ML072060564
| ML072060564 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 08/01/1989 |
| From: | Mercer L, Moran D US Dept of Interior, Fish & Wildlife Service, US Dept of the Army, Corps of Engineers |
| To: | Office of Nuclear Reactor Regulation |
| Davis J NRR/DLR/REBB, 415-3835 | |
| Shared Package | |
| ML072060321 | List:
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| References | |
| TR EL-82-4 82(11.109) | |
| Download: ML072060564 (25) | |
Text
Biological Report 82(11.109)
August 1989 TR EL.82-4 Species Profiles:
Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Mid-Atlantic)
WEAKFISH Coastal Ecology Group.
Waterways Experiment Station Fish and Wildlife Service U.S. Department of the Interior U.S. Army Corps of Engineers C~~z 4Iz 4 JAcc \\oaV
Biological Report 82(11.109)
TR EL-82-4 August 1989 Species Profiles:
Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Mid-Atlantic)
WEAKFISH by Linda P. Mercer North Carolina Division of Marine Fisheries Morehead City, NC 28557 Project Officer David Moran U.S. Fish and Wildlife Service National Wetlands Research Center
.1010 Gause Boulevard
- Slidell, LA 70458 Performed for Coastal Ecology Group U.S. Army Corps of Engineers Waterways Experiment Station Vicksburg, MS 39180 and U.S. Department of Interior Fish and Wildlife Service Research and Development National Wetlands Research Center Washington, DC 20240
This series may be referenced as follows:
U.S. Fish and Wildlife Service.
1983-19 Species profiles:
life histories and environmental requirements of coastal fishes and invertebrates.
U.S. Fish Wildl.
Serv. Biol.
Rep. 82(11).
U.S. Army Corps of Engineers, TR EL-82-4.
This profile may be cited as follows:
- Mercer, L. P.
1989.
Species profiles:
life histories and environmental requirements of coastal fishes and invertebrates (Mid-Atlantic)--weakfish.
U.S.
Fish Wildl.
Serv.
Biol.
Rep.
82(11.109).
U. S.
Army Corps of Engineers, TR EL-82-4.
17 pp.
PREFACE This species profile is one of a series on coastal aquatic organisms, principally fish, of sport, commercial, or ecological importance.
The profiles are designed to provide coastal managers, engineers, and biologists with a brief comprehensive sketch, of the biological characteristics and environmental requirements of the species and to describe how populations of the species may be expected to react to environmental changes caused by coastal development.
Each profile has sections on taxonomy, life history, ecological role, environmental requirements, and economic importance, if applicable.
A three-ring binder is used for this series so that new profiles can be added as they are prepared.
This project is jointly planned and financed by the U.S. Army Corps of Engineers and the U.S. Fish and Wildlife Service.
Millikin and Williams (1984) previously published a
review of the nomenclature,
- taxonomy, morphology, distribution, life history, population structure and dynamics, and the fishery of the blue crab.
Suggestions or questions regarding this report should be directed to one of the following addresses.
Information Transfer Specialist National Wetlands Research Center U.S. Fish and Wildlife Service NASA-Slidell Computer Complex 1010 Gause Boulevard
- Slidell, LA 70458 or U.S.
Army Engineer Waterways Experiment Station Attention: WESER-C Post Office Box 631 Vicksburg, MS 39180.
iii
CONVERSION FACTORS Metric to U.S. Customary Multiply millimeters (mm) centimeters (cm) meters (m) meters (m) kilometers (kin) kilometers (kin) square meters (m 2) square kilometers (km2 hectares (ha) liters (I) cubic meters (m cubic meters (m 3 )
.milligrams (mg) grams (g) kilograms (kg) metric tons (t) metric tons (t) kilocalories (kcal)
Celsius degrees (CC) inches inches feet (ft) fathoms statute miles (mi) nautical miles (nmi) square feet (ft2) square miles (mi2) acres By 0.03937 0.3937 3.281 0.5468 0.6214 0.5396 10.76 0.3861 2.471 0.2642 35.31 0.0008110 0.00003527 0.03527 2.205 2205.0 1.102 To Obtain inches inches feet fathoms statute miles nautical miles square feet square miles acres gallons cubic feet acre-feet ounces ounces pounds pounds short tons British thermal units Fahrenheit degrees 3.968 1.8(°C) + 32 U.S. Customary to Metric 25.40 2.54 0.3048
,1.829 1.609 1.852 0.0929 2.590 0.4047 millimeters centimeters meters meters kilometers kilometers gallons (gal) cubic feet (ft3) acre-feet ounces (oz) ounces (oz) pounds (Ib) pounds (Ib) short tons (ton)
British thermal units,Ttu)
Fahrenheit degrees ( F) 3.785 0.02831 1233.0 28350.0 28.35 0.4536 0.00045 0.9072 square meters square kilometers hectares liters cubic meters cubic meters milligrams grams kilograms metric tons metric tons kilocalories Celsius degrees 0.2520 0.5556 CF-32) iv
CONTENTS PREFACE.....................
CONVERSION TABLE ACKNOWLEDGMENTS Page iii
.v.
iv vi NOMENCLATURE/TAXONOMY/RANGE MORPHOLOGY/IDENTIFICATION AIDS REASON FOR INCLUSION IN THE SERIES LIFE HISTORY
.I
° Spawning.........
Fecundity Larvae..............
Juveniles Adults.............
GROWTH CHARACTERISTICS COMMERCIAL AND RECREATIONAL ECOLOGICAL ROLE.........
Food Habits Community Ecology Diseases............
ENVIRONMENTAL REQUIREMENTS Temperature Salinity............
Dissolved Oxygen.
Pollution...........
LITERATURE CITED FISHERIES 11 2
2 2
3 3
3 4
5 8
9 9
10 10 10 10 11 11 11 13 v
ACKNOWLEDGMENTS I
am grateful to Stuart Wilk and Tony Pacheco of the National Marine Fisheries Service, Sandy Hook, New Jersey, for their reviews of the manuscript and helpful suggestions.
vi
ig Figure 1. Weakfish (Cynoscion regalis) (from Goode 1884).
WEAKFISH NOMENCLATURE/TAXONOMY/RANGE Scientific name....
Cynoscion regalis Preferred common name..
. Weakfish (Figure 1)
Other common names.
Gray trout, squeteague, sea trout, trout, tide-runner Class....
.. Osteichthyes Order....
Perciformes Family....
Sciaenidae Geographical range Weakfish occur along the Atlantic coast of the United States from southern Florida to Massachusetts
- Bay, straying occasionally to Nova Sco-tia and into the eastern Gulf of Mexico (Goode 1884; Hildebrand and Schroeder 1928; Bigelow and Schroe-der 1953; Guest and Gunter 1958; Leim and Scott 1966; Struhsaker 1969; Weinstein and Yerger 1976; Chao 1978).
They are most abundant from North Carolina to New York (Figure 2).
MORPHOLOGY/IDENTIFICATION AIDS The following description is that of Johnson (1978),
summarized from Jordan and Evermann (1896),
Eigenmann (1901),
Hildebrand and Schroeder (1928),
Ginsburg (1929),
Perlmutter (1939),
Massmann (1963),
Tagatz (1967),
Miller and Jorgenson (1973),
and Chao (1978).
Dorsal rays 24-29, modally 27.
Anal rays 10-13, modally 12. Vertebrae 25.
Gill rakers 4-5 upper,10-12 lower, and typically 5 + 12.
A pair of large canine-like teeth at the tip of upper 1
jaw and a row of distinctly enlarged teeth in the lower jaw.
Body elon-
- gate, moderately compressed.
Head
- long, snout pointed.
Mouth
- large, oblique, lower jaw projecting, maxil-lary reaching to posterior margin of pupil or beyond.
Dorsal fin with a deep notch between the spinous and soft portions.
Caudal emarginate in individuals less than 300 mm total length (TL).
Color dark olive green above with the back and sides variously burnished with
large number of small dark spots which appear as oblique streaks running along scale rows above lateral line.
Lower surface forward to tip of jaw white or
- silvery, sometimes iridescent.
Dorsal fins
- dusky, the lower edge yellowish at base.
Pelvic and anal fins yellow; pectoral fin olive on outer side, usually yellow on inner side.
REASON FOR INCLUSION IN THE SERIES The weakfish is one of the most abundant fishes in the estuarine and nearshore waters of the Atlantic coast (Wilk 1979).
It is a valuable recrea-tional species and a major component of the gill-net, pound-net, haul-
- seine, and trawl fisheries along the coast (Hildebrand and Schroeder 1928; Wilk 1981).
Periods of high landings have generally been followed by sudden and precipitous declines in catch, the causes of which are not known.
Overfishing and habitat alterations have been suggested as possible causes.
LIFE HISTORY Spawning Weakfish mature at age I through-out their geographic range;
- however, length at maturity differs between northern weakfish (Delaware Bay and north) and weakfish from North Caro-Figure 2.
General distribution of the weakfish along the Atlantic coast of the United States (from Wilk 1976).
2
lina.
In northern
- fish, females matured at 256 mm and males at 251 mm TL (Shepherd and Grimes 1984);
in North Carolina females spawned at 230 mm and males at 180 mm TL (Merriner 1976).
Weakfish spawn in the nearshore and estuarine areas of the coast after the spring inshore migration (Welsh and Breder 1923; Hildebrand and Schroeder 1928).
The spawning season of weakfish is earlier and somewhat longer in North Carolina than in areas to the north; it extends from March to September, and peaks from April to June (Merriner 1976).
In the New York Bight (Delaware Bay to New York),
the season extends from May to mid-July (Shepherd and Grimes 1984).
Two spawning peaks are reported for weakfish in New York Bight estuaries:
the earlier mid-May peak, attributed to the largest individuals or "tide-runners,"
is followed by a June peak developed by smaller fish (Shepherd and Grimes 1984).
Fecundity Estimates of fecundity for southern weakfish differ from those for fish from the New York Bight.
A weakfish 500 mm TL from North Carolina produced 2,051,080 ova, whereas a northern fish of the same length produced only 306,159 ova (Merriner 1976; Shepherd and Grimes 1984).
The following relationships between fecundity (F) and standard length (SL) in milli-
- meters, total length (TL) in milli-meters, weight (W) in grams, and gut-ted weight (GW) in grams, where In is the natural logarithm and r is the coefficient of determination, were presented for weakfish in North Carolina (Merriner 1976):
F = 21,198 + 1,279 W; r 2 = 0.88 and the New York Bight (Shepherd and Grimes 1984):
In F = -16.322 + 4.659 In TL; r2 = 0.835 In F = 1.975 + 1.542 In GW; 2
r
= 0.839.
Larvae The embryology and larval devel-opment of weakfish were described by Welsh and Breder (1923),
Pearson (1941),
Harmic (1958),
Scotton et al.
(1973),
Lipp.son and Moran (1974),
Johnson (1978),
and Powles and Stender (1978).
Hatching occurs in 36-40 hours at 20-21 OC (Welsh and Breder 1923).
Weakfish larvae range from 1.5 to 1.75 mm TL at hatching and become demersal by 8 mm TL (Welsh and Breder 1923; Pearson 1941).
Weakfish larvae have been collected in nearshore waters to 70 km offshore in coastal ichthyoplankton surveys (Berrien et al.
1978).
Juveniles The *use of estuarine areas as nursery grounds by weakfish is well documented.
Juveniles are collected most frequently in trawl sampling of the deeper waters of rivers, bays, and
- sounds, rather than. in beach seine collections from shoal areas (Greeley 1939; Massmann et al.
1958; Schwartz
- 1961, 1964a; Richards and Castagna 1970; Thomas 1971; Chao and Musick 1977).
Extensive sampling of North Caro-lina sounds revealed that juvenile weakfish were most abundant in areas designated by the North Carolina Division of Marine Fisheries as secon-dary nursery areas (usually shallow bays or navigation channels character-In F = -2.154 + 2.776 In SL; r ý =0.85 In F = -1.884 + 2.642 In TL; 2
r = 0.86 3
ized by moderate
- depths, slightly higher salinities, and presence of sand and/or sand-grass bottoms) rather than in primary nursery areas (shallow tributaries of low salinity and mud and/or mud-grass bottom)
(Spitsbergen and Wolff 1974; Purvis 1976).
In Chesapeake Bay and Delaware Bay juvenile weakfish migrate from high to low salinity areas throughout the
- summer, return to high salinity waters in fall, and leave the estuaries by December (Hildebrand and Schroeder 1928; Massmann et al.
1958; Thomas 1971; Chao and Musick 1977).
Juvenile weakfish are distributed along the coast from Long Island to North Carolina at depths of 9-26 m in late summer and fall (Clark et al.
1969).
Young-of-the-year weakfish were caught in ocean trawl surveys along the coast of North Carolina in 1968-11981 at depths of 9-18 m during fall and
- winter, and from North Carolina to Florida at depths of 9-11 m in winter and early spring (Wilk and Silverman 1976).
Adults Adult weakfish migrate seasonally between inshore and offshore waters (Welsh and Breder 1923; Merriner 1973; Wilk
- 1976, 1979, 1980).
Warming of coastal waters in spring prompts an inshore and northerly migration of adults from their wintering grounds to
- sounds, bays, and estuaries (Figure 3).
The larger fish move inshore first and tend to congregate in the northern part of the range (Wilk and Silverman 1976; Wilk et al.
1977).
Catch records from the pound-net and haul-seine fisheries in Delaware Bay, Chesapeake
- Bay, and Pamlico Sound indicate that the large fish are fol-lowed by a
second group of smaller weakfish in sunmmer (Higgins and Pearson 1928; Massmann 1963; Daiber and Smith 1971; Sholar 1979; DeVries
- 1980, 1981).
Shortly after their initial appearance, weakfish return to the larger bays and possibly to the ocean to spawn.
In northern areas a
,y'.
t*o P
\\O.
-0.1 NC SC I
4
- ell, GA
'3'.
(PZr-
'Zý'
"IX.
Figure 3.
Movements of the weakfish along the Atlantic coast of the United States during spring and summer (from Wilk 1976).
4
greater proportion of the adults spend the summer in ocean waters rather than ME in estuaries.
NH A
As water temperatures decline in
- faHl, weakfish form aggregations and MA move offshore and generally southward along the coast (Nesbit 1954; Massmann CT et al.
1958;-Wilk 1976; Wilk and Sil-NY
\\\\\\
verman 1976)
(Figure 4).
The Conti-nental Shelf from Chesapeake Bay to
~NJ Cape Lookout, NC, appears to be the major wintering ground for weakfish.
A study of the winter trawl fishery off 0.
the Virginia and North Carolina. coasts indicated that most weakfish were MD
\\DE caught in the southern fishing area between Ocracoke Inlet and Bodie
- Island, NC, at depths of 18-55 m (Pearson 1932).
Some weakfish may VA remain in inshore waters throughout the winter from North Carolina southward (Goode 1884; Higgins and Pearson 1928; Hildebrand and Cable 0
1934).
NC GROWTH CHARACTERISTICS Weakfish growth is particularly rapid during the first year.
In Dela-ware Bay, juveniles may grow from 20 to 35 mm/month during June-September (Ichthyological, Associates 1980) and may attain lengths ranging from 100 to 175 mm TL throughout the range.
The GA variability of sizes within.
year classes results from the extended spawning season.
Massmann et al.
(1958) and Thomas (1971) found two distinct size groups of young-of-the-year weakfish in fall in Chesapeake Bay (45 and 85 mm) and Delaware Bay (30-40 and 110-130 mm).
This appar-FL ently reflects two. separate spawning peaks.
Thomas (1971) did not find a bimodal length distribution for adult weakfish which may be due to differen-tial mortality of late-spawned weak-fish or to compensatory growth.
\\0.
Weakfish age and growth studies Figure 4.
Movements of the weakfish indicated geographic variations in along the Atlantic coast of the United
- growth, with a pattern of increasing States during fall and winter (from size toward the northern end of the Wilk 1976).
5
range (Table 1).
Shepherd and Grimes (1983) found that northern weakfish collected between Cape
- Cod, MA, and Ocean City, MD, were largest at each age and attained a greater maximum size and longevity (810 mm TL at age XI).
Size at age of weakfish collec-ted between Virginia Beach, VA, and Cape Fear, NC, was lowest (370 mm TL at age III) and similar to that reported by Taylor (1916) and Merriner (1973).
In weakfish from Chesapeake Bay (Ocean
- Beach, VA) size at age and maximum size were intermediate and were comparable to what Seagraves (1981) reported for Delaware Bay in 1979.
Shepherd and Grimes (1983) suggested that these growth variations may result from differing allocations of energy to somatic growth according to environmental and migratory requirements.
Growth of weakfish of southern origin may also be limited by prey availability or by genetic differences.
Records of weakfish size at various ages show differences over time (Table 2).
A comparison of female weakfish from the New York Bight showed that age-IV females in 1929 averaged 340 mm Table 1.
Mean total lengths (mm) at Shepherd and Grimes 1983).
TL compared to 480 mm TL in 1952 and 580 mm TL in 1980 (Perlmutter et al.
1956; Shepherd and Grimes 1983).
Known longevity was 8 yr in 1929, 6 yr in 1952, and 11 yr in 1980.
Simila.r changes in growth and longevity were reported for weakfish in Delaware Bay (Seagraves 1981).
Growth of weakfish was described by the von Bertalanffy growth curve:
It
= L (1 - e -K(t-t 0 )),
where It is length at age t, L
is the asymptotic length, K
is the-Brody growth coefficient, t is age, and t is the hypothetical age at which th8 fish would have been zero length.
Von Bertalanffy growth parameters showed a trend of decreasing values of L
from north to
- south, with the exception of Delaware Bay weakfish in 1979 (Seagraves 1981; Shepherd and Grimes 1983)
(Table 3).
A larger asymptotic
.length was obtained for Delaware Bay weakfish in 1979 than in 1956.
Length-wei been deve throughout I
ght relationships have oped for weakfish from the Mid-Atlantic Region from three regions (from age of weakfish Ocean City, MD Virginia Beach, VA Cape Fear, NC to to to Cape Cod, MA Ocean City, MD Virginia Beach, VA Age 1979-81 1979-81 1979-81 group Male Female Male Female Male Female I
200 200 200 200 220 210 II 310 320 280 300 270 300 I11 460 480 450 460 320 370 IV 560 580 560 600 V
630 640 600 670 VI 660 680 710 VIl 660 700 VIII 680 720 IX 710 730 X
690 750 XI 700 810 6
Table 2.
Mean total lengths (mm) at age of weakfish.
Chesa-peake a9New York Delaware Ba1 Bay a North Caroling Age 1929a 1952a 1965_
1979-*
1929-1916k 1967-69
- group M
F M
F M &.F M
F M&F M& F M
F 1
200 190 210 200 189 198 196 173 209 185 192 2
260 260 280 280 246 324 327 263 277 264 272 3
300 300 360 360 286 451 455 301 328 323 347 4
320 340 480 480 319 543 553 342 405 384 432 5
360 380 560 560 604 618 386 486 496 509 6
410 410 640 640 681 635 440 479
- 680 7
440 430 675 489 560 8
520 440 737 589 9
762 a Perlmutter et al.
(1956).
c Taylor (1916).
b Seagraves (1981).
d Merriner (1973)
- TL approximated by:
TL = 1.21 SL.
Table 3.
Von Bertalanffy growth parameters for weakfish (sexes combined) where L
is the asymptotic length in mill'imeters (SL)
(Standard length approximated by:
Sr=TL/1.21),
t is the hypothetical age at which the fish would have been zero
- length, K is the Brody growth coefficient, and W is weight in grams.
Area L
t K
W(g) o0 Cape Cod, MA -
Ocean City, MDa 683 0.031 0.274 5237.0 Ocean City, MD Virginia Beach, VAa 567 0.051 0.350 3026.0 Virginia Beach, YA -
Cape Fear, N.C.
331
-1.270 0.550 608.3 Delawgre Bay 1956 315
-0.500 0.327 Delaware Bay 1979 735 0.084 0.236 a Shepherd and Grimes (1983).
b Seagraves (1981).
7
(Table 4).
Merriner (1973) found significant length-weight differences between males and females which he attributed to proportionately greater development of ovarian tissue relative to testicular tissue.
COMMERCIAL AND RECREATIONAL FISHERIES The principal commercial methods
.used to harvest weakfish include
- trawls, pound nets, haul seines, and gill nets.
In addition, weakfish are caught in purse
- seines, floating
- traps, trammel nets, fyke nets, hoop nets,.and hand lines.
Generally these fisheries *can be classified as mixed opportunistic fisheries that concen-trate directly on weakfish for brief periods (Wilk and Brown 1982).
During the mid-1970's, high-speed pelagic trawls in the form of paired trawls and mid-water trawls were introduced in the New Jersey-Delawarearea.
Although the methods used to harvest weakfish for food have essentially remained the same, there have been significant shifts in the contribu-tions of trawls and pound nets during the past 40 yr (Perlmutter 1959; Merriner 1973; Wilk 1981).
During the period 1940-49, pound nets, haul
- seines, gill
- nets, and trawls took approximately 63%,
11%,
3%,
and 23% of the total catch, respectively.
Dur-ing 1970-79, the contribution of these same four gear types was 20%,
11%,
9%,
and 60%,
respectively (Wilk 1981).
Commercial landings of weakfish have fluctuated widely since the late 1800's.
Two peaks in landings have occurred since 1940, an all-time high of 18,800 t in 1945 and 16,300 t in 1980.
The distribution of weakfish landings has shifted historically from one geographic. area to another (Wilk 1980)
(Figure 5).
The Chesapeake Bay region (Maryland and Virginia) contri-buted most to the total weakfish land-ings in the 1940's, followed by the Mid-Atlantic Region (New
- York, New
- Jersey, and Delaware),
and the South Atlantic Region (primarily North Caro-lina).
Weakfish landings remained low in all regions throughout the 1950's and 1960's.
Since
- 1971, South Atlantic Region landings have exceeded those in one or both of the northerly regions.
The shift in catch to the South Atlantic Region is probably more weakfish using the equation: log-W (g) in grams, L is length in millimeters Table 4.
Length-weight
= log a + b log L (mm),
(*TL,
+SL),
and a and b relationships for where W is weight are constant.
Length Location Sex Log a b
r n
range (mm)
New York Bighta*
Combined
-4.877 2.948 0.99 666 59-768 Cape Cod, MA b*
Ocean City, MD Combined
-5.030 2.976 0.99 418 Delaware Bayc+
Combined
-4.423 2.861 0.99 182 195-725 North Carolinad+
Male
-4.558 2.851 0.99 482 Female
-4.343 2.946 0.99 610 Combined
-4.374 2.934 0.99 1,650 a From Wilk (1979),.
c From Seagraves (1981).
b From Shepherd and Grimes (1983).
d From Merriner (1973).
8
Table 5.
Estimated number and weight of weakfish caught by recreational fishermen in the Mid-Atlantic Region (New York-Virginia) 1979-87.
(National Marine Fisheries Service Marine Rec-reational Fishery Statistics Survey, Atlantic and Gulf Coasts 1979-87).
Year Number Weight (thousands)
(t) 1979 5,157 5,793 1980 14,570 20,544 1981 8,833 6,397 1982 1,064 2,717 1983 5,779 5,397 1984 3,671 3,377 1985 3,099 3,013
- 1986, 11,106 N6,053 1987 6,982 4,093
- Preliminary data.
ECOLOGICAL ROLE Figure 5.
U.S. commercial landings of weakfish by geographic region.
a reflection of the increased mobility of the North Carolina fishing fleet, and a concomitant shift in the center of landings to North Carolina, rather than an actual shift in distribution of weakfish (Wilk 1981).
Weakfish have also been important to the recreational fishery since at least the 1800's (Goode 1884). Anglers take weakfish from boats while troll-ing and drift fishing,.and from boats and shore. while
- casting, live bait fishing, jigging, still fishing, and
- chumming, primarily during the warmer.
months of the year (Freeman and Wal-ford
- 1974a, b,
c,
- 1976a, b).
Data from the National Marine Fisheries Service Marine Recreational Fishery Statistics Survey also indicate a peak in recreational landings in 1980 (20,544 t) followed by a sharp decline by 1982 (Table 5).
Food Habits Weakfish feed predominantly on penaeid and mysid shrimps, anchovies, and clupeid fishes (Welsh and Breder 1923; Thomas 1971; Merriner 1975; Stickney et al.
1975; Michaels 1984).
A shift of food habits with'growth was reported by Thomas (1971),
Merriner (1975),
and Stickney et al.
(1975).
Young weakfish feed mostly on mysid shrimp and anchovies; older weakfish feed on whatever clupeid species are abundant in an area.
Michaels (1984) reported that anchovies (rather than clupeids) were the single most impor-tant prey fish of weakfish collected offshore (depths 6 m).
Cannibalism was reported to be signif-icant in weakfish (Thomas 1971; Merriner 1975).
Weakfish feed pri-marily between dusk and dawn (Lascara 1981; Michaels 1984).
Chao and Musick (1977) correlated feeding structures with the food habits of juvenile sciaenids.
The weakfish has an oblique mouth that enables it to cap-9
ture pelagic prey from above and in front of it.
Other adaptations for successful predation include a pair of large canine teeth at the tip of the upper jaw for grasping larger swimming prey and a fusiform body shape for fast pursuit.
A study of fish predator-prey interactions in areas of eelgrass (Zostera marina) in Chesapeake Bay indicated that weakfish are important top carnivores in this habitat (Lascara 1981).
Field data and lab-oratory observations have suggested that weakfish forage along the peri-phery of eelgrass beds during periods of low light (dusk to dawn).
The high percentage of blue crabs (Calli-nectes sapidus) (40) and spot (Leio-stomus xanthurus)
(18) in weakfish stomachs indicated that some feeding occurred in eelgrass beds, since these animals were considerably more abun-dant there than at adjacent non-vege-tated sampling sites.
The lack of eelgrass in stomachs and the oblique mouth position of the species sugges-ted, however, that weakfish feed pela-gically and not deep within the vege-tation.
In laboratory experiments, weakfish captured fewer prey as the percentage of vegetative cover in-creased (Lascara 1981).
Community Ecology Surveys along the Atlantic coast indicated that estuaries provide feed-ing areas and spawning grounds for adult weakfish and are important nursery areas for the young.
Studies in Delaware Bay (Thomas 1971) and Chesapeake Bay (Chao and Musick 1977) showed that several species of sciaenids, including weakfish, silver perch (Bairdiella chrysoura),
- spot, croaker (Micropogonias undulatus), and black drum (Pogonias cromis) were able to coexist in the estuaries; probable reasons include differences in spatial and temporal distribution, relative abundance (abundances of dominant competitors may be reduced by physical disturbance or predation),
and food habits.
Juveniles of these species enter the estuaries at different times of the year, and with-in a given period, the highest catches of each species are in different areas and depths.
Although weakfish and croaker both prefer the deeper water in or near channels, croaker do not enter estuarine areas until fall after most weakfish have left.
Differences in the morphology of the feeding apparatus enable each species to feed at different levels of the water column.
Diseases Mahoney et a]. (1973) reported that
- weakfish, especially juveniles, are one of the most susceptible species to the "fin rot" disease of marine -and euryhaline fishes in the New York Bight.
The consistent and most striking feature of the disease in weakfish is necrosis of the caudal fin followed by involvement on the other fins.
Pollution is suspected to have a
role in the disease.
This disease has also been observed in weakfish from Delaware Bay and Georgia.
ENVIRONMENTAL REQUIREMENTS Temperature Weakfish eggs in all stages of development were collected in Peconic
- Bay, NY, and Narragansett Bay, RI, at temperatures of 12-24 °C (Perlmutter 1939; Herman 1963).
Laboratory tests indicated that hatching of weakfish eggs was optimal between 18 and 24 C
(Harmic 1958).
Weakfish have been collected over a temperature range of 9.5 to 30.8 oC (Massmann et a].
1958; Richards and Castagna 1970; Merriner 1976).
In areas of highest abundance of juvenile weakfish in Delaware
- Bay, water temperatures ranged from 28.0
°C in July to 17.2
°C in October (Thomas 10
1971).
Decreasing water temperatures in fall appear to initiate movement of most weakfish out of the estuaries to deeper water.
Older weakfish appear to precede the young of the year, in moving out of the estuaries (Hildebrand and Cable 1934; Massmann et al. 1958; Thomas 1971).
Only a
few weakfish have been collected at temperatures below 10 oC in Delaware 'Bay or Chesapeake Bay (Massmann et al.
1958; Abbe 1967; Thomas 1971).
Hildebrand and Cable (1934) reported that some small weakfish (122-182 mm TL) remained in North Carolina estuaries and nearshore coastal waters year-round except dur-ing brief cold snaps.
Dead and numb weakfish were seen in shallow waters when water temperatures suddenly dropped to 5 oC (Smith 1907; Hilde-brand and Cable 1934).
Schwartz (1964b) subjected five weakfish collected at 20.7 °C to normal winter water temperatures.
Swimming speed slowed drastically as the water temperature approached 10 OC, feeding ceased at 7.9 OC, and'all fish died at 3.3 oC.
Wilk (1979) reported that as temperature was grad-ually increased (0.05 OC/h) from the acclimated temperature range of 19-20
°C to almost 29 9C, weakfish showed a 35% increase in swimming speed accom-panied by tighter and more frequent schooling; however, as the fish became acclimated to 29
°C their activity decreased to a point similar to that before the temperature was increased.
This increased activity may help to move the animals from regions of ad-verse high temperature.
Salinity Weakfish are euryhaline and have been collected at salinities ranging of 0.1 to 32.3 ppt (Massmann et al.
1958; Richards and Castagna 1970; Wilk and Silverman 1976; Wilk et al.
1977).
Harmic (1958) collected eggs and larvae in Delaware Bay at salinities of 12.1 to 31.3 ppt.
Juveniles have been taken in salinities from 0.1 to 31.7 ppt, but areas of most abun-dant catches had salinities of 2.0 ppt in June to 10.8 ppt in August (Mass-mann et al.
1958; Richards and Casta-gna 1970; Thomas 1971).
Adults were collected over a salinity range of 6.6 to 32.3 ppt (Richards and Castagna 1970; Wilk and Silverman 1976; Wilk et al.
1977).
Dissolved Oxygen Information on relationships be-tween dissolved oxygen and weakfish tolerance or preferences is scarce.
Thomas (1971) reported that upriver movement of juvenile weakfish in the Delaware River was blocked by low oxygen concentrations (1.0-2.3 ppm).
In areas of the most abundant catches of juvenile weakfish in Delaware Bay, mean dissolved oxygen ranged from 4.2 ppm in July to 7.4 ppm in October.
Pollution In ' a model of the effects of pollution on a multispecies group of coastal
- fishes, weakfish showed relatively large depressions in abundance in response to chronic or acute pollution, but then recovered relatively quickly (in 6-10 years)
(Schaaf et al.
1987).
11
LITERATURE CITED
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17 1
REPORT DOCUMENTATION 1
O.REPRT N
. Recieient's Accaesson No.
PAGE Biological Report 82(11.109)*
- 4. Title and SWMbt*tl S Raoit Data Species Profiles:
Life Histories and Environmental Requirements of August 1989 Coastal Fishes and Invertebrates (Mid-Atlantic)--Weakfish Oo
- 7. Author(s)
I Parming Orgaization Root No L.P. Mercer
- 4. Performing Oranization Name and Address
- 10. Proloct/Task/Work Unit No.
North Carolina Division of Marine Fisheries P.O. Box 769
- 11. Contrct(C) or Grant(G) No.
Morehead City, NC 28557 (C)
(GI
- 12. So*soring Organintlon Name and Address U.S. Department of the Interior U.S. Army Corps of Engineers
- 13. Typeo#ReportPeodCoverd Washington, DC 20240 Waterways Experiment Station Fish and Wildlife Service P.O. Box 631 National Wetlands Research Center Vicksburg, MS 39180 14.
IS. Supplementary NotOs U.S. Army Corps of Engineers Report No.
TR EL-82-4 14, Abstract (Umit: 200 words)
Species profiles are literature summaries of the taxonomy, morphology, range, life history, and environmental requirements of coastal aquatic species.
They are designed to assist in environmental impact assessment.
Weakfish are one of the most abundant fishes in the estuarine and nearshore waters of the Atlantic coast.
Weakfish mature at age I throughout their range and spawning takes place in coastal and estuarine waters from March.to September.
Juveniles utilize the deeper areas within estuaries as nursery grounds, migrate from high to low salinity areas throughout the summer, return to high salinity areas in fall, and most leave the estuaries by late fall.
Some may remain in estuarine and nearshore coastal waters in winter, particularly in southern areas.
Adult weakfish migrate seasonally, north in spring and south in fall and between inshore and offshore waters.
Growth rates, maximum size, and longevity of weakfish are higher at the northern end of the range.
Weakfish are an important recreational and commercial species in the Mid-Atlantic.
Weakfish feed predominantly on mysid shrimp and anchovies as juveniles, and on clupeids and anchovies as adults.
Weakfish have been found.over a temperature range of 9.5 to 30.8 °C.
Juvenile weakfish have been found over a wider salinity range (0.1-31.7 ppt) than adults (6.6-32.3 ppt).
- 17. Oocument Analysis
- a.
Descriptors Estuaries Temperature Fishes Growth Salinity Habitat requirements Life cycles Dissolved oxygen Food habits Fisheries
- b. Ideatfiers/Opeo-Endod Te*m Weakfish Cynoscion reqalis Spawning
- c. COSATI Field/Group
- 14. AvalailibtY S*tatemnt
- 19. Securit Classi (Thisi Repot
- 21. No. Of Pas" Unclassified 17 Unlimited 2.0..
- S curiy.las (hiPge) 2L-Pric Unclassified (Sea ANSI--Z3.8 OPTIONAL FORM 272 (4-77)
(Formerly NTIS-35)
DCpartment of Com ltoC
.1
As the Nation's principal conservation agency, the Department of the Interior has responsibility for most of our nationally owned public lands and natural resources. This includes fostering the wisest use of our land and water resources, protecting our fish and wildlife, preserving the environmental and cultural values of our national parks and historical places, and providing for the enjoy-ment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Depart-ment also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S.
administration.
U.S. DEPARTMENT OF THE INTERIOR FISH AND WlULIFE SERVICE TAKE PRIDE in America m
I II%.~&V. La IN I~
I UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE National Wetlands Research Center NASA-Slidell Computer Complex 1010 Gause Boulevard Slidell. LA 70458 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE, $300 POSTAGE AND FEES PAID U.S. DEPARTMENT OF THE INTERIOR INT-423