Quantifying movement and dispersal in adult weakfish, Cynoscion regalis:

Day vs. night comparison

Brian Reckenbeil*, Jason Turnure‡, Thomas Grothues‡, and Kenneth Able‡ *Undergraduate Biology, Moravian College, 1200 Main Street, Bethlehem, PA 18018

‡Rutgers University Marine Field Station, Institute of Marine and Coastal Sciences, 132 c/o 800 Great Bay Blvd. Tuckerton, NJ 08087

REU 2008RIOS

Research Internships in

Ocean Sciences

http://fishbase.ca/tools/aquamaps/imagethumb/file_destination/pic_Fis-23099.jpg

Range

Weakfish BackgroundWeakfish Background

• Weakfish spawn during the crepuscular Weakfish spawn during the crepuscular hours but spawning location preference hours but spawning location preference is relatively unknown and could be is relatively unknown and could be different from daytime habitat. different from daytime habitat.

• This study quantifies the hourly cycle This study quantifies the hourly cycle of weakfish dispersal using of weakfish dispersal using mobile mobile trackingtracking. .

Drugged with MS-222

T-bar tagging

Push Starting

Transport from/to capture site

Measurement then Release

Not All Survived

TrackingTracking

WeeklyWeeklyday (06:30—19:29) day (06:30—19:29)

night (19:30—06:29)night (19:30—06:29)

Top-side receiving Top-side receiving unit unit

mobile underwater mobile underwater hydrophone hydrophone

7 standardized 7 standardized sampling locations sampling locations

Salinity, Temp, Depth, Salinity, Temp, Depth, DO, Tide cycle, DO, Tide cycle, time, bearingtime, bearing

Above:

Deep Point, Mullica River –

Daytime hotspot

7 General Tracking Points specific fish location

SRX and mobile SRX and mobile hydrophonehydrophone

Data Collection

Audio Recordings

RESULTRESULTSS

• Data represents 6 fish ~ codeData represents 6 fish ~ code– 4 females ~ 64, 136, 137, 1564 females ~ 64, 136, 137, 156– 2 males ~ 62, 1032 males ~ 62, 103

•DrummingDrumming

•Thicker wallsThicker walls

• Day vs nightDay vs night

• MCP ~ Minimum Convex MCP ~ Minimum Convex PolygonPolygon

a n=103 contacts

b n=37 contacts

a b

c d

e

f

2 Male Day Locations

Not enough night tracking events to be able to compare data

Bonds upstream points came close to dusk, but still within day time hours (7:29pm)

Deep Point – Daytime Hotspot

Diel Movement Rate

Time (Hour of Day)

0 5 10 15 20

MD

PH

(lo

g)

0

1

2

3

4

Night NightDay

Conclusions Nocturnal dispersal events and nightly increases in movement

rate appear to be common, which may be due to evening spawning events and/or foraging behavior.

Aggregative dispersal and movement observed in several individuals suggests schooling activity during both day and night.

Similar results obtained in a smaller, urbanized estuary (Manderson et al. 2007; Navesink River, NJ) suggest that behaviors may be common in other parts of the weakfish’s range.

Caution must be exercised, however, in translating the results to a population level, since variation in individual fish behavior was observed, sample size was low, and a limited spatial area was covered.

Future Work Behavioral (i.e. spawning, foraging, predator avoidance) and

environmental (i.e. depth and water quality) correlates should be investigated to better describe potential drivers for observed differences in day/night patterns.

Quantitative measures of range and dispersal, such as MCP, become skewed based on behavioral differences between day/night. Therefore, more standardized techniques should be used in future studies.

Technological advances such as autonomous underwater vehicles (AUVs) with tracking capabilities may further elucidate movement patterns by obtaining more precise location and environmental data.

AUV ~ REMUS