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Atlantic salmon (Salmo salar) in New York State: evaluation
of restoration feasibility
Stephen M. Coghlan Jr.
The story of the Atlantic salmon is a testament to man's
misuse and abuse of natural resources. Before permanent settlers arrived
to Lake Ontario shores in the early 1700's, northern and central New York
were wilderness areas, home to abundant fish and wildlife populations.
To see the historic distribution of Atlantic salmon in New York State,
click here. First the Algonquins, and then the Iroquois
nations, subsisted largely on migratory salmon during the height of the
spawning run. To learn about the Atlantic salmon life cycle click
here. Early Jesuit missionaries (notably Fathers LeMoyne and LeMercier)
wrote fantastic accounts of rivers teeming with salmon, so abundant that
many hundreds could be harvested easily with pitchforks, wicker baskets,
or even bare hands, over the course of a few hours. Trappers, traders,
and infantry rangers also harvested salmon as an important source of food.
During the Seven Years' (1757-1763) and Revolutionary (1775-1783) Wars,
the Oswego River system and various other Lake Ontario tributaries were
used as strategic military transportation routes, and forts, trading posts,
and small villages soon began to appear. After the close of the Revolutionary
War, and later, the War of 1812 (1812-1815), New York State ceded large
tracts of previously untouched land for services rendered in the state
militias and Continental army. As settlers began to tame the wilderness
and develop the countryside, the salmon began to feel the effect of a
growing human population. Millers built dams on tumbling rivers, blocking
migratory adults from reaching spawning grounds. Loggers cleared trees
from stream banks, resulting in increased water temperatures, erosion,
and siltation of spawning gravel. Animal, human, and industrial waste
could be easily disposed of in rivers and lakes. Fishermen could overharvest
salmon by stretching huge nets across spawning streams. Salmon populations
declined precipitously, and by the 1850'
s
it was evident that the fish were becoming alarmingly scarce. Perhaps
the deathblow was dealt to the salmon by the establishment of exotic fish
species. Steelhead, or migratory rainbow trout (Oncorhynchus mykiss),
were intentionally introduced throughout New York waters to provide a
sport fishery, perhaps in response to declining salmon or native brook
trout (Salvelinus fontinalis) populations. Steelhead have very similar
ecological requirements to Atlantic salmon, and may have been strong competitors
for food and habitat. Alewife (Alosa pseudoharengus) became
established (accidentally introduced or via canals) in Lake Ontario around
1873, and began to replace whitefish / ciscoes (Coregonus,
Prosopium spp.) as dominant lake planktivores. Scientists have recently
shown that alewife tissues contain thiaminase, and enzyme that degrades
vitamin B-1 (thiamine). Atlantic salmon females that consume alewife deposit
thiaminase in developing eggs, thus leading to virtual reproductive failure.
It is likely that Atlantic salmon populations, already on the decline,
were simply not able to recover after faced with thiaminase-induced reproductive
failure. Sadly, the last wild Atlantic salmon was caught in Lake Ontario
in 1898.
When faced with the question of re-establishing populations of an extirpated species, researchers must deal with many issues. First, is the present-day ecosystem similar enough to the historic ecosystem so that the species in question has a niche to exploit? Second, are there any recent invaders that may prove to be important competitors, predators, or parasites of the extirpated species? Lastly, what is the public attitude towards a perhaps laborious, costly, and slow restoration process? Today, Lake Ontario is a very different ecosystem than it was in the 1800's. Establishment of exotic coho (O. kisutch) and chinook (O. tschawytsha) salmon, brown trout (Salmo trutta), zebra mussels (Dreissenia polymorpha), and spiny water fleas (Bythotrephes, Cercopagis pengoi) are just a few examples. Similarly, the ecology of tributary streams have changed as well.
The
purpose of our research is to evaluate the restoration potential of Atlantic
salmon from a variety of perspectives. For my dissertation, I am examining
survival and growth of stocked juvenile Atlantic salmon in several tributaries
in the Lake Ontario watershed, as well as investigating competition between
Atlantic salmon and steelhead juveniles. With other researchers at SUNY-ESF,
New York State Department of Environmental Conservation, US Fish and Wildlife
Service, and US Geologic Survey, I hope to contribute to answering the
question: "Is it ecologically feasible to restore Atlantic salmon
to the Lake Ontario watershed?"
Comparison of three stocking methods
Since the only chance of Atlantic salmon restoration lay in the success
of stocked fish, I developed a study to test the relative efficacies of
three stocking methods: embryo-stocking with and without hatching boxes,
and fry stocking.
Study Site Description
The Salmon River originates in the Tug Hill Plateau of north-central New
York as a network of spring-fed and snowmelt tributaries. Here, summers
are cool, winters are long and harsh, and shaded streams provide habitat
for wild brook trout. Twenty-five and twenty kilometers from the estuary,
respectively, the river is interrupted by the Salmon River and Lighthouse
Hill Reservoirs, formed as part of hydropower facility construction. In
between the two reservoirs is the Salmon River Falls, which served as
the historic barrier to upstream fish migration. Below the lower reservoir,
the Salmon River is managed for minimum base flows, ranging from 185 cfs
(cubic feet per second) in the summer, to 335 cfs in the fall, although
in flood conditions can reach 12,000 cfs (e.g., July 5, 1999). Since the
reservoir discharges epilimnetic water, summer river temperatures are
largely determined by air temperatures; in certain sections,
especially near the estuary below the village of Pulaski, the river can
become too warm for juvenile salmonines. Substrate is predominately cobble-gravel
mix, ideal for salmon egg incubation an
d
juvenile habitat, and aquatic insects abound. From September through April,
a world-class sport fishery exists for Pacific salmon and steelhead. I
chose 17 sites on the Salmon River, ranging from
the mainstem river below the reservoir (Upper Fly-Fishing Area), to side
channels and braids ten kilometers below, near Compactor Pool. Sites are
similar in substrate composition, but differed in discharge, temperature,
and occasionally fish community.
Methods
In December, 1999, I obtained 125,000 eyed Atlantic salmon embryos from
the Grande Island Fish Hatchery on Lake Champlain, Vermont. Equal numbers
of eggs were allotted to two different embryo stocking methods. For the
first method, 250 eggs were placed in each of 250 Whitlock-Vibert hatching
boxes, loaded into ice-filled coolers, and transported to streamside.
For each of five study sites, volunteers from SUNY-ESF, NYSDEC, and Trout
Unlimited chose five suitable reaches of stream,
and dug artificial nests in the gravel. We attempted to mimic wild Atlantic
salmon nest site-selection: prime areas are the tail ends of pools (where
the water increases invelocity before forming a riffle), with 10-40 cm
water depth and golf-ball-sized gravel. After digging 20-cm deep nests,
volunteers placed 10 hatching boxes in hardware cloth"cradles"
(designed to keep the boxes from shifting around), filled the cradles
with gravel, placed one cradle per nest, chained the cradle to rebar driven
into the stream bed, and covered with more gravel. The final design consisted
of 250 eggs per hatching box, 10 hatching boxes (2500 eggs) per cradle,
5 cradles (12,500 eggs) per site, and 5 sites (62,500 eggs) total.
For the second embryo-stocking method, sites were selected in the same
manner. However, instead of stocking
eggs protected by hatching boxes and cradles, volunteers simply inserted
sections of PVC pipe into excavated pits, poured in a small number of
eggs, covered with gravel, and removed the pipe. This procedure was repeated
until 2,500 eggs were deposited into several "egg pits" in one
large nest (very similar to what the female salmon actually does). As
with the previous method, 5 nests were built at each of 5 sites, for a
total of 62,500 eggs.
To estimate the survival from embryo to fry stage, I simply dug up each
hatching box and counted dead salmon. I subtracted the number of dead
eggs remaining from 250 to estimate survival to hatching. I could then
count the number of dead alevins from the estimated number of hatched
eggs to estimate the survival rate to emergence from the hatching boxes.
Measuring survival through hatching for the non-hatching box sites was
not possible given the experimental design. However, by fitting a s
ubsample
of nests with fry traps, I could estimate survival from embryo to emergence;
upon swimming out of the gravel into the water column, the fry encounter
the mesh screen and are herded into the collecting box.
In June 2000, I received 50,000 Atlantic salmon fry from the same hatchery.
Volunteers placed a given number of fry, corresponding to 2 fish per m2
of study site, in buckets of water and transported them to the river.
At each site, fry were scooped out of the buckets with minnow nets and
placed gently in calm areas behind rocks or at the water's edge. Volunteers
attempted to distribute the fish as evenly as possible over the entire
stud
y site. All
sites were separated by at least 100 m (usually much more) to prevent
intermixing of fish from different stocking methods. Throughout the summer
my field crew and I sampled each site by electrofishing. By isolating
reaches with blocking seines, we could determine the resultant density
of Atlantic salmon (and therefore estimate survival from stocking), as
well as that of all other fish species. By measuring length and weights
of all fish, we could estimate salmon growth and total fish biomass present
in each site.
Results
In Whitlock-Vibert boxes, survival from embryo to alevin was highly variable
(1 - 90 %), and survival from
alevin through emergence was generally high (>50 %); however, sampling
for fry several months after emergence yielded very few individuals. We
did not recover any salmon fry in fry traps, although we tested the traps
over known steelhead redds and found that they indeed caught at least
some emerging fish. Overall, out of 125,000 embryos stocked,
we recovered only 36 resultant fry. Fry stocking resulted in significantly
higher survival rates than either method of embryo stocking, although
there was much between-site variation. GRAPH OF FRY SURVIVAL.
Highest densities were found in the Upper Fly Fishing Area; through the
end of August, survival was estimated to be 9% of the original number
stocked. However, these are likely to be underestimates, as fry could
potentially have moved out of our study sites, and capture efficiencies
in mainstem sites (such as the Upper Fly) were low. Combining growth rates
with survival, total Atlantic salmon biomass varied between sites, but
did not change over the sampling season. GRAPH OF BIOMASS.
In the Upper Fly, Atlantic salmon fry accounted for 0.4 g/m2 of fish biomass,
the highest value of all sites.
Discussion
Based on this research, I recommend fry stocking over embryo stocking
as a reintroduction method. Whereas monetary costs of producing embryos
are lower than those of producing fry, fry stocking is much less labor-intensive
and results in higher survival. Although survival rates were lower than
anticipated, literature values are highly variable, and can be dependent
on, among other factors, stocking densities. One hypothesis is that density-dependent
mortality regulates juvenile salmonine populations, and can occur both
intra- and inter-specifically; that is to say, high densities of juvenile
Atlantic salmon and/or steelhead fry can depress salmon survival rates.
Salmonine fry have an inherent capacity for high growth rates, and given
favorable environmental conditions, a cohort should increase in biomass
over the first summer of life. Biomass values did not significantly increase
(losses from mortalities were equal to, or less than, gains from growth)
over time, indicating that there may be resource limitation (food or space),
and the Salmon River may be near carrying capacity of wild salmonines.
Preliminary fish community data indicate that total fish biomass (all
species included) is rather uniform across all sites at approximately
1.3 - 1.8 g/m2; this may reflect the inherent carrying capacity of the
Salmon River during this particular time period. Thus an appropriate question
to ask at this point may be "is there room in the Salmon River for
Atlantic salmon?". My current work examines the effect of juvenile
steelhead on Atlantic salmon fry success, both in the field and in a laboratory
setting; since steelhead are the closest ecological "equivalent"
to Atlantic salmon, their abundance may be an important limiting factor
to salmon success.
Acknowledgements
I'd like to thank my field crews from the last several years (Kelly Nightingale,
Karen Chapman, Patrick Malfi, Everett McNeill, Amy Dunbar, Autumn White,
Stefanie Kroll, Adam Storch, Ted Smith, Chris Gagnon, and Ben Reining)
for braving mosquitoes, blackflies, thunderstorms, floods, poison ivy,
heat exhaustion, hypothermia, and other miscellaneous treats in the name
of field research! Also, Fran Verdoliva, Les Wedge, and Dan Bishop of
NYSDEC for invaluable assistance and advice, Kevin Kelsey of Vt. Fish
and Wildlife for providing Atlantic salmon, numerous friends and colleagues
who graciously volunteered to help, and my advisor, Dr. Neil H. Ringler.
Special thanks to Trout Unlimited and the Embrace-A-Stream Foundation,
and especially the Roosevelt Wild Life Station, for providing funding.
About me:
I am a third-year doctoral student under the guidance of Dr. Neil H. Ringler.
I originally began my college career as a finance major, but (t
hankfully!)
had a change of heart. One crisp autumn day six years ago, I was walking
the banks of my favorite trout stream and happened upon several pairs
of spawning brown trout, digging redds in a shallow riffle. I was instantly
fascinated and enamored, and decided to devote my life to studying the
natural world, salmonine biology in particular. Other academic interests
include fish systematics and taxonomy, Amazonian catfish ecology, aquatic
insect ecology, and conservation of endangered and threatened fish species
in New York State. Recently, I have begun to dabble in ecological economics,
and may in fact find a calling there someday. Personal interests include
fly-fishing, fly-tying, camping, hiking, and playing guitar and bass for
Classic Rock Overdose.
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