SCANS-II Monitoring cetaceans

Transcription

1 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

2 Outline of presentation Background SCANS-II monitoring objectives Difficulties in monitoring cetaceans Methods available Evaluation of methods (power & cost benefit) Summary and recommendations

3 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

4 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.

5 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

6 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.

7 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.

8 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

9 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

10 Monitoring using visual methods Ship survey Aerial survey Platform of opportunity Land observations Photo-identification

11 Ship surveys - Abundance (line transect) - Distribution - Combine with oceanography and prey abundance - Combine with towed hydrophones

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

13 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

14 Photo-id - Individual identification Abundance (mark-recapture) Movements Survival rates Population growth

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

16 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

17 Porpoise click detector (T-POD) A powerful tool to detect changes in abundance within smaller areas 200m 100m 1.2% 1.0% Effect of a wind farm on porpoises PPM 0.8% 0.6% 0.4% 0.2% 0.0% Baseline Construction Operation 1 Operation 2

18 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

19 Harbour porpoises Important habitats from satellite tracking 2 0'0"E 3 0'0"E 4 0'0"E 5 0'0"E 6 0'0"E 7 0'0"E 8 0'0"E 9 0'0"E 10 0'0"E 11 0'0"E 12 0'0"E 13 0'0"E 14 0'0"E 15 0'0"E 16 0'0"E Norway 58 0'0"N Sweden 57 0'0"N 56 0'0"N Denmark 55 0'0"N Legend 54 0'0"N Kernel home range 25% 50% 75% 90% Danish border Kernel home range from 58 harbour porpoises Kernel home range fra 58 satellitmærkede marsvin Germany Kilometers 3 0'0"E 4 0'0"E 5 0'0"E 6 0'0"E 7 0'0"E 8 0'0"E 9 0'0"E 10 0'0"E 11 0'0"E 12 0'0"E 13 0'0"E 14 0'0"E 15 0'0"E

20 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.

21 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

22 Achievements during SCANS-II in relation to monitoring New data were collected and analysed to allow comparison of potential methods for monitoring

23 Effort and efficiency for visual and acoustic monitoring in the North Sea Regarding day length and weather Acoustic (seastate 0-5) Visual (daylight and SS 0-2) Hours in a day Jan April July October 1 Weather data taken from Sailing Directions for the North Atlantic Ocean Defence Mapping Agency

24 Acoustic encounter rate by sea state Combined data for all seven SCANS-II vessels (error bars show the standard error of the mean)

25 Effort and detection rates during SCANS-II SCANS II Effort (km) No. of sightings Detection rate Acoustic ship surveys ,024 Visual ship surveys ,024 Aerial surveys ,034 Detection rates are similar - but methods not necessarily equally good for monitoring

26 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

27 Relationship between effort and total CV for two methods Acoustic Seabird dependent errors independent errors

28 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 Acoustic Seabird independent errors dependent errors

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

30 Relationship between effort and power for two methods Acoustic Seabird

31 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.

32 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

33 Cost-benefit of the different methods July Daily rental rate (Euro) Observer salary Hours on effort Euro/hour on effort Euro/km on effort SCANS-II visual ship , Visual ship , Acoustic towed Platform of opportunity , Aerial T-POD station

34 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

35 Thanks! To everyone who has contributed to SCANS-II