Evaluating the Use of Motion-Activated Transmitters to Track Paralichthys dentatus in the Great Bay Estuary

Caitlin McGarigal*, Thomas M. Grothues‡, and Kenneth W. Able‡, McGarigalC@yahoo.com (413) 687-7043*University of Massachusetts Dartmouth, Dartmouth, MA 01082 ‡Rutgers University Marine Science Field Station, Tuckerton, NJ 08087Introduction

•Summer flounder, Paralichthys dentatus, is a common by-catch species in commercial fisheries.

•By-catch mortality rate is poorly known and could influence summer flounder populations.

•Evaluating mortality is important for stock assessment and effective management of this species.

•Comparing signals from released sensor-tagged by-catch with predetermined patterns based on live fish behavior can determine the survival status of the individual.

•Motion and pressure sensitive tags must be evaluated to provide parameters for live fish behavioral patterns.

ObjectiveEvaluate the ability of motion and pressure sensitive transmitters in determining by-catch mortality by providing criteria for live-fish behavior and evaluating tag sensor settings.

Question 3• How active are live summer flounder?

• Do they remain stationary for >6 hours?

• Do sensored tags help discern movement of live summer flounder at liberty? • Can environmental influence alone trigger the motion sensor?

Experiment

• Three fish; 325cm, 445cm, 326cm

• Three 8 hour trials video recorded

• One trial with tagged fish and hydrophone in the experimental tank

• Video reviewed to calculate the mean time fish spent in motion and mean time spent stationary

• Two fish tagged (453 and 435cm)

• 24 to 48 hour continuous tracking began upon fish’s release

• Constant GPS location recorded

• Two hydrophones towed behind boat

• Stationary hydrophone was placed in location

• Bottom temperature (° C), % DO, mg/L DO, Salinity (ppt) were recorded every 15 minutes

• Tag attached to flat lead weight

• Set 24 hours in creek near the fish and stationary hydrophone

Results

Figure 1. The average time in motion was 59 seconds. The average time stationary was 216 seconds. Red lines show trail durations.

Tagged Lab Fish Motion

Time

09:00:00 13:00:00 17:00:00 21:00:00 01:00:00 05:00:00 09:00:00

0

1

Fish ID # 54522 Depth

Time

14:00:00 18:00:00 22:00:00 02:00:00 06:00:00

Fis

h D

epth

(m

)

-3.4

-3.2

-3.0

-2.8

-2.6

-2.4

-2.2

Tid

al H

eigh

t (m

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Figure 2. The tag signal switched to ‘no motion’ (0) at 19:52. Accounting for the 6hr reset delay means that the fish became stationary at 13:52.

Figure 3. Changes in pressure are caused by tidal shifts. Tag signaled motion (1) for experiment duration (not shown).

Figure 4. Changes in pressure independent of tide height indicate vertical movement in the water column. Tag signaled motion (1) for experiment duration (not shown).

Lead Fish Motion and Depth

Time

7/15/2010 7/15/2010 7/16/2010 7/16/2010

-4

-3

-2

-1

0

1

2

Tid

al H

eig

ht

(m)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Time vs Signal Time vs Corrected Signal Time vs Pressure Col 9 vs Col 8

Figure 5. Signal registered no motion 9:15 hr after deployment. Tag was in motion 3:19 hr before becoming stationary for the 6hr delay

period.

Conclusions

Question 1 Question 2

ResultsResults

ExperimentExperiment

Conclusions Conclusions

• Lab observations suggest 12 hour periodic activity.

• Fish should be filmed for continuous 24 hours to help determine an appropriate motion-reset delay setting.

• Wild flounder are unlikely to remain stationary for >6 hrs, even while remaining in a small area, so tags will always register ‘motion.’

• Motion-reset delay should depend on the type of tracking • periodic tracking should use a longer (>6hr) reset

• appropriate if interested is recent history of fish activity• continuous tracking should use a shorter (<6hr) delay setting.

• Appropriate if real-time information on fish movement is desired.

• A drifting dead carcass may appear as a live fish due to ‘motion’ signals, but once carcass settles previous research shows signal should remain at 0.

• Environmental factors can cause the tags to move.

• Transmitters purchased in the future should be at less sensitive settings.

Submersible Hydrophone WHS_3050 Lotek Wireless Inc.

Motion and pressure sensitive acoustic transmitters. Signal burst rate is 5 seconds. Motion-reset delay period is 6 hours and transmitter sensitivity is 4.

Acknowledgements: Special thanks to the National Science Foundation and Rutgers Institute of Oceanographic Science for making this summer internship program possible. Thanks also to Matt Yergey for his assistance and guidance and I would like to recognize all the technicians, interns and volunteers who helped in the field at all hours of the day and night.

100 x 66cm

water depth 30cm

Towed LPH-1 Dual Hydrophones with RT-A processor Lead ‘Flounder’

00:00:00 06:00:00 12:00;00 18:00:00 00:00:00

1

2

3

Time

Fis

h

Lab Fish Motion Trials

Fish ID# 54708

Released 7/14

Fish ID# 54522 Released 7/21

Lotek 11x48mm MA Series Acoustic Sensor Transmitters (MA-PM11-12: 76KHz, 8.5g in

air, 4.5g in water).

Fish Depth (m)

Tidal Height (m)

Fish ID # 54708 Depth

Time

16:00:00 20:00:00 00:00:00 04:00:00 08:00:00 12:00:00

Fis

h D

epth

(m

)

-2.4

-2.3

-2.2

-2.1

-2.0

-1.9

-1.8

Tidal H

eight (m

)

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4Fish Depth (m) Tidal Height (m)

Fish Depth (m)

Tidal Height (m)

Motion Signal

Back-calculated Motion

Motion Signal

Back-calculated Motion

Tidal Height (m)

Fish Depth (m)