SCANS-II Monitoring cetaceans

Per Berggren, Jonas Teilmann, David Borchers, Louise Burt, Doug Gillespie, Jonathan Gordon, Phil Hammond, Kelly Macleod, Russell Leaper, Meike Scheidat, René

Swift and Arliss Winship

Outline of presentationBackground

SCANS-II monitoring objectives

Difficulties in monitoring cetaceans

Methods available

Evaluation of methods (power & cost benefit)

Summary and recommendations

Outline of presentation

Why monitor cetaceans?

SCANS-II monitoring objectives

Two types of monitoring; species/population and regional

Difficulties in monitoring cetaceans

Methods available

Comparison between methods

Conclusions

Why monitor cetaceans?

EU member states are obliged to undertake surveillance of the conservation status of species listed in Annex II of the Habitats Directive (all cetaceans) as well as designate special areas for conservation (Natura 2000 SACs) for species.

SCANS-II monitoring objective

Develop recommendations for the best monitoring method to be used mainly for:

- harbour porpoise

- bottlenose dolphin

- common dolphin

so that trends in abundance in time and space can be determined between major decadal surveys

Two types of monitoring

1) Population monitoring to monitor the status of a whole species / population

2) Regional monitoring of a specified region used by a sub-set of the population

Monitoring would mainly address inter-annual changes. But there is also need to address seasonal patterns of distribution if the population range changes, if the monitoring region or time changes, or if only part of the range is monitored.

Define objective for monitoring

1) Example of criteria for Population Level Monitoring:

- detect if relative abundance of a population changes by more than 10% per year over a 6 year period (reporting period according to the Habitats Directive).

2) Example of Regional Level Monitoring:

- monitor the status of relative abundance between and within years in e.g. national waters or important areas like SACs.

Available methods for monitoring

1. Visual surveys; ship, aircraft or land

2. Acoustic surveys; towed hydrophones

3. Stationary acoustic systems; e.g. T-POD

4. Photo-identification

5. Satellite telemetry

6. Density surface modelling

Cetaceans difficult to observe at sea

Difficulties- Occur in low densities & highly mobile- Difficult to see and follow at the surface- Majority of time spent diving

Therefore we need sophisticated methods- Visual or acoustic surveys (low temporal resolution)- Stationary acoustic systems (low spatial resolution)- Telemetry (inter-individual variation)

A combination of methods is often needed to determine changes in abundance, density and movements

Monitoring using visual methods

� Ship survey

� Aerial survey

� Platform of opportunity

� Land observations

� Photo-identification

Ship surveys

- Abundance (line transect)- Distribution- Combine with oceanography

and prey abundance- Combine with towed

hydrophones

Aerial surveys

- Abundance (line transect)- Distribution- Cover large area in short time will reduce bias from animal movements

Platform of opportunity

� Observations from ships that mainly have other purposes like ferries or research surveys– abundance (line transect)– distribution– little control on spatial coverage

Photo-id - Individual identification

Abundance (mark-recapture)MovementsSurvival ratesPopulation growth

Land based observations

Information on trends in relative abundance for restricted areas (e.g. narrow straits)

Acoustic methods

Moving (vessel) platforms or fixed platform (e.g. T-POD)

- relative abundance (possibly absolute in future)- less/or not weather dependent - not dependent on daylight- long or continuous data series- potentially diurnal and annual variation

Porpoise click detector (T-POD)A powerful tool to detect changes in abundance within smaller areas

100m200m

0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

1.2%

Baseline Construction Operation 1 Operation 2

PP

M

Effect of a wind farm on porpoises

Satellite telemetry

� Advantages� Details on single individuals� Migration routes� Important habitats

� Limitations� Individual variation - depending on species� Takes many animals to make conclusions at population level

Harbour porpoises –Important habitats from satellite tracking

2°0'0"E

3°0'0"E

3°0'0"E

4°0'0"E

4°0'0"E

5°0'0"E

5°0'0"E

6°0'0"E

6°0'0"E

7°0'0"E

7°0'0"E

8°0'0"E

8°0'0"E

9°0'0"E

9°0'0"E 10°0'0"E

10°0'0"E

11°0'0"E

11°0'0"E

12°0'0"E

12°0'0"E

13°0'0"E

13°0'0"E

14°0'0"E

14°0'0"E

15°0'0"E

15°0'0"E

16°0'0"E

54°0'0"N

55°0'0"N

56°0'0"N

57°0'0"N

58°0'0"N

0 50 10025 KilometersKernel home range fra 58 satellitmærkede marsvin

Legend

Kernel home range25%

50%

75%

90%

Danish border

Kernel home range from 58 harbour porpoises

Denmark

Norway

Sweden

Germany

Density surface modelling

� Data from any of the previous methods can be used to model density and to predict animal density in any part of the surveyed area.

� Spatial modelling does not rely on a randomised survey design provided there is sufficient survey coverage.

� Estimates of abundance can potentially be obtained from data collected on platforms of opportunity (e.g. research vessels).

� May explain environmental factors affecting animal density.

Important considerations before choosing monitoring methods

� Choose the species

� Choose whether to monitor population or region

� Define the population

� Define monitoring objectives

� Conduct statistical power analysis to find the best

method to meet monitoring objectives

� Consider logistics for the area to monitor

� Conduct a cost benefit analysis

Achievements during SCANS-II in relation to monitoring

New data were collected and analysed to allow comparison of potential methods for monitoring

Effort and efficiency for visual and acoustic monitoring in the North Sea

Regarding day length and weather1

1Weather data taken from Sailing Directions for the North Atlantic Ocean Defence Mapping Agency

0

5

10

15

20

25

Jan April July October

Hou

rs in

a d

ay

Acoustic (seastate 0-5)

Visual (daylight and SS 0-2)

Combined data for all seven SCANS-II vessels (error bars show the standard error of the mean)

Acoustic encounter rate by sea state

0,03454315800Aerial surveys

0,02448119900Visual ship surveys

0,02470529348Acoustic ship surveys

Detection rate

No. of sightings

Effort (km)SCANS II

Effort and detection rates during SCANS-II

Detection rates are similar - but methods not necessarily equally good for monitoring

Comparison between methods

� Each method is associated with variation (both in sampling and due to survey conditions) and this affects the Power of the method to detect changes in relative abundance.

� Since we have simultaneous data for both the indices (detection rates) and the density we can estimate the variation for the indices

� Using the information on variation we can then calculate the Power of each method

AcousticSeabird

independent errors

dependent errors

Relationship between effort and total CV for two methods

AcousticSeabird

independent errors

dependent errors

Relationship between effort and power for two methods to detect a 5% per annum decline in abundance over a

10 year period with annual monitoring

AcousticSeabird

Relationship between effort and sampling CV for two methods using only one vessel

AcousticSeabird

Relationship between effort and power for two methods

Other Methods

� Aerial surveys: – Power calculations relative to absolute abundance

not finished yet.

� T-PODs: – Potential to estimate trend directly– Need adequate spatial coverage.– Inadequate data available to make Power

analyses from absolute abundance.

Logistic considerations

� Visual ship surveys– Weather dependent (≤ sea state 2)– Shallow water restrictions (5 m)

� Acoustic surveys– Depend on willingness to survey 24 hours– Shallow water restrictions (10 m)

� Aerial surveys– Limited availability of usable aircrafts

– Constant standby for good weather (≤ sea state 2)

� Platforms of opportunity– Dependent on where the ship goes

– Weather dependent (≤ sea state 2)

� Stationary acoustic monitoring– Restrictions in placement

– Limited range

Cost-benefit of the different methods

2242215T-POD station

61100520003500Aerial

102005,510000Platform of opportunity

153002010005000Acoustic towed

5511005,510005000Visual ship

12024005,580005000SCANS-II visual ship

Euro/km on effort

Euro/hour on effort

Hours on effort

Observer salary

Daily rental rate (Euro)July

Summary and recommendations

� Towed acoustic, visual platforms of opportunity, visual, aerial dedicated surveys and stationary acoustic can be used for monitoring

� Sea state and day length negatively affect visual data collection to a much higher extent than acoustic methods

� Which method provides more statistical power depends on assumptions made about dependency of the errors

� Using the same platform and survey conditions reduces variation and improves Power

� Aerial surveys, towed acoustic surveys and platforms of opportunity are far cheaper but this needs to be related to the Power of each method

Thanks!To everyone who has contributed to

SCANS-II