and persistent pigmentation patterns and display consistent scarring and ectoparasites patterns [86][87][88]. Although scarring and parasite patterns can change over the years, individuals can typically be identified with certainty as these patterns change slowly and most animals are seen consistently over the year(s), providing a chronological photo record. ...
... Although scarring and parasite patterns can change over the years, individuals can typically be identified with certainty as these patterns change slowly and most animals are seen consistently over the year(s), providing a chronological photo record. Natural pigmentation, ectoparasites and scarring can also be used to reliably distinguish calves from yearlings, even in the absence of their mothers [86]. ...
The Western North-Pacific (WNP) gray whale feeding grounds are off the northeastern coast of Sakhalin Island, Russia and is comprised of a nearshore and offshore component that can be distinguished by both depth and location. Spatial movements of gray whales within their foraging grounds were examined based on 13 years of opportunistic vessel and shore-based photo-identification surveys. Site fidelity was assessed by examining annual return and resighting rates. Lagged Identification Rates (LIR) analyses were conducted to estimate the residency and transitional movement patterns within the two components of their feeding grounds. In total 243 individuals were identified from 2002–2014, among these were 94 calves. The annual return rate over the period 2002–2014 was 72%, excluding 35 calves only seen one year. Approximately 20% of the individuals identified from 2002–2010 were seen every year after their initial sighting (including eight individuals that returned for 13 consecutive years). The majority (239) of the WNP whales were observed in the nearshore area while only half (122) were found in the deeper offshore area. Within a foraging season, there was a significantly higher probability of gray whales moving from the nearshore to the offshore area. No mother-calf pairs, calves or yearlings were observed in the offshore area, which was increasingly used by mature animals. The annual return rates, and population growth rates that are primarily a result of calf production with little evidence of immigration, suggest that this population is demographically self-contained and that both the nearshore and offshore Sakhalin feeding grounds are critically important areas for their summer annual foraging activities. The nearshore habitat is also important for mother-calf pairs, younger individuals, and recently weaned calves. Nearshore feeding could also be energetically less costly compared to foraging in the deeper offshore habitat and provide more protection from predators, such as killer whales.
... Researchers record observations of calves during surveys of the PCFG. Discriminating between gray whale calves and juveniles while on the feeding grounds can be difficult, particularly once independent of their mother (Bradford et al., 2011). As a result, observations of calves likely underestimate the number born into the PCFG each year. ...
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.
... There is no hint, for this extinct genus and species, of what sort of host it might have been on. Cryptolepas murata was described from Upper Pleistocene deposits exposed at San Quintín, Baja California, Mexico, and is currently regarded as belonging to the same genus as Cryptolepas rhachianecti Dall, 1872, an obligate epibiont of grey whales (Eschrichtius robustus (Liljeborg, 1861)) (Newman & Abbott 1980;Bradford et al. 2011;Hayashi 2012;Taylor et al. 2022). (Although Bosselaers & Collareta (2016) were hesitant about the genus-level assignment of C. murata, the high-quality photographs provided by Taylor et al. (2022) clearly confirm that this extinct species belongs to Cryptolepas.) ...
A small lot of fossil whale barnacles from the Upper Pleistocene of California and the Middle Pleistocene (Chibanian) of Oregon (United States West Coast), described in a 1972 unpublished MA thesis, are formally described and illustrated herein. In that thesis, a new genus and species name were proposed; however, according to the International Code of Zoological Nomenclature, they have no taxonomic standing and are thus unavailable. Based on our reappraisal, two specimens in this lot belong to a new, extinct species that can be assigned to the purportedly extant genus Cetopirus. Cetopirus polysyrinx sp. nov. differs from congeners in that its secondary T-shaped flanges are multitubiferous internally, that is, they are perforated by a high number of irregularly-sized and irregularly-spaced tubules that result in a spongy aspect in transverse section. Whether or not this peculiar condition had any adaptive significance is difficult to determine. Considering that Cetopirus is currently known as an obligate epibiont of right whales (including the North Pacific form Eubalaena japonica (Lacépède 1818)), the host of C. polysyrinx sp. nov. was E. japonica or some other species of Eubalaena. The Plio-Pleistocene deposits of the Pacific coast of North America have yielded a rather idiosyncratic fossil whale barnacle fauna, inclusive of the genera Cetolepas, Cryptolepas and now Cetopirus, which seemingly contrasts with all other coeval assemblages worldwide, the latter being in turn dominated by Coronula spp.
... Among whale barnacles, C. rhachianecti is considered to be highly host-specific to the grey whale Eschrichtius robustus (e.g. Newman & Ross 1976;Newman & Abbott 1980;Scarff, 1986;Bradford et al. 2011;Hayashi 2012), although it has been exceptionally observed also on white whales which had previously been in firm contact with grey whales (Ridgeway 1997); therefore, the find of a compartment of C. rhachianecti can be taken as a very reliable indication of the past presence of E. robustus. Today, grey whales are restricted to the North Pacific; however, sub-fossil occurrences of E. robustus from the North Atlantic are well documented and most likely attest to two populations (northwestern, inhabiting the Atlantic coasts of North America, and northeastern, inhabiting the Atlantic coasts of Europe), which used to migrate between low-latitude winter breeding grounds and high-latitude summer feeding grounds (e.g. ...
An isolated compartment of a whale barnacle is herein described from Recent beach deposits in Zoutelande (Walcheren, The Netherlands). This specimen is identified as belonging to the extant coronulid species Cryptolepas rhachianecti, currently known as an epizoic symbiont of the grey whale Eschrichtius robustus. This find represents the first occurrence of C. Rhachianecti outside the North Pacific, and the first one as a (sub)fossil. In view of the fact that E. Robustus, which is currently confined to the North Pacific, is known as a subfossil from the northeastern Atlantic between late Late Pleistocene (c. 45,000 years ago) and historical (c. 1700 AD) times, we propose a similar (late Quaternary) age for the isolated compartment. The find indicates that the extinct late Quaternary northeastern Atlantic population of E. Robustus was infected by Cryptolepas rhachianecti. Our find is, therefore, compatible with the hypothesis of an ancient grey whale migration route running between the subtropical/temperate waters of the northeast Atlantic (or Mediterranean Basin), and the cold waters of the Baltic Sea (or southern Arctic Ocean), through the southern North Sea. Finally, we discuss the systematic placement of the fossil barnacle species Cryptolepas murata and propose the possibility of its removal from the genus Cryptolepas pending further investigations.
... (2) for independent first-summer calves: small diameters of epizootic barnacles and the absence of larger scars of previously detached barnacles (see Bradford et al., 2011 for examples); ...
Patterns of gray whale growth in body length and weight with age are evaluated using published values of foetal and post-natal body dimensions at reported ages, supplemented with previously unpublished measured lengths of 88 mid-gestation foetuses, 82 first-summer calves and 30 second-summer whales taken in the summer/autumn Chukotkan native subsistence fishery. Gompcrtz growth models are fitted to foetal and post-natal lengths at age, predicting mean lengths at birth in mid-January of 4.7m, 7.9m at weaning and 8.7m at one year. The late foetal diapause in growth of length is not supported by the available data. Two equations were derived for estimating body weights from the linear body dimensions of length and maximum girth. For biomass estimates, two equations based on length alone and on both girth and length arc derived. A multiple least squares regression equation fit to 14 measurements of the same whale over 14 months of captive rehabilitation predicts mean body weights at birth of l,100-l,200kg, 5,100-5,200kg at six months (weaning), and 6,700-6,800kg at one year of age.
... Second, some species of large baleen whales possess unique ectoparasites, including crustaceans whose hard parts do preserve well in the fossil record. Gray whales, for example, are the unique hosts of the barnacle species Cryptolepas rhachianecti (Bradford et al., 2011). Thus far, this taxon has no fossil record, but remains of this barnacle might be recovered from JY Reef with further investigation. ...
Wild animals are increasingly exposed to human‐induced threats in the ocean realm. Cetacean species, as predators and biomonitoring models, are subjected to a variety of stressors that may result in poor health, injuries, and persistent marks. These malformations can easily be documented by photography or video and can be used to infer about the animals' health, especially if combined with long‐term photographic identification. However, the value of such information for monitoring is vastly increased if a standardised language is used. We provide a broad definition of deformity, as a general concept for conditions or abnormal features in cetacean species, and categorise externally detected deformities in free‐ranging individuals.
We define six categories and 58 sub‐categories of deformities in cetaceans: anatomical malformations (11 sub‐categories), skin lesions (29), anomalous pigmentation (4), injuries due to physical impacts (14), emaciation, and epibionts.
Categorisation was based on peer‐reviewed literature published between 2000 and 2021 ( n = 253 studies), comprising 80 of the 101 extant species, documented in studies conducted across 50 countries; reviewed literature included papers from 86 scientific journals, with three journals contributing 100 out of the 253 documents.
Overall, and for both Odontoceti and Mysticeti, physical impact was the most reported category; injuries due to physical impacts were documented in 74% of the 253 studies we reviewed. This may be related to the common exposure of cetaceans to intense human marine traffic and fishing activities.
Especially with the growing use of open science, a consistent and common language is fundamental for data comparison and to support cetacean research, management and conservation efficiently. We suggest that researchers adopt these definitions and categories when describing abnormalities observed in free‐living cetaceans.
Offshore Exploration and Production (E&P) activities, such as seismic surveys and drilling, generate sound that can affect marine mammals in different ways. These effects range from permanent or temporary auditory impacts to disturbance or behavioral changes, and communication masking. Depending on the intensity and duration of these effects, and without implementation of appropriate mitigation measures, this can result in population-level consequences. The overarching objective of this study was to advance the protection of marine mammals during the implementation of E&P activities through the following themes: (1) enhancement of the state of knowledge of risk management, (2) efficacy of mitigation, (3) advanced monitoring technology, (4) implementation of advanced industry monitoring and mitigation measures and (5) measurement of heretofore unassessed E&P activities. In this study several marine mammal monitoring and mitigation programs associated with E&P projects are presented to further advance these themes. Topics being addressed include the use of autonomous camera systems for aerial monitoring of a narwhal population, long-term photo-identification studies of western gray whales to better understand site fidelity to their summer feeding grounds, mitigation of gray whales’ behavioral responses to a seismic survey near these feeding grounds and use of Passive Acoustic Monitoring to characterize seismic pulses and drilling activity as well as marine mammal presence in remote arctic areas. A synthesis of the main findings is provided that includes identification of future research needs. Conclusions and specific recommendations are made that will contribute to our ability to assess and mitigate risks of E&P sound to marine mammals.
A population assessment of the Sakhalin feeding aggregation of gray whales (Eschrichtius robustus) was conducted using photo-identification data collected on their summer feeding ground off Sakhalin Island from 1994 to 2015, fitted to an individually-based population model. The model is structured by age, sex and reproductive status, and annual transition probabilities of individuals between stages are modelled. The model allows for individual, stage-related and temporal heterogeneity in sampling probability, in the (successful) pregnancy rate and in the calf/yearling " survival and return " rate (to the Sakhalin feeding grounds). The model was fitted using both maximum-likelihood and Bayesian approaches. Comparison of model fits using the AIC criterion revealed strong evidence for differential sampling availability by reproductive stage and by individual, but no evidence for individual variation in productivity. There was strong evidence for annual variation in pregnancy rates and calf survival/return rates, but no evidence of variation in non-calf survival rates. The level of immigration is estimated to have been low or zero. Using the best fitting model, the aged 1+ (non-calf) population size is estimated to be 175 animals (Bayesian 95% confidence intervals 158-193) in 2016, and to have been growing over the previous 10 years (2005-2015) at an average rate between 2% and 4% p.a. Forward projections of the population model to 2025, assuming no change in the means and variances of demographic parameters, indicate a high probability (>95%) of continued population increase. The results indicate that both the pregnancy rate and the calf/yearling survival/return rate were unusually low in 2008. Projections of the population on the assumption that the average net reproductive rate would be reduced to the 2008 level show that under these circumstances the population would likely stop recovering. As noted by the Western Gray Whale Advisory Panel (IUCN, 2009; 2016), whale distribution in 2008 was noticeably different from previous years, even though food availability appeared normal, and this may have been due to high levels of anthropogenic noise from pile driving at Piltun lagoon. The current results suggest that the disturbance had detectable demographic consequences. This underlines the need to keep disturbance within reasonable levels in order not to jeopardize the recovery of the population.
We outline the rationale and process used by the Cetacean Density and Distribution Mapping (CetMap) Working Group to identify Biologically Important Areas (BIAs) for 24 cetacean species, stocks, or populations in seven regions within U.S. waters. BIAs are reproductive areas, feeding areas, migratory corridors, and areas in which small and resident populations are concentrated. BIAs are region-, species-, and time-specific. Information provided for each BIA includes the following: (1) a written narrative describing the information, assumptions, and logic used to delineate the BIA; (2) a map of the BIA; (3) a list of references used in the assessment; and (4) a metadata table that concisely details the type and quantity of information used to define a BIA, providing transparency in how BIAs were designated in a quick reference table format. BIAs were identified through an expert elicitation process. The delineation of BIAs does not have direct or immediate regulatory consequences. Rather, the BIA assessment is intended to provide the best available science to help inform regulatory and management decisions under existing authorities about some, though not all, important cetacean areas in order to minimize the impacts of anthropogenic activities on cetaceans and to achieve conservation and protection goals. In addition, the BIAs and associated information may be used to identify information gaps and prioritize future research and modeling efforts to better understand cetaceans, their habitat, and ecosystems.
Gray whales Eschrichtius robustus exist as 2 geographically and genetically distinct populations in the eastern and western North Pacific. Subjected to intensive commercial whaling during the 19th and 20th centuries, the western population presently numbers approximately 100 individuals and is regarded as one of the most endangered baleen whale populations in the world. Since 1997, ongoing studies of western gray whales have resulted in a photographic dataset that can be used for mark-recapture survival estimation. Pollock's robust design was applied to 129 individual whale encounter histories spanning 25 monthly capture occasions from 1997 to 2003. Using Akaike's Information Criterion (AICc) model selection, models incorporating individual heterogeneity in residency patterns and higher temporary emigration probabilities for younger whales provided better fits to the data. Non-calf and calf (1st year post-weaning) survival were estimated as 0.951 (SE = 0.0135, 95% Cl = 0.917 to 0.972) and 0.701 (SE = 0.0944, 95% Cl = 0.492 to 0.850), respectively, averaging across the best models (n = 13) in order to account for model uncertainty. The non-calf survival point estimate is similar to mark-recapture estimates for Gulf of Maine humpback whales, but lower than an indirect estimate for the eastern gray whale population. Although no statistically robust direct estimates of baleen whale calf survival exist for comparison to the current study, the calf survival estimate is markedly lower than a value suggested for Gulf of Maine humpback whales. Estimation of survival is necessary for assessing the status of western gray whales, which can contribute to increased protection, conservation, and management planning for this critically endangered population.
This study documents the range, abundance and movements of a feeding aggregation of gray whales ( Eschrichtius robustus) in the Pacific northwest. Identification photographs were collected by eight collaborating organisations between March and November 1998. Surv eys extended between northern California and southeastern Alaska. Effort was variable by region and was concentrated off the northe rn Washington coast and Vancouver Island. Of 1,242 occasions when suitable photographs of gray whales were obtained in 1998, 155 u nique whales were identified. Each individual was photographed an average of 8.0 times (SD = 8.4, range 1-42) and the average tenure of whales seen multiple times was 56 days (SD = 41, range 1-170). Whales seen longer than three months generally were seen in multiple regi ons. Movements among regions in 1998 were documented for 57 whales with the most frequent interchange among three adjacent areas fro m northern Washington to central Vancouver Island. The overall pattern of movements among regions was complex; whales were not al ways moving in the same direction at the same time of year. Movements within 1998 among more distant locations did occur but were le ss frequently observed. Total distances between resighting positions for individual whales ranged from < 1 to 526 n.miles. Most wha les photographed in 1998 had been identified in previous years when compared to photographs collected by some of the collaborators. At least 86 (55%) of the whales identified had been seen previously. The rate of inter-year resightings was highest for whales identifie d off northern Washington and three areas off British Columbia (from southern Vancouver Island to north of Vancouver Island). In these areas, from 70-100% of the whales seen in each region had been photographed previously. Mark-recapture abundance estimates based on compari sons to samples in 1996 and 1997 were 181 and 179, respectively. The management implication for these whales has become controversia l due to the resumption of whaling by the Makah tribe in northern Washington, an area used by both migrating and feeding whales. This research shows that there are a few hundred gray whales that range in summer months from at least northern California to southeastern Al aska. The mechanism by which these animals are recruited into this group and the degree to which they should be managed as a separate uni t from the overall population is not resolved.
The Eastern North Pacific gray whale (Eschrichtius robustus) is one population of large cetacean that has recovered from depletion resulting from commercial harvest in the mid-to late-1800s. It is believed that this population may be approaching, or possibly exceeding its carrying capacity as suggested by recent increases in mortality of all age and sex classes. Research on the breeding biology and phenology of gray whales that spend the winter in the coastal waters and lagoons of Baja California, Mexico has been conducted for many years. These studies contribute valuable information on the reproductive biology of this species, and the importance of their coastal lagoon habitats to their reproductive success. This paper reviews and summarises historical exploitation, conservation measures, the findings of research conducted on gray whales in their winter breeding range, potential natural and anthropogenic threats to this population, and makes recommendations for future research and monitoring. This review concentrates on the findings of research conducted since the mid-1970s.
A whale barnacle, Cryptolepas rhachianecti (Dall), previously considered an obligate commensal for the gray whale, Eschrichtius robustus (Lilljeborg), infested white whales, Delphinapterus leucas (Pallas), housed in San Diego Bay. The infestation occurred annually between January and April in concert with the northward migration of the gray whale, and did not occur during years when the white whales were housed elsewhere during these months. Although initial infestation elicited no apparent skin response, after successive years of exposure, massive cellular proliferation in the adjacent epidermis resulted in ejection of barnacles from the whales within a few weeks. This increasing epidermal response and the invasion of inflammatory cells at the juncture of skin and barnacle shell is suggestive of an immune reaction to the barnacles.
A bstract
Habitat utilization and prey species of Vancouver Island gray whales were investigated by (1) summarizing 26 yr of distribution and feeding data and (2) conducting intensive observations in Clayoquot Sound, Vancouver Island, from 1989 to 1996. Whale distribution and movements were monitored from March to November through systematic boat surveys and whale‐watch sighting programs. Prey species were collected by suction hose and plankton net or determined through analysis of fecal samples. Gray whales utilized virtually all of the southern west coast of Vancouver Island over the 26‐yr observation period. Distribution, prey species, and feeding behavior showed marked variability during any one season and between years. Some feeding areas were used on an annual basis, others with >10‐yr intervals between use. Feeding occurred in shallow sand or mud bays, eel grass beds, kelp beds, in the open water column, and at the surface. Young whales appeared to utilize habitat and prey species differently than adults. Main prey species included herring eggs/larvae ( Clupea harengus pallasi ), crab larvae ( Cancer magister megalops, Pachycbeles spp. zoea), mysids ( Holmesimysis sculpta, Neomysis rayii, Acanthomysis spp.), amphipods ( Ampelisca spp., Atylus borealis ), and ghost shrimp ( Callianassa californiensis ). The definition and relative importance of specific feeding grounds and the study of human impacts on this population are complicated by its broad and variable use of habitat and prey species.
Gray whales (Eschrichtius robustus) occur along the eastern and western coastlines of the North Pacific as two geographically isolated populations and have traditionally been divided into the eastern (California-Chukchi) and western (Korean-Okhotsk) populations. Recent molecular comparisons confirm, based on differences in haplotypic frequencies, that these populations are genetically separated at the population-level. Both populations were commercially hunted, but only the eastern gray whale has returned to near pre-exploitation numbers. In contrast, the western population remains highly depleted, shows no apparent signs of recovery and its future survival remains uncertain. Research off Sakhalin Island, Russia between 1995 and 1999 has produced important new information on the present day conservation status of western gray whales and provided the basis for the World Conservation Union (IUCN) to list the population as 'Critically Endangered' in 2000. The information presented here, in combination with potential impacts from anthropogenic threats throughout the range of this population, raises strong concerns about the recovery and continued survival of the western gray whale.
A collaborative Russia-U.S. research program on western gray whales (Eschrichtius robustus) summering off northeastern Sakhalin Island, Russia, has been ongoing since 1995 and has produced important information on the present day conservation status of this critically endangered population. This paper reviews findings from 2008 research activities and combines such with data from previous years, in some cases ranging back to an opportunistic survey in 1994. Photo-identification research conducted off Sakhalin Island in 2008 resulted in the identification of 45 whales, including three calves. No previously unidentified non-calves were observed. When combined with data from 1994-2007, a catalog of 172 photo-identified individuals has been compiled. Not all of these 172 whales can be assumed to be alive, however. One new reproductive female was recorded in 2008, resulting in a minimum of 25 reproductive females being observed since 1995. In addition to a number of biological difficulties that western gray whales are facing, the large-scale offshore oil and gas development programs near their summer feeding ground, as well as fatal net entrapments off Japan during migration, pose significant threats to the future survival of the population.
Annual gray whale (Eschrichtius robustus) calf production and mortality were empirically estimated from data collected in Laguna Guerrero Negro. Laguna Ojo de Liebre, and Laguna San Ignacio, Baja California Sur, Mexico between 1980 and 1982. A gross annual production of 1,185 calves with a 5.4% mortality based on lagoon strandings yielded a net production of 1,121 calves. This represents a 7.0% annual rate of production based on the best estimate of the current population size of 15,942 gray whales. By comparison, the proportion of calves passing Pt. Piedras Blancas, California in 1980 and 1981 was 4.3% (679) and 4.8% (769) respectively. suggesting a 31% calf decrease may occur between the lagoons and central California. Two periods critical to calf survival are postulated; the first period immediately follows birth, and the second corresponds to the calves departure from the lagoons and the beginning of the northward migration.
Studies were made on barnacle orientations with reference to water flow seen on Grey whales taken by the U.S. Fish and Wildlife Service in March, 1969. Water flow patterns were derived by laying cord transects along lines of barnacle orientation. Statistical evaluation of directional consistency within barnacle colonies revealed that 95% of the individuals were within 14° of a mean direction. Flow patterns were generally parallel to the long axis of the whales with modification in the areas of anterior rostrum, lips, throat, and flippers. No data were available concerning water flow on the flukes.
A bstract
The annual return, seasonal occurrence, and site fidelity of Korean‐Okhotsk or western gray whales on their feeding grounds off northeastern Sakhalin Island, Russia, were assessed by boat‐based photo‐identification studies in 1994‐1998. A total of 262 pods were observed, ranging in size from 1 to 9 whales with an overall mean of 2.0. Sixty‐nine whales were individually identified, and a majority of all whales (71.0%) were observed in multiple years. Annual sighting frequencies ranged from 1 to 18 d, with a mean of 5. 4 d. The percentage of whales reidentified from previous years showed a continuous annual increase, reaching 87.0% by the end of the study. Time between first and last sighting of identified individuals within a given year was 1‐85 d, with an overall mean of 40.6 d. Annual calf proportions ranged from 4.3% (1997) to 13.2% (1998), and mother‐calf separations generally occurred between July and September. The seasonal site fidelity and annual return of whales to this part of the Okhotsk Sea emphasize its importance as a primary feeding ground for this endangered population.
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