A pilot study for acoustic telemetry-based estimate of summer flounder A pilot study for acoustic telemetry-based estimate of summer flounder commercial discard mortality: laboratory studies and field observationscommercial discard mortality: laboratory studies and field observations

Field Assessment ResultsField Assessment ResultsIntroductionIntroduction

ObjectivesObjectives

MethodsMethods

Preliminary ObservationsPreliminary Observations

Live vs. Dead Fish Carcass MovementLive vs. Dead Fish Carcass Movement

Flume ConfirmationFlume Confirmation

Dead Fish Move!Dead Fish Move!

Conclusions To DateConclusions To Date

• Current management assumes an 80% discard mortality rate for summer flounder in the commercial fishery

• Approximately 5-10% (242-485 metric tons) of the summer flounder commercial landings were estimated as loss from discards in 2009 (Terceiro, 2009)

• Discard mortality is difficult to determine because on-board assessments miss latent mortality and longer term caging experiments are confounded by cage effects

• Acoustic telemetry provides a novel approach that circumvents some of the biases of previous studies

• Immediate: Develop new approaches to measure discard mortality for summer flounder and other commercial species.

• Long Term: Determine the rate of discard mortality as it varies with: length, age, reproductive status and relative to predation

• We attached transmitters to dart tags, allowing for quick deployment without the use of incision, suture, anesthesia, or antibiotics.

Tag Attachment MethodTag Attachment Method

Lotek 11x48mm MA Series Acoustic Sensor Transmitters (MA-PM11-12: 76KHz, 8.5g in air, 4.5g in water). 5 second signal rate

Two Tracking MethodsTwo Tracking Methods

• Submerged hydrophones provide high temporal resolution and fine scale movement of tagged fish

• Mobile tracking with towed stereo hydrophones provide greater spatial coverage but less temporal resolution

WHS 3050 SDL Hydrophone, Lotek Wireless

• Assumption: Dead fish remain relatively motionless on the bottom

• Tracking live fish (3; 356-471 mm) and dead fish (4; 316-370 mm) in the Mullica River - Great Bay estuary yielded counter-intuitive results

• The ability of tidal currents to influence dead fish movement was confirmed in a flume

• Carcasses (236-402 mm) were placed on a sandy bottom in a flume and subjected to increasing current speeds

• Carcasses were lifted and moved through the water column at mean speed of 27.3 cm/sec, with a range of 10.1- 47.6 cm/sec, speeds observed in nature

• The fish were captured with a commercial otter trawl• Tow times ranged from 76 to 129 minutes.• Each fish was scored with a condition index following

a prior study (E. Hasbrouck, pers. comm.) as Excellent , Good, Poor, and Dead

• Both live (n=40) and dead (n=16) summer flounder were tagged on 15 September 2009 at a location off Brigantine, New Jersey (Center Frame)

• Mobile tracking took place until October 11, 2009 (73.15 hours total)

Field Assessment ApproachField Assessment Approach

Matthew Yergey1, Kenneth W. Able1, Thomas M. Grothues1, Callie Crawford2, Kevin DeCristofer3

1Rutgers University Marine Field Station, 132 Great Bay Blvd., Tuckerton, NJ 080872 University of Rhode Island, Kingston, RI 02881

3 Richard Stockton College of NJ, PO Box 195, Pomona, NJ 08240

Fish left the hydrophone array after ~24hours, coinciding with a large

northeast storm event 22 fish (39.3% of tagged) were found after the storm via mobile tracking to the southeast of the

array, many were of poor (10) and dead (10) conditions

Non-parametric ordination (by MDS) of fish behavior based on detection patterns within the

array corroborates a long-term spatial separation apparent in mobile tracking (above) further suggesting grouping of potentially dead fish

• A clear discard mortality rate can not yet be determined, but the methods developed seem promising.

• The surprising scale of dead fish movement was compatible with storm induced flow and could be predictably modeled to formulate a mortality standard for future assessments.

• A latent mortality estimate could be calculated with a sustained mobile tracking effort.

AcknowledgementsAcknowledgementsWe thank Capt. Jim Lovegren and crew of the commercial trawler FV Viking II. Jessica Hoffman for her tagging studies as an intern. Jenna Rackovan, Tom Malatesta, Jen Smith, Jim Vasslides, and Pat Filardi assisted in the field and laboratory. Charlotte Fuller provided access to the IMCS flume facility and assisted with these observations. John Wilkins provided results of a flow model for the study period. This research was supported by a grant from the NOAARSA.

• Two live fish stayed in the tracking array for the duration of the study, the other left after 42.8 hours

• Dead fish moved had a mean residence time of 43.6 hours ± 49.2, and showed oscillating movement synchronous with tides

• Several of the dead fish were tracked leaving the estuary at stationary hydrophones 2,3, and 4 during a 3 day period (Above)

Mobile Hydrophone

Panel 1Panel 1 Panel 2Panel 2

Panel 3Panel 3

Deployment Departure

Storm (winds >= 30 mph)

Strong bottom currents during the storm were in the southeast direction, coinciding with dead fish movements

after the storm

Salinity

Bottom Current Speed

Reference Arrow:

0.05 m/s

Strongest currents in study area Found in the southeast groupNot found after the storm

Axi

s 1

Axis 2