Porpoise Density Research Articles

Density estimation of Yangtze finless porpoises using passive acoustic sensors and automated click train detection

A method is presented to estimate the density of finless porpoises using stationed passive acoustic monitoring. The number of click trains detected by stereo acoustic data loggers (A-tag) was converted to an estimate of the density of porpoises. First, an automated off-line filter was developed to detect a click train among noise, and the detection and false-alarm rates were calculated. Second, a density estimation model was proposed. The cue-production rate was measured by biologging experiments. The probability of detecting a cue and the area size were calculated from the source level, beam patterns, and a sound-propagation model. The effect of group size on the cue-detection rate was examined. Third, the proposed model was applied to estimate the density of finless porpoises at four locations from the Yangtze River to the inside of Poyang Lake. The estimated mean density of porpoises in a day decreased from the main stream to the lake. Long-term monitoring during 466 days from June 2007 to May 2009 showed variation in the density 0-4.79. However, the density was fewer than 1 porpoise/km(2) during 94% of the period. These results suggest a potential gap and seasonal migration of the population in the bottleneck of Poyang Lake.

Comparison of stationary acoustic monitoring and visual observation of finless porpoises

The detection performance regarding stationary acoustic monitoring of Yangtze finless porpoises Neophocaena phocaenoides asiaeorientalis was compared to visual observations. Three stereo acoustic data loggers (A-tag) were placed at different locations near the confluence of Poyang Lake and the Yangtze River, China. The presence and number of porpoises were determined acoustically and visually during each 1-min time bin. On average, porpoises were acoustically detected 81.7+/-9.7% of the entire effective observation time, while the presence of animals was confirmed visually 12.7+/-11.0% of the entire time. Acoustic monitoring indicated areas of high and low porpoise densities that were consistent with visual observations. The direction of porpoise movement was monitored using stereo beams, which agreed with visual observations at all monitoring locations. Acoustic and visual methods could determine group sizes up to five and ten individuals, respectively. While the acoustic monitoring method had the advantage of high detection probability, it tended to underestimate group size due to the limited resolution of sound source bearing angles. The stationary acoustic monitoring method proved to be a practical and useful alternative to visual observations, especially in areas of low porpoise density for long-term monitoring.

Relative abundance, density and distribution of the harbour porpoise (Phocoena phocoena) along the west coast of the UK

The harbour porpoise(Phocoena phocoena)is the most frequently sighted cetacean in the UK, yet there is a conservation need to assess both abundance and distribution for this species. During May–August, 2002–2004 a boat-based visual survey, employing effort-related line transect methodology was conducted for specified areas of the west coast of the UK. Estimates of relative abundance were made, with full DISTANCE analysis being carried out during 2004 for each of the areas surveyed. A generalized additive model (GAM) was constructed examining porpoise presence in relation to month, position (latitude and longitude), depth and sea surface temperature for all years and for each year of the study individually. Harbour porpoise density showed a significant decrease in the South West, with an increase for West Scotland over the study period, whilst the highest numbers for both Northern Ireland and the Firth of Clyde were recorded in 2003. The porpoise population in the south-west of England was estimated at 163 (67LCI–400UCI) individuals during the months of May and June, 387 (170LCI–877UCI) individuals were present off Northern Ireland during July, 1645 (823LCI–3289UCI) individuals around the Firth of Clyde in July and 3105 (2032LCI–4745UCI) off West Scotland during August and September. The GAM demonstrated that porpoise presence increased around the 100 m depth contour. Whilst further research is required in each of the areas throughout the year, this study provides important information on the distribution and habitat use of the harbour porpoise within UK waters.

Line Transect에서 발견율함수 추정에 사용되는 모델에 따른 상괭이, Neophocaena phocaenoides의 자원개체수 추정

Line transect sampling in a sighting survey is one of most widely used methods for assessing animal abundance. This study applied distance data, collected from three sighting surveys using line transects for finless porpoise that were conducted in 2004 and 2005 off the west coast of Korea, to four models (hazard-rate, uniform, half-normal and exponential) that can use a variety of detection functions, g (x). The hazard-rate model, a derived model for the detection function, should have a shoulder condition chosen using the AIC (Akaike Information Criterion), as the most suitable model. However, it did not describe a shoulder shape for the value of g(x) near the track tine and underestimated g (x), just as the exponential model did. The hazard-rate model showed a bias toward overestimating the densities of finless porpoises with a higher coefficient of variation (CV) than the other models did. The uniform model underestimated the densities of finless porpoise but had the lowest CV. The half-normal model described a detection function with a shape similar to that of the uniform model. The half-normal model was robust for finless porpoise data and should be able to avoid density underestimation. The estimated abundance of finless porpoise was 3,602 individuals (95% CI=1,251-10,371) inshore in 2005 and 33,045 individuals (95% CI=24,274-44,985) offshore in 2004.

Impacts of offshore wind farm construction on harbour porpoises: acoustic monitoring of echolocation activity using porpoise detectors (T-PODs)

Offshore wind farming is a new emerging technology in the field of renewable energies. This study investigates the potential impact of the construction of one of the first major, offshore wind farms (>100 MW) on harbour porpoises Phocoena phocoena by means of acoustic porpoise detectors (T-PODs) monitoring porpoise echolocation activity. The monitoring program was established as a modified BACI (before, after, control, impact) design, with 6 monitoring stations equally distributed between the impact area and a nearby reference area. Mean waiting times, defined as the period between 2 consecutive encounters of echolocation activity, increased from 6 h in the baseline period to 3 d in the wind farm area during the construction. This increase was 6 times larger than changes observed in the reference area. One specific construction activity, involving the ramming and vibration of steel sheet piles into the seabed, was associated with an additional significant increase in waiting time of 4 to 41 h, in both the construction and reference areas. Assuming that echolocation activity is related to harbour porpoise density, the analysis shows that their habitat-use changed substantially, with the porpoises leaving the construction area of the offshore wind farm. Acoustic monitoring from fixed positions provides data with a high temporal resolution, but low spatial reso- lution, which can be analysed at a variety of scales, and can be applied to harbour porpoises and other echolocating cetaceans.

Effects of fine-scale oceanographic features on the distribution and movements of harbour porpoises Phocoena phocoena in the Bay of Fundy

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 295:279-293 (2005) - doi:10.3354/meps295279 Effects of fine-scale oceanographic features on the distribution and movements of harbour porpoises Phocoena phocoena in the Bay of Fundy D. W. Johnston1,2,3,*, A. J. Westgate1,4, A. J. Read1 1Nicholas School of the Environment and Earth Sciences, Duke University Marine Laboratory, 135 Duke Marine Lab Road, Beaufort, North Carolina 28516, USA2Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, California 95039-9644, USA3Present address: National Marine Fisheries Service, Pacific Islands Fisheries Science Center, 2570 Dole Street, Honolulu, Hawaii 96822, USA4Present address: University of North Carolina Wilmington, 601 South College Road, Wilmington, North Carolina 28403, USA *Email: dave.johnston@noaa.gov ABSTRACT: We describe an integrative approach to studying the fine-scale distribution of harbour porpoises Phocoena phocoena in the Bay of Fundy, using satellite telemetry, line transect surveys and remote sensing techniques. Analysis of satellite telemetry data from 6 porpoises (5 male, 1 female) revealed that over the course of a month individuals ranged across large areas (7738 to 11289 km2) but concentrated their movements in small focal regions (August mean = 294 km2, September mean = 252 km2), often proximate to islands, headlands, or restricted channels. Line transect surveys (n = 25 flood tide, n = 20 ebb tide) in the focal region of 2 tagged animals revealed that relative porpoise density (animals km–2) was significantly greater during flood (9.59) than ebb tide phases (1.79). Hydro-acoustic prey surveys revealed aggregations of prey along localized fronts in this region. Remote sensing images indicated the presence of an island wake in the focal region during flood tides, providing an ecological context for our observations of high densities of porpoises. Remote sensing revealed the existence of a headland wake in the focal region of another porpoise near Campobello Island. These results support the hypothesis that regions of enhanced relative vorticity, like island and headland wakes, aggregate prey and represent important foraging habitat for harbour porpoises in the Bay of Fundy. KEY WORDS: Harbour porpoise · Foraging · Fine-scale oceanography · Island wake · Satellite telemetry · Line transects · Remote sensing Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 295. Online publication date: June 23, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

The effect of acoustic harassment devices on harbour porpoises ( Phocoena phocoena) in the Bay of Fundy, Canada

Many salmon aquaculture sites in the Bay of Fundy employ acoustic harassment devices (AHDs) to deter seals from approaching fish pens. These devices may also exclude harbour porpoises ( Phocoena phocoena) from important habitat. To determine the effects of AHDs on harbour porpoises an AHD was deployed experimentally in the Bay of Fundy, Canada. Relative porpoise abundance (visual scans) and porpoise movements (tracked by theodolite) were recorded for separate, daily, 2-h periods in the vicinity of either an active ( n=9) or inactive ( n=7) AHD. Fewer porpoises were sighted during active periods (0.22±0.44, mean±SD ) than inactive periods (2.91±1.29; P<0.05). The mean closest observed approach of porpoises to the AHD during active periods (991±302 m) was significantly greater than during inactive periods (364±261 m; P<0.01). Porpoise density was therefore reduced in the vicinity of active an AHD. These results should be considered before AHDs are deployed in porpoise habitat.

Abundance and distribution of harbour porpoisesPhocoena phocoena in selected areas of the western Baltic and the North sea

An aerial survey of harbour porpoises,Phocoena phocoena, was conducted in June–July 1992 in the western Baltic (Bay of Kiel, the Great Belt, Little Belt, an area north of Fyn) and a coastal area in the North Sea off the island of Sylt. Survey procedures and statistical analysis were identical to those of a similar survey in 1991 and survey results from the two years were compared. The highest density of porpoises was found in the North Sea area, whereas the Bay of Kiel and the Little Belt had low densities. The Great Belt and the area north of Fyn had intermediate densities and the area north of Fyn had a density similar to that found in the same area in 1991. The distribution of the perpendicular sighting distance from the surveys in 1991 and 1992 was identical in locality and dispersal, but gave rise to different estimates of effective search widths. Pod sizes for the 1992 survey were smaller than pod sizes estimated from boat surveys, but were within the range of those for the 1991 aerial survey.

Changes in Growth and Reproduction of Harbour Porpoises, Phocoena phocoena, from the Bay of Fundy

Changes in the growth and reproduction of harbour porpoises from the Bay of Fundy are described by comparing samples collected in 1969–73 and 1985–88. The most pronounced change was an increase in the length of calves, from 92.1 cm (SE 1.6) in 1969–73 to 108 cm (SE 1.3) in 1985–88. Females in 1985–88 attained sexual maturity at a significantly younger age (3.44 yr) and shorter length (143 cm) than females from the older sample (3.97 yr and 147 cm). These changes may be attributable to an increase in prey availability to individual porpoises. This presumed increase in prey availability may have resulted from a decrease in porpoise density caused by incidental mortality in commercial fisheries, a simultaneous increase in prey abundance, or a combination of these factors.

Aerial Surveys for Cetaceans in the Former Akutan, Alaska, Whaling Grounds

Randomized aerial surveys were flown between 26 July and 26 August 1984 to search for cetaceans in two areas of southwestern Alaska: one on both Bering Sea and Pacific Ocean sides of the Aleutian Islands near the defunct Akutan shore-whaling station, which operated from 1912 through 1938, the other overlapping continental slope and shallow continental shelf waters between the Aleutians and the Pribilof Islands. ... Searches covered about 3940 nautical miles (nm), including some 2403 nm of random transects. Sightings were made of gray whales (10 sightings, 14 individuals), fin whales (3, 11), minke whales (1, 1), unidentified beaked whales (1, 6), Dall's porpoises (47, 131), killer whales (8, 26), and harbor porpoises (4, 7). A Fourier series model was used to estimate density of Dall's porpoises as 115 individuals (CV=0.263) per 1000 sq nm on the whaling grounds and 16.6 individuals (CV=0.0) per sq nm in the Bering Sea north of the whaling grounds. These estimates are comparable to those previously reported for the same general areas (97.2 animals per 1000 sq nm, SD=49.5). There were too few sightings of other cetaceans to permit calculation of meaningful density estimates. At least four species of great whales (blue, fin, humpback and sperm) were sufficiently abundant during the first four decades of this century to support significant whaling activities within about 100 sq nm of Akutan (more than 5300 whales were caught during 23 years of whaling, 1912-39). Although previous studies of the fisheries showed a downward trend in catch per unit of effort and an increase in distance traveled to take whales, whales were still being taken at relatively high rates (0.28-0.51 whales per gross catcher day) at the end of the fishery in 1939. Populations of fin, humpback, blue and sperm whales were probably significantly reduced by shore and pelagic whaling conducted widely in the North Pacific since 1939. ...Key words: aerial surveys, cetaceans, Bering Sea, North Pacific Ocean, historical whaling