Investigation of foraging habits and prey selectivity by humpback whales using acoustic tags and...
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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
• 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Tremblay, unpublished software) – outputs 14 parameters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
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
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
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