Population Control of Brook Trout with YY Males, by Jacob Beckner

Growing up in the Appalachian Mountains it was always remarkable when an avid trout angler would catch something other than a hatchery raised Rainbow Trout (Oncorhynchus mykiss), such as a native Brook Trout (Salvelinus fontinalis), or Brown Trout (Salmo trutta) as it can be seen in the figure on right. However, many residents located outside of the Appalachian Mountains would argue that species of Salmonids such as Brook Trout are invasive, and demand eradication to restore the natural aquatic ecosystems where they were introduced. Until now, one of the proven methods for limiting Brook Trout in non-native environments was to manually remove each individual from the affected stream. However, the Idaho Department of Fish and Game have recently developed a new method that is possibly more efficient. They have proposed a method to limit populations by engineering Brook Trout with the Trojan Y chromosome which would effectively skew the entire invasive population towards male. Therefore, this would limit the amount of fecundity drastically and eventually leads to very limited reproduction. However, before a full-scale stocking program can arise, many additional trials and experiments are needed along with proper permits from the Food and Safety Administration (FDA) (Schill et al. 2015).

Non-native Brook Trout being reeled in at Palmer Lake, Colorado.  Photo by Heath Alseike.   Creative Commons Flickr

Before it is deliberated on how exactly scientists are manipulating this invasive species within the family of Salmonidae, it is imperative that proper definitions are ascertained. Initially, according to The National Wildlife Federation an invasive species is any kind of living organism that is not native to an ecosystem and causes negative impacts on the environment. Many invasive species are labeled due to their rapid growth, fast reproduction, and potential to cause harm (The National Wildlife Federation). As it can be observed on this map Brook Trout have spread drastically outside of their native range (highlighted in orange), and due to anthropogenic disturbances and introductions to non-native streams they have spread to the areas highlighted in red.

Native (orange) and non-native (red) distribution of the Brook Trout in USA.  Source: USGS. 

Furthermore, since the definition of an invasive species has been properly established, one would inquire what precisely Brook Trout are doing to disturb their non-native environment? Originally, non-native Salmonids were introduced as a game fish in certain parts of the country to encourage indigenous angling in streams (as it can be seen on the left), and to lower the threat of over harvesting on native species of Trout such as Oncorhynchus mykiss in many parts of the western United States. However, as many Evolutionary Biologists would propose, selective pressures imposed on an environment have shaped organisms within the ecosystem, and when a non-native species is introduced to a new ecosystem it will either succeed immensely or be crushed instantly. After several generations, Brook Trout grew to be more harmful than beneficial to their new, non-native environments, and reproduced exponentially way beyond the original purpose. They began to out compete the other native Salmonids of the region which has led to the destruction of the aquatic fauna in the region (Schill et al. 2015)  along with immense competition for other resources within their environment.

As it was previously stated, researchers at the Idaho Department of Fish and Game have developed a method to create a population of Brook Trout with the Trojan Y Chromosome (TYC) which is designed to specifically skew the population toward all male. Therefore, placing detrimental selective pressures on the population (Schill et al. 2015). One of the most significant concepts of this process is to integrate concealed _Y chromosomal material into the populations by circulating males that are genetically _YY instead of _XY, along with males that are phenotypically female (F_XY) (Schill et al. 2015). Finally, the objective of this study was to primarily create genetic indicators to determine the sex of Brook Trout and to produce a fecundate population of salmonids comprised of phenotypic males and females whose development could be measured along with the completion of progeny examinations to ensure genetic accuracy (Schill et al 2015).

This process was completed in three stages and can be comprehended by the diagram to the right. First, exogenous estrogen was used to engineer trout with the genetic composition of M_YY, also called “Super-Males”. Secondly, to change the gender of half of the _YY males at the fry stage using estrogenic hormones to turn them into “Neo-Females” (F_YY), and lastly to preserve groups of both M_YY and F_YY as a means of producing large numbers of _YY fish into the wild (Schill et al. 2015). This technique of transforming a population from Males (XY) into phenotypically fecundate Females (XY), and then breeding them with Males (XY) who have been manipulated to become phenotypically fecundate males (YY). This has been proven to slope the long-term population of Brook Trout into an all-males by ensuring the reproduction by two males into male offspring. After the execution of this study, it was recognized that there was tremendous hope for the future of this program. The statistics for the sex determination proved very effective as ninety out of ninety (100%) genotypes matched the acknowledged phenotypes of the Brook Trout (Schill et al. 2015). Subsequently, at the completion of the first step of the study, which was releasing estradiol infused feed that feminized Males (M_XY) into Neo-Females (F_XY), it was shown that this method of production was ninety-six efficient in producing viable females (Schill et al. 2015).

After assessments of these experiments it is possible to anticipate what the future of these experiments could be. As of now, the total cost of rendering this program is around ten thousand dollars from establishment to completion, including feed, labor, and genetic testing (Schill, Daniel J., et al.). It can be documented that this is not a very costly or extraneous procedure as compared to manually removing the invasive Brook Trout from the non-native streams. It can also be concluded that once this method of population control is reputable and further studied it can be possibly used as a guide to limit populations of other invasive species. As depicted in the graph above, there are current issues in Yellowstone National Park due to the introduction of Lake Trout (Salvelinus namaycush), which have greatly reduced the number of native Cutthroat Trout (Oncorhynchus clarkii) in the area. Additionally, for this specific example, it can be acknowledged that this invasive species has further contributed in the ecological trophic cascade of the area (Middleton, Arthur, et al). However, if this method of sex manipulation by the Idaho Department of Game and Fish proves further effective, safe, and efficient, it can be concluded that it could also be introduced to Yellowstone. Hopefully, this method can lead to the restoration of the natural aquatic habitat of Yellow Stone National Park.

 

The author with Brook Trout. 

In conclusion, this analysis was designed and established to prove if there were better methods of restraining invasive species of Salmonids in tributaries on the northwestern portions of the United States that contained Brook Trout. The Idaho Department of Fish and Game has investigated to see if they could produce a viable idea to selectively limit the populations and reduce their specific fecundity. They developed a system that would manipulate Brook Trout using the Trojan Y Chromosome (TYC) to effectively limit the invasive growth of the population (Schill et al. 2015). Researchers then hypothesized and demonstrated that the complete population would inherently shift toward the male sex thus greatly reducing fecundity. The results from these examinations were very promising, proposing that similar trials could be performed in the future and that this can be applied as a method of population regulation on naturally occurring aquatic ecosystems pertaining the invasive Brook Trout.

References

Berkshire Outdoorsman. Accessed April 26, 2018. http://www.berkshireoutdoorsman.com/category/fishing/trout-fishing/.

"Invasive Species | National Wildlife Federation." The National Wildlife Federation. Accessed April 26, 2018. http://www.nwf.org/Educational-Resources/Wildlife-Guide/Threats-to-Wildlife/Invasive-Species.

"Trout." White Oak Farm. January 24, 2017. Accessed April 26, 2018. https://whiteoakfarmny.com/trout/.

United States Geological Survey. Brook Trout (Salvelinus fontinalis) - Species Profile. Accessed April 26, 2018. https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=939.

"Case Studies of Lake Trout and Cutthroat Trout Interactions." Accessed April 26, 2018. http://www.cfr.washington.edu/classes.esrm.459/yellowstone/cutthroat/wildlife.htm.

Middleton, Arthur. "Is the Wolf a Real American Hero?"  March 09, 2014. Accessed April 26, 2018. https://www.nytimes.com/2014/03/10/opinion/is-the-wolf-a-real-american-hero.html.

Schill, Daniel J., Jeff A. Heindel, Matthew R. Campbell, Kevin A. Meyer, and Elizabeth R. J. M. Mamer.  2015. Production of a YY Male Brook Trout Broodstock for Potential Eradication of Undesired Brook Trout Populations. North American Journal of Aquaculture 78: 72-83.

On the Life of Kelly J. Meyer, by Don Orth

On October 24th I posted birthday wishes to Kelly Meyer on Facebook.  I sent him a photo of a Brook Trout for his birthday wishes. It was my last communication with him.   On the evening of November 4th, he died unexpectedly (see obituary), and, as is typical, I grasped for words to comfort his wife, Denise, and sons, Jack and Andrew, who I never knew, never met.  No words would come, only sadness.   Kelly was one of my graduate students from 1988 to 1990.  His life (vita from this 1990 MS thesis appears below) during his years at Virginia Tech remain among my fond, faded memories.  

During his time as a graduate student, Kelly studied the bioenergetics of Brook Trout (Salvelinus fontinalis) in streams of the Shenandoah National Park.  These unproductive, small streams are lined with dense Rhododendron and trout cannot move to find more suitable habitats during most seasons.   Brook Trout have adapted to these southern highland streams.  Kelly's thesis project explored the relation between the energy available in drifting insect prey and growth and consumption of brook trout.  The field work required sampling every six hours, flushing out stomach contents with lavage, and quantifying the mass of all items in stomachs and in the drift.  The waterproof, Ryan J (chart recording) thermograph recorded water temperatures continuously in this pre-digital era. The field work was strenuous enough just to hike into the study areas. Once there, you realized just how mal-adapted bipedal hominids are for wading these streams.  Few investigators have attempted this type of work, especially over the 24-hour cycle.  Kelly was interested in the challenge and was attracted to studying native Brook Trout in their natural habitats.    While in the Peace Corps, stationed in Lesotho, in southern Africa, Kelly managed to apply his skill set to survey isolated populations of the critically endangered Maloti Minnow Pseudobarbus quathlambae.  This minnow is still struggling to persist today (see recent story).

A mountain stream of Virginia and home to the native Brook Trout.

Kelly's thesis findings are significant to the survival and persistence of Brook Trout.   The southern strain of Brook Trout are adapted to life in the small, infertile mountain streams but growth rates can be very slow and adult body size is modest.   In some streams, the amount of energy Brook Trout could assimilate was barely enough to meet their standard metabolic needs, much less to permit energy for activity or growth.  Very few mountain streams provide the right combination of habitats and food.

Differences between assimilated and maintenance energy for Brook Trout in four study streams in Shenandoah National Park (Meyer 1990).

Consequently, it is the rare Brook Trout that captures sufficient prey and meets energetic needs to live and swim and grow large enough to produce mature eggs and contribute to the next generation.   Brook Trout in these mountain streams continuously monitor the available drifting insects and dart out to capture the larger, more energetically valuable prey. The best streams have an abundant canopy to shade the stream and keep water cool enough for optimum Brook Trout feeding (12-17°C).   The optimal Brook Trout streams also produce an abundant and diverse fauna of invertebrates, including aquatic and terrestrial forms.   Kelly's hypothesis that growth and consumption of Brook Trout was influenced by abundance of larger prey in the drift was supported by his field studies (see below), especially within streams.   He also identified an energy minimizing strategy by the Brook Trout that enabled them to reduce activity costs when prey levels were low.  Years later, Railsback and Rose (1999) confirmed that  growth of Rainbow Trout was strongly influenced by factors controlling food consumption.  Their work and most other more recent field investigations relied on model-estimated food consumption rather than diel sampling.  

Percent of consumption captured by Brook Trout in relation to density of large drifting prey (Meyer 1990)

One of the surprises in the study was the regular appearance Gypsy Moth (Lymatria dispar)  larvae in the guts of the Brook Trout.   Gypsy Moths are a devastating forest pest that feed on foliage and were marching through the Appalachian mountains at that time.   The pest has been in North American for 100 years. A major concern is the potential loss of economically critical and ecologically dominant oak (Quercus spp.) trees.  Yet, the examination of the diet demonstrated that this terrestrial pest was subsiding the Brook Trout in these forest-covered mountain streams.

Realizing the practical difficulties for numerous intensive field investigations, Kelly Meyer also developed an energetics-based model to analyze dynamics of trout populations in Appalachian streams.  The model included mathematical formulations for temperature effects, size-dependent mortality, seasonal mortality to predict population changes and  average trout size.  The model was programmed in the language of the times (FORTRAN).   These calculations are essential components to define the thermal niche of the Brook Trout.  They may be used in future efforts to project the effects of climate change on suitability of streams for Brook Trout in the southern Appalachian mountains.  Many partners are involved via the Eastern Brook Trout Joint Venture, to protect, restore, and enhance remaining Brook Trout 

Most of Kelly's fisheries career was with the White Mountain Apache Tribe Game and Fish Department and  Arizona Department of Game and Fish.  When he was first hired, he was the only fisheries biologist with the White Mountain Apache Tribe; he would joke that he was Chief of Fisheries.  In this role, his expertise was critical in the management and recovery of the federally endangered Apache Trout (Oncorhynchus apache).  Many actions are required for the recovery of  Apache Trout and the success of recovery depends on special people, such as Kelly Meyer, who possess the patience and skills to work with the many cooperators to set appropriate fishing regulations, improve stream habitats, negotiate agreements, install and maintain barriers, and prevent movements of non-native competitors.  He was a field scientist for all seasons and for all peoples.  We need more people like Kelly Meyer in this world.   I am very saddened with news of his passing.

REST IN PEACE

Kelly J. Meyer

1961-2015

References
Meyer, K. J. 1990.  Effects of drifting prey abundance on food consumption and growth of brook trout in Shenandoah National Park.  Master's Thesis. Virginia Polytechnic Institute and State University, Blacksburg, Virginia.  111 pp.
Meyer, K.J., and D.J. Orth.  1990.  Development and application of an energetics-based model for trout populations in Appalachian streams.  Final Report, U.S.D.A. Forest Service, Southern Forest Experiment Station. 129 pp.
Railsback, S.F., and K.A. Rose. 1999.  Bioenergetic modeling of stream trout growth: temperature and food consumption effects.  Transactions of the American Fisheries Society  128:241-256.