Marine Mammal and Turtle Division Southwest Fisheries Science Center

Transcription

1 Marine Mammal and Turtle Division Southwest Fisheries Science Center Data Collection Mandates, Theory, and Procedures Jessica V. Redfern

2 Mission and Mandates

3 Marine Mammal and Turtle Division Monitor and assess the status of marine mammals and turtles in U.S. waters or regions where the U.S. has a vested interest to provide a scientific basis for management advice Mandates: ESA MMPA IDCPA

4 Marine Mammal and Turtle Division

5 Marine Mammal and Turtle Division 16 surveys over 21 years 17,000 cetacean sightings 400,000 linear km of surveys

6 Eastern Tropical Pacific 21 million km 2 High Seas and waters of 12 Countries

7 Eastern Tropical Pacific Unique association of dolphins, tuna, and seabirds Reasons for the association are unknown Possibilities include: Prey availability Predator avoidance NOAA NMFS SWFSC PRD

8 Eastern Tropical Pacific Fishermen use easily spotted dolphins and seabirds to find tuna NOAA NMFS SWFSC PRD

9 Eastern Tropical Pacific Purse-seine fishing operations NOAA NMFS SWFSC PRD

10 NUMBER OF DOLPHINS KILLED (THOUSANDS) Eastern Tropical Pacific 600 Results DOLPHIN BYCATCH of purse-seine fishing on dolphins IN ETP TUNA FISHERY Incidental Dolphin Mortality: Total for all dolphins Over 6 million dolphin deaths in the nets since the inception of the fishery in the late 1950 s Gerrodette 2002

11 Eastern Tropical Pacific These unprecedented levels of mortality: Were one of three drivers in the creation of the U.S. Marine Mammal Protection Act Resulted in the Southwest Fisheries Science Center conducting 10 surveys to estimate dolphin abundance and trends - Strong survey protocols in response to a litigation-heavy issue (e.g., helicopter to calibrate school size estimates, survey encompassing a broad range of habitats for focal taxa) Gerrodette et al Gerrodette et al. 2008

12 Line Transect Basics

13 Strip-Transect Surveys

14 Strip-Transect Surveys Assumes all individuals within the strip are counted Strip width must be small enough to ensure that all individuals are detected May result in a high number of missed observations because the strip width is typically small

15 Strip-Transect Surveys Density of individuals: n D = (L 2 w ) n is the number of animals counted Number of individuals: N = A D where A is the size of the study area

16 Line-Transect Surveys

17 Line-Transect Surveys Assumes that all schools on the transect are detected Assumes that the distance to each school is accurately estimated It is important that the school does not approach or avoid the survey platform before the distance is estimated

18 Line-Transect Surveys We can calculate the perpendicular distance from the transect to a school using the angle and distance to the school: d = r sin θ Transect The angle can be estimated by eye or by using a horizontal angle board The distance can be estimated by eye or using a reticle scale A reticle scale is a series of equally spaced horizontal lines that are inscribed on binocular eye pieces To measure the distance to an animal in the water, the upper most reticle is placed at the horizon and the number of reticles to the animal is counted

19 Line-Transect Surveys To calculate the radial distance, we need the distance to the horizon H = 2 e h + h 2 e is the radius of the earth in kilometers (6371km) h is the binocular height above the sea surface in kilometers Transect

20 Line-Transect Surveys The radial distance is r = e + h sin α + ρc e 2 [ e + h cos(α + ρc)] 2 ρ is reticle reading (number of reticles from the horizon to the animal) C is the reticle conversion factor in radians α is atan(h/e) Transect The reticle conversion factor for the Fujinon 7x50 power FMT series binoculars is estimated to be To convert degrees per reticle to radians per reticle, multiply by π/180

21 Line-Transect Surveys An Excel spreadsheet to calculate the radial and perpendicular distance to a sighting

22 To estimate density Line-Transect Surveys Start with a histogram of the number of schools detected at different perpendicular distances from the transect

23 Line-Transect Surveys The histogram is rescaled so that the area of the bars in the histogram sums to one The detection function is fit to the rescaled data

24 Line-Transect Surveys The effective strip width (ESW) is the distance at which the area above the curve (number of schools missed within the ESW) is equal to the area below the curve (number of schools detected beyond ESW)

25 Line-Transect Surveys Density of schools: n D schools = (L 2 ESW) n is the number of schools counted Density of individuals: n E(s) D animals = (L 2 ESW) E(s) is the mean group size

26 Resources Line-Transect Surveys Buckland, S. T., D. R. Anderson, K. P. Burnham, J. L. Laake, D. L. Borchers, and L. Thomas Introduction to Distance Sampling: Estimating abundance of biological populations. Oxford University Press, Oxford. Thomas, L., S. T. Buckland, K. P. Burnham, D. R. Anderson, J. L. Laake, D. L. Borchers, and S. Strindberg Distance sampling. Pages in A. H. El-Shaarawi and W. W. Piegorsch, editors. Encyclopedia of Environmetrics. John Wiley & Sons, Ltd, Chichester.

27 Line-Transect Surveys 1. Histograms of perpendicular distances that indicate data collection problems Animals moving away from a ship before being detected Inadequate views of the transect in an aerial survey

28 Line-Transect Surveys 2. Histograms of perpendicular distances that indicate data collection problems Animals moving toward a ship (e.g., bow riders) before being detected Observers rounding to zero for animals close to the transect Observers searching the transect more than other areas

29 Line-Transect Surveys It is difficult to fit a detection function to these histograms Many shapes are possible Each shape results in a different estimate of abundance Solving these problems can be challenging Starting point Each observer systematically scans their entire area Animals are detected as early as possible

30 Line-Transect Surveys Survey Design Goal: Estimate abundance in a specific geographic location for a fixed time period Requirements Transects must be a random sample of the study area The location of individuals or groups must be independent of the transects Approach Use randomly placed transects Use a random start point for a systematic grid of transects

31 Line-Transect Surveys Survey Design Marine mammal challenges Highly mobile May be impossible to survey the entire range of a species Approach Draw the study area boundary and design survey time periods to ensure that movement is random with respect to the transects

32 Passing versus closing mode Passing mode The survey platform does not leave the transect Observers identify species and estimate group size from the transect Closing Mode Line-Transect Surveys Survey Design Normal survey protocols are stopped after a school is sighted (e.g., observers go off effort) The survey platform makes a close approach to the school before species are identified and group size is estimated

33 Passing versus closing mode Trade-offs Line-Transect Surveys Survey Design Species identification and group size estimation are improved on closing mode surveys Encounter rates may be underestimated on closing mode surveys Schwarz, L. K., T. Gerrodette, and F. I. Archer Comparison of closing and passing mode from a line-transect survey of delphinids in the eastern Tropical Pacific Ocean. J. Cetacean Res. Manag 11:

34 Passing mode protocol options SWFSC Line-Transect Surveys Survey Design Only the observer that made the sighting identifies the species and estimates group size Antarctic minke whale surveys One group of observers searches for animals while a second group is responsible for identifying the species and estimating group size Oceanographic surveys off southern California Species identifications and group size estimates are generally made by the lead observer, but are agreed on by all observers

35 SWFSC Data Collection Procedures Closing Mode

36 Resources SWFSC Procedures Kinzey D, Olson P, Gerrodette T (2000) Marine mammal data collection procedures on research ship line-transect surveys by the Southwest Fisheries Science Center. In. Southwest Fisheries Science Center, La Jolla Barlow J, Gerrodette T, Forcada J (2001) Factors affecting perpendicular sighting distances on shipboard line-transect surveys for cetaceans. Journal of Cetacean Research and Management 3: Gerrodette T, Forcada J (2005) Non-recovery of two spotted and spinner dolphin populations in the eastern tropical Pacific Ocean. Mar Ecol Prog Ser 291:1-21

37 Platforms Vessel size = 50-65m Observations are made from the flying bridge Height above sea surface = 10 to 15m David Starr Jordan McArthur II Length 52.1 m Obs height 10.7 m Length 68.3 m Obs height 15.2 m

38 Platforms Aerial surveys = used to calibrate densities estimated from ship surveys in the nearshore environment

39 Equipment Three pairs of pedestal-mounted, power binoculars on the flying bridge Pairs of 7 50 power handheld binoculars available All binoculars have a reticle scale inscribed on the eye pieces

40 Azimuth rings Equipment Mounted on the pedestals of the binoculars Kept near data recorder/observer Resolution = 1 increments

41 WinCruz Freely available Training session later in the workshop Data Recording

42 Fields recorded Data Recording Beginning and end of effort Observers on effort and their positions Viewing conditions Beaufort sea state, swell height, swell direction, and wind speed Navigation information Ship course and speed Weather Rain/fog, horizontal and vertical sun angle, wind direction, and visibility

43 Fields recorded Sightings Sighting number Bearing Reticle Observer Cue Sighting method Data Recording By eye or using power or 7 50 power binoculars Course, speed, and behavior of the school Can indicate whether a school is approaching or avoiding the survey platform

44 Sighting form Data Recording Drawing of each species Notes about the features that were used to identify the animals

45 Log books Data Recording Group size estimates Notes about sightings

46 Observers and effort This figure is taken from Kinzey et al. (2000)

47 Observers and effort Data Recorder / 7X50 Binoculars power binoculars Ship speed = 18.52km/hr (10knots) Ship can deviate up to 30 from the transect to avoid glare or rain Six observers Observers change positions every 40 minutes Shifts = 2 hours on watch followed by 2 hours of rest

48 Observers and effort Independent observers Sightings are not announced until they are 90 abeam Sightings used to estimate the number of schools that are missed

49 Sightings Sightings within 0.1 reticles are recorded The difference between 0.0 reticles and 0.1 reticles can be two miles (25x150 power binoculars, 10m high platform) Record bearing and reticle to the first animal seen Estimating the distance to the center of a school may not be possible because you might not see other individuals right away Sightings are only entered when an animal is seen Cues are not recorded Approach sightings that are made within 3nmi perpendicular to the transect

50 Sightings Identify species using field-observable morphological characteristics Species identification is decided by consensus among the observers Sightings may contain more than one species

51 Sightings It can be difficult to distinguish between a single sighting with multiple subgroups and separate sightings A single sighting is considered a school of animals that is traveling together with only temporary separations of subgroups Separate sightings are schools that will likely remain apart during the time needed to identify the species and estimate group size

52 Sightings It can be difficult to distinguish between a single sighting with multiple subgroups and separate sightings General approach = start by entering separate sightings and then delete the second sighting, if needed Allows the observers to make a single estimate of the number of animals in the area For long diving species (baleen whales), it can be difficult to determine whether an individual was already sighted and recorded If there is any doubt, assume the individual is part of the previous sighting and adjust the group size estimate to reflect the uncertainty about whether the animal was already sighted

53 Sightings Ship s course after a sighting Ship within 10nmi of transect = continue on a course parallel to the transect Ship more than 10nmi of transect = return to transect on a 20 course

54 Group Size One of the most important and hardest jobs!

55 Group Size Group size estimates are made by each observer independently Each observer makes a best, high, and low estimate High and low estimates define the range within which the observer is confident the true group size occurs Multiple species = estimate the number of all animals present and estimate the percentage of each species in the school Observers only have to make a single count of all animals in the area

56 Group Size Group size estimates are highly variable Methods to increase precision Use the mean of multiple, independent estimates Consensus results in just one estimate This estimate may represent the mean or the estimate from the most experienced observer Training

57 Group Size Exercise: Estimate the number of shorebirds Record the image number Record your best, high, and low estimate for the number of birds Taken from Training Resources for Citizen Scientists: Estimating Shorebird Flock Sizes

58 Group Size Image 1

59 Group Size Image 2

60 Group Size Image 3

61 Group Size Image 4

62 Group Size Image 5

63 Group Size Image 6

64 Group Size Image 7

65 Counting methods Group Size Small schools = direct count Larger schools = sub-unit count (e.g., counting groups of 10 animals) Make multiple counts Helps with high and low estimates Other ideas?

66 Counting methods Group Size Small schools = direct count Larger schools = sub-unit count (e.g., counting groups of 10 animals) Make multiple counts Helps with high and low estimates Other ideas? Don t guess Estimates must be made from counts

67 Group Size Exercise: Estimate the number of shorebirds Record the image number Record your best, high, and low estimate for the number of birds Taken from Training Resources for Citizen Scientists: Estimating Shorebird Flock Sizes

68 Group Size Image 1

69 Group Size Image 2

70 Group Size Image 3

71 Group Size Image 4

72 Group Size Image 5

73 Group Size Image 6

74 Group Size Image 7

75 Group Size Results

76 Calibration Group Size Group size estimates for many SWFSC observers have been calibrated against counts made from aerial photographs of dolphin schools Estimates from new observers are indirectly calibrated using estimates from calibrated observers

77 Special cases Sperm whales Group Size Behavior makes group size estimation difficult Long dives Individuals within a group may dive asynchronously 10 minute counts by on-effort observers 60 and 90 minute counts by all observers Sub-group locations openly discussed Others?

78 Acknowledgements Tim Gerrodette, Wayne Perryman, Jay Barlow, Lisa Balance, Annette Henry Mammal observers, cruise leaders, survey coordinators, officers, crews Funding was received from the NOAA Office of Science and Technology s International Program