A synthesis of senescence predictions for indeterminate growth, and support from multiple tests in wild lake trout

Senescence—the deterioration of functionality with age—varies widely across taxa in pattern and rate. Insights into why and how this variation occurs are hindered by the predominance of laboratory-focused research on short-lived model species with determinate growth. We synthesize evolutionary theories of senescence, highlight key information gaps and clarify predictions for species with low mortality and variable degrees of indeterminate growth. Lake trout are an ideal species to evaluate predictions in the wild. We monitored individual males from two populations (1976–2017) longitudinally for changes in adult mortality (actuarial senescence) and body condition (proxy for energy balance). A cross-sectional approach (2017) compared young (ages 4–10 years) and old (18–37 years) adults for (i) phenotypic performance in body condition, and semen quality—which is related to fertility under sperm competition (reproductive senescence)—and (ii) relative telomere length (potential proxy for cellular senescence). Adult growth in these particular populations is constrained by a simplified foodweb, and our data support predictions of negligible senescence when maximum size is only slightly larger than maturation size. Negative senescence (aka reverse senescence) may occur in other lake trout populations where diet shifts allow maximum sizes to greatly exceed maturation size.

Correlation of Mercury Occurrence with Age, Elemental Composition, and Life History in Sea-Run Food Fish from the Canadian Arctic Archipelago’s Lower Northwest Passage

As mercury emissions continue and climate-mediated permafrost thaw increases the burden of this contaminant in northern waters, Inuit from a Northwest passage community in the Canadian Arctic Archipelago pressed for an assessment of their subsistence catches. Sea-run salmonids (n = 537) comprising Arctic char (Salvelinus alpinus), lake trout (S. namaycush), lake whitefish (Coregonus clupeaformis), and cisco (C. autumnalis, C. sardinella) were analyzed for muscle mercury. Methylmercury is a neurotoxin and bioaccumulated with fish age, but other factors including selenium and other elements, diet and trophic level as assessed by stable isotopes of nitrogen (δ15N) and carbon (δ13C), as well as growth rate, condition, and geographic origin, also contributed depending on the species, even though all the fish shared a similar anadromous or sea-run life history. Although mean mercury concentrations for most of the species were ~0.09 µg·g−1 wet weight (ww), below the levels described in several jurisdictions for subsistence fisheries (0.2 µg·g−1 ww), 70% of lake trout were above this guideline (0.35 µg·g−1 ww), and 19% exceeded the 2.5-fold higher levels for commercial sale. We thus urge the development of consumption advisories for lake trout for the protection of pregnant women and young children and that additionally, periodic community-based monitoring be initiated.

A synthesis of senescence predictions for indeterminate growth, and support from multiple tests in wild lake trout

Senescence, or the deterioration of functionality with age, varies widely across taxa in pattern and rate. Insights into why and how this variation occurs are hindered by the predominance of lab-focused research on short-lived model species with determinate growth. We synthesize evolutionary theories of senescence, highlight key information gaps, and clarify predictions for species with low mortality and variable degrees of indeterminate growth. Lake trout are an ideal species to evaluate predictions in the wild. We monitored individual males from two populations (1976-2017) longitudinally for changes in adult mortality (actuarial senescence) and body condition (proxy for energy balance). A cross-sectional approach (2017) compared young (ages 4-10 years) and old (18-37 years) adults for (1) phenotypic performance in body condition, and semen quality - which is related to fertility under sperm competition (reproductive senescence), and (2) relative telomere length (potential proxy for cellular senescence). Adult growth in these particular populations is constrained by a simplified food web, and our data support predictions of negligible senescence when maximum size is only slightly larger than maturation size. Negative senescence (aka reverse senescence) may occur in other lake trout populations where diet shifts allow maximum sizes to be much larger than maturation size.

Updated distribution of four stenohaline fish species in Labrador, Canada

Distributions of freshwater fish species in Labrador are poorly documented as the region is remote and sparsely inhabited. Here, we update distributions of four species native to the Labrador Peninsula based on data collected over 10 years: Burbot (Lota lota), Round Whitefish (Prosopium cylindraceum), Lake Trout (Salvelinus namaycush), and Slimy Sculpin (Cottus cognatus). In northern Labrador, our findings extend their ranges inland and northwest of their formerly reported distributions. Their presence in previously unknown locations indicates an alternative post-glacial colonization pathway to one previously proposed that suggested an isolated pocket of Lake Trout in a northern coastal area colonized through marine invasion. Instead, we suggest that overland colonization occurred when glacial Lake Naskaupi withdrew across Quebec into several northern drainages. In southern Labrador, we found Lake Trout and Round Whitefish to the southeast of their previously reported ranges. The discovery of an isolated population of Lake Trout in a remote location of southeast Labrador implies that they may have existed in the area historically (6000 years ago), but have undergone a range contraction with a warming climate. In addition, 22 new locations are documented for Lake Trout within their established range.

Estimating catch curve mortality based on relative return rates of coded wire tagged lake trout in US waters of Lake Huron

We estimated total mortality using catch curves based on relative return rates (RRs) of coded wire tagged lake trout in US waters of Lake Huron. RR was calculated as age specific CPUE per million of fish stocked. Annual mortality for the late 1990s through early 2000s was estimated as 38% from the 1991-1995 year-classes with an effective age range of 5-10 years, and then was estimated as 24% for the post-2000 period from the 1996-2009 year-classes. The two estimates from simple catch curve regressions based on average RR at age values were the same as from a mixed model with individual RR values from all stocking events. These two estimates were also comparable to the findings from statistical catch-at-age assessments with fundamentally different assumptions. Our approach is not constrained by the assumption that the expected recruitment is a constant over time and thus has the advantage to use multiple observations on each age from multiple cohorts. Our approach has broad applicability to aquatic ecosystems in which multiple mark-and-release events of fish stocking have been implemented.