Alaska Fish & Wildlife News
December 2018

American Marten Field Guide

By Kerry Nicholson

The Alaska Department of Fish and Game recently created a field guide for trappers to help them quickly determine the age and sex of the marten they catch. This provides trappers with the ability to monitor their marten harvest and help prevent over-harvest of local populations.

Why monitor your marten harvest?

Marten are sensitive to over-harvest because they are easy to catch. This makes managing marten a challenge because there is no way to specifically select for a certain sex or age. At the start of trapping season there are more juveniles than adults available for harvest. As trapping continues, the number of juvenile martens captured will decline and this is when the resident breeding adults will be more vulnerable. In years with poor kit productivity, the harvest of those surplus juveniles can occur earlier in the trapping season. When the majority of the catch consists of breeding adults, trappers should reduce efforts in order to maintain that breeding population to supply next year’s harvest.

What is the ideal harvest ratio?

Unfortunately, there is no ideal or universal number of marten you should harvest. There are many variables that influence marten population dynamics. However, the research available and recommendations from some marten experts indicate you should catch at least three or four juveniles for every adult female. Going below this ratio increases the potential of over-harvesting your breeding population.

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Photo courtesy Stan Zuray.

If the catch ratio of juveniles to adult females declines, trappers should consider reducing the number of active traps or closing their lines because protecting the resident populations can help sustain future trapping efforts.

Determining the age and sex of marten

There are multiple skeletal or morphological methods to determine the age of a marten, although no single method is perfect. One of the most common and accurate ways to assess age is by cementum analysis. Much like counting growth rings of a tree, a tooth has cementum layers that are formed each year and when sliced in half, the layers can be counted under a microscope. This process is costly and time consuming. For a practical, rapid assessment in the field, the ADF&G guide walks you through several alternative methods we have used to determine age and sex classes. No single field method is 100% accurate and no field method will determine exact age, as the cementum analysis would.

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An Interior Alaska marten. Photo courtesy Bill Brophy.

The guide provides the tools necessary to help distinguish juveniles from adults (yearlings are grouped with adults for figuring out the harvest ratio). By the time trapping season rolls around in Alaska (November-February), the juveniles are already 7-10 months old. The yearlings, by this time, are 19-22 months old and the adults are anything beyond that. It is not as easy as you might think to separate the animals into just two groups. There are challenges caused by individual variation in the physical growth and development of marten, or it can become tricky because of how the animal was trapped or how it was skinned. Therefore, using multiple indicators will increase the accuracy of the classifications.

All Alaska Department of Fish and Game offices will have guides for you to pick up, or you can go on line and find a digital copy.

For more information about this resource contact Kerry Nicholson: 907-328-6117

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