2011 NORTHEASTERN NATURALIST 18(1):37–44
The Fish Assemblage Structure of the Saco River Estuary
Nathan B. Furey1,2,* and James A. Sulikowski1
Abstract - The Saco River estuary is a narrow estuary in southern Maine, for which the
fauna has not been described in nearly 30 years. Beach seining, otter trawling, and beam
trawling were conducted between April and October of 2007 and 2008 to assess seasonal
variation in fish assemblage structure. Twenty-four species were observed over the two
sampling seasons, and nearly all species were at lengths indicative of juvenile age. Clupea
harengus (Atlantic Herring), Pseudopleuronectes americanus (Winter Flounder),
Anguilla rostrata (American Eel), Microgadus tomcod (Atlantic Tomcod), Pomatomus
saltatrix (Bluefish), and Osmerus mordax (Rainbow Smelt) are either commercially or
recreationally valuable, while Acipenser oxyrynchus oxyrynchus (Atlantic Sturgeon),
Alosa aestivalis (Blueback Herring), and Rainbow Smelt are federally listed species of
concern. Substantial historical assemblage changes were observed, including both the
loss of commercially important species and the addition of species of concern. Regular
monitoring of estuarine habitats is necessary to identify changes in assemblages and to
better understand potential drivers of ecosystem change.
Introduction
The Saco River estuary is a small estuarine environment in Biddeford, ME.
To our knowledge, only one published study (Reynolds and Casterlin 1985)
has described the nekton of the Saco River estuary. Reynolds and Casterlin
(1985) sampled the entire extent of the Saco River and its surrounding coastal
waters with otter trawl, seine, bottom grab, hook and line, plankton net, and
hand net, and although effort was not quantified, the authors noted that sampling
occurred throughout all seasons of the years of 1979 to 1982. While
more recent studies have examined Saco River geology and hydrography
(Brothers et al. 2008, FitzGerald et al. 2002, Kelley et al. 2005), the estuary’s
flora and fauna have not been described in nearly 30 years. The present study
aimed to describe the fish assemblage of the Saco River estuary over a twoyear
period (20 April 2007 to 2 December 2008) to determine nursery ground
potential and identify possible assemblage changes since the previous study
(Reynolds and Casterlin 1985).
Methods
Field-site description
Sampling occurred in the Saco estuary at the mouth of the Saco River
(43°27.5'N, 70°22'W) (Fig. 1). Two jetties extend 1.5 km into Saco Bay to form
1Marine Sciences Department, University of New England, 11 Hills Beach Road, Biddeford,
ME 04005. 2Current address - Department and Wildlife and Fisheries Science, Texas
A and M University- Galveston, 5007 Avenue U, Galveston, TX 77551. *Corresponding
author - n.b.furey@gmail.com.
38 Northeastern Naturalist Vol. 18, No. 1
the Saco River mouth. Sampling occurred between the jetties as well as on a
shallow, sandy portion of the estuary known as Freddy Beach (Fig. 1). The estuary
ranges between 200 and 350 m in width and is characterized by sand and rock
bottoms, and little vegetation. The Saco River has a discharge rate of greater than
85 m3/s (USGS 2009). Under normal conditions, the estuary’s salinity is stratified
by salt wedge presence, and experiences a mean tidal range of 2.7 m (FitzGerald
et al. 2002). Sampling sites were chosen to ensure that estuarine water was being
sampled, rather than pure fresh- or saltwater.
Sampling gear
A 2-mm square mesh beach seine, 14 m long and 2 m high, was used to
sample Freddy Beach (Fig. 1). Three replicate seines, approximately 100 m in
length, were performed between low and mid-tide weekly in 2007 and twice
weekly in 2008. A small otter trawl (6 m wide and 25-mm mesh) and beam
trawl (2 m wide and 3-mm mesh) were towed between the jetties on a bimonthly
basis in 2007 and weekly in 2008 from the 7-m (23-ft) University of
New England research vessel Llyr. The use of trawls allowed for the sampling
of waters deeper than those attainable by seine, and the beam trawl was used
to sample areas close to the jetties rather than the deeper channel. The current
study focused on the estuarine portion of the river, coinciding with Stations 4
and 5 of Reynolds and Casterlin (1985).
Data collection
Sampling began in April 2007 and ended in October 2008. In both 2007 and
2008, sampling occurred from April through October. All captured fish were
identified to species and enumerated. For every sampling event where at least 100
Figure 1. Location of the Saco River estuary system in eastern Biddeford, ME. Star
denotes Freddy Beach where beach seines occurred. Trawls occurred between jetties as
outlined by rectangle.
2011 N.B. Furey and J.A. Sulikowski 39
fish of a species were captured, a subsample of 50 individuals was measured for
total length (TL). To approximate the age of observed species as either juvenile or
adult, mean lengths of fish species were compared to average adult and juvenile
sizes found in literature specific to the Gulf of Maine. To assess potential changes
in the fish assemblage, the presence of each species was compared to those observed
by Reynolds and Casterlin (1985).
Results
Overall
Twenty-four fish species were observed in the Saco River estuary over the
course of the 2-year study (Tables 1, 2), and Alosa aestivalis (Blueback Herring),
Menidia menidia (Atlantic Silverside), Clupea harengus (Atlantic Herring), Osmerus
mordax (Rainbow Smelt), and Ammodytes americanus (Sand Lance) were
the five most dominant species. More species were observed with seine (23) than
either beam trawl (8) or otter trawl (9).
Size (TL)
Sizes of observed fish during the study ranged from a minimum of 8 mm
TL (Atlantic Silverside) to a maximum of 1200 mm TL (Acipenser oxyrinchus
Table 1. Full nomenclature of all 24 fish species observed in the study.
Common name Scientific name Authority
Bluefish Pomatomus saltatrix L.
Largemouth Bass Micropterus salmoides (Lacèpede)
Striped Mullet Mugil cephalus L.
Red Hake Urophycis chuss (Waldbaum)
Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus Mitchill
American Eel Anguilla rostrata Laueur
Atlantic Herring Clupea harengus L.
Alewife Alosa pseudoharengus (Wilson)
Cunner Tautogolabrus adspersus (Walbaum)
Winter Flounder Pseudopleuronectes americanus Walbaum
Yellow Perch Perca flavescens (Mitchill)
Blueback Herring Alosa aestivalis Mitchell
Windowpane Scophthalmus aquosus (Mitchill)
Pumpkinseed Lepomis gibbosus (L.)
Rainbow Smelt Osmerus mordax Mitchell
Atlantic Tomcod Microgadus tomcod Walbaum
Northern Pipefish Syngnathus fuscus Storer
Sand Lance Ammodytes americanus Dekay
Atlantic Silverside Menidia menidia L
Mummichog Fundulus heteroclitus heteroclitus (L.)
Threespine Stickleback Gasterosteus aculeatus L.
Banded Killifish Fundulus diaphanus (Lesueur)
Ninespine Stickleback Pungitius pungitius occidentalis Cuvier
Fourspine Stickleback Apeltes quadracus Mitchill
40 Northeastern Naturalist Vol. 18, No. 1
Table 2. Overall mean total lengths (TL) and standard deviations (SD) for all 24 fish species observed in the study. Also given are average and maximum adult
TL (or standard length, SL, when noted) cited in scientific literature for each species. Asterisk (*) denotes source is as cited in Collette and Klein-MacPhee
2002. An “X” in “Present” indicates the species was previously observed within the estuarine portion of the river that matches the current study’s extent
(Stations 4 and 5, Reynods and Casterlin 1985).
Seine (mm) Otter trawl (mm) Beam trawl (mm) Literature value (mm)
Common name Present Mean SD Mean SD Mean SD Average Max Source*
Bluefish 66.21 5.88 113 NA NA NA NA 1150 Collette and Klein-MacPhee 2002
Largemouth Bass 61.00 40.22 NA NA NA NA NA 970 Page and Burr 1991
Striped Mullet 55.27 17.42 NA NA NA NA NA 600 McDonough and Wenner 2003*
Red Hake 75.50 10.29 NA NA NA NA NA 500 Musick 1967*
Atlantic Sturgeon NA NA 1132.50 95.46 NA NA 880–2000 NA Damon-Randall et al. 2010
American Eel X 52.00 0.82 NA NA 85 43.84 NA 1200 Bigelow and Shroeder 1953*
Atlantic Herring 48.50 5.74 52.12 6.96 38 3.46 NA 430 Collette and Klein-MacPhee 2002
Alewife 56.27 8.26 NA NA 46.63 10.65 NA 300 Ross 1991*
Cunner 11.50 NA NA NA NA NA 150–250 NA Bigelow and Shroeder 1953*
Winter Flounder X 71.35 55.19 131.47 52.12 134.75 29.47 NA 580 Fields 1988*
Yellow Perch 25.00 NA NA NA NA NA NA 400 Page and Burr 1991
Blueback Herring 43.38 14.73 66.14 6.84 NA NA NA 300 Ross 1991*
Windowpane 56.58 19.34 123.55 48.03 NA NA 250–305 NA Bigelow and Shroeder 1953*
Pumpkinseed 49.00 NA NA NA NA NA NA 400 Page and Burr 1991*
Rainbow Smelt 49.68 13.18 49.21 6.45 NA NA 180–230 NA Collette and Klein-MacPhee 2002
Atlantic Tomcod X 41.87 9.49 NA NA 33.35 21.57 228–300 NA Collette and Klein-MacPhee 2002
Northern Pipefish 102.64 51.28 NA NA 148.33 28.04 NA 305 Nichols and Breder 1927*
Sand Lance X 68.26 27.67 60.00 27.55 58.71 9.48 NA 168 Nizinski et al. 1990*
Atlantic Silverside 68.56 20.30 44.62 4.44 NA NA 105 NA Conover and Ross 1982*
Mummichog 46.76 13.11 NA NA NA NA NA 100 Able 1990*
Threespine Stickleback 31.03 16.46 NA NA NA NA 40–70 NA Collette and Klein-MacPhee 2002
Banded Killifish 44.03 8.78 NA NA NA NA 152–178 NA Clemmer and Schwartz 1964
Ninespine Stickleback 33.22 4.18 NA NA NA NA 35–55 SL 76 Scott and Scott 1988*;
Ayvazian and Krueger 1992*
Fourspine Stickleback 30.50 7.51 NA NA 53.50 3.53 23–44 NA Blouw and Hagen 1984*
2011 N.B. Furey and J.A. Sulikowski 41
oxyrinchus [Atlantic Sturgeon]). All but three observed fish (2 Atlantic Sturgeon
and 1 Pseudopleuronectes americanus Walbaum [Winter Flounder]) were less
than 250 mm TL. Except one Winter Flounder (TL = 552 mm), all individuals
captured with seine were less than 200 mm TL. All fish observed by beam trawl
were between 16 mm and 166 mm TL, and besides two Atlantic Sturgeon, all fish
observed by otter trawl were less than 300 mm TL. When compared to literature
examining the size of northwest Atlantic fishes, only 3 species—Gasterosteus
aculeatus (Threespine Stickleback), Apeltes quadracus (Fourspine Stickleback),
and Pungitius pungitius occidentalis (Ninespine Stickleback)—were not considered
to be juvenile (Table 2).
Discussion
Twenty-four fish species were observed in the Saco River estuary over a
2-year period, and nearly all species observed were at juvenile lengths. Atlantic
Herring, Winter Flounder, Anguilla rostrata (American Eel), Microgadus
tomcod (Atlantic Tomcod), Pomatomus saltatrix (Bluefish), and Osmerus
mordax (Rainbow Smelt) are either commercially or recreationally valuable.
In addition, the Alosa pseudoharengus (Alewife), Atlantic Sturgeon, Blueback
Herring, and Rainbow Smelt are federally listed as species of concern (NMFS
2009). Of these economically valuable and threatened species, four (Blueback
Herring, Alewife, Winter Flounder, and Rainbow Smelt) were observed over
multiple months, indicating that their presence was not an anomaly. All of
these species were observed as juveniles, indicating the estuary’s value as a
nursery ground.
The number of fish species observed within the Saco River estuary (24) is
comparable to other Maine estuaries, including Penobscot Bay (22) (Lazzari
and Tupper 2002), Wells Harbor (24) (Ayvazian et al. 1992), Kennebec Point
(27) (Lazzari et al. 1999), the Weskeag River (22) (Lazzari 2002), and Casco
(25) and Muscongus bays (24) (Lazzari 2002). Furthermore, the estuaries of
Penobscot Bay, Wells Harbor, Kennebec Point, and Casco Bay are of greater
width and volume than the studied Saco River estuary. Only two of these compared
studies, however, included beach seines as sampling gear (Ayvazian
et al. 1992, Lazzari et al. 1999). The other aforementioned studies collected
fish via beam trawl, otter trawl, or throw traps. Because the species observed,
along with their abundance, can be affected by gear type (Rozas and Minello
1997), comparing species richness among these ecosystems is difficult. Regardless,
these comparisons describe the Saco River estuary as ecologically
valuable to the region despite its relatively modest size.
Substantial differences exist between the fish assemblage observed by Reynolds
and Casterlin (1985) and that observed in the current study (Table 2). Of the
five most abundant species in the current study, only Sand Lance was observed by
Reynolds and Casterlin (1985). An additional six species (Fundulus heteroclitus
heteroclitus [Mummichog], Urophycis chuss [Red Hake], Scophthalmus aquosus
[Windowpane], Fourspine Stickleback, Threespine Stickleback, and Ninespine
42 Northeastern Naturalist Vol. 18, No. 1
stickleback) were common to both studies, but were only observed by Reynolds
and Casterlin (1985) outside of the current study’s sampling area.
Notable species that were only observed in the current study include Alewife,
Atlantic Sturgeon, Blueback Herring, and Rainbow Smelt, all of which are federal
species of concern (NMFS 2009). Both Leucaraja erinacea Mitchill (Little
Skate) and Pollachius virens L. (Pollock) were observed by Reynolds and Casterlin
(1985) within the estuary, but not in the current study. Both of these species
are commercially important in the Gulf of Maine.
Comparisons to historical data can identify at-risk species (Smith et al. 2008),
and regular monitoring will allow for identification of possible drivers of assemblage
change. Continual monitoring of estuarine habitats should be a priority for
conservationists and managers alike, given the observed loss of commercially
important species, and the apparent additions of at-risk species observed in the
Saco River estuary in a period of less than 30 years.
Acknowledgments
We would like to thank Tim Arienti, Marie Quinlan, Angela Cicia, Andrew Wargo,
and Devin Flawd for assisting in field work. This project was supported by the University
of New England Biological Sciences Honors Program, the University of New England
College of Arts and Sciences (CAS), and the University of New England Provost’s Faculty
Grant Program. This manuscript represents MSC contribution number 32.
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