STATUS OF BOBCATS IN WYOMING 2015-2016 Wyoming Game and Fish Department August, 2016 INTRODUCTION The Wyoming Game and Fish Department has compiled the following data on bobcats (Lynx rufus) since the 1977-78 trapping season: harvest, trapper success, trapping effort, sex and age of harvested bobcats, and geographic distribution of harvest. These data are used to monitor the bobcat population and provide guidance to the Division of Scientific Authority (DSA) and the U.S. Fish and Wildlife Service regarding the export of bobcats harvested in Wyoming. Historically, analyses of bobcat population data collected in Wyoming have been comprehensive and costly to prepare. Since 2003-04, we have relied on harvest and effort indices, which provide an adequate and reliable assessment of bobcat population trends. Our last comprehensive report was submitted to the DSA in September, 2002. Please refer to the 2002 report (covering the 2001-02 trapping season) to access historical data and detailed population analysis. The recommended citation is: Wyoming Game and Fish Department. 2002. Population Analysis of Bobcats in Wyoming: 2001-2002: a report submitted to the U.S. Fish and Wildlife Service, Office of Scientific Authority in satisfaction of requirements of the Convention on International Trade in Endangered Species. Cheyenne, WY. 39pp + appendices. HARVEST MANAGEMENT PRINCIPALS Bobcat populations have naturally high rates of annual reproduction and mortality. From a management perspective, they are in a category of game animals that are protected from overexploitation by the “law of diminishing returns.” This is particularly the case in Wyoming, where trapping participation is comparatively low in relation to the large land area and abundance of opportunity. Harvest of bobcats through customary hunting and trapping methods is largely compensatory to other sources of mortality and is not the ultimate factor that regulates bobcat populations. When environmental conditions limit abundance of bobcats, they become more difficult to catch or hunt, catch rates decline and many trappers give up or put less effort into trapping bobcats. Even when the commercial value of pelts is high, the law of diminishing returns limits the number of bobcats taken by trappers and hunters. In addition, large tracts of occupied bobcat habitat are inaccessible to trappers and hunters due to remoteness or because access is restricted on private lands. These inaccessible areas serve as population reservoirs. In Wyoming, the bobcat population is limited principally by environmental conditions that affect prey availability. Based on a 25-year data set (1977-78 through 2001-02), the 1 estimated spring-to-fall survival of kittens is highly correlated (r = 0.93) with the abundance of the principal prey, cottontail rabbits (WGFD 2002). Similarly, the proportion of kittens in the harvest, a measure of recruitment, is strongly correlated with prey abundance. Throughout the period of record, the annual harvest of bobcats did not exceed the estimated annual recruitment of kittens in the fall (WGFD 2002) Pelt prices can have a strong bearing on trapper participation. Although pelt values of all furbearing species collectively influence trapper interest, values of bobcat pelts seem to have the highest correlation with numbers of trapping licenses sold annually in Wyoming. A regression analysis based on 26 years of data (through 2002-03) yielded the following relationship: Y = 1.75X + 766 r = 0.79 Where: Y is the annual number of licenses sold; and X is the average inflation-adjusted price (2003 $$) paid by non-resident fur dealers for bobcat pelts each year (most Wyoming bobcat pelts are sold out-of-state). This relationship accounted for the majority of the variation in annual numbers of trapping licenses sold. We re-ran the regression for all 39 years of data based on 2015 inflation-adjusted dollars resulting in the following relationship: Y = 0.86X + 1166 r = 0.32 The lower correlation coefficient (r) appears the result of higher trapper participation in recent years despite comparatively modest bobcat pelt prices relative to historic high prices in the 1970s and 1980s. The number of furbearer licenses sold generally increased from 1990 through 2013, although 2015-16 was the second consecutive year of declining sales (2,274 licenses sold – Table 1). Demand by foreign fur buyers caused pelt prices to increase in the recent past. However, pelt prices declined substantially during the 2015-16 trapping season (the third year in a row – Table 1), which may have contributed to the reduction in furbearer license sales and relatively unchanged harvest statistics. HARVEST MANAGEMENT AND MONITORING The 2015-16 furbearer regulation (Chapter 4, Wyoming Game & Fish Commission Regulations) is provided as Attachment 1. Furbearer trapping licenses are valid statewide; however 6 management areas have been established for the purpose of compiling and reporting bobcat harvest data (see map in Attachment 2). Beginning with the trapping season of 1982-83, through 2001-02, sex and age data were obtained by analyzing cementum annuli of tooth samples collected from bobcats. Results of past tooth analyses are reported in WGFD (2002). Detailed age structure data are not needed to manage bobcats in Wyoming. Therefore, the collection and submission of teeth for cementum annuli analysis (a costly monitoring 2 program) was discontinued beginning with the 2002-03 trapping season. Currently, information collected at the time pelts are presented for mandatory tagging includes: age distinguished as juvenile (kitten) or adult, sex, numbers of traps and days set, and locations trapped. The age and sex composition of statewide harvests since the 2002-03 season, are reported in Attachment 3. The statewide harvests from 1982 through 2002 were distributed among management areas in the following proportions: Area 1 (0.5%); Area 2 (23.0)%; Area 3 (40.8%); Area 4 (12.2%); Area 5 (11.3%); and Area 6 (12.2%) (Wyoming Game and Fish Department 2002). This harvest distribution does not change appreciably from year to year. Management Area 3 has consistently produced the largest bobcat harvests in Wyoming. The average monthly distribution of pelts tagged is: October (0.1%), November (11.6%), December (28.7%), January (30.5%), February (23.9%), and March (5.1%). POPULATION TREND ANALYSIS The Department has assembled a continuous record of catch rates and catch effort since 1977 (Table 1, Figs. 1 and 2). The average annual catch rate is 4.2 bobcats per trapper (n = 39 years, and has ranged from 2.3 in 2002-03 to an all-time high of 9.4 in 2004-05. The period of record includes 10 years in which the catch rate was 3.0 or fewer bobcats per trapper, and 10 years in which the catch rate was 5.0 or more bobcats per trapper. The annual catch rate was high during the 1990s (avg. = 4.8 bobcats per trapper), when pelt prices were low and fewer trappers (avg. = 889) were afield. The annual catch rate was lowest during the 1980s (avg. = 3.3 bobcats per trapper) when pelt prices were exceptionally high and substantially more trappers (avg. = 1,448) were afield. Average catch rates in the 1980s were low despite above average prey abundance and kitten recruitment. Relatively lower prey abundance during the latter 1990s and from 2008 through 2013 resulted in lower kitten survival, and undoubtedly somewhat lower bobcat populations. However, trapper success and effort did not suggest a substantial decline in the population. The number of bobcats caught per trapper was higher than average and trapping effort lower than average from 2003-04 through 2008-09 (Table 1). Based on field reports, the cottontail rabbit population declined sharply during summer and fall of 2008 and tularemia was detected in several regions of the State. This decline in prey abundance was reflected in a lower average cottontail harvest in the 2009-10 through 2013-14 harvest survey results (4.8 3.6, 3.4, 3.6 and 4.0 rabbits per hunter, respectively), signifying an end to the abundant prey population that had been at a cyclic high since 2003-04 (Table 1). However, in 2015-16 the average harvest of rabbits per hunter (10.2) increased for the second year in a row, suggesting the available prey base has again increased. This was also accompanied by a slight increase in percent kittens in the harvest, although bobcats harvested per trapper decreased slightly. While the proportion of kittens in the harvest did increase, it remained below the long term average of 21.1%. Catch effort in 2015-16 decreased slightly to 370 trap days per bobcat and remained below the long term average of 489 trap days per bobcat (Table 1). All 3 trend indices (trapper success, catch effort, and proportion of kittens in the harvest) were within the historical range of variation, indicating Wyoming’s bobcat population remains healthy. We have relied on the numbers of pelts tagged as a consistent means to estimate annual bobcat harvest since 1993-94. From that time through the present, there have been three periods of low 3 prey abundance and two periods of relatively higher prey abundance that are highly correlated with bobcat kitten recruitment (r=0.89 – Fig. 3, Table 3). Kitten recruitment and bobcat harvest success appear to decrease markedly when the cottontail prey index falls below 5 rabbits per hunter. Table 1. Trend data used to monitor Wyoming bobcat harvest, trapper activity and catch effort. Pelt Prices Paid by Catch No. Fur- N/R Fur Buyers No. Bobcat Percent Prey Index Catch Rate