Population Demographics of Broad Whitefish Spawning Near Mcgrath, Alaska, 2014 and 2015 Alaska Fisheries Data Series Number 2017-06

U.S. Fish & Wildlife Service

Population Demographics of Broad Whitefish Spawning Near McGrath, Alaska, 2014 and 2015 Alaska Fisheries Data Series Number 2017-06

Kenai Fish and Wildlife Conservation Office Soldotna, Alaska November 2017

The Alaska Region Fisheries Program of the U.S. Fish and Wildlife Service conducts fisheries monitoring and population assessment studies throughout many areas of Alaska. Dedicated professional staff located in Anchorage, Juneau, Fairbanks and Kenai Fish and Wildlife Offices and the Anchorage Conservation Genetics Laboratory serve as the core of the Program’s fisheries management study efforts. Administrative and technical support is provided by staff in the Anchorage Regional Office. Our program works closely with the Alaska Department of Fish and Game and other partners to conserve and restore Alaska’s fish populations and aquatic habitats. Additional information about the Fisheries Program and work conducted by our field offices can be obtained at:

http://alaska.fws.gov/fisheries/index.htm

The Alaska Region Fisheries Program reports its study findings through the Alaska Fisheries Data Series (AFDS) or in recognized peer-reviewed journals. The AFDS was established to provide timely dissemination of data to fishery managers and other technically oriented professionals, for inclusion into agency databases, and to archive detailed study designs and results for the benefit of future investigations. Publication in the AFDS does not preclude further reporting of study results through recognized peer-reviewed journals.

Disclaimer: The use of trade names of commercial products in this report does not constitute endorsement or recommendation for use by the federal government. The findings and conclusions in this article are those of the author and do not necessarily represent the views of the U.S. Fish and Wildlife Service.

Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

Population Demographics of Broad Whitefish Spawning Near McGrath, Alaska, 2014 and 2015 Kenneth S. Gates, Ken C. Harper, and James K. Boersma

Abstract Broad Whitefish Coregonus nasus are relatively large compared to other whitefish species, migrate long distances in search of prime feeding and spawning areas, and are an important subsistence species harvested throughout the Kuskokwim River drainage. Current knowledge of discrete population demographics is limited and there is a growing concern from subsistence fishers of fewer large whitefish available for harvest today compared to recent history. To begin addressing this concern and to provide for repeatable comparisons of population structure in the future, we collected baseline data that describes the current population demographics of Broad Whitefish from one of two previously identified main-stem spawning groups in the Kukskokwim River. Our sampling included 1,193 collections of age, sex, length, and weight information from Broad Whitefish in 2014 and 2015. Fish were sampled prior to spawning as they migrated in the Kuskokwim River near McGrath, Alaska. Ages of fish sampled ranged between 4 and 26 years (n = 600) in 2014 and between 2 and 22 years (n = 593) during 2015. The average age of sampled fish was 8.5 years during each sample year. Females comprised 38% of the sample during 2014 and 30% during 2015. The mean fork length of sampled fish was 488 mm in 2014 and 485mm in 2015. Mean weights were 1.79 kg in 2014 and 1.70 kg in 2015. Overall, samples of Broad Whitefish collected during 2014 and 2015 were similar with only a few differences observed primarily between male and female weights within and among years. Age, length, and weight data collected during 2014 and 2015 are similar to other populations of Broad Whitefish found throughout the Yukon River drainage and Arctic Region.

Introduction There are seven whitefish species (Family: Salmonidae, Subfamily: Coregoninae) present in the Kuskokwim River drainage in Alaska (Alt 1972; Russell 1980; Harper et al. 2007). Inconnu Stenodus leucichthys, Broad Whitefish Coregonus nasus, and Humpback Whitefish C. pidschian (a nominate form of C. clupeaformis complex according to McDermid et al. 2005) are relatively large (1 kg or greater, mature weight) and are actively sought in subsistence fisheries throughout the region (Fall et al. 2007; Krauthoefer et al. 2007; Simon et al. 2007). Bering Cisco C. laurettae, Least Cisco C. sardinella, and Round Whitefish Prosopium cylindraceum are relatively small (~0.3 - 1.0 kg, mature weight) and are thought to be a lesser component of the subsistence fishery in the Kuskokwim region. Pygmy Whitefish P. coulteri are the smallest species and are only known to exist in one lake within the headwaters of the Stony River near the middle Kuskokwim River.

General life history characteristics are thought to be similar for all riverine whitefish (i.e., Inconnu, Broad Whitefish, Humpback Whitefish, Bering Cisco, and Least Cisco) residing in the Kuskokwim River. They are broadcast-spawners, spreading their eggs over gravel substrate (McPhail and Lindsey 1970) in the fall and larvae emerge after a winter of developing. Larvae are distributed downstream by river currents to feeding areas (Naesje et al. 1986, 1995;

Authors: Kenneth S. Gates and Ken C. Harper are fisheries biologists and James K. Boersma is fisheries biological technician with the U.S. Fish and Wildlife Service. The authors can be contacted through the Kenai Fish and Wildlife Conservation Office, 43655 Kalifornsky Beach Road, Soldotna, Alaska 99669; or [email protected], [email protected], and [email protected]. Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

Shestakov 1991, 1992; Bogdanov et al. 1992) where they rear up to several years. Once mature, fish migrate upstream from feeding areas to fall spawning grounds (Harper et al. 2009, 2012). Harvest of whitefish throughout Alaska is mostly unmanaged. Federal and state subsistence regulations in the Kuskokwim River region allow for unlimited year-round harvest of all species and the only limitation in state sport fishing regulations is for Inconnu (10 per day, 10 in possession, no size limit). Much of the subsistence harvest occurs in the main-stem Kuskokwim River and connected tundra ponds within the Yukon Delta National Wildlife Refuge. There has been a growing concern from residents throughout the region that fewer whitefish are available for harvest today compared to the recent past, particularly larger whitefish (i.e., Broad Whitefish and Inconnu). These larger whitefish species are preferred and are thought to be the least abundant of all whitefish species in the Kuskokwim region.

Information documenting whitefish harvest in the Kuskokwim region is generally community or area-specific and lack species-specific reporting. For example, Krauthhoefer et al. (2007) noted during an interview of a subsistence fisher that there are fewer whitefish now compared to the past and that whitefish previously reached much larger sizes. Krauthhoefer et al. (2007) also reported that whitefish were the most important to the village of Aniak of all non-salmon harvested fish during 2001 and 2002. Similarly, Simon et al. (2007) documented that the most non-salmon resident fish species harvested by Bethel residents in the lower Kuskokwim River drainage during 2001 was whitefish. Simon et al. (2007) also estimated subsistence whitefish harvest by Bethel residents in 2001 was 32,900 lb, 36,880 lb in 2002, and 12,725 lb in 2003.

The importance of whitefish to subsistence users has prompted several studies throughout the Kuskokwim region. The most recent studies included a fish weir at the outlet of Whitefish Lake south of Aniak from 2001 to 2003 (Harper et al. 2007), which described species composition, run timing, abundance, age, length, sex, and incidental information. There were several years of radiotelemetry studies focused on movements and distributions of primarily Broad and Humpback whitefish and Inconnu throughout the Kuskokwim River (Harper et al. 2009; Stuby 2010). There is also an ongoing Bering Cisco radiotelemetry study (FIS 12-313), and a recent pilot study developing capture and aging techniques of Broad Whitefish spawning upstream of McGrath, Alaska (U.S. Fish and Wildlife Service, unpublished data). Most of the recent work has focused on Broad Whitefish, Inconnu, and Bering Cisco because of their low abundance and harvest preference by subsistence users.

Recent movement studies show that most whitefish are highly migratory throughout the Kuskokwim River drainage (Harper et al. 2009, 2012; Stuby 2010). Initial indications of long migrations were determined from analysis of otoliths collected from Broad and Humpback whitefish and Least Cisco captured in Whitefish Lake. Results from otolith microchemistry data indicate that most fish rear in brackish or marine waters for part of their life before migrating to freshwater feeding areas (Harper et al. 2007). Subsequent radiotelemetry studies of adult fish confirm that migrations often times exceed several hundred river kilometers. For example, some Broad Whitefish radio-tagged downstream of Bethel at rkm 112 migrated to two distinct spawning locations in the middle and upper Kuskokwim River: one near the confluence of the Swift River (rkm 560) and the other between McGrath and Medfra (rkm 700; Harper et al. 2012).

The spawning season for Broad Whitefish occurs during October and November (Shestakov 2001; Tallman et al. 2002; Harper et al. 2009, Carter 2010), which is later than other whitefish species (Alt 1972, 1979; Stein et al. 1973; Brown 2000, 2006; Howland et al. 2000; Underwood 2000; Harper et al. 2009; Stuby 2010). Harper et al. (2009) found that spawning migrations

2 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

typically took several weeks and occurred between late summer and early fall. This timing was also observed during a pilot study in 2012 by the Kenai Fish and Wildlife Field Office that focused on testing different capture techniques for Broad Whitefish as they migrated past McGrath, Alaska, from mid-September to mid-October. A total of 294 Broad Whitefish were captured and sampled for age, sex, length, and weight in this pilot study (U.S. Fish and Wildlife Service, unpublished data).

In general, whitefish mature slowly and vary by age and length at first maturity. Maturity can also vary by latitude, river system, and species (Reist and Bond 1988; Harper et al. 2007, 2009, 2012). For example, Broad Whitefish reach maturity between age-5 and age-8 from the Mackenzie River in Canada and the Yukon River in Alaska (Van Gerwen-Toyne et al. 2008; Carter 2010), whereas Humpback Whitefish mature at age-11 in Teshekpuk Lake (Moulton et al. 1997), and age-4 in the Kuskokwim River (Harper et al. 2007). The minimum length at maturity for Broad Whitefish ranges from 380 mm in the Ob River basin (Prasolov 1989) to 450 mm or more in the Selawik and Yukon drainages (Alt 1976; Brown 2004). The smallest mature male Broad Whitefish reported from the Kuskokwim River was 380 mm, whereas the smallest mature female was 470 mm (Harper et al. 2007). Once mature, whitefish can spawn multiple times throughout their lives, and reach ages of 30 years or more depending on the species (Bond and Erickson 1985; VanGerwen-Toyne et al. 2008). Spawning in consecutive years has been documented for Inconnu, Broad Whitefish, and Humpback Whitefish using radiotelemetry (Brown 2006; Hander et al. 2008, Harper et al. 2012) but to what extent is largely unknown. Brown and Burr (2012) found that 22% of Inconnu captured and radio-tagged in the Innoko River spawn in consecutive years. Reist and Bond (1988) also suggest that large components of coregonid populations do not spawn the year following spawning.

Broad Whitefish are vulnerable to overharvest because they have intricate life history characteristics (i.e., slow maturation, long migrations, and limited spawning areas). Current knowledge of spawning abundance and age, sex, length, and weight of spawning adults are inadequate, especially considering that harvest is unlimited and unmanaged. Inaccurate or systematic underestimates of life history characteristics such as age at maturity, reproductive life span, survivorship and growth can lead to errors in management (Mills and Beamish 1980, Chilton and Beamish 1982, Beamish and McFarlane 1983; Yule et al. 2008). To date, studies of Broad Whitefish in the Kuskokwim River have only provided general information about spawning locations and demographics, and often times are based on small sample sizes. Accurate assessments of Broad Whitefish spawning populations as described by Harper et al. (2009, 2012) need to be conducted to establish valuable baselines to compare with future stock assessments.

Information reported here is intended to inform managers and to assist the U.S. Fish and Wildlife Service (Service) in meeting the legislative intent of Section 303 (7) (B) of ANILCA. This section of ANILCA, which is why the Yukon Delta National Wildlife Refuge (Refuge) was established, mandates the Service to: (i) conserve fish and wildlife populations and habitats in their natural diversity, and (ii) provide, in a manner consistent with the purposes set forth in paragraph (I), the opportunity for continued subsistence uses by local rural residents. The information herein also addresses a biological objective developed for Broad Whitefish in the Service’s Strategic Habitat Conservation approach to landscape-scale conservation of managing Broad Whitefish in the Yukon and Kuskokwim rivers for sustainable subsistence and commercial fisheries. In addition, population-specific length and age data identified by Brown et al. (2012) was carried forward as a specific priority information need outlined by the 2014

3 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

Federal Subsistence Fisheries Resource Monitoring Program (U.S. Fish and Wildlife Service 2012). Specific project objectives were to: (1) estimate the proportional age and sex composition of mature Broad Whitefish spawning upstream of McGrath, Alaska, such that estimates are within 5% of the actual population proportions 95% of the time; and (2) estimate the mean length and weight of mature Broad Whitefish spawning upstream of McGrath, Alaska, such that estimate are within 10% of the actual population means 95% of the time. Two tasks were also identified: (1) assess the feasibility of using mark-recapture techniques to estimate Broad Whitefish abundance; and (2) record and catalog any reported harvests of Floy® T-bar anchor- tagged fish from this study during subsequent subsistence fisheries.

Study Area

The Kuskokwim River is the second largest drainage in Alaska, draining an area of approximately 125,000 km2 (Kammerer 1990; Revenga et al. 1998). It flows for more than 1,500 rkm from the headwaters of the North Fork Kuskokwim River to its mouth in Kuskokwim Bay (Figure 1). Average annual flow near the Kuskokwim River mouth is approximately 1,900 m3/s (Kammerer 1990; Dynesius and Nilsson 1994). The mean average discharge at McGrath measured by the U.S. Geological Survey from 1963 to 1973 was 378.4 m3/s (Dorava 1994). The southern tributaries of the Kuskokwim River drainage, from the Stony River upstream, originate in glaciated regions of the western Alaska Range. These drainages contribute a substantial quantity of suspended sediment to the Kuskokwim River during the summer months. The lower Kuskokwim River channel meanders slowly with predominately soft-bottom substrates. The last 200 rkm flow through the Yukon-Kuskokwim delta, an area formed by deposits from the Yukon and Kuskokwim rivers (U.S. Fish and Wildlife Service 1988). This area is covered by lakes and ponds, varying in size from less than one hectare to thousands of hectares (Brown 1985). Many are small shallow thaw ponds or lakes less than 3 m in depth and are connected to the Kuskokwim River by low gradient streams. River ice begins forming from upstream to downstream locations, and the river freezes at McGrath during October. Ice breakup generally occurs during early May at McGrath (Alaska Pacific River Forecast Center 2013).

The study area extends from approximately 26 rkm downstream of McGrath (rkm 779) to 75 rkm upstream of McGrath (Figure 1). The primary spawning area of Broad Whitefish is between rkm 815 and 850 (Harper et al. 2009, 2012). Water depth varies with location and river stage height and numerous sand and gravel bars are present upstream and downstream of McGrath. The river width varies between 130 and 380 m and can change dramatically with river stage height depending on location. River width immediately upstream of the airport at McGrath is 377 m wide.

4 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

]

[ [ ]

FIGURE 1.–Map of the Kuskokwim River watershed showing the study location in the upper Kuskokwim River. Four communties along the Kuskokwim River are highlighted as reference points.

Methods Project design This study used a boat-mounted electrofishing unit as the primary means to collect age, sex, length, and weight information from mature Broad Whitefish destined for spawning areas near McGrath, Alaska, during 2014 and 2015. Samples were collected between August 29 and September 29, 2014, and August 20 and September 29, 2015. This sampling method was based on a feasibility study that used multiple sampling methods including electrofishing, gillnets, and Merwin traps from September 18 to October 10, 2012 (U.S. Fish and Wildlife Service, unpublished data). Information collected from the feasibility study indicated that electrofishing was the most versatile method and produced the greatest number of Broad Whitefish. Gillnets set in strategic locations were also successfully used late in the season when fish were found in larger groups near or on spawning areas. Therefore, set gillnets were available as back-up sampling equipment during this study in the event the electrofishing boat required extended servicing or maintenance.

Preliminary investigations of gear selectivity during the 2012 feasibility study indicated no difference between electrofishing and gillnetting when comparing sex, lengths, and weights of fish captured (U.S. Fish and Wildlife Service, unpublished data; Appendix 1). Similarly, analysis of sex, lengths, and weights of sampled fish from 2012 indicated no difference between fish sampled early in the season versus fish sampled late in the season (U.S. Fish and Wildlife

5 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

Service, unpublished data; Appendix 2). Therefore, sampling was not stratified by time, and samples could have been collected anytime in the season. However, due to the scale of the study area, a daily goal of 11 Broad Whitefish was used to guide sampling efforts throughout the season during the proposed study period each year.

Sample size determination —A sample size of 510 fish was determined to be large enough to estimate the age and sex composition of spawning Broad Whitefish (objective 1). With this sample size there was a 95% probability that all proportional estimates of age and sex will be simultaneously within 0.05 of the true population proportion (Thompson 1987; Appendix 3). We used a multinomial estimator for proportions to determine a sample size for multiple proportions assuming no prior knowledge of population proportions because prior sample sizes were insufficient to accurately determine the true number of age groups within the population. A sample size to estimate population mean length and weight within 10% of the actual population mean 95% of the time is less (n = 386, estimated using Lenth 2006-9) than what is needed to estimate age and sex composition. However, the larger sample size of 510 was used because the samples collected during 2014 and 2015 will be used during future assessments to measure proportional changes (e.g., changes in the proportion of fish greater than 10 years old) in the population. An additional 100 fish were added to the target sample size of 510 as a buffer to account for incomplete aging data or unmeasured variables.

Fish capture —Electrofishing occurred from approximately 26 rkm downstream of McGrath (rkm 779; N62.82629; W155.614151, NAD 83) to approximately 75 rkm upstream of McGrath (N62.99231; W155.20682, NAD 83; Figure 1). A standardized catch per unit effort (CPUE, number of fish caught per hour) was calculated each day by dividing the total number of fish captured each day by the total number of electrofishing time each day. Variables such as electrofishing time measured in seconds, water temperatures, and river water conductivity were recorded daily. Water temperatures were measured using a boat-mounted GPS chart plotter transducer and river conductivity was measured using an EXTECH Instruments, ExStik® II pH/conductivity/TDS meter. Daily sample locations were recorded using latitude and longitude coordinates (decimal degrees, NAD 83) with either a hand-held or boat-mounted Global Positioning System (GPS). Individual fish locations were not recorded for analysis purposes, but were used to help guide daily sampling activity.

A single boat outfitted with an electrofishing unit and a three person crew was used to sample all Broad Whitefish. Two crew members located on the bow of the boat identified and dip-netted Broad Whitefish while the third crew member piloted the boat and operated the electrofishing unit. Once fish were dipped from the river, they were immediately placed in a large tote filled with river water. Fish were processed in a timely manner, monitored, and released. All crew members were Service-certified electrofishing operators and followed safety and operational guidelines outlined in Reynolds (1996) and USFWS (2004).

The boat was equipped with a pulsed-DC variable-voltage pulsator (Model: SRI VVP-15B), powered by a 5,000-W single-phase gasoline generator. Anodes consisted of two adjustable umbrella arrays (Model: SRI AUA-6) equipped with a series of approximately 4.7-mm diameter steel cables (1.5-m long). Each anode was mounted to a 3 m fiberglass boom mounted to the bow of the boat. The anodes were spaced approximately 2 m apart and arranged at a 60° angle from the long axis of the boat. Four cathode arrays consisting of 32 one-meter dropper cables (diameter = 4.7 mm) were mounted to the bow and sides of the boat. The electrical output (voltage, amperage, and duty cycle) was adjusted to the minimum level necessary to achieve

6 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

electrotaxis (forced swimming) and was adjusted based on observed responses of shocked fish to minimize stress.

Biological sampling —Broad Whitefish were sampled for age, sex, length, and weight. Scales and fin rays were collected for aging. Fin rays were the primary aging method for all Broad Whitefish and scales were archived. Otoliths were collected from 150 Broad Whitefish during 2014 to confirm fin ray ages. Results from this comparison are not reported here. Scales and fin rays from each individual fish were placed in a weatherproof scale envelope marked with a unique identification number (UIN). The first fin ray on the left pectoral fin was removed by cutting distal to the articulation with the pectoral girdle using bone shears to ensure the inclusion of the early growth portion of the fin ray ensuring accurate age determination (Chilton and Bilton 1986; Howland 2001). Scales were collected as a secondary aging method and were taken from the preferred area similar to scale collections from salmon using methods described by Mosher (1968) and Koo (1962). The preferred area is located on the left side of the fish on a diagonal line extending from the posterior insertion of the dorsal fin to the anterior insertion of the anal fin two scale rows above the lateral line.

All Broad Whitefish were measured for fork length (FL) to the nearest one mm. Sex was determined using visible external characteristics. Gravid females are discernable from males by having tight extended bellies. Stomachs of males are less robust than females, often sunken in and loose to the touch, and are thicker in the body wall. Presence or absence of tubercles can also be a useful indicator of sex. However, this characteristic alone is not 100% accurate because some females have tubercles. Preliminary investigations from the feasibility study indicated that males exhibit tubercles nearly 100% of the time, whereas females seldom exhibited this trait (U.S. Fish and Wildlife Service, unpublished data). A digital electronic scale was used to weigh fish to the nearest gram for accuracy purposes and later converted to kilograms. Once all data were collected, sampled fish received a Floy® T-Bar anchor tag applied near the base of the dorsal fin to identify recaptured fish and to facilitate the collection of information regarding future time and area of subsistence harvested fish. The fin ray removed from the pectoral fin denotes a second mark.

Data collection and reduction ―Data from captured Broad Whitefish were recorded on weather resistant field forms and included a UIN for each sample, the date (dd/mm/year), sample start and end times, time of capture, capture method, samplers, mesh size (if applicable), sample location (GPS coordinates reference the daily sample area), species, length, sex, weight, presence of spawning tubercles, and Floy® tag number. Scales and fin rays were placed in a weatherproof scale envelope numbered with a UIN matching the data sheet. Data were transcribed from field forms to an electronic format in-season using Microsoft Excel. Transcribing information in- season allowed for real time corrections to sampling protocols and data discrepancies. Broad Whitefish scales were cleaned and affixed to gummed scale cards and pressed using acetates. Fin rays were processed post season using methods similar to Mills and Chalanchuk (2004). Once aging was completed, ages were linked to the corresponding fish samples in the Excel database.

Data analysis ―Data summaries, scatter plots, and statistical analyses were used to describe the age, sex, length, and weight of Broad Whitefish spawning upstream of McGrath, Alaska. Two- tailed t-tests were used to compare mean age, length, and weight of Broad Whitefish sampled during 2014 and 2015. P-values were Bonferroni-corrected and significant differences were identified at P-values <0.05. The fish samples were not stratified by time or area based on data

7 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

collected during the feasibility study. However, because the samples were collected daily over the entire study period, collections could be stratified later if warranted using a stratified sample design similar to Cochran (1977). Linear regression of logarithmically transformed weight and length data was used to explore weight-length relationships of sampled Broad Whitefish as described by Anderson and Neumann (1996).

Results

A total of 1,253 Broad Whitefish were captured during 2014 and 2015 (Table 1) between August 20 and September 29. Sampling occurred over a 32 d period during 2014 and 41 d during 2015. Complete age, sex, length, and weight information was obtained from 1,193 fish (2014, n = 600; 2015, n = 593). The remaining 60 fish were comprised of 45 recaptured fish (2014, n = 16; 2015, n = 29), 2 fish with missing biological information (2014, n = 1; 2015, n = 1), and 13 fish with undetermined ages (2014, n = 9; 2015, n = 4). Time spent electrofishing each sample day averaged 3.35 h (2014) and 3.69 h (2015). Mean daily catches of Broad Whitefish were greater during 2014 than 2015 (2014 = 19.56 fish/d; 2015 = 15.68 fish/d). Similarly, the mean daily CPUE was greater during 2014. CPUE increased over time and was greatest near the end of the study period each year (Figures 2, 3). Daily catches of Broad Whitefish were also greatest later in the sample period during each year (Figures 4, 5). Daily catches during both years ranged from 1 to 79 fish. A total of 1,058 Broad Whitefish were tagged and released with unique identification during 2014 (n=460) and 2015 (n=598). No tag loss was observed for recaptured fish. Intra-year recaptures comprised 3.5% of the sample during 2014 and 4.6% during 2015. One Broad Whitefish tagged in 2014 was recaptured in 2015. Days between intra-year capture events ranged from 1 d to 19 d during 2014 and 1 d to 32 d during 2015 (Figures 6, 7). The average number of days between capture events was 8.6 d during 2014 and 8.8 d during 2015. Water temperatures were similar between years ranging from 3.2 °C to 10.6 °C during 2014 and 2.9 °C to 11.1 °C during 2015 (Table 1; Figure 8). River stage heights were also similar between years averaging 3.27 m during 2014 and 3.42 m during 2015 (National Weather Service, Pacific River Forecast Center, Historical Stage Height; Table 1; Figure 8). Conductivity was only measured during 2015 and averaged 422 μS/cm (range 267 μS/cm to 680 μS/cm) (Table 1; Figure 9).

Biological Data Complete age, sex, length, and weight samples were collected from 1,193 Broad Whitefish between August 20 and September 29, 2014 (n = 600) and 2015 (n = 593) (Table 2). Females comprised 30% of the sample during 2014 and 38% during 2015.

No differences were detected in overall mean ages of Broad Whitefish sampled during 2014 and 2015 (Table 3; t-test: t Stat = -0.1105; df = 1,190; P = 0.9121). The mean age determined from fin-ray analysis was 8.5 years during each sample year (Tables 2, 3). Ages ranged between 4 years and 26 years during 2014 and 2 years and 22 years during 2015 (Table 2; Figure 10). Comparison of fin-ray ages detected a difference between male and female Broad Whitefish sampled during 2015. Results indicated that females were significantly older than males (Tables 2, 3; t-test: t Stat = -2.8080; df = 378; P = 0.0210, Bonferroni-corrected). No difference was observed in mean ages between years of like-sexed fish. Twenty-five percent of the sampled fish

8 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service were older than age-10 during each sample year. Age-6 fish were the most frequently caught fish during 2014, whereas age-8 fish were predominant in 2015 (Figure 10; Appendix 4). More fish less than age-5 were observed during 2015, of which, 96% were males (Appendix 4).

TABLE 1. —Summary statistics of Broad Whitefish sampling efforts during 2014 and 2015. 2014 (August 29 - September 29) n Mean Minimum Maximum SE Days sampled 32 — — — — Total hours fished 107.1 — — — — Total Catch 626 — — — — Sample used for age, sex, length, weight analysis 600a — — — — Fish tagged and released with a Floy® T-bar anchor tag 460b — — — — Daily electrofishing time (hr) 3.35 0.65 6.05 0.22 Daily Broad Whitefish catch 19.56 1.00 46.00 1.72 Daily CPUE (number of fish/hr) 6.12 1.33 16.42 0.54 River water temperature (°C; August 29 to September 29) 6.97 3.17 10.16 0.33 River stage heighte (m) 3.27 2.81 4.00 0.05 River Conductivity (μS/cm) — — — —

2015 (August 20 - September 29) Days sampled 40 — — — — Total hours fished 147.41 — — — — Total Catch 627 — — — — Sample used for age, sex, length, weight analysis 593c — — — — Fish tagged and released with a Floy® T-bar anchor tag 598d — — — — Daily electrofishing time (hr) 3.69 1.47 4.57 0.11 Daily Broad Whitefish catch 15.68 1.00 79.00 2.12 Daily CPUE (number of fish/hr) 4.55 0.27 33.62 0.84 River water temperature (°C; August 22 to September 29) 6.74 2.89 11.10 0.40 River stage heighte (m) 3.42 3.13 4.00 0.04 River Conductivity (μS/cm) 422.35 267.00 680.00 12.52

a A total of 26 fish were omitted from the age, sex, length, and weight analysis due to being recaptured (n =16), having incomplete biological information (n =1), or having undetermined ages (n =9). b Otoliths were collected from n =150 Broad Whitefish to validate fin ray aging technique. c A total of 34 fish were omitted from the age, sex, length, and weight analysis due to being recaptured (n =29), having incomplete biological information (n =1), or having undetermined ages (n =4). d One Broad Whitefish did not recover from the capture method and therefore was not tagged. e Source: bational Weather Service at http://www.weather.gov/aprfc/rivobs#.

9 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

20 2014

10 CPUE

5 umber of fish caught/hour fished) caught/hour of fish N umber

( 0

Date

FIGURE 2. —Daily CPUE of Broad Whitefish captured with electrofishing gear near McGrath, Alaska, 2014.

20 2015

10 CPUE

umber of fish caught/hour fished) caught/hour fish of N umber 0 (

Date

FIGURE 3. —Daily CPUE of Broad Whitefish captured with electrofishing gear near McGrath, Alaska, 2015. CPUE for September 29 was 34 fish per hour and was omitted from the figure because it was over three times greater than any other day.

10 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

50 45 2014 (n=626) 40 35 30 25 20 15 10 5 Daily capture of Broad Whitefish 0

Date

FIGURE 4. —Daily capture of Broad Whitefish using electrofishing gear near McGrath, Alaska, 2014. 50 45 2015 (n=627) 40 35 30 25 20 15 10 5 Daily capture of Broad Whitefish 0

Date FIGURE 5. —Daily capture of Broad Whitefish using electrofishing gear near McGrath, Alaska, 2015. Daily Catch for September 29 was 79 fish and was omitted from the figure because it was over two times greater than the next highest daily catch.

11 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

5 2014 (n=16)

2 umber of fish N

0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Days between capture events FIGURE 6. —Frequency of recaptured Broad Whitefish using electrofishing gear near McGrath, Alaska, 2014. 5 2015 (n=29) 4

2 umber of fish N

0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 Days between capture events FIGURE 7. —Frequency of recaptured Broad Whitefish using electrofishing gear near McGrath, Alaska, 2015.

12 4.5 4 10 3.5 8 3 2.5 6 2014 temperature 2 4 2015 temperature 1.5 2014 stage height 1 2 Surface water temperature (⁰C)

2015 stage height 0.5 (m) Alaska McGrath, at height Stage 0 0 8/20 8/27 9/3 9/10 9/17 9/24 Date FIGURE 8. —Kuskokwim River surface water temperature and stage height near McGrath, Alaska, 2014 and 2015. River stage height information was obtained from http://www.weather.gov/aprfc/rivobs#.

12 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

800 700 600 S/cm)

μ 500 400 300

Conductivity ( Conductivity 200 2015 conductivity 100 0

Date FIGURE 9. —Kuskokwim River water conductivity measured near McGrath, Alaska, 2015.

Lengths of Broad Whitefish averaged 488 mm FL during 2014 and 485 mm during 2015. No difference was detected in overall lengths of fish sampled between 2014 and 2015 (Table 3; t- test: t Stat = 1.3345; df = 1,133; P = 0.1823). However, female lengths were larger than male lengths measured during 2015 (Table 3; t-test: t Stat = -3.8708; df = 418; P = 0.0005, Bonferroni-corrected). Lengths ranged from 406 mm to 600 mm FL in 2014 and 346 mm to 616 mm FL during 2015 (Table 2, Figure 11). Twenty-five percent of the Broad Whitefish sampled were greater than 504 mm FL during 2014 and 507 mm FL during 2015.

Weights of Broad Whitefish averaged 1.79 kg during 2014 and 1.69 kg during 2015 (Table 2). Significant differences were detected in all comparisons except for females sampled during each year (Table 3). Weights ranged from 1.04 kg to 3.37 kg in 2014 and 0.56 kg to 3.54 kg in 2015 (Table 2; Figure 12). Twenty-five percent of the fish were greater than 1.97 kg during 2014 and 1.91 kg during 2015 (Table 2).

Length at age generally indicated that as fish aged they grew longer (Figure 13). However, there is also overlap in lengths between individual age groups (Figure 13). For example, an age-6 fish sampled during 2014 could be the same length as an age-22 fish. Similar overlap was observed in 2015, but not to the degree observed in 2014.

Weight at age showed a positive trend similar to length at age (Figure 14). When compared to fork length at age, the separation between age groups was even less for weight at age for each year. The youngest age groups can weigh as much as the oldest age groups.

The weight-length relationship illustrates a typical curvilinear relationship between weight and measured lengths (Figure 15). The data in Figure 15 was logarithmically transformed in Figure 16 to present the data in a linear format. The slopes of 2.8173 (2014) and 2.8979 (2015) are similar suggesting that fish become less rotund as length increases (Figure 16).

13 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

TABLE 2. —Descriptive statistics for fin-ray age, fork length, and weight of Broad Whitefish near McGrath, Alaska, 2014 and 2015. 2014 n Mean Min - Max SE 25% 50% 75% Fin-ray age (yr) Male 373 8.6 4 - 26 0.17 6 8 10 Female 227 8.3 4 - 18 0.18 6 8 10 Combined 600 8.5 4 - 26 0.13 6 8 10 Fork Length (mm) Male 373 486 430 - 600 1.51 468 483 501 Female 227 489 406 - 565 1.77 470 488 505 Combined 600 488 406 - 600 1.15 469 485 504 Weight (kg) Male 373 1.71 1.04 - 3.0 0.02 1.49 1.66 1.88 Female 227 1.97 1.34 - 3.37 0.02 1.65 1.89 2.12 Combined 600 1.79 1.04 - 3.37 0.01 1.52 1.74 1.97

2015 n Mean Min - Max SE 25% 50% 75% Fin-ray age (yr) Male 416 8.3 2 - 22 0.15 6 8 10 Female 177 9 4 - 18 0.20 7 8 11 Combined 593 8.5 2 - 22 0.12 7 8 10 Fork Length (mm) Male 416 482 346 - 596 1.81 463 483 505 Female 177 493 415 - 616 2.19 474 489 512 Combined 593 485 346 - 616 1.44 466 485 507 Weight (kg) Male 416 1.62 0.56 - 3.15 0.02 1.39 1.58 1.8 Female 177 1.87 1.09 - 3.54 0.03 1.59 1.77 2.09 Combined 593 1.69 0.56 - 3.54 0.02 1.44 1.64 1.91

14 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

TABLE 3. —Two-tailed t-test of fin-ray age (yr), fork length (mm), and weight (kg) for Broad Whitefish during 2014 and 2015 near McGrath, Alaska. Reported p-values are Bonferroni-corrected and significant differences are identified at α < 0.05. P-value (Bonferroni- Significant t-test 2014 Mean 2015 Mean t Stat df corrected) Difference Fin-ray age Male Female Male Female 2014 x 2015 All Fish 8.49 8.47 -0.1105 1,190 0.9121 No 2014 Male x 2014 Female 8.58 8.34 – – 0.9265 543 1.0000 No 2015 Male x 2015 Female – – 8.26 8.97 -2.8080 378 0.0210 Yes 2014 Male x 2015 Male 8.58 – 8.26 – -1.3946 762 0.6541 No 2014 Female x 2015 Female – 8.34 – 8.97 2.2809 383 0.0924 No

Fork length (mm) Male Female Male Female 2014 x 2015 All Fish 488 485 1.3345 1,133 0.1823 No 2014 Male x 2014 Female 486 489 – – -1.2178 511 0.8954 No 2015 Male x 2015 Female – – 482 493 -3.8708 418 0.0005 Yes 2014 Male x 2015 Male 486 – 482 – 1.9809 775 0.1918 No 2014 Female x 2015 Female – 489 – 493 -1.2386 361 0.8652 No

Weight (kg) Male Female Male Female 2014 x 2015 All Fish 1.79 1.69 4.2347 1,173 2.46E-05 Yes 2014 Male x 2014 Female 1.71 1.91 – – -7.0579 456 2.53E-11 Yes 2015 Male x 2015 Female – – 1.62 1.87 -6.9813 312 7.06E-11 Yes 2014 Male x 2015 Male 1.71 – 1.62 – 3.4981 787 0.0020 Yes 2014 Female x 2015 Female – 1.91 – 1.87 1.2551 354 0.8411 No

15 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

120 2014 fin-ray (n=600) 100

0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 umber of fish

N 120 2015 fin-ray (n=593) 100

0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Age (years)

FIGURE 10. —Frequency histogram of fin-ray ages sampled from Broad Whitefish near McGrath, Alaska, 2014 and 2015.

16 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

100 2014 fork length (n=600) 90 80 70 60 50 40 30 20 10 0 340 349 - 360 369 - 380 389 - 400 409 - 420 429 - 440 449 - 460 469 - 480 489 - 500 509 - 520 529 - 540 549 - 560 569 - 580 589 - 600 609 -

umber of of umber fish 100 N 2015 fork length (n=593) 90 80 70 60 50 40 30 20 10 0 340 349 - 360 369 - 380 389 - 400 409 - 420 429 - 440 449 - 460 469 - 480 489 - 500 509 - 520 529 - 540 549 - 560 569 - 580 589 - 600 609 - Length (mm)

FIGURE 11. —Frequency histogram of fork lengths sampled from Broad Whitefish near McGrath, Alaska, 2014 and 2015.

17 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

80 2014 weight (n=600) 70 60 50 40 30 20 10 0 <.59 >3.50 .70 - .79 .90 - .99 1.10 1.19 - 1.30 1.39 - 1.50 1.59 - 1.70 1.79 - 1.90 1.99 - 2.10 2.19 - 2.30 2.39 - 2.50 2.59 - 2.70 2.79 - 2.90 2.99 - 3.10 3.19 - 3.30 3.39 - umber of of umber fish

N 80 2015 weight (n=593) 70 60 50 40 30 20 10 0 <.59 >3.50 .70 - .79 .90 - .99 1.10 1.19 - 1.30 1.39 - 1.50 1.59 - 1.70 1.79 - 1.90 1.99 - 2.10 2.19 - 2.30 2.39 - 2.50 2.59 - 2.70 2.79 - 2.90 2.99 - 3.10 3.19 - 3.30 3.39 - Weight (kg)

FIGURE 12. —Frequency histogram of weights sampled from Broad Whitefish near McGrath, Alaska, 2014 and 2015.

18 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

650 2014 Broad Whitefish length at age (n=600) 600

550

500

450

400

350

300 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

650 Fork length Broad Whitefish length at age (n=593) 600

550

500

450

400

350

300 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Fin-ray age (yr)

FIGURE 13. —Fork length at age for Broad Whitefish sampled near McGrath, Alaska, 2014 and 2015.

19 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

3.95 2014 Broad Whitefish weight at age (n=600) 3.45

2.95

2.45

1.95

1.45

0.95

0.45 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

3.95 Weight (kg) Weight 2015 Broad Whitefish weight at age (n=593) 3.45

2.95

2.45

1.95

1.45

0.95

0.45 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Fin-ray age (yr)

FIGURE 14. —Weight at age for Broad Whitefish sampled near McGrath, Alaska, 2014 and 2015.

20 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

4 2014 Broad Whitefish weight-length relationship (n=600) 3.5 y = 0.1083e0.0057x 3 R² = 0.7122 2.5 2 1.5 1 0.5 0 300 350 400 450 500 550 600 650

4 Weight (kg) Weight 2015 Broad Whitefish weight-length relationship (n=593) 3.5 y = 0.0862e0.0061x 3 R² = 0.8175 2.5

1.5

0.5

0 300 350 400 450 500 550 600 650 Fork length (mm)

FIGURE 15. —Weight-fork length relationship for Broad Whitefish sampled near McGrath, Alaska, 2014 and 2015.

21 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

3.8 2014 Broad Whitefish weight-length relationship (n=600) 3.6 y = 2.8173x - 4.4436 R² = 0.7134 3.4

3.2

2.8

2.6

2.4 2.5 2.55 2.6 2.65 2.7 2.75 2.8 2.85

weight (g) weight 3.8 10 2015 Broad Whitefish weight length relatuionship (n=593) Log 3.6 y = 2.8979x - 4.5627 R² = 0.8221 3.4

3.2

2.8

2.6

2.4 2.5 2.55 2.6 2.65 2.7 2.75 2.8 2.85

Log10 fork length (mm)

FIGURE 16. —Logarithmic relationship of weight-fork length information presented in Figure 15 for Broad Whitefish sampled near McGrath, Alaska, 2014 and 2015. Weights were converted to grams from kilograms prior to logarithmically transforming the data.

Discussion Boat-mounted electrofishing equipment was used to capture 1,253 Broad Whitefish during 2014 and 2015 during their fall spawning migration. This is the most effective technique presently available to capture, handle, and release large numbers of Broad Whitefish in the main-stem Kuskokwim River and similar habitats. The 2014 and 2015 collections are likely the largest samples of Broad Whitefish collected during an individual study. A fish weir operated on a tributary to the Kuskokwim River near Aniak, Alaska, between 2001 and 2003 was also effective at capturing Broad Whitefish (Harper et al. 2007). However, catches of Broad Whitefish were much less than electrofishing and often took several months to obtain adequate samples, whereas Broad Whitefish during 2014 and 2015 were collected in a short period (2014 = 32 d; 2015 = 41 d). Total catches during 2014 and 2015 are on the low end of what potentially could be caught

22 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

during this time frame. An example of a high daily catch occurred on September 29, 2015, when 79 Broad Whitefish were sampled in one day. Total catch could be much higher if sampling were continued beyond September into October and if multiple crews were deployed. Sampling ended early during 2014 and 2015 due to uncertainty in federal budgets but we suspect our daily catches and CPUE would have increased substantially in October. A recommendation for future studies would be to sample until freeze up. Freeze up data collected at McGrath indicate unsafe boating conditions begin as early as October 4 and as late as November 17 (National Oceanic and Atmospheric Administration, National Weather Service, Alaska Pacific River Forecast Center, Freeze up data). Daily catches of Broad Whitefish in the Kuskokwim River using electrofishing were influenced by several factors. These include daily travel time to the sample area, river depth, boat operator experience, crew dipnetting experience, crew species identification experience, and the ability for the boat operator to identify potential habitat occupied by Broad Whitefish. However, despite the factors affecting our success, catch rates consistently increased throughout the season each year as the spawning migration progressed. To reduce the variability in catch rates, each crew member was assigned a role to perform daily. This method allowed crew members to become proficient at their roles and helped achieve our sample goals each year. Sampling a river reach the size of our study area allowed the field crew to sample an area each day that was not sampled during the previous two days. In general, the crew would begin sampling each day at the end point from the previous day. This method allowed the crew to sample “new” water for unmarked fish. However, the crew would sometimes overlap sample areas on two consecutive days when fish availability or catch rates were high in one area during the prior day. Recapture of marked fish was minimal throughout 2014 and 2015. The total number of recaptured Broad Whitefish was 45 fish comprising 3.5% of the sample during 2014 and 4.6% during 2015. In general, the frequency of recaptures decreased as the number of days increased from the initial capture and marking event. Recapturing fish was not a goal of this study; however, assessing the feasibility of future mark-recapture study was identified as a task and several factors could influence a mark-recapture study including the total number of recaptured fish. Factors affecting the number of recaptures likely include the size of the sample area, river depth, fish migrating upriver or moving downriver after the initial capture and exiting the study area, fish mortality from handling, and the sample design. The daily sampling design was not developed to focused on one particular group of migrating fish, this allowed fish to move through the study area without being sampled on consecutive days. This alone likely reduced the number of recaptures assuming that fish continually migrated through the area. In addition, marked and unmarked fish could go undetected due to the size of the river. The river varies in width from 180 m to 380 m and reaches depths of over 10 m throughout the study area. Several islands and gravel/sand bars also exist which provide more habitat for Broad Whitefish than could be sampled in a day. Electrofishing is an acceptable method to capture Broad Whitefish in the Kuskokwim River. Captured and recaptured fish were examined throughout the study. We observed only one mortality and no visible external injuries in two years of sampling. All captured fish were held in a live well up to an hour or more while sampling. This allowed field crews to process multiple fish at once and assess the immediate effects of electrofishing on captured fish. All recaptured fish were lively and released in good condition with no indication of external injuries. Broad Whitefish sampled for otoliths during the 2012 feasibility study and during 2014 were additionally examined for internal injuries and none were noted.

23 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

The overall demographics of fish sampled during 2014 were similar to those in 2015. There was no detectable difference in the samples for the mean age and length of Broad Whitefish. However, a difference was observed in mean weights of Broad Whitefish between 2014 and 2015. The difference in mean weight is thought to be attributable to the greater number of male fish less than age-5 in 2015. We determined that male Broad Whitefish weigh less than females and younger fish weigh less than older fish. Several factors may have contributed to more young Broad Whitefish being observed during 2015 including improved recruitment to the spawning population, reduced fishing pressure, improved environmental conditions that affected spawning maturity, and independent spawning aggregates returning between years. The frequency of spawning in consecutive years for Broad Whitefish in the Kuskokwim River is unknown but can be affected by several factors influencing gamete development. Information collected during 2014 and 2015 indicate the samples were unique from one another because there was only one recapture between years. This could be evidence that Broad Whitefish skip spawn some years or that the sample population is much larger than expected. All fish handled during 2014 were double marked and tag loss is not considered a factor. Future sampling should span a minimum of four years if recapturing fish is a goal and if spawning in alternate years or infrequent spawning is prevalent. This would allow for at least one full recapture event and a complete assessment of Broad Whitefish spawning near McGrath, Alaska. Age, length, and weight data for Broad Whitefish spawning near McGrath illustrate substantial diversity. Ages of putative spawning adults range from 2 years to 26 years and average 8.5 years. Most recruitment to the spawning population begins near ages 4 and 5 based on our study. Age (median = 9; range 5–16 yr), length (median = 540 mm FL; range 390–640 mm FL) and weight (median = 2.25; range 0.72–3.43 kg) data of Broad Whitefish (n ≤ 119) collected from the middle Yukon River (Carter 2010) were similar to the information collected in the upper Kuskokwim River during 2014 and 2015. Lengths of Broad Whitefish captured for radio- tagging between 2003 and 2005 in Teshekpuk Lake Region of the National Petroleum Reserve were also similar to those observed in the upper Kuskokwim River during 2014 and 2015 (Morris 2006). Brown (2009) also identified Broad Whitefish (n = 23) with similar lengths (median = 520 mm FL; range 460–615 mm FL) and weights (median = 1.81 kg; range 1.32–3.22 kg) from the upper Koyukuk River drainage between 2003 and 2005. The Broad Whitefish collected from the upper Kuskokwim River during 2014 and 2015 show that lengths and weights also substantially overlap for multiple age classes. A general trend of positive growth in terms of length was observed as fish aged. However, slower growth was also observed in weight-length relationships as fish aged and became less rotund as they grew in length. Recommendations for future whitefish work include an assessment of exploitation and abundance of mature Broad Whitefish in the Kuskokwim River drainage and further radiotelemetry work to identify any potential effects of a boat-mounted electrofishing unit on Broad Whitefish. Understanding what percentage of the spawning population is being exploited annually can be used to assess fishery impacts on the population. Presently, the whitefish fishery is unrestricted on the Kuskokwim River and species-specific harvest and abundance information is virtually unknown. Although fewer than five marked Broad Whitefish were reported as harvested, it is noteworthy that these fish were harvested in the lower Kuskokwim River between Tuluksak and Bethel, Alaska, during late November. The few reported marked fish indicate that Broad Whitefish can travel long distances in a short time after spawning to seek overwintering habitat. However, there was no effort to notify subsistence users about the marked fish nor was there incentive to report a marked fish.

24 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

In conclusion, an electrofishing unit operated from a boat was a very effective technique and presently the most feasible method available to capture, handle, and release large numbers of Broad Whitefish from the Kuskokwim River with relatively minimal effort. Sampling and marking Broad Whitefish near McGrath, Alaska, with multiple field crews could yield much larger sample sizes than was done during 2014 and 2015. In addition, future sampling should extend into October until freeze up when densities of fish are likely much higher. We also recommended that the Broad Whitefish population spawning near McGrath, Alaska, be quantified. A mark-recapture study and actively notifying subsistence users throughout the Kuskokwim River drainage of the importance of reporting harvested marked fish could provide the first useful information to identify exploitation rates, locations and times, and abundance. More information on Broad Whitefish is needed to inform the development of management goals. Acknowledgements Special appreciation is extended to all those who participated in project setup and support, data collection, and analysis. Austin Huff, Andrew Waldo, and Taylor Gregory were responsible for project operations and data collection during 2014. Andrew Waldo, Mike Canino, and Chanice Davies were responsible for project operations and data collection during 2015. Chanice Davies literally ground her way mounting, grinding and reading fin-ray ages. A special thanks to the Koyukuk/ Nowitna/ Innoko National Wildlife Refuge Complex staff who were responsible for loaning equipment and building facilities for field operations based out of McGrath, Alaska.

25 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

References Alt, K. T. 1972. A life history study of Sheefish and whitefish in Alaska. Federal Aid in Fisheries Restoration, Annual Report of Progress, 1971-1972. Project F-9-4, R II. Alaska Department of Fish and Game, Sportfish Division, Juneau, Alaska. Alt, K. T. 1976. Age and growth of Alaskan Broad Whitefish, Coregonus nasus. Transactions of the American Fisheries Society 105:526-528. Alt, K. T. 1979. Contributions to the life history of the Humpback Whitefish in Alaska. Transactions of the American Fisheries Society 108:156-160. Anderson, R. O. and R. M. Neumann. 1996. Length, weight, and associated structural indices. Pages 447-482 in B.R. Murphy and D.W. Willis, editors. Fisheries Techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland. Beamish, R. J., and G. A. McFarlane. 1983. The forgotten requirement for age validation in fisheries biology. Transactions of the American Fisheries Society 112:735-743. Bogdanov,V. D., S. M. Mel'nichenko, and I. P. Mel'nichenko. 1992. Larval whitefish from the spawning region in the Man'ya River (Lower Ob Basin). Journal of Ichthyology 32:1-9. Bond, W. A., and R. N. Erickson. 1985. Life history studies of anadromous coregonid fishes in two freshwater lake systems on the Tuktoyaktuk Peninsula, Northwest Territories. Department of Fisheries and Oceans, Canadian Technical Report of Fisheries and Aquatic Sciences, Number 1336, Winnipeg. Brown, C. M. 1985. Alaska’s Kuskokwim River region: a history. Bureau of Land Management, Anchorage, Alaska. Brown, R. J. 2000. Migratory patterns of Yukon River Inconnu as determined with otolith microchemistry and radiotelemetry. Master’s thesis, University of Alaska Fairbanks. Brown, R. J. 2004. A biological assessment of whitefish species harvested during the spring and fall in the Selawik River delta, Selawik National Wildlife Refuge, Alaska. U.S. Fish and Wildlife Service, Alaska Fisheries Technical Report Number 77, Fairbanks, Alaska. http://alaska.fws.gov/fisheries/fish/reports.htm Brown, R. J. 2006. Humpback Whitefish, Coregonus pidschian, of the upper Tanana River drainage. U.S. Fish and Wildlife Service, Alaska Fisheries Technical Report Number 90, Fairbanks, Alaska. http://alaska.fws.gov/fisheries/fish/reports.htm Brown, R. J. 2009. Distribution and demographics of whitefish species in the upper Koyukuk River drainage, Alaska, with emphasis on seasonal migrations and important habitats of Broad Whitefish and Humpback Whitefish. U.S. Fish and Wildlife Service, Alaska Fisheries Technical Report Number 104, Fairbanks, Alaska. http://alaska.fws.gov/fisheries/fish/reports.htm Brown, R. J. and J.M. Burr. 2012. A radiotelemetry investigation of the spawning origins of Innoko River Inconnu (sheefish). Alaska Department of Fish and Game, Fishery Data Series Number 12-54, Anchorage, Alaska. Brown, R. J., C. Brown; N. M. Braem, W. K. Carter III, N. Legere, and L. Slayton. 2012. Whitefish biology, distribution, and fisheries in the Yukon and Kuskokwim river drainages in

26 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

Alaska: a synthesis of available information. U.S. Fish and Wildlife Service, Alaska Fisheries Data Series Number 2012-4, Fairbanks, Alaska. Carter, W. K. 2010. Life history and spawning movements of Broad Whitefish in the middle Yukon River. Master’s Thesis, University of Alaska Fairbanks. www.arlis.org/docs/vol1/B/608584074.pdf Chilton, D. E., and R. J. Beamish. 1982. Age determination for fishes studied by the Groundfish Program at the Pacific Biological Station. Canadian Special Publication of Fisheries and Aquatic Sciences 60. Chilton, D. E., and H. T. Bilton. 1986. New method for ageing Chinook Salmon (Oncorhynchus tshawytscha) using dorsal fin rays, and evidence of its validity. Canadian Journal of Fisheries and Aquatic Sciences 43(8):1588-1594. Cochran, W. G. 1977. Sampling techniques, third edition. John Wiley and Sons, New York. Dorava, J. M. 1994. Overview of environmental and hydrogeologic conditions at McGrath, Alaska. U.S. Geological Survey, Open-File Report 94-119, Anchorage, Alaska. Dynesius, M., and C. Nilsson. 1994. Fragmentation and flow regulation of river systems in the northern third of the world. Science 266:753-762. Fall, J. A., D. Caylor, M. Turek, C. Brown, T. Krauthoefer, B. Davis, and D. Koster. 2007. Alaska subsistence salmon fisheries 2004 annual report. Alaska Department of Fish and Game, Division of Subsistence Technical Paper No. 317. Juneau. Hander, R. F., R. J. Brown, and T. J. Underwood. 2008. Comparison of Inconnu spawning abundance estimates in the Selawik River, 1995, 2004, and 2005, Selawik National Wildlife Refuge. U.S. Fish and Wildlife Service, Alaska Fisheries Technical Report Number 99. Harper, K. C., F. Harris, R. Brown, T. Wyatt, and D. Cannon. 2007. Stock assessment of Broad Whitefish, Humpback Whitefish and Least Cisco in Whitefish Lake, Yukon Delta National Wildlife Refuge, Alaska, 2001-2003. U.S. Fish and Wildlife Service, Alaska Fisheries Technical Report Number 88, Kenai, Alaska. Available: http://alaska.fws.gov/fisheries/fish/reports.htm (accessed on December 2011). Harper, K. C., F. Harris, S. Miller, and D. Orabutt. 2009. Migration timing and seasonal distribution of Broad Whitefish, Humpback Whitefish, and Least Cisco from Whitefish Lake and the Kuskokwim River, Alaska 2004 and 2005. U.S. Fish and Wildlife Service, Alaska Fisheries Technical Report Number 105, Kenai, Alaska. http://alaska.fws.gov/fisheries/fish/reports.htm Harper, K. C., F. Harris, S. J. Miller, J. M. Thalhauser, and S. D. Ayers. 2012. Life history traits of adult Broad Whitefish and Humpback Whitefish. Journal of Fish and Wildlife Management 3:56-75. Howland, K. L., R. F. Tallman, and W. M. Tonn. 2000. Migration patterns of freshwater and anadromous Inconnu in the Mackenzie River system. Transactions of the American Fisheries Society 129:41-59. Howland, K. L., M. A. Treble, and R. F. Tallman. 2001. A biological analysis and population assessment of Northern Pike, Inconnu and Lake Whitefish from the Mackenzie River delta exploratory fishery, 1989-1993. Canadian Technical Report of Fisheries and Aquatic Sciences 2330.

27 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

Kammerer, J. C. 1990. Largest rivers in the United States. Department of the Interior, U.S. Geological Survey, Water Fact Sheet, Open-File Report 87-242. http://pubs.usgs.gov/of/1987/ofr87-242/ Koo, T. S. Y. 1962. Age determination in salmon. Pages 37-48 in T. S. Y. Koo, editor. Studies of Alaskan red salmon. University of Washington Press, Seattle, Washington. Krauthoefer, T., J. Simon, M. Coffing, M. Kerlin, and W. Morgan. 2007. The harvest of non- salmon fish by residents of Aniak and Chuathbaluk, Alaska, 2001-2003. Alaska Department of Fish and Game, Division of Subsistence, Technical Paper No. 299, Juneau, Alaska. Lenth, R.V. 2006-9. Java Applets for power and sample size [computer software]. Retrieved March 2013 from http://www.stat.uiowa.edu/~rlenth/Power. McDermid, J. L., J. D. Reist, and R. A. Bodaly. 2005. Phylogeography and postglacial dispersal of whitefish (Coregonus clupeaformis complex) in northwestern North America. Advances in Limnology 60:91-109. McPhail, J. D., and C. C. Lindsey. 1970. Freshwater fishes of Northern Canada and Alaska. Fisheries Research Board of Canada, Bulletin 173. Mills, K. H., and R. J. Beamish. 1980. Comparison of fin-ray and scale age determinations for Lake Whitefish Coregonus clupeaformus and their implications for estimates of growth and annual survival. Canadian Journal of Fisheries and Aquatic Sciences 37:534-544. Mills, K. H., and S. M. Chalanchuk. 2004. The fin ray method of aging Lake Whitefish. Annals Zologici Fennici 41:215-223. Morris, W. 2006. Seasonal movements and habitat use by Broad Whitefish Coregonus nasus in the Teshekpuk Lake region of the National Petroleum Reserve-Alaska, 2003-2005. Alaska Department of Natural Resources, Office of Habitat Management and Permitting, Technical Report Number 06-04. Mosher, K. H. 1968. Photographic atlas of sockeye salmon scales. U.S. Fish and Wildlife Service, Bureau of Commercial Fisheries, Fishery Bulletin Number 2:243-274. Moulton, L. L., L. M. Philo, and J. C. George. 1997. Some reproductive characteristics of Least Ciscoes and Humpback Whitefish in Dease Inlet, Alaska. American Fisheries Society Symposium 19:119-126. Naesje, T. F., B. Jonsson, and O. T. Sandlund. 1986. Drift of cisco and whitefish larvae in a Norwegian River. Transactions of the American Fisheries Society 115:89-93. Naesje, T. F., B. Jonsson, and J. Skurdal. 1995. Spring flood: a primary cue for hatching of river spawning Coregoninae. Canadian Journal of Fisheries and Aquatic Sciences 52:2,190-2,196. National Oceanic and Atmospheric Administration, National Weather Service, Alaska Pacific River Forecast Center. 2013. Freeze up data. https://www.weather.gov/aprfc/freezeUp National Oceanic and Atmospheric Administration, National Weather Service, Alaska Pacific River Forecast Center, Historical River Observation Database. http://www.weather.gov/aprfc/rivobs#. Prasolov, P. P. 1989. On the biology of the Broad Whitefish, Coregonus nasus, from the lower Ob River basin. Journal of Ichthyology 29:47-53.

28 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

Reist, J. D., and W. A. Bond. 1988. Life history characteristics of migratory coregonids of the lower Mackenzie River, Northwest Territories, Canada. Finnish Fishery Research 9:133-144. Revenga, C., S. Murray, J. Abramovitz, and A. Hammond. 1998. Watersheds of the world: ecological value and vulnerability. World Resources Institute, Washington, DC. Reynolds, J. B. 1996. Electrofishing. Pages 221–253 in B. R. Murphy and D. W. Willis, editors. Fisheries techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland. Russell, R. 1980. A fisheries inventory of waters in the Lake Clark National Monument area. Alaska Department of Fish and Game, Division of Sport Fish, and U.S. Department of the Interior, National Park Service, Juneau. http://science.nature.nps.gov/im/units/swan/index.cfm?theme=inventory_species Accessed August 15, 2012 Shestakov, A. V. 1991. Preliminary data on the dynamics of the downstream migration of coregonid larvae in the Anadyr River. Journal of Ichthyology 31:65-74. Shestakov, A. V. 1992. Spatial distribution of juvenile coregonids in the floodplain zone of the middle Anadyr River. Journal of Ichthyology 32:75-85. Shestakov, A. V. 2001. Biology of the Broad Whitefish Coregonus nasus (Coregonidae) in the Anadyr basin. Journal of Ichthyology 4:746-754. Simon, J., T. Krauthoefer, D. Koster, and D. Caylor. 2007. Subsistence salmon harvest monitoring report, Kuskokwim fisheries management area, Alaska, 2004. Alaska Department of Fish and Game, Division of Subsistence, Technical Paper 313, Juneau, Alaska. Stein, J. N., C. S. Jessop, T. R. Porter, and K. T. J. Chang-Kue. 1973. Fish resources of the Mackenzie River valley, interim report II. Canada Department of the Environment, Fisheries Service, Winnipeg. Stuby, L. 2010. Spawning locations, seasonal distribution, and migratory timing of Kuskokwim River Sheefish using radiotelemetry, 2007-2009. Alaska Department of Fish and Game, Fishery Data Series Number 10-47, Anchorage. Tallman, R. F., M. V. Abrahams, and D. H. Chudobiak. 2002. Migration and life history alternatives in a high latitude species, the Broad Whiteﬁsh, Coregonus nasus Pallas. Ecology of Freshwater Fish 11:101–111. Thompson, S. K. 1987. Sample size for estimating multinomial proportions. The American Statistician 41:42-46. Underwood, T. J. 2000. Abundance, length composition, and migration of spawning inconnu in the Selawik River, Alaska. North American Journal of Fisheries Management 20:386-393. U.S. Fish and Wildlife Service. 1988. Yukon Delta National Wildlife Refuge: Final Comprehensive Conservation Plan, Environmental Impact Statement. U.S. Department of the Interior, Anchorage, Alaska. U.S. Fish and Wildlife Service. 2004. Electrofishing. Chapter 6, part 241. Safety operations, occupational safety and health. USFWS, Washington, D.C.

29 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

U.S. Fish and Wildlife Service. 2012. Priority information needs: federal subsistence fisheries, 2014 Fisheries Resource Monitoring Program. Pages 167–171 in Yukon-Kuskokwim Delta subsistence Regional Advisory Council meeting materials, October 10–11, 2012. U.S. Fish and Wildlife Service, Office of Subsistence Management Anchorage, Alaska. Van Gerwen-Toyne, M., J. Walker-Larsen, and R. F. Tallman. 2008. Monitoring spawning populations of migatory coregonids in the Peel River NWT: the Peel River fish study 1998-2002. Canadian Manuscript Report of Fisheries and Aquatic Sciences 2851, Winnipeg. Yule, D. L., J. D. Stockwell, J. A. Black, K. I. Cullis, G. A. Cholwek, and J. T. Myers. 2008. How systematic age underestimation can impede understanding of fish population dynamics: lessons learned from a Lake Superior cisco stock. Transactions of the American Fisheries Society 137:481–495.

30 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

31 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

APPENDIX 1. —Comparison of sex (% female: t = 0.232; df = 207; P = 0.817), length (t = 1.86; df=185; P = 0.064), and weight (t = 2.28; df = 259; P = 0.053) of Broad Whitefish including 95% confidence intervals captured with a boat-mounted electrofishing unit and set gillnets during a feasibility study conducted near McGrath, Alaska, 2012 (U.S. Fish and Wildlife Service, unpublished data).

1850 Electrofisher Gill Net 1800

1750

1700

1650

1600

1550 AverageAverage weightweight (g) (g) 1500

1450

1400

495 Electrofisher Gill Net 490

485

480

475

470

465 AverageAverage fork fork length length (mm) (mm) 460

455

100%

90% Electrofisher Gill Net

80%

70%

60%

50%

40%

30% FemaleFemale contribution contribution (%) (%) 20%

10%

Capture method

32 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

APPENDIX 2. —Comparisons of sex, length, and weight of Broad Whitefish including 95% confidence intervals over three time strata from September 18 to October 11, 2012. Stratum 1 and 3 were comprised of 5 days, whereas stratum 2 was 14 days (U.S. Fish and Wildlife Service, unpublished data).

2400

2200

2000

1800

1600 Average weight (g)

1400

1200

510 505 500 495 490 485 480 475

Average fork length (mm) 470 465 460

45%

40%

35%

30%

25%

20%

15%

Female contribution (%) 10%

Stratum 1 Stratum 2 Stratum 3

33 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

APPENDIX 3. —A graph of sample size versus confidence levels to determine sample size when no prior knowledge of population proportions exists. This figure was adapted from Table 1 in Thompson (1987). A margin of error of 0.05 is considered to be the worst/best case (Thompson 1987) and is fixed at 0.05 for this figure.

0.95 0.9

0.85 0.8

0.75 0.7

Confidence Level 0.65 0.6

0.55

0.5 0 200 400 600 800 1000 1200 1400 1600 1800

Sample size

34 Alaska Fisheries Data Series Number 2017-06, November 2017 U.S. Fish and Wildlife Service

APPENDIX 4. —Composition of male and female Broad Whitefish by age during 2014 and 2015 sampling near McGrath, Alaska. 2014 2015 Cumulative Cumulative Age (yr) Male (n ) Female (n ) N Proportion Proportion Male (n ) Female (n ) N Proportion Proportion

2 1 0 1 0.0017 0.0017 3 9 0 9 0.0152 0.0169 4 7 2 9 0.0150 0.0150 44 2 46 0.0776 0.0944 5 47 18 65 0.1083 0.1233 31 13 44 0.0742 0.1686 6 69 49 118 0.1967 0.3200 32 14 46 0.0776 0.2462 7 37 39 76 0.1267 0.4467 59 24 83 0.1400 0.3862 8 55 30 85 0.1417 0.5883 66 37 103 0.1737 0.5599 9 47 23 70 0.1167 0.7050 46 19 65 0.1096 0.6695 10 25 22 47 0.0783 0.7833 36 23 59 0.0995 0.7690 11 34 15 49 0.0817 0.8650 29 17 46 0.0776 0.8465 12 17 6 23 0.0383 0.9033 25 11 36 0.0607 0.9073 13 11 5 16 0.0267 0.9300 12 9 21 0.0354 0.9427 14 4 8 12 0.0200 0.9500 11 2 13 0.0219 0.9646 15 6 0 6 0.0100 0.9600 10 0 10 0.0169 0.9815 16 3 3 6 0.0100 0.9700 3 1 4 0.0067 0.9882 17 5 2 7 0.0117 0.9817 3 1 4 0.0067 0.9949 18 3 2 5 0.0083 0.9900 0 2 2 0.0034 0.9983 19 3 0 3 0.0050 0.9950 0 0 0 0.0000 0.9983 20 0 0 0 0.0000 0.9950 0 0 0 0.0000 0.9983 21 1 0 1 0.0017 0.9967 0 0 0 0.0000 0.9983 22 1 0 1 0.0017 0.9983 1 0 1 0.0017 1.0000 23 0 0 0 0.0000 0.9983 24 0 0 0 0.0000 0.9983 25 0 0 0 0.0000 0.9983 26 1 0 1 0.0017 1.0000