Environ Biol Fish (2015) 98:755–762 DOI 10.1007/s10641-014-0309-9 The effect of multiple spawning events on cohort genetic diversity of lake sturgeon (Acipenser fulvescens) in the Kaministiquia River Amy B. Welsh & Melinda R. Baerwald & Michael Friday & Bernie May Received: 4 December 2013 /Accepted: 9 July 2014 /Published online: 18 July 2014 # Crown Copyright as represented by: The Province of Ontario 2014 Abstract Lake sturgeon Acipenser fulvescens popula- were also measured in the adult population (n=85).The tions have experienced declines throughout much of the larval cohorts had a high Nb (2005: 54; 2006: 73) Great Lakes. Understanding key demographic charac- relative to the Ne of the adult population (Ne=28). teristics about lake sturgeon populations can help iden- Multiple spawning events did not result in more tify potential limiting factors to their recovery. Within a breeders, but did result in lower relatedness among the single spawning season, there may be multiple resulting offspring. Therefore, environmental factors spawning events, which could affect genetic diversity should be maintained that encourage an extended of the resulting cohort. Our objective was to determine spawning season, increasing the likelihood of multiple whether multiple discrete spawning events resulted in a spawning events and decreasing the relatedness among larger effective number of breeders and higher genetic individuals in the cohort. diversity. Larval samples were collected following the spawning periods in 2005 (n=479) and 2006 (n=279). In 2005, there were two discrete spawning events and a Keywords Lake sturgeon Genetic Number of . longer spawning season; in 2006, the spawning events breeders Multiple spawning events were less discrete and the spawning season was shorter. Genetic samples from larval sturgeon were analyzed at 12 microsatellite loci. The effective number of breeders Introduction (Nb), genetic diversity (observed heterozygosity, expect- ed heterozygosity, allelic richness, inbreeding coeffi- Lake sturgeon are found in the Great Lakes, Hudson cient), and relatedness were measured for each cohort. Bay drainage, and the Mississippi River system. Most The effective population size (N ) and genetic diversity e lake sturgeon Acipenser fulvescens populations are be- low historic sizes and the species is listed as endangered A. B. Welsh (*) or threatened in most states and provinces in the U.S. Division of Forestry and Natural Resources, West Virginia and Canada within its historic range (Welsh 2004). University, P.O. Box 6125, Morgantown, WV 26506, USA Primary reasons for their decline include overfishing e-mail: [email protected] and habitat alterations caused by dams, pollution, and M. R. Baerwald : B. May destruction of spawning or nursery habitat (Auer 2004). Department of Animal Science, University of California – Although some of these problems have been alleviated, Davis, 1 Shields Avenue, Davis, CA 95616, USA few lake sturgeon populations have fully recovered, M. Friday likely due to their life history traits. Lake sturgeon are Ontario Ministry of Natural Resources, 173 25th Side Road, a long-lived species with late sexual maturity (females: Rosslyn, ON P7K 0B9, UK 18–27 years of age, males: 12–15 years of age) and 756 Environ Biol Fish (2015) 98:755–762 intermittent spawning (females: once every 4–9years, 800 m downstream of Kakabeka Falls. Multiple annual males: once every 1–3 years) (Peterson et al. 2007). spawning events have been documented in the In the Great Lakes, lake sturgeon spend the majority Kaministiquia River with spawning occurring at tem- of their time in the lakes and enter the rivers and tribu- peratures of approximately 13 °C (mid to late May) and taries to spawn (Harkness and Dymond 1961). Environ- then again at 16 °C (timing variable, up to late June; mental factors, such as water temperature and flow, Friday 2005). In 2005, based on radio telemetry often determine when lake sturgeon enter the spawning data and separate larval drift events, two discrete area. The highest number of arriving adults has been spawning events were identified, with the first occurring observed during periods of lower river discharge and between May 21and May 23 and the second event warming water temperature (Forsythe et al. 2012a). occurring between May 28 and June 3 (Friday 2005). Rivers with conditions affected by hydroelectric opera- Sturgeon either participated only in the first spawning tions could therefore have an impact on lake sturgeon event (n=4; sex unknown) or in both spawning events reproductive success. On the Sturgeon River, the dura- (n=8; sex unknown); no tagged sturgeon participated tion of the spawning season was shortened, more fish only in the second spawning event. In 2006, spawning were observed, and reproductive readiness increased in occurred over a shorter span of time, with less temporal years where flows were close to normal, unregulated distinction between the two spawning events (Friday rates (Auer 1996). 2006). The first spawning event occurred between Within a spawning season, the presence of two May 19 and May 22, followed by a second spawning spawning events at a single site has been observed at eventbetweenMay22andMay26.Basedonthe several places in the Great Lakes (Kempinger 1988; temporal separation between the departure of the first LaPan et al. 2000;AuerandBaker2002; Bruch and and second group of radio tagged lake sturgeon from the Binkowski 2002;Nicolsetal.2003; Smith and King spawning site (3 days) and water temperature differ- 2005). Male lake sturgeon typically enter the spawning ences when these fish were at the spawning site, we area before females and will remain in the spawning concluded that there were two spawning events in 2006. area until most females have departed (Bruch and The first spawning event occurred around May 21 Binkowski 2002). Females, however, will leave the (13.6 °C). The second spawning event occurred on spawning area as soon as they are spent. In the Lake May 24 (15.2 °C). In 2006, two tagged individuals Winnebago system, spawning was interrupted by a drop participated only in the first spawning event, 15 may in water temperature (Bruch and Binkowski 2002). have participated in both spawning events, and one Some males remained in the spawning area and, when sturgeon participated only in the second spawning the water temperature increased, new gravid females event. The objective of our study was to determine the entered the spawning area. In some systems, high indi- effect of discrete spawning events in a single season on vidual repeatability has been observed in spawning the effective number of breeders and genetic diversity of times, resulting in a distinction between early and late the offspring. spawning individuals (Forsythe et al. 2012b). The focus of this study is the lake sturgeon popula- tion on the Kaministiquia River (Ontario, Canada), Methods flowing into Lake Superior. Unlike most other popula- tions in the Great Lakes, the individuals in this popula- Study site and sample collection tion may be year-round river residents (Friday and Chase 2005). High genetic differentiation from other The study area (Easting 306123, Northing 5363936) Great Lakes spawning populations suggests that few stretched 800 m from the base of Kakabeka Falls on migrants enter the river for spawning (Welsh et al. the Kaministiquia River downstream to the generat- 2008). Spawning takes place just downstream of ing station. Drift netting for larvae occurred on the Kakabeka Falls, a 39 m waterfall located approximately east shore of the river approximately 400 m down- 47 km from the confluence of Lake Superior. The river stream of Kakabeka Falls (Fig. 1). Stainless steel, D- flow upstream of Kakabeka Falls is diverted by a control frame drift nets were used that measured 0.76 m dam that transfers water through a series of penstocks to across the base, 0.53 m high, and had a 3.6-m a four-unit generating station located approximately tapered mesh bag that terminated at a collection Environ Biol Fish (2015) 98:755–762 757 Fig. 1 Location of the Kaministiquia River, Ontario, including lake sturgeon spawning site and drift netting and telemetry sites container with filtering holes covered by water, the collection container was detached and the 1,000 μm mesh. In 2005, drift netting was carried contents rinsed out in a shallow white sorting pan. out from June 2 to June 28. Twelve drift nets were Dead larval sturgeons were measured to the nearest deployed during each overnight sampling event (n= millimeter on a white ruler, placed in glass vials and 23) and were set at dusk and lifted the following preserved in 70 % ethanol for genetic analysis. Live day (276 net sets). Nets were set for an average of sturgeon were removed from the sorting pan with an 10.36 h (±0.047 SD). In 2006, drift netting was aquarium net, measured (mm) and immediately re- carried out from June 1 to June 20. Twelve drift leased downstream of the netting site. Water temper- nets were deployed during each overnight sampling ature at the drift net site was recorded hourly using event (n=18) and were set at dusk and lifted the a Vemco Minilog - T data logger. Water velocity following day (216 net sets). Nets were set for an (m s−1) and depth (mm) was measured at the open- average of 10.44 h (±0.052 SD). To examine the ing of each drift net upon deployment. Time of drift catch, the cod end of the net was lifted from the netting corresponded to the first movement of radio- 758 Environ Biol Fish (2015) 98:755–762 tagged adult lake sturgeon from the spawning area lowest allele frequency used was 0.02, and 95 % (n=16 in 2005 and n=14in2006)andtooptimal parametric confidence intervals were calculated. The water temperature for larval hatch (130–150 cumula- effective population size (Ne) of the adult population tive daily water temperature units, based on in the Kaministiquia River (n=85; data published in Kempinger (1988)).