Sperm whale seismic study in Gulf of Mexico-acoustics focus

General background My role: 3D tracking tagged/untagged

animals—working a few months at a time Single array localization-2000 Tag/array integration-2001 Dual-array localization-2002-?

Upcoming plans

Aaron Thode, Marine Physical Lab, SIO, UCSD

MMS

Minerals Management ServiceMarine Fisheries Service

Background-SWAMP cruises 2000-2001

Sponsors Minerals Management Service International Association of Geophysical Contractors Marine Fisheries, SE, 2000-2001

Focus: effect of seismic exploration on sperm whales Endangered species Acoustically active “Resident” populations

Mississippi Canyon De Soto

photo: Keith Mullin,SE Fisheries Service

Present SWSS study centers on two types of tags

Bruce Mate’s satellite tag (STAG) Long duration deployments—long-term habitat shift? Over 15 animals tagged, mostly on one day

WHOI digital recording tag (DTAG) Also pressure, orientation, acceleration High-resolution behavioral responses, energy studies,

3D pseudeotracks Visual, biopsy, acoustic component Nineteen animals tagged in 2002, three simultaneously

under controlled seismic exposure, many more under uncontrolled exposures.

Gulf of Mexico an acoustically unfavorable propagation environment

Measured and computed detection ranges predict 3-10km, depending on

source depth

Three different towed array systems 30-100m depth, give ~6km range

Source:MATLABKRAKEN(should alsoBe repeatedWith Bellhop)

Bottom-mounted sensors have similar predicted ranges

Stennis Space Center (George Ioup) has placed bottom-mounted sensors in general vicinity of SWSS. Some coordination, little overlap so far.

To date passive acoustic data collection program uses towed arrays with few elements->close range work

Outgrowth of Jay Barlow work,Outgrowth of Jay Barlow work,SWFSC.SWFSC.Also arrays from Ecologic,Also arrays from Ecologic,WHOIWHOI

My focus has been tracking untagged animals, under various conditions

Goal: statistically significant samples of low-resolution dive profiles under tagging/seismic conditions Complements high-resolution low volume

tagging runs. Three branches:

Single array localization-2000 Tag/array integration-2001 Dual-array localization-2002-?

SWSS acoustic work involves close follows at slow speeds

NOAA ship Gordon Gunther 0.5-1.5 kts

• Overnight tracking allowed biopsy, tagging in morning

• July 3 typical-slow tow through middle of traveling pod

• Silty/muddy flat bottom, depth measured with fathometer

• Pod composition assumed to be females and juveniles

• TDR was NOT attached during this particular sequence

930 md

s

b

t

tds tdbtdt

Bearing 1

Bearing 2

R

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Example from one dive: Good depth resolution

from 100 m depth Range uncertainty

increases with animal depth

Tracking ends when bottom returns vanish

Ray refraction may be neglected for ranges less than 1 km

True range (m)

During first stage of dive cycle inter-click interval is closely related to two-way travel time from whale to bottom.

During second stage bottom bounces vanish and timing becomes irregular.

Why so many clicks related to bottom? (New Zealand counterexample)

Some work has been performed on merging tag/array data

Simultaneous recordings on tag/array corrects pseudotrack.

Acoustics does not have control of ship during most tagging operations, with interesting results.

Time (sec)

Arr

ay b

earin

g (d

eg)

The inter-click interval (ICI) used to identify tagged whale out of 7-13 other

animals

Using surface reflections only gives three different time-of-arrivals, with

two arrays

Ishmael display: David Mellinger

Two arrays can eliminate need for bottom reflection, if array depths measured

RdsdddRds

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Fa

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Restrictions: Array depths known (difficult!) Depths > 40 m (slow towing speed) Doesn’t work broadside. Assumes straight-line propagation

Sept. 5 proof-of-concept

trial demonstrated

results● Array depth had to be estimated for one array.

●Measured descent rate of 91 meters per minute, similar to 88 meter per minute measurements from next-day tag.

broadside

endfire

Range vs. time

Depth vs. time

Two arrays plus tag refines localization-”leverages” tag info

2001-Array depths still the bug-bear!

Everything seems up in the air, as opposed to in the water

What ship for seismic playback? There was a lot of uncontrolled seismic exposures in

2002 What ship for research?

Last year’s ship was way too noisy What “holes” are there?

The off axis acoustic signature of seismic vessels is not known.

Modeling by IAGC free-space only, no waveguide effects included.

Better arrays needed Bottom-mounted sensors? Stennis?