Elk Population

Population of Elk (Cerphus elaphus) have been fluctuating in certain areas across North America for various reasons. One of the reasons includes their reintroduction to East Tennessee (Murrow 2007). Fluctuating populations create a need for research on elk for more effective and efficient use of resources by wildlife managers, and to monitor how well they are transitioning. Capture research has been conducted on two of the four current subspecies of elk. The two subspecies are Roosevelt Elk (Cervus elaphus roosevelti) and Rocky Mountain Elk (Cervus elaphus nelsoni). Adult Rocky Mountain Elk can weigh anywhere from 230 to 318 kg. They are found in the ecosystems along the Rocky Mountains and surrounding states. Adult Roosevelt Elk can weigh
anywhere from 318 to 499 kg (Kreeger 1996). Their size difference is attributed to multiple reasons. One of which is that Roosevelt Elk are commonly found in the relatively more productive rainforest ecosystem and in areas further northwest of the Rocky Mountain Elk’s home-range. These Areas include the northwestern United States and Elk Island National Park.
Trapping elk has been deemed an effective management practice in areas where hunting is restricted (Lovaas 1973). Biologists and researchers have also been trapping elk for various studies; including articles this paper reviews. These two reasons for trapping have created a long evolutionary history of capture techniques along with extensive literature detailing capture success and failure. This paper covers 13 different articles containing three trapping methods used. Six articles focus on the effectiveness of a capture method used in their study. Six separate articles display effective trapping methods used as a means to gather research, and will be used as reinforcement to a trap’s effectiveness in different terrain, habitat, and weather conditions. One piece of literature is not a research article; instead, it is a guide to chemical immobilization used by many of the research articles within this review.
Baits
Baiting and pre-baiting trap sites is an effective method that can be used to increase trap yield. Using the correct bait is essential to attract the maximum number of elk across a large area. Therefore, the next question that needs answering is what bait should be used? Three articles in particular address baits they found effective Pedersen’s study addresses the effectiveness of 11 different baits. The baits tested were: “Alfalfa, grass-hay, barley, rolled oats, molasses, anise oil, dill oil, banana oil, salt and ‘Sweet-Lix, [and] a supplemental stock block’” (Pedersen 1977). The various baits were monitored from 1971 to 1976 during a trapping study. Pedersen noted that, “salt proved the most effective bait”. While the effectiveness of bait was determined by the number of elk attracted, measurements for each bait were not provided. However, he did note that,
Elk used newly established salt licks within 24 hours and in one instance 68 kg of rock salt was removed from an established lick within 5 days. It was common to have 23 kg of salt removed within 48 hours. (Pedersen and Adams 1977)
While Salt was generally the most effective, anise oil was effective in dry summers. Pedersen and Adams found that, “28-113 g of anise oil resulted in an immediate increase of elk visits to the trap sites.” However, anise oil also attracted mule deer that would set off the trap before the active hours of elk (1977). While this study performed research on many known baits, it did not test the effectiveness of apples. Couey and Mace used rotten apples and noticed mentionable results.
Couey noted that in 1949 the Utah Fish and Game Agency has the most experience trapping elk. They used rotten apples as bait to capture anywhere from five to 25 elk at a time, and in one instance caught 87 at once which was over the safety capacity of the corral trap used (Couey 1949). Although baiting with apples is promising, the Oregon State Game Commission had trouble finding and obtaining apples due to state climate and price (Mace 1971). This demonstrates one of the problems with deciding the most effective bait. Deciding an effective bait depends on weather, ecosystem, nutrition, and economy, a turn in any one of these variables can change the type of bait used. However, bait is not required for all
traps.
Trapping Methods Net Gun The first study that will be discussed is Seward’s use of net guns to capture elk (Seward et al 2005). Generally net guns are used on mammals smaller than elk (Silvy 2012). Seward discovered an instance where the net gun is effective at capturing Rocky Mountain Elk. The study required pregnant elk to be trapped so that vaginal transmitters could be attached. The trapping area consisted of 7,400 ha of land in southeastern Kentucky while snow was on the ground. Also, a helicopter was used to cover the large tract of land and allowed aerial firing of the net gun. The combination of these variables allowed the capture method to be effective. Although the technique was not described in detail, the results of the capture method were given. The amount of trapping days were not given. Assuming the trapping days were during winter, there were approximately 90 trap days. This approximates to 2.25 trap nights/elk. Even though this method is efficient, it did cause some unfortunate injuries. Seward noted that, “[…] 14 died from trap related injuries during the first 6 weeks post release.” (et al 2005). The numbers come out to a casualty rate of 35%. One notable feature of this trapping method is that it does not rely on bait, but does rely heavily on the helicopter which can become expensive. They found that the average cost was around $250/flight to monitor their research. No expense reports were given for both the cost of flights to capture and the cost of pharmaceuticals. However, it can be interpreted that costs added up quickly (Seward et al 2005). Collapsible Clover Trap Thompson used a modified collapsible clover trap for his study which once again targets the smaller Rocky Mountain Elk (et al 1989).
The collapsible clover trap is essentially a large box trap with one open end and is collapsible. Sparrowe and Springer give a detailed explanation to how it was constructed (1970). The initial cost of construction averaged $268.00/trap. The traps were baited with alfalfa hay during the winter and pieces of salt chips during the summer. Although the sites were not pre baited, they made use of bait trails where the results were found to, “[…] [lead] elk and deer into traps from a distance of several hundred meters.” When the elk entered the trap, a trip wire would be set off and the door. The trap was check every 24 hours by at least two people. Two people were necessary for restraining the elk by collapsing the trap on top of it (see figure 1). This requires practice and caution as Thompson’s group did encounter some issues. When two elk were in the trap at once, they always released one to prevent injury. Also, they made sure to keep the neck from doubling back to keep from snapping it during folding. They sawed off the antlers of any male elk caught in the trap to prevent entanglement. After the elk was restrained, they made sure to apply eye ointment and cloth to the eyes to prevent drying out. This trap has potential for high mortality rates. They recorded that, “Six elk died during handling or as a direct result of capture (3.0% of all
elk captured).” Capture myopathy is a risk with this trap as one cow died from it. Thompson stated that, “Costs of traps, supplies (trap maintenance, bait, miscellaneous), and travel (km travel x $0.18/km) per captured elk averaged […] (excluding labor) of $111.41/elk.” Prices can also go up depending on labor. Overall the collapsible clover trap had a capture rate of, “[…] (13.7 trap-nights/elk). Capture rates generally improved each year […]” The trap did have two forms of trap bias. The trap was not effective at capturing over two year old males as they were hesitant to enter the trap. Also, the same elk sometimes returned to the trap for bait, but this was remedied by moving the trap every week. It was transportable by folding and placing in back of a truck, or could be carried 100m with relative ease (Thompson et al 1989). This trap was effective and recommended for widespread use when needing to capture cows (Thompson et al 1989). Corral Pens Corral pens are semi-temporary trap that rely on bait to attract both Rocky Mountain Elk and Roosevelt Elk. There are many different ways a corral trap can be built. They can be stationary or portable depending on what is needed. The articles under review built temporary traps that could be moved in order to prevent trap bias. The baits used were namely salt, apples, hay, and anise oil (Couey 1949, Mace 1971, and Pedersen 1977). Pre baiting was performed in both Mace and Pedersen’s trapping attempts. The coral pen is a passive trap consisting of six 8ft high panels and two gates. A tripwire at the back of the pen will trigger the gate to close (see figure 2). The average expense per animal without netting was $118 (Mace 1971). The corral traps were effective at capturing the required number of elk for their respective studies. With the panel corral trap, Mace had a capture rate of 2.71 trap nights/elk (1971). In the final year of trapping Pedersen had a capture rate of 1.4 trap nights/elk (1977). While the corral pen has potential, the first few years were not as successful and took trial and error to become more efficient. The capture rate of the first year was 9 trap nights/elk. No mortality rates were provided.
Discussion
Each trap has its short comings. For example, the net gun method was effective at capturing animals across a large landscape. This technique required experienced people to operate the helicopter and net gun. The mortality rate was also higher than any of the other techniques. Although the reason of deaths were not given, it echoes the fact that experience is necessary for this technique. The collapsible clover trap had sexual bias and the trapping of male elk could effect fitness. The corral pen required either a lot of time or man power to maintain, and the price of labor could add up. All of the traps listed used chemical immobilization to calm animals while captured. Common drugs used were succinylcholine chloride or a carfentanil citrate/xylazine hydrochloride mixture (Kreeger 1996, Mace 1971, and Murrow 2007). The drugs reduce stress on capture animals and prevent possible mortality. After examination of the trapping methods, the corral pen was the most effective (see table 1). Also, there seems to be a correlation to amount of manpower to better capture rates. More examination of this trend is needed as it may change as technology improves.