Assessing the reproductive contributions of sympatric anadromous and freshwater‐resident brook trout

Abstract

The d 13 C, d 15 N and d 34 S isotope values of newly emerged, brook trout Salvelinus fontinalis alevins (free-swimming individuals beginning exogenous feeding) were examined to determine if progeny of anadromous female spawners could be detected and their contributions to reproduction assessed in river systems with mixed migration strategies. Separation of anadromous and freshwater resident and immigrant sources of progeny could be detected primarily using d 13 C values before alevins reached a size of 28 mm fork length and c. 20 days after exogenous feeding began. Among 10 populations, the contributions of anadromous females ranged from 0 to 42% of newly emerged alevins. Correlations between anadromous contributions and estimates of total brook trout density and alevin production were unexpectedly negative. # 2005 The Fisheries Society of the British Isles

The origins and persistence of anadromy in brook charr

“…5). There are distinct, within river groupings which have been reported for other populations of brook charr (Rogers and Curry 2004;Curry 2005); however, the grouping in the three rivers were not explained by movement patterns, i.e., travelling upstream, downstream, or by season. Without clear and consistent genotypic separation of sympatric resident and sea-run forms and given the complex history of re-colonization of the region, we conclude that Hypothesis 1-freshwater resident and anadromous forms are divergent forms in secondary contact, and Hypothesis 2-anadromous forms are emerging repeatedly from freshwater resident populations, are insufficient by themselves to explain the evidence in-hand.…”

“…Size can impart fitness advantages, but densitydependent factors such as intraspecific competition also influence fitness of newly emerged and juvenile salmonids (e.g., McLaughlin et al 1999;Milner et al 2003;Grant and Imre 2005). Where sea-run and residents spawn together, their respective contributions of free-swimming alevins, i.e., newly emerged youngof-the-year, does not appear to be dominated by searun offspring (Curry 2005;Jardine et al 2008). The work of Morinville and Rasmussen (2006) suggests that less suitable habitats for brook charr, i.e., faster flows with greater energetic demands, are used by individuals that migrate to the sea.…”

“…Whatever the mechanism, fewer individuals translates to a smaller effective population size. Curry's (2005) and Jardine et al (2008) observation of variable and unexpected low reproductive contributions of sea-run females to some populations may reflect the threat of low numbers of this form in these populations. Ultimately, the loss of sea-run forms translates to a continuing threat to the aquatic biodiversity of the region (http://www.eman-rese.ca/ eman/reports/publications/rt_biostrat) where the fish species richness is already depauperate as a consequence of the last glaciations (e.g., Curry 2007).…”

Discrimination between farmed and free-living invasive salmonids in Chilean Patagonia using stable isotope analysis

“…Somatic growth is likely to be the factor that affects isotopic discrimination of aquaculture escapees the most, because growth affects carbon and nitrogen turnover rates, and therefore the production of new tissue (Herzka and Holt 2000;Bosley et al 2002;Jardine et al 2004). Data from North America indicates that brook trout alevins originating from anadromous parents lose their maternal marine signature when they reach *30 mm in length, corresponding to a fivefold increase in weight (Curry 2005). In the Connecticut River, juvenile Atlantic salmon retained distinct hatchery-specific SIS for 5 weeks, and C signatures from the hatchery were still detectable in the scales of 3 month-old fish (Kennedy et al 2005).…”

Estimating Differential Reproductive Success From Nests of Related Individuals, With Application to a Study of the Mottled Sculpin,Cottus bairdi

“…Nielsen et al (2001) used this approach to compare the reproductive success of dominant and subordinate males in North Atlantic humpback whales. A multitude of questions in evolutionary and conservation biology can be addressed with this approach: examples include estimating whether there are differences in reproductive success between nest-tending and cuckolding males (Neff et al 2000), resident vs. immigrant males ( Johannesen and Andreassen 1998), freshwater vs. anadromous trout (Curry 2005), wild vs. hatchery-reared fish (Dannewitz et al 2004), or different age classes of individuals that contribute to particular nests (Røed et al 2005).…”