Location Matters

Science may ban me now.

I wrote last week of the two types of grad student vacations, conferences and field work. But, there’s another holiday that’s even rarer (at least for me) and merits even more celebration. I’m talking about your advisor’s vacation week, otherwise known as Grad Student Independence Week.
 
Truth be told, my advisor’s whereabouts don’t really influence my work ethic. For the time being, I’m working at my own self-defined pace (cross my fingers I can keep it that way).  But, the closer we get to the beginning of the semester, the more sparse the office gets. With no one to pester during the day, why bother going in?
 
So, I didn’t. I slept in a little later (which for me is 6am), enjoyed coffee on my patio, and had one main goal: start working on the hatchery-wild hybridization manuscript. Data analysis is still on going, but at this point I know what the results are going to say. There’s no need to wait for the final numbers to crunch to start the long process of preparing the work for publication.
 
When I was an undergrad, I always thought that scientific publications were the works of brilliant scientists who wrote the equivalent of Shakespearian prose. I never thought I’d be smart enough to accomplish a similar feat. I actually still think that, except I’ve somehow been let into that elite crowd of published scientists seven times now. It still hard to believe I’ve reached the point in my career where I am the authority on a topic- someone out there is reading my manuscript and thinking I am the brilliant scientist. Crazy.
 
One thing I have learned along the way is that regardless of how smart you are, how great your research is, or how well you write, all manuscripts start in the same place. With a blank Word document that just stares at you. For me, it’s probably the single most intimidating and frustrating part of the publication process. Literally anything I put down “on paper” would represent an improvement over the blank page, but I just sit there for hours- staring, erasing, and getting more frustrated. 
 
There’s all sorts of advice out there about how to be the best, most efficient writer- outline your ideas, write 30 minutes every day, discuss your paper beforehand, etc.- and I defy every single recommendation. That long, frustrating, fight with the blank page is just part of my process, and I need to work through before I can write something worth saving. And, the fight needs to be long and uninterrupted. Not a great task for tackling at the office where distractions are imminent, but a perfect job for celebrating my Grad Student Independence Week at home. 

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One lake in Algonquin Provincial Park. Number one habitat requirement for brook trout seems to be that it is "pretty." Photo courtesy of amusingplanet.com.

I actually only got one full day at home, but it was enough to win the battle and get a solid start on the manuscript. Time to save it, back it up, and not look at it for at least a few days. In the meantime, I go back to square one- read published manuscripts that I know are important for my study and that I will cite in my own publication to support why our study was needed and to add credibility to the results we found.
 
As I’ve said before, there aren’t a lot of studies on hatchery-wild interbreeding in brook trout.  But, I did find one by Andrew Harbicht and colleagues (see below for a link to the manuscript) that looked at how the probability that hatchery trout will breed with wild trout changes depending on the environment. I’m still not releasing the result of our analysis, but studies like this are important regardless of what we find. Whether we find a high degree of interbreeding or not much at all, we need to know WHY we are getting that result.  And, it makes sense that environmental conditions influence how much hatchery trout breed with their wild counterparts.
 
The study was conducted on several lakes in Algonquin Provincial Park in Ontario, Canada, of which some were never stocked with hatchery brook trout, and others had historic stocking that had been stopped 10+ years prior to their study. Immediately, you’ll notice there are some differences between their study and ours: we work on streams, and in areas that are currently being stocked with high densities of fish. Nevertheless, their results are important to keep in mind as we move forward. Most importantly, they found:

• The degree of interbreeding between wild and hatchery fish varies considerably among lakes.  This means that the probability of interbreeding is not the same across systems, even those that are in close proximity to one another and with very similar habitat.
• Lakes with higher conductivity and at lower elevations had less interbreeding, perhaps because of negative density-dependent fitness effects. Let’s unravel this important result a bit.  As pH decreases (i.e., water becomes more acidic), macroinvertebrate densities and egg survival declines, thus leading to decreases in natural brook trout populations. Likewise, at higher elevations, water bodies become less productive and cannot support large populations of trout. So, the authors’ result of “negative density-dependence” means that smaller wild trout populations (i.e., those found at low pH and/or high elevation) are more susceptible to wild-hatchery interbreeding.
• Lakes stocked earlier in the year had a higher probability of interbreeding. This is a little unexpected as it is generally believed that older fish have a higher probability of survival.  However, fish stocked earlier in the year may have more of a chance to acclimate to the system, thus making them more prepared to spawn come fall.
• Lakes that were more accessible to fishing had a higher probability of interbreeding. This suggests that fishing increases the probability of interbreeding. How?  First, highly accessible lakes probably get stocked more frequently because it’s easier and because there is a higher demand from anglers to stock those systems.  But, there’s a second, less obvious answer. Large fish produce the most offspring, but they are also the ones harvested from the stream.  Large, wild fish removed from the lake can only get replaced through natural reproduction, a process that takes several years of growth and even then only produces a handful of large fish. Large fish with hatchery genes can get replaced through natural production, but also through stocking. In a sense, stocking is kind of like cutting the line- you can put as many large fish in the system as you want, without having to wait years for natural growth and production. Put another way, angling removes wild genes from the system faster than it removes hatchery genes because hatchery genes can get replaced faster than wild.

 
So, why is this study important for us?  For starters, streams often support lower populations of brook trout than lakes, making us nervous that interbreeding may be more prevalent in streams than lakes- particularly, again, because stocking in our systems is frequent and on going. Our streams also have a wide range accessibility, pH, and other environmental variables (e.g., gradient and temperature) that influence population sizes and competition. Big picture, this study just shows us that introgression isn’t an all or nothing phenomena. Location matters a whole lot, and our results can’t be taken as the definitive response of trout to stocking.
 
But, all of this presumes that we are finding interbreeding.  Which I’m not saying we are.  I’m also not saying we aren’t. You’ll just have to stay tuned. 

*Note: Content in this post is my own and may not reflect the opinion of the manuscripts' authors or the agencies they represent.  I encourage you to read the manuscript, found here, so you can contribute to the discussion.

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