DOI: 10.5285/a271c430-739f-44a2-9fb0-29404740a625
title: At-sea surveys of seabirds and marine mammals, South Georgia, Antarctica, 2010-2011

description: At-sea surveys of seabirds around South Georgia were undertaken during the austral winter (May to September) in 2010 and 2011. Surveys were conducted in set transects which covered areas primarily targeted by the krill industry, and as well as areas not normally fished. 
Surveys consisted of simultaneous recordings of seabirds and marine mammals on the surface of the water within a continuous 300m wide strip transect on one side of the vessel, and 'snapshots' at 300m intervals. Species, positional, environmental and trip data were recorded for each survey. The aim of the project was to investigate the potential interactions between higher predators and the South Georgia krill fishery. 

These surveys were carried out as part of a wider Overseas Territories Environment Programme (OTEP; SGS701) funded project 'Identifying important and vulnerable marine areas for conservation at South Georgia.' Phil Trathan (BAS) applied for this grant.
description: The methodology relies on the simultaneous recording of seabirds and marine mammals on
the surface of the water within a continuous 300m wide strip transect on one side of the
vessel (the side offering the better viewing conditions) and 'snapshots' at 300m intervals.
The 300m limit of the transect is defined using callipers with the jaw width determined using
Heinemann's (1981) formula.

Seabirds and marine mammals recorded in contact with the water are assigned to one of five
distance bands; A 0-50m, B 50-100m, C 100-200m, D 200-300m, E 300m. This
element of distance sampling within the strip transect enables the observer to assess the
detectability of species at distance and where necessary correct for animals that go
undetected. In the southern oceans, certain species of seabird (notably penguins and diving-
petrels) and marine mammals spend much of the time below the surface and can be difficult
to detect when on the surface. It is therefore important to consider sea state and visibility (for
cetaceans) when analysing sightings of these species. With sufficient data, more than 1,000
animals recorded, species specific correction factors can be calculated to compensate for the
lower detection rates in the outer bands of the transect. Assuming that seabirds and marine
mammals do not alter their behaviour in response to the survey vessel and all animals in
bands A and B are detected, the number of animals recorded in each transect band should
occur in the ratio of 1:1:2:2 (A:B:C:D). However, in practice fewer than expected birds are
generally recorded in the outer bands (C and D).

In addition to the continuous strip transect, a second count of flying birds is made using a
'snapshot' technique. The snapshot is designed to give an instantaneous count of flying birds
and therefore standardise the effort devoted to recording flying birds and birds on the water's
surface. The timing of the snapshot is dictated by the speed of the vessel and occurs
whenever the vessel travels 300m.

Records of all birds and marine mammals recorded in transect can be used to calculate the
density of animals (animals per km 2 ) for any given area. Animals recorded 'out of transect'
can be combined with those recorded 'in transect' to calculate the number of animals
recorded per km travelled. This is useful for infrequently encountered species, like cetaceans,
that are often sighted 'out of transect.''

Full details of the survey method can be found in Tasker et al. (1984), Webb and Durinck
(1992), Buckland et al. (2001) and Camphuysen (2004).

All animals observed on surveys are identified to species level, where possible. It is important
to be certain of species identification. Where there is doubt animals are recorded as such (e.g.
if the is doubt whether a bird was a prion or blue petrel record it as BP/Pr, do not guess.
However, some species are particularly difficult to identify to species level, so most prions,
diving-petrels and Mesoplodon beaked whales are not specifically identified.

For each record age, sex, plumage type, distance from the survey base, direction of flight, behaviour and
associations between species are noted whenever possible and appropriate.
As has been noted elsewhere (e.g. Griffiths 1982), the tendency for some species to follow
ships can lead to biases in the study of seabird distributions. As a rule, seabirds that are
obviously associating with the survey base are omitted from the survey. This may have led
to under-recording of some species, particularly giant petrels and Cape petrel. However, with
experience it is still possible to record naturally occurring aggregations of these species.

In addition to seabird and marine mammal data, routine environmental and positional data are
collected during surveys. Environmental data collected includes wind strength and direction,
sea state, precipitation, sun strength and direction, cloud cover and visibility. These variables
affect the detectability of many species and this data allows the relationship between survey
conditions and the numbers and species of seabirds and marine mammals recorded to be
examined. For example, the detection rates of seabirds on the sea are likely to decrease as sea
state increases. Consequently, surveys were rarely conducted in sea states of 6 or above.
Positional data; the ship's position, course and speed, are recorded at the start and end of each
observation period. Additionally, mid-points (position, speed and course) are recorded
whenever the vessel significantly changes course or speed. If the observer can predict when a
significant course change will take place (for example, at the end of a transect) it is advisable
to stop observing for a few minutes until the vessel completes it's manoeuvre (remembering
to take the relevant end and start positions). A good survey is conducted on a set, know,
course and speed. Positional data allows the interpolation of intermediate positions along the
survy track, which are linked to higher predator observations. Sightings can be grouped into
'bins' according to location, which enables observations to be effort related (usually
expressed as 'birds per km 2' or 'birds per km travelled').

Data is usually recorded in set time periods (usually 5 or 10 minute-periods) which are then
assigned to larger units of area (usually on the scale of the 1/4 ICES square, 15'Latitude by
30'Longitude). However, during the current project, data are recorded on the scale of the
snapshot (the highest resolution possible). This enables every observation to be linked with a
300x300m area of ocean and allows the distribution of animals along the priority transects to
be better determined.

Species, positional, environmental and trip data are recorded on specially designed forms and
transcribed from data sheets onto computer.
description: Before commencing an observation period, the observer should assess the suitability of
conditions for recording higher predator observations.
 
- Firstly, what is the survey vessel's current activity? If engaged in fishing or other
sampling, it is not possible to conduct a meaningful survey. Ideally, the vessel should
be steaming on a set course at a constant speed (greater than 5 knots, ideally 10+
knots) before the starting observations.

- Environmental conditions influence the detectability of many species and therefore an
assessment of the prevailing conditions is required. Wind speed and direction, sea
state, swell height and direction, cloud cover, precipitation and the intensity of sun
glare can all influence the quality of the data collected. All these variables are
recorded prior to the start of each observation period and whenever they change
during an observation period. If conditions are unacceptable (sea state greater than 6,
heavy snow or thick fog) do not start surveying.

- Environmental conditions (particularly wind direction and sun glare) will determine
which side of the vessel is observed. The observer should stand outside, where vision
is unobstructed, the bridge wings of the FPV Pharos SG provide an adequate viewing
position.

- Following the commencement of the survey, the observer should continuously scan
the 300m wide transect to a distance of at least 300m ahead of the vessel. Any
animals present should be detectable with the naked eye, subsequent use of binoculars
can be useful to confirm species identification, behaviour or prey type. For each
observation, an almost instantaneous assessment of the species, number, behaviour,
distance from the vessel's track or direction of flight and whether the animal is 'in
transect' or not must be made and the information recorded on the species form. It is
important to do this as quickly as possible to allow the observer to refocus on
detecting the next animal to be recorded.

- Each record is assigned a time, which relates to a particular 300x300m area of ocean
the highest resolution possible. To aid data entry, it is recommended to use the
snapshot time for all animals associated with a particular snapshot. The snapshot time
is dependant on the ship's speed, The use of a watch with a repeatable countdown function is a useful way of
alerting the observer when a snapshot is due.


- Seabirds and marine mammals recorded sitting on the water are assigned to one of
five distance bands (A 0-50m, B 50-100m, C 100-200m, D 200-300m, E 300m),
which run parallel to the ship's track and are measured from the side of the ship. With sufficient data, this allows Correction Factors to be calculated for animals that are undetected in the Bands furthest from the ship's track.

- All behaviour indicative of attempted or successful foraging is recorded using a
combination of movement, searching and foraging codes adapted in part from Harper
et al. (1985) and Camphuysen and Garthe (2004). It was also attempted to identify
prey items, although this was rarely possible.

- For flying birds, the direction of travel should be assessed and recorded. Whether a
bird is recorded as 'in transect' or not is determined by the 'snapshot'. The timing of
snapshots is determined by the ship's speed and are spaced at 300m intervals along
the transect. For example, a vessel travelling at 10knots moves 300m every
60 seconds and therefore 'snapshots' are taken at 60 second intervals. If a flying bird
is within the transect at the time of a snapshot, that record is classed as 'in transect'.
Under most conditions, birds that pass through the transect between snapshots are still
recorded (as 'out of transect'). These records can help determine the age structure of
the population, moult cycles, migratory routes and increase the likelihood of
recording rare species.

Problems and recommendations
- Observers used to collect higher predator data over the relatively short periods covered by
research cruises should have prior experience of seabird and marine mammal surveys in the
southern hemisphere. It is possible for most people to learn the methodology and become
competent observers over a period of several weeks but data collected in the early days or
weeks of the cruise would be unreliable.

- An assumption of both the snapshot and of distance sampling methods is that animals are
detected before they react to the presence of the survey platform. However, for most air
breathing marine predators this assumption is poor. Many species of flying seabird for
example are attracted to and follow ships. This tendency is especially prevalent in the
Procellariiformes (Hyrenbach 2001), the dominant group in the Southern Ocean. Further
complications occur with diving species, such as penguins and marine mammals, which may
move towards or away from the survey vessel whilst submerged. For cetaceans at least this
difficulty has recently been surmounted by the use of double platform surveys (Buckland et
al. 2004). These rely on a second team of observers, who track an animal's movements in
response to the approach of the survey ship. The rate of avoidance or attraction can then be
modelled and used to correct the primary observers' results. Similar methods have recently
been employed to investigate the avoidance of approaching ships by flying birds (e.g.
Borberg et al. 2005). A number of more subjective strategies have also been suggested for
identifying which flying birds are following the survey ship, so that these individuals are not
over recorded (e.g. Spear et al. 2004). Despite these complications, abundance estimates of
some species of flying seabirds based on at-sea data accord with estimates from colony
censuses (Clarke et al. 2003). Furthermore, for the purposes of studies of the distribution of
marine predators versus prey or for investigating the effects of environmental correlates,
relative rather than absolute abundance may be used (e.g. Ryan Cooper 1989, Ainley et al.
1993, van Franeker et al. 2002, Woehler et al. 2003, Chapman et al. 2004, Littaye et al.
2004). The assumption implicit in studies taking this approach is that each species reacts in a
consistent manner to approaching survey vessels.
In addition, it is increasingly recognised that considerable insights can be gained by recording
the behaviour of higher predators at sea, for example to identify foraging areas (Veit 1999,
Camphuysen Garthe 2004).

- It is clear that there are some issues regarding the associations between flying birds and the
survey base. It is relatively easy to disregard those animals that persistently form close
associations with the vessel, Cape and giant petrels are particularly notable ship associates.
However, most species of flying birds will associate with the vessel to some extent and
whether a bird is recorded or not can become subjective. Throughout this project, the use of
consistent methodology and observers will help to standardise the recording procedure. A
detailed description of the method used will help to maintain consistency on future cruises.
- Ideally, two experienced observers should be used in tandem. Working in shifts, this would
allow continuous coverage even in mid-summer when day length can be 18 hours. It would
also allow for a more robust assessment of observer error and ensure standardised
methodology.

- At times the density of animals encountered can be over whelming. To maintain the quality
of the data collected it is possible to switch from recording all animals to just recording those
'in transect'. This would require a new Trip Key whenever the method changes