Total Population Estimates Research Articles

Stautus of the Australian sea lion, Neophoca cinerea, in the Great Australian Bight

In August 1994, a systematic survey of potential haulout sites of the Australian sea lion, Neophoca cinerea, was conducted along the coastline of the Great Australian Bight from Twin Rocks to Wilson Bluff, a distance of 206 km. A total of 289 Australian sea lions was recorded at 23 sites widely dispersed at the base of the Bunda Cliffs, hauled out on perched platforms formed by collapsed sections of cliff at various levels above the sea. Of these, 37 sea lions were recorded in a deep cave accessed from the sea. The total included 86 pups aged under 12 months, which were probably born in the region; six of these had almost completed moulting their natal pelage and were estimated to be near four months old. Only 12 New Zealand fur seals, Arctocephalus forsteri, were recorded. The Australian sea lion sites located in 1994 were surveyed again in August-September 1995, during a predicted breeding season. In this survey, a total of 284 sea lions was recorded at nine sites in South Australia and one site in Western Australia. This included 90 pups under six months of age, of which 44 were still in lanugo. Overall, we recorded 10 breeding sites and 14 haulout sites. Breeding events were recorded at one colony over three seasons and were consistent with an 18-month cycle. By extrapolating from the number of sea lion pups found in 1994, the population for the Great Australian Bight region in South Australia is estimated to be 613-774. This addition increases the previous estimate for South Australia by 9.3% and the previous total population estimate by 6.6%.

Internal Validity Analysis: A Method for Adjusting Capture-Recapture Estimates of Prevalence

The authors propose a method for adjusting results of log-linear multi-source capture-recapture estimates of total population. The method compares the totals in some subpopulations of known size with estimates derived from various capture-recapture approaches to these subpopulations. The authors term such an approach an "internal validity analysis". Trends in the ratios of the estimates to the known true values of these subpopulations provide a plausible indicator of the bias of some types of estimates of the total population especially when underlying assumptions of the methods used have not been met in analysis of the total population. The authors apply this method to published data on an open population of injection drug users that had been previously analyzed with a standard capture-recapture analysis as if it were a closed population. Internal validity analysis suggests that the size of this population is about 15% greater than that previously estimated.

Index Numbers for Waterbird Populations. III. Long-Term Trends in the Abundance of Wintering Wildfowl in Great Britain, 1966/67-1991/92

1. A new approach to estimating the relative size (indexing) of waterbird populations was applied to monthly counts for 17 wildfowl species obtained over 26 winter seasons from 1966/67 to 1991/92. 2. The wetland count units included in the index computations were those with at least 50% of the potential counts available. All index numbers were based on these count units, and on the winter months of maximum abundance for each species, ascertained by examination of monthly indices. 3. A mean of 69% (37-99%) of the maximum species count for the whole of Britain in 1991-92 was present on the count units included in the indexing process, and thus the indices were applicable to the counted population. Compared to total British population estimates, the count units selected supported relatively high proportions (>56%) of the total populations of 10 of the 17 species considered. Thus, most index numbers were considered to be representative of the whole population. 4. Spectacular and sustained increases were apparent for the Bewick's swan, Canada goose, dark-bellied brent goose and gadwall, and less dramatic, though sustained, increases were found for four species of ducks (teal, shelduck, red-breasted merganser and goosander). Populations of the two remaining swans (mute swan and whooper swan) had undergone sharp increases since the mid-1980s, whilst those for four further duck species (pintail, shoveler, tufted duck and goldeneye) had increased sharply during the mid to late-1960s and have increased or decreased slightly subsequently. The pochard population appears to be smaller now than it was in the early and mid-1970s, whilst that for mallard was relatively stable. Index numbers for wigeon were variable, with no obvious trend. 5. The index numbers for goosander implied that the population follows a regular cycle, with winters of peak abundance separated by three or four winters of low, and often, decreasing numbers. 6. The reliability of the index numbers is discussed together with trends for individual species, recent changes in European populations and possible causal factors.

Size, trend, distribution and conservation of the brown bear Ursus arctos population in Sweden

The density of adult (≥3 years) female brown bears Ursus arctos was estimated in two areas of Sweden from ratios of radio-marked and unmarked females consorting with radio-marked adult males during the breeding season. The resulting densities were 1·2 ± 0·81 (95% confidence interval) adult females/1000 km 2 in a northern study area and 1·06 ± 3·44 adult females/1000 km 2 in a southern area. These estimates were extrapolated to obtain a population estimate for Sweden using relative densities throughout the range of the species in Sweden, based on hunter-kill statistics, and observed rates of reproduction and juvenile and subadult survival. The total population in spring 1991 was estimated to be about 620 bears, with almost all females confined to four geographically separated areas, termed female core areas. A supplementary estimate, based on estimated kill rates of adult females in the study areas, was about 660 bears. Estimates based on hunter kill rates of marked bears gave minimum and maximum estimates of about 300 and 900 bears, respectively. Although these are not confidence intervals of the total population estimate, we believe that the true population size is included within these limits. Densities within the female core areas varied from 50 to 100% of those in similar habitats in European Russia. The bear population in Sweden appeared to have increased at a stable rate of about 1·5% annually during the past 50 years. Mean annual rate of legal harvest during 1943–1991 was estimated to be 5·5% (±2·1% SD), suggesting a maximum sustainable rate of 7·0% for this population. The harvest increased at a rate of 9·6% annually during 1981–1991, and apparently was at the maximum sustainable level during 1987–1991.

The abundance and distribution of bottlenosed dolphins (Tursiops truncatus) in Doubtful Sound, New Zealand

Photographic identification and standardized zigzag surveys were used to study the distribution and abundance of bottlenose dolphins in Doubtful Sound, New Zealand. Forty individuals were identified from nicks and markings on their dorsal fins. Chapman's and Bailey's modifications to the Lincoln–Petersen estimate and the computer program CAPTURE were used to estimate the number of marked individuals in the population, which ranged from 30 to 40 animals for three survey periods (two summers and a winter). The proportion of identifiable individuals in the population was assessed empirically as 65.5%. These data resulted in a total population estimate of approximately 58 individuals. The majority of the dolphins in the catalogue were found in each survey period, indicating their residency in the fiord. Movements of dolphins around the sound were not predictable, but there were areas in which dolphins were more likely to be found and other areas in which dolphins were never seen. However, there were no obvious seasonal or daily movement patterns.

Assessing and managing the impact of duck hunting in Victoria — a new approach: R. H. Loyn, Wildfowl, 42, 1991, pp 155–161

The impact of duck hunting in Victoria was assessed by comparing the take of game species and the of protected species with initial numbers of birds on large samples of wetlands. Numbers of birds were also measured on these wetlands after the opening weekend and at the end of the season. Estimates of annual production were made by examining samples of bagged ducks. This approach avoids the need to estimate total take or total population. Estimates of total population are expensive and impractical in many parts of the world. The kill of protected species had little impact on numbers of any species except Freckled Duck Stictonetta naevosa. The take of game ducks exceeded annual production until 1990, when hunter numbers halved after introduction of a compulsory video test of their ability to identify water birds. Various other management options have been introduced or considered as part of a general review.

Estimating Annual Total Heron Population Counts

A method is presented for estimating the annual total count for a heron population by using patchy counting data from nesting sites. A standard error is also computed. Where a count is not available for a particular nesting site in a particular year, an estimate is made from a weighted average of ratio estimates across years. Two systems of weights are considered: equal weights and weights chosen to minimize the variance of the total population estimate. In the latter system the weights must satisfy various sets of constraints. Problems associated with nesting sites for which there are not sufficient data to obtain an estimate are discussed. A simple way of incorporating counting variation is also investigated

Status of woodland caribou in western north America

A review of current population size and trends of woodland caribou (Rangifer tarandus caribou) in seven jurisdictions in western North America shows a wide range of situations. A total maximum population estimate of woodland caribou west of the Ontario/Manitoba border is 61 090. Of 44 herds or populations described in this review: 14 are stable; two are stable to slightly decreasing; four are decreasing; four are increasing; and 22 are of unknown status. Caribou are classified as a threatened species in Alberta and as an endangered species in Washington/Idaho. The decline of caribou in North America following settlement (Bergerud, 1974) has continued along the southern edge of woodland caribou distribution. Direct loss of habitat to logging, mines and dams continued throughout the I960s, 1970s and 1980s. The secondary effects of these habitat changes, (i.e. increased roads leading to increased hunting and poaching, and increased early succession habitat leading to increased alternate prey/predator densities) has led in some cases to the total loss or decreased size of local herds. Three ecotypes of woodland caribou are described and their relative distribution delineated. These ecotypes live under different environmental conditions and require different inventory and management approaches. Woodland caribou herds in northern B.C., Yukon and N.W.T. generally are of good numbers and viable (stable or increasing), and management primarily is directed at regulating human harvest and natural predation to prevent, herd declines. Land use activities such as logging or energy development are not extensive. Managers in southern caribou ranges stress the need for a better understanding of caribou population stability within mixed prey/predator regimes; how habitat changes (eg. through logging) affect these regimes; and how to develop effective land use guidelines for resource extraction that can sustian caribou populations and maintain resource industries. Caribou managers have suggested that herds may be priorized for research and management efforts. Unstable, remnant populations may be left to their own fate. The limited research dollars available and difficult management decisions should be applied to caribou herds that are apparently sustainable and provide the greatest potential for long-term viability.

Large herbivores in Upper Lupande Game Management Area, Luangwa Valley, Zambia

SummaryUpper Lupande Game Management area in Luangwa Valley, Zambia currently supports good populations of sixteen large and medium‐sized herbivores. Impala was the most abundant constituting 34% of the total population estimates, followed by buffalo (19%), zebra (12%), wildebeest (10%), warthog (8%), elephant (6%) and hippopotamus (3%). Other species made up the remaining 8%. The survey zone contained a herbivore biomass of 10,796.18 times 103 kg. Elephants contributed 50.2% and buffalo 25.1% of the total herbivore biomass of the area. The estimated maximum sustainable off‐take potential in Upper Lupande was 1110.14 times 103kg per annum. The distribution of most of the species studied suggested favourable recruitment status. There were species‐specific distribution patterns and densities in the survey zone.

Population survey of macaques in northern Sulawesi.

A field survey of 25 sites in Sulawesi Utara (north Sulawesi) in 1987 and 1988 found macaques in 16 of these sites. The most viable population of Macaca nigra was found in the Tangkoko reserve at an estimated density of 76.2 monkeys/km2, which is less than one-third the abundance reported in the late 1970s by the MacKinnons. The adjacent reserves of Batuangus and Duasudara had only 22 monkeys/km2, yielding a population estimate for these three contiguous reserves of only 3,655 individuals. Maccaca nigrescens were found in the central and western portions of Dumoga-Bone National Park in densities of 15.5 and 16.4 monkeys/km2, significantly below the density of 27/km2 reported by the MacKinnons. The more peripheral areas of Dumoga-Bone had only 8.15 monkeys/km2, yielding a population estimate of M. nigrescens in Dumoga-Bone of less than 34,000. Our total population estimate for M. nigra and M. nigrescens combined is less than 50,000 individuals, which is considerably below that reported in recent litreture. M. hecki were observed in only two locations, Tangale and Panua Reserves, at low densities of 3.3 to 5.2 monkeys/km2, suggesting its range and abundance have declined since the observations of Groves (pp. 84-124 in THE MACAQUES: STUDIES IN ECOLOGY, BEHAVIOR AND EVOLUTION. D. G. Lindburg, ed. New York, Van Nostrand Reinhold, 1980). Several factors have contributed to population decline in these species: habitat shrinkage, increasing human population pressure, and drought conditions. Group sizes were significantly smaller in our study than in previous ones, and we found a shortage of juveniles and infants.

The distribution of mucosal lymphoid nodules in the equine respiratory tract

Mucosal lymphoid nodules were identified within the equine respiratory tract by an acetic acid fixation technique. Nodules were identified in foetuses from nine months gestational age, and estimates of total and regional module populations were made in foetal, neonatal and adult horses. Nodules occurred at specific sites within the tract, which probably relate to areas where inhaled antigens accumulate. The largest populations of nodules occurred in the nasopharynx and larynx, with smaller numbers in the nasal cavity, trachea and bronchi. There was an age-related change in the size of these nodule populations, with an increase in number from late gestation to the neonatal period to early adulthood (up to 5 years of age), followed by a decrease in older adults.

Point Count Censusing from a Submersible to Estimate Reef Fish Abundance Over Large Areas

Point count estimates of fish abundance were taken from a research submersible at thirty-two sites on a 0.5 km2 patch reef on the Florida Middle Grounds, off the West Florida Shelf. Of the fifty species recorded, nine species were selected for total population estimates based on their behavior and visibility. Data from the individual point counts were extrapolated to the entire reef. Best estimates of total populations of these species varied from 320 for the short big eye (Pristigenys alta) to 307,600 for the purple reeffish (Chromis scotti). The estimate for the commercially important red grouper (Epinephelus morio) was 1,560, a concentration reasonably similar to the 960 simultaneously estimated from a mark-recapture assessment.

Factors Affecting Aerial Surveys of Marine Fauna, and Their Relationship to a Census of Dugongs in the Coastal Waters of the Northern-Territory

Some factors that may affect the aerial counts of dugongs, dolphins and turtles were examined experimentally. Tidal influence did not affect the counts of dugongs or dolphins, but those of turtles increased around high tide. A combined doubling of survey altitude and transect width reduced observed density of all three classes of animals by 50%. The counts of four observers did not differ significantly, but further data counsel caution. Overcast weather depressed counts of dugongs and turtles. Dolphin counts were affected by water surface condition, counts being lowest in choppy seas. A mark-recapture model was used on tandem observations to derive correction factors for groups of animals missed on the surface of a transect. Observers missed between 33% and 75% of dugong groups on the surface, the probability of detection decreasing with increased survey altitude and transect width. A similar range and pattern of probabilities was found for dolphins and turtles. Dugongs were censused in the coastal waters of the Northern Territory between the Daly River and Millingimbi in December 1983, an area of 28 746 km*2. Sampling intensity was 7.6%. A minimum population of 2953 � 530 (standard error) was estimated, an overall relative density of 0.11 � 0.02 km-2. A theoretical correction for submerged dugongs not seen yielded a total population estimate of 38 000, an overall density of 1.46 km-2. The distribution of dugongs in the survey area was patchy, the highest densities being associated with shallow coastal waters, sheltered bays, and large islands.

The efficiency of a new electrofishing technique in determining fish numbers in a large river in Central Poland

A new method of determining fish numbers in a large river, which involved electrofishing from boats downstream to an AC electrical barrier, produced capture efficiencies for different species ranging from 28 to 82% when successive pairs of catches were combined. Estimates of population density, biomass and production for the 18 species in a 2.538 ha segment of the Pilica River, Poland revealed a decline in total numbers of the fish in species diversity between 1963 and 1980. This is attributed to increased fishing pressure, and to a loss in habitat diversity following the loss of many water mills and associated dams. The total production estimate of 0.85 g m−2 year−1 is low compared with the few published estimates for other large rivers. Roach, dace, chub, gudgeon and bream were the most numerous fish and they constituted 75% of the total population estimate, and 68% of the standing crop and annual production.

Loggerhead sea turtle nesting in North Carolina: Applications of an aerial survey

Aerial surveys of the beaches of North Carolina were performed during two consecutive summers. From these surveys the first comprehensive picture of the relative density and distribution of loggerhead sea turtle nesting efforts in North Carolina was developed. The results of the 1981 survey were compared with those of concurrent ground surveys on several beaches in an attempt to obtain an accurate conversion factor for estimating total seasonal nesting activity from the aerial samples. It was concluded that an aerial survey is useful for determining relative density and distribution of nesting attempts. However, differential retention of crawl tracks on individual beaches precluded using aerial crawl surveys for total population estimates.

Environmental distribution of Zoogloea strains

Enrichment culture techniques were employed to examine the environmental distribution of fingered zoogloea (FZ)-forming bacteria. FZ were detected in surface films of cultures started with various wastewaters, polluted pond and stream waters, duck feces, garbage disposal wastes and fish aquarium waters, but were not observed in cultures started with food scraps or soils. According to most probable number estimates of FZ-forming bacteria and total populations formed in enrichment cultures. less than 0.01% of the viable bacterial population in domestic wastewater and aerobic mixed liquor suspended solids (MLSS) contained the specific zoogloea-forming bacteria. However, FZ-forming bacteria were present in 10-fold greater concentrations in MLSS than in the raw wastewater solids. An isolation procedure, employing an inoculum of concentrated and sonically treated washed FZ yielded 70 strains of zoogloea-producing bacteria, 61 of which formed typical finger-like zoogloeae in pure culture. Isolates were removed also by direct streaking of enrichment culture films. The bacteria were isolated from enrichment cultures started with raw wastewaters, polluted pond waters, greenhouse drainage, fish aquarium water and duck feces. The zoogloea-producing strains were gram negative, motile rods possessing catalase and oxidase and the ability to denitrify, hydrolyze gelatin in plates and meta cleave m-toluic acid. Certain biochemical activities were located among isolates in relation to the various habitats from which they originated. The bacteria were considered to be strains of Zoogloea ramigera.

Serving aboard the world's largest flag of convenience fleet: some geographical implications concerning crew's nationality

The approximately 2500 ships which fly the Liberian flag are manned by officers and sailors from some 100 countries. For some, providing mariners to ships of other nations is an important means of obtaining foreign exchange and since the Liberian flag dominates world shipping, it is service aboard her vessels which is important. Obtaining nationality data for crews of the Liberian fleet and deducing the best estimates of total mariner populations for countries which contribute the most men to this fleet and, by use of Regression Analyses, it is suggested that there are several developing or advanced-status developing countries remarkably dependent upon the Liberian flag fleet for employing its mariners. Taiwan is the outstanding example. This massive flag of convenience, flag of necessity or open registry fleet is remarkable by the fact that it does not carry a proportional share of Liberia's foreign maritime commerce, a not insignificant commerce for such a small developing country. Lastly, it is proposed that perhaps some of the international organizations most outspoken in denouncing open registry fleets may in this matter have less Third World support than imagined.

Measuring Temporal Stability in Regression Models of Population Estimation

This paper introduces an empirical indicator designed to measure the temporal stability of regression models used to produce subnational population estimates. Analusis of 67 counties in Florida centers on 1970 total population estimates generated from ratio-correlation and difference-correlation models. Comparisons are made between eight different regression specifications and employ a quantitative measure of relative estimate accuracy. The major findings of this study are that (a) variable measurement and type are important determinants of estimate accuracy, and (b) although temporal stability of the coefficients impacts estimation errors, the influence is not as pervasive as is suggested in the literature.

Comparison of first‐order error analysis and Monte Carlo Simulation in time‐dependent lake eutrophication models

Estimates of variance for a nonlinear, seasonal food chain, nutrient cycle eutrophication model of Saginaw Bay, Lake Huron, calculated by first‐order variance propagation and Monte Carlo analyses, do not always agree. A comparison of estimates of state variables indicates that Monte Carlo means are most like the measurements, whereas Monte Carlo medians are most like the deterministic model output. Best agreement between Monte Carlo and first‐order estimates of both state variable values and their variances occurs when Monte Carlo output distributions are symmetric. Under these conditions, both estimates are measures of variance associated with total populations (i.e., all algae). Those distributions, however, change dramatically in time for most state variables. For asymmetric distributions, first‐order variance estimates measure variability about the typical component of the total population (i.e., the typical algal species) and Monte Carlo variance estimates measure variability of the mean component (which is more reflective of the total). One must be cognizant of these differences when estimating variance associated with model projections.

A Helicopter Quadrat Census for Mule Deer on Uncompahgre Plateau, Colorado

Mule deer (Odocoileus hemionus) were censused by 2 observers in a helicopter during 3 consecutive winters on 193 0.6475-km2 quadrats distributed, in a stratified random sampling design, throughout 1,688 km2 of pinyon-juniper (Pinus edulis-Juniperus osteosperma) winter range on the Uncompahgre Plateau, in southwestern Colorado. Quadrats were plotted on maps and aerial photos, and the 4 corners were permanently marked on the ground. Estimates of total deer population and 90% confidence limits for the 3 years were 11,401 + 2,205, 17,884 + 4,042, and 17,085 ? 2,951, respectively. During the 2nd and 3rd years the sample was sufficient to permit estimation of the population within 22.6 and 17.3% of the mean number of deer per 2.59 km2, respectively, with 90% confidence. Stratified random sampling reduced variance of the mean number of deer seen per 2.59 km2 by 42, 21, and 37%, respectively, relative to simple random sampling during the 3 years of the census. Procedures for conducting a census of this type and methods for minimizing observer error are detailed. J. WILDL. MANAGE. 44(3):632-639 This study was initiated as a result of widespread concern among wildlife managers and the public that Colorado mule deer populations had suffered recent declines. These declines could not be documented, however, due to lack of deer census systems that had been implemented and tested on a large scale (Gill 1976, Wallmo et al. 1976). The need for such a census sytem was, therefore, clearly recognized. Mountainous terrain and relative inaccessibility of many areas in the West compound problems of censusing deer. A technique employing a helicopter to survey randomly located quadrats was selected for assessment of feasibility because it appeared to offer a reasonable solution to those problems. Numerous studies have evaluated aerial census systems for large ungulates. Many of these have involved counting African animals along transects (Goddard 1967, Bell et al. 1973, Norton-Griffiths 1973). Bergerud (1963) used the transect method to count caribou (Rangifer tarand s) in Newfoundland and Labrador, and Caughley et al. (1976) used it in Australia to count kangaroos (Megaleia rufa, Macropus giganteus and fuliginosus) and domestic sheep. The transect system is suited only to use in relatively flat terrain, however, because counting errors occur in mountainous terrain due to variations in altitude and banking the aircraft, which affect definition of the transect strip (Pennycuick 1969). Big game animals on quadrats can be censused using a helicopter in the steepest mountain