Geology topics

Justin H. Bohling

Publications and source records attributed to Justin H. Bohling.

4 recordsLinked to original sources

USGS2022

Streamwide evaluation of survival and reproduction of MYY and wild Brook Trout populations

Brook Trout Salvelinus fontinalis have been introduced across the western USA, where the species competes with and often replaces native salmonids. Nonnative Brook Trout are difficult to eradicate; thus, new removal strategies are needed. One novel methodology couples the partial suppression of wild Brook Trout with the replacement of M YY Brook Trout (males with two Y chromosomes). If M YY fish survive to reproduce with wild female Brook Trout, their progeny will be 100% male, which eventually shifts the sex ratio and theoretically extirpates the population. However, the effectiveness of this approach depends on survival and reproduction of M YY fish relative to the surviving wild conspecifics. From 2018 to 2020, we annually removed an estimated 45.7% of wild Brook Trout from three streams in New Mexico and stocked fingerling M YY Brook Trout (mean TL = 94 mm; range = 61–123 mm) targeting 50.0% of wild annual abundance estimates. Annual survival for M YY and wild Brook Trout was similar in Leandro Creek (M YY = 0.63 and wild = 0.63) and Rito de los Piños (M YY = 0.37 and wild = 0.46) but differed in Placer Creek (M YY = 0.28 and wild = 0.75). During spawning, we evaluated the reproductive potential of M YY Brook Trout by comparing the percentage of sexually mature male Brook Trout comprised of M YY fish to the percentage of hybrid (M YY × wild) F 1 progeny. By the second spawning season (2019), M YY fish comprised 59.8, 50.4, and 34.5% of milt-producing Brook Trout, which resulted in 55.1, 33.3, and 0% hybrid progeny in Leandro Creek, Rito de los Piños, and Placer Creek, respectively. We demonstrated that M YY fish exhibit similar vital rates compared with wild conspecifics in two of three streams; however, differences among streams highlights unforeseen variables that influence M YY survival and reproduction. The study offers promising results of the M YY approach for potentially eradicating unwanted Brook Trout populations.

New Mexico↗

USGS2021

Hybridization between historically allopatric Chinook salmon populations in the White Salmon River, WA

Chinook Salmon spawning in the White Salmon River consist of members of three historically distinct populations: spring Chinook Salmon, Tule fall Chinook Salmon and Upriver Bright (URB) fall Chinook Salmon. Previous work examined juveniles captured in 2006-2008 and reported hybridization between introduced URBs, and the native threatened Tules. Recent increases in nearby hatchery URB release numbers raised the question of whether hybridization rates were increasing. We estimated hybrid frequencies among juveniles collected in the lower White Salmon River between 2016 and 2019. We also evaluated the frequencies at which non-target fish and hybrids were incorporated into the broodstocks of adjacent hatcheries. We observed that frequencies of hybrids in juvenile samples from the White Salmon River were greater in 2017-2019 (17-32%) than they had been in 2006-2008 (4-15%), but that a few (2/9) comparisons exhibited overlapping confidence intervals, suggesting that the rate has increased over time, but also that more sampling is needed to understand the importance of year-to-year variation. Further, differences in the habitat following dam removal and in the sampling sites complicated interpretation of our results. Examination of broodstocks of nearby hatcheries revealed low rates (< 0.5%) of incorporation of non-target populations and higher rates (< 9.0%) of incorporation of hybrids into those broodstocks. The relative compositions of all hatchery and natural-origin collections were similar: most individuals were one of the two parental stocks, a very small fraction were F1 hybrids, and a larger minority fraction were back-crosses. This pattern, in the context of hybridization which we know has been happening for several generations, is consistent with a hypothesis of selection against hybrids in which F1 hybrids are less fit than backcross hybrids.

Washington↗

USGS2015

Population and genetic outcomes 20 years after reintroducing bobcats ( Lynx rufus ) to Cumberland Island, Georgia USA

In 1988–1989, 32 bobcats Lynx rufus were reintroduced to Cumberland Island (CUIS), Georgia, USA, from which they had previously been extirpated. They were monitored intensively for 3 years immediately post-reintroduction, but no estimation of the size or genetic diversity of the population had been conducted in over 20 years since reintroduction. We returned to CUIS in 2012 to estimate abundance and effective population size of the present-day population, as well as to quantify genetic diversity and inbreeding. We amplified 12 nuclear microsatellite loci from DNA isolated from scats to establish genetic profiles to identify individuals. We used spatially explicit capture–recapture population estimation to estimate abundance. From nine unique genetic profiles, we estimate a population size of 14.4 (SE = 3.052) bobcats, with an effective population size ( N e ) of 5–8 breeding individuals. This is consistent with predictions of a population viability analysis conducted at the time of reintroduction, which estimated the population would average 12–13 bobcats after 10 years. We identified several pairs of related bobcats (parent-offspring and full siblings), but ~75% of the pairwise comparisons were typical of unrelated individuals, and only one individual appeared inbred. Despite the small population size and other indications that it has likely experienced a genetic bottleneck, levels of genetic diversity in the CUIS bobcat population remain high compared to other mammalian carnivores. The reintroduction of bobcats to CUIS provides an opportunity to study changes in genetic diversity in an insular population without risk to this common species. Opportunities for natural immigration to the island are limited; therefore, continued monitoring and supplemental bobcat reintroductions could be used to evaluate the effect of different management strategies to maintain genetic diversity and population viability. The successful reintroduction and maintenance of a bobcat population on CUIS illustrates the suitability of translocation as a management tool for re-establishing felid populations.

Georgia↗

USGS2013

Re-introduction of Bobcats to Cumberland Island, Georgia, USA: Status and lessons learned after 25 years

The bobcat ( Lynx rufus ) is a medium-sized spotted cat (4 - 18 kg), widely distributed in North America. Bobcats are legally harvestable in most of their range, and are currently classified as Least Concern by IUCN and listed in Appendix II of CITES, due to similarity of appearance with other spotted cat species. Bobcats in the coastal plain region of Georgia, USA, occur at densities of 0.4 - 0.6 per km2. The most common prey of bobcats across most of their range are cottontail rabbit species ( Sylvilagus sp). Cumberland Island is the largest of Georgia’s Atlantic coastal barrier islands. Since 1972, approximately 80% of the island has been administered by the National Park Service as Cumberland Island National Seashore (CINS). The island has a subtropical climate and contains approximately 85 km2of upland habitat. It is accessible only by boat or small plane. Thirty-two bobcats were released on CINS during 1988 – 1989.

Georgia↗