Unmarked Ones Research Articles

Estimating population size from a removal experiment

A modification of a removal experiment is proposed here to estimate the size of a closed population. The modification is that a known number of marked (or tagged) animals is released into the population before the experiment commences. The removal process is observed for a fixed number of occasions and the removal probabilities are allowed to be time dependent. We derive a maximum likelihood estimator for the population size. The existence and unimodality of the estimator are examined. A simulation study is given on the performance of the estimator under various conditions of the removal process. A goodness of fit test is given to test the homogeneous mixing assumption between the marked and the unmarked ones.

Incidence and Effects of Sea Lamprey (Petromyzon marinus) Parasitism on Breeding Pink Salmon (Oncorhynchus gorbuscha) from the Carp River, Eastern Lake Superior

The potentially important effect of Great Lakes pink salmon (Oncorhynchus gorbuscha) numbers on the population dynamics of parasitic sea lamprey (Petromyzon marinus) has thus far remained unassessed. This study reveals that despite their small size, pink salmon from the Carp River, eastern Lake Superior, sustain parasitism at rates and in body locations similar to other Great Lakes salmonids. In general, the incidence of sea lamprey parasitism increased with salmon length. Differences in marking rates between male and female salmon were attributable to their dimorphism in size: female pink salmon grew slower than males and bore more fresh wounds than males when sampled. Lamprey attacked fish of similar sizes in 1983 and 1984, but smaller ones in 1985. This parasitism had a negative impact on host breeding potential: marked fish were in poorer condition than unmarked ones. Marked males invested less biomass in gonad than did unmarked males, and wounded males occupied the spawning grounds for less time, thus reducing their reproductive potential. These results indicate that the population dynamics of both species may be determined in part by their mutual interaction.

A mark-recapture experiment with the filariasis vector Anopheles punctulatus in Papua New Guinea.

A capture-recapture experiment with the filariasis vector Anopheles punctulatus from Papua New Guinea (PNG) is described. Eight hundred and ninety-seven engorged females collected indoor resting or in landing catches were released, and 82 were subsequently recaptured. Infection rates were higher in recaptured mosquitoes than in unmarked ones. Recapture rates declined exponentially with distance from the release site, but an infected female was recaptured 1.8 km from the release site. The estimated oviposition interval of 2.90 days was shorter than that obtained from the same species elsewhere in PNG, but daily survival rates were similar. Infection with Wuchereria bancrofti did not appear to affect the survival of the mosquito. Collections adequately sampled the resting population from inside a room of an experimental house.

Investigation into the edge effect by use of capture‐recapture data in a vole population

SummaryA substantial explication of the edge effect has been attempted by use of capture‐recapture data for a vole population (Microtus montebelli), gathered intwo plots of 100×100 m or less during 12 days, cheked twice daily, in August 1970; the sample was quite sufficient for the aim.The edge effect as guessed by increased catch per trap is usually suspected to ensue from range‐settlers in the outside boundary strip of a plot and immigrants. But by a theoretical analysis I could attain a tentative conclusion that no increased catch per trap will occur unless any invasion takes place. Then it follows that, apart from the effect of invasion, the role of the adjoining outside settlers in the edge effect is essentially required to be studied in the light of knowledge on the truth of size and shift in home range.The variation in range behavior for 183 adult voles, captured 6 times or more, could be grouped into eight types, of which the range‐conservative type possessed 52% of the sample and the group of the type was justly utilized for giving averages of range size. Besides, it was seen from the observed frequency of types that a considerable number of immigrants onto the census plot were induced perhaps being allured by trap baits, but the majority of them proved to be assigned to the voles that have their ranges inside the assessment line ofDice; the rest referable to effective immigrants was only a few (7%). I could perceive no reason such as disproves the idea ofDice's additional boundary strip.Viewed from maps of ingress shift of ranges, the effect of ingress must have been greater in the outer trap rows than in the inner within the plot, so that it might well be called edge effect in general; such effect, however, is seen gradually diminishing toward the center, and hence it is almost unlikely that one should find any clear‐cut intra‐plot assessment lines demarcating such an inner square as quite free from edge effects.Averages of observed range length and width (ORL and ORW), as reliable measures for the true range size, were determined from the above group of specimens; as a result, the remarkable concept of elliptic range shape was established by regarding ORL as long axis and ORW as short one, and, directly from these averages, the mean range sizes worked out at 0.04 for females and 0.09 for males in acreage which proved to be surprisingly well agreeable with those of isotope‐revealed ranges for voles given byGodfrey (1954) andAmbrose (1969).The catchability for marked voles () was estimated by the maximum likelihood method by use ofJolly's formulae (1965), but that for unmarked ones () was made by the regression census formula; as a result it was shown that the population was clearly of π>p type and that the trap‐experience that voles underwent one month or more ago can make them retain as high catchability as π.

Effects of Tagging and of Fin-clipping on the Survival and Growth of Atlantic Salmon Between Smolt and Adult Stages

Rates of recapture of Atlantic salmon marked as naturally produced smolts in the Northwest Miramichi River, New Brunswick, were 2.9 for tagged and 3.9% for fin-clipped grilse and 0.7 for tagged and 1.8% for fin-clipped larger salmon. There are indications that survival to the adult stage is much higher for unmarked smolts than for tagged or fin-clipped fish. Length measurements of 117 tagged, 607 fin-clipped, and 301 unmarked grilse taken above tidehead in the Northwest Miramichi showed that those entering freshwater early in the season were smaller that those entering later. Tagged grilse were shorter than fin-clipped grilse which returned at the same time, and the fin-clipped grilse were shorter than unmarked ones. Rates of increase in size among tagged, fin-clipped, and unmarked grilse during the season of return to freshwater (June through October) did not differ significantly.

Responses of Small Mammals to Live-traps and Weather Conditions

A comparison was made between the responses to livetraps of marked and unmarked individuals of Microtus pennsylvanicus and Peromyscus leucopus. Previously captured individuals of M. pennsylvanicus were more readily captured than were the unmarked ones, even after an interval of a month. There was no difference in the rates of capture of marked and unmarked P. leucopus. Comparisons of a given live-trapping technique utilized in two different habitats (marsh and old field) indicated no significant difference in its effectiveness after the second day of trapping. M. pennsylvanicus, in an old field, was found to abandon diurnal activity in favor of nocturnal and/or crepuscular activity when the temperature rose above 200 C. During the winter, when the temperature dropped below 00 C, activity was much less at all times. Except for less activity during the days the temperature rose above 200 C, such responses were not observed in the marsh. Blarina brevicauda was found to be more active on cloudy days than on those that were sunny or rainy. No correlations between activity and temperature variations was observed for this species. Estimates of population densities of small mammals are normally derived from trapping data. The results depend upon a variety of factors in addition to the actual abundance of the mammals. Variations in responses to traps, positioning of the traps, home range size, amount of movement within the population, and weather conditions influence the estimates of population densities (Sealander and James, 1958; Goodnight and Koestner, 1942; Hayne, 1950; Calhoun and Casby, 1958; Getz, 1961a). Responses to traps are particularly important. A method widely used in determining population densities from trapping data is the proportional method (Lincoln Index or modifications thereof; Hayne, 1949). A basic assumption involved in this method is that the probability of capture of the marked animals is the same as that of the unmarked animals. Morris (1955) and Chitty and Kempson (1949) found that marked individuals entered traps more readily than did those that had not been captured previously. Tanaka (1956) found the same to be true of certain species, while in others the probability of capture decreased after the initial capture. He further found that some may be isoresponsive. Leslie (1952) assumed the marked and unmarked individuals to be captured with equal facility, although prebaiting was utilized to overcome any initial reluctance of individuals to enter traps (this initial reluctance has been discussed by Sealander, et al., 1958). Responses to weather conditions also influence estimates of population densities, particularly those sampled by means of snap-back traps. Burt (1940), Gentry and Odum (1957), Pearson (1959, 1960)

The Winter Society of the Oregon Junco: The Flock

mountains, has an elevation of 5000 feet and is about fourteen miles long by four miles wide. It has no settlement except the Deep Springs School, which operates a cattle ranch and has about 150 acres under cultivation. Lines of large cottonwoods follow the irrigation ditches. Lawns, deciduous trees, and shrubs partly surround the buildings. About 25 feet away from the feeding station a belt of fifteen deciduous trees separated it from the low desert vegetation of the basin as a whole and furnished perching places. In Seattle the feeding station was in a residential area but was about 300 feet from a heavily wooded section to the north and about 200 feet from a narrow strip of woods to the east. Connecting this wooded strip with the feeding station area was a vacant lot covered with weedy hummocks and heaps of stones and brush. This lot had nine large conifers. There was also a line of trees, largely conifers, running along the back lot lines of the houses in the block. Canary grass seed and chick feed were the foods provided. The feeding stations were strips of ground twelve feet by four, running parallel with and about six feet from the wall of the house, centered on a window, and bordered on the ends and outer side by heaps of brush from three to seven feet high, in which the birds perched, rested, and took cover. Being indoors the observer was able to make prolonged day-to-day observations regardless of weather. At Deep Springs, 435 hours were spent at the post of observation between October 24, 1948, and January 25, 1949. Observations were resumed on February 20 and totalled about 50 hours before the departure of the birds in March. In Seattle 365 hours were spent in observation between December 28, 1949, and April 3, 1950. The birds were marked by cementing (with Duco) one or two trout-fly feathers to the top pair of tail feathers close to the body. These markers were durable and varied naturally in shape, texture, and the curve of the shaft, as well as in color. They were trimmed if necessary to about the length of the tail and were cemented to it wrong side up, to be made more readily recognizable by the upward curve of the shaft away from the tail. The markers were conspicuous but did not seem to be noticed either by the wearer or its fellows. When eating in a high wind the marked birds had a little more difficulty with their footing than the unmarked ones, but not to a serious extent. The birds were easily distinguishable as individuals. Marked individuals were named with letter symbols by assigning a different letter to each type of feather; B stood for blue, N for black, and so on. This system brought the name of the bird instantly to mind, a crucial point in observations which rely on the correct identification of swift-moving little birds. Furthermore, the relative positions of the feeding station and the observer were such as to bring the birds within a range of about six to fifteen feet. For observations outside the station binoculars were used as needed. The observer at a feeding station cannot choose his material. Not knowing which species would prove useful, the writer marked every bird trapped, with the resultant discovery that the juncos formed the only stable visiting group. At Deep Springs 239

標識放流の実驗的研究

(1) Tagging experiments were carried out in ponds with Mugii cephalus and Carassius auratus as the materials in order to test the twofold effects on the fish; the one was the wound directly inflicted by the tagging operation, and the other was the lengthy effect of the tag which lasted for a long time after the operation. (2) In Mugil, the former effect was scarce; the mortality cases of the tagged fish in 23 days after their liberation were almost as little as that of untagged ones. The latter effect was, however, remarkable; the growth rate and fatness (Body weight/Body lengthy3) of the tagged fish in about ten months after the operation was much less than those of the untagged ones, and owing to the said ill effect lots of tagged fish died from the cold weather. In Carassius, the either effect did not occur at all. (3) The method usually used for estimating the stock of fish by the total catch and the recapturing rate of marked fish was examined with Cyprinus carpio and Carassius auratus. The conclusion was as follows: in marking or tagging experiments we should be careful for the method of fishing, i.e. when the fish caught by angling were marked and liberated in the pond, the rate of reangling of the marked fish was much larger than that of angling of unmarked ones, therefore the total stock of the fish underestimated.

Is the Striped Bass (Roccus Lineatus) of Chesapeake Bay a Migratory Fish?

From October 8, 1936 to June 3, 1937 some 1,563 striped bass were tagged. The great majority of these fish belonged to the 1934 year class, which was extremely abundant in Chesapeake Bay. During nine months 632 recaptures, or 42.4 per cent, were made. There is sufficient evidence that at least 300 tags from recaptured fish were not turned in as yet. Although these data indicate very intensive fishing, they are by no means conclusive as to the percentage of the striped bass population removed by the fishery within the bay, since the ratio of tagged fish to unmarked ones was unknown. The great majority (97.5 per cent) of the recaptures was made within Chesapeake Bay, and only eighteen fish, or less than 2.5 per cent, were taken outside of the bay. During October, 1936 when the principal tagging at Galesville and Tilghman was done, the great majority of returns was taken locally. From the middle of November to the first week of December fish were recaptured on their down-bay migration as far south as the James River, Virginia. From the end of February to the end of April fish migrating up-bay were caught principally in Tangier Sound and the upper Potomac River. These localities are probably the chief spawning grounds for Maryland striped bass. The results of tagging in the James River indicate that the local fish belong to a distinct school, which is evidently non-migratory. The recaptures of tagged fish outside of Chesapeake Bay were made from February through the entire summer of 1937, from Delaware to Massachusetts inclusive. Not a single tagged fish was recaptured south of Chesapeake Bay.

Minerva Ornaments

I NOTICE that a correspondent writing from America expresses his scepticism as to the figural character of certain stone objects in Dr. Schliemann's collection at South Kensington. Judging from the analogy of similar objects found in America, he pronounces them to be “net-sinkers” and not idols. Whatever, however, may be the nature of the American objects, I think there can be but little doubt that Dr. Schliemann is right in considering the objects discovered by him at Hissarlik to be rude representations of a deity. At first sight they certainly have but little resemblance to anything of the sort, but a careful examination shows that several are marked with the rude delineation of a human face—or, as Dr. Schliemann believes, of an owl's face—as well as of a triple necklace, and sometimes also the characteristics of a woman. Occasionally the hair is represented on the back of the head by straight lines. The delineation is sometimes incised, sometimes painted, though the paint is mostly worn off. As the marked objects are of the same shape as the unmarked ones, we can have no hesitation in inferring that both were intended for the same purpose.