Investigation of foraging habits and prey selectivity by humpback whales using acoustic tags and concurrent fish surveys Briana H. Witteveen 1, Robert.

Investigation of foraging habits Investigation of foraging habits and prey selectivity by humpback and prey selectivity by humpback

whales using acoustic tags and whales using acoustic tags and concurrent fish surveysconcurrent fish surveys

Briana H. Witteveen1, Robert J. Foy1, Kate M. Wynne1, & Yann

Tremblay2

1University of Alaska FairbanksSchool of Fisheries and Ocean Sciences

2University of California Santa CruzLong Marine Laboratory

• Generalists feeding on euphausiids and pelagic fish species– Many prey species are linked to other consumers

• Need for reliable species-specific estimates of seasonal abundance, diet composition,and prey consumption

Humpback whales - one of many apex Humpback whales - one of many apex predatorspredators

• Tagging animals can determine depth of dive explicitly

• Acoustic time depth transmitters (ATDTs) allow for continuous dive depth data to be received in real time

• Utility in combining ATDTs and prey sampling to describe prey selectivity and habits of baleen whales

• This study reports first efforts to investigate humpback whale foraging habits with ATDTs while concurrently assessing prey availability

• 3 – 8 August 2004• Effort within ~144 km2 area 10

miles east of Spruce Island• Area selected based on the

presence of a large aggregation of humpback whales

Suction cup

VEMCO ATDT

Telonics VHF

Crossbow deployment

R/V Soundwave

• Visual coding• Dive data analyzed using IKNOS (Y.

Tremblay, unpublished software) – outputs 14 parameters

• Means of parameters were averaged across whales

• T-tests of parameters

Concurrent Prey SamplingConcurrent Prey Sampling

Sub-area 1

Sub-area 2

F/V Alaskan Track

Hydroacoustics• Simrad EK 60

echosounder• 38/120 kHz freq.• Calibrated 3x per

year• Hull mounted

transducer• SonarData Echoview

Commercial Nets• DanTrawl Bering

Billionaire • Midwater Trawl• 5m Nets V-doors

• 4 successful attachments

• ~17 hours total tracking

• 104 dives

ResultsResults

Mean Parameter

1,2,4,& 6 3 5

Number of Dives 42 5 57

Max Depth (m) 64.4 106.2 100.4Dive Duration (s) 265.4 401.0 410.1Bottom Time (s) 96.8 237.7 244.2

Descent Time (s) 72.6 78.5 78.2Descent Rate (s) 0.8 1.3 1.1

Ascent Time (s) 96.0 84.8 87.7Ascent Rate (s) 0.6 1.2 1.1

Post Dive Interval (s) 69.2 99.7 105.0

"Wiggles" on descent 1.9 1.1 1.2

"Wiggles" on bottom 5.2 14.1 13.3

"Wiggles" on ascent 2.0 1.1 1.1Bottom Distance (m) 27.4 77.4 107.1Bottom Range (m) 16.3 23.5 29.8Effeciency 0.2 0.5 0.5

Dive Type

• 3 and 5 labeled as “foraging”– Mean depth = 106.2 m (SD: 93 - 120m)

• 3 and 5 differentiated by bottom range– Range of depth covered during bottom phase– Indicator of oscillations at depth

0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 4 :5 7 :0 7 1 4 :5 8 :3 4 1 5 :0 0 :0 0 1 5 :0 1 :2 6 1 5 :0 2 :5 3 1 5 :0 4 :1 9 1 5 :0 5 :4 6 1 5 :0 7 :1 2 1 5 :0 8 :3 8 1 5 :1 0 :0 5

T im e o f D ay

Dep

th (m

)

Horizontal ForagingHorizontal Foraging Vertical Lunge Vertical Lunge ForagingForaging

3 5

CapelinAge-0 PollockWhale Tracks

0 20 40 60 80 100

<8

9-22

23-36

37-50

51-64

65-78

79-92

93-106

107-120

121-134

135-148

149-162

163-176

Dep

th (m

)F ish/ km2

0 5 10 15 20 25 30

<8

9-22

23-36

37-50

51-64

65-78

79-92

93-106

107-120

121-134

135-148

149-162

163-176

Dep

th (m

)

Number of Dives

Distribution of Humpback

Foraging Dives

Distribution of Capelin/km2

Hydroacoustic Prey SamplingHydroacoustic Prey SamplingD

ep

th

adult pollock, eulachon & euphausiids

Dep

th

capelin

Summary and ConclusionsSummary and Conclusions

• Fish surveys showed that pollock and capelin were present in significant densities within the study area and should be available as whale forage.

• Examination of the fish present along the tracks of the tagged whales suggests a preference for capelin as a prey source.

• Humpback whale foraging dives (types 3 and 5) occurred at an average depth of 106.2 meters and corresponded to the highest numbers of available capelin

Summary and Conclusions Cont.Summary and Conclusions Cont.

• Were there simply more capelin available?• No quantitative assessment of

zooplankton, but backscatter showed them at depths exceeding humpback foraging dives

• Real-time dive data allow for fine-tuned sampling of prey and improve the ability to describe prey selectivity

Future DirectionsFuture Directions• Addition of zooplankton assessment in prey

surveys• Concurrent tagging on humpbacks and fin

whales when co-occurring spatially• Tag redesign to increase deployment

efficiency and length of attachment

• Captain and crew of the F/V Alaskan• Jordy Thomson, Casey Clark, & Petra

Reimann for field assistance• Robin Baird, Gregg Schorr, Don Croll, &

Kelly Newton • Funding provided by NOAA Grant

#NA16FX1270• Research conducted under NMFS

Scientific Research Permit No. 1049-1718-00, UAF IACUC #02-38, UAF IACUC #04-21, ADF&G #CF-04-031, and NFMS LOA #2004-06.

AcknowledgementsAcknowledgements