Movement of Sub-Adult Striped Bass (Morone saxatilis) within an
Estuarine
Ecosystem
Is there a spatial
*Undergraduate Marine Biology, Sacramento City College
3845 Freeport Blvd. Sacramento, CA 95822-1386
† Rutgers University Marine Field Station, Institute of Marine and Coastal Sciences, 132 c/o 800 Great Bay Blvd. Tuckerton, NJ 08087
RESULTS
ABSTRACT
Hydrophone
separation in adult
and sub-adult
striped bass
populations ?
Paul Clerkin*, Thomas Grothues†, and Kenneth Able†
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Small Fish 132
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Small Fish 148
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Fig. 1 Striped Bass (Morone saxatilis)
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There was minimal movement of the tagged sub-adult striped bass. After release, subadults were most frequently detected in an upstream location of the estuary. Tagged
adult striped bass also moved very little after release, residing primarily an open water
bay portion of the estuary. Figures 8 and 9 shows this age segregation of the adult and
sub-adult populations.
This spatial separation of the two populations shows no clear preference for either water
temperature or salinity (Fig. 10). Water temperature data indicate no age related
preference. Salinity data exhibit adult and sub-adult clusters, but with no discernible
pattern.
There seemed to be no similarity in adult and sub-adults striped bass’s movements. The
sub-adults were found farther up stream while the adults were more often found out in
the bay (Fig. 11)
We compared the movements of sub-adult striped bass, Morone saxatilis
with those of adults in the Mullica River-Great Bay estuary in southern New
Jersey. We used ultrasonic telemetry, both mobile and fixed listening
stations to track fish tagged with acoustic transmitters. The movement of
sub-adult bass were not similar to that of adults. Sub-adults occupied
different areas of the Mullica River-Great Bay estuary from adults.
Movement was sporadic but limited. Occupied areas were similar in both
temperature and salinity, differing only in location, suggesting that
segregation is based on factors not addressed in this study
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Fig. 9 Time vs. hydrophone graph showing which stationary hydrophone the fish were at
DISCUSSION
The striped bass is keystone species in the Mullica River-Great Bay estuary (Fig. 1).
Although they are not commercially harvested in New Jersey, the mid-Atlantic striped bass
commercial catch has shown vulnerability to the mismanagement of spawning and nursery
habitats. Recreational fishing for striped bass impacts local economies through the sale of
fishing tackle and equipment, boat rentals, and motel and restaurant revenues. As an
important striped bass spawning and nursery habit, the coastal rivers of New Jersey make
a significant contribution to the mid-Atlantic striped bass stock.
A considerable research interest in this species has focused on describing the movements
of adult striped bass within an estuarine study area (Tupper & Able 2000) . Consequently,
there is a large amount of data available for comparative analysis. Young striped bass are
frequently observed in shallow, close-to-shore locations (Ng, 2006). To examine the
possibility and cause of age-segregated movements, we used a system of stationary
wireless hydrophones located strategically throughout the Mullica River-Great Bay estuary
as well as mobile hydrophones to track the movements of acoustically tagged fish
(Grothues et al. 2005) (Fig. 2).
The spatial separation by age with this species seems unrelated to water
temperature or salinity. Of examined environmental factors, geography (i.e.,
river vs. bay) appears to be the most important factor related to age
segregation. This suggests a behavioral, rather than physiological
explanation of the age separation, in which older, larger fish exclude, smaller,
younger fish from prime feeding habitats. Such competitive exclusion based
on dominance of prime territory by adults would effectively separate the
species into two habitat utilization patterns based on age. Given that the diet
of younger bass differs from that of adults and that only after two years are
striped bass considered fully piscivoroius, spatial separations could have diet
related variable as well. Further investigation is warranted.
Fig. 2 Stationary and mobile hydrophones
35
30
Surface Temperature
INTRODUCTION
over time
Big Fish 59
Big Fish 61
Big Fish 102
Small Fish 132
Small Fish 134
Small Fish 141
Small Fish 143
Small Fish 148
Big Fish 175
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Surface Salinity
B
Fig. 10 Temperature vs. salinity graph, showing the
environment in which the fish were found
METHODS
Fig. 3 Acoustic
transmitter, measuring
11X5mm
A
Tagging: We caught six sub-adult striped
bass by hook and line. Each fish was placed
in a tank containing the anesthetic
aminobenzoic acid ethyl ether. We surgically
implanted an ultrasonic transmitter (Fig. 3)
into the peritoneal cavity of each fish and
closed the incision with three sutures (Fig.
4). An injection of oxytetracycline
(Liquamycin) was administered into the
dorsal musculature to guard against latent
infection. The fish were marked with
external tags to alert anglers of their status
and then released (Fig. 5).
Fig. 6 A portable hydrophone (A ) coupled with
Tracking: We tracked the fine scale movements an SRX-400 receiver/processor (B) was used
from a boat to track the fine scale movements
of tagged fish from a boat using a portable
of
hydrophone at pre-set points. For this, we
sub-adult striped bass.
employed a baffled hydrophone coupled with an
SRX-400 receiver/processor (Fig. 6). Contacts
were recorded and used to map the locations of
individuals. This data was compared to
previously collected data for adult striped bass.
Our mobile data complements that collected
from an array of fixed hydrophones used for
examining coarse-scale movements in serial
fashion ( Fig. 7).
REFFERENCES
Grothues, T.M., K.W. Able, J. McDonnell and M.M. Sisak. “An Estuarine Observatory
for Real-Time Telemetry of Migrant Macrofauna: Design, Performance and
Constraints”. Limnology and Oceanography Methods 3: 275-289, 2005
Fig. 4 Implanting a transmitter into an
B
A
anesthetized fish. A) making a incision
using a sterilized surgical scalpel. B)
suturing closed incision after
implantation
Ng, C.L.H. “Habitat Utilization and Movement Patterns of Adult Striped Bass, Morone
Saxatilis, in a Aouthern New Jerest Estuary Using Acoustic Telemetry”. A Masters
thesis.
Fig. 11 Locations where large fish (blue dots) and small fish (red
Fig. 8 Time vs. hydrophone
dots) were detected by portable hydrophones. locations of the points
routinely checked by portable hydrophone (inset).
vs. number of contacts
Fig. 7 Stationary telemetric infrastructure in the Mullica RiverFig. 5 Release of
acoustically tagged subadult striped bass.
Tupper, M., and K.W. Able “Movement and Food Habits of Striped Bass”. Marines
Biology, 137, 1049-1057, 2000
Great Bay estuary.
Acknowledgments. I want to thank Clare Ng, Jay Turnure and Paige Roberts for generously sharing their expertise on fish tracking, fellow novice trackers Gregory Henkes and Margaret Malone for always lending a helping hand when needed, and many others at the
Rutgers Marine Field Station for all the kind assistance they have given this project.