A Thesis

entitled

Lake Whitefish Spawning Locations and Overwinter Egg Survival in Western

by

Zachary John Amidon

Submitted to the Graduate Faculty as partial fulfillment of the requirements for the

Master of Science Degree in

Biology

______Dr. Christine Mayer, Committee Chair

______Dr. Janice Kerns, Committee Member

______Dr. Song Qian, Committee Member

______Dr. Robin DeBruyne, Committee Member

______Dr. Christopher Vandergoot, Committee Member

______Dr. Cyndee Gruden, Dean College of Graduate Studies

The University of Toledo

May 2019

Select copyright license. 2018 Zachary John Amidon

This work is licensed under a Creative Commons Attribution-NonCommercial- NoDerivatives 4.0 International License. https://creativecommons.org/licenses/by-nc- nd/4.0/

An Abstract of

Lake Whitefish Spawning Locations and Overwinter Egg Survival in Western Lake Erie

by

Zachary John Amidon

Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Master of Science Degree in Biology

The University of Toledo May 2019

Lake Erie’s Lake Whitefish population has experienced a recent decline in age-3 recruitment to the commercial fishery. Juvenile Lake Whitefish index surveys indicate the recruitment bottleneck occurs before fall age-0 suggesting that factors responsible for survival likely occur in the early life history stages. To examine temporal dynamics of

Lake Whitefish early life history stages and investigate their relationship to fall age-0 recruitment, eggs were collected at 4-6 locations in Maumee Bay, six locations in the mid-lake reefs, and 17 additional locations outside of Maumee Bay and the mid-lake reefs throughout two spawning and incubation seasons (fall 2016-spring 2017; fall 2017- spring 2018). Post hatch, larvae were collected and abundances compared with similar available historical data from 1995-1998 to look for changes between the two time periods. To investigate if ice cover and water temperature were related to fall age-0 recruitment, maximum Lake Erie ice cover data were plotted against fall age-0 CPUE.

Viable eggs were collected at 27 of 31 sampled locations, verifying that Lake Whitefish spawned in Maumee Bay, on the mid-lake reefs, and other locations in 2016 and 2017.

Although eggs were collected at all sites within Maumee Bay and the mid-lake reefs, in the spring near the end of the incubation period, no viable eggs were collected in

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Maumee Bay and few eggs were collected in the mid-lake reefs. Larval abundances in

2017 and 2018 were similar to those observed in the same location from 1995-1998 when age-3 Lake Whitefish were abundant in the fishery, indicating that eggs are hatching and surviving to the pelagic larval stage and have the potential to recruit to the fishery. Lake

Whitefish recruited to fall age-0 in years that ice cover was greater than 85% during incubation. However, not all cohorts that experienced greater than 85% ice cover recruited to fall age-0. Our research indicates the recruitment bottleneck is occurring during or after the pelagic larval stage and before fall age-0, and ice cover or water temperature during incubation may have an influence on recruitment.

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Acknowledgements

I wish to thank Dr. Edward Roseman at the United States Geological Survey

Great Lakes Science Center and the members of my graduate thesis committee: Dr.

Christine Mayer, Dr. Song Qian, Dr. Robin DeBruyne, Dr. Christopher Vandergoot, and

Dr. Janice Kerns. Their input and guidance from the inception of this project facilitated the sampling, analyzing, writing, and editing process. At the University of Toledo, I would like to thank Pam Struffolino, Rachel Lohner, Ben Kuhaneck, Nicole King, Stevie

King, Jason Fischer, Maddie Tomczak, Marty Simonson, Eva Kramer, and Alex Lytten.

v

Table of Contents

Abstract ...... iii

Acknowledgements ...... v

Table of Contents ...... vi

List of Tables ...... vii

List of Figures ...... viii

1 Spatial Extent of Contemporary Lake Whitefish Spawning in Western Lake Erie .1

1.1 Introduction ...... 1

1.2 Methods...... 4

1.3 Results ...... 6

1.4 Discussion ...... 8

2 Lake Whitefish ( clupeaformis) overwinter egg retention and larval

dynamics in western Lake Erie Lake Erie ...... 13

2.1 Introduction ...... 13

2.2 Methods...... 17

2.3 Results ...... 20

2.4 Discussion ...... 24

References ...... 37

vi

List of Tables

1.1 Egg collection locations and biological data ...... 11

2.1 Coordinates of egg collection locations ...... 34

2.2 Coordinates of larvae collection locations ...... 35

2.3 Larval sampling dates ...... 36

vii

List of Figures

1 – 1 Egg sampling location and detection map ...... 10

1 – 2 Lake Whitefish annual commercial harvest in Lake Erie ...... 11

2 – 1 Lake Whitefish annual commercial harvest in Lake Erie ...... 28

2 – 2 Mean age-0 and age-1 Lake Whitefish catch per hectare ...... 28

2 – 3 Bathymetric map of Lake Erie and egg and larvae sampling locations ...... 29

2 – 4 Lake Whitefish 2017-2018 and 2018-2019 egg catch per unit effort ...... 30

2 – 5 Average weekly spring larvae abundance from 1995-1998 and 2017-2018 ...... 31

2 – 6 Larvae, Depth, Water transparency, and Water temperature measurements ...... 32

2 – 7 Average weekly surface water temperatures ...... 33

2 – 8 Maximum ice cover on Lake Erie from 1973-2018 ...... 33

2 – 9 Maximum ice cover and fall age-0 Lake Whitefish...... 34

viii

Chapter 1

Spatial Extent of Contemporary Lake Whitefish Spawning in Western Lake Erie

1.1 Introduction

Lake Erie is at the southernmost geographic range of Lake Whitefish (Coregonus clupeaformis) (Lawler 1965). Lake Erie’s bathymetry (average depth = 19m) (Bolsenga and Herdendorf 1993) and relatively warm water temperatures cause Lake Whitefish to segregate summer feeding habitat from winter spawning areas. During the warm summer months, Lake Whitefish remain in the cooler, deeper waters of the central and eastern basin of Lake Erie (Trautman 1981) (Figure 1-1). As water temperatures cool in October and November, a majority of the spawning population travels west along the shorelines to spawn in the shallow western basin (Goodyear et al. 1982; Regier and Hartman 1973) and (Roseman et al. 2007; Roseman et al. 2012) where their eggs incubate until hatching in March and April. Historically, Lake Erie supported large catches of

Lake Whitefish (Baldwin et al. 2009) (Figure 1-2). Commercial fishers targeted Lake

Whitefish in the western basin and Detroit River in November and December, noting ripe fish wherever a shallow, hard bottom (rock, gravel, firm sand) was present (Goodyear et al. 1982). Such reports of specimens in spawning condition provide the only knowledge of Lake Whitefish spawning areas within Lake Erie (Goodyear et al. 1982). Historic 1

spawning areas identified include the Detroit River, Maumee Bay, and western basin shallow reefs and shoals. However, by the 1950s, overfishing and environmental degradation contributed to a population collapse, leaving only a remnant population, resulting in a severe reduction in commercial harvest (Ludsin et al. 2001; Ryan et al.

2003) (Figure 1-2). There was a recent resurgence in Lake Whitefish numbers in Lake

Erie beginning in the early 1990s, but the population abundance has again declined, beginning in 2010. It is possible that the habitat and water quality changes during the intervening years (1950s-1980s) may have shifted spawning locations away from historically reported areas.

Habitat degradation in historical Lake Whitefish spawning areas suggests that some areas may no longer be suitable for spawning. The construction of shipping channels in the Detroit River in the early 20th century removed or covered up much of the spawning habitat within the river (Bennion and Manny 2011). As a result, the Lake

Whitefish spawning runs were quickly and significantly reduced; the last recorded spawning fish was caught in the Detroit River in 1925 (Roseman et al. 2007). At the same time, the Maumee River, a tributary of western Lake Erie, experienced increased silt load from the Maumee River watershed that smothered Lake Whitefish spawning areas in

Maumee Bay (Hartman 1973; Trautman 1981). By 1918 the once prolific Maumee Bay spawning grounds were no longer used by Lake Whitefish, leaving only open lake spawning stocks in Ohio and Ontario waters to support the expanding fishery (Hartman

1973; Trautman 1981). During the 1950s, the Lake Erie population collapsed due to overfishing, degradation of the remaining spawning grounds, changes in benthic food, and low bottom oxygen (Hartman 1973; Regier and Hartman 1973). The precipitous 2

decline of remnant Lake Whitefish and other native fish populations prompted the United

States and Canada to pass The Water Quality Agreement in an effort to restore and maintain the chemical, physical, and biological integrity of Great Lakes waters (Ebener et al. 2008; Hartman 1973). However, it is not known if these restoration efforts have made historical Lake Whitefish spawning areas suitable for spawning again.

Little information exists about what contemporary habitats Lake Whitefish use for spawning in Lake Erie. As part of a walleye egg deposition and survival study, viable overwintered Lake Whitefish eggs were documented on two western basin reefs and pelagic Lake Whitefish larvae were documented in the western basin from 1994-1999

(Roseman et al. (2007), providing evidence of successful hatches. Lake Whitefish early- life history studies continued in the Detroit River beginning in 2005 when ripe males, viable eggs, and subsequent drifting larvae were collected, serving as the first scientific evidence of Lake Whitefish spawning in the Detroit River in nearly 80 years (Roseman et al. 2007). Currently, the majority of Lake Erie’s commercial Lake Whitefish harvest occurs in the western basin during October and November, with the majority of harvest occurring in Maumee Bay and around the Ontario open-water reef complex (Coldwater

Task Group 2017), suggesting that Lake Whitefish may once again be spawning in the area. However, confirmation of Lake Whitefish spawning within Maumee Bay and other historical spawning locations in the western basin has not been documented.

Consequently, the objective of this study was to determine the contemporary distribution of Lake Whitefish spawning in western Lake Erie by sampling suspected historical and contemporary spawning locations. An accurate description of current spawning habitat is

3

needed for future habitat protection and restoration targeting Lake Erie’s Lake Whitefish population.

1.2 Methods

To determine Lake Whitefish spawning distribution in western Lake Erie, a total of 31 potential spawning locations were sampled for eggs in the fall of 2016 and 2017

(Figure 1-1). Western Lake Erie is a shallow basin with little variability in depth and contours, except near the island complex on the eastern side and the reef complex near the mid-southern shore. All sample locations were selected based on historical (Goodyear et al., 1982; Schaefer et al., in press) or contemporary evidence of spawning activity in shallow water (≤ 5m) with hard substrate (Roseman, 1997; Roseman, 2000) because the egg sampling gear used does not operate on soft bottom types and we wanted to maximize our chances of identifying Lake Whitefish spawning locations. This method of egg collection is especially suitable to detect the presence of eggs over relatively large areas when the exact spawning location is unknown (Stauffer et al., 1981); however, its efficiency varies among substrate types, resulting in biased egg density estimates.

Because of this gear bias, combined with the limited timing of sampling, our between-site comparisons are restricted to the presence or absence of eggs. To detect the onset of spawning, six locations in Maumee Bay and six locations within a mid-lake reef complex

(both historically documented sites) were sampled weekly beginning on October 31, 2016 and November 1, 2017 until viable eggs were detected at each location. Two of the six

Maumee Bay sites differed between 2016 and 2017 due to logistical considerations. The mid-lake reef sites were the same between 2016 and 2017 (Table 1.1). After the first egg 4

collection in Maumee Bay or mid-lake reef areas, additional sites outside these areas

(Figure 1-1) were sampled to better describe the spatial extent of spawning. Five additional sites were sampled in 2016 and 12 in 2017 to detect spawned eggs across the basin. These 17 additional locations were considered exploratory and were sampled only once.

Each sample site was located using GPS and reached by boat. The shallowest portion of the site was temporarily marked with an anchored buoy to easily maintain visual proximity to the target location while sampling. Depth (m), bottom temperature

(°C), and substrate composition were then recorded in the field at each site. Substrate composition was determined by visual observation of dominate substrate particles collected in samples with eggs and an estimation of particle type (hard or soft bottom) by tactile probing with a pole (Roseman et al., 2002). Eggs were collected using a 39-kg iron sled attached to a diaphragm pump on the boat deck by a flexible 5 cm diameter hose

(Stauffer, 1981). The sled was towed for 2 - 5 minutes at a tow speed of about 1 meter per second. This process was replicated three times at each site visit. The benthic samples

(containing sand, benthic organisms, eggs, vegetation, gravel, and detritus) pumped onto the boat deck were filtered through a two-stage sieve, separating egg-sized particles from larger debris and sands. The first stage was a .06 m3 basket lined with 6 mm square galvanized wire mesh, to strain out large debris. The remaining sample was then filtered with a 1.5 mm square fiberglass screen that retained eggs and smaller debris. The screen, with the remaining sample, was placed into a labeled plastic bag and stored on ice until laboratory processing which occurred 2 to 48 hours after collection.

5

In the lab, samples were placed into a glass pan and examined for eggs. Eggs were identified and counted based on size, color, and oil globule. Within Lake Erie, only coregonids and salmonids are known to spawn in the fall and their eggs can be separated by size. Coregonid eggs range from 1.5 mm to 3.5 mm while salmonid eggs are larger, ranging from 4.0 mm to 6.5 mm (Auer, 1982). Currently the two coregonine species suspected to spawn in Lake Erie are Lake Whitefish and (), although cisco are rare (Ryan et al., 2003; Oldenburg et al., 2007). Cisco eggs are smaller than Lake Whitefish eggs; approximately 2.0 mm to 2.2 mm diameter while Lake

Whitefish eggs are approximately 3.0 mm diameter, have a colorless chorion, multiple oil globules, and amber-colored yolk (Auer, 1982). All ruptured eggs or eggs showing signs of opaqueness were classified as dead. All clear or eyed eggs were classified as viable.

Once classified, eggs were placed in 95% ethanol for archiving. Catch per unit effort

(CPUE) of eggs was calculated as the number of eggs per minute sampled (pooled replicates), with standard deviation at each sample site. Since Maumee Bay and mid-lake reef sites were sampled multiple times to detect to onset of spawning, only the first positive sampling event for eggs was included in the results at these locations. Additional exploratory sites were sampled only once and are included in the results regardless of a positive or negative egg detection.

1.3 Results

Viable eggs were collected at 27 of 31 sampled locations, verifying that Lake

Whitefish spawned at 8 Maumee Bay locations, 6 mid-lake reefs locations, and at 13 additional exploratory sites in 2016 and 2017 (Figure 1-1; Table 1.1). Dreissenid mussels and shells, and sand were the dominate substrate particles observed in collected samples. 6

In 2016, the first eggs were detected on November 22 at four locations in

Maumee Bay (MB2, MB4, MB5, and MB6) and five locations in the mid-lake reef complex (Locust, Crib, Round, Toussaint, and Niagara) when water temperatures were ≤

7.3 °C (Table 1.1). Viable eggs were verified at the remaining Maumee Bay sites (MB3 and MB7) on November 29, 2016 and the remaining mid-lake reef site (Cone) on

November 30, 2016. Viable Lake Whitefish eggs were detected at West Sister Island reef on November 30, 2016. Due to winter ice conditions, no sampling occurred between

December 1, 2016 and January 24, 2017. On January 24, 2017, viable Lake Whitefish eggs were collected at Buckeye, Kelleys, Starve, and West Reef. Lake Whitefish egg

CPUE ranged from 0.1 (±0.1) to 9.3 (±2.3) eggs per minute of tow for the 2016 spawning season (Table 1.1).

On November 18, 2017 the first spawned eggs were detected at four Maumee Bay locations (MB1, MB3, MB4, MB8) when water temperatures were ≤ 6.0 °C (Table 1.1).

Viable eggs were verified at all six mid-lake reef sites (Locust, Crib, Round, Toussaint,

Cone, and Niagara) on November 22, 2017, and the remaining Maumee Bay sites (MB2 and MB5) on November 29, 2017. Viable Lake Whitefish eggs were detected at EXP3 on

November 22, 2017, and at Middle Sister, North Harbour, East Sister, Big Chicken, Little

Chicken, Chickenolee, and Rattlesnake reefs on November 27, 2017. At sites where Lake

Whitefish eggs were collected during the 2017 spawning season, CPUE ranged from 0.2

(±0.3) to 3.8 (±0.3) eggs per minute of tow. Eggs were not detected at EXP1, EXP2,

EXP4 and Gull sites.

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1.4 Discussion

A reduction in available spawning habitat in the early 20th century was identified as a major contributing factor to the Lake Whitefish population collapse in the 1950s

(Trautman, 1981; Roseman et al., 2007). However, a recent increase in commercial fish harvest and catch of early-life history stages of Lake Whitefish in the western basin of

Lake Erie prompted research into their contemporary spawning distribution. We found viable Lake Whitefish eggs at 27 of 31 sampled sites, confirming that Lake Whitefish are once again using some of their historical spawning areas and other available spawning habitat in western Lake Erie.

We found evidence of spawning across the western basin at a variety of depths and distances from shore. This utilization of diverse spawning areas can contribute to population stability and resilience (DuFour et al., 2015). It is especially important that spawning locations cover a range of depths and are spatially distant as egg mortality varies across physically diverse sites depending on regional weather exposure. For example, strong wind events can cause high egg mortality and reduce production by dislodging incubating eggs from western basin reefs and shoals where Lake Whitefish spawn (Busch et al., 1975; Roseman et al., 2001). Shallow spawning locations are subject to more wave energy caused by winds than deeper spawning locations. As a result, deeper spawning locations may see a lower egg loss rate than shallower spawning locations in the same region. In addition, spawning locations in bays or near the island complex are likely less affected by the winds and ice over sooner, thereby protecting eggs from wind and waves. Collecting viable eggs at spatially distant spawning areas suggest

8

the entire basin is important to Lake Whitefish reproduction and available spawning habitat may no longer be limiting recruitment to the commercial fishery.

The lack of egg detection at four locations may be a result of sampling variability, natural egg removal, or a true lack of spawning activity in the area. Lake Erie’s western basin rarely stratifies due to wind and wave action across the basin and the shallow spawning locations (1.3 – 4.8 m) are frequently exposed to high wave energy known to remove eggs from spawning grounds (Freeberg et al., 1990; Roseman et al., 2001).

Mortality during the egg and larval stages can be severe and strong annual variations in recruitment may arise from relatively small fluctuations in survival (Freeberg et al.,

1990). Lake Erie’s Lake Whitefish population is often dominated by a single year class

(Coldwater Task Group, 2017) suggesting that heavy losses during the egg and larval stage may be limiting recruitment within the system. Our identification of contemporary spawning areas aids current research into the temporal dynamics of Lake Whitefish early life history stages, including quantifying relationships between environmental conditions and egg and larvae abundance and survival in western Lake Erie. Further, identification of specific spawning locations can inform future habitat protection or restoration projects.

An improved understanding of these mechanisms affecting Lake Whitefish egg and larvae survival will help facilitate efforts to restore Lake Erie and its fisheries.

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Figure 1-1: Egg sampling locations in the western basin of Lake Erie. Site numbers correspond to Map ID in Table 1.1. Black numbers represent locations where viable eggs were detected. Grey numbers represent locations where viable eggs were not detected. Locations not marked as Maumee Bay or Mid-Lake Reef are exploratory sites.

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Figure 1-2: Lake Whitefish annual commercial harvest in Lake Erie from 1900 to 2016 (Baldwin et al. 2009; Coldwater Task Group, 2017).

Table 1.1: Coordinates of egg collection locations, depth, bottom temperature, CPUE, and substrate particles (M = Dead and/or live mussels, SH = Crushed or broken mussel shells, S = Sand) for all egg sites sampled from November 22, 2016 to November 27, 2017. Map ID numbers correspond to site locations in Figure 1-1.

Map ID Site ID Region Latitude Longitude Date Depth Bottom Substrate CPUE (Fig. 1-1) Sampled (m) Temp (°C) Particles #eggs/min (SD) 1 MB1 Maumee Bay 41.7333 -83.4008 11/18/17 1.3 5.4 M, S, SH 3.8 (0.3) 2 MB2 Maumee Bay 41.7521 -83.3904 11/22/16 2.0 6.0 M, S, SH 0.8 (0.8) 3 MB3 Maumee Bay 41.7464 -83.3726 11/29/16 1.5 5.8 M, S, SH 3.7 (2.9) 4 MB4 Maumee Bay 41.7429 -83.3502 11/22/16 3.0 6.3 M, S, SH 3.0 (3.0) 5 MB5 Maumee Bay 41.7354 -83.3653 11/22/16 2.5 6.1 M, S, SH 2.2 (1.9) 6 MB6 Maumee Bay 41.7173 -83.4054 11/22/16 1.8 5.4 M, S, SH 3.7 (0.3) 7 MB7 Maumee Bay 41.7300 -83.3272 11/29/16 4.0 6.4 M, S, SH 0.5 (0.5) 8 MB8 Maumee Bay 41.7226 -83.3923 11/18/17 1.8 5.1 M, S, SH 0.2 (0.3) 9 Locust Mid-Lake Reef 41.6458 -83.0654 11/22/16 2.5 6.8 M, SH 9.3 (2.3) 10 Cone Mid-Lake Reef 41.6668 -83.0463 11/30/16 4.8 5.9 M, SH 2.0 (1.6) 11 Niagara Mid-Lake Reef 41.6645 -82.9750 11/22/16 2.5 7.3 M, SH 0.2 (0.3) 12 Crib Mid-Lake Reef 41.6464 -83.0088 11/22/16 3.3 6.9 M, SH 1.2 (1.0) 13 Toussaint Mid-Lake Reef 41.6316 -83.0166 11/22/16 3.8 6.8 M, SH 3.3 (2.3) 14 Round Mid-Lake Reef 41.6185 -82.9873 11/22/16 3.4 6.8 M, SH 2.3 (0.6) 15 West Sister Exploratory 41.7338 -83.1026 11/30/16 3.0 6.5 M, SH 6.3 (4.5) 16 West Reef Exploratory 41.7130 -82.8543 1/24/17 5.0 0.7 M, SH 0.1 (0.1) 17 Buckeye Exploratory 41.6710 -82.7870 1/24/17 2.0 0.9 M, SH 0.4 (0.3) 18 Kelleys Exploratory 41.6390 -82.6473 1/24/17 3.0 1.1 M, SH 0.1 (0.1) 19 Starve Exploratory 41.6128 -82.8143 1/24/17 4.0 1.3 M, SH 0.1 (0.1) 20 EXP1 Exploratory 41.9297 -83.2638 11/22/17 4.0 4.6 M, SH 0.0 21 EXP2 Exploratory 41.9267 -83.3186 11/22/17 4.0 5.0 M, S, SH 0.0 22 EXP3 Exploratory 41.8844 -83.3228 11/22/17 4.2 4.8 M, S, SH 1.8 (2.0) 23 EXP4 Exploratory 41.8565 -83.3444 11/22/17 4.8 7.7 M, SH 0.0 24 Middle Sister Exploratory 41.8458 -83.0001 11/27/17 2.4 4.8 M, SH 0.5 (0.5) 11

25 North Harbour Exploratory 41.8480 -82.8525 11/27/17 1.7 5.1 M, SH 1.3 (0.6) 26 East Sister Exploratory 41.8226 -82.8421 11/27/17 4.8 5.0 M, SH 2.2 (2.0) 27 Big Chicken Exploratory 41.7736 -82.8150 11/27/17 3.0 5.2 M, SH 0.7 (0.3) 28 Little Chicken Exploratory 41.7772 -82.7960 11/27/17 1.6 5.1 M, SH 1.5 (0.9) 29 Chickenolee Exploratory 41.7172 -82.6275 11/27/17 1.6 5.5 M, SH 0.7 (0.3) 30 Gull Exploratory 41.6591 -82.6897 11/27/17 1.4 5.5 M, SH 0.0 31 Rattlesnake Exploratory 41.6821 -82.8588 11/27/17 3.4 5.2 M, SH 0.3 (0.3)

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Chapter 2

Lake Whitefish (Coregonus clupeaformis) Overwinter Egg Retention and Larval Stage Dynamics in Western Lake Erie

2.1 Introduction

Before the 1950s, large numbers of adult Lake Whitefish (Coregonus clupeaformis) supported a valuable commercial fishery in Lake Erie (Baldwin et al.

2009) (Figure 2-1). During this time, age-3 and older fish were regularly harvested, suggesting continual recruitment to the fishery (Coldwater Task Group 2017). Due to the loss of spawning habitat, and increased harvest in the 1950s, the Lake

Whitefish fishery collapsed, leaving only a remnant population (Hartman 1973). During the 1990s, catches of age-3 Lake Whitefish increased following an improvement in the quality of the lake (Figure 2-1) (Ebener et al. 2008; Hartman 1972). However, catches again steadily declined from 2009-2017. The recent decline is thought to be due to poor recruitment in the early life stages given that age-3 fish were no longer entering the commercial fishery (Coldwater Task Group 2017).

Juvenile Lake Whitefish index surveys also support the idea that decreased recruitment in early life stages is a factor in decreased age-3 fishery catches. Fall bottom trawl assessment surveys in Lake Erie’s central basin provide an annual estimation of age-0 and age-1 Lake Whitefish abundance. In the years when age-0 Lake Whitefish 13

were detected in the fall, they were subsequently detected the following fall at age-1, indicating that if larvae survive until fall age-0, they likely to survive to fall age-1 and recruit to the fishery (Ohio Division of Wildlife 2017). Since fall age-0 fish are likely to survive, an estimation of fall age-0 abundance can be used as a rough indicator of recruitment success. For instance, from 1990-2005, fall age-0 fish were consistently detected and the resurgence in commercial catches has been attributed to successful recruitment during that time (Coldwater Task Group 2017) (Figure 2-2). Conversely, from 2006-2017, detection of fall age-0 Lake Whitefish was very low, coinciding with the decline in the commercial catch (Coldwater Task Group 2017). Given that survival to fall age-0 indicates likely recruitment to the adult population, a characterization of early life stage dynamics within Lake Erie would provide insight on factors responsible for survival to fall age-0 (e.g., habitat, environmental variability).

Lake Whitefish are known to spawn in late November and early December over shallow, hard substrate in the western basin of Lake Erie (Amidon et al. in press;

Goodyear et al. 1982; Regier and Hartman 1973) where their eggs incubate until hatching in March and April. While spawning occurs throughout the western basin, the highest egg abundances were found in Maumee Bay and the mid-lake reefs (Amidon et al. in press)

(Figure 2-3). In Maumee Bay, most spawning occurs adjacent to the Maumee Bay

Navigation Channel on hard shallow shoals created by the historical placement of dredged material with a surface substrate consisting of sand, Dreissenid mussels, and shell fragments (Amidon et al. in press; Roseman et al. 2002). The mid-lake reefs are a natural offshore reef complex with six prominent reefs that extend to within 0.6 m of the surface. The mid-lake reefs consist of a varied surface substrate ranging from silt to 14

boulders and exposed bedrock, Dreissenid mussels, and shell fragments with numerous crevices and cavities (Amidon et al. in press; Herdendorf and Braidech 1972). Post hatch,

Lake Whitefish larvae are transported by lake currents, commonly clustering in nearshore areas (Brown and Taylor 1992; Roseman et al. 2005; Veneranta et al. 2013). Historically, western Lake Erie’s shoreline was marshland fronted by low barrier beaches providing a warm, shallow refuge known to produce abundant prey resources and provide favorable nursey habitat (Brown and Taylor 1992; Herdendorf 1987; Veneranta et al. 2013).

However, anthropogenic development has diminished the nursery habitat by armoring most of the lake’s shoreline, disconnecting the terrestrial and water interface and eliminating critical wetlands and shallow nursery areas (Herdendorf 1992). While the western basin of Lake Erie hosts numerous spawning locations, human induced changes to shoreline habitat may have reduced the quality of larval nursery areas.

Since Lake Whitefish are a northern species of fish, preferring cooler water, and

Lake Erie is at the southern edge of Lake Whitefish range, more productive year classes may occur during cold winters (Freeberg et al. 1990; Lawler 1965). Winter air temperatures over the Great Lakes basin contribute to variation in ice cover and water temperature that effect incubating eggs (Wang et al. 2012). An early cold winter season promotes the formation of ice cover, which forms a barrier, shielding the water from strong winds that produce turbulence and strong currents powerful enough to dislodge eggs and transport them to areas less suited for incubation. Therefore, increased ice cover retains eggs near the original spawning locations which are assumed to be more suitable for incubation, thus increasing their chances for survival (Brown et al. 1993; Freeberg et al. 1990; Taylor et al. 1987). A cold winter also translates into cold water temperatures 15

which influence the timing and success of embryonic development and the fitness of post hatch larvae (Mueller et al. 2015; Price 1940). Under constant incubation water temperatures, the most effective range for Lake Whitefish eggs is between 0.5 ̊C-6.0 ̊C, producing higher hatch rates and fewer abnormalities as compared to higher incubation temperatures (Price 1940). Temperatures changes during the final third of embryonic development alter hatch timing, size at hatch, survival, and energy use of Lake Whitefish embryos (Mueller et al. 2015). An increase in incubation temperature results in faster development, producing fewer and smaller hatchlings, and decreases larval fitness

(Mueller et al. 2015; Price 1940). Therefore, to increase hatch rates and improve post hatch larval fitness, eggs need to incubate in cool water temperatures for the duration of the incubation period. Since 1900, Lake Erie has experienced a trend for lower ice cover duration, with a notable decline from the early 1960s onward and a prominent decline in seasonal ice cover since the late 1970s (Assel 2004). If trends toward decreased ice cover and increased temperature during incubation are contributing to decreased recruitment, a trend toward decreased overwinter egg survival between historical and contemporary data may occur.

An improved understanding of Lake Whitefish early life history dynamics and factors effecting recruitment are essential to facilitate population restoration efforts and

Lake Erie’s fisheries. In this study, we examine temporal dynamics of Lake Whitefish early life history stages and investigate their relationship to fall age-0 recruitment. Our specific objectives are to (1) estimate overwinter egg abundance at known spawning locations to quantify egg retention, (2) quantify the abundance of Lake Whitefish larvae and compare abundances with similar available historical data to identify spatial and 16

temporal trends, and (3) explore the relationship of ice cover and water temperature with respect to fall age-0 recruitment.

2.2 Methods

Lake Erie is the southernmost and warmest North American Great Lake, stretching a length of 388 km and width of 92 km with its longitudinal axis oriented east- northeast (Bolsenga and Herdendorf 1993; Herdendorf 1992). The lake is divided into three basins (western, central, and eastern) based on its bathymetry (Figure 2-3). The eastern basin is deep and bowl-shaped with most of the basin's bottom lying below 25 m and a maximum depth of 64 m (Herdendorf 1992). The central basin has a flat bottom with an average depth of 18.5 m and a maximum depth of 26 m. The western basin, where our work occurs, is the shallowest and warmest basin with most depths between 7 m and 10 m (Herdendorf 1992). In contrast with the other two basins, the western basin has a number of bedrock islands and shoals along its eastern edge (Herdendorf and

Braidech 1972; Herdendorf 1992). Its long fetch and shallow depths increase potential for strong wave and current formation which keep the western basin well mixed (Busch et al.

1975; Roseman et al. 2001).

Egg sampling locations were in Maumee Bay and the mid-lake reef complex following recent work identifying these regions as important spawning areas (Amidon et al. in press) (Figure 2-3). Eggs were sampled over two spawning and incubation seasons.

The first season was from November 1, 2016 to February 23, 2017 and included four locations in Maumee Bay and six locations within the mid-lake reef complex. The second spawning and incubation season was from November 1, 2017 to March 24, 2018 and 17

included six Maumee Bay and six mid-lake reef complex locations. During each season, all sites were sampled about once per week until winter ice conditions prohibited lake access. In the spring after the retreating ice allowed for boat access, all sites were sampled again to document the abundance of viable overwintered eggs in areas of confirmed spawning.

For each egg sampling event we used a boat to pull a 39-kg iron sled attached to a diaphragm pump on the boat deck by a flexible 5 cm diameter hose in a small circle on top of known spawning locations (Amidon et al. in press; Stauffer 1981). Bottom substrate and debris was pumped to the boat deck where it was filtered through a series of sieves, retaining egg-sized particles (1.5-6 mm). This process was replicated three times at each site and mean depth (m), bottom temperature (°C), and substrate composition were recorded. Samples were stored on ice until laboratory processing where Lake

Whitefish eggs were pulled from samples, identified and counted. All sites in each region

(Maumee Bay; mid-lake reefs) were sampled on the same day when possible. Catch per unit effort (CPUE) of eggs at a site was calculated as the number of eggs per minute sampled (pooled replicates), with standard error. Sites were then split between Maumee

Bay and the mid-lake reefs where region CPUE was calculated as the average number of eggs per minute of all sites sampled on the same day, with standard error. Region CPUE was plotted over each sample period for Maumee Bay and mid-lake reefs. This method of egg collection varies in efficiency between substrate types. Consequently, we do not to make between-site egg abundance comparisons. However, we do compare egg abundances within region from fall to spring when the same sites are present in both datasets. 18

To document the presence of successfully hatched eggs we sampled larval fish immediately following spring egg collections. The larval sampling locations and protocol for this study largely followed previous larval sampling by Roseman (1997, 2000) conducted between 1995 and 1998, which allows for comparison between the two time periods. In total, 27 sites adjacent to the overwinter egg sampling sites were chosen

(Figure 2-3) and larvae were sampled at each site weekly from March-June. Samples were collected by boat, towing a 60cm diameter, paired bongo net with 500micron mesh in a circle at approximately 1.0 m/sec for 5 minutes. Nets were towed horizontally in the top 2m of water during daylight hours and all weekly samples were collected on the same day when possible. A flow meter was attached to the center of each net opening to measure volume sampled. The samples were rinsed from the net into a jar and preserved with 95% ethanol and stored until laboratory processing. Average water depth (m), surface water temperature (°C) at 1m depth, and water transparency (secchi disk to nearest 0.1 m) were recorded in the field at each site.

In the laboratory, Lake Whitefish were identified and counted following Auer

(1982). The abundance of larval Lake Whitefish was estimated using CPUE, where catch is the number of fish collected and effort is the total volume of water sampled. CPUE was converted to the number of larvae/1,000 m3 of water. We then calculated weekly mean larval abundance and standard error using mean densities from all sites sampled each week. Weekly abundance was reported on the mean date for the range of dates sampled each week. To create spatial graphical representations of geographic patterns in larval fish, depth, water temperature, and water transparency across our study area, we used

ArcMap to plot the seasonal mean for each attribute at each sampling site as discrete 19

point samples. We classified the data into five categories using the natural break function and applied graduated symbols so sites with higher values are represented by larger symbols. Additionally, 2017 and 2018 temporal surface water temperature trends within the sample area were calculated by averaging the temperatures (±SD) from all sites sampled each week and reported on the mean date for the range of dates sampled each week.

Higher maximum ice cover is experienced during colder winters, which produce colder water temperatures affecting Lake Whitefish recruitment. Lake Erie maximum ice cover data from the National Oceanic and Atmospheric Administration Great Lakes

Environmental Research Laboratory (Great Lakes Environmental Research Laboratory

2018) were plotted through time to examine recent annual trends in ice cover. To examine how ice cover and water temperature relate to fall age-0 recruitment, the maximum Lake Erie ice cover data (Great Lakes Environmental Research Laboratory

2018) were plotted against fall age-0 Lake Whitefish CPUE for years in which the data overlap (1990-2017).

2.3 Results

During the 2016-2017 spawn and incubation season, four locations within

Maumee Bay (MB3, MB4, MB5, and MB6) and six locations within the mid-lake reef complex (Round, Toussaint, Crib, Niagara, Cone, and Locust) were monitored for eggs

(Figure 2-3; Table 2.1). Eggs were detected at all locations in fall 2016. Eggs were first detected in Maumee Bay and on the mid-lake reefs on November 22, 2016 with the highest CPUE observed on November 29, 2016 in Maumee Bay (CPUE = 7.58 ± 3.48 20

SE) and November 30, 2016 on the mid-lake reefs (CPUE = 16.99 ± 6.50SE) (Figure 2-

4). Cone, Crib, and Round were not sampled on November 2, 2016 and MB3 was not sampled on November 22, 2016. Due to poor weather and ice conditions on the lake, no sites were visited between November 30, 2016 and February 17, 2017. Spring 2017 egg collections occurred on February 17, 2017 at Round, Toussaint, Crib, Niagara, Cone,

Locust, MB4, and MB5, and on February 23, 2017 at MB3 and MB6. Although spring egg collections in Maumee Bay were split between two sample days, they are treated as one collection and reported on the mean sample day (February 20, 2017). During spring

2017 egg collections, no viable eggs were detected in Maumee Bay, and few viable eggs were detected on the mid-lake reefs (CPUE = 0.37 ± 0.15SE), accounting for a 2.2% retention rate from fall 2016 peak CPUE.

During the 2017-2018 spawn and incubation season, six locations within Maumee

Bay (MB1, MB2, MB3, MB4, MB5, and MB8) and six locations within the mid-lake reef complex (Round, Toussaint, Crib, Niagara, Cone, and Locust) were monitored for eggs

(Figure 2-3; Table 2.1). Eggs were detected at all locations in fall 2017. Eggs were first detected in Maumee Bay on November 18, 2017 and the mid-lake reefs on November 22,

2017 with the highest CPUE observed on November 29, 2017 in Maumee Bay (CPUE =

12.39 ± 4.18SE) and November 22, 2017 on the mid-lake reefs (CPUE = 18.28 ±

11.48SE) (Figure 2-4). MB2 and MB8 were not sampled on November 1, 2017 and

November 6, 2017. Due to poor weather and ice conditions on the lake, no sites were visited between December 4, 2017 and March 23, 2018. Spring 2018 egg collections occurred on March 23, 2018 at Round, Toussaint, Crib, Niagara, Cone, and Locust.

Spring collections occurred at MB1, MB2, MB3, MB4, MB5, and MB8 on March 24, 21

2018. During spring 2018 egg collections, no viable eggs were detected in Maumee Bay, and few viable eggs were detected on the mid-lake reefs (CPUE = 0.07 ± 0.05SE), accounting for a 0.4% retention rate from fall 2017 peak CPUE.

In 2017, weekly larval collections began on March 19 and ended on June 2, totaling 11 weeks. The number of days it took to collect larvae at all 27 sites each week varied from 1-4 days with an average of 2 days (Table 2.2; Table 2.3). Throughout the sampling period, CPUE showed considerable variation. The highest CPUE (average

CPUE = 69.96 ± 33.68SE) was measured during the week of April 23-April 29 (mean sample date = April 24, 2017) (Figure 2-5). Larvae were detected in at least one collection each week except the final week (mean sample date = June 1). Lake Whitefish larvae were not detected at all 27 sites each week, however they were detected at all sites at some point during the sample period except for site 24 (Figure 2-3). Highest densities of Lake Whitefish larvae were collected near the shallow southern shoreline where water temperatures were warmer and water transparency was lower (Figure 2-6). Larval catches increased in the water column similar to 1995-1998 and the average peak CPUE was similar (Figure 2-5). Weekly surface water temperatures ranged from 1.5 °C to 19.0 °C, gradually increasing over the entire sampling period (March 19-June 1) (Figure 2-7).

In 2018, weekly larval collections began on March 28 and ended on May 24, totaling nine weeks. For each week sampled, all 27 sites were sampled in one day (Table

2.2; Table 2.3). Throughout the sampling period, CPUE showed considerable variation.

The highest CPUE (average CPUE = 38.86 ± 12.32SE) was measured during the week of

April 29-May 5 (mean sample date = April 30, 2018) (Figure 2-5). Larvae were detected in all weeks sampled. Lake Whitefish larvae were not detected at all 27 sites each week, 22

however they were detected at all sites at some point during the sample period. Highest densities of Lake Whitefish larvae were collected near the shallow southern shoreline where water temperatures were warmer and water transparency was lower (Figure 2-6).

Larval catches increased in the water column about one week later than they did from

1995-1998 and the average peak CPUE was similar (Figure 2-5). Weekly surface water temperatures ranged from 3.8 °C to 17.5 °C, remaining low in the beginning (March 28-

April 18) and gradually increasing over the remainder of the sampling period (April 18-

May 24) (Figure 2-7).

Since 1973, maximum peak ice cover on Lake Erie has usually been high, reaching at least 80%, and in the years it does not reach 80%, the ice cover has been low, usually below 40% (Figure 2-8). Five out of seven low ice cover years occurred from1998-2017. When maximum ice cover was plotted against fall age-0 CPUE it revealed a threshold in which Lake Whitefish recruited to fall age-0 in years that the lake experienced greater than 85% ice cover the previous winter (Figure 2-9). However, not all cohorts that experienced greater than 85% ice cover recruited to fall age-0. The winter of 2016-2017 was unseasonably warm for the , suppressing ice formation on Lake Erie which reached a maximum peak ice cover of 35.5% (Figure 2-8).

In contrast, the 2017-2018 winter was very cold, reaching a maximum peak ice cover of

95.1% (Figure 2-8). Consequently, Lake Whitefish spawning grounds were exposed to more wind generated lake currents during the 2016-2017 incubation period than the

2017-2018 incubation period.

23

2.4 Discussion

Ice cover retains eggs in their spawned locations which increases their chance of survival and higher numbers pelagic larvae have been attributed to higher rates of egg survival as a result of increased ice cover in (Freeberg et al. 1990). We measured egg abundance in Lake Erie during two incubation seasons that experienced contrasting ice cover. When compared to Lake Erie long-term trends, the winter from

2016-2017 experienced low ice cover (peak ice cover = 36%) and the winter from 2017-

2018 experienced high ice cover (peak ice cover = 95%). If ice cover influenced Lake

Whitefish overwinter egg survival in Lake Erie, we would expect to see increased overwinter egg retention and a higher peak larval CPUE in 2017-2018 when compared to

2016-2017. However, we observed similarly low overwinter egg retention and similar peak larval CPUE during both sample seasons. Further, larval abundances observed in

2017 and 2018 were similar to abundances from 1995-1998 when adult Lake Whitefish were recruiting to the fishery, indicating that there is sufficient survival through the egg stage to result in recruitment to the fishery. The lack of evidence for an ice cover effect may be a result of Lake Erie’s latitudinal position, and the long incubation period for

Lake Whitefish eggs. Due to its southern location, Lake Erie does not freeze for the duration of Lake Whitefish egg incubation, especially in the western basin. Western basin ice begins to form after the fall spawn and begins to break up mid-February with last ice usually occurring by the end of March (Assel 2005; Wang et al. 2012), leaving eggs exposed to wind driven lake currents. This low overwinter egg retention likely occurs in

Lake Erie on an annual basis. Therefore, the egg stage does not appear to be a recruitment bottleneck. 24

Larval abundance peaked in our samples on April 24, 2017 and April 30, 2018 and gradually decreased thereafter, corresponding to a time when a majority of the larvae are pelagic and are susceptible to the sampling gear type. The gradual decrease in observed density is likely a combination of natural mortality and morphological development. Pelagic larvae are known to experience high mortality during this time as they transition from endogenous to exogenous feeding (Taylor and Freeberg 1984). Also during this time they begin to develop fins that facilitate mobility to actively evade our gear type, move outside of the study area, and leave the surface waters in preference for benthic prey items (McKenna Jr and Johnson 2009; Ryan and Crawford 2014). Due to

Lake Whitefish’s expanded range of mobility and limitations of our gear type, we cannot speculate about survival beyond the pelagic larval stage and conclude that the recruitment bottleneck is likely occurring during or after the pelagic larval stage and before fall age-0.

Although the recruitment bottleneck is likely occurring during or after the pelagic larval stage, there is evidence that factors affecting early life survival are influenced by winter water temperatures. We observed a threshold relationship between ice cover and fall age-

0 CPUE from 1990-2017 (Figure 2-2), a threshold was observed in which Lake Whitefish recruited to fall age-0 in years that the lake experienced greater than 85% ice cover the previous winter. However, not all cohorts that experienced greater than 85% ice cover recruited to fall age-0, suggesting there are other factors affecting recruitment. The relationship between maximum ice cover and survival to fall age-0 may be linked to water temperature during incubation (Christie 1963; Lawler 1965) and not linked to the presence of ice cover. If similar numbers of larvae are produced within Lake Erie regardless of ice cover, maximum ice cover is likely more reflective of an average 25

seasonal water temperature, assuming that cooler seasonal conditions reflect cooler waters and a higher maximum ice cover. The cooler winter observed in 2018 was reflected in spring water temperatures at the time of larval collections. Variation in water temperature regimes during incubation can alter hatch timing, size at hatch, survival, and energy use of Lake Whitefish embryos which may have effects on post hatch fitness

(Mueller et al. 2015; Price 1940). While winter water temperature appears to have an influence on recruitment, the mechanism is unknown. Since Lake Erie is at the southern edge of Lake Whitefish distribution, successful year classes may be tied to cold winters and the recent decline of cold winters as reflected in maximum peak ice cover may have decreased the likelihood of producing a successful year class. A critical examination between water temperature patterns and the success of Lake Whitefish year classes could provide information to management agencies aimed at the restoration of Lake Whitefish.

Lake Erie’s western basin water circulation patterns are driven by wind forcing and inflows from the Detroit and Maumee Rivers (Beletsky et al. 2013). Inputs of sediments, nutrients, and water from these sources can drive spatiotemporal variability in temperature, zooplankton, and water transparency (Frost and Culver 2001; Roseman et al.

2005). While ichthyoplankton are able to take advantage of differential movement of surface and bottom currents by vertical migration, they have little ability to maintain their location (McKenna Jr and Johnson 2009). As such, we found larval Lake Whitefish concentrated in shallow nearshore areas, likely moved there by lake currents. Water temperatures along the shoreline were generally warmer and water clarity was lower than offshore sites (Figure 2-6). Warm, shallow waters are known to produce abundant prey resources and are favorable as nursery habitat for larval Lake Whitefish to promote good 26

growth and survival (Brown and Taylor 1992; Fraker et al. 2015; Roseman et al. 2005;

Taylor and Freeberg 1984). The nearshore concentration of Lake Whitefish larvae highlights the importance of nearshore areas as a larval nursery habitat for Lake

Whitefish as they transition to benthic feeding juveniles (Claramunt et al. 2010). With over 80% of Lake Erie’s shoreline armored, creating steep nearshore gradients, high quality nursery habitat has likely been reduced (Herdendorf 1987). Restoration of Lake

Erie’s shoreline may improve nursery habitat and survival for Lake Whitefish larvae as well as other valuable species known to utilize the same nursery areas, such as walleye

(Roseman et al. 2005).

The Lake Whitefish population in Lake Erie has experienced a decline in age-3 recruitment in recent years and juvenile Lake Whitefish index surveys have indicated that factors leading to poor recruitment occur before fall age-0. Despite evidence of poor overwinter egg retention, larval abundances were similar to those observed in the same location from 1995-1998 when age-3 Lake Whitefish were recruiting to the fishery regularly. The consistent presence of larvae in spring collections in 2017-2018, and 1995-

1998 indicates that eggs are hatching and surviving to the pelagic larval stage on an annual basis and have the potential to recruit to the fishery, therefore spawning habitat restoration may not be needed at this time to improve Lake Whitefish recruitment. While the recruitment bottleneck is occurring during or after the pelagic larval stage and before fall age-0, winter water temperature appears to influence recruitment, although the mechanisms driving this relationship require further research.

27

Figure 2-1. Lake Whitefish annual commercial harvest in Lake Erie from 1900 to 2017 (Baldwin et al. 2009; Coldwater Task Group 2018).

Figure 2-2. An estimation of mean age-0 and age-1 Lake Whitefish post-stratification (fall) catch per hectare by cohort. Data was collected in Lake Erie’s Ohio central basin from October 9 through November, 1990-2017 (Ohio Division of Wildlife 2017). Mean age-1 data from the 2017 cohort is not shown because it was unavailable at the time of publication.

28

Figure 2-3. Top left: Lake Erie’s position among the Great Lakes. Top right: bathymetric map of Lake Erie and boundary lines identifying the three basins. Bottom: egg and larvae sampling locations in the southern portion of Lake Erie’s western basin. Letters represent individual egg sampling locations and correspond to the Map ID column in Table 2.3. Numbers represent individual larvae sampling locations and correspond to the ID column in Table 2.2.

29

Figure 2-4. Lake Whitefish egg CPUE (± S.E.) collected average per 1-min tow from Maumee Bay and the mid-lake reefs. The thin dotted line represents the period of time we were unable to sample due to weather and ice.

30

Figure 2-5. Weekly average larvae abundance (no. larvae /1,000 m3) by year of age-0 Lake Whitefish in western Lake Erie, 1995-1998 and 2017-2018. Error bars represent standard error.

31

Figure 2-6. Spatial distribution of mean 2017 and 2018 seasonal measurements for (A) Lake Whitefish larvae (No./1000 m3), (B) Depth (m), (C) Water transparency (m), and (D) Water temperature (̊C) at sampling sites in the southern portion of western Lake Erie for spring 2017 (left) and spring 2018 (right).

32

Figure 2-7. Average weekly surface water temperatures (±SD) collected at spring larvae sites in the western basin of Lake Erie.

Figure 2-8. Maximum percent ice cover reached on Lake Erie for each ice season from 1973-2018. An ice season starts the previous fall and ends during the spring of the year listed (e.g., Ice season 2018 = fall 2017-spring 2018) (Great Lakes Environmental Research Laboratory 2018).

33

Figure 2-9. Maximum ice cover (Figure 8) plotted against an estimation of age-0 post- stratification (fall) Lake Whitefish catch per hectare (Figure 2) for each year the data overlapped (1990-2017).

Table 2.1. Coordinates of egg collection locations sampled from 2016-2018. Map ID corresponds to locations in Figure 2-3. Map ID Site ID Latitude Longitude A MB1 41.7333 -83.4008 B MB2 41.7521 -83.3904 C MB3 41.7464 -83.3726 D MB4 41.7429 -83.3502 E MB5 41.7354 -83.3653 F MB6 41.7173 -83.4054 G MB8 41.7226 -83.3923 H Locust 41.6458 -83.0654 I Cone 41.6668 -83.0463 J Niagara 41.6645 -82.9750 K Crib 41.6464 -83.0088 L Toussaint 41.6316 -83.0166 M Round 41.6185 -82.9873

34

Table 2.2. Coordinates of larvae collection locations sampled in 2017 and 2018. ID numbers correspond to locations in Figure 3. ID Latitude Longitude 1 41.72500 -83.40000 2 41.69500 -83.34356 3 41.73333 -83.33333 4 41.68000 -83.30000 5 41.70000 -83.30000 6 41.72167 -83.30000 7 41.65086 -83.23543 8 41.68007 -83.23347 9 41.61740 -83.12958 10 41.64273 -83.12660 11 41.66667 -83.12500 12 41.72167 -83.12500 13 41.58783 -83.05704 14 41.59658 -83.03796 15 41.63167 -83.01667 16 41.70000 -83.04167 17 41.73333 -83.04167 18 41.51829 -82.93496 19 41.54167 -82.93500 20 41.60833 -82.93500 21 41.65000 -82.91667 22 41.73333 -82.93500 23 41.70000 -82.88333 24 41.64293 -82.83803 25 41.60868 -82.83909 26 41.53829 -82.86695 27 41.53833 -82.88333

35

Table 2.3. Range of dates defining the sample week (Week), number of days from first to last sample of the week (Days), and the mean day for the range of dates that sampling occurred (Mean) for larvae collected in 2017 and 2018. 2017 2018 Week Days Mean Week Days Mean 3/19 - 3/25 2 3/19 3/26 - 4/1 2 3/28 3/25 - 3/31 1 3/28 4/2 - 4/8 2 4/2 4/1 - 4/7 1 4/2 4/9 - 4/15 2 4/12 4/8 - 4/14 1 4/9 4/16 - 4/22 4 4/18 4/15 - 4/21 1 4/18 4/23 - 4/29 3 4/24 4/22 - 4/28 1 4/26 4/30 - 5/6 1 5/3 4/29 - 5/5 1 4/30 5/7 - 5/13 2 5/9 5/6 - 5/12 1 5/8 5/14 - 5/20 1 5/15 5/13 - 5/19 1 5/16 5/21 - 5/27 3 5/22 5/20 - 5/26 1 5/24 5/28 - 6/3 2 6/1

36

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