Alternative tactics in spawning site selection by brook trout (Salvelinus fontinalis) related to incubation microhabitats in a harsh winter environment

Abstract

Summary 1. Species with distributions that span a broad range of latitudes may have populations that exhibit distinct life history traits associated with environmental gradients. The majority of previous studies have indicated a strong association between spawning site selection by brook trout (Salvelinus fontinalis) and the presence of upwelling groundwater, but does this generalisation extend to the thermal regimes experienced at northern sites? 2. We investigated the role of hyporheic flow in redd site selection by brook trout in a relatively high‐latitude boreal system. Hyporheic flows through streambed substratums can be dominated by groundwater or surface water and may be influenced by the presence of morphological features. For autumn spawners such as brook trout, embryos situated in microhabitats where hyporheic flow in the shallow substratum is groundwater dominant (i.e. warmer in winter) are likely to experience accelerated development rates relative to embryos in redds where there is downwelling surface water (i.e. colder in winter). 3. We measured vertical hydraulic gradients (VHG) at the microhabitat scale and spatial and temporal variation in upwelling/downwelling flow and thermal regimes in brook trout spawning/incubation habitats. Additionally, we noted the proximity of redd sites to stream morphological features (e.g. riffle crests). 4. Our results indicate that upwelling flow was not a decisive cue in redd site selection at the microhabitat scale (100 m) as an approximately equal number of redds were situated in microhabitats with upward flow as compared to microhabitats with downward flow through the redd. Redds situated on bedforms with convex longitudinal profiles (e.g. riffle crests, log steps) were associated with downward flow, whereas redds not immediately adjacent to these bedform features were associated with upward flow. Winter streambed temperatures confirmed that both sites with steady upwelling (i.e. warm incubation regime) and downwelling (i.e. cold incubation regime) were indeed selected by spawners. 5. Our observations that spawners utilised both cold‐regime and warm‐regime sites suggests the existence of distinct reproductive tactics related to hyporheic flow patterns in this boreal system. As temperature is the dominant factor controlling rates of embryonic development, the use of spawning microhabitats with distinct thermal regimes implies substantial differences in the timing of hatching and the phenology of emergence.

Effects of fine sediment, hyporheic flow, and spawning site characteristics on survival and development of bull trout embryos

“…Although the sample size was small, the majority of natural redds were located on convex or transitional bedforms, where downwelling was prevalent (Bowerman 2013). Other researchers have also observed that bull trout and closely related brook trout (Salvelinus fontinalis) often select spawning microhabitats with localized downwelling (Baxter and Hauer 2000;Franssen et al 2013). In this study, the greatest downwelling rates occurred at spawning sites located above steep riffles and logjams, each of which created a defined vertical step in the streambed.…”

“…3). Within each redd where data were available, the difference between intragravel and surface water temperature was calculated as ⌬T = |intragravel temperaturestream temperature| (Franssen et al 2013). Groundwater inputs into shallow streambed sediments can be identified by high ⌬T (e.g., ⌬T > 2) and stable hyporheic temperatures similar to average groundwater temperatures in the Metolius basin (7 to 9°C; Gannett et al 2003).…”

“…Groundwater inputs into shallow streambed sediments can be identified by high ⌬T (e.g., ⌬T > 2) and stable hyporheic temperatures similar to average groundwater temperatures in the Metolius basin (7 to 9°C; Gannett et al 2003). In contrast, intragravel temperatures that exhibit diel fluctuations and low ⌬T (e.g., ⌬T < 2) more likely indicate hyporheic conditions substantially influenced by surface water (Franssen et al 2013). To test for groundwater upwelling into non-redd shallow sediments, a temperature sensor was installed in undisturbed sediment at a depth of 20 cm in the middle of each study area.…”

Physical Controls on Salmon Redd Site Selection in Restored Reaches of a Regulated, Gravel‐Bed River

“…Surface water infiltration into the streambed is driven by gradients in bed topography and water surface elevation, which are greatest near riffle crests (Marzadri et al, 2010;Tonina & Buffington, 2007). While hyporheic fluxes often are proposed as important cues for salmon redd site selection, previous studies have reported mixed results, with some finding that redds were located in areas of high hyporheic flows (Baxter & Hauer, 2000;Bean et al, 2015;Geist & Dauble, 1998), while others did not (Benjankar et al, 2016;Curry & Noakes, 1995;Franssen et al, 2013).…”

Convergent polymorphism between stream and lake habitats: the case of brook char

“…Alternately, phenotypic divergence may arise from differences in developmental patterns associated with rearing habitat. In this region, most stream-dwelling brook trout spawn in riffle-crest habitats associated with up-or downwelling flows (Franssen et al 2013), making reproduction isolation an unlikely driver of phenotypic variation. Without interspecific competition and (or) predation (at least from other fish), fish in this system would fill available areas in an assortative manner based on hierarchy and home territories.…”