history and population biology of adfluvial brown trout in ... · life history and population of...

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,


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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.



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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-



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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



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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.



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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.



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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.



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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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