Dall's sheep horn growth and harvest management in the Mackenzie Mountains,Northwest Territories,Canada

Across most of their native North American range, the horns of mountain sheep (Ovis spp.) males are getting smaller, a pattern attributed to selective hunting pressure. We measured the horns of 755 Dall's sheep males (Ovis dalli dalli) in the southern Mackenzie Mountains, Northwest Territories, between 2002 and 2017. For each male, we measured the circumference and length of each annulus for the right horn and calculated horn volume for each year. We examined changes in horn size in 4 different outfitter areas, using age at harvest as a covariate. Hunting pressure across years in the study area was consistently low, and this population did not experience the decline in horn size observed in several other mountain sheep populations in Canada. Over the 16-year period, the average horn volume of harvested males was stable and even increased in 1 outfitter area. Local management of Dall's sheep delivered independently by the guide outfitters in the Mackenzie Mountains appears to contribute to maintaining a population of males that has not been adversely affected by strong selective hunting pressure. The resilience of this management strategy may be challenged by environmental changes associated with rapid warming in northern mountain environments.     

Environmental Influences on Dall's Sheep Survival

Understanding how species respond to environmental conditions can assist with conservation strategies and harvest management, especially in arctic and boreal regions that are experiencing rapid climate change. Although climatic influences on species distributions have been studied, broad-scale effects of climate on survival are less well known. We examined the interactive effects of meteorological and remotely sensed environmental variables on survival of Dall's sheep (Ovis dalli dalli) lambs and adults by synthesizing radio-telemetry data across their range. We used data from 9 studies of adult sheep and 2 studies of lambs that were conducted between 1997 and 2012 at sites spanning the species' range in Alaska, USA, and northwestern Canada. We obtained environmental variables throughout the range of Dall's sheep, including the normalized difference vegetation index (NDVI) from optical remote sensing, freeze-thaw frequency (FTF) from passive microwave remote sensing, and gridded climate variables such as snow water equivalent, temperature, and precipitation. We used Cox proportional hazard regression to investigate the effects of environmental variables recorded during summer, winter, and the previous winter on annual survival rates of Dall's sheep lambs and adults. Summer NDVI was the most influential environmental factor affecting lamb survival, with improved lamb survival occurring in years with a high maximum NDVI. Also, lamb predation by coyotes (Canis latrans) and golden eagles (Aquila chrysaetos) decreased substantially with increasing NDVI. The previous winter FTF had the strongest effect on adult survival, with decreased survival occurring after winters with high FTF. In addition, these remotely sensed environmental factors interacted with meteorological factors to affect survival, such that effects of winter temperature depended on summer NDVI and winter FTF. Warm winters increased lamb survival only when preceded by summers with high NDVI, and warm winters increased adult survival only when winter FTF was low. Thus, potential benefits of climate warming may be counteracted if wintertime freeze-thaw events markedly increase. Correlations among environmental variables across sites were low, and regional climate cycles such as the Pacific Decadal Oscillation (PDO) had weak effects, indicating substantial local variability in climatic conditions experienced by Dall's sheep across their range. These findings can help managers anticipate how Dall's sheep populations will respond to changes in local environmental conditions. Our results also highlight the utility of multiple remotely sensed environmental conditions for ungulate management, especially passive microwave products that provide valuable information on winter icing events. © 2020 The Wildlife Society.     

Eimeria dalli sp. n. (Protozoa: Eimeriidae) from Dall Sheep Ovis dalli

Eimeria dalli sp. n. is described from fecal samples collected from Dall sheep, Ovis dalli, from the Kenai Peninsula, Alaska. The oocysts are spherical or subspherical with mean dimensions of 43.7 × 37.4 μm. The outer oocyst wall is rough and irregular. No micropyle, micropylar cap or residuum was observed. Sporocysts were elongate ovoid with mean dimensions of 19.0 × 10.7 μm. Stieda bodies were not discernible.     

The role of phenotypic plasticity in responses of hunted thinhorn sheep ram horn growth to changing climate conditions

When phenotypic change occurs over time in wildlife populations, it can be difficult to determine to what degree it is because of genetic effects or phenotypic plasticity. Here, we assess phenotypic changes over time in horn length and volume of thinhorn sheep (Ovis dalli) rams from Yukon Territory, Canada. We considered 42 years of horn growth from over 50 000 growth measurements in over 8000 individuals. We found that weather explained a large proportion of the annual fluctuation in horn growth, being particularly sensitive to spring weather. Only 2.5% of variance in horn length growth could be explained by an individual effect, and thus any genetic changes over the time period could only have had a small effect on phenotypes. Our findings allow insight into the capacity for horn morphology to react to selection pressures and demonstrate the overall importance of climate in determining growth.     

INTERMINGLING OF DALLI-TYPE DALL'S PORPOISES INTO A WINTERING TRUEI-TYPE POPULATION OFF JAPAN: IMPLICATIONS FROM COLOR PATTERNS

There are two major color morphs, truei and dalli types, of the Dall's porpoise and the latter includes two minor morphs. A small number of dalli types are found among truei types off the Pacific coast of Japan, where truei types normally winter. Based on differences in the patch size of dalli -type porpoises taken by the harpoon fishery, we determined that those dalli types contain both minor morphs. Although the total number of both types in the sample was similar, the proportion of the two types varied seasonally. Sex ratio, body length, and maturity rate were different among the dalli and truei types. These facts strongly suggest that these dalli types were not members of the truei -type population and were actually migrants from adjacent dalli -type populations. The definition of the subspecies Phocoenoides dalli dalli and P. d. truei as polymorphic groups is not supported, although we consider that each of the three color morphs is worthy of full subspecific status.     

RETINAL GANGLION CELL SIZE AND DISTRIBUTION PREDICT VISUAL CAPABILITIES OF DALL'S PORPOISE

The structure of the retina, the distribution of ganglion cells, and the extent of the tapetum lucidum were studied in Dall's porpoise ( Phocoenoides dalli ) with the aim of understanding the role vision plays in this species of cetacean. The basic organization of the retina was similar to that of other vertebrates. Average ganglion cell size was 21.5 μm. The distribution of the ganglion cells in the retina was not even and there were two high-density areas, one in the temporal and one in the rostral part of the retina. Retinal resolving power was estimated using a terrestrial animal model incorporating the density of ganglion cells and other morphological data. The resolving power in the right eyes of two individuals was 2.60 and 2.64 cycles per degree. These values were close to those of other oceanic cetaceans, but inferior to those of terrestrial mammals. On the basis of amino acid analyses, it was shown that the choroid tapetum lucidum in Dali's porpoise contained collagen. The tapetum lucidum was thick at the fundal but thin at the peripheral part of the choroid.     

AGE,GROWTH, AND REPRODUCTIVE PATTERNS OF DALL'S PORPOISE (PHOCOENOIDES DALLI) IN THE CENTRAL NORTH PACIFIC OCEAN

Life history parameters were estimated for Dall's porpoise, Phocoenoides dalli, from biological specimens collected in the western Aleutian Islands, during 1981–1987. Of 2,033 males and 3,566 females examined, reproductive data were available for 1,941 males and 1,906 females; ages were determined for 813 males and 1,297 females. Female sexual maturity was based on the presence of one or more corpus on either ovary; 845 were sexually immature and 1,061 were sexually mature. Two estimates of female average age at sexual maturity (ASM) were 3.8 and 4.4 yr; average length at sexual maturity (LSM) was 172 cm. Males were considered sexually mature when evidence of spermatogenesis was detected; 1,136 were sexually immature and 805 were sexually mature. Two estimates of male ASM were 4.5 and 5.0 yr; LSM was 179.7 cm. Physical maturity was assessed for 246 males and 446 females by examining the degree of fusion in thoracic vertebral epiphyses. For both sexes, the average age at physical maturity was 7.2 yr. Average length at physical maturity was 202.6 cm for males and 192.7 cm for females. Average lengths of physically mature males (x?= 198.1 cm, SE = 0.8566) and females (x?= 189.7 cm, SE = 0.4002) were significantly different(P < 0.0001). Early postnatal growth was rapid in both sexes. A secondary growth spurt in both mass and length was characteristic for both sexes; the increase in length preceded the mass increase by 1–2 yr. Average length at birth (LOB) was approximately 100 cm; birth mass averaged 11.3 kg (SE = 0.0772). By the time the umbilicus had healed (<2 mo), the average length and mass had increased to 114.1 cm and 23.8 kg, respectively. Gestation period based on projections using LOB was 12 mo, but this was considered an overestimate. Calving was modal, centered in early July; an annual reproductive interval was indicated. Among the sexually mature females, 120 were pregnant, 55 were pregnant and lactating, 321 were pregnant with colostrum, and 33 were “resting.” By 3 July (95% CI =x? 1 d), 50% of births had occurred, during each of the seven years sampled. The ovulation rate was estimated at 0.914 ovulations per average reproductive year. Enlarged follicles and recent ovulations were observed in postpartum females in late July.     

GEOGRAPHIC VARIATION AND SEXUAL DIMORPHISM IN THE SKULL OF DALL'S PORPOISE, PHOCOENOIDES DALLI

Abstract: Two hundred and eighty-nine skulls of Dall's porpoises from the North Pacific Ocean, Sea of Japan, Sea of Okhotsk, and Bering Sea were investigated morphometrically. A clear pattern of geographic variation was found in overall size of the skull. In the North Pacific, overall skull size became gradually smaller eastward from the coast of Japan to the offshore eastern Pacific, and it became larger again off the coast of California. Specimens from the Sea of Japan-Okhotsk and Bering Sea had larger skulls than those from the central North Pacific. The distribution of primary productivity corresponds well with this pattern of geographic variation, suggesting that quantity of food might affect the overall size of Dall's porpoise skulls. By canonical discriminant analyses, about 70% (male) and 90% (female) of specimens of the Sea of Japan-Okhotsk population were distinguished from those of other populations. This agrees with the results of genetic studies.     

A genome-wide set of SNPs detects population substructure and long range linkage disequilibrium in wild sheep

The development of genomic resources for wild species is still in its infancy. However, cross-species utilization of technologies developed for their domestic counterparts has the potential to unlock the genomes of organisms that currently lack genomic resources. Here, we apply the OvineSNP50 BeadChip, developed for domestic sheep, to two related wild ungulate species: the bighorn sheep (Ovis canadensis) and the thinhorn sheep (Ovis dalli). Over 95% of the domestic sheep markers were successfully genotyped in a sample of fifty-two bighorn sheep while over 90% were genotyped in two thinhorn sheep. Pooling the results from both species identified 868 single-nucleotide polymorphisms (SNPs), 570 were detected in bighorn sheep, while 330 SNPs were identified in thinhorn sheep. The total panel of SNPs was able to discriminate between the two species, assign population of origin for bighorn sheep and detect known relationship classes within one population of bighorn sheep. Using an informative subset of these SNPs (n=308), we examined the extent of genome-wide linkage disequilibrium (LD) within one population of bighorn sheep and found that high levels of LD persist over 4 Mb.     

Using distance sampling and hierarchical models to improve estimates of Dall's sheep abundance

Management of large mammal populations has often been based on aerial minimum count surveys that are uncorrected for incomplete detection and lack estimates of precision. These limitations can be particularly problematic for Dall's sheep (Ovis dalli dalli) due to the high cost of surveys and variation in detection probability across time and space. The limitations of these methods have been recognized for some time, but previously proposed alternatives for sheep surveys proved to be too costly and logistically unfeasible in most circumstances (Udevitz et al. 2006). We assessed the potential for a combination of distance sampling surveys and a hierarchical modeling approach to provide a more efficient means for estimating Dall's sheep abundance by conducting aerial contour transect surveys over all sheep habitat in Gates of the Arctic National Park and Preserve (GAAR), Alaska in 2009 and 2010. We estimated the population of Dall's sheep was 8,412 (95% CI: 6,517–11,090) and 10,072 (95% CI 8,081–12,520) in 2009 and 2010, respectively. Abundance within the Itkillik Preserve area within GAAR was 1,898 (95% CI: 1,421–2,578) and 1,854 (95% CI: 1,342–2,488) in 2009 and 2010, respectively. Estimates of lamb abundance in 2010 were more than double those of 2009 after correcting for detection bias related to group size, suggesting that the apparent estimate of lambs in the population may be biased in some years depending on the degree of aggregation. Overall, the contour transect surveys were feasible logistically, cost 70–80% less than minimum count surveys, and produced precise estimates of abundance, indicating that the application of these methods could be used effectively to increase the statistical rigor and spatial extent of Dall's sheep abundance surveys throughout Alaska. These methods could be used to improve the assessment of long-term trends in populations and productivity and provide valuable information for harvest management at both local and landscape scales at reduced costs in comparison to traditional minimum count surveys. © 2011 The Wildlife Society.     

Rumen Ciliate Fauna of Alaskan Moose (Alces americana), Musk-Ox (Ovibos moschatus) and Dall Mountain Sheep (Ovis dalli)*

Total numbers, generic distribution and percentage species distribution were determined for the ciliate protozoa in rumen contents obtained from Alaskan moose (Alces americana), musk-ox (Ovibos moschatus) and Dall mountain sheep (Ovis dalli). The musk-ox has a fauna somewhat similar to that previously observed in reindeer and caribou. In contrast, only protozoa in the genus Entodinium were observed in moose, while Dall mountain sheep have a fauna unique among Alaskan ruminants studied to date. Other than Entodinium exiguum which was common to all animals, only 2 additional species of Entodinium, observed in the moose and musk-ox, occurred in more than one animal species. Four new species of protozoa are described, Entodinium dalli sp.n., Entodinium constrictum sp.n. and Polyplastron alaskum sp.n. from the Dall mountain sheep and Entodinium alces sp.n. from moose.     

SEGREGATIVE MIGRATION OF DALL'S PORPOISE (PHOCOENOIDES DALLI) IN THE SEA OF JAPAN AND SEA OF OKHOTSK

Dall's porpoises from the Sea of Japan population taken by a dolphin fishery vessel were examined. Estimated body lengths at sexual maturity were similar to those for the truei -type population off the Pacific coast of Japan but larger than those for the offshore dalli -type in the North Pacific. The Sea of Japan population is known to migrate to the Pacific coast of Japan through Tsugaru Strait and to the Sea of Okhotsk through Soya Strait in summer. From the difference of catch composition, individuals of different reproductive status in this population are considered to have different patterns of summer migration. Most of the individuals which migrate into the Pacific Ocean through Tsugaru Strait are sexually immature, while those migrating into the Sea of Okhotsk are mature. The Sea of Okhotsk is thought to be a breeding area for this population. The calving season is estimated to be May through June, which is earlier than that of the truei -type off the Pacific coast of northern Japan. This may be an adaptation to lower water temperatures in the Sea of Japan during winter.     

GEOGRAPHICAL VARIATION OF THE PARASITE, PHYLLOBOTHRIUM DELPHINI (CESTODA), IN BALL'S PORPOISE, PHOCOENOIDES DALLI, IN THE NORTHERN NORTH PACIFIC, BERING SEA, AND SEA OF OKHOTSK

Prevalence of the larval cestode, Phyllobothrium delphini , was estimated from 2,445 Dall's porpoise, Phocoenoides dalli , from the incidental take of the Japanese high seas salmon drift-net fishery in the northwestern North Pacific Ocean, Bering Sea, and a local hand harpoon fishery in the southern Sea of Okhotsk. Prevalence of P. delphini was 22.7% in the northwestern North Pacific Ocean and 1.4% in the Bering Sea. This parasite was not found in the southern Sea of Okhotsk. Geographical differences in the prevalence of P. delphini may be due, at least in part, to regional differences in abundance of elasmobranchs known to feed on marine mammals and suspected as hosts of the parasite. Estimated intensity of infection of individual porpoises by P. delphini was low (estimated mean intensity of 3.5 plerocercoids per animal). This is a low intensity of infection compared to other species of small cetaceans studied and may be due to both differences in regional abundance of elasmobranchs and the comparatively short life span of P. dalli.     

Harassment and killing of porpoises (“phocoenacide”) by fish-eating Southern Resident killer whales (Orcinus orca)

Endangered Southern Resident killer whales (Orcinus orca) are fish-eaters that preferentially prey on adult Chinook salmon (Oncorhynchus tshawytscha). Despite being salmon specialists, individuals from all three killer whale pods (J, K, L) have been observed harassing and killing porpoises (family Phocoenidae) without consuming them. Retrospectively, we identified and analyzed 78 episodes of Southern Resident killer whales harassing porpoises between 1962 and 2020, of which 28 resulted in the porpoise's death (“phocoenacide”). Fifty-six episodes involved harbor porpoise (Phocoena phocoena), 13 involved Dall's porpoise (Phocoenoides dalli), and the porpoise species was unreported for nine episodes. Southern Resident killer whales often targeted young porpoises that were similar in size to adult Chinook salmon. Both sexes participated in porpoise harassment. Juveniles engaged in the behavior the most; however, their rates of engagement were not found to differ significantly from most other age classes. The behavior was passed through generations and social groupings, as it was first observed in L pod and spread to the other two pods. Killer whales are highly complex animals known to exhibit social learning and cultural transmission of learned behaviors, but the reason(s) for this behavior is unknown. Hypotheses include the social and developmental benefits of play, hunting practice, or displaced epimeletic behavior.     

SUMMER FEEDING HABITS OF DALL'S PORPOISE, PHOCOENOIDES DALLI, IN THE SOUTHERN SEA OF OKHOTSK

Stomach contents were analyzed from 85 Dall's porpoises, Phocoenoides dalli , taken in the southern Sea of Okhotsk during the summer of 1988. Thirteen species of fish and five species of cephalopods were identified. Fishes comprising 9 families were predominant and made up 79.9% of the total number of prey, with an overall occurrence in the stomachs of 100%. Three families of cephalopods made up 20.1% of the total number of prey ingested, with an overall occurrence of 74%. The Japanese pilchard, Sardinops sagax melanostictus , was the primary prey and represented 72.0% of the total prey in 97.3% of the stomachs examined. The gonatid squid, Berryteuthis magister , ranked second and made up 16.9% of the total prey in 61.6% of the stomachs. Walleye pollock, Theragra chalcogramma , was the third most abundant prey item consumed and represented 6.0% of the total, with an occurrence of 53.4%. Composition of the sample by the calculated total mass and caloric intake supports the numeric findings on the relative importance of the three major prey species to the DaIl's porpoise diet. The Japanese pilchard was clearly dominant using these indices and constituted 65.4% of the total mass and 80.7% of the caloric intake. Berryteuthis magister made up 26.8% of the mass and 15.5% of the caloric intake. Walleye pollock contributed the least to the diet with 7.9% of the total mass and 3.8% of the caloric intake. Volumetric data indicate that porpoises are feeding heavily on Japanese pilchard throughout the daylight hours. Berryteuthis magister was probably fed upon in the late night or early morning hours. Occurrence of both Dall's porpoise and Japanese pilchard in the coastal waters of the southern Sea of Okhotsk is seasonal. The summer movements of Dall's porpoise into this region may be related to the seasonal migration and abundance of the Japanese pilchard.     

Predator-Mediated Indirect Effects of Snowshoe Hares on Dall's Sheep in Alaska

ABSTRACT Indirect interactions among species can strongly influence population dynamics and community structure but are often overlooked in management of large mammals. We estimated survival of Dall's sheep (Ovis dalli) in the central Alaska Range, USA, during years of differing snowshoe hare (Lepus americanus) abundance to test whether indirect interactions with a cyclic hare population affect Dall's sheep either negatively, by subsidizing predators (apparent competition), or positively, by diverting predation (apparent commensalism). Annual survival of adult female sheep was consistently high (0.85 for all yr and age classes combined). In contrast, annual estimates of lamb survival ranged from 0.15 to 0.63. The main predators of lambs were coyotes (Canis latrans) and golden eagles (Aquila chrysaetos), which rely on hares as their primary food and prey on lambs secondarily. Coyotes and eagles killed 78% of 65 radiocollared lambs for which cause of death was known. Lamb survival was negatively related to hare abundance during the previous year, and lamb survival rates more than doubled when hare abundance declined, supporting the hypothesis of predator-mediated apparent competition between hares and sheep. However, stage-specific predation and delays in predator responses to changes in hare numbers led to a positive relationship between abundance of adult Dall's sheep and hares. Lacking reliable estimates of survival, a manager might erroneously conclude that hares benefit sheep. Thus, support for different indirect effects can be obtained from different types of data, which demonstrates the need to determine the mechanisms that create indirect interactions. Long-term survey data suggest that predation by coyotes is limiting this sheep population below levels typical when coyotes were rare or absent. Understanding the nature of indirect interactions is necessary to effectively manage complex predator–prey communities.