Environ Biol Fish DOI 10.1007/s10641-014-0247-6 New insight into the spawning behavior of lake trout, Salvelinus namaycush, from a recovering population in the Laurentian Great Lakes T. R . B i n d e r & H. T. Thompson & A. M. Muir & S. C. Riley & J. E. Marsden & C. R. Bronte & C. C. Krueger Received: 3 July 2013 /Accepted: 18 February 2014 # Springer Science+Business Media Dordrecht 2014 Abstract Spawning behavior of lake trout, Salvelinus expand the current conceptual model. Lake trout namaycush, is poorly understood, relative to stream- spawning consisted of at least four distinct behaviors: dwelling salmonines. Underwater video records of hovering, traveling, sinking, and gamete release. spawning in a recovering population from the Hovering is a new courtship behavior that has not been Drummond Island Refuge (Lake Huron) represent the previously described. The apparent concentration of first reported direct observations of lake trout spawning hovering near the margin of the spawning grounds in the Laurentian Great Lakes. These observations pro- suggests that courtship and mate selection might be vide new insight into lake trout spawning behavior and isolated from the spawning act (i.e., traveling, sinking, and gamete release). Moreover, we interpret jockeying for position displayed by males during traveling as a T. R. Binder (*) unique form of male-male competition that likely Great Lakes Fishery Commission and Michigan State evolved in concert with the switch from redd-building University, Hammond Bay Biological Station, 11188 Ray Rd., Millersburg, MI 49759, USA to itinerant spawning in lake trout. Unlike previous e-mail: [email protected] models, which suggested that intra-sexual competition and mate selection do not occur in lake trout, our model H. T. Thompson includes both and is therefore consistent with evolution- United States Geological Survey, Hammond Bay Biological Station, 11188 Ray Rd., ary theory, given that the sex ratio on spawning grounds Millersburg, MI 49759, USA is skewed heavily towards males. The model presented : in this paper is intended as a working hypothesis, and A. M. Muir C. C. Krueger further revision may become necessary as we gain a Great Lakes Fishery Commission, 2100 Commonwealth Blvd. Suite 100, Ann Arbor, MI 48105, more complete understanding of lake trout spawning USA behavior. S. C. Riley . Great Lakes Science Center, United States Geological Survey, Keywords Reproductive ecology Itinerant spawning 1451 Green Rd., Ann Arbor, MI 48105, USA Courtship . Male-male competition J. E. Marsden The Rubenstein School of Environment and Resources, University of Vermont, Introduction 308D Aiken Center, Burlington, VT 05405, USA Lake trout, Salvelinus namaycush, were the apex pred- C. R. Bronte United States Fish and Wildlife Service, ator in the Laurentian Great Lakes, and supported a 2661 Scott Tower Drive, New Franklin, WI 54229, USA valuable commercial fishery until the 1950s. However, Environ Biol Fish after invasion of the upper Great Lakes by predatory sea rocky substrates with clean interstitial spaces where lamprey, Petromyzon marinus, lake trout populations, embryos incubate over winter (Gunn 1995; Marsden already in decline due to expanding commercial harvest et al. 1995). Males mature at younger ages, arrive on (Hile 1949;Hileetal.1951), were lost from all but a few spawning grounds earlier and stay longer, and are gen- regions of lakes Superior (Hansen et al. 1995)and erally present in higher numbers than females (Royce Huron (Eshenroder et al. 1995). Despite intensive sea 1951;Eschmeyer1955; Martin 1957;McCrimmon lamprey control (Smith and Tibbles 1980) and more 1958;DeRoche1969; Peck 1986;Bronteetal.2007; than 50 years of stocking juvenile lake trout, self- Muir et al. 2012b). Females arrive on spawning grounds sustaining populations have only recovered where rem- after males and appear to remain for a shorter duration nant stocks remained after the crash, in Lake Superior than males. However, contrary to reproductive theory, (Hansen 1999;Bronteetal.2003) and in Parry Sound, which predicts that males should compete for females Lake Huron (Reid et al. 2001). In lakes Michigan, Erie when the sex ratio on spawning grounds is skewed and Ontario, rehabilitation has been slow and popula- towards males (Clutton-Brock and Parker 1992; tions continue to rely on stocking (Muir et al. 2012a). Kvarnemo and Ahnesjö 1996), observations of agonis- However, catches of wild lake trout juveniles and adults tic interactions among males are rare (Royce 1951; in annual assessments over the last decade suggest that Esteve et al. 2008;Muiretal.2012b). reproduction is widespread in Lake Huron (Riley et al. Three distinct spawning behaviors have been previ- 2007;Heetal.2012) and increasing in Lake Michigan ously identified from observations of lake trout (Hanson et al. 2013). For example, in the Drummond spawning at a shallow-water (<1 m) site in Kushog Island area of northern Lake Huron, wild fish now Lake, in southern Ontario (Esteve et al. 2008): 1) trav- comprise about 50 % of the adult spawning population eling, 2) sinking, and 3) gamete release. Within the (He et al. 2012), but population density is still below context of mating ritual, these behaviors are expressed historic levels. The recent reproductive success of lake as follows. Courtship begins with traveling, wherein a trout in Lake Huron presents a useful opportunity to female swims rapidly over spawning grounds with one understand the reproductive ecology of lake trout from or more attending males alongside or behind. Males a recovering population in the Great Lakes. quiver next to her and brush and nibble at her vent Compared to stream-spawning salmonines, relatively region. After making several large loops, the female little is known about spawning behavior of lake trout. and attending male(s) stop swimming and sink slowly Direct observations of spawning behavior are rare be- to the substrate. Once on the substrate, the group quivers cause lake trout spawn mainly at night, in deeper water vigorously with jaws agape and release gametes into the than stream-spawning salmonines, and during a logisti- substrate. Following gamete release, which lasts only a cally challenging season for field observations when second or two, the group returns immediately to travel- autumn weather changes to winter. Most information ing and the cycle is repeated (Esteve et al. 2008). Muir comes primarily from studies in small inland lakes et al. (2012b) expanded that conceptual model, based on (Martin 1957;McCrimmon1958;Gunn1995; Esteve observations at Great Bear Lake, Northwest Territories, et al. 2008). Most studies in the Great Lakes described to include splashing and porpoising display courtship, variables that affected timing and location of spawning and a novel display behavior that they termed ‘finning’. activity, and density, origin, and composition of recov- Finning involved two or more lake trout hovering or ering spawning populations, rather than spawning be- moving very slowly just beneath the surface of the havior (e.g., Eschmeyer 1955; Peck 1986; Marsden and water. The name ‘finning’ refers to the fully erect dorsal Krueger 1991; Selgeby et al. 1995;Bronteetal.2002; and adipose fins that conspicuously broke the water Claramunt and Jonas 2005). In the Great Lakes, lake surface. While jumping has been observed in studies trout spawn on shoals, although some historical popu- on other lakes (Merriman 1935; Royce 1951;Marsden lations were adfluvial (Loftus 1958). Spawning occurs and Krueger 1991), finning has not been observed out- mainly in October and November for the lean side of Great Bear Lake. This may indicate greater morphotype, but timing varies with latitude and weather dependence on visual courtship displays in Great Bear (DeRoche 1969; Peck 1986; Scott and Crossman 1998). Lake, a hypothesis supported by a greater degree of Unlike other salmonines, lake trout do not construct sexual dimorphism among lake trout populations in nests (i.e., redds). Lake trout deposit their eggs over Great Bear Lake, relative to more southern lakes (Muir Environ Biol Fish et al. 2012b). Alternatively, an absence of observations of high-quality spawning habitat (i.e., several layers of of finning elsewhere may be an artifact of most cobble substrate with clean interstitial spaces for over- spawning behavior studies being limited to spawning winter egg incubation) on the north-most tip of the east sites shallower than 1 m in depth (Merriman 1935; arm of Horseshoe Reef, a submerged drumlin on the Royce 1951; DeRoche 1969; Esteve et al. 2008). south side of Drummond Island (Fig. 1). The spawning In this paper, we describe the first reported observa- site is located on top of the reef in 3 to 4 m of water, tions of spawning behavior in a recovering population adjacent to a steep slope (~ 50°) where water depth of lake trout (lean morphotype) from the Laurentian increases from 4 to 10 m. An ongoing fine-scale acous- Great Lakes. Our objectives were first, to describe tic telemetry study on adult lake trout has identified this spawning behaviors of lake trout at Drummond Island, site as the most highly-used spawning site within the Lake Huron, in comparison to those observed else- 27 km2 study area, and recovery of fertilized eggs and where. Second, based on our observations in Lake emergent fry at this site in 2011, 2012, and 2013 indi- Huron, we revise the current conceptual framework for cated successful spawning (Binder unpubl. data). lake trout spawning behavior. The revised conceptual framework advances a foundation for development of hypotheses centered on understanding the evolution of Video observations the lake trout spawning strategy, which is unique among salmonines. Behaviors reported herein occurred at the peak of the spawning period, on 22 and 24 October 2012. Diver surveys 6 days earlier on 16 October found few lake Materials and methods trout at the site, although eggs were found in the sub- strate, which indicated that some spawning had already Study site occurred.