Geographic variation in the growth of white croaker,Pennahia argentata,off the coast of northwest Kyushu,Japan

We examined geographic variation in the growth of white croaker,Pennahia argentata, off the coast of northwest Kyushu, Japan, Ariake Sound, Tachibana Bay, Omura Bay and the Goto Sea by examination of otoliths. The outer margins of the otoliths showed that a opaque zone was formed once a year, with its peak in June, and could be used as an annulus. White croaker caught during this study reached a maximum age of 10years in the Goto Sea. The growth curves for both sexes in all localities were expressed by the von Bertalanffy growth equations from back-calculated total length of fish. We found significant sexual differences in growth curves in Ariake Sound, Tachibana Bay and the Goto Sea. For both sexes, white croaker in the Goto Sea reached the largest length at each estimated age of the four localities. The growth curves for both sexes showed significant differences among four localities, suggesting that several stocks may exist in the study area although the greatest distance between each locality was at most 30 km.     

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.     

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。     

The harbour porpoise (<Emphasis Type="Italic">Phocoena phocoena</Emphasis>) in the central German Bight: phenology,abundance and distribution in 2002–2004

The harbour porpoise (Phocoena phocoena) is widely distributed in the North Sea. During both the SCANS 1994 and 2005 surveys, porpoises were commonly encountered in offshore waters, for example in the central German Bight. However, information on year-round abundance and distribution of harbour porpoises in that area on a monthly basis was lacking. Between 2002 and 2004, we undertook 26 aerial line-transect surveys in a 2,600 km² area in the central German Bight, 100 km north of the Island of Borkum (Eastern Frisia). Data were analysed with DISTANCE software. A total of 406 porpoises were sighted. Sighting rates (=sightings/km transect) peaked in July 2002, February, May and September 2003, and in January and April 2004. Absolute densities (g(0) corrected) ranged between 0.14 and 1.54 animals/km² (peak in April 2004). Proportion of calves varied between 3.4 and 27.3%. Our results show a highly irregular appearance of harbour porpoises in the study area with no apparent seasonal trends in occurrence but peaks in single months. We propose that the area is used as a transit route with harbour porpoise moving in from regions of high density in summer (Northern Frisia) and early spring (Eastern Frisia).     

厦门水域中华白海豚出现于围头湾

厦门海域的中华白海豚是一个受威胁的种群。以往有关该种群的调查范围主要集中在厦门以及邻近的南部漳州海域。为了获得厦门岛东部海域（包括晋江围头湾、小嶝岛以及大嶝岛部分水域）白海豚的分布和数量等信息,本文于2013年6—8月对该水域进行了船基样线法调查和照相识别研究。调查期间共目击到白海豚26群,照相识别白海豚个体27头。所有照相识别的白海豚个体均与厦门中华白海豚个体识别数据库中的个体匹配,表明厦门中华白海豚的分布区至少向东延伸至围头湾。本文白海豚遇见率为5.8群/100km和24.8头/100km,均要高于以往在厦门水域的调查结果,表明大嶝岛—围头湾水域是厦门中华白海豚的重要栖息地之一,值得优先保护和管理。     

加州Santa Monica海湾鳍足类的生态学

研究了加州Santa Monica海湾鳍足类的生态学.从1997-2007年乘船调查了277次,发现海狮(Zalophus californianus)是最常见的动物(89%,见到的次数为1393次),其次是港海豹(Phoca vitulina richardsi,8%,n=131)和北象海豹(Mirounga angustirostris,1%,n=15).在29%的遇见次数(观察到瓶海豚205次)中,发现海狮(偶尔也发现港海豹)与瓶鼻海豚集群(Tursiops truncatus);短喙真海豚(Delphinus delphis)与长喙真海豚(D.capensis)在53% 的遇见次数(遇见真海豚次数n=155)中,发现短喙真海豚(Delphinus delphis)与长喙真海豚(D.capensis)集群;一般在沿岸水域(离岸边距离<500 m)见到海狮和港海豹,但在整个海湾也能见到,表现出这两个物种对海底峡谷的偏爱.北象海豹仅见于近海,主要在海底峡谷附近. 经常看到海狮、港海豹和北象海豹游动(50%,n=728)、进行热调节(14%,n=205)、以及取食(3.2%,n=47),但几乎见不到有社会性活动(0.21%,n=3).     

HARBOR PORPOISE (PHOCOENA PHOCOENA) ABUNDANCE IN ALASKA: BRISTOL BAY TO SOUTHEAST ALASKA, 1991-1993

Between 1991 and 1993, Alaska harbor porpoise ( Phocoena phocoena ) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entrance in Southeast Alaska. Line-transect methodology was used, and only those observations made during optimal conditions were analyzed. Survey data indicated densities of 4.48 groups/100 km², or approximately 3,531 harbor porpoises (95% C. I. 2,206-5,651) in Bristol Bay and 0.54 groups/100 km², or 136 harbor porpoises (95% C. I. 11-1,645) for Cook Inlet. Efforts off Kodiak Island resulted in densities of 1.85 groups/100 km², or an abundance estimate of 740 (95% C. I. 259-2,115). Surveys off the south side of the Alaska Peninsula found densities of 2.03 groups/100 km² and an abundance estimate of 551 (95% C. I. 423-719). Surveys of offshore waters from Prince William Sound to Dixon Entrance yielded densities of 4.02 groups/100 km² and an abundance estimate of 3,982 (95% C. I. 2,567-6,177). Combining all years and areas yielded an uncorrected density estimate of 3.82 porpoises per 100 km², resulting in an abundance estimate of 8,940 porpoises (CV = 13.8%) with a 95% confidence interval of 6,746-11,848. Using correction factors from other studies to adjust for animals missed by observers, the total number of Alaska harbor porpoises is probably three times this number.     

Occurrence,Growth and Food of Longheaded Eagle Ray, <Emphasis Type="Italic">Aetobatus flagellum</Emphasis>, in Ariake Sound,Kyushu, Japan

Synopsis The longheaded eagle ray, Aetobatus flagellum, has recently increased significantly in numbers in Ariake Sound. It is assumed that it feeds on bivalves and so, to prevent predation by eagle rays on bivalves, a ‘predator control program’ aimed at reducing the ray population has been in place since 2001. We examined their occurrence, age, growth and food in Ariake Sound to obtain data on the ecology of the eagle ray and provide basic information on their potential impact on bivalve stocks in Ariake Bay. The eagle ray is a seasonal visitor to Ariake Sound, increasing in numbers from April, and peaking during the summer. None were captured during surveys in December and February. Their movement pattern around the bay differed according to sex. Pregnant females were caught in the estuary during August and September. Females grew to a larger size than males and apparently lived longer. The maximum ages were 19 years for females and 9 years for males. Growth until two years was similar in both sexes, but after 2 years females grew larger. The eagle ray fed only on bivalves, especially Ruditapes philippinarum and Atrina pectinata, very important fishery species farmed in Ariake Bay.     

固化河岸对长江江豚栖息活动的影响

长江江豚主要栖居在近岸浅水水域,喜好泥沙质类型的河岸。但在长江干流,有很多自然河岸被固化,河岸固化给长江江豚分布和栖息活动造的影响仍不甚清楚。2016年3月—2017年1月,对长江干流2个自然河段江豚的数量和分布做了12次考察,并收集了这2个河段岸型的相关数据,来分析固化河岸对江豚栖息活动的影响。12次考察累计发现江豚215头次,平均每次考察观察到江豚(17.92±7.09)头次。研究区域的固化河岸约占岸线总长的59%,分析发现,仅约13.9%的江豚分布在固化河岸水域,86.1%的江豚均分布在自然河岸水域。江豚在单位河岸长度的分布数量与该段固化河岸长度所占的比例呈显著负相关(r=-0.639,P0.01)。在自然河岸,分布在近岸50 m水域的江豚占31.8%,而在固化河岸,仅观察到2头江豚活动在近岸50 m水域内。由此可见,固化河岸对江豚的近岸分布有明显影响。调查还发现,安庆城区建设带约10 km江段12次考察均未发现江豚分布,城区建设带可能对江豚栖息已造成严重影响。长江干流的固化河岸所占比例非常高,研究结果提示这可能导致长江干流江豚栖息地的丧失和破碎化加剧,在制定长江江豚保护措施必需慎重考虑此因素的影响,并据此提出相应的栖息地保护和恢复方案。     

Sighting of Stenella attenuata, the spotted dolphin, in Culebra Bay, Costa Rica, 1999-2000

Parallel to a zooplankton study (1999-2000) observations were made (from an inflatable boat), on the presence of dolphins along a transect (-8 km long) on the axis of Culebra Bay (24 km2), Gulf of Papagayo, Pacific coast of Costa Rica. Dolphins were found during 20 of the 31 boat surveys conducted. The only species of cetacean found in the bay was Stenella attenuata, the spotted dolphin. These sightings were more frequent during the rainy season, particularly during the month of May of both years. The presence of S. attenuata in Culebra Bay might be associated to the abundances of fish and mollusks (their presumed prey: for example, squids), as evidenced by fishery statistics available for this zone of the Pacific coast of Costa Rica.     

TRENDS IN MANATEE (TRICHECHUS MANATUS LATIROSTRIS) COUNTS AND HABITAT USE IN TAMPA BAY, 1987–1994: IMPLICATIONS FOR CONSERVATION

Aerial surveys ( n = 88) were used to document locations and count sightings of manatees ( Trichechus manatus latirostris ) in the inshore waters of Tampa Bay, Florida, between November 1987 and May 1994. We made 5,358 sightings of manatees in 1,958 groups. Calves represented 8% of the manatees sighted. Counts were significantly higher in winter ( = 79, n = 29 flights) than in non-winter ( = 46, n = 47) months. Counts of manatees in winter increased significantly during the study, but warm-season counts did not. Regression models demonstrated a relationship between counts and environmental factors. Year-round counts were related to air temperatures and seasons, with highest counts in winter. However, in the winter season, counts were significantly correlated only with wind speed, not air temperature. Yearround counts were predicted to be curvilinear with highest counts at 15°C average air temperature. Areas used differed with season: in cold weather, 76% of all sightings occurred in zones with warm-water sources. High-use areas were identified for summer months. Spatial filter analysis was used to compare manatee density in high-use areas between two two-year time periods. The data indicate that (1) manatee use of Tampa Bay was high and increasing in winter, (2) there are particular zones of the bay where conservation of manatees and habitat should be a priority, and (3) sufficient information has been collected for management agencies to develop and implement manatee protection plans.     

Potential distribution of Tridentiger barbatus (Günther 1861) and Tridentiger nudicervicus (Tomiyama 1934) in the Seto Inland Sea,western Japan

We developed distribution models for two near-threatened gobiid fishes, Tridentiger barbatus and Tridentiger nudicervicus, based on distribution data and geographic variables in the Ariake Sea, the Yatsushiro Sea, and Suonada Bay. Subsequently, we estimated the potential distribution of both species across all areas of the Seto Inland Sea based on the model predictions. The models indicated high accuracy and demonstrated that both species inhabit shoal and relatively enclosed waters. Predicted potential distribution areas of the two species included all sites with previous records and a few new sites without existing records.     

Temporal–spatial distribution of an island‐based offshore population of common bottlenose dolphins (Tursiops truncatus) in the equatorial Atlantic

A little‐studied common bottlenose dolphin (Tursiops truncatus) population inhabits the offshore waters surrounding Saint Paul's Rocks, a Brazilian marine protected area in the equatorial Atlantic Ocean. Five field expeditions (May 2011–May 2013) were conducted to characterize the habitat use, population size, and site fidelity of this population. Three different survey methods were employed: line‐transect surveys, land‐based surveys, and photo‐identification surveys. A population size of 23 individuals (19–28, CI 95%), which were present on most sampling days (>90% of surveys), was estimated. The maximum resighting interval of photo‐identified animals was 9 yr and 3 mo for five distinct individuals, based on data from nonsystematic efforts that have been ongoing since 2004. The dolphins exhibited strong site fidelity, as the minimum convex polygon (MCP, 95%) method revealed that they restricted their movements to a 0.5 km² area across seasons and a 0.99 km² area across years (95% kernel). The dolphins preferred shallow waters close to the archipelago (<1.2 km from the islands), especially on the eastern and southeastern sides, where oceanographic models have revealed persistent upwelling that may result from underwater currents and where food may be more predictably available.     

长江安庆段航道整治对长江江豚数量和分布的时空影响

栖息地丧失和破碎化是威胁长江江豚(Neophocaena asiaeorientalis)种群长期发展的主要因素之一。航道整治工程是导致江豚栖息地丧失和破碎化的一个主要原因,研究工程施工和运行对江豚数量和分布的影响可为江豚栖息地管护提供有益信息。通过对湖口-吉阳矶水域江豚数量和分布的持续调查,分析了安庆段航道整治工程施工和运行对江豚的影响。12次目视调查共在研究水域发现江豚258群次613头次,工程施工前、施工期和初步运行期单次考察分别平均观察到江豚(67.0±24.3)头次、(35.6±22.2)头次和(50.0±2.8)头次。在主要施工区共发现江豚79群次185头次,施工前、施工期和初步运行期单次考察分别平均观察到江豚(18.60±12.03)头次、(10.4±7.3)头次和(20.0±4.2)头次。工程不同时期主要施工区江豚的数量及占比在统计学上没有显著差异。主要施工区S2和S3工程段施工期江豚平均分布密度((0.18±0.17)头/km、(0.04±0.08)头/km)较施工前((0.62±0.16)头/km、(0.40±0.29)头/km)显著下降,S5和S6工程段施工期平均...     

AERIAL SURVEYS FOR COASTAL DOLPHINS: ABUNDANCE OF HECTOR'S DOLPHINS OFF THE SOUTH ISLAND WEST COAST, NEW ZEALAND

Line-transect surveys of abundance depend critically on the estimation of detection probability, which includes corrections for availability and visibility. In this aerial line-transect survey for Hector's dolphin ( Cephalorhynchus hectori ) we recorded dive times from a helicopter to estimate the proportion of time that dolphins could be seen at or near the water surface and were therefore "available" to be counted. The proportion of available sightings that were counted on transect lines was estimated by comparing sightings by two independent teams of two observers in the fixed-wing plane. The survey covered the area between Farewell Spit and Milford Sound, off the west coast of the South Island of New Zealand. Survey effort was stratified according to existing distribution data. A total of 142 separate sightings was made on 1,355 km of trackline. Average availability for fifty Hector's dolphin groups observed from the helicopter (161 dive/surface cycles) was 46.3% (CV = 4.2%). Data from the two independent observer teams indicated that 96.2% (CV = 2.3%) of the dolphin groups that were at the surface and on the trackline were seen. The abundance estimate for the South Island west coast, corrected for visibility and availability, was 5,388 Hector's dolphins (CV = 20.6%). The total population estimate for South Island Hector's dolphins is 7,270 (CV = 16.2%).     

Abundance, distribution and conservation of Chinese White Dolphins (Sousa chinensis) in Xiamen, China

In recent years, human activities appear to present the greatest threat to the Chinese white dolphin (Sousa chinensis). Increasing death records of this species in Xiamen have already become a focus of attention among the local government, the public, and the media. A comprehensive understanding about the status of Xiamen population is important not only to evaluate the conservation measures taken previously, but to design adaptive measures appropriate to this population. In this study, a survey using line-transect methodology was carried out to cover an area of about 700 km² in Xiamen waters. A total of 102 separate sightings were made on 6157 km of transect line. The abundance estimate ranged from 67 (CV=41.6%) to 93 (CV=26.34%), with an average of 86 (CV=20.16%). Overall, Xigang (West harbor) and Jiyu represented the major area of distribution in Xiamen. Significant seasonal changes in distribution were found. In spring, significant numbers of dolphins occurred in Xigang and few in other areas, while in other seasons, the sighting rate in Xigang decreased relatively with sightings in Jiyu, Dapan, and Dadeng increasing obviously, suggesting an outward movement pattern of Chinese white dolphins from the inside harbor to outside waters after spring. Some suggestions for redesigning the Xiamen Nature Reserve and other management measures are put forward.     

ABUNDANCE OF CETACEANS IN THE OCEANIC NORTHERN GULF OF MEXICO, 1996–2001

The Gulf of Mexico is a subtropical marginal sea of the western North Atlantic Ocean with a diverse cetacean community. Ship-based, line-transect abundance surveys were conducted in oceanic waters (>200 m deep) of the northern Gulf within U. S. waters (380,432 km²) during spring from 1996 to 1997 and from 1999 to 2001. Data from these five surveys were pooled and minimum abundance estimates were based on 12,162 km of effort and 512 sightings of at least 19 species. The most commonly sighted species (number of groups) were pantropical spotted dolphin, Stenella attenuata (164); sperm whale, Physeter macrocephalus (67); dwarf/pygmy sperm whale, Kogia simalbreviceps (58); Risso's dolphin, Grampus griseus (38); and bottlenose dolphin, Tursiops truncatus (24). The most abundant species (number of individuals; coefficient of variation) were S. attenuata (91,321; 0.16); Clymene dolphin, S. clymene (17,355; 0.65); spinner dolphin, S. longirostris (11,971; 0.71); and striped dolphin, S. coeruleoalba (6,505; 0.43). The only large whales sighted were P. macrocephalus (1,349; 0.23) and Bryde's whale, Balaenopteraedeni (40; 0.61). Abundances for other species or genera ranged from 95 to 2,388 animals. Cetaceans were sighted throughout the oceanic northern Gulf and, whereas many species were widely distributed, some had more regional distributions.     

POPULATION ANALYSES OF INDO-PACIFIC HUMPBACK DOLPHINS SOUSA CHINENSIS IN ALGOA BAY,EASTERN CAPE,SOUTH AFRICA1

Mark-recapture analyses were performed on photo-identification data for Indo-Pacific humpback dolphins (Sousa chinensis) inhabiting Algoa Bay, on the Eastern Cape coast of South Africa. Boat-based photo-ID surveys were undertaken between May 1991 and May 1994. The rate of discovery of newly identified dolphins, distribution of sightings and frequency of resightings of known individuals indicate a high level of seasonal immigration of humpback dolphins into, and emigration from, the Algoa Bay region in summer. Consequently, humpback dolphins from Algoa Bay appear to be part of a substantially larger population that uses a considerable length of the coastal zone. The minimum population size is estimated to be about 466 dolphins.     

A comparison of image and observer based aerial surveys of narwhal

From 25 to 30 August 2014 a double‐observer line‐transect survey was conducted over Melville Bay, home to one of two summering populations of narwhal (Monodon monoceros) off West Greenland. A total of 1,932 linear kilometers was surveyed along 33 transects. In addition to using observers, the aircraft was equipped with two oblique cameras to capture a comparable data set. Analysts reviewed the images for narwhal sightings, which were then matched to the observer sightings. The objectives of the study were to determine advantages and disadvantages of the detection capabilities of both methodologies, and to conduct a comparative analysis of population abundance estimates. Correcting for the truncated detection distance of the images (500 m), the image analysts recorded more sightings (62) and a lower mean group size (2.2) compared to aerial observers (36 and 3.5, respectively), resulting in comparable numbers of individuals detected by both platforms (135 vs. 126). The abundance estimate based on the image sightings was 2,536 (CV = 0.51, 95% CI: 1,003–6,406), which was not significantly different from the aerial observers estimate of 2,596 individuals (CV = 0.51; 95% CI: 961–7,008). This study supports the potential of using UAS for marine mammal abundance studies.     

Unmanned Aerial Vehicles (UAVs) for Surveying Marine Fauna: A Dugong Case Study

Aerial surveys of marine mammals are routinely conducted to assess and monitor species’ habitat use and population status. In Australia, dugongs (Dugong dugon) are regularly surveyed and long-term datasets have formed the basis for defining habitat of high conservation value and risk assessments of human impacts. Unmanned aerial vehicles (UAVs) may facilitate more accurate, human-risk free, and cheaper aerial surveys. We undertook the first Australian UAV survey trial in Shark Bay, western Australia. We conducted seven flights of the ScanEagle UAV, mounted with a digital SLR camera payload. During each flight, ten transects covering a 1.3 km² area frequently used by dugongs, were flown at 500, 750 and 1000 ft. Image (photograph) capture was controlled via the Ground Control Station and the capture rate was scheduled to achieve a prescribed 10% overlap between images along transect lines. Images were manually reviewed post hoc for animals and scored according to sun glitter, Beaufort Sea state and turbidity. We captured 6243 images, 627 containing dugongs. We also identified whales, dolphins, turtles and a range of other fauna. Of all possible dugong sightings, 95% (CI = 90%, 98%) were subjectively classed as ‘certain’ (unmistakably dugongs). Neither our dugong sighting rate, nor our ability to identify dugongs with certainty, were affected by UAV altitude. Turbidity was the only environmental variable significantly affecting the dugong sighting rate. Our results suggest that UAV systems may not be limited by sea state conditions in the same manner as sightings from manned surveys. The overlap between images proved valuable for detecting animals that were masked by sun glitter in the corners of images, and identifying animals initially captured at awkward body angles. This initial trial of a basic camera system has successfully demonstrated that the ScanEagle UAV has great potential as a tool for marine mammal aerial surveys.