AERIAL CENSUS OF PACIFIC WALRUSES IN THE CHUKCHI SEA, 1985

The U.S. Fish and Wildlife Service conducted a survey of the walruses in the pack ice of the Chukchi Sea between 16 September and 2 October 1985, as part of a joint effort with the Soviet Union to estimate the size of the Pacific walrus population. American observers conducted censuses from two aircraft along randomly selected north–south lines over the pack ice. The observers counted walruses within a constant viewing angle that corresponded to a total strip width of 1.38 km at an altitude of 152 m.
In nine days of flying, 15,312 walruses were observed, of which 10,140 were on 5,764 km² of census strips. Few walruses were observed east of 161°W longitude or west of 170°W longitude, hence the census effort was stratified. Walrus concentrations between 161° and 170° shifted slightly westward during the 2-wk duration of the censuses. The differences among days in observed walrus density were due to changes in the numbers of walruses on the ice within 37 km of the ice edge. The number of observable walruses in pack ice of the eastern Chukchi Sea was estimated to be 62,177 (SD = 19,480), based on censuses conducted on 29 and 30 September and 1 October. At that time there were also at least 15,238 in Bristol Bay, Bering Sea. The Soviets counted 39,572 on the shores of the western Chukchi and Bering seas and estimated 115,531 in pack ice of the western Chukchi Sea. Summing U.S. and Soviet estimates, the total population of Pacific walruses in 1985 was 232,518. This number was comparable with earlier estimates from censuses conducted jointly by the U.S. and the Soviets. However, information on fraction hauled out, segregation, and movements is needed for more precise estimates.     

MANAGING THE EXPLOITATION OF PACIFIC WALRUSES: A TRAGEDY OF DELAYED RESPONSE AND POOR COMMUNICATION1

The Pacific walrus population has been depleted and subsequently allowed to recover three times in the past 150 yr. As we see it, the population has been made to fluctuate like an r-selected species, rather than being maintained at a high, stable level, as befits a K-selected species. The latest depletion began in the 1930s but was not recognized until 25 yr later, by which time the population had been reduced by at least half. Without benefit of communication, the U.S.S.R. and the State of Alaska put similar protective measures into place by 1960, and in the next two decades the walrus population recovered again, at least doubling in size. By 1980, it already was showing density-dependent signs of having approached or reached the carrying capacity of its environment. As productivity and calf survival declined sharply in the late 1970s and early 1980s the catches more than doubled. We believe that the combined effects of natural curtailment and human intervention may be bringing the population down again rather rapidly. With the present, crude monitoring methods, delayed management responses, and poor international communications, however, the downward trend may not be acknowledged for at least another decade, by which time the unilateral Soviet and American corrective measures are likely to be too much, too late. Walrus management needs to be based less on response to immediate crisis and more on long term prediction than it has been in the past. Because the U.S.A. and U.S.S.R. are trying to manage the same walrus population, without sufficient communication or consensus and sometimes to opposite ends, an international joint management program needs to be implemented.     

IMMOBILIZATION OF WALRUS WITH ETORPHINE HYDROCHLORIDE AND ZOLETIL®

Abstract: The paper describes the use of the drugs Zoletil® and etorphine for the immobilization of walrus ( Odobenus rosmarus rosmarus ) for attachment of satellite telemetry equipment. Three animals weighing approximately 1,500 kg each were injected intramuscularly with Zoletil® at a dose between 1.4 and 2.2 mg/kg. One walrus died while the two others were adequately restrained. The induction time was between 14 and 29 minutes and the effect lasted for 75-220 min.
Thirty-eight animals of weight 900-1,500 kg were darted intramuscularly with etorphine at a dose between 3.3 and 8 mg/kg. Thirty-six were immobilized although one died later. The induction time for etorphine was two to ten minutes. The action of this drug was terminated with an injection of the antidote di-prenorphine.
The use of etorphine was accompanied by convulsive movements and apnoea while Zoletil® produced a gradual and smooth entry into and withdrawal from immobilization.     

FEMALE REPRODUCTIVE PATTERNS AND FETAL GROWTH OF ATLANTIC WALRUSES (ODOBENUS ROSMARUS ROSMARUS) IN FOXE BASIN,NORTHWEST TERRITORIES,CANADA

We examined the reproductive tracts of 79 female Arlantic walruses (Odohenus rosmarus rosmarus) caught in July and August by Inuit hunters in northern Foxe Basin, NWT, Canada. We found no evidence of past or present ovulation in animals less than 5 yr old, but the poor representation of juvenile and adolescent animals precluded statistical analysis of the average age of maturity. The ovulation frequency of 64 mature females (0.52) indicated biennial ovulation, while the pregnancy rate (0.33) and birth rate (0.30) suggested that females gave birth once every three years. The sex ratio of 17 fetuses was not significantly different from 1:1. Fetuses increased 2.9 mm d^-1 in crown-rump length and 0.12 g^1/3 d^-1 in mass over the range of collection dates. Based on the inverse regressions of fetal growth, implantation occurred in late June early July.     

THE DISTRIBUTION OF BOWHEAD WHALES, BALAENA MYSTICETUS, IN THE CHUKCHI SEA

Under a U.S.-U.S.S.R. cooperative Marine Mammal Project, shipboard cruises were made in 1979, 1980 and 1982, primarily to determine whether there is a substock of western Arctic bowhead whales ( Balaena mysticetus ) that summers in the western Chukchi Sea instead of migrating to the Beaufort Sea. More than 100 bowheads were sighted along the north Chukotka coast of Siberia in October 1979, and more than 200 bowheads were sighted there in September 1980. None were seen anywhere in the Chukchi Sea in late July and August 1982. We conclude that the September and October sightings were of animals returning early from the Beaufort Sea and that, other than occurrences peripheral to the main migration, there are no large concentrations in the Chukchi in the summer and there is apparently no western Chukchi substock.     

花蓟马Frankliniella bispinosa的生长繁殖特性及种群动态研究(英文)

本文提出一种用香蒲 (Typhadomingensis)花粉饲养花蓟马 (F .bispinosa)的方法 ,恒温饲养表明 ,在1 5℃时 ,该蓟马的世代历期长达 3 7 5d ,雌成虫平均寿命为 3 0d ;在 2 0℃和 2 5℃恒温下 ,世代历期分别为1 8 9和 1 3 8d ,雌成虫寿命分别为 2 9 0和 2 3 3d。平均产卵量在 2 5℃时达到最高 (1 2 3 2头 雌 ) ,而在其他几种恒温下产卵量显著减少。在佛罗里达南部 ,终年可见该蓟马在鬼针三叶草 (BidenspilosaL .)花上发生 ,而种群高峰期在三月中旬到四月初 ,平均每朵花中蓟马成虫数最高时可达 48 7头。     

CATCHES OF HUMPBACK AND OTHER WHALES FROM SHORE STATIONS AT MOSS LANDING AND TRINIDAD, CALIFORNIA, 1919–1926

Logbook data from California shore whaling stations at Moss Landing (1919–1922 and 1924) and Trinidad (1920 and 1922–1926) are analyzed. The logs for the two stations record the taking of 2,111 whales, including 1,871 humpbacks, 177 fin whales, 26 sei whales, 3 blue whales, 12 sperm whales, 7 gray whales, 1 right whale, 1 Baird's beaked whale, and 13 whales of unspecified type (probably humpbacks). Most whales were taken from spring to autumn, but catches were made in all months of some years. The sex ratios of humpback, fin, and sei whales (the three species with sufficient sample sizes to test) did not differ from parity. Primary prey, determined from stomach contents, included sardines and euphausiids for both humpback and fin whales, and 'plankton' (probably euphausiids) for sei whales. The prevalence of pregnancy was 0.46 among mature female humpbacks and 0.43 among mature female fin whales, although these values are reported with caution. Information on length distribution for all species is summarized. Analysis of the catch data for this and other areas supports the current view that humpback whales along the west coast of the continental United States comprise a single feeding stock and also suggests that the present population is well below pre-exploitation levels.     

A COMPUTER SIMULATION MODEL OF POPULATION DYNAMICS OF BROWN PLANTHOPPER, NILAPARVATA WGENS STÅL

Abstract A comprehensive computer model, based on the concept and analysis of the population life system, was developed to simulate effects of major environmental variables on the population dynamics of brown planthopper (BPH), Nilaparvata lugens Still. The basic frame of the model consists of a multiple column matrix, which was used to describe the stage overlapping phenomenon and the age-stage-structure of the BPH population, and a set of difference equations, which was employed to calculate the growth of individuals from one age-class and stage to the next in the BPH population. The life cycle of BPH was incremented in the model into 10 degree-days age classes and simulations were run with daily time steps. The model incorporates 1) temperature-dependent developmental rates or eggs, nymphs, and adults; 2) stage-specific survival rates obtained from the life table data of BPH; 3) immigration patterns and rates of macropterous adults; and 4) female fecundity. General validation of the model was established by comparisons between simulated and observed population densities for five years at three locations, which represent plain, hilly, and mountainous aresa in Fujian Province, using actual daily weather data and immigration patterns of macropterous adults for each year as model inputs. Simulation results from the model output were also compared by varying the model inputs within realistic limits in order to analyze the model behavior. We think that this model may serve as the framework for further studies on biology and ecology of BPH, and used to study various integrated BPH management strategies. Moreover, this model could be adapted to describe the population life systems of other insects with minor modification.     

OCCURRENCE, PHOTO-IDENTIFICATION AND PREY OF PACIFIC WHITE-SIDED DOLPHINS (LAGENORHYNCUS OBLIQUIDENS) IN THE BROUGHTON ARCHIPELAGO, CANADA 1984–1998

This study summarizes occurrence of Pacific white-sided dolphins ( Lagenorhyncus obliquidens ) in the Broughton Archipelago on the west coast of Canada, from October 1984 through December 1998. Dolphins were detected on 472 d. The annual percent of total occurrence rose from 0.4% in 1984 to 19% in 1994 and then declined to 2% in 1998. Seasonal occurrence peaked from 1 October through January. Dolphin group size ranged from 2 to 1,000; the most common range was 11-50. While unreported for the Broughton Archipelago prior to 1984, the species is represented by teeth distributed throughout the past 2,000 yr of First Nations midden sediment, suggesting sporadic long-term occurrence. Increased water temperature from the 1937–1984 mean of 8.6°C, to the 1985–1998 mean of 9.3°C and increased abundance of two fish populations in the study area are considered potential factors in the recent increase in occurrence. Of the 675 naturally marked dolphins that were photo-identified, 214 were resighted. A pair of dolphins was photographed swimming in tandem, fourteen months apart. Tight groups, of five or fewer extensively scarred dolphins with extremely falcate dorsal fins were seen within every aggregation of over 50 animals, suggesting the existence of all-male associations. Prey species were collected from 25 encounters with feeding dolphins; they included herring ( Clupea harengus ), capelin ( Mallotus villosus ), and Pacific sardine ( Sardinops sagax ). Predation on eulachon ( Thaleichthys pacificus ) is suspected. Unreported for the Broughton Archipelago, the capelin sampled in this study may belong to the Bering Sea population. Pacific sardines returned to commercial viability on the British Columbia coast in 1997 after a 60-yr population collapse. Dolphin frequency of occurrence declined following introduction of underwater acoustic deterrent devices into the study area.     

MAXIMUM NET PRODUCTIVITY LEVEL ESTIMATION FOR THE NORTHERN FUR SEAL (CALLORHINUS URSINUS) POPULATION OF ST. PAUL ISLAND, ALASKA

The goal of this study was to assess the maximum net productivity level for the northern fur seal ( Callorhinus ursinus ) population of St. Paul Island, Alaska. Definitive determination of this level is not possible due to uncertainty in life table parameters and density-dependent changes in those parameters. To account for such uncertainty, repetitive numerical simulations were used to generate frequency distributions of estimates for the maximum net productivity level and related population parameters. This approach systematically varied simulation input parameters, ran a separate simulation with each input parameter combination, and validated the simulations on the basis of comparison with historical observations. Results from validated simulations were compiled in frequency distributions to provide a measure of confidence for MNPL estimates. The distributions confirm that this population is probably well below its maximum net productivity level. Because they reflect the uncertainty in our understanding of northern fur seal population dynamics, these distributions are a more realistic basis for management than single point estimates.