Monarchs aren't the only species being altered by captive-rearing
(this photo taken by Jonathan Armstrong, a former student of Tom's)
I have something very interesting to talk about in today's blog, which directly relates to the topic from the previous post about captive-reared monarchs. It's not necessarily about a new study, but more of a summary of research from outside the world of monarchs. Recall that in the last post I described the newest study from the Davis lab which was a comparison of captive-reared and wild monarchs. Well, after that study was published, I was contacted by a fellow scientist named Thomas Quinn, who had read the paper and reached out to offer some congrats. We got to talking over emails about his research, which is absolutely fascinating, and, long story short - today's blog is all about him! It turns out, he has some fascinating insights to offer to those of us who love and study monarchs, and which are especially pertinent to the issue of captive-rearing.
Tom is a professor and scientist at the University of Washington, and a world expert on salmon! Here is a link to his faculty profile at UW. Tom has been studying salmon and trout for a long time, and he has oodles of scientific studies published (way more than me). In fact, he literally wrote the book on salmon! His lab website is actually called salmonscience! Hey, salmonscience, monarchscience...Anyway, given all of this accumulated knowledge, his thoughts on this topic should not be taken lightly.
If you think about it, there are actually a lot of parallels between salmon and monarchs! As you might know, salmon are migratory. There are a number of salmon species, and each has it's own migration timing, such that there is a migration happening each month of the year. Salmon spend their early life in rivers (from a few days to years, depending on the species and population), and then swim down to the sea where they grow to adulthood and gain almost all of their body mass. When they have matured, they return to the rivers to spawn. Like with monarchs, these migrations are really, really hard, and only the strongest individuals survive to pass on their genes. In other words, the migrations ensure that the entire population is robust and healthy.
Another similarity is in their reproductive strategy: salmon females lay about 3000 eggs, according to Tom. This is a very important point here. Like monarchs, salmon females purposely lay way more eggs than needed, because their natural survival level is low. But keep in mind here, this low survival in the wild is NOT a bad thing - a lot of folks get this part wrong. There are a lot of animal species, like salmon and monarchs, which have evolved this same reproductive strategy - and it works! Think about it - if you don't want to invest a lot into caring for young until they grow up (like humans do), then the best thing to do is have a lot of offspring, so that one or two eventually survive.
So as you can see, both species have some interesting similarities, including a very critical, long-distance migration, and (vaguely) similar reproduction systems. The other interesting parallel is in the research on captive-rearing, which apparently, is quite large in salmon (and complicated, according to Tom).
As you can imagine, there is a long history of artificially raising salmon and other sport-fish in hatcheries, for eventual release into the wild. Most states and provinces have a branch of government devoted to "managing" the local fisheries, and some of this involves keeping the rivers stocked. This is where captive-rearing (hatcheries) comes in.
In fish hatcheries, the goal is to produce as many fish as possible for release back into the wild. Thus, the salmon (or trout, or whatever fish in question) are typically raised from eggs in sterile bins or artificial streams. They are fed as much as they wish, and they are protected from predators and other natural stressors for their entire upbringing. Importantly, the eggs are obtained from females in a way that maximizes the clutch size, so that all offspring from each female are raised.
As an aside, the way they do this is actually pretty cool - Tom tells me that in some species the females are killed and the gametes poured or squirted into buckets and in some this is done live, as depicted in the pictures below.
Crazy, right? These pictures were taken by a former student of Tom's, Harry Rich, Jr., who now works to manage salmon in Washington State. The thing that blows me away with these images is just how many eggs are obtained from each female! (Actually, Tom tells me that compared to most fish, salmon actually have fewer eggs per female, but it's still a lot).
So I know that this isn't how monarch eggs are laid or obtained by people who rear them, but the important thing here is that in the hatchery setting, all (or most) of the eggs from a clutch are raised, and this IS similar to what happens with monarch rearing, where people bring in all of the eggs laid in their backyard, and surrounding yards. Also similar is the fact that the hatchery environment protects the young from all natural predators and provides a sterile environment - just like monarchs being raised in tupperware bins. Tom said that depending on the species, maybe 10% of a salmon clutch might survive in a natural river whereas in a hatchery it would be close to 90%. These rates are not that different than those of reared vs. wild monarch eggs.
Now, let's talk about the research on hatchery fish. Tom was kind enough to provide me with a few studies, but apparently, there is a lot of research on this topic in the fish world, and some of this dates back even 60 years ago. Apparently, fish scientists have long been studying how the captive-rearing environment affects the resulting fish that are released. In fact, in one early study from 1960, the scientists basically did what I had done with monarchs (only better), that is, they directly compared the physical traits of captive-reared fish to those of wild fish. They compared their behavior, growth rates, size, and swimming performance!
So what did they find? What is the difference between reared fish vs wild? Well, that one study, plus a host of subsequent research which I won't get into here, all basically points to the same thing. Quoting Tom, "This and subsequent studies built a large body of scientific evidence showing that wild trout and salmon out-perform hatchery-produced fish, for a variety of reasons."
Tom provided a short summary of these reasons, or in other words, the main differences found between captive-reared and wild salmon, based on all of the research thus far. I've listed these below.
- Color - hatchery fish are in concrete raceways and are often paler than wild fish (which makes them stand out to predators when in the wild)
- Behavior - hatchery fish tend to be fed at the surface whereas much of the invertebrate prey of wild fish is below the surface, and the tendency of hatchery fish to rise to the surface exposes them to bird predators
- Behavior - high densities in hatcheries affect social interactions and dominance behavior, which can benefit or harm hatchery fish, depending on circumstances
- Physiology - hatchery fish are typically released at a set, convenient date, and this is not necessarily at the right time to prepare the fish for the migration. The complex circannual rhythms, adjusted by photoperiod and stimulated by flow and temperature that set up the complex sequence of endocrine events and other physiological functions needs to be just right or the fish fare poorly during the migration.
- Culling - in the wild, the poor quality fish die in the river prior to seaward migration, whereas in the hatchery, everyone survives (bypassing natural selection).
- Diseases - hatchery fish may have low levels of disease (high density, etc.) and this makes them vulnerable after release
This is Andy now - I look through each of these items and I can see direct similarities to the monarch butterfly, and what happens when they are reared in captivity. In fact, a lot of what we have found so far with captive-reared monarchs is eerily similar to this body of work.
There was one item on Tom's list that he didn't point out, but it seems very relevant to the monarch world, that is the navigational ability of hatchery fish. As you might imagine, the salmon migration is a very complex and finely-tuned product of evolution over eons of time. There is now evidence that hatchery-raised fish don't navigate as well, and are more prone to "straying", or winding up in the wrong river. There is a very good summary article on migratory straying here, which describes some of the work of Tom's lab and colleagues. Anyway, this issue is also eerily similar to the latest work on monarchs, which recall that showed how captive-reared butterflies have inferior navigational ability to wild ones.
So at this point you might be thinking, well, if the hatchery-raised fish are so inferior to wild ones, then why has this practice been going on for so long in the fisheries? Well, the short answer is, that is works! Think about it - if salmon numbers are low in a river, you can readily supplement the population with reared ones, resulting in higher overall numbers of fish in said river. Fisheries people have been doing this for decades, and in some places, most of the fish in a river are now hatchery-raised. But here's the catch (get it?) - the many deficiencies of these additional salmon means you are also lowering the fitness of the entire population by adding these. In other words, these releases, year after year, are gradually altering the local and regional salmon populations. For the monarch folks reading this, I think this is the biggest lesson we should learn from all of the salmon research.
I'm going to end this post by re-iterating three main points raised here, based on the work by Tom and his colleagues. And for each of these points, you could easily substitue the word "salmon" for "monarch!"
1. Releasing captive-reared salmon does boost the numbers of fish in a river
2. A plethora of research shows captive-reared salmon have reduced fitness (biology, migration ability, survival in the wild, etc.)
3. Over time, releases of reared salmon weaken the wild population
Many thanks to Tom Quinn for his perspective, and for showing his wealth of fish knowledge! And thanks for reading.
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