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Page 1: A Review and Updated Assessment of Florida's Anadromous Shads: American Shad and Hickory Shad

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A Review and Updated Assessment ofFlorida's Anadromous Shads: AmericanShad and Hickory ShadRichard S. McBride a & Jay C. Holder ba Florida Fish and Wildlife Conservation Commission , 100 EighthAvenue SE, St. Petersburg, Florida, 33701-5020, USAb Florida Fish and Wildlife Conservation Commission , 5450 U.S.Highway 17, DeLeon Springs, Florida, 32130, USAPublished online: 08 Jan 2011.

To cite this article: Richard S. McBride & Jay C. Holder (2008) A Review and Updated Assessment ofFlorida's Anadromous Shads: American Shad and Hickory Shad, North American Journal of FisheriesManagement, 28:6, 1668-1686, DOI: 10.1577/M07-066.1

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Page 2: A Review and Updated Assessment of Florida's Anadromous Shads: American Shad and Hickory Shad

A Review and Updated Assessment of Florida’s AnadromousShads: American Shad and Hickory Shad

RICHARD S. MCBRIDE*1

Florida Fish and Wildlife Conservation Commission,100 Eighth Avenue SE, St. Petersburg, Florida 33701-5020, USA

JAY C. HOLDER

Florida Fish and Wildlife Conservation Commission,5450 U.S. Highway 17, DeLeon Springs, Florida 32130, USA

Abstract.—This paper reviews the history of fishing, regulations, and stock assessments for Florida’s

anadromous shad species—American shad Alosa sapidissima and hickory shad A. mediocris—and assesses

their status in Florida’s St. Johns River based on a creel survey and an electrofishing survey. Historically,

these anadromous shads constituted an important fishery in Florida. Landings were first reported in the 1860s,

and scientific assessments occurred in the 1950s, 1960s, and early 1970s. Netting restrictions effectively

ended the commercial fishery in the 1990s. We used recreational catch rates as a proxy for stock size and

found it to be low but stable during 1993–2005. The mean length of American shad was significantly less

during 2002–2005 than it was historically (1958), and the recent proportions of female American and hickory

shad were significantly lower than the historical proportions. These data were interpreted as demonstrating a

negative, but perhaps only an historical, effect of fishing. The rebuilding of Florida’s anadromous shad stocks

via fishing regulations was not evident; this may require more time, or perhaps factors other than fishing are

interfering with the rebuilding process.

American shad Alosa sapidissima and hickory shad

A. mediocris are anadromous clupeids that spawn in

rivers but spend most of their adult lives at sea. Along

the U.S. East Coast, American shad spawn from

Canada to Florida (Limburg et al. 2003) and hickory

shad from Maryland to Florida (Harris et al. 2007). In

Florida, American and hickory shad spawn during

winter in rivers of the northeastern part of the state;

their juveniles migrate to the lower reaches of the river

and out into coastal habitats during the following fall

(McBride 2000; Trippel et al. 2007).

Worldwide, the biology and management of Alosa

and other shad species (Alosinae) have received

considerable attention (e.g., Limburg and Waldman

2003). In North America, American and hickory shad

constituted very important fisheries, but declining

landings coupled with the expansion of other fisheries

have reduced their economic and cultural importance

(Walburg and Nichols 1967). Along the U.S. East

Coast, anadromous shad stocks are managed by a

fishery management plan (FMP) overseen by the

Atlantic States Marine Fisheries Commission (ASMFC

1985, 1999). In the most recent stock assessment

(ASMFC 2007), over one-half (19 of 32) of the

American shad stocks were reported to be either

declining or unknown; only two stocks were consid-

ered to be increasing in abundance.

This paper presents a case study of American and

hickory shad in Florida’s St. Johns River as an example

of this ongoing stock assessment process by the

ASMFC and its member states. The central east coast

of Florida is the southern limit of the distribution for

both species, and the St. Johns River (Figure 1) is the

only river within Florida with sufficient data for the

analysis of either species (Rulifson 1994; Florida Fish

and Wildlife Conservation Commission, unpublished

data). The St. Johns River is 499 km in length and

flows slowly from south to north; because it drops only

9.1 m in elevation (,2 cm/km) and widens at various

points to create several shallow lakes and appends to

others, it is known as a ‘‘river of lakes.’’

This paper begins with a brief review of the

fisheries, fishing regulations, and stock assessments

of Florida’s American and hickory shad (see McBride

2000 for a more detailed review). The remainder of the

paper assesses the status of these two stocks using data

from recent fishery-dependent and fishery-independent

collections in the upper St. Johns River and, where

appropriate, unpublished data from earlier research by

Florida’s state research programs (e.g., Williams and

Bruger 1972; Williams et al. 1975). The underlying

* Corresponding author: [email protected] Present address: National Marine Fisheries Service,

Northeast Fisheries Science Center, 166 Water Street, WoodsHole, Massachusetts 02543-1026, USA.

Received April 10, 2007; accepted April 21, 2008Published online November 20, 2008

1668

North American Journal of Fisheries Management 28:1668–1686, 2008� Copyright by the American Fisheries Society 2008DOI: 10.1577/M07-066.1

[Article]

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FIGURE 1.—Map of the St. Johns River and related lakes. River lengths are indicated at 100-km intervals from the mouth of the

river near Mayport.

ANADROMOUS SHADS OF FLORIDA 1669

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purposes of this study were (1) to review the available

data and information regarding Florida’s American and

hickory shad and (2) to assess the recovery of these

stocks in light of the extensive reductions in commer-

cial fishing effort that have occurred recently.

Historical Review

Fisheries. —Florida’s native Americans most likely

fished for anadromous fishes, but unlike in other states,

there are no specific records of this (McBride et al.

2003, poster at the 23rd Annual Meeting of the Florida

Chapter of the American Fisheries Society). Commer-

cial shad fishing began in Florida’s St. Johns River as

early as the 1860s (Baird 1874; Osborn 1882; Dempsey

1887), but Florida’s was the last shad fishery to

develop along the U.S. East Coast and it was relatively

small compared with those in other states (McBride

2000). The expansion of railroads into Florida

increased the value of Florida’s fishery because the

fish could then be readily transported to northern

markets (Brice 1898), and by 1889–1890 the landings

(.0.9 million kg) and value (US$100,000) of Florida’s

shad stocks were higher than those of any other marine

product harvested within the state (Smith 1893).

Landings of Florida’s shad stocks peaked at the turn

of the century at about 1.4 million kg and fluctuated

between 0.09 and 0.4 million kg from the 1920s to the

1960s. Thereafter, commercial landings of Florida’s

shad stocks continued to decline and dropped dramat-

ically to zero in the 1990s (Table 1; Walburg 1960a,

1960b; Walburg and Nichols 1967; Williams and

Bruger 1972; ASMFC 1985; McBride and Richardson

2005).

Landings of Florida’s shad stocks declined during

the last century for a variety of reasons. Although

overfishing has been implicated (Williams and Bruger

1972), commercial landings and effort have both

declined because of shrinking markets for these species

and because of increasingly restrictive netting regula-

tions within Florida. The most recent decline in

commercial landings of Florida’s shad stocks was a

result of netting restrictions that reduced gill-net effort

to zero in the 1990s (McBride 2000).

At the beginning of Florida’s commercial shad

fishery, only gill nets were used (Baird 1874). By the

1900s, fishing methods had expanded to include drift

gill nets, haul seines, and anchored or staked gill nets

(Smith 1898; Stevenson 1899; Walburg and Nichols

1967). In the 1950s, haul seines were the primary gear,

and gill nets were secondary (Walburg 1960a). Today,

netting for shad is no longer a significant commercial

enterprise in Florida. During the early 1970s, haul

seines were discontinued in the St. Johns River

(Williams and Bruger 1972), and by the late 1990s

gill nets were so heavily regulated that they were

virtually eliminated as commercial gear (McBride

2000).

Florida’s commercial shad fishing grounds have

shifted over time as well. In the 1860s, shad fishing

became established near the mouth of the St. Johns

River, between Mayport (river kilometer [rkm] 0;

Figure 1) and Jacksonville, and also farther upstream,

near Palatka (rkm 127; Baird 1874). By the 1950s,

harvest was primarily by set gill nets in the lower river

and by haul seines in the middle river (near Palatka;

Walburg and Nichols 1967). The use of gill nets around

the Mayport jetties had increased by the 1970s, and by

the early 1990s nearly all of the shad harvested came

from gill nets fished in coastal waters just offshore of

Mayport (Williams and Bruger 1972; McBride 2000).

Fishing offshore of Atlantic states other than Florida

(i.e., the ‘‘ocean-intercept’’ fishery) probably added

additional fishing pressure on Florida’s shad stocks. In

the 1980s and 1990s gill-net landings of shad from this

ocean-intercept fishery more than doubled (ASMFC

1999). By 2005, ocean-intercept fishing was phased out

because of concerns that fishing on mixed stocks in the

ocean could be adversely affecting smaller shad stocks,

which were by and large poorly monitored (ASMFC

1985, 1998, 1999; Hoenig et al. 2008).

TABLE 1.—Annual (1987–2005) commercial landings of

anadromous American and hickory shad, combined, from

Florida’s Nassau, Duval, and St. Johns counties (all coastal),

and Putnam county (inland). The geographic area was chosen

to limit misreporting of other species that are commonly called

‘‘shad’’ (i.e., menhadens Brevoortia spp. on Florida’s west

coast and gerreids in south Florida). A fishing year covers the

period from July of one year to June of the next year (e.g.,

1987¼ July 1986–June 1987). Total landings combine ocean

and riverine catches. Source: Florida Marine Fisheries

Information System.

Fishing year Ocean landings (kg) Total landings (kg)

1987 64,557 70,6501988 121,023 121,0791989 74,927 75,0511990 77,219 131,4971991 26,732 32,5421992 22,560 22,6351993 11,138 11,1381994 11,332 11,3491995 12,178 12,2211996 1,659 1,6591997 25 251998 8 81999 218 2182000 364 3642001 0 02002 0 02003 0 02004 0 02005 0 0

1670 MCBRIDE AND HOLDER

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Although sportfishing for shad stocks in the St.

Johns River occurred as early as the late 1800s (Pfeiffer

1975), it was the introduction of spinning tackle in the

1940s that helped popularize shad sportfishing (Snyder

1949; Nichols 1959; Walburg 1960a, 1960b). During

the 1950s and 1960s, the shad sport fishery in the St.

Johns River was estimated to be larger than the shad

sport fisheries in any of the other Atlantic states

(Nichols 1959, 1966; Walburg and Nichols 1967).

Today, most shad in Florida are caught by recreational

anglers practicing catch and release (see Assessment

Update). Fly-fishing for shad in particular has become

popular in Florida (Lindsay 1999). Anglers fishing for

shad use public boat ramps and fish camps on the St.

Johns River between DeLand and Lake Poinsett (rkm

238–378; Walburg 1960a; Branyon 1999; McPhee

2002), traditional access points being found near

‘‘Shad Alley’’ at Cameron Wight Park (rkm 281),

Mullet Lake Park (rkm 285), Lemon Bluff (rkm 290),

Puzzle Lake (accessible from C. S. Lee Park [rkm

310]), and Hatbill Park (rkm 330). The certified state

record fish (a tie) for American shad (2.36 kg) were

caught in the St. Johns River within Seminole and

Volusia counties (Florida Fish and Wildlife Conserva-

tion Commission, floridafisheries.com/record.html).

Regulations.—Commercial fishing regulations for

Florida’s shad stocks have existed since 1896,

including (1) effort restrictions (no fishing on Sundays),

(2) mesh size restrictions (to allow the escapement of

smaller fish), and (3) closed areas (nets prohibited

within inlets and in the lake portions of the St. Johns

River) (Stevenson 1899; Walburg and Nichols 1967).

By 1960, regulations included (1) a commercial season

(November 15 to March 15) and (2) an area closed to

commercial nets south of Lake George (rkm 197). In

the 1990s, a series of mesh size and net-tending

regulations culminating in a net limitation referendum

(Constitution of Florida, article X, section 16) caused

sharp reductions in Florida’s commercial shad landings

and effort (McBride 2000). Consequently, although

sale of American and hickory shad is not prohibited, the

commercial net fishery for shad has been effectively

eliminated within state waters.

Sportfishing for Florida’s shad stocks has been

regulated by bag limits since 1955. In 1973, the initial

bag limit of 15 American shad was lowered to 10 fish/d

(Williams 1996). Since 1990, a saltwater fishing

license has been required of most anglers who fish

for marine species, including anadromous species.

Since 1997, hook and line has been the only allowable

fishing gear for American shad, hickory shad, and

Alabama shad Alosa alabamae, and it has been

unlawful to possess more than 10 fish in any

combination of these species (Florida Administrative

Code, chapters 46–52.001).

Management of all U.S. East Coast shad and river

herring (Alosa) species is overseen by the ASMFC

according to an FMP subscribed to by the individual

Atlantic coast states (ASMFC 1985, 1999). Amend-

ment 1 to the ASMFC’s shad and river herring FMP

calls for (1) a 5-year phaseout of the ocean-intercept

fishery, (2) regulating the in-river fishery at target

exploitation rates, and (3) implementing bag limits of

10 fish/d in the recreational fishery (ASMFC 1999).

Amendment 1 also established monitoring programs

for all states; it requires Florida to monitor commercial

and recreational shad fisheries and to complete fishery-

independent surveys of American shad.

Stock assessments.—Stock assessments of Florida’s

St. Johns River shad stocks were initially limited to

occasional surveys of the fishery and comments from

the public. For example, reports of the 1896 Florida

shad fishery document hundreds of people involved in

the harvest of about 450,000 shad worth about $62,000

(Stevenson 1899). Concerns were expressed over a

century ago that downstream nets ‘‘completely block

the river, and prevent any shad from coming up’’

(Osborn 1882: 351). Also, requests for a hatchery on

the St. Johns River began so that ‘‘the yield should be

increased by artificial means’’ (Henshall 1898:254).

The first scientific assessments of Florida’s St. Johns

River shad stocks began in the 1950s. Talbot and Sykes

(1958) tagged 882 American shad during the 1953

spawning run and had a 21.3% recapture rate. Walburg

(1960a) tagged another 950 American shad during the

1958 spawning run and reported a recapture rate of

12.7%. These data were used to estimate the stock size

of American shad in Florida’s St. Johns River, resulting

in a production of 0.41–1.7 million kg annually

between 1953 and 1965 (Walburg 1960a; 1960b;

Nichols 1964, 1965, 1966a). Stock size during this

period was roughly equal to the peak yields of

Florida’s American shad in the early 1900s. Thus, this

stock was much larger at the beginning of its

exploitation than during the 1950s, the mortality rates

were astonishingly high in the early 1900s, or both.

During the 1950s, when fishing mortality was

reasonably low, management of Florida’s shad stocks

focused on allowing sufficient escapement to maintain

viable fisheries. In the St. Johns River, total biomass

harvest ranged between 15% and 37% of the stock;

depending on the year, about 2–8% were taken by

commercial gill nets, another 7–20% by commercial

haul seines, and 3–8% by hook-and-line sport anglers

(Walburg 1960a, 1960b; Walburg and Nichols 1967;

ASMFC 1985).

Biological studies and descriptions of Florida’s shad

ANADROMOUS SHADS OF FLORIDA 1671

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Page 6: A Review and Updated Assessment of Florida's Anadromous Shads: American Shad and Hickory Shad

stocks were also completed by Williams and Bruger

(1972) and Williams et al. (1975). Their studies

provide habitat-based management recommendations

regarding proposed alterations of river flow and

channelization in areas where shad spawn. An updated

review of shad habitat requirements, specifically in

relation to river water levels and flows, was recently

completed by Harris and McBride (2004).

The conservation of shad stocks faced a new

challenge when ocean-intercept landings doubled in

the 1980s and 1990s, eventually accounting for 60% of

the total coastwide catch (ASMFC 1999; Brown et al.

1999; Hoenig et al. 2008). Concern arose that smaller

stocks, particularly those that were not being monitored

closely, were adversely but cryptically affected by this

interjurisdictional fishery. For example, an ASMFC

(1998) stock assessment of shad populations included

assessments of only 12 populations from Maine to

Georgia; no Florida rivers were included because of

insufficient data. Furthermore, efforts to identify

diagnostic characteristics of river-specific or state-

specific stocks failed, so that monitoring the stock

composition from the ocean-intercept fishery’s catch

was of little use in terms of assessing the impact of this

fishery on individual shad stocks (Epifanio et al. 1995;

Brown et al. 1999; ASMFC 1999).

Commercial fishing data have been reported to

Florida’s Marine Fisheries Information System since

1986 (Table 1), when state law required reporting of all

wholesale transactions of marine organisms landed

within Florida. These data represent a census of all

legal commercial landings, but the corresponding catch

rates may be biased because trips that do not catch fish

do not need to be reported. Also, landings are not

separated by shad species, although American shad is

frequently the target species and is generally much

more abundant than hickory shad in Florida. These data

depict the decline of commercial shad landings due to

netting restrictions implemented during the 1990s, but

otherwise, they are of little use for continued

assessment of Florida’s shad stocks.

Recreational landings can be downloaded from the

Marine Recreational Fisheries Statistics Survey

(MRFSS) Web site (http://www.st.nmfs.gov/st1/);

however, no landings of Florida’s shad stocks were

reported to this Web site. Apparently, the MRFSS does

not intersect with the recreational shad fishery on

Florida’s St. Johns River, presumably because this

fishery is concentrated well upstream. Walburg (1960a)

summarized the data from a creel survey of the 1958

American shad sport fishery on the St. Johns River.

This included a riverwide survey of all major fish

camps, seasonality of catch, and numbers of male and

female American shad and hickory shad per week.

Walburg (1960a) also estimated the sport catch from

spawning years 1953–1958. Other estimates of recre-

ational landing were reported in Nichols (1964, 1965),

Walburg (1960b), Williams and Bruger (1972), and

Williams (1996). No biological samples were attempt-

ed during these other surveys except to identify sex in

some instances. In 2000, a pilot access-point creel

survey was implemented by the Florida Fish and

Wildlife Conservation Commission at three public boat

ramps (rkm 281, 285, and 310) during the peak fishing

period (January–March). Only three shad were ob-

served in six sampling days, which led us to conclude

that widely scattered public boat ramps and private

access points, as well as a high incidence of catch-and-

release fishing, confounded such an access-point

survey design. To date, creel surveys had produced

little more than a single point estimate of catch and

effort, precluding much in the way of comparisons

between decades, but we report herein on a multiyear

(1993–2005), roving creel survey that is suitable as a

proxy for following Florida shad stock size.

Life history information has been challenging to

apply to the assessment of Florida’s shad stocks. For

example, there is strong evidence that anadromous

shad return to their native rivers to spawn (Hollis 1948;

Talbot and Sykes 1958; Nichols 1960; Judy 1961;

Leggett and Whitney 1972), but no significant tagging

programs or juvenile surveys have occurred for several

decades, precluding estimates of population size or

stock–recruitment relationships within Florida (Trippel

et al. 2007). Furthermore, in the St. Johns River, there

is no fall line to concentrate fish, and most of the

spawning ground is highly braided, shallow habitat,

which can complicate tag–recapture designs. As

another example, fish size is a simple variable with

which to assess stock status, although it requires

recognition that American shad are larger than hickory

shad and females are larger than male conspecifics

(LaPointe 1957; Walburg 1960a; Leggett 1969;

Williams et al. 1975). Age is a more informative

variable to monitor fisheries, and many shad species

are managed based on mortality benchmarks (i.e., F30

),

which are typically estimated from age data. Nonethe-

less, a validated aging method exists for only one

American shad stock (i.e., the Connecticut River),

which is so geographically distinct that age-based

assessment methods cannot be readily applied to

Florida’s stock (McBride et al. 2005). Even if a

validated aging method existed for Florida’s shad, it is

not clear the data would be helpful for monitoring

mortality: recruitment to the spawning grounds is

incomplete in any particular year and both species are

reported to be relatively short-lived (6–7 years;

LaPointe 1957; Walburg 1960a; Leggett 1969; Wil-

1672 MCBRIDE AND HOLDER

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Page 7: A Review and Updated Assessment of Florida's Anadromous Shads: American Shad and Hickory Shad

liams et al. 1975; Harris et al. 2007). Finally, several

estimates of yolked oocyte numbers have been

published (Davis 1957; Walburg 1960a; Leggett

1969; Leggett and Carscadden 1978), but Olney et al.

(2001) concluded that American shad have indetermi-

nate fecundity and asynchronous oocyte development;

therefore these historical estimates cannot be readily

applied to egg production models in Florida (Olney and

McBride 2003).

Methods

Stock assessment data.—As identified above, many

standard assessment approaches (i.e., stock–recruit-

ment, mark–recapture, age-based, or egg production)

are not tractable for assessing the status of Florida’s

anadromous shad stocks at this time. In this data-poor

situation, we turned to a relatively recent but

reasonably long time series of catch per unit effort

data from a creel survey. We also had data from a

recent but shorter time series of electrofishing catch-

per-unit-effort data, which we used to validate the creel

survey data as a proxy for stock size. The electrofishing

survey also supplied information about shad species,

sex ratio, and fish size.

The temporal and spatial extent of sampling (creel

and electrofishing) was based on previous reports of

shad spawning in Florida’s St. Johns River. The

seasonal range of the spawning runs is reported to

occur from November to May (Baird 1874; McLane

1955; Walburg 1960a; Leggett and Whitney 1972;

Williams et al. 1975; Davis 1980; Harris et al. 2007).

Thus, even though the run was typically sampled in

two calendar years, we refer to the most recent year as

that of the spawning run (e.g., the 2002 spawning run

began in 2001 and ended in 2002); this terminology is

compatible with the reporting of spawning runs in

northern states. Our sampling areas were concentrated

in the upper river (i.e., the southern portion),

specifically to target American shad. American shad

spawning grounds are well documented from rkm 230

to rkm 415 based on egg surveys (Walburg 1960a;

Nichols 1966a; Williams and Bruger 1972; Williams et

al. 1975) and the distribution of females in spawning

condition (Glebe and Leggett 1981). Moody (1961)

concluded that hickory shad do not migrate as far up

the river to spawn as American shad, but Harris et al.

(2007) reports evidence (gonad histology) of spatial

overlap in the spawning grounds of the two species in

the St. Johns River.

Electrofishing survey.—Spawning seasonality, hab-

itat distribution, sex ratios, and the sizes of anadromous

shad were determined during a standardized electro-

fishing survey of the upper St. Johns River. Estimates

of abundance from the electrofishing survey were also

compared with independent estimates of abundance

from a longer-term, roving creel survey (see below).

Electrofishing was conducted every 2–3 weeks

throughout the 2002–2005 spawning runs between

the south end of Lake Monroe and the north end of

Lake Harney (approximately rkm 274–307; Figure 1);

this area is referred to as the ‘‘creel area’’ because it

overlaps a roving creel survey area. Electrofishing also

occurred in five other areas: (1) the Wekiva River, a

major tributary entering the St. Johns River at rkm 253

downstream of Lake Monroe, (2) the Puzzle Lake area,

an expansive, shallow portion of the St. Johns River

immediately upstream of Lake Harney and extending

into the diffuse Puzzle Lake region (rkm 308–315), (3)

the Econlockhatchee River, another major tributary that

enters the St. Johns River at rkm 311, (4) a shallow,

braided area of the St. Johns River main stem south of

Lake Cone (rkm 330), and (5) a shallow stretch of the

main stem just north of Lake Poinsett (rkm 378).

Preliminary sampling in these five additional areas

began in 2003, and regular sampling occurred every 3–

6 weeks per area during the spawning runs of 2004 and

2005.

Measures of fish abundance adhered to standardized

procedures. Fish were shocked with pulsed direct

current using either 340 or 680 V and 60 Hz to

standardize power transfer at 10–12 A; the actual

power measured for the 700 transects completed in this

study was 11.4 6 2.1 A (mean 6 SD). The electric

charge was released in a pattern of 25 s on and 5 s off

until a total on-time of 600 s was achieved. Each

transect followed a sinusoidal path in a downstream

direction at a speed of about 2 knots. This meandering

extended from shore to shore, where the width of the

river was less than approximately 50 m. Where the

river was wider, the meandering of each transect

extended between the shoreline and midchannel; to

randomize the sampling locations the initial riverbank

(side) was chosen by a coin toss every 4–5 transects per

day, and the subsequent transects alternated down-

stream from side to side. Two biologists, each with a

long-handled dip net, dipped for shad adults on most

(97.1%) transects; otherwise, only one biologist was

available for netting fish, but this was not considered to

appreciably affect (i.e., lower) the measures of

anadromous shad abundance in those 20 transects.

All transects reported herein were sampled during

daylight hours.

Fish abundance was calculated as a geometric mean

number of fish per transect (GM), based on data from 5

to 10 transects per area per day:

GM ¼ antilog1

n

Xn

i¼1

logeY þ 1;

ANADROMOUS SHADS OF FLORIDA 1673

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where n is the number of transects in a specified fishing

area for a single day and Y is the number of fish dipped

per transect (either American shad, hickory shad, or

both species combined).

All anadromous shads were sampled without

replacement or were marked with a hole punched in

a medial fin so that recaptures were identifiable. Only 3

of 245 marked fish were recaptured, and no further

conclusions were reached regarding these preliminary

mark–recapture efforts. All fish brought back to the

laboratory were measured to the nearest millimeter fork

length (FL) and weighed to the nearest 0.1 g total body

weight. The sex of each fish was determined by

macroscopic inspection of the gonads. Before release,

marked fish were measured for fork length; their sex

was recorded as male if milt was expressed when the

abdomen was squeezed or female if milt was not

apparent (this method was determined to be reliable by

examining unmarked fish in the laboratory; McBride,

unpublished data). A four-way analysis of variance

(ANOVA) was used to determine whether FL varied

significantly as a result of gender, sampling month,

year, or location. A full model was possible for

American shad, but third-order and fourth-order

interactions were not included in the model for hickory

shad because the sample size was too small. Results

were deemed statistical significant at a ¼ 0.05.

Roving creel survey.—A roving creel survey was

used to monitor angler catches of American and

hickory shad during 11 of the 13 spawning runs from

1993 to 2005. Angler interviews and instantaneous

counts of the number of anglers were completed within

an 11.9-km stretch of the St. Johns River between Lake

Jesup and Lake Harney. This creel area was historically

well known for shad fishing and includes such fishing

locations as Shad Alley, Lemon Bluff, and Iron Bend

(Branyon 1999; McPhee 2002). Sampling was strati-

fied by day of the week (weekday versus weekend) and

diurnal period (0730–1230 hours and 1230–1730 hours

before 1997 and 0700–1030 hours, 1030–1400 hours,

and 1400–1730 hours beginning in 1997. Shad fishing

is concentrated on weekends and holidays (Walburg

1960a), so three weekdays and two weekend days were

sampled every 2 weeks. Holidays were counted as

weekend days. Each 2-week period started on a

Monday and ended 14 d later.

Random, equal probability determined whether the

instantaneous count of fishing effort was measured on

the upstream or downstream run. Instantaneous counts

were made of all anglers in all boats within the main-

stem of the St. Johns River between the power lines

across from the boat-launching ramp at rkm 279.7 to

the power lines upstream of Iron Bend at rkm 291.6.

Anglers were interviewed on the complementary run

(i.e., downstream or upstream) and asked what species

they targeted, how many hours they fished, how many

fish they caught (by species or species groups), and

how many fish they kept (by species or species

groups). No fish were sampled for sex or size; in fact,

American shad and hickory shad were recorded only as

‘‘anadromous shad’’ because many anglers cannot

distinguish between these species; blueback herring

Alosa aestivalis, on the other hand, are more readily

identified and are not targeted in the sport fishery, so

they are not mixed in with these catch data.

Catch and effort data from the roving creel surveys

were expanded by using a mean-of-ratios estimator for

incomplete-trip interviews (Hoenig et al. 1997), that is,

Rh ¼1

n

Xn

j¼1

cj

lj;

where Rh

is the mean-of-ratios estimate for the species

in stratum h, cjis the catch in interview j, l

jis the total

angler-hours in interview j, and n is the total number of

interviews in stratum h. This estimate of angling

success included only trips with anglers that said they

were targeting shad, and fishing trips less than 0.5 h

long at the time of the interview were discarded.

Models.—We used a falsification approach to test

four hypotheses regarding the possible positive effects

of the in-state netting restrictions implemented during

the 1990s on St. Johns River shad stocks. The first two

hypotheses were designed to investigate evidence of

size- and sex-selective harvesting effects. In particular,

mesh size of gill nets could be used to select for fish

size, whereas haul seines and hook-and-line gear

cannot inherently be used in this manner (although

females may be preferentially harvested with any gear

because they are bigger and their roe has a high value;

Walburg 1960a). This concern was raised by Williams

and Bruger (1972), who noted that there was a 5.6:1

female : male ratio in landings from the gill nets (;13-

cm stretch mesh) fished near the Mayport jetties in the

early 1970s. They also noted that the sex ratio in the

recreational catch had declined from 1.1:1 in the 1950s

to 0.71:1 and 0.53:1 in 1969 and 1970. Here, we

compared recent data collected by electrofishing with

historical data collected by haul seine or hook and line

to see if size- and sex-selective harvesting effects

continued to exist.

The four hypotheses were as follows:

(1) Fish sizes are not different between decades.

Student’s t-tests were used to test whether monthly

or annual mean fish sizes were different from

historical estimates of mean fork length. No

differences would indicate a stable trend in fish

size, but decreased size in recent years could

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indicate a negative effect of size-selective harvest

practices, and increased size could indicate a

rebuilding trend. These tests were completed

independently for each species and each sex, and

because multiple comparisons were made, signif-

icance was set at 0.01.

(2) Sex ratios are not different between decades.

Historical sex ratios were approximately 1:1, which

are assumed to be optimal. Goodness-of-fit (chi-

square) tests were used to test whether recently

measured shad sex ratios were different from

historical estimates. Sex ratios that are stable

between decades are postulated to be desirable.

Female-biased sex ratios would not be expected, at

least as measured by electrofishing, and strongly

male-biased sex ratios would indicate a negative

effect of size-selective harvest practices. Again,

because multiple comparisons were to be made,

significance was set at 0.01.

(3) Angling success (i.e., angler catch rates) is not

related to fisheries-independent estimates of abun-

dance. This hypothesis was tested by correlating

success (mean-of-ratios estimates from the creel

survey) and geometric mean abundance of shad

collected by electrofishing. This hypothesis is not a

biological question per se but rather a validation

test as to whether the time series of angling success

estimates may be used as a proxy for spawner

abundance. If so, angling success should be

significantly and positively correlated with electro-

fishing abundances during the period both surveys

occurred (2002–2005).

(4) The annual time series trend of angling success is

zero. This hypothesis was tested with regression

analysis of the creel survey abundance time series

for the 1993–2005 spawning runs. If this hypoth-

esis is not rejected, the time series represents no

measurable change in anadromous shad abundance

during this 13-year period. If it is rejected, the time

series may indicate either a decreasing or an

increasing trend in abundance. An increasing trend

would be consistent with the postulate that netting

restrictions and other fishing regulations imple-

mented in the 1990s are helping to increase

Florida’s shad stock abundance. This hypothesis

assumes that catchability remained constant, which

seems reasonable because no innovations in fishing

methods occurred during this period.

Results

Spawning Runs of 2002–2005

American shad adults arrived on the spawning

grounds at the same time as or later than hickory shad

adults (Figures 2, 3). Hickory shad were collected

south of Lake Monroe up to 4 weeks earlier at the

beginning of the 2002 and 2003 spawning runs (i.e., by

mid-December 2001 and early December 2002) than

were American shad (i.e., mid-January 2002 and early

January 2003). Both species were first collected

together during the same week of the 2004 and 2005

spawning runs (i.e., mid-December 2003 and early

January 2005). American shad were present in the river

much longer, until May (Figure 2), whereas hickory

shad were not encountered in sampling areas after

March (Figure 3).

Hickory shad did not migrate as far upstream as

American shad did (Table 2). The Wekiva River, which

represented the most downstream electrofishing loca-

tion, was the only sampling area where hickory shad

were more abundant than American shad. In the creel

survey area, hickory shad were occasionally as

numerous as American shad. American shad were

even more abundant farther upstream. In contrast,

hickory shad adults were present in low or variable

numbers within the Puzzle Lake area and Econlock-

hatchee River, and they were not collected further

upstream.

American shad grew larger than hickory shad

(Figure 4a, c). The longest American shad was 464

mm FL (1,153 g total body weight) and the heaviest

was 1,700 g (450 mm); both were females. The longest

hickory shad was 414 mm FL (995 g) and the heaviest

was 1,027 g (400 mm); both were females. Males were

smaller than females in each species (Figure 4a, c). The

longest male American shad was 423 mm FL (no body

weight measured) and the heaviest was 1,095 g (419

mm). The longest male hickory shad was 400 mm FL

(770 g) and the heaviest was 913 g (373 mm).

The length of American shad was affected by factors

other than species and gender. According to a four-way

ANOVA, American shad fork length varied by sex (P, 0.0001), month (P¼ 0.018), year (P , 0.0001), and

sampling area (P¼ 0.0018); no interactive effects were

significant. Most striking was how American shad were

longer at the beginning of the spawning run than later

in the run. Mean female size was greater than 400 mm

FL in December and January but less than 390 mm by

April and May; mean male size exceeded 355 mm FL

in December and January but was less than 350 mm by

April. In the last 2 years of sampling, females averaged

about 1 cm longer than they were in the first 2 years,

and male size varied without an obvious trend over the

same 4-year period. Lengths of both sexes varied

between sampling areas but without an obvious pattern.

Sex, month, year, and area interacted to affect the

length of hickory shad (secondary interactions, P ,

0.05). Females were longer than males, and average

ANADROMOUS SHADS OF FLORIDA 1675

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female length increased about 2 cm from 2002 to 2005.

Samples sizes were, however, fairly small, and no other

patterns were discernible.

The weight of female American shad declined

steadily and significantly over the spawning season

(Figure 4b). An analysis of covariance that regressed

fish weight linearly on length with period (2-month

intervals) as a covariate showed no significant

interaction between slopes (P¼ 0.26) but significantly

different intercepts between the bimonthly groups (P¼0.001).

The mean sizes of both sexes of American shad were

larger historically (1958) than in recent years (2002–

2005; Figure 5). Mean female lengths were 390, 385,

394, and 402 mm FL in the 2002–2005 spawning runs,

respectively, whereas males averaged 356, 346, 365,

and 349 mm. In the 1958 shad run, the weighted mean

length was 427 mm FL for females and 386 mm for

males (Walburg 1960a). Multiple t-tests of sex-specific

fish size confirmed that these historical size differences

were significantly larger than in recent years (P . 0.01;

for statistical purposes, all eight comparisons assumed

FIGURE 2.—Abundance of American shad within six sampling areas along the St. Johns River, from downstream to upstream:

(A) the Wekiva River, (B) the roving creel survey area (Lake Monroe to Lake Harney), (C) the Econlockhatchee River, (D) the

Puzzle Lake area (Lake Harney to Puzzle Lake), (E) south of Lake Cone, and (F) north of Lake Poinsett. Note the different

scales of the y-axes. The thin vertical lines represent 95% confidence intervals; the numbers atop some error bars give the upper

confidence limit when it is off the scale.

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FIGURE 3.—Abundance of hickory shad within four sampling areas along the St. Johns River, from downstream to upstream:

(A) the Wekiva River, (B) the roving creel survey area (Lake Monroe to Lake Harney), (C) the Econlockhatchee River, and (D)the Puzzle Lake area (Lake Harney to Puzzle Lake). Lake Cone and Lake Poinsett were also sampled but no hickory shad were

collected at those locations. See Figure 2 for additional details.

TABLE 2.—Total numbers of American shad and hickory shad adults collected via electrofishing from spawning runs in the St.

Johns River, by sampling year and location. Sample years cover the period from November of one calendar year to May of the

following year (e.g., 2002¼November 2001 to May 2002). Sampling locations are ordered from north to south (i.e., downstream

to upstream).

Year Sampling locationa American shad Hickory shad Transects sampled

2002 Creel area 56 19 422003 Wekiva River 0 0 3

Creel area 225 29 104Econlockhatchee River 5 0 3N Puzzle Lake 209 3 33N Lake Cone 40 0 10N Lake Poinsett 2 0 6

2004 Wekiva River 4 12 20Creel area 33 36 119Econlockhatchee River 161 8 24N Puzzle Lake 247 2 50N Lake Cone 50 0 21N Lake Poinsett 3 0 18

2005 Wekiva River 2 21 25Creel area 23 18 102Econlockhatchee River 26 10 13N Puzzle Lake 186 3 53N Lake Cone 133 0 30N Lake Poinsett 11 0 24

Total 1,416 161 700

a The creel area extends from the southern end of Lake Monroe to the northern end of Lake Harney.

Some locations are approximate.

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the variance for the 1958 fish equaled the maximum

variance observed in the 2002–2005 spawning runs

because variance was not reported in Walburg 1960a).

Davis (1980) reported modal female sizes of 433 mm

FL for the 1971 and 464 mm for the 1972 spawning

runs (male modes: 401 and 360 mm FL), but he did not

report mean values so no further analyses were

attempted.

No obvious gender differences in hickory shad sizes

were detected between decades. The average hickory

shad lengths measured in 1972 and 1973 fell within the

95% confidence limits of those measured during 2002–

2005 (Figure 5).

Male and female American shad were found together

within all sampling areas, but the sex ratio varied

widely among months (Figures 6, 7). In each year

sampled, more males were collected at the beginning of

the spawning run and more females at the end of the

run. Hickory shad sex ratios did not appear to have a

strong seasonal trend.

The proportion of American shad females (Pf) was

significantly biased for the 2002 (Pf¼ 0.12) and 2003

(0.18) spawning runs (chi-square test; P , 0.001),

whereas the sex ratios for the 2004 (0.52) and 2005

(0.51) spawning runs were not significantly different

from 1:1 (P . 0.1). During the 1958 spawning run,

female American shad were significantly more abun-

dant than males (P , 0.001); however, the value of Pf

(0.53) was close to 0.5, and its significance seemed to

have been influenced by the particularly large sample

size of 63,693 (data from Walburg 1960a).

The sex ratios of hickory shad were significantly

different from 1:1 in each of the years 2002–2005 (P ,

0.01) and actually declined over time, from 0.27 to

0.32, 0.16, and 0.15. This is the opposite of the pattern

that was observed for American shad during this same

period, and it differs significantly from the historical

ratios for hickory shad. During the 1958 spawning run,

hickory shad were significantly biased toward females

(chi-square test: N¼ 1,553, Pf¼ 0.56, P , 0.001; data

from Walburg 1960a); during the 1972 and 1973

spawning runs the sex ratios (pooled for both years)

were not different from 1:1 (N ¼ 118, Pf¼ 0.54, P .

0.1; data from Williams et al. 1975).

Sport Fishery in 1993–2005

The estimated sport catch of shad within the 11.9-km

creel survey area ranged from 1,270 to 12,600 fish/

year, averaging 5,880 fish/year (SD ¼ 3,680). These

estimates were calculated over 13 years (1993–2005

but excluding 1997 and 2000) for the 20-week periods

beginning in early December and ending in late April.

Over the entire 13-year period, both catch and effort

declined (Figure 8). In average or poor sportfishing

FIGURE 4.—Scattergram of total body weight versus fork

length for American and hickory shad collected by electro-

fishing in the upper St. Johns River (Wekiva River to Lake

Poinsett) during the 2002–2005 spawning runs. The middle

panel shows time-varying data: December–January (plus

signs), February–March (dots), and April–May (times signs).

Data for all sample areas and years are combined.

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years, angling success was below 1.0 shad/h, whereas

in better years it was above 1.0 shad/h (Table 3; Figure

9).

Catch and release was commonly practiced; 79% of

the shad caught by angling in the 2002 spawning run

were released, along with 77% in 2003, 71% in 2004,

and 79% in 2005. Although some anglers may release

hickory shad preferentially, it is more common for

anglers to release males and keep females regardless of

species. Anglers fishing for freshwater fish, particularly

black crappie Pomoxis nigromaculatus, also caught

American shad; this could add to the total harvest rate

but was not calculated here.

A statistically significant and positive relationship

was found between the shad abundance measured by

electrofishing and that measured by the roving creel

survey (Figure 10). This was observed when the creel

survey estimates were correlated to electrofishing

within either the creel area (i.e., Lake Monroe to Lake

Harney: r ¼ 0.41, N ¼ 39, P ’ 0.01) or within an

adjacent, upstream section (Lake Harney to Puzzle

Lake: r¼0.69, N¼16, P , 0.01). Thus, the time series

of angler catch rates was an appropriate proxy for

measuring annual variation in population size.

The linear trend of angling success for the period

1993–2005 was not statistically different from zero

(Figure 9). During this period, angler success rates

have fluctuated without trend around 1 shad/h in the

creel survey area. These relatively stable estimates of

success have occurred during a period of generally

declining effort in the recreational shad fishery (Figure

8).

Discussion

Spawning Runs

American shad are winter spawners in Florida.

Although we did not collect any American shad on

the spawning grounds before December, they are

reported to enter the St. Johns River in November in

association with declining water temperatures (Wal-

burg 1960a; Leggett and Whitney 1972). We observed

only a single peak in fish abundance, generally during

February, which was also reported by Williams et al.

(1975) for the 1972 spawning run. In contrast,

Williams et al. (1975) and Davis (1980) reported two

peaks in abundance during some spawning runs of the

early 1970s. Davis (1980) noted that males predomi-

nated the first peak in abundance, and he suggested that

FIGURE 5.—Mean fork length of shad in the St. Johns River during different decades. Triangles depict American shad data for

1958 (from commercial haul seines as reported in Table 15 of Walburg 1960a) or hickory shad data in 1972–1973 (from

commercial haul seines as reported in Table 2 of Williams et al. 1975); diamonds depict electrofishing data for 2002–2005, the

thin vertical lines representing 95% confidence intervals. The American shad data are monthly means, the hickory shad data

means by sampling date.

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a second peak was milling or run-back behavior that

increased catchability. Florida’s American shad do not

appear to spawn in more than 1 year, a postulation

based on a lack of a downstream migration (Stevenson

1899), the absence of spawning marks on their scales

(LaPointe 1957; Walburg 1960a; Leggett 1969), and

energetic evidence (Glebe and Leggett 1981). Thus, the

decline in American shad abundance during spring

represents mortality rather than migration out of the

river.

Hickory shad are also winter spawners, but they are

found in the St. Johns River for a shorter period and do

not migrate as far upstream as American shad. They

have been collected by early December (Walburg

1960a; Williams et al. 1975; Harris et al. 2007) and

inhabit more of the lower St. Johns River, including

‘‘deeper waters of Lake George’’ (Moody 1961:13).

Our sampling appears to have adequately captured the

seasonality of the hickory shad spawning run, but

future investigations of this species should include a

larger part of the lower river. Hickory shad are thought

FIGURE 6.—Monthly proportions of female American shad

and hickory shad collected by electrofishing in the upper St.

Johns River (Wekiva River to Lake Poinsett) during the 2002–

2005 spawning runs. Months in which fewer than 10 fish of a

species were collected were excluded.

FIGURE 7.—Proportions of female American shad and

hickory shad during the spawning run in the St. Johns River

during different historical periods: 1958 (census card survey

of anglers from Table 6 in Walburg 1960a), 1972 and 1973

(haul seine collections between the towns of Palatka and

Welaka from Table 2 in Williams et al. 1975), and 2002–2005

(electrofishing collections). Months in which fewer than 10

fish were collected were excluded.

FIGURE 8.—Time series of total estimated recreational

catches (filled boxes) and fishing effort (open boxes) for

anglers targeting the St. Johns River spawning runs of

American and hickory shad, as derived from a creel survey

in the upper river during 1993–2005. The two species are

combined because many anglers cannot distinguish them and

simply target ‘‘shad.’’ The data are a subset of the seasonal

data (periods 3–8, or approximately January to March), when

catch and effort are highest; the trends based on other 2-week

aggregates (i.e., periods 1–10) did not differ (see Table 3 for

specific periods in three representative years).

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to be iteroparous in Florida (Harris et al. 2007), so their

declining seasonal abundance in early spring represents

a migration back to sea after spawning, as well as

natural and fishing mortality.

Status of the Fishery

Florida’s anadromous shad fishery has become

dominated by recreational angling, and most American

and hickory shad caught in the upper St. Johns River

are released. The total estimated catch for the creel

survey area did not exceed 12,600 for any year during

1993–2005, and the catch currently appears to be at

historic lows (1,270 in 2004–2005). Walburg (1960a)

recorded 65,246 American and hickory shad caught

recreationally during the 1958 spawning run, and

Williams and Bruger (1972) reported a catch of 21,300

shad at a single fish camp in 1970. Walburg (1960a)

also reported an average catch rate of 5 shad/angler-

day, and Williams and Bruger (1972) reported 4.5

shad/angler-day. If 3–4 h is typical for a day of shad

fishing, then catch rates during the 1950s and 1970s

ranged from 1.1 to 1.7 shad/h. In contrast, catch rates

during 1993–2005 were greater than 1.0 shad/h in only

3 of 11 years (range, 0.43–1.29 shad/h). Thus, the

TABLE 3.—Estimates of fishing effort (angler hours directed at shad), catch (combined number of American and hickory shad),

and success (shad/h) in a creel survey area on the St. Johns River during three representative spawning runs: 1994–1995 (an

average year), 1998–1999 (the highest-catch year), and 2004–2005 (the lowest-catch year). The sample size for effort (NE) is the

number of sample days with interviews, that for catch (NC) is the number of all interviews reporting at least 0.5 h fished, that for

success (NS) is the number of interviews with shad-directed effort reporting at least 0.5 h fished. Asterisks indicate the 2-week

periods referred to as periods 1–10 in each creel survey.

Sample date

Effort Catch Success

NE

Hours fished SE NC

Number of shad SE NS

Shad/h SE

Calendar years 1994–1995

Nov 3–16 5 0 9 0Nov 17–30 1 0 1 0Dec 1–14*Dec 15–28* 2 109 4 38 1 0.50Dec 29–Jan 11* 5 213 20 129 8 0.73Jan 12–25* 5 821 31 449 23 0.49Jan 26–Feb 8* 5 1,089 41 423 32 0.44Feb 9–22* 4 1,057 30 733 22 0.80Feb 23–Mar 8* 5 3,105 88 2,400 73 0.79Mar 9–22* 5 1,198 65 919 25 1.01Mar 23–Apr 5* 4 473 40 275 8 0.53Apr 6–19* 4 24 73 0 1 0.00Apr 20–May 3 5 0 81 0Total 50 8,089 483 5,366 193 0.71

Calendar years 1998–1999

Dec 4–17*Dec 18–31*Jan 1–14* 4 338 150 22 660 340 6 1.34 0.61Jan 15–28* 5 2,672 511 91 3,419 676 42 1.17 0.11Jan 29–Feb 11* 5 2,175 522 58 3,304 823 24 1.57 0.22Feb 12–25* 5 2,116 635 62 1,722 589 31 0.99 0.11Feb 26–Mar 11* 5 1,490 319 55 2,392 752 25 1.36 0.33Mar 12–25* 4 522 95 42 511 332 10 0.93 0.18Mar 26–Apr 8* 5 181 99 60 98 66 3 0.47 0.12Apr 9–22* 4 25 21 36 0 0 1 0.00Total 37 9,518 1,039 426 12,106 1,509 142 1.20 0.09

Calendar years 2004–2005

Nov 29–Dec 12* 3 0 0 1 0Dec 13–26* 5 0 0 10 0 0Dec 27–Jan 9* 5 63 47 13 35 35 3 1.49 1.49Jan 10–23* 3 76 61 14 25 19 1 0.38Jan 24–Feb 6* 4 865 446 31 466 176 12 0.53 0.11Feb 7–20* 4 530 355 20 454 190 8 0.76 0.25Feb 21–Mar 6* 4 262 160 21 221 194 5 0.36 0.29Mar 7–20* 5 14 10 18 68 37 1 0.50Mar 21–Apr 3* 5 0 0 22 0 0Apr 4–17* 5 0 0 13 0 0Apr 18–May 1 4 50 36 14 0 0 1 0.00Total 47 1,860 598 177 1,270 328 31 0.63 0.16

ANADROMOUS SHADS OF FLORIDA 1681

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populations of American shad and hickory shad in

Florida’s St. Johns River can best be described as low

but stable.

McBride (1999, report to the Atlantic States Marine

Fisheries Commission on an American shad fishing

and recovery plan) had proposed that a sustained or

increasing catch rate greater than 1.0 fish/h during

2002–2005 would be sufficient for concluding that

Florida’s shad stocks benefited from netting regulations

implemented in the 1990s. It was predicted that the in-

state netting regulations implemented in the 1990s

would allow increased passage of shad—particularly

larger spawning females—into the St. Johns River.

However, the findings of this study offer no evidence

that shad stock size increased during the period 1993–

2005, and the fish sizes and sex ratios that we found

suggest continued effects of historical gill-netting

practices.

These data do not, however, lead us to conclude that

there have been no benefits from the 1990s netting

restrictions in Florida. First, the in-state restrictions

were aimed at other species, such as striped bass

Morone saxatilis within the St. Johns River and striped

mullet Mugil cephalus in coastal waters, and in fact, the

fishing mortality of striped mullet has decreased since

the 1990s, with concomitant increases in catch rates

and spawning stock biomass (Mahmoudi 2005).

Second, there may be benefits to anadromous shad

stocks, but the data-poor nature of this stock assess-

ment did not reveal this unequivocally. For example,

the sudden shift in American shad sex ratio between

2002 and 2003 and 2004–2005 was an encouraging

trend, but this was not accompanied by increases in

either geometric mean abundance estimates or angling

success estimates. Concerns about size-selective fish-

ing mortality had emerged as early as the 1970s, when

Williams and Bruger (1972:35) concluded ‘‘that heavy

fishing pressure, especially for female shad, may have

contributed to a decrease in population size.’’ We also

expressed concern at the onset of our study over the

potential for size-selective fishing effects, but at the

FIGURE 9.—Time series of annual mean recreational catch

rates (fishing success) of American and hickory shad

combined in the creel survey area of the St. Johns River

during 1993–2005. The slope of the relationship between

fishing success and year (y ¼ �0.0099x þ 20.5) was not

significantly different from zero (P . 0.05). The data

presented here are for periods 3–8, or approximately January

to March of each fishing year, when catch rates are highest;

the results based on other 2-week aggregates (i.e., periods 1–

10) did not differ.

FIGURE 10.—Scattergrams of the mean geometric abun-

dance of American and hickory shad in the St. Johns River

determined by electrofishing versus the combined shad fishing

success during the same 2-week period in each of 4 years

(2002–2005). Fishing success was measured by a creel survey

between Lake Monroe and Lake Harney, whereas electrofish-

ing abundance was measured (n¼ the number of independent

estimates) in (A) the creel area and (B) the Puzzle Lake area

from Lake Harney to the north end of Puzzle Lake. The

relationship between fishing success and electrofishing rates

was significantly and positively correlated in both examples

(P , 0.01).

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same time we recognized that it is difficult to interpret

changes in size structure to be solely the effect of

fishing (Marshall and McAdam 2007). Nonetheless,

the dramatically smaller shad sizes observed in some

years can lead to much smaller fishery yields (Law

2000), and the smaller sizes and reduced proportions of

females can lead to reduced egg production and

potentially to recruitment limitation (Olney and

McBride 2003).

Perhaps more time is necessary for the benefits to

become apparent. In the course of this study, the effect

of in-state netting regulations had only a decade to

demonstrate an effect. Moreover, ocean-intercept

fishing continued during this period. The effects of

this ocean-intercept fishery have been recognized

elsewhere, such as in the Hudson River, where during

the early 1990s the mean age and incidence of repeat

spawning among American shad started to decline

(Limburg et al. 2003). Although it is unclear how much

time will be necessary to reverse these effects, the most

recent coastwide American shad stock assessment

showed no immediate benefits from the phaseout of

the ocean-intercept fishery (ASMFC 2007). For striped

bass, which is also managed by the ASMFC, rebuilding

took over a decade following severe catch reductions in

1981 (Richards and Rago 1999). So, if the ocean-

intercept fishery had accounted for a significant

amount of mortality on Florida’s anadromous shad,

then more years (i.e., 1–2 shad generations or until

2010–2015) may be needed before benefits are realized

by these stocks in the St. Johns River.

Continued monitoring is desirable to document the

dynamics of the abundance, sex ratios, and sizes of

Florida’s anadromous shad stocks. The current

ASMFC monitoring requirements will satisfy most of

these data needs (ASMFC 1999). Still, the recreational

creel survey may lose its value as a monitoring tool if

recreational fishing effort continues to decline. Fortu-

nately, a suitable baseline of fishery-independent data

has been established with the electrofishing survey,

which will increase in value over time.

Alternative Hypotheses

The patterns of bycatch would be very relevant to

the assessment of various fisheries. There are no

studies of release mortality by Florida’s in-river

recreational fishery, and more research and education

is critical because so many anglers practice catch-and-

release fishing. Although the ocean-intercept fishery

targeting shad has been closed, nontargeted shad

mortality in coastal and ocean nets may still be

important. Documentation of shad bycatch and live

release by other states with active coastal net fisheries

is important in this regard.

Further efforts to rebuild Florida’s shad stocks

should proceed within a comprehensive framework,

one that considers more than the potential fishing

effects. More research on wildlife interactions is

needed to understand the trophic linkages between

Florida’s shad stocks and nonhuman predators (Will-

son and Halupka 1995). Obvious in-river predators on

Florida shad stocks are the osprey Pandion haliaetus,

longnose gar Lepisosteus osseus, and American

alligator Alligator mississippiensis. In addition, the

introduction of armored catfishes (e.g., Callichthyidae

and Loricariidae) to the St. Johns River—species that

feed indiscriminately on benthic prey (Mol 1995)—

raises concerns about new sources of predation on the

eggs of anadromous fishes; these nonnative catfishes

have recently extended their distribution to the shad

spawning grounds, and at least one species (brown

hoplo Hoplosternum littorale) supports an artisanal

fishery (Johnson 2003). How these trophic linkages

affect anadromous shad population dynamics is poorly

understood.

During 2002–2005, visible ulcerations of the

epidermis and underlying tissue were observed in

9.9% of American shad and 3.0% of hickory shad.

Although anecdotal accounts indicate that ulcerated

shad are not new, the causes, dynamics, and conse-

quences of these pathological phenomenon are poorly

understood (Sosa et al. 2007). For example, these

ulcerations could be due to the stress of a long,

energetically costly upstream migration. In general, it

has been noted that Florida’s shad stocks are at the

southern range of both species, and, therefore, may be

thermally stressed. Moreover, it is interesting that the

American shad, which migrates farther upstream and is

semelparous, had a higher incidence of ulcers, which

would support this hypothesis.

Temperature fluctuations affect the migratory pat-

terns of anadromous shad (Quinn and Adams 1996). In

Florida, where American and hickory shad are at their

southern distributional limit, coastal temperatures need

to cool sufficiently to facilitate coastal migration to

northeast Florida and entry into the St. Johns River.

According to Keller et al. (2006), coastal surface

temperatures have cooled to 15.08C by December in

recent years, well within the range of temperatures with

which shad are associated (Leggett and Whitney 1972).

Thus, a thermal bottleneck is probably not preventing

shad from entering the St. Johns River.

Nonetheless, other environmental variations may be

affecting anadromous shad in the St. Johns River. For

example, during the course of our monitoring (1993–

2005), unusually heavy rains from at least one major El

Nino–Southern Oscillation event occurred (1997–

1998; Patterson et al. 2004), which was followed by

ANADROMOUS SHADS OF FLORIDA 1683

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2 years of drought conditions. Moreover, increased

rainfall associated with the Multidecadal Oscillation

has occurred in the past decade (Delworth and Mann

2000). Water flow can affect the survival of anadro-

mous shad eggs and larvae (Williams and Bruger

1972), and river flow rates may be particularly

important in the St. Johns River because it is a low-

flow river that lacks a fall line. Williams and Bruger

(1972:35) noted that ‘‘most spawning occur[s] in

currents of 1–1.5 ft/s [;0.30–0.45 m/s] where there

is a clean sand bottom less than 4 m in depth.’’

Competing demands for water resources, which include

human and wildlife and fisheries needs, are increasing.

Preservation of sufficient water quality, flows, and

levels will certainly continue to be important for

maintaining anadromous shad stocks in the St. Johns

River in the future.

Acknowledgments

This research was a collaborative effort between the

Florida Fish and Wildlife Conservation Commission

(FWC) laboratories at St. Petersburg and DeLeon

Springs. Many other individuals from the FWC assisted

with this special team project; in particular, we thank G.

Chandler, B. Coleman, F. Cross, R. Davis, B.

Eisenhauer, M. Guy, J. Harris, R. Hyle, J. Jenkins, P.

Korpas, E. Lundy, K. Maki, G. Nelson, C. Paxton, A.

Richardson, D. Van Genechten, S. Whitaker, and J.

Wren. We also thank A. Ross (University of Tampa) for

assistance, and L. Connor for providing user-friendly

software for estimating angling success. C. Mundy (St.

Johns River Water Management District), R. Collaro,

and K. O’Keife helped produce Figure 1 and determine

the river distances. N. Trippel and R. Hyle provided

helpful reviews of an earlier draft. The primary source

of funds for this research was the U.S. Fish and Wildlife

Service (Federal Aid in Sport Fish Restoration project

F-106). Other funding came from the State of Florida’s

Marine Research Conservation Trust Fund, the Atlantic

States Marine Fisheries Commission, and the St. Johns

River Water Management District (contract

SG346AA). We thank all of them.

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