17 research outputs found
Incorporating Animal Movement Into Distance Sampling
Distance sampling is a popular statistical method to estimate the density of wild animal populations. Conventional distance sampling represents animals as fixed points in space that are detected with an unknown probability that depends on the distance between the observer and the animal. Animal movement can cause substantial bias in density estimation. Methods to correct for responsive animal movement exist, but none account for nonresponsive movement independent of the observer. Here, an explicit animal movement model is incorporated into distance sampling, combining distance sampling survey data with animal telemetry data. Detection probability depends on the entire unobserved path the animal travels. The intractable integration over all possible animal paths is approximated by a hidden Markov model. A simulation study shows themethod to be negligibly biased (\u3c5%) in scenarioswhere conventional distance sampling overestimates abundance by up to 100%. The method is applied to line transect surveys (1999– 2006) of spotted dolphins (Stenella attenuata) in the eastern tropical Pacific where abundance is shown to be positively biased by 21% on average, which can have substantial impact on the population dynamics estimated from these abundance estimates and on the choice of statistical methodology applied to future surveys. Supplementary materials for this article, including a standardized description of the materials available for reproducing the work, are available as an online supplement
Point process models for spatio-temporal distance sampling data from a large-scale survey of blue whales
Distance sampling is a widely used method for estimating wildlife population
abundance. The fact that conventional distance sampling methods are partly
design-based constrains the spatial resolution at which animal density can be
estimated using these methods. Estimates are usually obtained at survey stratum
level. For an endangered species such as the blue whale, it is desirable to
estimate density and abundance at a finer spatial scale than stratum. Temporal
variation in the spatial structure is also important. We formulate the process
generating distance sampling data as a thinned spatial point process and
propose model-based inference using a spatial log-Gaussian Cox process. The
method adopts a flexible stochastic partial differential equation (SPDE)
approach to model spatial structure in density that is not accounted for by
explanatory variables, and integrated nested Laplace approximation (INLA) for
Bayesian inference. It allows simultaneous fitting of detection and density
models and permits prediction of density at an arbitrarily fine scale. We
estimate blue whale density in the Eastern Tropical Pacific Ocean from thirteen
shipboard surveys conducted over 22 years. We find that higher blue whale
density is associated with colder sea surface temperatures in space, and
although there is some positive association between density and mean annual
temperature, our estimates are consitent with no trend in density across years.
Our analysis also indicates that there is substantial spatially structured
variation in density that is not explained by available covariates.Comment: 33 pages 19 figure
Assessing the Environmental Status of the short-beaked common dolphin (Delphinus delphis) in North-western Spanish waters using abundance trends and safe removal limits
Monitoring and assessment of the status of marine mammal populations is a requirement of the European Marine Strategy Framework Directive (MSFD). Due to the difficulty of collecting data in the marine environment and because many populations of these highly mobile species inhabit waters of several Member States, monitoring of marine mammals is particularly challenging. In the present work we have used a 10- year time-series of data collected from multidisciplinary research surveys to estimate common dolphin (Delphinus delphis) abundance and trends in continental shelf waters of the northwest Spanish sub-region. We argue that this approach provides a valuable addition to large-scale dedicated surveys, offering a shorter interval between surveys and hence offering the possibility to track abundance changes at a regional scale. Trends in the number of dolphins present in the study area over the last 10 years show a mean increase of about 9.6% per year, which results in an evaluation of Good Environmental Status for the species in the area using the abundance indicator adopted in the framework of the MSFD. Data obtained from dedicated dual-platform surveys have been used to correct the detection bias in our data collected using single-platforms (attraction toward the observation platform and animals missed on the track-line), to obtain absolute abundance estimates for calculating bycatch limits. The average abundance over the study period was 12831 dolphins [CI 95%; 9025, 18242] calculated with the conventional distance sampling methodology, 4747 [3307, 6816] corrected for attraction and missed animals on the track-line, and 22510 [15776, 32120] corrected only for missed animals on the track-line. The estimated safe bycatch limit for this area calculated from these abundance values were 218 [153, 310], 81 [56, 115] and 383 [268, 546] per year, respectively. Comparing these figures with estimates based on different sources, the percentage of dolphins that die in this study area is higher than the maximum limit allowable under the OSPAR criteria for population mortality adopted as an indicator for the MSFD.Versión del editor3,26
Abundance and distribution of the common dolphin (Delphinus delphis) in the north of the Iberian Peninsula
Common
dolphin
s
(
Delphinus delphis
)
are
one of the most abundant species of small
cetacean in Northeast Atlantic Ocean and the most abundant in Atlantic
shelf
waters
of the Iberian Peninsula. However, the abundance
, distribution and population trends
in the recen
t years
of this species
are
poorly known
,
but such information is needed
to
develop population dynamic models
.
Thus far, the only
absolute
abundance estimate
in the shelf Atlantic waters of the Iberian Peninsula
was
obtained
in 2005
during
the
SCANS
-
II survey.
Along
the north and northwest coast
s
of the Iberian Peninsula
,
t
he
Spanish Institute of Oceanography has
carried
out
annual acoustic survey
s
to estimate
pelagic fish
biomass
for
the last two decades. Since 2007
,
an observer program
for
top
predators
has been integrated in
to
these survey
s
,
collecting
sightings on cetaceans,
seabirds and other species
using line
-
transect
method
ology
.
Common d
olphin
sightings
from 2007 to 201
4
were
analyzed
with Distance software
to
estimate
relative
population size
.
Because attraction to the vessel could
inflate population estimates,
c
ommon dolphin a
bundance was
estimated using a detection function only from
sightings
where no
attraction
were recorded
and
also using Bayesian methods to
combine previou
s data on attraction collected during SCANS
-
II with data collected
from
the
acoustic fish surveys.
D
olphin density estimated with
both
methods
w
as
<
0.3
dolphin
s/
Km
2
,
which
is
similar
to
the
density estimated
by SCANS
-
II
.
T
he Bayesian
framework
allows us
to work with the scarcity and uncertainty of the data
,
particularly
when
obtaining annual estimates.
Because c
etacean sightings
were collected
during
fish
acoustic surveys
,
pelagic fish
abundance
(
e.g. S
ardine
and
Blue whiting
)
, obtained
concurrently to
the sightings,
can be used
,
along with other
environmental
variables
,
to model dolphin
habitat and
to
predict
dolphin
abundance and distribution
Review of potential line-transect methodologies for estimating abundance of dolphin stocks in the eastern tropical Pacific
A twelve-year hiatus in fishery-independent marine mammal surveys in the eastern tropical Pacific Ocean (ETP), combined with a mandate to monitor dolphin stock status under international agreements and the need for reliable stock status information to set dolphin bycatch limits in the tuna purse-seine fishery, has renewed debate about how best to assess and monitor ETP dolphin stock status. The high cost of replicating previous ship-based surveys has intensified this debate. In this review, transect methods for estimating animal abundance from dedicated research surveys are considered, with a focus on both contemporary and potential methods suitable for surveying large areas for dolphin species that can form large, multi-species aggregations. Covered in this review are potential improvements to the previous ship-based survey methodology, other ship-based methods, alternative approaches based on high-resolution imagery and passive acoustics, and combinations of ship-based and alternative approaches.
It is concluded that for immediate management needs, ship-based surveys, with some suggested modifications to improve precision, are the only reliable option despite their high cost. However, it is recommended that a top research priority should be development of composite methods. Pilot
studies on the use of high-resolution imagery and passive acoustics for development of indices of relative abundance to be used in composite methods should be part of any future ship-based survey efforts
Evaluación del estado ambiental de la población de delfín común en el norte y noroeste de la Península Ibérica
El objetivo de las Estrategias Marinas
es permitir el uso sostenible del medio
marino mediante la gestión de las actividades y presiones humanas siguiendo
un enfoque ecosistémico. La
evaluación del estado de conservación de las especies marinas y su monitorización
para determinar si alcanza el Buen Estado Ambiental (BEA) son sus pilares básicos. Para
establecer medidas de gestión que permitan a una población alcanzar el BEA, se debe
estudiar el estado de la misma y el efecto que diferentes niveles de amenazas
antropogénicas pueden tener sobre ella.
La creación de modelos dinámicos permite
estudiar las posibles trayectorias de una población ante diferentes escenarios. La fuente de información biológica más importante
que poseemos es aquella proveniente de los varamientos, que también proporcionan información sobre la causa de la muerte.
El análisis de las muestras de individuos varados nos permite calcular tasas de natalidad, mortalidad, estructura de edad poblacional y el impacto directo o indirecto de las presiones antropogénicas (captura accidental, colisiones con embarcaciones, contaminación, etc.). Asimismo, los patrones observados en los varamientos nos dan
información sobre la tendencia en la abundancia de una especie y sobre
posibles desplazamientos. La abundancia de una población puede ser obtenida mediante
campañas de avistamiento y, dependiendo de la metodología empleada, pueden obtenerse estimas relativas o absolutas. Además, la dieta de los cetáceos nos permite estudiar sus preferencias alimentarias
y el papel que pueden estar jugando en el ecosistema. Los modelos multiespecíficos
(p.ej. Gadget) posibilitan estudiar su interacción con los stocks pesqueros e informar una gestión ecosistémica. En este trabajo se presentan datos preliminares sobre abundancia del delfín común en el N y NW
peninsular, tendencias en la abundancia, parámetros biológicos y su estructura
poblacional, mortalidad natural, pesquera
y ejemplos de puntos de referencia
que permitan determinar si la población
alcanza el BEA
Current and Future Patterns of Global Marine Mammal Biodiversity
Quantifying the spatial distribution of taxa is an important prerequisite for the preservation of biodiversity, and can provide a baseline against which to measure the impacts of climate change. Here we analyse patterns of marine mammal species richness based on predictions of global distributional ranges for 115 species, including all extant pinnipeds and cetaceans. We used an environmental suitability model specifically designed to address the paucity of distributional data for many marine mammal species. We generated richness patterns by overlaying predicted distributions for all species; these were then validated against sightings data from dedicated long-term surveys in the Eastern Tropical Pacific, the Northeast Atlantic and the Southern Ocean. Model outputs correlated well with empirically observed patterns of biodiversity in all three survey regions. Marine mammal richness was predicted to be highest in temperate waters of both hemispheres with distinct hotspots around New Zealand, Japan, Baja California, the Galapagos Islands, the Southeast Pacific, and the Southern Ocean. We then applied our model to explore potential changes in biodiversity under future perturbations of environmental conditions. Forward projections of biodiversity using an intermediate Intergovernmental Panel for Climate Change (IPCC) temperature scenario predicted that projected ocean warming and changes in sea ice cover until 2050 may have moderate effects on the spatial patterns of marine mammal richness. Increases in cetacean richness were predicted above 40° latitude in both hemispheres, while decreases in both pinniped and cetacean richness were expected at lower latitudes. Our results show how species distribution models can be applied to explore broad patterns of marine biodiversity worldwide for taxa for which limited distributional data are available
Assessing the environmental status of the short-beaked common dolphin (Delphinus delphis) in North-western Spanish waters using abundance trends and safe removal limits
Monitoring and assessment of the status of marine mammal populations is a requirement of the
European Marine Strategy Framework Directive (MSFD). Due to the difficulty of collecting data
in the marine environment and because many populations of these highly mobile species
inhabit waters of several Member States, monitoring of marine mammals is particularly
challenging. In the present work we have used a 10-year time-series of data collected from
multidisciplinary research surveys to estimate common dolphin (Delphinus delphis) abundance
and trends in continental shelf waters of the northwest Spanish sub-region. We argue that this
approach provides a valuable addition to large-scale dedicated surveys, offering a shorter
interval between surveys and hence offering the possibility to track abundance changes at a
regional scale. Trends in the number of dolphins present in the study area over the last 10 years
show a mean increase of about 9.6% per year, which results in an evaluation of Good
Environmental Status for the species in the area using the abundance indicator adopted in the
framework of the MSFD. Data obtained from dedicated dual-platform surveys have been used to
correct the detection bias in our data collected using single-platforms (attraction toward the
observation platform and animals missed on the track-line), to obtain absolute abundance
estimates for calculating bycatch limits. The average abundance over the study period was 12,831
dolphins [CI 95%; 9025, 18,242] calculated with the conventional distance sampling
methodology, 4747 [3307, 6816] corrected for attraction and missed animals on the track-line,
and 22,510 [15,776, 32,120] corrected only for missed animals on the track-line. The estimated
safe bycatch limit for this area calculated from these abundance values were 218 [153, 310], 81
[56, 115] and 383 [268, 546] per year, respectively. Comparing these figures with estimates based
on different sources, the percentage of dolphins that die in this study area is higher than the
maximum limit allowable under the OSPAR criteria for population mortality adopted as an
indicator for the MSFD