Sighting Data Research Articles

Bayesian analysis of abundance for binomial sighting data with unknown number of marked individuals

The mark-resight method for estimating the size of a closed population can in many circumstances be a less expensive and less invasive alternative to traditional mark-recapture. Despite its potential advantages, one major drawback of traditional mark-resight methodology is that the number of marked individuals in the population available for resighting needs to be known exactly. In real field studies, this can be quite difficult to accomplish. Here we develop a Bayesian model for estimating abundance when sighting data are acquired from distinct sampling occasions without replacement, but the exact number of marked individuals is unknown. By first augmenting the data with some fixed number of individuals comprising a marked “super population,” the problem may then be reformulated in terms of estimating the proportion of this marked super population that was actually available for resighting. This then allows the data for the marked population available for resighting to be modeled as random realizations from a binomial logit-normal distribution. We demonstrate the use of our model to estimate the New Zealand robin (Petroica australis) population size in a region of Fiordland National Park, New Zealand. We then evaluate the performance of the proposed model relative to other estimators via a series of simulation experiments. We generally found our model to have advantages over other models when sample sizes are smaller with individually heterogeneous resighting probabilities. Due to limited budgets and the inherent variability between individuals, this is a common occurrence in mark-resight population studies. WinBUGS and R code to carry out these analyses is available from http://www.stat.colostate.edu/~jah/software.

Goodness of Fit of Probability Distributions for Sightings as Species Approach Extinction

Estimating the probability that a species is extinct and the timing of extinctions is useful in biological fields ranging from paleoecology to conservation biology. Various statistical methods have been introduced to infer the time of extinction and extinction probability from a series of individual sightings. There is little evidence, however, as to which of these models provide adequate fit to actual sighting records. We use L-moment diagrams and probability plot correlation coefficient (PPCC) hypothesis tests to evaluate the goodness of fit of various probabilistic models to sighting data collected for a set of North American and Hawaiian bird populations that have either gone extinct, or are suspected of having gone extinct, during the past 150 years. For our data, the uniform, truncated exponential, and generalized Pareto models performed moderately well, but the Weibull model performed poorly. Of the acceptable models, the uniform distribution performed best based on PPCC goodness of fit comparisons and sequential Bonferroni-type tests. Further analyses using field significance tests suggest that although the uniform distribution is the best of those considered, additional work remains to evaluate the truncated exponential model more fully. The methods we present here provide a framework for evaluating subsequent models.

Exploring habitat use by cheetahs using ecological niche factor analysis

AbstractUnderstanding the basis of habitat choice having important implications for explaining the distribution of organisms, as well as helping to differentiate between habitats of different quality for effective management. In this study, the effects of sex, age and reproductive status on habitat use patterns of cheetahs Acinonyx jubatus in the Serengeti plains were explored using Ecological Niche Factor Analysis (ENFA). Our results showed that gender and territoriality did not affect patterns of habitat use. However, females tended to be more specialized when they were young than when they were older, displaying a more restricted ecological niche. Likewise, older females without cubs were more specialized than the same adult females with young cubs. This result did not hold for younger females. Altogether, the ENFA approach allowed us to (1) use the large amount of incidental sighting data collected over 12 years on cheetah spatial distribution; (2) identify the importance of reproductive status and age on the relationship between animals and their habitat; (3) further demonstrate that ENFA is applicable in a wide range of situations, including for exploring individual variation in niche definition.

Using sighting records to declare eradication of an invasive species

Summary A major challenge for eradication managers is deciding when a programme can be deemed successful. Regan et al. (2006) were the first to pose this problem within a decision theory framework, minimizing the net expected cost of the decision. The optimal time to declare eradication was based on the number of consecutive surveys in which the species was not found (‘absent surveys’). Their formulation used estimates of detectability and persistence – parameters that are often difficult to estimate – to calculate the probability that the invasive species is still present. Here we use a similar decision‐making framework but instead predict presence based on the pattern of sightings, using a method developed by Solow (1993a) that assumes a constant sighting rate. This method does not require estimates of detectability and persistence. We find the number of absent surveys after which eradication should be declared, using three approaches: a stochastic dynamic program, which finds the exact optimal solution, a rule of thumb, and an approximation. We then compare these results with a method assuming a declining sighting rate. Both the rule of thumb and approximation give results that are close to the exact optimal solution. The rule of thumb with the declining sighting rate method generally gives a larger optimal number of absent surveys. Synthesis and applications. Analysing this problem within a decision theory framework enables us to minimize the expected cost of declaring eradication. By using the more readily available sighting data, we make this framework applicable to a wider range of invasive species. Our approximation is a simple calculation, making it an accessible tool that could be applied by managers of eradication programmes for invasive species.

The importance of accurate landuse/landcover maps for assessing habitat suitability for black bear (<em>Ursus americanus</em>) in the Trans-Pecos region of Texas.

Landcover/landuse layers can be used to map species’ distributions as a potential indicator of habitat selection. We used this approach to assess habitat selection by a small population of black bears ( Ursus americanus ) in the Trans-Pecos of Texas. We compared the accuracy of the Gap Analysis Program (GAP) landcover/landuse layer and a second derived landcover/landuse layer (derived) from LANDSAT images. We then determined habitat selection using sighting data collected from 1901-2003 for both landcover/landuse layers. The derived landcover/landuse layer was 40% more accurate than the GAP layer and there was only 44% agreement between the classifications from the two layers. The discrepancy resulted in different landocover/landuse selections and different predictions of black bear occurrence depending on which layer was used. We recommend managers use derived landcover/landuse layers along with sighting databases to aid management of population when little data on species distribution and habitat use are available.

Assessing age distributions of killer whale Orcinus orca populations from the composition of endogenous fatty acids in their outer blubber layers

Knowledge of the age distributions of killer whale Orcinus orca populations is critical to assess their status and long-term viability. Except for accessible, well-studied populations for which historical sighting data have been collected, currently there is no reliable benign method to deter- mine the specific age of live animals for remote populations. To fill this gap in our knowledge of age structure, we describe new methods by which age can be deduced from measurements of specific lipids, endogenous fatty acids (FAs) and FA ratios present in their outer blubber layers. Whereas cor- relation of wax and sterol esters with age was reasonable for female 'resident' killer whales, it was less well-defined for males and 'transients.' Individual short-, branched-, and odd-chain FAs corre- lated better with age for transients and residents of both sexes, but these single parameter relation- ships were population specific and seemingly varied with long-term diet. Alternatively, a simple, empirical multi-linear model derived from the combination of 2 specific FA ratios enabled the ages of individual eastern North Pacific killer whales to be predicted with good precision (σ = ±3.8 yr), appeared to be independent of individual diet and was applicable to both genders and ecotypes. The model was applied to several less well-studied killer whale populations to predict their age distribu- tions from their blubber FA compositions, and these distributions were compared with a population of known age structure. Most interestingly, these results provide evidence for the first time that adult male transient killer whales appear to have lower life expectancies than do their resident counter- parts in Alaska.

La ballena franca del sur, Eubalaena australis (Desmoulins, 1822) en aguas chilenas: análisis de sus registros desde 1976 a 2008

Sighting data of Eubalaena australis from Chilean waters from 1964 to 2008 were analyzed. During these 44 years, 124 sightings of 232 whales were recorded, i...

An assessment of shore‐based counts of gray whales

AbstractCounts of migrating whales depend on accurate sightings data. In this study, teams of shore‐based observers independently tracked whale pods during the southbound migration of gray whales (Eschrichtius robustus) while a routine (“standard watch”) census was underway. A comparison of sighting records showed that time and location accuracy was limited to 45 s, 3° (magnetic) horizontally, and 0.0057° (0.2 reticles) vertically. Of 242 attempts to track whale groups, 72 failed, 120 were “good tracks,” and 83 qualified as “best tracks” because they had ≥8 sightings/pod, ≥16‐min observation time, and unequivocal matches to sightings in the standard watch during uncompromised visibility. Between paired tracking teams, 39 attempts to conduct concurrent tracks resulted in 21 “good tracks” with complete agreement in 71% of the cases. Of 133 comparisons between trackers and the standard watch, 43% of the pod‐size estimates were the same, but the standard watch overestimated 10% of the pods and underestimated 47%. Thus, according to results from tracking teams, pods recorded as size 1 by observers on the standard watch should be corrected by +0.6; pods of 2 by +0.5; pods of 3 by +0.8; and pods >3 (4–10) were overestimated and should be corrected by −0.6.

Modelling habitat preferences for fin whales and striped dolphins in the Pelagos Sanctuary (Western Mediterranean Sea) with physiographic and remote sensing variables

One of the needs of the Pelagos Sanctuary for the Conservation of Mediterranean Marine Mammals is information on critical habitats for cetaceans. This study modelled habitat use and preferences of fin whales and striped dolphins (the two most abundant species in the area) with the aim of providing this information, using sighting data collected between 1993 and 1999. The study area was divided into a 2′ latitude by 2′ longitude grid. The explanatory variables considered in the models were physiographic variables (mean, range and standard deviation of depth and slope, and distance from the nearest coastline) and remotely-sensed data (Sea Surface Temperature and Chlorophyll- a concentration). The former were calculated for each cell using GIS tools, while the latter were obtained from AVHRR and SeaWiFS sensors. Generalized Additive Models (GAMs) with multidimensional smoothers were used to model the distribution of fin whales and striped dolphins in relation to these variables, and Classification And Regression Trees were used for habitat characterization and predictive models. The GAMs were coupled with Generalized Estimating Equations (GEEs) to account for temporal autocorrelation in the errors and to help ensure model selection was reliable; the QIC statistic was used alongside GEE-based p-values. Bathymetric features were the most valuable predictors in the Pelagos Sanctuary area for both species. Sea Surface Temperature values were indicators of striped dolphin and fin whale presence, with both species showing a tendency to prefer colder waters (21–24 °C). Chl- a levels were selected by the GAM models only for striped dolphins, and with large associated uncertainty; this may be related to the relatively brief period examined (only 2 years) and/or to any functional relationship operating at a different geographical or temporal scale. The boosted classification trees however indicated an importance of Chl- a for both species. The techniques applied to this dataset proved to be valuable tools to describe habitat use and preferences of cetaceans, and the use of the remotely-sensed data can substantially improve the predictions. The results of this study will be used for assessing critical habitats within the Pelagos Sanctuary and will provide information for conservation and management in the Sanctuary.

Factors Affecting the Occurrence and Demographics of Common Dolphins (<I>Delphinus</I> sp.) in the Hauraki Gulf, New Zealand

The common dolphin (Delphinus sp.) is the most frequently observed cetacean species in the Hauraki Gulf, a large shallow body of water on the northeastern coastline of North Island, New Zealand. Herein, we present the first data relating to the occurrence and distribution of common dolphins in this region and assess the possible effects of abiotic parameters on the demographics of this population. The presence of associated marine species is quantified, and differences in the occurrence and demographics of single and multi-species groups are examined. Sightings data were collected between February 2002 and January 2005 during boat-based surveys. We recorded 719 independent encounters with common dolphins, involving 1 to > 300 animals. Dolphin presence was significantly affected by month, latitude and depth. Group size varied significantly by month, season, depth, sea surface temperature (SST) and latitude, and was highly skewed towards smaller groups made up of < 50 animals. Larger aggregations were most frequent during the austral winter when nutrient upwelling typically leads to increased prey availability within the region. Over 70% of groups encountered contained immature animals and 25% of groups included neonates. Calves were observed throughout the year but were most prevalent in the austral summer months of December and January. Month, season, depth, and SST significantly affected group composition. Common dolphins were observed in association with four cetacean and eight avian species, most frequently with the Australasian gannet (Morus serrator) and the Bryde’s whale (Balaenoptera brydei). The distribution of dolphin-only groups differed significantly from that of dolphin-whale groups, with mono-specific groups found on average in waters that were 3.6 m shallower and 3.1oC warmer. The year-round occurrence and social organisation of common dolphins in Hauraki Gulf waters suggest this region is important both as a calving and nursery ground.

Distribution and disease prevalence of feral hogs in Missouri

No attempts have been made to document the distribution of feral hogs (Sus scrofa) in Missouri. Also, antibody prevalence for pseudorabies virus and swine brucellosis have not been reported from Missouri. Our objectives were to characterize the current distribution of feral hogs in Missouri and to determine prevalence and distribution of feral hogs with antibodies against selected important diseases. We collected feral hog sighting data both from the public and Missouri Wildlife Services and Missouri Department of Conservation wildlife biologists. We determined prevalence of antibodies against pseudorabies virus, swine brucellosis, tularemia, and classical swine fever. From 2000 to 2005, the public reported 115 hog sightings statewide. We evaluated 321 feral hog sera for antibody presence from 1993 to 2005. Antibodies against pseudorabies virus and classical swine fever were not detected; however, 1 feral hog had antibodies against swine brucellosis (0.3% prevalence) and 1 feral hog had antibodies against tularemia (1.3% prevalence). Continued disease surveillance is critical to be able to react to any diseases that are found and eliminate them before they become established in feral hog

Interaction between Monk Seals, Monachus monachus (Hermann, 1779), and artisanal fisheries in the Foça Pilot Monk Seal Conservation Area, Turkey

The present study examines some aspects of the interaction between critically endangered Monk Seals Monachus monachus and artisanal fisheries in the Foça Pilot Monk Seal Conservation Area, Turkey, between 1994 and 2002. One to four permanent researchers collected the data on this interaction during seal sighting data enquiries. Interviews with the fishermen provided a total of 448 seal sighting records, of which 142 were collected around the fishing gear. Loligo vulgaris taken from a lure and Conger conger were reported by fishermen for the first time as Monk Seal prey. Of the 142 encounters by Monk Seals with the fishing gear, 6 were of animals entangled by the floating rope of the nets. The establishment of permanent or temporary nofishing zones (in view of the 4-month lactation period) to prevent the entanglement of suckling pups in breeding sites is proposed as an appropriate management practice.

Statistical modeling of North Atlantic right whale migration along the mid-Atlantic region of the eastern seaboard of the United States

North Atlantic right whale feeding and calving behaviors provide predictable spatial and temporal windows in which to conduct surveys and facilitate collection of opportunistic sightings data. Migration behavior makes it more difficult to locate and sample marine animals systematically or to observe them opportunistically. The lack of data creates a critical gap in understanding social behavior; it also hampers the development of mitigation strategies to anthropogenic disturbances such as vessel strikes, acoustic pollution and entanglements. We employ regression analysis to fill this gap to model northerly movements of North Atlantic right whales in the coastal mid-Atlantic migratory corridor of the United States. The modeling suggests an early to mid-March departure from Jacksonville, Florida, with a 30 day departure range; an average travel time of 21–24 days to the tip of Long Island, corresponding to a mean migration/displacement rate of 1.5–1.7 knots (2.8–3.1 km/h). Right whales migrating with calves begin their northern migration several days after right whales migrating without calves. These statistical models can supplement the absence of migratory survey data and help direct and stratify survey efforts in migratory corridors. The combination of rigorous statistical prediction with direct observation also should facilitate the creation of more effective mitigation measures. The methods employed here can be applied to other megafauna elsewhere around the world in many situations where migratory data are sparse.

Baleen whales are not important as prey for killer whales Orcinus orca in high-latitude regions

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 348:297-307 (2007) - DOI: https://doi.org/10.3354/meps07015 Baleen whales are not important as prey for killer whales Orcinus orca in high-latitude regions Amee V. Mehta1,*, Judith M. Allen2, Rochelle Constantine3, Claire Garrigue4, Beatrice Jann5, Curt Jenner6, Marilyn K. Marx7, Craig O. Matkin8, David K. Mattila9, Gianna Minton10, Sally A. Mizroch11, Carlos Olavarría12,17, Jooke Robbins13, Kirsty G. Russell3, Rosemary E. Seton2, Gretchen H. Steiger, 14Gísli A. Víkingsson15, Paul R. Wade11, Briana H. Witteveen16, Phillip J. Clapham11,17 1Boston University Marine Program, 7 MBL Street, Woods Hole, Massachusetts 02543, USA 2Allied Whale, College of the Atlantic, 105 Eden Street, Bar Harbor, Maine 04609, USA 3School of Biological Sciences, Private Bag 92019, University of Auckland, Auckland, New Zealand 4Opération Cétacés, BP12827, Noumea 98802, New Caledonia 5Swiss Whale Society, Via Nolgio 3, 6900 Massagno, Switzerland 6Centre for Whale Research, PO Box 1622, Fremantle, Western Australia 6959, Australia 7New England Aquarium, Central Wharf, Boston, Massachusetts 02110, USA 8North Gulf Oceanic Society, 3430 Main Street, Suite B1, Homer, Alaska 99603, USA 9Hawaiian Islands Humpback Whale National Marine Sanctuary, 726 South Kihei Road, Kihei, Hawaii 96753, USA 10Oman Whale and Dolphin Research Group, PO Box 81, Muscat, Oman 11National Marine Mammal Lab, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, Washington 98115, USA 12Centro de Estudios del Cuaternario (CEQUA), Plaza Muñoz Gamero 1055, Punta Arenas, Chile 13Center for Coastal Studies, PO Box 1036, Provincetown, Massachusetts 02657, USA 14Cascadia Research, 218½ W. 4th Avenue, Olympia, Washington 98501, USA 15Marine Research Institute, Skúlagata 4, PO Box 1390, 121 Reykjavík, Iceland 16University of Alaska Fairbanks, 118 Trident Way, Kodiak, Alaska 99615, USA 17South Pacific Whale Research Consortium, Box 3069, Avarua, Rarotonga, Cook Islands *Email: ameevm@gmail.com ABSTRACT: Certain populations of killer whales Orcinus orca feed primarily or exclusively on marine mammals. However, whether or not baleen whales represent an important prey source for killer whales is debatable. A hypothesis by Springer et al. (2003) suggested that overexploitation of large whales by industrial whaling forced killer whales to prey-switch from baleen whales to pinnipeds and sea otters, resulting in population declines for these smaller marine mammals in the North Pacific and southern Bering Sea. This prey-switching hypothesis is in part contingent upon the idea that killer whales commonly attack mysticetes while they are in these high-latitude areas. In this study, we used photographic and sighting data from long-term studies of baleen whales in 24 regions worldwide to determine the proportion of whales that bear scars (rake marks) from killer whale attacks, and to examine the timing of scar acquisition. The results of this study show that there is considerable geographic variation in the proportion of whales with rake marks, ranging from 0% to >40% in different regions. In every region, the great majority of the scars seen were present on the whales’ bodies when the animals were first sighted. Less than 7% (9 of 132) of scarred humpback whales with multi-year sighting histories acquired new scars after the first sighting. This suggests that most killer whale attacks on baleen whales target young animals, probably calves on their first migration from low-latitude breeding and calving areas to high-latitude feeding grounds. Overall, our results imply that adult baleen whales are not an important prey source for killer whales in high latitudes, and therefore that one of the primary assumptions underlying the Springer et al. (2003) prey-switching hypothesis (and its purported link to industrial whaling) is invalid. KEY WORDS: Predation · Killer whale · Baleen whale · Scars · North Pacific · Whaling Full text in pdf format PreviousCite this article as: Mehta AV, Allen JM, Constantine R, Garrigue C and others (2007) Baleen whales are not important as prey for killer whales Orcinus orca in high-latitude regions. Mar Ecol Prog Ser 348:297-307. https://doi.org/10.3354/meps07015Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 348. Online publication date: October 25, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Damage by monk seals to gear of the artisanal fishery in the Foça Monk Seal Pilot Conservation Area, Turkey

The present study examines the operational interaction between critically endangered monk seals Monachus monachus and artisanal fisheries in the Foça Pilot Monk Seal Conservation Area, Turkey between 1994 and 2002. One to four permanent researchers collected the data on this interaction during the seal sighting data inquiries. Interviews with the fishermen provided 142 direct interactions with monk seals around the fishing gear. Among these encounters damage to fishing gear, including gill nets (53%), trammel nets (37%), longlines (9%) and a lure (1%) was recorded 90 times. However, no difference was found in damage between gill and trammel nets. Although, the damage inflicted by seals per occasion was found to be substantial (maximum 462.5 USD per occasion), the overall annual economic impact on the artisanal fishery was found to be modest. Limitation in soaking time of nets; long-line use instead of nets in MPAs where monk seals survive; and low interest credits to be given to those fishermen who suffer monk seal damage, are proposed as appropriate management practices.

Population characteristics, space use and habitat associations of the seahorse Hippocampus reidi (Teleostei: Syngnathidae)

This paper provides a case study of a threatened seahorse species, Hippocampus reidi, highlighting the importance of using ecological information to assist conservation and management initiatives. Underwater visual sighting data (50 x 2m transect) gathered along the NE, SE and S portions of the Brazilian coast revealed an unequal distribution across localities, perhaps related to harvesting pressure, and a mean density of 0.026 ind.m-2. Our findings suggest some restricted spatial use by H. reidi, which was consistent with its estimated home range, and with re-sighting of specimens. Reproduction was recorded year-round, however productive peaks may exist. Components of habitat structure mostly used as anchoring points were mangrove plants, macroalgae, cnidarians, seagrass, sponges, and bryozoans. Conservation recommendations include: further characterization and mapping of habitats; assessment of availability and condition of microhabitats in selected areas, and studies on dispersal routes during initial life stages.

Survival and Natal Dispersal of Juvenile Snowy Plovers (Charadrius Alexandrinus) in Central Coastal California

AbstractJuvenile survival and dispersal rates are important demographic parameters in predicting the viability of avian populations, but estimates are seldom available because mortality is usually confounded with permanent natal dispersal in analyses of live-encounter data. We used the Barker model for combined captures, recoveries, and resightings to estimate juvenile survival in fledgling Snowy Plover (Charadrius alexandrinus) for the 6.5-to-10.5-month period between fledging at 28 days and 1 April the following year, on the central California coast, for a 16-year period, 1984-1999. By using a large body of year-round sighting data from throughout the species' Pacific-coast range, we estimated true survival and quantified natal dispersal rates and distances. Juvenile survival estimates varied annually between 0.283 ± 0.028 (mean ± SE) and 0.575 ± 0.061 with no trend over the study, and paralleled higher adult survival in our most parsimonious models. In comparison, annual survival of banded chicks from hatching to fledging at age 28 days was 0.285–0.483 (x̄ = 0.382 ± 0.014 SE) for those 16 years. Males were more likely to disperse from Monterey Bay for winter and females were more likely to disperse for breeding. Dispersal distances to breeding sites were usually within 10 km of natal sites (64%) and seldom &gt;50 km (16%). The present study provides the first estimate of true survival for a juvenile shorebird and new information on survival and dispersal rates that will be useful for modeling Snowy Plover population viability. Studies of local winter residents, focused on predator pressure and weather conditions, could further advance our understanding of factors determining Snowy Plover survival.Supervivencia y Dispersión Natal de Juveniles de Charadrius alexandrinus en la Costa Central de California

Prey landscapes help identify potential foraging habitats for leatherback turtles in the NE Atlantic

Identifying key marine megavertebrate habitats has become ever more important as concern increases regarding global fisheries bycatch and accelerated climate change. This will be aided by a greater understanding of the patterns and processes determining the spatiotemporal distribution of species of conservation concern. We identify probable foraging grounds for leatherback turtles in the NE Atlantic using monthly landscapes of gelatinous organism distribution constructed from Continuous Plankton Recorder Survey data. Using sightings data (n = 2013 records, 1954 to 2003) from 9 countries (UK, Ireland, France, Belgium, The Netherlands, Denmark, Germany, Norway and Sweden), we show sea surface temperatures of approximately 10 to 12 degree C most likely indicate the lower thermal threshold for accessible habitats during seasonal foraging migrations to high latitudes. Integrating maps of gelatinous plankton as a possible indicator of prey distribution with thermal tolerance parameters demonstrates the dynamic (spatial and temporal) nature of NE Atlantic foraging habitats. We highlight the importance of body size- related thermal constraints in structuring leatherback foraging populations and demonstrate a latitudinal gradient in body size (Bergmann's rule) where smaller animals are excluded from higher latitude foraging areas. We highlight the marine area of the European continental shelf edge as being both thermally accessible and prey rich, and therefore potentially supporting appreciable densities of foraging leatherbacks, with some suitable areas not yet extensively surveyed.

Noise level correlates with manatee use of foraging habitats

The introduction of anthropogenic sound to coastal waters is a negative side effect of population growth. As noise from boats, marine construction, and coastal dredging increases, environmental and behavioral monitoring is needed to directly assess the effect these phenomena have on marine animals. Acoustic recordings, providing information on ambient noise levels and transient noise sources, were made in two manatee habitats: grassbeds and dredged habitats. Recordings were made over two 6-month periods from April to September in 2003 and 2004. Noise levels were calculated in one-third octave bands at nine center frequencies ranging from 250 Hz to 64 kHz. Manatee habitat usage, as a function of noise level, was examined during four time periods: morning, noon, afternoon, and night. Analysis of sightings data in a variety of grassbeds of equal species composition and density indicate that manatees select grassbeds with lower ambient noise for frequencies below 1 kHz. Additionally, grassbed usage was negatively correlated with concentrated boat presence in the morning hours; no correlation was observed during noon and afternoon hours. This suggests that morning boat presence and its associated noise may affect the use of foraging habitat on a daily time scale.

Pilot cetacean survey of the sub-Arctic North Atlantic utilizing a cruise-ship platform

Using a large passenger cruise-ship (MV ‘Discovery’) as a platform, a cetacean survey was conducted between 1 August and 3 September 2005 across the northern North Atlantic Ocean and back, covering waters between the UK, Iceland, Greenland and Canada. The objective was to collect sightings data for all cetacean species encountered to begin to collate information for a large-scale sightings database. Two observers employed standard-distance sampling techniques and visual observations (naked eye) to scan for cetaceans during daylight hours and favourable weather conditions. Approximately 112 h were spent surveying over 23 d. A total of 13 cetacean species were encountered, with 173 separate sightings recorded, totalling over 2000 animals. The most commonly sighted species were minke whales (Balaenoptera acutorostrata: N=44), Atlantic white-sided dolphins (Lagenorhynchus acutus: N=34, with group sizes of up to 600), and humpback whales (Megaptera novaeangliae: N=31). The distribution of minke whales, Atlantic white-sided dolphins and fin whales was linked to underlying oceanographic variables. Overall patterns of distribution were consistent with our understanding of the summer distributions for the species encountered. The survey highlighted the cetacean diversity of the northern North Atlantic region. Repeat work using this methodology will allow an examination of species' distributions and estimation of their relative abundance.