Ganaraska Region Conservation Authority
2216 County Road 28 Port Hope, ON L1A 3V8
Phone: 905-885-8173 Fax: 905-885-9824
www.grca.on.ca
MEMBER OF CONSERVATION ONTARIO
Life History and Population Biology
of Adfluvial Brown Trout in Wilmot Creek,
Ganaraska River and Cobourg Creek
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Life History and Population of Adfluvial Brown Trout in Wilmot Creek,
Ganaraska River and Cobourg Creek
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Table of Contents List of Figures ................................................................................................................................................ ii
Introduction .................................................................................................................................................. 1
Methods ........................................................................................................................................................ 2
Results ........................................................................................................................................................... 4
Discussion.................................................................................................................................................... 11
Acknowledgments ....................................................................................................................................... 15
References .................................................................................................................................................. 16
Appendix 1 – Migratory Brown Trout Photos ............................................................................................. 20
Appendix 2 – Resident Brown Trout Photos ............................................................................................... 24
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List of Figures
3 Ganaraska Region Conservation Authority watersheds where Brown Trout were collected.
5 Sex ratio of migratory and resident Brown Trout sampled from Wilmot Creek in 2013.
6 Length frequency of migratory and resident Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
6 Smolt age for migratory Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
7 Lake age at first spawning for migratory Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
7 Number of spawning events for migratory Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
8 Age structure for migratory and resident Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
9 Total mortality for migratory Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
10 Average length at age for migratory Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
10 Average length at age for resident Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
11 Average number of YOY Brown Trout sampled from Wilmot Creek.
Life History and Population of Adfluvial Brown Trout in Wilmot Creek,
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Introduction
Numerous fishes in the family Salmonidae have evolved multiple life history forms that utilize
different degrees of anadromy. Some of those species include Rainbow Trout (Oncorhynchus
mykiss) (McMillan et al. 2007), Sockeye Salmon (O. nerka) (Burgner 1991), and Brown Trout
(Salmo trutta) (Skaala and Naevdal 1989). The forms range from individuals that can undertake
extensive ocean migrations before returning to spawn in freshwater (anadromous form) to those
that complete their entire life cycle in freshwater (nonanadromous resident form) (McMillan et al.
2007). Within the nonanadromous form, individuals may migrate between river and lake
habitats (adfluvial) in a similar manner as anadromous forms, or remain entirely within a river
environment (fluvial) (Hendry et al. 2004). Partial migration, the phenomenon of migratory and
resident individuals coexisting in the same population, is a common expression of life history
plasticity in fishes (O’Neal and Stanford 2011). Within species, spatially variable freshwater
environmental conditions appear to shape the proportion of migratory individuals (Berejikian et
al. 2013). Phenotypic plasticity in migration is evident from population responses to temporal
changes in freshwater conditions within watersheds (O’Neal and Stanford 2011) and from
experimental studies that manipulate environmental conditions (e.g. temperature regime)
(Beckman et al. 2003). In partially migratory populations, male residency is common, while a
higher proportion of females may migrate (e.g. Atlantic Salmon S. salar: Fleming 1998; Rainbow
Trout/steelhead: Pascual et al. 2001). To be sustained, fitness benefits of migration, such as
increased reproductive output, must outweigh mortality and other fitness costs (Gross 1987).
The extent of anadromy and residency has implications for population viability through
influences on abundance, intra- and inter-population diversity, resilience, structure, and
productivity (Waples et al. 2007). Understanding partial migration is important from a
conservation and management perspective in the same way that understanding the portfolio
effect is helpful in financial realms (Schindler et al. 2010). For example, greater life history
diversity in O. mykiss spreads mortality risk over space and time, thereby dampening population
fluctuations and increasing resiliency to environmental variability (Moore et al. 2014). Further,
resident males mating with anadromous females (McMillan et al. 2007) and the contribution of
anadromous offspring from residents and vice-versa (Christie et al. 2011) offer important
avenues for buffering genetic and demographic stochasticity that are much less available to
other species (e.g. Pacific Salmon) (Quinn 2005).
Brown Trout is an iteroparous species that displays diverse life history strategies within the
genus Salmo spp. (Behnke 2002). The most common forms are riverine/fluvial,
lacustrine/adfluvial and anadromous (Behnke 2002). Adfluvial and anadromous Brown Trout
generally spend 1-4 years in riverine habitats and 1-4 years in the lake or ocean prior to
spawning in freshwater (Lamond 1916, O’Neal and Stanford 2011). Brown Trout that spend
their entire life in freshwater and may remain relatively sedentary or undertake extensive
migrations within rivers (Behnke 2002, Zimmer 2004).
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Brown Trout and other salmonids have been widely introduced across North America with the
first introductions of Brown Trout occurring in 1880 (Behnke 2002). The first introductions in the
Lake Ontario Watershed occurred in the Genesee River watershed (NY) by Seth Green after
1883 (Behnke 2002). The early introductions consisted of two strains of Brown Trout, a large
lake form (Seeforelle strain), and a small stream form (Bachforelle strain) (Behnke 2002). Later
egg sources were derived from a diversity of forms and locations within Europe. Brown Trout
were later introduced into the Ganaraska River and Wilmot Creek, with 675 yearlings stocked
into the lower Ganaraska River in 1933 and 1934 (Department of Energy and Resource
Management 1966). It was noted that Brown Trout were caught in Lake Ontario by 1944
(Richardson 1944), and a good population was in Wilmot Creek by 1966 (Department of Energy
and Resource Management 1966). The source, and thus life histories, of Lake Ontario
introductions are not known. It’s possible that the two strains introduced in New York noted
above were used for introductions on the Ontario side of the lake or possibly a resident strain of
Brown Trout was used because these life history variants were established in tributaries by the
early 1960’s (MacKay 1963). Since initial introductions, both a migratory life history and
resident life history have developed, with migratory populations being noted in Oak Ridges
Moraine Ontario tributaries to Lake Ontario by the early 1980’s (Nettles 1983). Both life
histories are currently maintained through natural reproduction within many Lake Ontario Oak
Ridges Moraine tributaries.
Brown Trout support important recreational fisheries both within Lake Ontario as well as
tributaries feeding into Lake Ontario. These fisheries are supported by a mix of naturally
reproducing and stocked Brown Trout, with two dominant life history types or variants; resident
and migratory (adfluvial). Only the latter life history is currently stocked into tributaries and Lake
Ontario. Within Lake Ontario, the Ontario Ministry of Natural Resources (OMNR) stocks a
broodstock strain of Brown Trout derived from individuals captured from the Ganaraska River.
This broodstock was collected in the early 1980’s, and has not been refreshed since (John
Sager, OMNR pers comm.). Current stocking sites are generally located across the basin of
Lake Ontario, with only of approximately 15% of stocked individuals from Ontario (OMNR 2013).
The OMNR stocks the western basin of Lake Ontario with the majority of stocked Ontario Brown
Trout, with approximately 165,000 stocked yearlings in 2012. The New York State Department
of Conservation (NYSDEC) stocked 419,410 in 2012 across the central and eastern basins of
Lake Ontario. All Brown Trout stocked by Ontario and New York are planted as 1 year old
yearlings/smolts, which allows for a means to decipher between hatchery and wild life history
traits based on the year of smolting. The purpose of this assessment is to characterize the life
history characteristics of naturalized adfluvial and resident life history pathways for adult Brown
Trout in tributaries to Lake Ontario. Describing rates of natural or total mortality are also
examined within this study.
Methods There are three tributaries (Cobourg Creek, Ganaraska River, and Wilmot Creek) within the
Ganaraska Region Conservation Authority (GRCA) jurisdiction that are known to contain self-
Life History and Population of Adfluvial Brown Trout in Wilmot Creek,
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sustaining populations of migratory adfluvial Brown Trout. The Ganaraska River is the largest
watershed out of the three with a watershed area of 278km2. The Ganaraska River has several
large dams that prevent migratory fish from accessing portions of the watershed. Resident
Brown Trout are present above most of these barriers. Access from Lake Ontario was not
possible until a fishway was constructed at the lowest dam (Corbett’s) in 1974. Cobourg Creek
is the second largest watershed in the study with a watershed area of 123km2. Similar to the
Ganaraska River, there are several dams that prevent upstream access to migratory fish, and
there are resident Brown Trout above these dams. Wilmot Creek is the smallest watershed in
the study at 98km2. Wilmot Creek does not have any major barriers to prevent access to
migratory fish where there are Brown Trout above the barrier (Figure 1).
Adult Brown Trout were captured during the summer/fall adult spawning migration by
electrofishing (backpack and boat) and through the use of a fishway (Ganaraska River).
Captured Brown Trout were sampled for fork length, and checked for existing tags/fin clips, sex,
maturity, lamprey scars, and gonad condition. Scale samples (n=10) were collected from an
area above the lateral line and below the dorsal fin, and tissue sample (5 mm circle of fin tissue,
ETOH preserved) were taken from the dorsal fin from most fish for age and genetic analysis.
Figure 1: Ganaraska Region Conservation Authority watersheds where Brown Trout were collected
Life History and Population of Adfluvial Brown Trout in Wilmot Creek,
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Various life history traits can be determined from scales, including stream age, lake age, total
age and number of times the individual has spawned (Davis and Light 1986). All removed
scales are placed shiny side up on a soft acetate plastic slide and then rolled onto the slide
using a hand scale press to make a strong impression on the slide. The acetate slide is then
placed in a microfiche reader and read using an "H" lens (50 X to 60 X) magnification. Age
determination was performed in accordance with Davis and Light (1986) and Elliot and
Chambers (1996). Any ‘plus’ growth that indicated an incomplete portion of the annulus was
rounded up to the year end to give total age. Only individuals 250mm fork length and larger
were sampled as part of this study. Repeat spawning was identified by looking for spawning
checks (Hartman 1959, Niemuth 1967), which are eroded portions adjacent to annuli when
spawning occurred.
Survival and total mortality was calculated using the methodology outlined in Hartman (1959),
where the ratio of maiden fish and successive spawners in the spawning population determined
survival rate. The following equation was used:
s = S2 + S3 + S4…. S1 + S2 + S3….
Where S1 is a fish spawning for the first time (maiden spawner), S2 is a fish spawning for the
second time, and so on. Generally, angler caused exploitation is used to determine the rate of
natural mortality within a population, but this information is not available for these populations.
In lieu of angler creel data, Rainbow Trout population biology was used as a surrogate.
Clarkson and Jones (1997) was used as a model for migratory Brown Trout, based on the
assumption that approximately 30% natural mortality will occur within the adult spawning
population each year. Based on Clarkson and Jones, at least 55% of the population should be
a repeat spawner for the population to be considered healthy. This would allow for up to
approximately 15% of the population to be exploited by anglers.
An estimate of juvenile Brown Trout year class strength was conducted on Wilmot Creek. The
GRCA conducts annual late summer electrofishing at 5 index sites along the length of the main
branch of Wilmot Creek. Electrofishing followed the single pass methodology outlined within the
Ontario Stream Assessment Protocol (Stanfield 2010). Year class was determined by the
abundance of young-of-the-year (YOY) present across all sampling sites. YOY were
characterized as any Brown Trout less than 100mm total length (Jones & Stockwell 1995).
Results A total of 111 adult Brown Trout were captured during this survey in 2013, with 81 having a
migratory life history, 20 having a resident life history, and four not assigned to either group
because their scales could not be read. Fin clipped fish or fish exhibiting dorsal erosion were not
captured. Twenty-three (28.4%) of the migratory Brown Trout were males, 58 (71.6%) were
female. Six (30%) of the resident Brown Trout were males, 14 (70%) were female, and four
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were not identifiable as male or female. The migratory portion of the population was skewed
towards female, while the resident population was skewed towards males (Figure 2).
The fork lengths of the migratory Brown Trout sampled averaged 594.2 mm, ranged from 319-
783 mm, while the resident portion averaged 409.2 mm ranged from 261-657 mm, (Figure 3).
Migratory fish had slower growth rates until the time of smolting, and then the growth rates
between annuli increased when the fish began growing in Lake Ontario. Stream resident Brown
Trout had consistent growth rates between annuli, indicating the individual did not migrate into
Lake Ontario. The prominent smolt age was age 2, but ranged from age 1-4 (Figure 4). The
dominant lake age prior to first spawning for migratory fish was age two, with lake durations
ranging from one to three years (Figure 5). Repeat spawning was more prominent in females
than males, with overall repeat spawning rates being 55.3% SD. The number of spawning
events ranged from one (maiden) through five (Figure 6). Repeat spawning was difficult to
interpret for resident fish, and was not included within the analysis. The prominent total age for
migratory Brown Trout was four years, with the remainder being age two through to age eight
(Figure 7) and an average of 4.6 years. Year classes represented within the adult population
are from 2005 to 2011 (Figure 7). The prominent total age for adult resident fish was six years,
with the range being age four through to age ten (Figure 7) and an average age of 6.2 years.
The adult resident Brown Trout were represented by year classes from 2003 until 2009 (Figure
7).
Figure 2: Sex ration of migratory and resident Brown Trout sampled from Wilmot Creek in 2013.
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Figure 3: Length frequency of migratory and resident Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
Figure 4: Smolt age for migratory Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
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Figure 5: Lake age at first spawning for migratory Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
Figure 6: Number of spawning events for migratory Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
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Figure 7: Age structure for migratory and resident Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
Total survival for the migratory component of the population was 56.6% of the fish, with a total
mortality of 43.4% (Figure 9).
Migratory and resident adult Brown Trout become larger the older they are, but expressed
different rates of growth (Figure 10, Figure 11). This trend is observed across the three
watersheds examined as part of this study.
Juvenile (Young-of-the-year - YOY) abundance and year class strength are variable over time,
but do not show as much variability as other salmonid species (GRCA unpublished data).
There has been a general decline in YOY abundance, but has remained fairly constant for the
last five years (Figure 12).
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Figure 8: Total Mortality for migratory Brown Trout sampled fro Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
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Figure 8: Average length at age for migratory Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
Figure 10: Average length at age for resident Brown Trout sampled from Wilmot Creek, Ganaraska River and Cobourg Creek in 2013.
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Figure 11: Average number of YOY Brown Trout captured from Wilmot Creek.
Discussion The plasticity of life history traits has played a substantial role in the successful colonization and
establishment of Brown Trout within the Lake Ontario basin. The early populations likely
consisted solely of resident Brown Trout, with a migratory form developing over time to exploit
all accessible habitats following the construction of fishways and improvements in stream
habitat and connectivity. This polymorphic strategy has been documented for Brown Trout in
both their native and introduced range (Malison et al. 2008, O’Neal and Stanford 2011), as well
as for iteroparous species with life history plasticity such as Rainbow Trout (McMillan et al.
2007).
Since the Brown Trout within any watershed likely form a polymorphic unit, it is not surprising
that there may be spawning interaction between resident and adfluvial life histories. Migratory
fish in Wilmot Creek are skewed towards females, whereas, the resident component of the
population is skewed towards males. This is likely due to the competitive advantage of
migratory females over resident females when spawning in sympatry due to larger body size
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and higher fecundity (Malison et al. 2008). A female biased migratory population has been
described for other populations, such as the Rio Grande River, were 75% of the population was
female (Malison et al. 2008).
The dominant age of smolting (age 2) expressed in naturalized migratory Brown Trout is similar
to that displayed in anadromous populations (Neimuth 1967, O’Neal and Stanford 2011). The
majority of individuals spent two years in Lake Ontario, prior to spawning for the first time, which
is similar to other adfluvial populations within the Great Lakes (Neimuth 1967). With the
majority of smolts being age two, this indicates that these are all naturally reproduced (wild
origin) individuals. Also, the lack of individuals with fin clips or other signs of previous hatchery
life (e.g. dorsal, pectoral fin erosion) indicates that all Brown Trout in this study are likely wild
origin
Repeat spawning was found to occur up to five times, with repeat spawning occurring up to 11
times in other anadromous populations (Harris and Milner 2006), while spawning may not occur
every year in more northern populations (Antonsson and Johannsson 2012). It has been noted
for populations in their native range that spawning up to five times was fairly common (Harris
and Milner 2006) and up to six times in other introduced populations (O’Neal 2008) . In the
Brule River, Wisconsin, adfluvial adults were documented to live up to seven years, and it was
noted that high levels of natural mortality occurred due to furunculosis infections in addition to
angling exploitation (Neimuth 1967). A high rate of repeat spawning was identified within the
three tributaries, with 55% of all sampled adfluvial Brown Trout being a repeat spawning
individual. Repeat spawning was more common in female Brown Trout, which is common for
iteroparous salmonids (Antonsson and Johannsson 2012). High rates of repeat spawning have
been documented within populations of anadromous Brown Trout (UK – Lamond 1916; Rio
Grande – O’Neal and Stanford 2011; and adfluvial populations Brule River – Neimuth 1967).
Within unexploited or minimally exploited populations it is common to have fish spawning up to
seven times and have a total repeat spawning rate as high as 63% (Lamond 1916). It has been
noted that there is often longitudinal gradient in the rate of repeat spawning, with Brown Trout in
the southern part of their native range exhibiting a younger age at maturity but more spawning
events within their life, versus individuals at the northern end of their range maturing later but
spawning less (Jonsson and L’Abee-Lund 1993). In other populations within the Great Lakes,
high rates of mortality have been expressed due to furunculosis infections during spawning
(Neimuth 1967). In Neimuth’s study, based on recovery of carcasses, mortality rates ranged
from 17.9% to 18.6% with mortality due to furuncolosis being strongly male biased. It was also
noted that infections rates where correlated with water temperature, with 10 – 15.5°C (50 –
60°F) considered to be optimum temperature for furunculosis development. The naturalized
populations sampled within Lake Ontario did not display the longevity expressed in some
populations (e.g. Rio Grande), but had similar total levels of repeat spawning. Older fish may
potentially be within the population, but the actual age may not be transparent when utilizing
scales as the sole aging structure. It is believed that maintaining a population with a high
proportion of repeat spawners is more robust as the population is able to spread the risk to
survival across a greater number of year classes and cohorts, as well as facilitating greater total
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lifetime fecundity (Harris and Milner 2006). Tagging individuals for future recapture and aging
validation would be helpful to elucidate a more accurate age structure.
As demonstrated within this study, across all populations there was a total mortality of 43%.
This total mortality is higher than that observed for a population that does not receive angler
exploitation (Malison et al. 2008), but lower than many European populations. Based on the
previous studies of adfluvial Rainbow Trout within the Great Lakes, there should be an annual
total natural mortality of approximately 30% each year. The higher mortality rate (>30%)
expressed in the Brown Trout populations is likely attributable to angler exploitation both within
their spawning tributaries and Lake Ontario. Based on the assumption that approximately 45%
total mortality (30% natural/15% angler) is appropriate for these populations, the total mortality
is at the upper threshold for maintaining a healthy population (Clarkson and Jones 1997). A
popular recreational fishery is present for adfluvial Brown Trout, but assessments have not been
conducted to quantify harvest or angling pressure for Brown Trout within these watersheds. It is
also known that adfluvial Brown Trout are utilized as an egg source as bait by anglers for
recreational fisheries, with many females being stripped of eggs and released alive. It is
unknown how this may influence recruitment in addition to existing harvest and mortality rates.
The age structure of the population is similar to other populations that do not receive
exploitation (O’Neal 2008), with the absence of fish older than age 8 within the Lake Ontario
populations, which have been observed in other naturalized Great Lakes populations (Sholl et
al. 1984) and other introduced populations (O’Neal 2008). The average age of the naturally
reproducing populations is older than what is observed within the Lake Ontario boat fishery,
where the harvest is comprised of 74.6% age 2, 21.3% age 3 fish, 3.3% age 4, and <1% age 5
(NYDEC 2013). From 1993-2012, very few age 6 Brown Trout or older have been observed (9
age 6 and 1 age 7 – NYDEC 2013). In 2012, 59% (23,305) of Brown Trout caught in US waters
of Lake Ontario were harvested (NYDEC 2013). The fish that are harvested within the US boat
fishery are displaying a different age distribution and a younger age structure than observed in
the study watersheds, perhaps due to higher exploitation rates. This may indicate that Brown
Trout from the study streams do not stray far while in Lake Ontario by migrating across to the
south shore of Lake Ontario.
The average size of migratory Brown Trout observed was larger than those observed for other
populations within the Great Lakes (e.g. Brule River, Niemuth 1967, Scholl et al. 1984), and
smaller than other introduced populations (e.g. Rio Grande, O’Neil 2008). The maximum size
observed within the study streams (female 804mmFL in 2012) was slightly smaller than
described for European populations (850-900mm, L’Abee-Lund 1991), and much smaller than
for introduced anadromous populations (1200mm, O’Neil 2008), yet similar to other Great Lakes
populations (Scholl et al. 1984).
Several parameters were not determined for the resident portion of the populations. Total
repeat spawning and total number of spawning events for the populations/ individual were not
always discernible, and therefore omitted from this study. Correspondingly, because the
number of spawning events could not be accurately determined, total mortality could not be
calculated. Based on the presence of a large age distribution within the populations, it is
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estimated that total mortality is similar or slightly lower than observed for the migratory trout.
The largest sample size and largest individuals for resident Brown Trout was from Wilmot
Creek, which also is the largest unfragmented watershed within the study. For resident Brown
Trout, there is a positive correlation between the length of the individual and the size of the
individual’s home range, or displacement distance (Zimmer 2004). Resident adult Brown Trout
become larger the older they are, but expressed different rates of growth based on the
watersheds examined. This observed has been observed for other populations in Ontario
(Devitt 1961), such as the Arrow River, Lake Superior watershed (J. George. Retired OMNR,
Pers. Comm).
Genetic studies in the Great Lakes have shown genetic differentiation between these two life
history variants with a watershed stocked approximately 40 years previously (Krueger and May
1987). Local adaptation and rapid evolution has been documented for introduced salmonids,
including Sockeye Salmon (O. nerka) (Hendry et al. 2000), and Chinook Salmon (O.
tshawytscha) (Quinn et al. 2000) populations. This local adaptation of introduced species occurs
within the timeframe outlined by Stockwell et al. 2003 for local adaptation and differentiation to
occur across a range of taxa.
Environmental conditions such as cold wet summers seem to help support stronger year
classes (GRCA unpublished data), but other variables such as mean October discharge may
help facilitate upstream access for adults into spawning areas and increase year class strength
the following year (NYDEC 2013). To fully estimate year class strength and YOY abundance, it
would be valuable to determine the proportion of YOY Brown Trout sampled that are adfluvial or
resident life histories. Currently, it is unknown whether adfluvial adults spawn in certain
locations, or if they utilize all habitats in sympatry with resident adults. Spawning surveys and
fry surveys may help elucidate spawning habitat use and early habitat use of each life history
variant. In addition, adult escapement sizes would allow for the development of stock-
recruitment model.
It is recommended that a mark-recapture study determine population size estimates and
validate aging and spawning checks. Marked individuals can also be used to look at straying
rates and Lake Ontario habitat use and movement and seasonal run timing both upstream and
downstream. It is also recommended that monitoring examine the behaviour of smolts and
determine when smolts are leaving these tributaries. Limited sampling has indicated primarily a
spring emigration. In other tributaries to the Great Lakes it has been documented that adfluvial
Brown Trout generally smolt during the spring, but fall smolting has been documented from the
Brule River (Neimeth 1967). Continued life history monitoring can help calibrate the Clarkson
and Jones (1997) model, and provide clarity on rates of mortality with these populations. In
addition, continued monitoring will aid in determining the relationship between resident and
adfluvial individuals within each tributary. It is suggested that both the adfluvial and the resident
populations of naturally reproducing Brown Trout be managed based on the recommendations
within Clarkson and Jones (1997), and as well for abundance, spatial distribution, diversity (life
history and genetic), and productivity to ensure the most resilient populations over the long-
term.
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Acknowledgments I would like to thank Jon George for his expertise aging these samples, and for valuable
discussions around life history interpretation and significance. Field assistance was provided by
Sarah Hogg, Nick Jones, Jason Whyte, Kaela Whyte, JT Whyte, Jon Sager, and Matt Brailey. I
would like to acknowledge Toronto Sportsman’s Show for funding the life history portion of the
study. Phil Bird and Nick Jones reviewed this manuscript.
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Appendix 1 – Migratory Brown Trout Photos
A1.1: Recently hatched Brown Trout, Wilmot Creek, May 10, 2012. Unknown whether Brown Trout is resident or migratory.
Life History and Population of Adfluvial Brown Trout in Wilmot Creek,
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A1.2: Brown Trout young-of-the-year (YOY) from Wilmot Creek (lower) and YOY Rainbow Trout upper captured August 2013. Unknown whether Brown Trout is resident or migratory.
A1.3: Brown Trout smolt from Cobourg Creek captured April 2012.
Life History and Population of Adfluvial Brown Trout in Wilmot Creek,
Ganaraska River and Cobourg Creek
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A1.4: 717mmFL adult female Brown Trout captured on Ganaraska River July 27, 2011.
A1.5: Adult Brown Trout ascending fishway on Ganaraska River August 9, 2011.
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A1.6: Adult female Brown Trout, Wilmot Creek, August 16, 2012. Photo courtesy of Dan Moore.
A1.7: Adult male Brown Trout, Cobourg Creek, October 22, 2013. Photo courtesy of John Sager.
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A1.8: Adult female Brown Trout Cobourg Creek, October 22, 2013. Photo courtesy of John Sager.
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Appendix 2 – Resident Brown Trout Photos
A2. 1: Adult male resident Brown Trout, Wilmot Creek, August 26, 2008.
A2. 2: 655mmFL adult female resident Brown Trout, Wilmot Creek, August 16, 2013.
Life History and Population of Adfluvial Brown Trout in Wilmot Creek,
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A2. 3: Adult male resident Brown Trout, Wilmot Creek, August 16, 2013.
A2. 4: 220mmFL adult male resident Brown Trout, Wilmot Creek, August 25, 2010.
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