The Ups and Downs of Fisher-dom

My goal for the past week was to get in touch with fisher ‘history’, if you will, and hopefully start to understand what we know about basic fisher ecology and how the fisher population in the Northeast has changed over time. As it turns out, I was thinking  on far too small a scale- I found information on thousands of years of fisher existence and I learned about the history of many animals in New Hampshire- get ready for a wild ride.

A long time ago in our very own galaxy, fishers first made their appearance. Thanks to the wonders of genetic analysis, Wisely et al. (2004) could even suggest a general area for fisher evolution and then a dispersal pattern. (The basic idea goes like this: the longer a species has been in an area, typically the greater the genetic diversity because there has been more time for mutations to develop. Genetic diversity will be greatest in the location where the species evolved and be least in those newly colonized areas where just a few individuals founded the population. If it helps, think about the town of Rock Ridge in “Blazing Saddles”- everyone there had the last name “Johnson” and that said something about their respective family trees- well, I think there were a few “van Johnsons”, but you get the idea.) By analyzing the genetic diversity of fishers along the Pacific Coast and comparing it with previous data from the Midwest and East, Wisely et al. (2004) suggested that fishers, after originating in eastern North America, spread west to the Canadian Pacific coast starting less than 5,000 years ago before turning south and making it to California. Fishers in the Sierra Nevada have low genetic diversity when compared with other populations. Why is this important? Well, populations with lower genetic diversity are at greater risk for extinction when conditions around them change (such as habitat loss, disease, etc.)


Much more recently and in my own backyard, fishers in the Granite State were nearly gone by the time of the Civil War as a result of over-trapping and loss of habitat from logging and increased agricultural activity (see NH Fish and Game and NH Fish and Wildlife News for more info). They were granted full protection from hunting 1934-1962 and again 1977-1979, and, as a result of greater protection and transition of agricultural land back to forest, now are abundant throughout the state. That final piece of information is intriguing, because I found a list of NH mammals from 1922 (Jackson 1922) stating that fishers were rare and only in northern sections. In 90 years the fisher population has changed dramatically, and that’s not the only big change I found when I looked through Jackson’s list- moose and raccoons and harbor seals had also changed quite a bit. (Check out my “Just Fascinating Stuff” page for a complete comparison of Jackson’s list with the current situation- trust me, it’s worth it!) Fishers from NH have even been translocated to other states as part of reintroduction programs, which gives you a sense of how stable the population here is.

Why would you want fishers in your state? Well, there are a few reasons that I can think of, although, as a conservation biologist, I’m ready to admit that not everyone will agree “because they are amazing animals” is adequate justification.

  • As I mentioned in my first post on fishers, they prey on porcupines. (Apparently they harass the porcupine by continually attacking its head and face until it’s exhausted- you have to admit that’s a bold strategy.) According to Zielinski & Duncan (2004), fishers prey on a wide variety of animals, but are known for predation of hares and porcupines throughout most of their range. Porcupines are herbivores with impressive appetites (I helped care for an orphaned juvenile in Texas before it was released, and we went through a lot of fruits and veggies),  and they chew through the bark of trees (especially conifers) in the winter for food; as a result, high densities of porcupines can damage forests (not such a great thing if you are trying to harvest tall, straight trees). There is an inverse relationship between the number of fishers in an area and the number of porcupines, which was part of the strategy behind reintroducing fishers in some locations.
  • Another reason for welcoming fishers has to do with small mammal cycles. You may be familiar with the regular boom-bust cycles of some mammals, such as lemmings, voles, and hares- the population swells and collapses over a regular period of years. Some carnivores, such as lynxes, specialize on a certain prey species, so, when the prey population increases, the predator population also increases, contributing to an eventual decline in prey, which causes the predator population to decrease, then helping the prey population to expand again (hence, the cycle). Fishers, on the other hand, will take what they can get for food in many situations. Bowman et al. (2006) found that fishers in the St. Lawrence-Great Lakes area switched to other sources of food when hare populations declined. If a predator is a generalist and switches between food sources, its population will remain relatively stable even if one prey species collapses; it can therefore be first-on-scene when the prey population starts to recover and actually help to dampen the up-and-down swings in prey numbers (Hanski et al. 1991). So fishers can help keep prey numbers from getting out of control and then crashing.

Having looked a little at where fishers have been (and it does seem like they will be a long-time fixture in some ecosystems and have a tenuous hold in others), I’m curious about how they interact (or don’t) with our society and what their presence means for us- should we welcome them, fear them, ignore them? I’m also curious if any results of a fisher study over the last few years were really surprising.

So stay tuned for the next installment as I ponder the statement “Give a man a  fish and he eats for a day, give a man a fisher and all bets are off.”

Works Cited:

Bowman, J., D. Donovan, and R.C. Rosatte. 2006. Numerical response of fishers to synchronous prey dynamics. Journal of Mammalogy 87(3): 480-484.

Hanski, I., L. Hansson, and H. Heikki Henttonen. 1991. Specialist predators, generalist predators, and the microtine rodent cycle. Journal of Animal Ecology 60(1): 353-367.

Jackson, C. F. 1922. Notes on New Hampshire mammals. Journal of Mammalogy 3(1): 13-15.

Wisely, S.M., S.W. Buskirk, G.A. Russell, K.B. Aubry, and W.J. Zielinski. 2004. Genetic diversity and structure of the fisher (Martes pennanti) in a peninsular and peripheral metapopulation. Journal of Mammalogy 85(4): 640-648.

Zielinski, W.J., N.P. Duncan. 2004. Diets of sympatric populations of American martens (Martes americana) and fishers (Martes pennanti) in California. Journal of Mammalogy 85(3): 470-477.

Posted July 9, 2012 by Mirka Zapletal in Mustelids

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