Estimation of population size and trends for highly mobile species with dynamic spatial distributions

Seasonal distribution of Dall's porpoise in Prince William Sound, Alaska

Pleistocene environmental changes are generally assumed to have dramatically affected species’ demography via changes in habitat availability, but this is challenging to investigate due to our limited knowledge of how Pleistocene ecosystems changed through time. Here, we tracked changes in shallow marine habitat availability resulting from Pleistocene sea level fluctuations throughout the last glacial cycle (120–14 thousand years ago; kya) and assessed correlations with past changes in genetic diversity inferred from genome‐wide SNPs, obtained via ddRAD sequencing, in Caribbean hawksbill turtles, which feed in coral reefs commonly found in shallow tropical waters. We found sea level regression resulted in an average 75% reduction in shallow marine habitat availability during the last glacial cycle. Changes in shallow marine habitat availability correlated strongly with past changes in hawksbill turtle genetic diversity, which gradually declined to ~1/4th of present‐day levels during the Last Glacial Maximum (LGM; 26–19 kya). Shallow marine habitat availability and genetic diversity rapidly increased after the LGM, signifying a population expansion in response to warming environmental conditions. Our results suggest a positive correlation between Pleistocene environmental changes, habitat availability and species’ demography, and that demographic changes in hawksbill turtles were potentially driven by feeding habitat availability. However, we also identified challenges associated with disentangling the potential environmental drivers of past demographic changes, which highlights the need for integrative approaches. Our conclusions underline the role of habitat availability on species’ demography and biodiversity, and that the consequences of ongoing habitat loss should not be underestimated.

Temporal variation in animal population size and the related concept of population stability are of substantial interest to animal ecologists (e.g., MacArthur 1955, Holling 1973). Empirical studies of variation in population size are not new (e.g., Watt 1964) but have become especially popular in recent years. Recent empirical work has included interesting research on the relationships between temporal variation in population size and such factors as extinction probability (Karr 1982, Pimm et al. 1988, Schoener and Spiller 1992, Tracy and George 1992), mean population density (Taylor and Woiwod 1980), latitude (Wolda 1978), human disturbance (Pechmann et al. 1991), body size (Gaston 1988, Gaston and Lawton 1988), food habits (Gaston and Lawton 1988, Redfearn and Pimm 1988), geographic range (Gaston 1988, Gaston and Lawton 1988), and taxonomy (Connell and Sousa 1983, Schoener 1985). However, of temporal variation in population size is not a simple matter (Greenwood 1989, Mc Ardle 1989, McArdle et al. 1990). McArdle et al. (1990: 439) recently discussed associated with the measurement and interpretation of population density variability that have confounded most, if not all, previous studies of the subject. These problems include artefactual patterns induced by commonly used transformations and misleading conclusions resulting from comparisons of populations sampled at different spatial and temporal scales. McArdle et al. (1990) also argued that the dependence of population variability on mean density should be considered in making comparisons of variability among species and populations. Recent contributions to the literature conclude with statements emphasizing the importance of properly estimating and comparing population variability and recommending additional statistical and biological work on the topic (McArdle et al. 1990, Schoener and Spiller 1992). Despite the fairly extensive literature on population variability and its estimation, there has been little discussion of the fact that virtually all of the empirical work has relied on estimates or indices to animal abundance (see McArdle and Gaston 1993). That is, estimates of population variability are not based on a time series of true population sizes measured without error, but on a series of estimates or indices (count statistics assumed to be related to population size by a proportionality constant, see Lancia et al. in press). Measures of population variability computed using point estimates of population size over time represent the sum of at least two conceptually distinct variance components. One component is temporal variation in actual population size and is relevant to interesting biological hypotheses. Another component is variation, defined here as the variation associated with the population procedure. This component is sometimes called error of estimation and occurs whenever it is impossible to directly enumerate all individuals in the population. This component is not relevant to biological hypotheses and should not be included in measures of population variability computed for the purpose of addressing such hypotheses. We believe that the inclusion of this unwanted variance component in previous studies of population variability is at least as serious a problem as those associated with transformations and scale discussed by McArdle et al. (1990). For studies in which population size is estimated rather than indexed, it is usually possible to estimate the sampling variance of the population estimates. This component can then be subtracted from the total variance (e.g., based on point estimates) to estimate the variance component of interest. This basic approach has been used to estimate variance of survival probabilities among replicate groups of animals receiving different experimental

Heart size and blood oxygen (O2) in Dall's porpoises (Phocoenoides dalli), Pacific white‐sided dolphins (Lagenorhynchus obliquidens), and common bottlenose dolphins (Tursiops truncatus) correlate with reported swim speeds and dive behavior. Deep‐dive capacity is often associated with smaller relative lung masses, larger “inexpensive” tissue masses (locomotor muscle + blubber + bone masses), and larger total O2 stores. To gain insight into dive behaviors and surface travel of small pelagic cetaceans, we compared body compositions of Dall's porpoises, Pacific white‐sided dolphins, and northern right whale dolphins (Lissodelphis borealis) to the bottlenose dolphin. Relative lung masses, inexpensive tissue masses, and total O2 stores of Dall's porpoises and Pacific white‐sided dolphins were consistent with deeper dive capacities than in the coastal bottlenose dolphin. In contrast to known low myoglobin concentrations in northern right whale dolphins, inexpensive tissue mass suggested intermediate dive capacity. The estimated body O2 store of Dall's porpoise was among the highest of any cetacean. The relatively large hearts of Dall's porpoises, Pacific white‐sided dolphins, and northern right whale dolphins are hypothesized as especially important during high‐speed surface travel. Based on similarities in locomotory performance, morphology, and physiology to those of the horse, we consider Dall's porpoise a thoroughbred of the sea.

Tissue-specific bioaccumulation of long-chain perfluorinated carboxylic acids and halogenated methylbipyrroles in Dall's porpoises (Phocoenoides dalli) and harbor porpoises (Phocoena phocoena) stranded in northern Japan

Moisture content in Dall's porpoise ( Phocoenoides dalli) tissues: a reference base for conversion factors between dry and wet weight trace element concentrations in cetaceans

Dall's porpoise (Phocoenoides dalli) is a small toothed cetacean, widely inhabiting the North Pacific Ocean and adjacent seas, between about 30 and 62°N; however, only limited studies of its ecology have been made in nearshore areas. A cetacean sighting survey lasting 60 days was conducted during the 2012 summer cruise of the T/S Oshoro Maru (Hokkaido University, Japan) in the North Pacific Ocean and Bering Sea. Based on this data, the distribution of Dall's porpoises and the factors controlling it in the pelagic habitat were investigated. A total of 808 individual Dall's porpoises in 166 groups were sighted during a total of 469.6 hr and 4946.6 nm observations. The cruise consisted of three legs and the average porpoise group size was significantly larger in Leg 1. The sightings were concentrated at water depths of less than 1000 m and near eastern Aleutian passes. Sighting clusters were found on the 200 m isobath of the southeastern Bering Sea continental slope. There was a peak in sightings where the sea surface temperature (SST) was relatively cold, between 5 and 7°C. Although similar track routes were taken in Leg 1 and Leg 3, the number of sightings per unit effort was larger in Leg 1. This difference may have arisen from the significant rise in SST as the season progressed. Relatively large group size found in this study might relate with prey abundance along the Aleutian Islands.

Concentrations of artificial radionuclide 137Cs and natural radionuclide 4°K in Dall's porpoise, Phocoenoides dalli, from the Pacific coast of northern Japan in 1996 are presented. Concentrations of 137Cs in muscle tissue from two male Dall's porpoises were 0.153 ± 0.01 l and 0.234 ± 0.016 Bq kg-1 wetweight, and those of4°K were 104.0 ± 0.3 and 107.8 ± 0.9 Bq kg-1 wet weight, respectively. Concentration factors (CF, concentration in animal/concentration in sea water) for the two porpoises are 59 and 90 for 137Cs, respectively. These concentrations and CF values are within published ranges for marine fish in coastal waters. The CFs obtained in this study suggest that the trophic position of Dall's porpoises is similar to that of the large piscivorous fish in the marine community in coastal waters of Japan.

In the California Current off the United States West Coast, there are three offshore cetacean species that produce narrow-band high frequency (NBHF) echolocation pulses: Dall's porpoise (Phocoenoides dalli) and two species of Kogia. NBHF pulses exist in a highly specialized acoustic niche thought to be outside the hearing range of killer whales and other potential mammal-eating odontocetes. Very little is known about the dwarf and pygmy sperm whales (K. sima and K. breviceps), including their NBHF pulse characteristics. This paper presents a multivariate clustering method using data from unmanned drifting acoustic recorders and visually verified porpoise recordings to discriminate between probable porpoise and Kogia clicks. Using density clustering, this study finds three distinct clusters whose geographic distributions are consistent with the known habitat range for Kogia and Dall's porpoise. A Random Forest classification model correctly assigned 97% of the clicks to their cluster. Visually verified Dall's porpoise clicks from towed hydrophones were strongly associated with one of the clusters, while a second cluster tended to be outside the geographic range of Dall's porpoise and unlike the Dall's porpoise cluster. These clicks, presumed to be made by Kogia, exhibited greater spectral variance than previous Kogia echolocation studies. It is possible that the structure of Kogia NBHF pulses may not be as stereotypical as previously described.

Feeding habits of Dall's porpoises ( Phocoenoides dalli) in the subarctic North Pacific and the Bering Sea basin and the impact of predation on mesopelagic micronekton

A 60-cm female fetus recovered from a Dall's porpoise (Phocoenoides dalli) found dead in southern British Columbia was fathered by a harbour porpoise (Phocoena phocoena). This is the first report of a hybrid within the family Phocoenidae and one of the first well-documented cases of cetacean hybridization in the wild. In several morphological features, the hybrid was either intermediate between the parental species (e.g., vertebral count) or more similar to the harbour porpoise than to the Dall's porpoise (e.g., colour pattern, relative position of the flipper, dorsal fin height). The fetal colour pattern (with a clear mouth-to-flipper stripe, as is found in the harbour porpoise) is similar to that reported for a fetus recovered from a Dall's porpoise to off California. Hybrid status was confirmed through genetic analysis, with species-specific repetitive DNA sequences of both the harbour and Dall's porpoise being found in the fetus. Atypically pigmented porpoises (usually traveling with and behaving like Dall's porpoises) are regularly observed in the area around southern Vancouver Island. We suggest that these abnormally pigmented animals, as well as the previously noted fetus from California, may also represent hybridization events.

Relationships between fluvial aquatic habitat availability and discharge are often assumed to remain static when used with hydrologic datasets to analyze changes in habitat availability over time. Despite this assumption, studies have observed significant changes in aquatic habitat availability before and after restoration projects, dam removals, and extreme flood events. However, research is lacking on how aquatic habitat changes as a result of morphodynamic processes during more commonly occurring hydrologic conditions. This study compared Chinook salmon (Oncorhynchus tshawytscha) rearing habitat availability at 19 discharges before and after a relatively mild 8‐year hydrologic period punctuated with modest floods on the lower Yuba River in California, USA. During this time, the total area of rearing habitat remained relatively consistent at discharges <2× bankfull but decreased by up to 25% at discharges >2× bankfull. Significant decreases in rearing habitat area appeared to be the result of widespread erosion on floodplains, terraces, and lateral bars, even after only modest floods. As a result, spatially delineated areas of lost habitat tended to increase in water depth and velocity at baseflow, bankfull, and floodplain‐filling discharges, while areas of gained habitat decreased in depth and velocity. Although these specific results may not apply to all rivers around the world, the finding that habitat–discharge relationships change as a result of morphodynamic processes likely does transfer globally and should be considered when making long‐term regulatory and management decisions, such as instream flow requirements and habitat restoration plans.

Sexual dimorphism of Dall's porpoise and harbor porpoise skulls

Biological accumulation of chlordane compounds in marine organisms from the northern North Pacific and Bering Sea

Accurate estimates of density and population size are fundamental for appropriate monitoring of populations. Forest dwelling large mammals that live in herds are particularly difficult for estimating population density and size because of the heterogeneity of their spatial distribution at local scales and the difficulty of counting groups. Previous work has dealt with heterogeneity of spatial-temporal distribution by the independent use of gas movement theory and spatially explicit distribution models. Here we propose to combine both approaches, and a novel probabilistic method to minimize inflation of group size estimates, to estimate density and population size of a Neotropical social mammal, the white-lipped peccary ( Tayassu pecari ). From February to August 2013, we placed ten camera-traps at distinct locations approximately 2 km apart from one another, at Ilha do Cardoso State Park, a 110-km 2 protected area in the Atlantic forest of Brazil. We estimated groups/area using a gas movement function, and individuals/group from a pathway probability function, and used both to derive a final density estimate (individuals/area). We then generated a habitat suitability model based on seven environmental layers and 32 location points, and extracted the area with high probability of occurrence to estimate population size in the park. In 1232 camera trap*days, we recorded 309 10-second videos of white-lipped peccary herds. Simple minimum density estimates (from subtracting individuals that leave the screen) were sensitive to the time interval used to separate independent events, but density estimates using the pathway probability function were not, with a final density estimate of 6.2-9.8 inds/km 2 . Habitat suitability analyses revealed that four environmental variables (distance from continental edge, altitude, vegetation, and slope) collectively explained 84% of the variation in white-lipped occurrence. Using a model threshold of 0.27 (maximum test sensitivity and specificity), we determined that only 21% of the park’s area was in fact suitable for the species, with a final population size estimate ranging from 175 to 275 individuals. The present study reveals that a combination of analytical tools allows for more robust estimates of population density and size of forest-dwelling social mammals. Our approach also permits disentangling distinct factors affecting population size (group size, group density, and suitable area), and facilitates pinpointing sources of variation in population size over time.