Marilyn E. Dahlheim's research while affiliated with Southwest Fisheries Science Center and other places

Publications (47)

Article
Organochlorine (OC) profiles have been used as chemical “fingerprints” to infer an animal's foraging area. North Pacific killer whale (Orcinus orca) populations are exposed to different levels and patterns of OCs based on their prey, distribution, and amount of time spent in a particular area. To characterize concentrations and profiles of OCs foun...
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Determining management units for natural populations is critical for effective conservation and management. However, collecting the requisite tissue samples for population genetic analyses remains the primary limiting factor for a number of marine species. The harbour porpoise (Phocoena phocoena), one of the smallest cetaceans in the Northern Hemis...
Article
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In the northeastern Pacific Ocean, there are three “ecotypes” of killer whales that differ in diet, ecology, behavior, acoustics, genetics, and morphology. Previous attempts to describe the morphological differences among populations of killer whales (Orcinus orca) have been limited to descriptive accounts or categorical studies. We used elliptical...
Article
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Reproductively and geographically isolated populations of predators may be synchronized by a phenomenon known as the Moran effect—specifically if they exhibit common responses to external processes, such as climate, density dependence (parasites, disease), or prey. Prey has the ability to synchronize predators if geographically isolated predator po...
Article
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Abundance of harbor porpoise (Phocoena phocoena) was estimated from data collected during vessel surveys conducted throughout the inland waters of Southeast Alaska. Line-transect methods were used during 18 seasonal surveys spanning 22 years (1991–2012). Estimates were derived from summer surveys only because of the broader spatial coverage and gre...
Data
Number of samples used in this study by predefined population. Table S2 Demographic estimates from ∂a∂i for the MI/AT/OS analysis. Table S3 Demographic estimates from ∂a∂i for the AT/OS/AR analysis. Table S4 Model comparisons for order of population splitting for the MI, AT, OS analysis. Table S5 Model comparisons for order of population splitting...
Article
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The evolution of diversity in the marine ecosystem is poorly understood, given the relatively high potential for connectivity, especially for highly mobile species such as whales and dolphins. The killer whale (Orcinus orca) has a worldwide distribution, and individual social groups travel over a wide geographic range. Even so, regional populations...
Article
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For many highly mobile species, the marine environment presents few obvious barriers to gene flow. Even so, there is considerable diversity within and among species, referred to by some as the 'marine speciation paradox'. The recent and diverse radiation of delphinid cetaceans (dolphins) represents a good example of this. Delphinids are capable of...
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Ecosystem function and resilience is determined by the interactions and independent contributions of individual species. Apex predators play a disproportionately determinant role through their influence and dependence on the dynamics of prey species. Their demographic fluctuations are thus likely to reflect changes in their respective ecological co...
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In this study we present empirical data on predator numbers, movements and area usage, and predation obtained from tracking transient killer whales Orcinus orca throughout the inland waters of southeastern Alaska, USA. During 1991-2007, we documented 155 transient killer whales via photo-identification methodology within the large study area (27,80...
Article
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We used photographic mark-recapture methods to estimate the number of mammal-eating “transient” killer whales using the coastal waters from the central Gulf of Alaska to the central Aleutian Islands, around breeding rookeries of endangered Steller sea lions. We identified 154 individual killer whales from 6,489 photographs collected between July 20...
Article
In social species, breeding system and gregarious behavior are key factors influencing the evolution of large-scale population genetic structure. The killer whale is a highly social apex predator showing genetic differentiation in sympatry between populations of foraging specialists (ecotypes), and low levels of genetic diversity overall. Our compa...
Article
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The diversity of exon-2 (peptide-binding region) of the DQB1 locus (Class II, major histocompatibility complex, MHC) was investigated on an extended sample of populations of three focal cetacean species (two sibling delphinid species and another in the same family). We tested the hypothesis that dolphin populations with a worldwide distribution acr...
Article
Aim  To assess the distribution, group size, seasonal occurrence and annual trends of cetaceans.Location  The study area included all major inland waters of Southeast Alaska.Methods  Between 1991 and 2007, cetacean surveys were conducted by observers who kept a constant watch when the vessel was underway and recorded all cetaceans encountered. For...
Article
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Knowledge of the age distributions of killer whale Orcinus orca populations is critical to assess their status and long-term viability. Except for accessible, well-studied populations for which historical sighting data have been collected, currently there is no reliable benign method to deter- mine the specific age of live animals for remote popula...
Article
Beginning in the late 1980s, large groups of previously unidentified killer whales (Orcinus orca) were sighted off the west coast of Vancouver Island and in the Queen Charlotte Islands, British Columbia. Scientists working in this region produced two killer whale photo-identification catalogues that included both transient (mammal-eating) whales an...
Article
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We examined the incidence of rake mark scars from killer whales Orcinus orca on the flukes of humpback whales Megaptera novaeangliae throughout the North Pacific to assess geo- graphic variation in predation pressure. We used 3650 identification photographs from 16 wintering or feeding areas collected during 1990 to 1993 to determine conservative e...
Article
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Springer et al. (2003) contend that sequential declines occurred in North Pacific populations of harbor and fur seals, Steller sea lions, and sea otters. They hypothesize that these were due to increased predation by killer whales, when industrial whaling's removal of large whales as a supposed primary food source precipitated a prey switch. Using...
Article
Intraspecific resource partitioning and social affiliations both have the potential to structure populations, though it is rarely possible to directly assess the impact of these mechanisms on genetic diversity and population divergence. Here, we address this for killer whales (Orcinus orca), which specialize on prey species and hunting strategy and...
Article
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Killer whale (Orcinus orca Linnaeus, 1758) abundance in the North Pacific is known only for a few populations for which extensive longitudinal data are available, with little quantitative data from more remote regions. Line-transect ship surveys were conducted in July and August of 2001–2003 in coastal waters of the western Gulf of Alaska and the A...
Article
Top predators in the marine environment integrate chemical signals acquired from their prey that reflect both the species consumed and the regions from which the prey were taken. These chemical tracers-stable isotope ratios of carbon and nitrogen; persistent organic pollutant (POP) concentrations, patterns and ratios; and fatty acid profiles-were m...
Article
Humpback whales feed in several high-latitude areas of the North Pacific. We examined the interchange of humpback whales between one of these areas, off California, and those in other feeding grounds in the eastern North Pacific:. Fluke photographs of 597 humpback whales identified off California between 1986 and 1992 were compared with those off O...
Article
1 SAIC, Maritime Services Division, 3990 Old Town Ave., Suite 105A, San Diego, California 92110, U. S. A.; e-mail: sue_moore@cpqm.saic.com
Article
Estimations of gray whale abundance have generally assumed that shore-based observers record all whales migrating through the viewing area during periods uncompromised by visibility. We tested the repeatability of data collected at the standard gray whale census site at Granite Canyon Marine Laboratory in central California by using pairs of observ...
Article
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Blubber biopsy samples from adult male North Pacific killer whales (Orcinus orca), were analyzed for fatty acids, carbon and nitrogen stable isotopes and organochlorine contaminants. Fatty acid profiles were sufficiently distinct among the three reported ecotypes ("resident," "transient" or "offshore") to correctly classify the whales in this study...
Article
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Killer whale predation on belugas in Cook Inlet, Alaska, has become a concern since the decline of these belugas was documented during the 1990s. Accordingly, killer whale sightings were compiled from systematic surveys, observer databases, and anecdotal accounts. Killer whales have been relatively common in lower Cook Inlet (at least 100 sightings...
Article
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A low level of genetic variation in mammalian populations where the census population size is relatively large has been attributed to various factors, such as a naturally small effective population size, historical bottlenecks and social behaviour. The killer whale (Orcinus orca) is an abundant, highly social species with reduced genetic variation....
Article
Despite the extensive use of photographic identification methods to investigate humpback whales in the North Pacific, few quantitative analyses have been conducted. We report on a comprehensive analysis of interchange in the North Pacific among three wintering regions (Mexico, Hawaii, and Japan) each with two to three subareas, and feeding areas th...
Article
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Vocalizations of feeding humpback whales from southeast Alaska were analyzed to characterize quantitatively the predominant vocalization associated with feeding and assess variation among vocalizations. Whales uttered series of cries similar in acoustic structure to those described previously as stereotyped, rhythmic ‘feeding calls’. Individual cri...
Article
Between 1991 and 1993, Alaska harbor porpoise (Phocoena phocoena) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entrance in Southeast Alaska. Line-transect methodology was used, and only those observations made during optimal conditions were an...
Technical Report
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Two cruises were conducted in the eastern North Pacific Ocean to investigate the precision of large whale call locations as determined by the National Oceanic and Atmospheric Administration (NOAA) and Pacific Marine Environmental Laboratory’s (PMEL) implementation of a localization and tracking routine using data from the U.S. Navy’s Sound Surveill...
Article
The known summer feeding range of the North Pacific humpback whale (Megaptera novaeangliae) extends from California, along the coasts of Oregon, Washington, and Alaska, into the Bering Sea, along the Aleutian Islands, the Sea of Okhotsk (Tomilin 1957), and to northern Japan (Rice 1977). In feeding areas of the northeastern Pacific Ocean, humpback w...
Article
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Killer whales from the coastal waters off California through Alaska were compared for genetic variation at three nuclear DNA markers and sequenced for a total of 520 bp from the mitochondrial control region. Two putative sympatric populations that range throughout this region were compared. They can be distinguished by social and foraging behavior...
Article
The pelagic and coastal waters over the Outer Continental Shelf of the Gulf of Alaska are expected to be important areas for oil and gas development and tanker traffic. Coastal areas near oil-lease sites contain important habitat for breeding marine mammals and seasonally migrating animals. Pelagic offshore waters over the continental shelf are als...
Article
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Photo-identification studies of individual killer whales inhabiting Prince William Sound were collected from 1989-91 to determine the impact of the spill on whale abundance and distribution. Concurrent photo-identification studies were also conducted in Southeast Alaska to determine if PWS killer whales were displaced to other areas. Despite increa...

Citations

... Zollett and Read, 2006;Brotons et al., 2007;Lauriano et al., 2009;Powell and Wells, 2011;Hamer et al., 2012). Also, depredation can be applied to situations that involve mortality or injury of marine predators resulting from interactions with fishing gear (bycatch), often including consideration of how to mitigate such mortality and injury, and to reduce the extent of catch removal and gear damage (Gilman et al., 2006;Hamer et al., 2012;Dawson et al., 2013;Götz and Janik, 2013;Werner et al., 2015;Mitchell et al., 2018;Dahlheim et al., 2022). ...
... Population estimates are generally below 50 mature individuals. Waring et al. (2015)'s abundance estimate of 33 remaining individuals is considered the best existing estimate (Corkeron et al., 2017;Rosel et al., 2016;Rosel et al., 2021); other estimates have ranged between 15-44 individuals throughout American waters within the GoMx (Hansen et al., 1995;Mullin & Fulling, 2004;Mullin, 2007;Roberts et al., 2015;DWH MMIQT, 2015). While the causes behind the brink remain subject to further research, it is unlikely that historical whaling was a major factor (DWH MMIQT, 2015). ...
... Generally, POPs experience biomagnification within food webs since dietary intake acts as the main route for contaminant accumulation. Thus, high levels of POPs have been documented in killer whales from different geographical areas (mostly from the northern hemisphere; Desforges et al., 2018;Andvik et al., 2020;Lawson et al., 2020;Remili et al., 2021). Substantial differences due to their ecotype (based on prey specialization) influence the accumulation of contaminants in killer whales, which may exert different effects on different populations worldwide (Desforges et al., 2018). ...
... In aquatic environments, eDNA can be collected by filtration, precipitation or centrifugation of water samples (Ficetola et al., 2008;Tsuji et al., 2019) and then amplified using assays targeting specific DNA sequences ( Figure 1). Thus, eDNA can be used to detect the presence of single species via PCR amplification using species-specific primers (Ficetola et al., 2008;Foote et al., 2012;Baker et al., 2018;Parsons et al., 2018) while multiple species can be identified simultaneously through eDNA metabarcoding using universal primers coupled with next-generation sequencing (NGS) (Thomsen et al., 2012;Miya et al., 2015;Valsecchi et al., 2020;Xie et al., 2021). In addition, multiple primer pairs targeting different species or taxa can be combined in a single PCR reaction (i.e., multiplex PCR assay) (Ramón-Laca et al., 2021). ...
... A Procrustes fit was also required to align shapes. This method of alignment is often employed in studies that use elliptical Fourier analysis to quantify shapes with few major protrusions such as orca fins, human crania, and posterior lobes of Drosophila (Emmons et al., 2019;Friess & Baylac, 2003;Takahara & Takahashi, 2015). ...
... The available information on the impacts of oil on odontocetes has been largely focused on coastal species and environments, specifically killer whales following the Exxon Valdez Oil Spill (EVOS; Matkin et al., 2008) and GoMex Bay, Sound, and Estuarine (BSE) bottlenose dolphins following DWH (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016; Schwacke et al., 2017). In both cases, long-term impacts on the observed populations were high, with elevated rates of chronic disease and mortality, and suppressed long-term reproductive capacity (Dahlheim and Matkin, 1994;Matkin et al., 2008;Schwacke et al., 2013;Schwacke et al., 2017;Smith et al., 2017;Takeshita et al., 2017). Population recovery time for Barataria Bay bottlenose dolphins following DWH is estimated to be 39 years . ...
... This is especially important since reduced quality nutrition may contribute to physiological stress as observed in at least one of the surrogate species, SRKW (Ayres et al., 2012). The ranking of prey reduction as a "high" threat in the SRKW Recovery Plan may have prompted research efforts to assess prey quality, abundance, and distribution within their summer range, the Pacific Northwest, and the relationship between fecundity and mortality of SRKW to prey levels (e.g., Ford et al., 2010;O'Neill et al., 2014;Ward et al., 2016). The number of SRKW records (both peer-reviewed and gray literature) related to prey reduction, doubled from 2018 to 2019 (e.g., Joy et al., 2019;Tennessen et al., 2019), suggesting an increased focus on investigating the role of prey reduction on stress and reproduction in that population, studies that could potentially be applied to CIB. ...
... One year following the EVOS, 13 individuals from a single killer whale pod died, of which the majority were reproductive females and juveniles. The mortality rate for this pod during 1989 and 1990 was 19.4% and 20.7% respectively, significantly higher than historical rates (Matkin et al. 1994). The EVOS also had chronic effects on this species (Matkin et al. 2008). ...
... Of the 50 species, 14 species, ecologically distinct units, or distinct population segments of species (28%) are listed by one or more of the four listing jurisdictions in the Salish Sea as endangered, threatened, sensitive, of special concern, or candidates for listing [27]. Possibly [28] Likely [29] Likely [30] Possibly [16] Unlikely [a] Unlikely [a] Data Deficient [31] Unlikely [a] Killer whale Likely [32] Likely [33] Unlikely [b] Possibly [16] Unlikely [c] Unlikely [c] Data Deficient [31] Possibly [34] Avian Bald Eagle Likely [33] Unlikely [d] Unlikely [d] Possibly [16] Likely [35] Likely [35] Data Deficient [31] Possibly [34] Great Blue Heron Possibly [36] Unlikely [d] Unlikely [d] Possibly [16] Possibly [36] Possibly [36] Data Deficient [31] Possibly [34] Double- crested Cormorant Likely [37] Unlikely [d] Unlikely [d] Possibly [16] Likely [37] Possibly [37] Data Deficient [31] Possibly [34] Common Murre ...
... Furthermore, fluke photographs of 142 humpback whale individuals obtained from the same study area were randomly taken and examined in order to identify rake-marks or scars caused by KW attacks (Mehta et al., 2007;Pitman et al., 2015), based on categories described by Steiger et al. (2008). ...