Cisco Diversity in a Historical Drainage of Glacial Lake Algonquin

Canadian Journal of Zoology

Journal: Canadian Journal of Zoology

Manuscript ID cjz-2018-0233.R2

Manuscript Type: Article

Date Submitted by the 04-Mar-2019 Author:

Complete List of Authors: Bell, Allan; Ontario Ministry of Natural Resources and Forestry, Harkness Laboratory of Fisheries Research, Aquatic Research and Monitoring Section, Trent Univ. Piette-Lauziere,Draft Gabriel; Université Laval , Département de biologie Turgeon, Julie; Université Laval , Département de biologie Ridgway, Mark; Ontario Ministry of Natural Resources and Forestry, Aquatic Research and Monitoring Section, Trent Univ.

Is your manuscript invited for consideration in a Special Not applicable (regular submission) Issue?:

ECOLOGY < Discipline, THERMAL < Discipline, HABITAT < Habitat, FISH Keyword: < Taxon, SALMONIDAE < Taxon

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Cisco Diversity in a Historical Drainage of

Glacial Lake Algonquin

Allan H. Bell1, Gabriel Piette-Lauzière2, Julie Turgeon2, & Mark S. Ridgway1

1Harkness Laboratory of Fisheries Research

Aquatic Research and Monitoring Section, Ontario Ministry of Natural Resources and Forestry,

Trent University, 1600 West Bank Dr., Peterborough, ON, Canada K9L 0G2

2Département de biologie, Université Laval,

1045 avenue de la Médecine, Québec, QC, Canada G1V 0A6 Draft

Contact: [email protected]

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Title: Cisco Diversity in a Historic Drainage of Glacial Lake Algonquin

Authors: Allan H. Bell1, Gabriel Piette-Lauzière2, Julie Turgeon2, and Mark S. Ridgway1

Abstract

Cisco forms (Coregonus artedi (sensu lato) Lesueur, 1818) matching in appearance Blackfin Cisco from the Laurentian Great Lakes occur in four lakes in Algonquin Park, a historical drainage of glacial Lake

Algonquin (precursor of Lakes Michigan and Huron). Their occurrence may represent colonization from glacial Lake Algonquin drainage patterns 13,000 cal. years BP or independent evolution within each lake.

Gill-raker numbers, temperature at capture depth during lake stratification and hurdle models of habitat distribution are summarized. Blackfin (nigripinnisDraft-like) in the four lakes had higher gill-raker numbers than artedi-like cisco captured in nearby lakes or within the same lake. Two lakes have a bimodal gill- raker distribution indicating co-occurrence of two forms. Blackfin occupied the hypolimnion with a peak depth distribution at 20-25 m. Maximum depth for blackfin was 35-40 m. The presence of Mysis diluviana Lovén, 1862 appears necessary for the occurrence of cisco diversity in lakes but not sufficient in all cases. The presence of two forms of cisco in at least two lakes points to the possibility of the colonization or ecological speciation hypotheses as accounting for this phenomenon. Genetic analysis is needed to determine which of these hypotheses best accounts for the occurrence of blackfin in

Algonquin Park.

Key words: cisco, Coregonus artedi (sensu lato), Algonquin Park, glacial drainage, blackfin

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Introduction

Fish species in the genus Coregonus went through repeated ecological speciation and niche

diversification in lakes of North America and Fennoscandia (Schluter 1996; Bernatchez 2004; Praebel et

al. 2013; Mee et al. 2015). Consistent features in each case are separation of incipient species or forms

based on heritable traits such as gill-raker number as well as niche diversification based on differences in

depth distribution and diets. Generally, higher gill-raker counts correspond to greater planktivory and

occupancy of pelagic habitats in cases of ecological speciation (Schluter and McPhail 1992; Kahilainen et

al. 2011).

Cisco (Coregonus artedi (sensu lato = ‘in the broad sense’) Lesueur, 1818) has diversified into

several forms in lakes across Canadian Shield landscapes. The forms are defined by different patterns of gill-raker number, depth distribution and lifeDraft histories (Muir et al. 2014; Turgeon et al. 2016). The cisco flock of the Laurentian Great Lakes has long been known (Dymond 1926; Koelz 1929), with several deep-

water forms now extirpated (Smith 1964; Zimmerman and Krueger 2009; Eshenroder et al. 2016).

Inland lakes with different cisco forms but similar in appearance to the Great Lakes cisco flock were

regarded as sharing common taxonomic designations stemming from a belief in shared phylogenetic

history (Smith and Todd 1984; Etnier and Skelton 2003). Great Lakes forms were assumed to have

colonized inland lakes based on glacial history of the region. This assumption no longer has support as

patterns in genetic diversity repeatedly demonstrate independent cases of ecological speciation among

Great Lakes as well as inland lakes forms (Turgeon et al. 1999, 2016; Turgeon and Bernatchez 2003).

Therefore, past taxonomic descriptions of cisco forms in the Great Lakes and inland lakes can no longer

be assigned with confidence based on a belief in a common shared phylogenetic history.

The term “form” is used here as a recognized label for cisco diversity based on a review of

ciscoes in the Laurentian Great Lakes (Eshenroder et al 2016). For example, Blackfin Cisco (C. nigripinnis)

in the Laurentian Great Lakes can be recognized using only its species’ epithet. Similarly, the Shortjaw

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Cisco is the zenithicus form as recommended in Table 1 of Eshenroder et al. (2016). As a matter of convention, we adopt the use of capitalized common names (and species name as a form at first mention) when identifying Laurentian Great Lake forms. Uncapitalized common names identify forms that may converge in morphology and ecology to Laurentian Great Lake forms but exist in lakes not recognized as the Laurentian Great Lakes.

In Algonquin Park, Ontario, White Partridge Lake is one example of where multiple cisco forms have evolved that are more closely related to each other than to similar forms in other lakes (Turgeon et al. 2016). The lake has a zenithicus-like form of shortjaw and pelagic artedi-like forms of cisco. White

Partridge Lake lies within a historical drainage of glacial Lake Algonquin via the Fossmill outlet that drained Lake Algonquin for approximately a millennium (13,000 -12,000 cal yrs BP; Dyke 2004; Ridgway et al. 2017). It contains Mysis diluviana Lovén,Draft 1862 (hereafter Mysis), an indicator species shared by lakes < 381 m in elevation in Algonquin Park that were inundated by drainage from Lake Algonquin in the past (Martin and Chapman 1965; Dadswell 1974). Lakes above 381 m were not inundated by Lake

Algonquin via the Fossmill outlet and have Chaoborus punctipennis (Say, 1823) (hereafter Chaoborus) as the dominant diel migrator (Barth et al. 2014). The Fossmill outlet is a recognized zoogeographic feature for freshwater fish distribution in the region (Mandrak and Crossman 1992; Mandrak 1995; Ridgway et al. 2017).

Glacial Lake Algonquin was the precursor of Lakes Michigan and Huron, where deep-water ciscoes including Blackfin Cisco (nigripinnis form), Shortjaw Cisco (zenithicus form), and others are present or extirpated or extinct (Schmidt et al. 2011; Eschenroder et al. 2016; Blanke et al. 2018). Given the timing and operational lifespan of the Fossmill outlet as a pour point of Lake Algonquin, it is possible that this direct link from the precursor of much of the Laurentian Great Lakes resulted in the dispersal of early cisco forms into inland lakes of Algonquin Park. This is the colonization hypothesis for cisco forms in inland lakes stemming from early assessments of cisco diversity (Smith and Todd 1984; Etnier and

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Skelton 2003). Unlike previous proposed colonization narratives (e.g., Smith and Todd 1984), the unique

position of Algonquin Park and its drainage history represents the best opportunity for the colonization

hypothesis. Forms of cisco in Algonquin Park could therefore represent Laurentian Great Lake forms

given patterns of lake drainage from glacial Lake Algonquin (Mandrak and Crossman 1992; Ridgway et

al. 2017), or their occurrence could represent ecological speciation of the kind detected for inland lake

cisco pairs (Turgeon et al. 2016).

To begin to address these alternative hypotheses a survey of lakes with cisco in Algonquin Park

above and below the 381 m elevation contour was conducted throughout the region affected by the

Fossmill outlet. This study focused on the distribution and ecology of cisco in this region for the purpose

of: 1) describing the zoogeography of cisco diversity in areas of Algonquin Park subject to past glacial lake outflow vs areas not inundated with glacialDraft lake drainage; 2) modeling habitat distribution of any benthic form in lakes where they occur to test the hypothesis that they occupy hypolimnetic habitat

(Bunnell et al. 2008), and 3) determining whether the distribution of gill-raker numbers in forms of

Algonquin Park match the distribution observed historically in the Laurentian Great Lakes (Eshenroder et

al. 2016).

Methods

Study Lakes

Lake surveys (2010-2016) were conducted in Algonquin Park on 28 lakes ranging in surface area

(53-2,538 ha), depth (max. depth, 8.7-58.6 m), and above or below the 381 m elevation1. Figure 1

presents the lake locations and their position relative to the 381 m elevation contour line.

Gear description and survey design:

1 See Supplement cjz_2018_0233_suppla for lake locations and characteristics

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Bathymetric maps for each lake were developed prior to surveys. Depth data were collected using Garmin GPSMap 526s depth-sounder / GPS combination units recording depth-at-position every two seconds. Surveys consisted of two shoreline perimeter transects and cross-basin transects spaced

100 meters apart to ensure even coverage. A Triangulated Irregular Network (TIN) of depth for each lake was created and converted to a depth raster with a cell size of 5 m using ArcGIS (versions 9.3-10).

This was in turn smoothed using nearest-neighbour averaging with a 3 m radius.

Ciscoes were captured in bottom gillnets and pelagic gillnets. Two bottom-gillnet types were used as OMNR transitioned from one net type targeting lake trout (Salvelinus namaycush (Walbaum in

Artedi, 1792) to the North American standard gillnet (Lester et al. 2009). For the first net type, bottom- set gillnets measured 64 m x 2 m (lxh) and contained panels of 57, 64, 70, 76, 89, 102, 114 and 127 mm stretch mesh. Mesh series for any given netDraft were one of three different randomly selected orders. Gillnets were set for two hours between 08:00 - 16:00 hours. In the North American gillnet standard, bottom-set gillnets measured 25 m x 2 m (lxh) with each set comprised of two nets tied together in tandem. Panels contained 38, 51, 64, 76, 89, 102, 114, and 127 mm stretch mesh and were randomly placed within a net. North American standard bottom gillnets were set for one hour between 08:00 and

16:00.

Bottom-net locations were stratified random within depth intervals, with the number of sites allocated to each stratum in proportion to its surface area relative to total lake area. The number of netting sites was determined using the equation from Sandstrom and Lester (2009) modified into the following form: Number of Sets = 0.0184(Area (ha) > 2 m) + 24. Since the calculated number of sites represented a minimum effort, the number of sites was often increased by approximately 10% resulting in 103, 36, 41, and 49 sites for Cedar, Hogan, Mink, and Radiant lakes, respectively. Netting sites were positioned by overlaying points on a grid pattern of a lake bathymetric map stratified into depth zones in ArcGIS (versions 9-10.1). Spacing among net sites was at least 250 m. Nets were set so the midpoint of

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the net fell at the site location. Net location coordinates were collected at the midpoint of the net using

handheld GPS units. Depths were recorded at the beginning, middle and end of each net set. Set and lift

times were recorded for each net set.

Ciscoes captured in the pelagic zone were caught in both North American and European

standard pelagic nets. Pelagic-net location was in the centre of each lake and not randomly stratified.

Pelagic nets were for detecting the presence of cisco and capturing fish for biological samples. North

American pelagic gillnets are 25 m x 6 m (lxh) containing panels with stretched mesh sizes of 13, 19, 25,

32, 38, 51, 64, 76, 89, 102, 114, and 127 mm (Lester et al. 2009). European pelagic gillnets are 30 m x 6

m (lxh) containing panels with stretched mesh sizes of 10, 12.5, 16, 20, 25, 31, 39, 48, 58, 70, 86, and

110 mm (CEN 2005). Pelagic nets were suspended at 6 and 12 m of depth and fished for 1 to 4 hours during the day and evening. In each study lake,Draft additional non-standardized sampling using the gears described above was used to increase sample sizes for counting gill rakers.

Fish were identified to species, measured (fork length, mm), and kept for gill-raker counts. The

left anterior gill arch of each retained cisco specimen was removed and preserved in 70% ethanol.

Except for Hogan Lake, gut contents of each sampled fish were examined visually.

Gill-Raker Numbers:

All cisco gill-raker numbers were from the upper segment (epibranchial segment) and lower

segments of gill arch (combined ceratobranchial and hypobranchial segments), with total gill-raker

number being the sum of the counts of both segments. All vestigial gill rakers located near the ends of

both the upper and lower gill arch segments were included in the total gill-raker number. Gill-raker

numbers are summarized for lakes with adequate sample sizes. For Chaoborous lakes, gill-raker

numbers are from Big Crow, Burntroot, Carl Wilson, Catfish, Craig and Dickson lakes (Fig. 1). For Mysis

lakes, gill-raker counts are from Cauchon, Cedar, Grand, Hogan, Kioskokwi, Mink, Radiant and Threemile

lakes (Fig. 1).

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Gear Selectivity and Size Structure:

A relative retention selectivity curve (peak = 1.0) was generated for cisco caught in benthic nets using the ‘omnr.gillnet’ package (program R)2. Length frequency of cisco was corrected for retention selectivity using the relative selectivity coefficient in each length class

퐿푒푛푔푡ℎ ( 푖 푆푒푙푒푐푡푖푣푖푡푦푖).

Habitat Models:

Habitat models were based on bottom-net sets. Net depth was averaged using the beginning, middle, and end depths recorded for each net set. Average net depth was standardized (converted to z- scores) using mean lake depth and standard deviation from the depth raster. The standardized depth of each net (hereafter depth) was used as a covariate (including squared and cubed depth covariates) to model linear and non-linear effects that depthDraft may have on blackfin depth distribution. A single temperature and dissolved-oxygen profile was taken in the main basin of each lake during the period of sampling. Temperature (°C) and dissolved oxygen (mg/L) were recorded at 1m intervals starting at the surface, to a depth of 20 m, with 5 m intervals being used at greater depths.

These data were then fitted with smoothing splines in R (R development core team 2017) so that temperature and dissolved oxygen could be predicted for each netting site, and lake-wide, using average site depth and depth rasters, respectively.

The lowest observed DO concentration in any of the study lakes was 6.7 mg/L. This is well above

DO levels needed for survival by cisco (2-3 mg/L; Evans et al. 1996), avoidance levels by cisco (1.3 mg/L;

Aku et al. 1997), and lower lethal limits (1.0 mg/L across a range of temperatures; Jacobson et al. 2008).

As a result, DO was not used as a covariate.

Hurdle models:

2 See Supplement cjz_2018_0233_supplb for retention selectivity analysis

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Habitat distribution of cisco forms captured in bottom nets was estimated using hurdle models

(Martin et al. 2005; Potts and Elith 2006; Dorazio et al. 2013). Hurdle models are comprised of a

binomial component based on presence or absence of fish (1 or 0, respectively) and a zero-truncated

count model based on discrete distributions such as Poisson or negative binomial distributions. The two

components address processes producing presence or absence and processes generating quantitative

gradients in counts as a function of covariates (Hilbe 2014).

Separate models using temperature and depth covariates were created to assess which

covariate better explained blackfin depth distribution. Initial hurdle models with only linear covariate

effects performed poorly (via Δ AIC) and were not considered further in the analysis. Second- and third-

order polynomials of the covariates were modeled to assess non-linear effects. Temperature preferences of fish are non-linear as shownDraft in laboratory studies of aerobic scope (Farrell 2016). For each lake, the variance of zero-truncated blackfin catches was 1.7 to 2.9 times greater than the mean,

indicating the data did not meet the assumption of equivalent mean and variance for Poisson models.

For this reason, all combinations of covariates were modeled using both Poisson (henceforth Poisson

hurdle) and negative binomial (henceforth negative binomial hurdle) models as the count component

(Hilbe 2014).

Akaike Information Criterion (AIC) was used to rank models. Models with Δ AIC values less than

2 had substantial support, models with Δ AIC values between 2 and 4 had less support but were still

plausible, and models with Δ AIC values greater than 4 had little to no support (Burnham and Anderson

2002). Model fit was assessed using Pearson’s χ2 goodness of fit test. Analysis was based on package

‘pscl’ in R using the function ‘hurdle’ (R development core team 2017; Zeileis et al. 2008).

Site-level cisco abundance was predicted across the range of depths found in each lake using the

top model (Δ AIC). Predictions of blackfin occupancy across a specified range of depths were generated

using the binomial component of the hurdle model. Using the same range of depths as the binomial

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10 component, estimates of blackfin numbers were generated using the count component of the hurdle model (zero-truncated). Finally, cisco site-level abundance was calculated by multiplying the estimates from the binomial and count components together at each depth value. Progression of the prediction process was contingent on statistical significance (p < 0.05) of model parameters of both components of the hurdle model. If neither model components contained significant parameters, no habitat predictions were generated. Significance of binomial component parameters allowed for occupancy prediction, but abundance prediction was only possible with significant count component parameters. If count component parameters were not significant, model-based predictions were limited to occupancy.

Maps of cisco depth distribution based on modeled site-level occupancy or abundance were created in ArcGIS using the same prediction procedure outlined above. The depth raster for each lake was reclassified to a cell size of 64 m, correspondingDraft to the length of a traditional net. Predictions were generated for each cell of this raster using the top model selected by AIC. Occupancy (0 to 1 scale) and count estimates were generated for each raster as a function of covariates.

Results

Lake Surveys:

The northern region of Algonquin Park including surveyed lakes and the abandoned town of

Fossmill are shown in Figure 1. Fossmill represents the pour point for the eastward drainage of glacial

Lake Algonquin. Two lakes, Waterclear (#10; Fig. 1) and Philip (#22; Fig. 1), did not have Mysis confirmed as being present despite being below 381 m elevation and are not included in our analyses. Sixteen lakes were surveyed below 381 m elevation that contained Mysis and cisco3. Eight lakes above 381 m were surveyed that contain Chaoborus and cisco3 . For lakes above 381 m, all ciscoes were typical for C. artedi

3 See Supplement cjz_2018_0233_suppla

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(sensu lato) occupying the pelagic zone in inland lakes – small (< 22 cm) and silver in colouration with no

distinguishing morphological features beyond the typical species description (Scott and Crossman 1998).

The survey revealed four lakes with atypical forms of cisco below the 381 m elevation contour

(Table 1), in addition to the known cisco diversity of White Partridge Lake (Turgeon et al. 2016). Cisco

similar to the external appearance of the Blackfin Cisco form described from the Laurentian Great Lakes

(Fig. 2; Eschenroder et al. 2016) were found in Mink (#8 in Fig. 1), Cedar (#16 in Fig. 1), Hogan (#21 in Fig.

1), and Radiant lakes (Fig. 2; #23 in Fig. 1). Common external features shared by forms in the four lakes

and the Great Lakes are heavily pigmented paired fins (grey colouration in Mink Lake), black pigment

along the dorsal region extending to the head including the nasal region, and a purple/blue metallic

iridescence of the scale region above the lateral line (Fig. 2; see description in Koelz 1929; Eshenroder et al 2016). Because of this external similarity,Draft particularly pigmented paired fins, the cisco forms in the four lakes are described as nigripinnis-like blackfin. All net locations and catch data for the four blackfin

lakes are summarized in a supplement4.

Blackfin were captured in bottom nets indicating occupancy of benthic habitat at least during

daylight hours in the study lakes. The forms labelled here as blackfin distinguishes them from typical

artedi-like cisco captured in pelagic nets in the lake survey.

Of the four lakes, Mink Lake now drains to the west as part of the Amable du Fond river system.

Cedar and Hogan lakes drain to Radiant Lake as part of the Petawawa River and have been separated

from Mink Lake by the Mink Lake Sill (MLS in Fig. 1) since approximately 11,000 years BP (Ridgway et al.

2017). All four lakes are oligotrophic (TP 4.6 to 6.6; OMNRF unpublished data).

Five (including White Partridge Lake) of 16 lakes below 381 m elevation had cisco forms that

differed from what is accepted as the typical artedi-like cisco form (Scott and Crossman 1998). The

4 See Supplement cjz_2018_0233_supplc for net locations and blackfin catches in the study lakes

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12 remaining 11 lakes below 381 m had cisco matching in appearance the artedi-like cisco captured in lakes above 381 m. All cisco in the 11 Mysis lakes were captured in pelagic nets as in lakes with Chaoborus (>

381 m).

Bathythermal distribution:

In total, 308 blackfin were caught in 229 bottom-net sets in the four lakes with blackfin. In all four study lakes, blackfin were never captured at depths shallower than 10 m, even though at least 10 percent of netting effort was allocated to these depths in each study lake (Fig. 3). The thermocline depth was 7 - 8 m in all four study lakes (Fig. 3). In Cedar, Radiant and Mink lakes, most catches occurred at depth ranges of 10 to 20 m, with catch diminishing at greater depths (Fig. 3). The distribution of catch was somewhat different in Hogan Lake where peak catch was found at depths greater than 25 m. Blackfin caught in Cedar, Radiant, and MinkDraft lakes did not appear to prefer the deepest zones of the lake, whereas in Hogan Lake the deepest zones were preferred (Fig. 3).

Temperatures at capture depth were well within the hypolimnion (Fig. 3). Mean weighted

(weights =count of fish at each net site; ±1SD) temperature at capture depth was 5.86°C (±0.44) in

Hogan Lake, 8.43°C (±0.74) in Radiant Lake, 7.74°C (±0.46) in Cedar Lake, and 7.52°C (±0.28) in Mink

Lake.

Gill Rakers:

Gill-raker numbers for cisco sampled in lakes with the artedi-like cisco form only were combined based on Chaoborus (N=156 cisco) vs Mysis (N=116 cisco) as the dominant diel migrator (Fig. 4). In both categories, gill-raker distribution fell within a range expected for artedi-like cisco (41-51 for Chaoborus lakes, 푥 = 46; 41-52 for Mysis lakes, 푥 = 47 ). In contrast, the range of gill-raker numbers included two modes in Cedar (N=133 fish) and Hogan (N=236 fish) lakes. One mode was found in Mink (N=73 fish) and

Radiant (N=129 fish) lakes (Fig. 4). Gill-raker number varied from 45 to 54 (푥 = 49 ) in Mink Lake (Fig. 4).

The upper mode in Hogan Lake ranged from 52 to 61 (푥 = 55 ) and lower mode from 41 to 51 (푥 = 47 )

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(Fig. 4). The upper mode in Cedar Lake ranged from 52 to 66 (푥 = 59 ) and lower mode from 43 to 49 (푥

= 46) (Fig. 4). The lower mode in both lakes fell within the artedi-like cisco range observed in both

Chaoborus and Mysis lake categories. Raker number was not bimodal in Radiant lake and ranged from

41 to 66 (푥 = 56 ). In Radiant Lake, gill-raker numbers ranging from 52 to 66 (푥 = 58 ) represented most

of the gill-raker distribution and was equivalent to the upper mode in Cedar Lake. Radiant Lake receives

flow from both Cedar and Hogan lakes farther upstream.

Examination of stomach contents in Cedar, Mink and Radiant blackfin indicated Mysis in 18%

(N=94), 71% (N=14), and 48% (N=52) of samples, respectively. Mysis occurred in stomach contents from

Hogan Lake (pers. obs.), but frequency was not recorded. Digestive state of gut contents limited a

complete analysis of all contents. The proportion of blackfin with empty stomachs was approximately 25 percent in each of the three populations examined.Draft Size structure:

Size of typical cisco identified as artedi-like and blackfin differed among lakes (Fig. 5). The

artedi-like cisco captured in pelagic gillnets from Mysis-based food webs in lakes below 381 m had a

grand 푥 FL = 179 mm (±1SD=29). The artedi-like cisco captured in pelagic gillnets from Chaoborus-based

food webs in lakes above 381 m had a grand 푥 FL= 174 mm (±1SD=26). In contrast, length-frequency

distributions were similar among three blackfin populations in Cedar (푥 FL = 262 mm; ±1SD=28), Hogan (

푥 FL = 279 mm; ±1SD=26) and Radiant (푥 FL = 269 mm; ±1SD=37) lakes (Fig. 5). Mink Lake had the

smallest blackfin (푥 FL= 217 mm; ±1SD=9). Consistent with the bimodal gill-raker distribution, size of

cisco in Cedar and Hogan lakes were bimodal with artedi-like cisco representing the smaller mode and

blackfin representing the larger mode (Fig. 5). The smallest blackfin captured in the multi-mesh gillnet in

all 4 lakes were larger than artedi-like cisco captured in pelagic nets.

Habitat models:

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Habitat models based on sampling depth as a covariate were only developed for Cedar and Radiant lakes for two reasons. First, hurdle models for Hogan and Mink lakes could not be fit to the data regardless of covariates and nonlinear terms. This appears to be the result of sample size with Hogan and Mink Lake sample areas being smaller than for Cedar and Radiant lakes. Second, water temperature as a covariate describing blackfin depth distribution did not result in useful models for

Cedar and Radiant lakes. In addition, all models that included the third-order polynomial of temperature failed to converge. Models that contained the second-order polynomial of temperature did converge but produced coefficients (β) with large negative values, which indicated lack of model fit.

All depth models for Cedar and Radiant lakes converged and produced model coefficients (β) with reasonable values. Among depth models, negative binomial (count regression component) hurdle models had the greatest AIC support for bothDraft Cedar and Radiant lakes (Table 2). For Cedar Lake, negative binomial hurdle models had the highest AIC weight (0.784) of the four models and were the only models with ΔAIC values less than 4 (Table 2). Poisson hurdle models had little to no AIC support with high ΔAIC values of 32.65 for the depth+depth2 model (Table 2).

For Radiant Lake, the negative binomial hurdle models had the highest AIC weight (0.779) of the four models and were the only models with ΔAIC values less than 4 (Table 2). The two Poisson hurdle models collectively had a low AIC weight and little AIC support as neither model had a ΔAIC value less than 4 (Table 2). Including the cubic polynomial of depth increased the standard errors of the all coefficients over that of the depth+depth2 model and are not considered further.

The intercept+depth+depth2 model was the highest ranked for Cedar and Radiant lakes (Table

3). This model was selected for estimating coefficients and mapping. The binomial component of the hurdle models produced significant parameter estimates for depth and depth2 (Table 3). Pearson’s χ2 goodness of fit test showed the binomial coefficients of hurdle models were reasonable fits for both

Cedar (χ2 = 114.4; 100df; p=0.15) and Radiant lakes (χ2 = 43.4; 46df; p=0.58). The zero-truncated

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negative binomial count models for both Cedar and Radiant lakes did not produce significant

coefficients with confidence limits covering 0 for all parameters (Table 3).

Because the depth parameters were standardized the coefficients represent relative non-linear

change (in standard deviation units) in habitat occupancy. For both Cedar and Radiant lakes, the

positive and relatively large coefficient for depth (Table 3; 훽 = 3.210 in Cedar Lake; 훽 = 5.866 in

Radiant Lake) points to a sharp rise in occupancy at a 10-15 m. The negative coefficient for depth2 points

to a lower limit on habitat occupancy for blackfin in both lakes that is not represented by maximum

depth of each lake.

Predicted blackfin occupancy peaked at 0.74 at a depth of 23 m in Cedar Lake (Fig. 6). Predicted

occupancy was very low at or above the thermocline (Fig. 6) and below 40 m which was consistent with patterns in raw catch data (Fig. 3). PredictedDraft blackfin occupancy sharply peaked in Radiant Lake at 0.99 between 21-25 m of depth and with a broader depth range of peak occupancy relative to Cedar Lake

(Fig. 6). Peak predicted occupancy in Radiant Lake was equivalent to Cedar Lake (23 m) but the range of

peak occupancy for Radiant Lake remained high through 30 m before declining at 35 m (Fig. 6).

Mapping the binomial model component for both lakes shows the sharp increase in depth

occupancy reflected in the parameter estimates (Table 3), and distribution (Fig. 6) was associated with

occupancy just below the thermocline (Fig. 7). The mapped depth distribution of blackfin in both lakes is

defined at its upper range by the thermocline and at its lower range by a depth of 35-40 m. The lower

range is not associated with the deepest locations in Cedar or Radiant lakes (Fig. 7). During the day,

Cedar and Radiant lakes have large areas of bottom habitat suitable for blackfin (Fig. 7).

Discussion

Four lakes in Algonquin Park had blackfin in locations once part of the drainage system of glacial

Lake Algonquin that flowed approximately 13,000 cal. years BP. Lake Algonquin was the precursor of

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Lakes Michigan and Huron where Blackfin Cisco occurred prior to its extirpation. All lakes where blackfin were detected have Mysis as the dominant diel migrator in the planktonic food web, but not all lakes with Mysis surveyed in this study contained blackfin (Fig. 1). Since all Mysis lakes in the park share a common glacial drainage, the presence of benthic cisco that closely resemble Blackfin Cisco of the

Laurentian Great Lakes in some but not all lakes points to two possible hypotheses.

First, during the centuries-long drainage era for glacial Lake Algonquin (Ridgway et al. 2017), not all current lakes were suitable habitat for the blackfin because of flow, temperature or other conditions present at that time. However, the common form of Cisco is present in most lakes within the drainage system including lakes without blackfin. Presumably, under the colonization hypothesis, Cisco from Lake

Algonquin with lower gill-raker numbers (left mode for Cedar and Hogan lakes in Fig. 3) also arrived in the glacial era but were able to occupy a widerDraft set of lakes (Fig. 1). This hypothesis implies that the Fossmill outlet was the source of fish for the park landscape as recognized by fish zoogeographers

(Mandrak and Crossman 1992) and, as a result, blackfin were present in Lake Algonquin along with Cisco form during its drainage through the Algonquin Park landscape 13,000 cal. years BP and is monophyletic with Blackfin Cisco in the Great Lakes.

Second, blackfin detected in this study represent another case of in situ cisco diversification as found in White Partridge Lake in Algonquin Park and other inland lake locations (Turgeon et al. 2016).

For Cedar, Hogan, Radiant and Mink lakes ecological speciation has resulted in a blackfin form closely converging on the Blackfin Cisco of the Laurentian Great Lakes. This hypothesis implies no specific entry route to the Algonquin Park landscape but relies on ecological speciation as a candidate process driving the diversification observed in gill-raker numbers, habitat and colouration. Ecological speciation in our study lakes may stem from sympatric evolution or multiple invasions during the drainage era in a manner like that observed in sticklebacks (Schluter and McPhail 1992). Data in this study cannot fully resolve whether the colonization or ecological speciation hypothesis represents the most likely

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explanation for the presence of blackfin in Algonquin Park. Gill-raker distribution for blackfin in this

study was the trait with the strongest departure from patterns observed for Blackfin Cisco in the

Laurentian Great Lakes (Eshenroder et al. 2016).

The weight of genetic and ecological evidence supports ecological speciation in many instances

of multiple Coregonus forms in lakes including European whitefish (C. lavaretus (Linnaeus, 1758);

Kahilainen et al. 2014), lake whitefish (C. clupeaformis (Mitchill, 1818); Mee et al. 2015), and North

American ciscoes (Turgeon and Bernatchez 2003). Ecological speciation of forms into shortjaw and cisco

in White Partridge Lake has also occurred widely in other inland lakes (Turgeon et al. 2016). Assessing

the relative strengths of the colonization vs. ecological speciation hypotheses for blackfin in Algonquin

Park will require a similar genetic analysis. The distribution of gill-raker numbersDraft (Fig. 3) among three of the four blackfin populations in Algonquin Park exceed the known ranges of Cisco gill-raker numbers from the Laurentian Great Lakes

(gill-raker counts: 43.9 ± 2.5 (SD) for Lake Superior; 46.0 ± 1.8 (SD) for Lake Michigan; 43.0 ±1.9 for Lake

Huron; 48.5 ± 2.1 (SD) for Lake Ontario; 46.3 ±2.1 (SD) for Lake Nipigon; Eshenroder et al. 2016). Only

blackfin from Mink Lake (range, 45-54; Figure 3) are within the gill-raker distribution of Blackfin Cisco

from the Lakes Huron and Michigan (Eshenroder et al. 2016). Gill-raker numbers in the other three

populations are either bimodal (Cedar or Hogan lakes) with an upper mode greater than observed in the

Great Lakes historically, or unimodal with a wide range in gill-raker numbers (Radiant Lake) including fish

that are within the artedi range to fish with gill-raker numbers ≥ 60. Blackfin with gill-raker numbers ≥

55 are well above observed patterns in historical samples from the Great Lakes. Radiant Lake is

downstream of both Cedar and Hogan lakes (each in separate watersheds; see Fig. 1) so the gill-raker

distribution for blackfin in this lake likely stems from fish arriving from both upstream lakes. Mink,

Cedar and Hogan lakes have been separated for approximately 13,000 years following glacial retreat

from this landscape (Ridgway et al. 2017).

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High gill-raker counts (counts in the 50s to mid-60s) matching those observed in Algonquin Park have been observed in cisco forms from other large inland lakes referred to as Coregonus nipigon.

Dymond (1926) described this form from Ombabika Bay, Lake Nipigon (50° 6' 0.4"N; 88° 9' 38.9"W) and

Black Sturgeon Lake (49° 21' 29.7"N; 88° 52'; 19.6"W). Etnier and Skelton (2003) attributed cisco from

Saganaga Lake (48° 14' 39" N; 90° 54' 42.8"W) with very high gill-raker counts to this form (gill-raker count 푥 = 56.3; range, 45-70). C. nipigon was synonymized with C. artedi (Scott and Crossman 1998) and is not a recognized form in a recent review of Great Lakes ciscoes (Eshenroder et al. 2016). Of the cisco species that were historically described, only the gill-raker numbers of C. nipigon (54-66 reported by

Koelz (1929); 50-59 reported by Dymond (1926)) match the gill-raker counts observed in Algonquin Park blackfin. Clearly, gill-raker numbers of forms in inland lakes can exceed numbers observed in all forms from the Laurentian Great Lakes. Draft Models of blackfin distribution in Cedar and Radiant lakes provided a good fit and interpretable coefficients. Temperature models failed to fit correctly, and dissolved oxygen in each lake was non- limiting. For both lakes, models containing the second order polynomial of depth were selected by AIC as the models that best described the patterns in blackfin depth distribution. Predicted occupancy from the top models captured the patterns observed in the catch data, with predicted occupancy being low in depths shallower than 10 m and greater than 30 m. This pattern in predicted occupancy was similar between Cedar and Radiant lakes indicating similar depth distributions in proximity to lake bottom.

Patterns of blackfin occupancy in three of the four study lakes revealed the deepest areas of each lake are not preferred habitat based on the declining trend for occupancy with depth (Figs. 3, 6, and 7). In contrast, most blackfin in Hogan Lake were captured in the deepest areas of the lake (Fig. 3).

DO was not a limiting factor. The distribution of blackfin in the Algonquin Park lakes more closely resembles the distribution of the extant Blackfin Cisco in Lake Nipigon. This form in Lake Nipigon historically inhabited depths up to 104 m but were more common at 37 m of depth in the summer

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(Dymond 1926), and more recently have been caught at depths between 10 to 50 m (Turgeon et al.

1999). Dymond’s (1926) historical description of Blackfin Cisco abundance at 37 m is deeper but close to

peak occupancy patterns observed in Radiant and Cedar Lake. A contemporary description of Blackfin

Cisco catches occurring at 10-50 m of depth in Lake Nipigon shares the same depth distribution detected

in Cedar and Radiant lakes (COSEWIC 2007).

Peak occupancy for blackfin in Cedar and Radiant lakes was in the range of 20-25 m, at

hypolimnetic temperatures below 10°C. The depth of blackfin may be correlated with the resting depth

of Mysis. Mysis were frequently observed in the diet of blackfin captured during the day in Algonquin

Park. Mysis are known to avoid bright light, preferring light intensities between 10-5 and 10-6 lux, and this

sensitivity to light intensity affects their depth distribution within a lake (Beeton and Bowers 1982; Gal et al. 1999; Boscarino et al. 2010). This in turnDraft may affect the depth distribution of blackfin. Regulating buoyancy and pursuing Mysis at depth and through diel movement is hypothesized to be the primary

selective gradient in the evolution of deepwater cisco diversity in the Great Lakes (Eshenroder et al.

1998).

Mysis is an important diet element for cisco forms in other lakes. Gut contents and isotopic

signatures of two sympatric forms of cisco in Great Bear Lake were found to correspond to gill-raker

count, with Mysis being the predominant dietary item of the morph with low gill-raker count, and

copepods being the main dietary item of the morph with high gill-raker count (Howland et al. 2013). This

observation is opposite of what was found for blackfin in this study based on gut content analysis.

Some blackfin were captured in pelagic nets during evening hours indicating possible diel

movements. Given the rarity of blackfin populations and uncertainty about population sizes in each

lake, a full description of diel distribution in the study lakes using gill nets was not a desired option. The

depth distribution of the artedi-like cisco form was largely confined to the 6-12 m depth zone in most

lakes reflecting some proximity to the metalimnion. Because pelagic nets used in this study were 6 m in

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20 height, it was not possible to refine that distribution especially in the metalimnion. Future work on habitat distribution of cisco and blackfin should include hydroacoustic surveys to capture a more precise depth distribution in the pelagic zone for cisco and to assess any shift in diel vertical distribution for both forms.

Some nets failed to detect blackfin based on model-derived predictions (catch = 0 in areas of high occupancy). Hurdle models incorporate zero detection through the binomial modelling component and interpret lack of detection as true absence (Dorazio et al. 2013). Our results show that there is undoubtedly imperfect detection in the netting survey. A more robust approach to account for imperfect detection is to conduct multi-pass surveys where each site is sampled more than once, resulting in a detection history that is used to directly estimate imperfect detection (Mackenzie et al. 2017). Draft We adopted a naming convention for distinguishing diversity among inland lake ciscoes from those in the Laurentian Great Lakes. This approach reflects the growing recognition that past taxonomic practices and assumptions used initially for Great Lakes ciscoes are not consistent with current discoveries of ecological speciation. If 1947 is taken as the adoption of the modern synthesis of evolution (Mayr 1982), then the original observations of cisco diversity in the Great Lakes by Koelz

(1929) predates recognition of the central role of the modern synthesis by at least two decades. In contrast, initial recognition of stickleback diversity followed the modern synthesis by two decades (e.g.,

Hagen 1967; McPhail 1969). In the latter case, the modern synthesis underpinned thinking from the beginning regarding the role of selection in generating form and niche diversity (Hagen and McPhail

1970).

Past practice when confronted with inland lake cisco diversity in areas of eastern North America was to attribute cisco forms to Great Lakes taxa (e.g., Bailey and Smith 1981; Smith and Todd 1984;

Etnier and Skelton 2003). Glacial lakes such as Lakes Agassiz and Algonquin that directly influenced the

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formation of the modern Laurentian Great Lakes also covered areas far greater than the current Great

Lakes Basin during their lifespan (Lewis et al. 1994; Veillette 1994; Teller and Leverington 2004). Their

drainage and movement across landscapes was facilitated by the capture of lower elevation drainage

points because of isostatic rebound. This led to widespread coverage of regions now defined by many

inland lakes. The presence of Mysis is an indicator of glacial lake coverage or glacial lake drainage in

inland lakes across the Canadian Shield (Martin and Chapman 1965; Dadswell 1974). Therefore, it was a

reasonable hypothesis that cisco forms detected in inland lakes matching forms described from the

Laurentian Great Lakes were of the same phylogenetic lineage. This hypothesis requires that the forms

found in the Great Lakes existed during the retreat of the Laurentide ice sheet. For Algonquin Park,

blackfin located in lakes once occupied by the outflow of glacial Lake Algonquin offer the best evidence to date for the colonization hypothesis. GeneticDraft analysis will need to resolve whether this hypothesis or ecological speciation offer the best explanation of blackfin status in Algonquin Park

Acknowledgements

We thank Emily Cowie for help in counting gill rakers, and Nick Lacombe and Courtney Taylor and many

summer students for field assistance. We thank the reviewers for very helpful comments.

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Figure captions

Figure 1. Lakes surveyed for native cisco (Coregonus artedi (sensu lato) Lesueur, 1818) in Algonquin

Park. The red dotted contour line represents 381 m elevation. Below this elevation was the drainage of

glacial Lake Algonquin at its maximum level from west to east at Fossmill, approximately 12,000 –

13,000 years BP. Lakes below 381 m elevation have Mysis diluviana Lovén, 1862 if sufficiently deep.

Lakes in black have blackfin, lakes in red have Mysis and artedi-like cisco but no discernable blackfin.

Lakes in blue are above the 381 m elevation and have Chaoborus punctipennis (Say, 1823) as the

dominant diel migrator and artedi-like cisco. Lake numbers represent 1=Craig; 2=North Tea; 3=Biggar;

4=Manitou; 5=Three Mile; 6=Kioshkokwi; 7=Lauder; 8=Mink; 9=Whitebirch; 10=Waterclear; 11=Mouse;

12=Cauchon; 13=Little Cauchon; 14=Laurel; 15=Carl Wilson; 16=Cedar; 17=Catfish; 18=Burntroot; 19=Longer; 20=Big Crow; 21=Hogan; 22=Philip;Draft 23=Radiant; 24=Lavieille; 25=Dickson; 26=White Partridge; 27=Carcajou; 28=Grand. MLS = Mink Lake Sill, an elevation separating eastward and westward

flow post-Lake Algonquin. Shading reflects elevation with dark shading being lower elevation. Thin black

lines are boundaries of tertiary watersheds. Map data: Land Information Office (LIO), Open Government

License – Ontario.

Figure 2. A blackfin form of cisco (Coregonus artedi (sensu lato) Lesueur, 1818) captured in Radiant Lake.

The black paired fins, black dorsal region and blue/purple iridescence are external characters used to

describe Blackfin Cisco in Lakes Michigan and Huron (Eschenroder et al. 2016). Black paired fins are a

definitive trait for identifying the Blackfin Cisco (nigripinnis form) in the Great Lakes.

Figure 3, Frequency (%) of total netting effort allocated to each stratum (white bars) and percentage of

total blackfin (Coregonus artedi (sensu lato) Lesueur, 1818) catch in each stratum (black bars) in each

study lake with overlaid temperature profile. Number of net sets (Nsites) and number of blackfin caught

(Nfish) are listed in bottom corner of each plot for each lake.

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Figure 4. Frequency distribution of gill-raker numbers from ciscoes collected in Algonquin Park.

Combined lakes with artedi-like cisco (Coregonus artedi (sensu lato) Lesueur, 1818) and Chaoborus (N=6) and artedi-like cisco and Mysis (N=4) are shown in the upper left and right panels, respectively. Gill- raker distributions for lakes with blackfin (Coregonus artedi (sensu lato) Lesueur, 1818) and Mysis are shown for Cedar, Hogan, Mink and Radiant Lakes. The left mode in gill-raker numbers for Cedar and

Hogan Lakes are from artedi-like cisco captured in pelagic gill nets.

Hogan Lakes. Distributions are corrected for retention selectivity of gillnets (see Supplement 2). N = sample size. Total length (blackfin) = Fork Length*1.1009Draft + 5.5916; R2=0.986. Figure 6. Predicted blackfin (Coregonus artedi (sensu lato) Lesueur, 1818) occupancy probability based on the depth+depth2 model for Cedar and Radiant lakes (black line) with 90% confidence limits represented by gray bands. Dashed horizontal line represents thermocline depth. Graph is rotated to emphasize the depth aspect of the hurdle model.

Figure 7. Predicted blackfin (Coregonus artedi (sensu lato) Lesueur, 1818) occupancy in Cedar and

Radiant lakes based on the depth+depth2 model with thermocline at the time of sampling represented by the dashed contour line. Map data: Land Information Office (LIO), Open Government License –

Ontario.

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Table 1. Location and physical characteristics of lakes in Algonquin Park with the blackfin form

(Coregonus artedi (sensu lato) Lesueur, 1818).

Lake Latitude Longitude Area (ha) Maximum Mean

Depth (m) Depth (m)

Cedar 46° 01’ 17” N 78° 28’ 35” W 2579 58.4 13.4

Hogan 45° 52’ 37” N 78° 29’ 51” W 1335 31.3 7.0

Mink 46° 03’ 43” N 78° 47’ 23” W 229 45.4 15.4

Radiant 45° 59’ 31” N 78° 17’ 18” W 638 36.4 8.7

Draft

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Table 2. AIC rankings of Cedar Lake and Radiant Lake hurdle model comparisons. Models consisted of second-order (depth+depth2) and third-order polynomials (depth+depth2+depth3) of the covariate depth. The column Distribution refers to the discrete distribution used for the count component of the hurdle model based on: negative binomial (NB) or Poisson. K is the number of parameters in each model. Hurdle models combining binomial component and zero-truncated negative binomial of the count regression component are top ranked.

Cedar Lake Models Distribution AIC ΔAIC Weight K

depth+depth2 NB 281.5 0.00 0.784 7

depth+depth2+depth3 NB 284.1 2.58 0.216 9 depth+depth2 Poisson Draft314.2 32.65 0.000 6 depth+depth2+depth3 Poisson 316.7 35.18 0.000 8

Radiant Lake Models Distribution AIC ΔAIC Weight K

depth+depth2 NB 153.2 0.00 0.779 7

depth+depth2+depth3 NB 156.9 3.71 0.122 9

depth+depth2 Poisson 157.6 4.41 0.086 6

depth+depth2+depth3 Poisson 161.4 8.19 0.013 8

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Table 3. Coefficients (β; ± SE) of the top-ranked negative binomial hurdle models for Cedar Lake (top)

and Radiant Lake (bottom). Count and binomial coefficients identified under model component,

significance (p), and 90% confidence limits are shown. Both models were of the second-order

polynomial of depth (depth+depth2). Coefficients for the zero-truncated negative binomial component

are not significant.

Model Covariate β SE p Lower Upper

Component 90% CI 90% CI

Cedar Lake

Count Intercept 0.379 0.752 0.615 -0.859 1.614 depth 1.387Draft1.863 0.457 -1.678 4.451 depth2 -1.425 1.410 0.312 -3.744 0.894

Log(θ) -0.808 1.086 0.457

Binomial Intercept -0.468 0.324 0.148 -1.001 0.065

depth 3.210 0.875 <0.001 1.770 4.650

depth2 -1.683 0.461 <0.001 -2.441 -0.924

Radiant Lake

Count Intercept -0.175 0.755 0.817 -1.416 1.067

depth 1.910 1.275 0.134 -0.187 4.007

depth2 -0.706 0.464 0.128 -1.470 0.057

Log(θ) 0.687 0.884 0.437

Binomial Intercept -1.597 0.809 0.049 -2.928 -0.266

depth 5.866 1.672 <0.001 3.117 8.616

depth2 -1.762 0.516 <0.001 -2.611 -0.913

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Draft

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Draft

Figure 1. Lakes surveyed for native cisco (Coregonus artedi (sensu lato) Lesueur, 1818) in Algonquin Park. The red dotted contour line represents 381 m elevation. Below this elevation was the drainage of glacial Lake Algonquin at its maximum level from west to east at Fossmill, approximately 12,000 – 13,000 cal. years BP. Lakes below 381 m elevation have Mysis diluviana Lovén, 1862 if sufficiently deep. Lakes in black have blackfin, lakes in red have Mysis and artedi-like cisco but no discernable blackfin. Lakes in blue are above the 381 m elevation and have Chaoborus punctipennis (Say, 1923) as the dominant diel migrator and artedi-like cisco. Lake numbers represent 1=Craig; 2=North Tea; 3=Biggar; 4=Manitou; 5=Three Mile; 6=Kioshkokwi; 7=Lauder; 8=Mink; 9=Whitebirch; 10=Waterclear; 11=Mouse; 12=Cauchon; 13=Little Cauchon; 14=Laurel; 15=Carl Wilson; 16=Cedar; 17=Catfish; 18=Burntroot; 19=Longer; 20=Big Crow; 21=Hogan; 22=Philip; 23=Radiant; 24=Lavieille; 25=Dickson; 26=White Partridge; 27=Carcajou; 28=Grand. MLS = Mink Lake Sill, an elevation separating eastward and westward flow post-Lake Algonquin. Shading reflects elevation with dark shading being lower elevation. Thin black lines are boundaries of tertiary watersheds. Map data: Land Information Office (LIO), Open Government License – Ontario.

279x215mm (300 x 300 DPI)

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Figure 2. A blackfin form of cisco (Coregonus artedi (sensu lato) Lesueur, 1818) captured in Radiant Lake. The black paired fins, black dorsal region and blue/purple iridescence are external characters used to describe Blackfin Cisco in Lakes Michigan and Huron (Eschenroder et al. 2016). Black paired fins are a definitive trait for identifying the Blackfin Cisco (nigripinnis form) in the Great Lakes.

167x48mm (300 x 300 DPI)

Draft

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Draft

Figure 3, Frequency (%) of total netting effort allocated to each stratum (white bars) and percentage of total blackfin (Coregonus artedi (sensu lato) Lesueur, 1818) catch in each stratum (black bars) in each study lake with overlaid temperature profile. Number of net sets (Nsites) and number of blackfin caught (Nfish) are listed in bottom corner of each plot for each lake.

181x181mm (300 x 300 DPI)

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Draft

Figure 4. Frequency distribution of gill-raker numbers from ciscoes collected in Algonquin Park. Combined lakes with artedi-like cisco (Coregonus artedi (sensu lato) Lesueur, 1818) and Chaoborus (N=6) and artedi- like cisco and Mysis (N=4) are shown in the upper left and right panels, respectively. Gill-raker distributions for lakes with blackfin (Coregonus artedi (sensu lato) Lesueur, 1818)and Mysis are shown for Cedar, Hogan, Mink and Radiant Lakes. The left mode in gill-raker numbers for Cedar and Hogan Lakes are from artedi-like cisco captured in pelagic gill nets.

181x163mm (300 x 300 DPI)

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Draft

Figure 5. The length-frequency distributions for blackfin (Coregonus artedi (sensu lato) Lesueur, 1818) captured in bottom set gillnets in each lake. The left mode of length-frequency distributions are for artedi- like cisco (Coregonus artedi (sensu lato) Lesueur, 1818) captured in pelagic nets in Cedar and Hogan Lakes. Distributions are corrected for retention selectivity of gillnets (see Supplement 2). N = sample size. Total length (blackfin) = Fork Length*1.1009 + 5.5916; R2=0.986.

181x153mm (300 x 300 DPI)

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Figure 6. Predicted blackfin (Coregonus artedi (sensu lato) Lesueur, 1818) occupancy probability based on the depth+depth2 model for Cedar and RadiantDraft lakes (black line) with 90% confidence limits represented by gray bands. Dashed horizontal line represents thermocline depth. Graphs are rotated to emphasize the depth aspect of the hurdle model.

159x89mm (300 x 300 DPI)

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Figure 7. Predicted blackfin (Coregonus artedi (sensu lato) Lesueur, 1818) occupancy in Cedar and Radiant lakes based on the depth+depth2 model with thermocline at the time of sampling represented by the dashed contour line. 182x80mmDraft (300 x 300 DPI)

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