Estimating the success of protected areas for the vaquita,Phocoena sinus

Bycatch in artisanal gill nets threatens the vaquita, Phocoena sinus, with extinction. In 2008 the Mexican government announced a conservation action plan for this porpoise, with three options for a protected area closed to gill net fishing. The probability of success of each of the three options was estimated with a Bayesian population model, where success was defined as an increase in vaquita abundance after 10 yr. The model was fitted to data on abundance, bycatch, and fishing effort, although data were sparse and imprecise. Under the first protected area option, the existing Refuge Area for the Protection of the Vaquita, bycatch was about 7% of population size, and probability of success was 0.08. Under the second option with a larger protected area, the probability of success was 0.35. The third option was large enough to eliminate vaquita bycatch and had a probability of success >0.99. Probability of success was reduced if elimination of vaquita bycatch was delayed or incomplete. Despite considerable efforts by the Mexican government to support vaquita conservation, abundance will probably continue to decline unless additional measures to reduce vaquita bycatch are taken, such as banning gill nets within the vaquita's range and developing effective alternative fishing gear.     

FIRST ESTIMATES OF VAQUITA ABUNDANCE

The abundance of the only population of vaquitas, Gulf of California harbor porpoise ( Phocoena sinus ), is estimated from four surveys conducted in Mexico between 1986 and 1993, using a variety of methods. A line-transect approach was applied, using some parameters estimated from a related species, the harbor porpoise ( Phocoena phocoena ). Vaquita abundance is estimated as 503 (CV = 0.63) from 1986–1988 boat surveys, 885 (CV = 0.50) from 1988–1989 aerial surveys, 572 (CV = 1.43) from a 1991 aerial survey, and 224 (CV = 0.39) from a 1993 ship survey. A weighted log-linear regression indicates a rate of population change (decline) of −17.7% per year (95% CI =−43.2% to +19.3%) between 1986 and 1993. All of these estimates of vaquita abundance indicate that the species is at a critically low level.     

ABUNDANCE OF BLUE AND HUMPBACK WHALES IN THE EASTERN NORTH PACIFIC ESTIMATED BY CAPTURE-RECAPTURE AND LINE-TRANSECT METHODS

We estimated humpback and blue whale abundance from 1991 to 1997 off the west coast of the U. S. and Mexico comparing capture-recapture models based on photographically identified animals and line-transect methods from ship-based surveys. During photo-identification research we obtained 4,212 identifications of 824 humpback whales and 2,403 identifications of 908 blue whales primarily through non-systematic small-boat surveys along the coast of California, Oregon, and Washington. Line-transect surveys from NOAA ships in 1991, 1993, and 1996 covered approximately 39,000 km along the coast of Baja California, California, Oregon, and Washington out to 555 km from shore. The nearshore and clumped distribution of humpback whales allowed photographic identification from small boats to cost-effectively sample a substantial portion of the population, but made it difficult to obtain effective samples in the line-transect surveys covering broad areas. The humpback capture-recapture estimates indicated humpback whale abundance increased over the six years (from 569 to 837). The broader more offshore distribution of blue whales made it harder to obtain a representative sample of identification photographs, but was well suited to the line-transect estimates. The line-transect estimates, after correction for missed animals, indicated approximately 3,000 blue whales (CV = 0.14). Capture-recapture estimates of blue whales were lower than this: approximately 2,000 when using photographs obtained from the line-transect surveys as one of the samples. Comparison of the results from the two methods provides validation, as well as insight into potential biases associated with each method.     

A population size estimate of the finless porpoise,Neophocaena phocaenoides, from aerial sighting surveys in Ariake Sound and Tachibana Bay, Japan

We estimated the population size of the finless porpoise (Neophocaena phocaenoides) in Ariake Sound and Tachibana Bay of western Kyushu, southwestern Japan, from aerial sighting surveys using line transect methods. All 12 surveys were conducted from May 1993 to May 1994 (8 in Ariake Sound and 4 in Tachibana Bay). In addition to these, 14 surveys were also carried out to obtain information on porpoise occurrence in Tachibana Bay (5 surveys) and in neighboring Sumo Nada (5) and Yatsushiro Sound (4). In Ariake Sound, 225 porpoise groups (369 animals) were detected during all flights totalling 1,694.4 km. In Tachibana Bay, a total of 997.8 km was surveyed and 55 groups (290 animals) were sighted. However, no sightings were recorded in Sumo Nada (distance searched = 148.7 km) and Yatsushiro Sound (208.4 km). In Ariake Sound, few sightings were recorded from waters shallower than 5 m in depth. In Tachibana Bay all animals were detected from waters of less than 50 m depth. The population size was estimated as 1,983 animals in Ariake Sound (95% CI = 1,382-2,847), 1,110 in Tachibana Bay (95% CI = 642-1,920), and 3,093 in the 2 waters (1.3 individuals/km², 95% CI = 2,278-4,201).     

Developing ultraviolet illumination of gillnets as a method to reduce sea turtle bycatch

Fisheries bycatch of marine animals has been linked to population declines of multiple species, including many sea turtles. Altering the visual cues associated with fishing gear may reduce sea turtle bycatch. We examined the effectiveness of illuminating gillnets with ultraviolet (UV) light-emitting diodes for reducing green sea turtle (Chelonia mydas) interactions. We found that the mean sea turtle capture rate was reduced by 39.7% in UV-illuminated nets compared with nets without illumination. In collaboration with commercial fishermen, we tested UV net illumination in a bottom-set gillnet fishery in Baja California, Mexico. We did not find any difference in overall target fish catch rate or market value between net types. These findings suggest that UV net illumination may have applications in coastal and pelagic gillnet fisheries to reduce sea turtle bycatch.     

FIELD EXPERIMENTS SHOW THAT ACOUSTIC PINGERS REDUCE MARINE MAMMAL BYCATCH IN THE CALIFORNIA DRIFT GILL NET FISHERY

A controlled experiment was carried out in 1996–1997 to determine whether acoustic deterrent devices (pingers) reduce marine mammal bycatch in the California drift gill net fishery for swordfish and sharks. Using Fisher's exact test, bycatch rates with pingers were significantly less for all cetacean species combined ( P < 0.001) and for all pinniped species combined ( P = 0.003). For species tested separately with this test, bycatch reduction was statistically significant for short-beaked common dolphins ( P = 0.001) and California sea lions ( P = 0.02). Bycatch reduction is not statistically significant for the other species tested separately, but sample sizes and statistical power were low, and bycatch rates were lower in pingered nets for six of the eight other cetacean and pinniped species. A log-linear model relating the mean rate of entanglement to the number of pingers deployed was fit to the data for three groups: short-beaked common dolphins, other cetaceans, and pinnipeds. For a net with 40 pingers, the models predict approximately a 12-fold decrease in entanglement for short-beaked common dolphins, a 4-fold decrease for other cetaceans, and a 3-fold decrease for pinnipeds. No other variables were found that could explain this effect. The pinger experiment ended when regulations were enacted to make pingers mandatory in this fishery.     

渤海江豚种群现状初探

渤海是黄渤海江豚种群的重要分布区,但是有关该区域江豚的种群数量的资料极其匮乏。2015年至2016年,采用截线抽样法在渤海水域开展了6个航次的目视调查,收集了渤海江豚的分布数据,首次评估了区域内的江豚种群数量,为制定有效的渤海江豚种群生态保护策略提供了基础资料。调查结果显示,在2015年8月、2016年5~7月、9月和11月进行的6个调查航次共计8972 km的有效航程中,发现江豚87次、136头次。江豚在渤海各海湾和中部水域都可观察到;14:00-18:00时段、离岸15~35km范围内较易观察到江豚;黄河口外、秦皇岛东北侧老龙口和莱州外沿岸河口水域,江豚出现频次较多。各季节中,以5月在黄河口外20~40km范围内发现江豚的频次和数量最多。采用Distance 7.0软件估算渤海江豚种群数量,其中探测概率分别取值0.399、0.85和1时,渤海江豚种群数量估算值分别为7883头（CV=0.21）、3701头（CV=0.21）和3124头（CV=0.21）,对应的种群密度分别为1.441头/km2、0.066头/km²和0.056头/km²,均低于已报道的南黄海和日本海江豚种群相应值。受海上天气、调查条件和经验所限,本文估值可能存在偏差,但限于渤海江豚历史资料缺乏的现状,本文的结果对于认识渤海江豚的种群状况仍具有重要参考意义。     

A combined visual and acoustic estimate of 2008 abundance,and change in abundance since 1997, for the vaquita,Phocoena sinus

A line‐transect survey for the critically endangered vaquita, Phocoena sinus, was carried out in October–November 2008, in the northern Gulf of California, Mexico. Areas with deeper water were sampled visually from a large research vessel, while shallow water areas were covered by a sailboat towing an acoustic array. Total vaquita abundance in 2008 was estimated to be 245 animals (CV = 73%, 95% CI 68–884). The 2008 estimate was 57% lower than the 1997 estimate, an average rate of decline of 7.6%/yr. Bayesian analyses found an 89% probability of decline in total population size during the 11 yr period, and a 100% probability of decline in the central part of the range. Acoustic detections were assumed to represent porpoises with an average group size of 1.9, the same as visual sightings. Based on simultaneous visual and acoustic data in a calibration area, the probability of detecting vaquitas acoustically on the trackline was estimated to be 0.41 (CV = 108%). The Refuge Area for the Protection of the Vaquita, where gill net fishing is currently banned, contained approximately 50% of the population. While animals move in and out of the Refuge Area, on average half of the population remains exposed to bycatch in artisanal gill nets.     

THE EFFECTS OF ACOUSTIC ALARMS ON THE BEHAVIOR OF HARBOR PORPOISES (PHOCOENA PHOCOENA) IN A FLOATING PEN

In an attempt to test the effectiveness of sounds in deterring harbor porpoises from nets and reducing porpoise bycatch in gill net fisheries, two harbor porpoises, kept in a large floating pen at Neeltje Jans, The Netherlands, were subjected to 3 different underwater sounds. The effect of each sound was judged by comparing the animals' behavior during a 15-min test period with that during a 15-min baseline period immediately before the test and a 15-min recovery period immediately after the test. The effects of the alarms were quantified as the distance between the porpoises' surfacings and the alarm and the animals' respiration rates. Each alarm was tested in two positions in the pen. The behavior observed was related to the sound-pressure-level distribution in the pen. All three alarms: the standard Dukane alarm (a commercially available alarm with a regular pulse interval of 4.3 sec used to deter dolphins from fishing nets), the random Dukane alarm (the same alarm with random pulse interval of between 2 and 30 sec), and the "bird alarm" (a sound from a generator) resulted in increases in both the distance of the animals' surfacings from the alarms and their respiration rates. The standard Dukane alarm and the bird alarm were more effective than the random Dukane alarm in inducing the animals to swim away from the sound source.     

Exploring Trade-Offs between Fisheries and Conservation of the Vaquita Porpoise (Phocoena sinus) Using an Atlantis Ecosystem Model

Background

Minimizing fishery bycatch threats might involve trade-offs between maintaining viable populations and economic benefits. Understanding these trade-offs can help managers reconcile conflicting goals. An example is a set of bycatch reduction measures for the Critically Endangered vaquita porpoise (Phocoena sinus), in the Northern Gulf of California, Mexico. The vaquita is an endemic species threatened with extinction by artisanal net bycatch within its limited range; in this area fisheries are the chief source of economic productivity.

Methodology/Principal Findings

We analyze trade-offs between conservation of the vaquita and fisheries, using an end-to-end Atlantis ecosystem model for the Northern Gulf of California. Atlantis is a spatially-explicit model intended as a strategic tool to test alternative management strategies. We simulated increasingly restrictive fisheries regulations contained in the vaquita conservation plan: implementing progressively larger spatial management areas that exclude gillnets, shrimp driftnets and introduce a fishing gear that has no vaquita bycatch. We found that only the most extensive spatial management scenarios recovered the vaquita population above the threshold necessary to downlist the species from Critically Endangered. The scenario that excludes existing net gear from the 2008 area of vaquita distribution led to moderate decrease in net present value (US$ 42 million) relative to the best-performing scenario and a two-fold increase in the abundance of adult vaquita over the course of 30 years.

Conclusions/Significance

Extended spatial management resulted in the highest recovery of the vaquita population. The economic cost of proposed management actions was unequally divided between fishing fleets; the loss of value from finfish gillnet fisheries was never recovered. Our analysis shows that managers will have to confront difficult trade-offs between management scenarios for vaquita conservation.     

Biological tags for stock separation in Pacific herring Clupea harengus pallasi in California.

A survey of the parasites of Pacific herring (Clupea harengus pallasi) off northern California identified 1 species of Acanthocephala, 1 species of Cestoda, 2 species of Copepoda, 1 species and 1 family of Digenea, 3 species of Nematoda, and 3 species of Protozoa. From this survey, Lacistorhynchus dollfusi (Cestoda), Parahemiurus merus (Digenea), and Anisakis simplex, Contracaecum sp., Hysterothylacium sp. (Nematoda) were selected as potential tags. Herring were collected in Tomales, San Francisco, and Monterey bays for the following 9 yr and examined for these select parasites. The results suggest that these parasites can be used to distinguish the spawning stocks of San Francisco and Tomales bays. The distribution of the definitive hosts of the respective parasites suggests that the Tomales Bay fish are offshore during the nonbreeding season and the San Francisco Bay fish onshore. The similarity in parasitism between San Francisco Bay and the nonspawning population in Monterey Bay suggests that these 2 populations represent a single stock.     

三疣梭子蟹增养殖过程对野生种群的遗传影响——以海州湾为例

为探明三疣梭子蟹人工增殖与养殖活动对野生资源的遗传影响,本文利用20对SSR引物对海州湾三疣梭子蟹野生群体与两个养殖群体进行群体遗传结构和遗传分化研究。结果表明,野生种群遗传多样性明显高于养殖群体,其群体杂合度Ho为0.8509,而两个养殖群体的杂合度Ho分别为0.4525和0.5283。海州湾野生三疣梭子蟹的 Ne、Ho、He、PIC均显著高于两个养殖群体（P<0.05）但两养殖群体的 Ne、Ho、He、PIC均无显著差异（P>0.05）。以上结果说明海州湾天然三疣梭子蟹群体的遗传多样性显著高于养殖群体。三群体间遗传分化处于中度水平（Fst,0.1085~0.1448）,基因流Nm处于1.5-2.0间,野生群体与养殖群体的遗传分化比养殖群体内部之间大,基因流也较养殖群体内部之间要小,表明野生群体与养殖群体存在一定的分化,基因流处于中等程度。因此,当前海州湾天然三疣梭子蟹遗传状况良好,养殖活动和人工增殖放流对天然资源的遗传影响还很有限,这可能与海州湾人工养殖三疣梭子蟹时间较短、人工放流的规模较小、时间较短有关。     

Harbour porpoisesPhocoena phocoena in the North Sea: Numerical responses to changes in environmental conditions

Changes during the last 40 years of abundance and occurrence of harbour porpoises in the North Sea are illustrated as consequences of changes in environmental factors. The major changes in environmental conditions which influenced the presence of harbour porpoises in the North Sea, in particular the southern North sea, are postulated to be changes in prey availability and changes in accidental catches. Limitations of prey made them move out of the coastal areas, but accidental catch has reduced their overall abundance. Prey availability was affected by limitation of herring and mackerel as the major food source, caused initially by overfishing, followed by a shift in spawning and feeding areas towards the North. Without ignoring the possible complementary impact of pollution and disturbance, it is believed that accidental catch is the only other major threat. The present size of the harbour porpoise population(s) in the northeast Atlantic, including the stock in the Danish inner waters, is estimated to average 160,000 (range 70,000–225,000) specimens. However, this should not divert the attention from the fact that bycatch and directed catch have significantly reduced the size of the North Sea harbour porpoise populations (including the Baltic), by at least between 53,000–89,000 animals, and more likely the higher end of the range. It is emphasized that management measures should be taken in order to reduce the bycatch of porpoises as was already agreed at the latest Ministerial North Sea Conference. The only short-term, pragmatic and efficient way to assess whether the population will benefit from increasing prey availability is to organise international sighting surveys. Then it may be possible to obtain a clear perception of whether the porpoise has only temporarily moved out of the southern North Sea or whether we are dealing with a decreased population, unable to recover because it can not sustain the existing accidental catches.     

CURRENT STATUS AND CONSERVATION NEEDS OF DUGONGS IN SOUTHERN JAPAN

We conducted aerial surveys of dugongs ( Dugong dugon ) using the line-transect method and snorkeling surveys of dugong feeding trails in 1998 and 1999 around Okinawa Island (26°30'N, 128°00'E) and the Sakishima Islands, southern Japan. A total of ten dugongs were sighted and feeding trails were confirmed in the sea grass beds off the east coast of Okinawa Island. In the Sakishima Islands, however, no dugongs were observed, and there was no evidence of feeding trails despite the existence of apparently suitable sea grass beds for feeding. The results of these surveys and other available information suggest that Okinawan dugongs represent a small, geographically isolated population. Our sightings of dugongs during the daytime, offshore of sea grass beds where feeding trails were recorded, suggest that Okinawan dugongs principally feed at night when human activities are limited. Survival of this remnant dugong population is threatened by habitat degradation and occasional entanglement mortality in fishing nets.     

Distribution,abundance, and density of harbor porpoises in Hood Canal,Washington

Harbor porpoises (Phocoena phocoena) are the only cetaceans routinely sighted in Hood Canal, a narrow fjord that comprises the western edge of Puget Sound, Washington, USA. Harbor porpoises are sensitive to anthropogenic sounds, including noise from recreational and commercial vessel traffic, and the United States Navy, which conducts military training and testing within Hood Canal that can include underwater sound sources. This study was funded as part of the Navy monitoring program to assess potential impacts of naval activities on cetaceans. We conducted vessel-based line-transect surveys for harbor porpoises in Hood Canal in 2022–2023 to derive seasonal estimates of abundance and density. We carried out surveys over 37 days and surveyed the entire canal twice per season totaling 2,176 km of on-effort track line. We recorded 809 on-effort harbor porpoise groups and 1,385 individuals. Seasonal abundance estimates were lowest in winter (308 animals, 95% CI = 189–503) and gradually increased through spring and summer to a peak of 1,336 animals (95% CI = 826–2,160) in fall. Overall porpoise density was highest in central Hood Canal, an area that includes a designated United States Navy training range, though porpoise sightings were notably absent in a 21-km² area adjacent to the naval submarine base within this otherwise high-density region. Though we collected only a single year of data, these results suggest that harbor porpoise abundance in Hood Canal increased significantly since it was last estimated (2013–2015). The notable seasonal fluctuation of harbor porpoise abundance suggests Hood Canal may host a larger percentage of the overall Washington Inland Waters stock during the fall season, raising important management considerations.     

STOCK STRUCTURE OF SEA OTTERS (ENHYDRA LUTRIS KENYONI) IN ALASDA

Sea otters in Alaska are recognized as a single subspecies ( Enhydra lutris kenyoni ) and currently managed as a single, interbreeding population. However, geographic and behavioral mechanisms undoubrably constrain sea otter movements on much smaller scales. This paper applies the phylogeographic method (Dizon et al . 1992) and considers distribution, population response, phenotype and genotype data to identify stocks of sea otters within Alaska. The evidence for separate stock identity is genotypic (all stocks), phenotypic (Southcentral and Southwest stocks), and geographic distribution (Southeast stock), whereas population response data are equivocal (all stocks). Differences in genotype frequencies and the presence of unique genotypes among areas indicate restricted gene flow. Genetic exchange may be limited by little or no movement across proposed stock boundaries and discontinuities in distribution at proposed stock boundaries. Skull size differences (phenotypic) between Southwest and Southcentral Alaska populations further support stock separation. Population response information was equivocal in either supporting or refuting stock identity. On the basis of this review, we suggest the following: (1) a Southeast stock extending from Dixon Entrance to Cape Yakataga; (2) a Southcentral stock extending from Cape Yakataga to Cape Douglas including Prince William Sound and Kenai peninsula coast; and (3) a Southwest stock including Alaska Peninsula coast, the Aleutians to Attu Island, Barren, Kodiak, Pribilof Islands, and Bristol Bay.     

Declining Abundance of Beaked Whales (Family Ziphiidae) in the California Current Large Marine Ecosystem

Beaked whales are among the most diverse yet least understood groups of marine mammals. A diverse set of mostly anthropogenic threats necessitates improvement in our ability to assess population status for this cryptic group. The Southwest Fisheries Science Center (NOAA) conducted six ship line-transect cetacean abundance surveys in the California Current off the contiguous western United States between 1991 and 2008. We used a Bayesian hidden-process modeling approach to estimate abundance and population trends of beaked whales using sightings data from these surveys. We also compiled records of beaked whale stranding events (3 genera, at least 8 species) on adjacent beaches from 1900 to 2012, to help assess population status of beaked whales in the northern part of the California Current. Bayesian posterior summaries for trend parameters provide strong evidence of declining beaked whale abundance in the study area. The probability of negative trend for Cuvier''s beaked whale (Ziphius cavirostris) during 1991–2008 was 0.84, with 1991 and 2008 estimates of 10771 (CV = 0.51) and ≈7550 (CV = 0.55), respectively. The probability of decline for Mesoplodon spp. (pooled across species) was 0.96, with 1991 and 2008 estimates of 2206 (CV = 0.46) and 811 (CV = 0.65). The mean posterior estimates for average rate of decline were 2.9% and 7.0% per year. There was no evidence of abundance trend for Baird''s beaked whale (Berardius bairdii), for which annual abundance estimates in the survey area ranged from ≈900 to 1300 (CV≈1.3). Stranding data were consistent with the survey results. Causes of apparent declines are unknown. Direct impacts of fisheries (bycatch) can be ruled out, but impacts of anthropogenic sound (e.g., naval active sonar) and ecosystem change are plausible hypotheses that merit investigation.     

Assessing the impact of bycatch on dolphin populations: the case of the common dolphin in the eastern North Atlantic

Fisheries interactions have been implicated in the decline of many marine vertebrates worldwide. In the eastern North Atlantic, at least 1000 common dolphins (Delphinus delphis) are bycaught each year, particularly in pelagic pair-trawls. We have assessed the resulting impact of bycatch on this population using a demographic modeling approach. We relied on a sample of females stranded along the French Atlantic and western Channel coasts. Strandings represent an extensive source of demographic information to monitor our study population. Necropsy analysis provided an estimate of individual age and reproductive state. Then we estimated effective survivorship (including natural and human-induced mortality), age at first reproduction and pregnancy rates. Reproductive parameters were consistent with literature, but effective survivorship was unexpectedly low. Demographic parameters were then used as inputs in two models. A constant parameter matrix proposed an effective growth rate of -5.5±0.5%, corresponding to the current situation (including bycatch mortality). Subsequently, deterministic projections suggested that the population would be reduced to 20% of its current size in 30 years and would be extinct in 100 years. The demographic invariant model suggested a maximum growth rate of +4.5±0.09%, corresponding to the optimal demographic situation. Then, a risk analysis incorporating Potential Biological Removal (PBR), based on two plausible scenarii for stock structure suggested that bycatch level was unsustainable for the neritic population of the Bay of Biscay under a two-stock scenario. In depth assessment of stock structure and improved observer programs to provide scientifically robust bycatch estimates are needed. Effective conservation measures would be reducing bycatch to less than 50% of the current level in the neritic stock to reach PBR. Our approach provided indicators of the status and trajectory of the common dolphin population in the eastern North Atlantic and therefore proved to be a valuable tool for management, applicable to other dolphin populations.     

Molecular resolution of marine turtle stock composition in fishery bycatch: a case study in the Mediterranean

Based on an extensive sampling regime from both nesting populations and bycatch, frequency analyses of mitochondrial (mt) DNA control region haplotypes in the Mediterranean were used to assess the genetic structure and stock composition of the loggerhead sea turtle, Caretta caretta, in different marine fisheries. The analyses show the following. (i) In drifting longline fisheries working in Mediterranean pelagic habitats 53–55% of turtles caught originated from the Mediterranean stock; (ii) In bottom-trawl fisheries all turtle bycatch is derived from this regional stock; (iii) This regional stock contribution to fishery bycatch suggests that the population size of the Mediterranean loggerhead nesting population is significantly larger than previously thought. This is consistent with a recent holistic estimate based on the discovery of a large rookery in Libya. (iv) Present impact of fishery-related mortality on the Mediterranean nesting population is probably incompatible with its long-term conservation. Sea turtle conservation regulations are urgently needed for the Mediterranean fisheries. (v) The significant divergence of mtDNA haplotype frequencies of the Turkish loggerhead colonies define this nesting population as a particularly important management unit. Large immature and adult stages from this management unit seem to be harvested predominantly by Egyptian fisheries. (vi) Combined with other data, our findings suggest that all the nesting populations in the Mediterranean should be considered as management units sharing immature pelagic habitats throughout the Mediterranean (and possibly the eastern Atlantic), with distinct and more localized benthic feeding habitats in the eastern basin used by large immatures and adults. (vii) Between the strict oceanic pelagic and the benthic stages, immature turtles appear to live through an intermediate neritic stage, in which they switch between pelagic and benthic foods.     

鸟类种群密度调查和估算方法初探

为探讨不同调查方法对鸟类种群密度估计的差异,于2010年12月15~20日,对云南省昆明市嵩明县嘉丽泽地区常见的四种鸟(白脊鹡鸰Motacilla alba、黑喉石駑(嶋)Saxicola torquata、白鹭Egretta garzetta、苍鹭Ardea cinerea)进行调查研究.之后分别采用无距离样线法、固定距离样线法以及可变距离样线法(Distance软件)分析,得出其相对丰富度、种群密度等相关信息.对比三种样线法在鸟类数量估计方面的优劣,认为无距离样线法不能真实地反映鸟类数量的多少,固定距离样线法结合样带计数法往往低估鸟类种群密度,呵变距离样线法结合Distance软件分析是相对更为先进和精准的种群密度估算方法.对如何进一步利用Distance软件的分析结果也进行了初步探讨.