Geology topics

Nick M. Sard

Publications and source records attributed to Nick M. Sard.

2 recordsLinked to original sources

USGS2020

Egg and larval collection methods affect spawning adult numbers inferred by pedigree analysis

Analytical methods that incorporate genetic data are increasingly used in monitoring and assessment programs for important rate functions of fish populations (e.g., recruitment). Because gear types vary in efficiencies and effective sampling areas, results from genetic‐based assessments likely differ depending on the sampling gear used to collect genotyped individuals; consequently, management decisions may also be affected by sampling gear. In this study, genetic pedigree analysis conducted on egg and larval Lake Sturgeon Acipenser fulvescens collected from the St. Clair–Detroit River system using three gear types was used to estimate and evaluate gear‐specific differences in the number of spawning adults that produced the eggs and larvae sampled ( N s ), the effective number of breeding adults ( N b ), and individual reproductive success. Combined across locations and sampling years, pooled estimates were 330 ( N s ; point estimate) and 317 ( N b ; 95% CI = 271–372). Mean reproductive success was 4.35 with a variance of 5.33 individuals/spawner. Mean ± SE estimated numbers of unique parents per genotyped egg or larva (i.e., adult detection rate) from 2015 samples were 1.140 ± 0.003 for vertically stratified conical nets, 0.836 ± 0.002 for D‐frame nets, and 0.870 ± 0.002 for egg mats. Using samples from 2016, adult detection rates were 0.823 ± 0.001 for D‐frame nets and 0.708 ± 0.001 for egg mat collections. Coancestry values were negatively correlated with adult detection rate. Although genetic pedigree analyses can improve the understanding of recruitment in fish populations, this study demonstrates that estimates from genetic analyses can vary with the targeted life stage (a biologically informative outcome) and sampling methodology. This study also highlights the influence of sampling methods on the interpretation of genetic pedigree analysis results when multiple gear types are used to collect individuals. Development of standardization approaches may facilitate spatial and temporal comparisons of genetic‐based assessment results.

Michigan, Ontario↗

USGS2020

Genetic family reconstruction characterizes Lake Sturgeon use of newly constructed spawning habitat and larval dispersal

Since 2004, seven spawning reefs have been constructed in the St. Clair–Detroit River system to remediate lost spawning habitat and increase recruitment of Lake Sturgeon Acipenser fulvescens . Assessment of management actions by collecting and enumerating eggs and larvae provided evidence of spawning Lake Sturgeon and survival of eggs until larval dispersal at constructed reef sites. However, the number of spawners contributing sampled offspring ( N s ), effective number of breeders ( N b ), and extent of larval dispersal was unknown. Genetic reconstruction of familial relationships assigned eggs and larvae ( n = 725) collected in 2015 and 2016 to full‐ and half‐sibling groups and estimated N s , N b , and genetic connectivity. We used a modified COLONY simulation module to simulate and convert 18 microsatellite loci (13 disomic and 5 polysomic) to 205 dominant present/absent markers to increase marker number and familial assignment accuracy in family reconstruction analysis. We assessed COLONY's ability to accurately infer familial relationships across small ( n = 50), moderate ( n = 125), and large ( n = 750) larval sample sizes using two assumed allele frequency distributions for polysomic loci. We found that with fewer offspring sampled, COLONY underestimated N s and with large sample sizes overestimated N s . However, estimates were usually within 12–16% of the simulated true N s . Across reefs, estimates of N s were 151 in 2015 and 208 in 2016, and N b was similar (158 in 2015 and 198 in 2016). Evidence of full‐ and half‐sibling larvae collected at multiple locations indicated that individual Lake Sturgeon spawned at multiple locations within years and larvae dispersed considerable distances. Estimating N s , N b , larval dispersal, and inferred genetic connectivity between locations provides managers with population demographic parameters to assess habitat remediation projects. Continued monitoring, including genetic family reconstruction, may provide insight into the long‐term effects of constructed spawning habitat on recruitment and population‐level genetic diversity.

St. Clair–Detroit River system, Lake Michigan, Lak↗