California Bighorn Sheep Population Inventory Management Units 3-17, 3-31 and 3-32 March 20 & 27, 2006 Prepared for: Environmental Stewardship Division Fish and Wildlife Science and Allocation Section Thompson Region by: S. L. Lemke D.N. Jury May 2006
SUMMARY Bighorn sheep sightings, MUs 3-17, 3-31 and 3-32, March 2006. MU Survey Date Rams Ewes Lambs Ylg Ram, Ewe & Lamb U/C Adult Total Sheep Ylg I II III IV U/C Total 3-17 20-Mar-06 0 1 5 7 0 0 13 65 7 0 0 85 3-31 20-Mar-06 0 5 15 10 0 0 30 98 23 0 0 151 3-32 27-Mar-06 3 5 15 13 1 0 37 73 9 0 0 119 Totals 3 11 35 30 1 0 80 236 39 0 0 355 Bighorn sheep herd composition, MUs 3-17, 3-31 and 3-32, March 2006 MU Survey Date Total Count Lambs/100 Ewes Rams/100 Ewes % Juvenile 3-17 20-Mar-06 85 11 20 9 3-31 20-Mar-06 151 23 31 15 3-32 27-Mar-06 119 12 51 8 Sheep sighting rates by MU, MUs 3-17, 3-31 and 3-32, March 2006 MU Total Sheep Search time (hrs.) Sheep/hour 3-17 85 1.9 44 3-31 151 2.8 55 3-32 119 3.7 32 Totals 355 8.4 42 ii
Table of Contents SUMMARY... ii INTRODUCTION... 1 2006 SURVEY RESULTS... 1 Animal Sightings... 1 Management Unit 3-17 (Lillooet-Kelly Creek; Fraser River portion)... 2 Management Unit 3-31 (Kelly Creek Canoe Creek; Fraser River portion)... 2 Management Unit 3-32 (Fraser West; Fraser River portion)... 2 Sighting Rates and Group Size... 3 DISCUSSION... 3 Population Trends and Herd Composition... 3 Management Unit 3-17... 3 Management Unit 3-31... 5 Management Unit 3-32... 6 Recent Population Declines... 7 Harvest Strategy and Ram Harvest... 8 Management Unit 3-17... 8 Management Unit 3-31... 9 Management Unit 3-32... 11 RECOMMENDATIONS... 12 REFERENCES... 14 List of Tables Table 1. Bighorn sheep sightings and classifications, MUs 3-17, 3-31 and 3-32, March 2006... 1 Table 2. Bighorn sheep classifications, MU 3-17, 20 March 2006... 2 Table 3. Bighorn sheep herd composition, MU 3-17, 20 March 2006... 2 Table 4. Bighorn sheep classifications, MU 3-31, 20 March 2006... 2 Table 5. Bighorn sheep herd composition, MU 3-31, 20 March 2006... 2 Table 6. Bighorn sheep classifications, MU 3-32, 27 March 2006... 3 Table 7. Bighorn sheep herd composition, MU 3-32, 27 March 2006... 3 Table 8. Sheep sighting rates by MU, MUs 3-17, 3-31 and 3-32, March 2006... 3 Table 9. Summary of MU 3-17 California bighorn sheep herd composition data from aerial surveys, 1988-2006... 4 Table 10. Summary of MU 3-31 California bighorn sheep herd composition data from aerial surveys, 1988-2006... 6 Table 11. Summary of MU 3-32 California bighorn sheep herd composition data from aerial surveys, 1988-2006... 7 iii
List of Figures Figure 1. Population trend for MU 3-17 California bighorn sheep, based on a population projection model, 1985 2006... 4 Figure 2. Population trend for MU 3-31 California bighorn sheep, based on a population projection model, 1985 2006... 5 Figure 3. Population trend for MU 3-32 California bighorn sheep, based on a population projection model, 1985 2006... 7 Figure 4. Estimated hunter effort and California bighorn ram harvest, MU 3-17, 1994 2004... 8 Figure 5. Proportion of rams observed in age/horn curl classes, MU 3-17, 1988 2006. 9 Figure 6. Estimated hunter effort and California bighorn ram harvest, MU 3-31, 1994 2004... 10 Figure 7. Proportion of rams observed in age/horn curl classes, MU 3-31, 1988 2006.... 10 Figure 8. Estimated hunter effort and California bighorn ram harvest, MU 3-32, 1994 2004... 11 Figure 9. Proportion of rams observed in age/horn curl classes, MU 3-32, 1988 2006.... 12 iv
INTRODUCTION The California bighorn sheep (Ovis canadensis californiana) holds significant value in British Columbia as a challenging quarry for recreational hunters, a memorable wildlife viewing/photographic experience for outdoor enthusiasts and as an important part of the wildlife heritage of the province. Informed management and effective conservation of wildlife populations require accurate and consistent inventory information; perhaps for no group of populations is this more important than for the California bighorn sheep of the southern interior portion of the Fraser River basin, many of which have recently undergone dramatic population declines. The aim of formal inventory work is to provide an unbiased estimate of abundance and an index of the sex and age composition of the target populations. To this end, classification count surveys are frequently conducted to assess the status of sheep herds and provide a stronger basis for determining recent population trends. Without this data, regional wildlife managers will be forced to manage populations based on outdated information about dynamic animal populations. The purpose of the current survey is to obtain current, precise population inventory data for California bighorn sheep in those portions of Management Units (MUs) 3-17 (northern), 3-31 and 3-32 bordering the Fraser River. Each of these herds was most recently surveyed in 2002. 2006 SURVEY RESULTS Animal Sightings Three hundred and fifty-five (355) sheep were seen over the two-day survey period (Table 1). Of sheep sighted, 316 (89%) were classified as adults; ewes accounted for 75% of the total adult count. Thirty-nine (39) lambs (approaching one year old) comprised 11% of the total count. Table 1. Bighorn sheep sightings and classifications, MUs 3-17, 3-31 and 3-32, March 2006. MU Survey Date Rams Ewes Lambs Total Sheep Ylg I II III IV U/C Total 3-17 20-Mar-06 0 1 5 7 0 0 13 65 7 85 3-31 20-Mar-06 0 5 15 10 0 0 30 98 23 151 3-32 27-Mar-06 3 5 15 13 1 0 37 73 9 119 Totals 3 11 35 30 1 0 80 236 39 355 1
Management Unit 3-17 (Lillooet-Kelly Creek; Fraser River portion) Eighty-five bighorns were classified in the northern portion of Management Unit 3-17. The total included 13 rams, 65 ewes and 7 lambs (Table 2). Herd composition ratios determined from these data were: 11 lambs/100 ewes, 20 rams/100 ewes and a 9% juvenile component (Table 3). Table 2. Bighorn sheep classifications, MU 3-17, 20 March 2006 MU Survey Date Rams Ewes Lambs Total Sheep Ylg I II III IV U/C Total 3-17 20-Mar-06 0 1 5 7 0 0 13 65 7 85 Table 3. Bighorn sheep herd composition, MU 3-17, 20 March 2006 MU Survey Date Total Count Lambs/100 Ewes Rams/100 Ewes % Juvenile 3-17 20-Mar-06 85 11 20 9 Management Unit 3-31 (Kelly Creek Canoe Creek; Fraser River portion) Bighorn sheep observed in MU 3-31 were classified as follows: 30 rams, 98 ewes and 23 lambs (Table 4). An adult sex ratio of 31 rams/100 ewes and a productivity index of 23 lambs/100 ewes were calculated from this data. Fifteen percent of the animals classified were juvenile (Table 5). Table 4. Bighorn sheep classifications, MU 3-31, 20 March 2006 MU Survey Date Rams Ewes Lambs Total Sheep Ylg I II III IV U/C Total 3-31 20-Mar-06 0 5 15 10 0 0 30 98 23 151 Table 5. Bighorn sheep herd composition, MU 3-31, 20 March 2006 MU Survey Date Total Count Lambs/100 Ewes Rams/100 Ewes % Juvenile 3-31 20-Mar-06 151 23 31 15 Management Unit 3-32 (Fraser West; Fraser River portion) One hundred and nineteen (119) sheep were classified in MU 3-32 on 27 March 2006 37 rams, 73 ewes and 9 lambs (Table 6). Eight (8) percent of the total count was comprised of juvenile animals, while herd composition indices were calculated at 51 rams/100 ewes and 12 lambs/100 ewes (Table 7). 2
Table 6. Bighorn sheep classifications, MU 3-32, 27 March 2006 MU Survey Date Rams Ewes Lambs Total Sheep Ylg I II III IV U/C Total 3-32 27-Mar-06 3 5 15 13 1 0 37 73 9 119 Table 7. Bighorn sheep herd composition, MU 3-32, 27 March 2006 MU Survey Date Total Count Lambs/100 Ewes Rams/100 Ewes % Juvenile 3-32 27-Mar-06 119 12 51 8 Sighting Rates and Group Size Sheep sighting rates were highest in MU 3-31, where 151 sheep were observed in 2.8 hours of search time (55 sheep/hour). The lowest sighting rate was in 3-32 at 32 sheep/hour (Table 8). The overall sighting rate for the surveys was 42 sheep/hour. Average group sizes were 7.7, 7.2 and 7.9 animals for MUs 3-17, 3-31 and 3-32, respectively. A few animals were observed alone, while the largest group sighted was 46 animals (36 ewes, 8 lambs, 1 yearling ram and 1 Class II ram). Table 8. Sheep sighting rates by MU, MUs 3-17, 3-31 and 3-32, March 2006 DISCUSSION MU Total Sheep Search time (hrs.) Sheep/hour 3-17 85 1.9 44 3-31 151 2.8 55 3-32 119 3.7 32 Totals 355 8.4 42 Population Trends and Herd Composition Management Unit 3-17 Management Unit 3-17 includes range of both California and Rocky Mountain bighorn sheep, with the former occupying the more northerly portion of the unit, and the Rocky Mountains inhabiting the southern areas. A region of overlap of the two subspecies is centred on Lillooet. For inventory purposes, animals occurring north of Lillooet to the northern boundary of the unit at Kelly Creek are considered exclusively California bighorns. The number of animals observed during surveys has fluctuated quite dramatically over the years. The trend since the early 1990s has been toward declining numbers (Figure 1). Lamb:ewe ratios calculated from survey counts have also varied widely between 1989 and 1999; however, this may be an artifact of variability in survey 3
timing rather than an actual trend in recruitment (Table 9). The most recent surveys, including the 2006 effort, however, have recorded very low lamb:ewe ratios, and ground crews have observed weak lambs that were unable to keep up with the ewes since 2002. The adult sex ratio has ranged from 20 to 102 rams per 100 ewes, with the lowest recorded ratio from the current (2006) survey. Survey counts, recruitment and adult sex ratios all point to a population in trouble. 300 250 Bighorn Sheep 200 150 100 50 0 1980 1985 1990 1995 2000 2005 2010 Year Survey Count Pop Estimate Trend Figure 1. Population trend for MU 3-17 California bighorn sheep, based on a population projection model, 1985 2006. Table 9. Summary of MU 3-17 California bighorn sheep herd composition data from aerial surveys, 1988-2006 Survey Date Total Count Lambs/100 Ewes Rams/100 Ewes % Juvenile 29-Mar-88 82-29-Mar-89 153 40 90 12 28-Mar-90 207 51 67 18 30-Nov-92 219 57 102 12 24-Nov-93 254 38 46 17 23-Nov-94 227 19 32 6 8-Aug-95 155 68 38 21 12-Jan-96 200 37 26 20 21-Apr-99 69 44 56 17 27-Mar-01 175 26 34 13 15-Mar-02 107 9 22 7 8-Apr-02 159 8 28 6 20-Mar-06 85 11 20 8 4
Management Unit 3-31 Total survey counts and high lamb:ewe ratios in the late 1980s and early 1990s indicated a healthy, increasing population on the east side of the Fraser River (Figure 2, Table 10). With the population at its highest recorded levels, reports of weak lambs and poor lamb survival were first reported in the autumn of 1993, and lungworm-bacterial pneumonia caused mortality was confirmed in 1995. In an effort to reduce pressure on heavily utilized winter habitats and to spur lamb growth rates and recruitment, animals were removed for transplant to the western U.S. (102 animals between 1994 and 1996) and ewe harvests under Limited Entry Hunting (LEH) were increased. Despite these efforts, recent survey data indicate a continuing decline in total counts and, perhaps most significantly, in the lamb:ewe ratio. Although the productivity index is not as low as in the adjacent MUs surveyed in 2006, the downward trend in this indicator over the past 5 years, similar to that seen in MUs 3-17 and 3-32, is cause for concern. Ram:ewe ratios seem to be declining as well. The current population appears to be approximately 40% that of the 1990 estimate. 700 600 Bighorn Sheep 500 400 300 200 100 0 1980 1985 1990 1995 2000 2005 2010 Year Survey Count Pop Estimate Trend Figure 2. Population trend for MU 3-31 California bighorn sheep, based on a population projection model, 1985 2006. 5
Table 10. Summary of MU 3-31 California bighorn sheep herd composition data from aerial surveys, 1988-2006 Survey Date Total Count Lambs/100 Ewes Rams/100 Ewes % Juvenile 29-Mar-88 145-30-Mar-89 496 42 42 18 28-Mar-90 525 52 65 18 30-Nov-92 468 66 193 9 23-Nov-93 450 26 41 15 23-Nov-94 219 31 38 18 8-Aug-95 294 48 44 11 12-Jan-96 32 29 24 19 21-Apr-99 65 39 58 20 27-Mar-01 165 32 45 18 15-Mar-02 130 30 20 20 8-Apr-02 121 26 23 17 20-Mar-06 151 23 31 15 Management Unit 3-32 Recent survey data for the Fraser West herd indicates that the herd may be heading towards a decline (Figure 3). A significant decline in the lamb:ewe ratio since 2001 has occurred and, if it continues, will lead to similar population decline as seen in the East Fraser herds. The number of animals observed in the 2006 survey was promising (as was the adult sex ratio), although the recruitment index remains depressed at 12 lambs per 100 ewes (Table 11). 6
300 250 Bighorn Sheep 200 150 100 50 0 1980 1985 1990 1995 2000 2005 2010 Figure 3. Population trend for MU 3-32 California bighorn sheep, based on a population projection model, 1985 2006. Table 11. Summary of MU 3-32 California bighorn sheep herd composition data from aerial surveys, 1988-2006 Survey Date Total Count Lambs/100 Ewes Rams/100 Ewes % Juvenile 14-Mar-88 59 - - - 27-Mar-90 76 27 37 13 23-Nov-93 128 39 61 20 22-Mar-94 37 36 32 22 11-Sep-96 41 16 13 12 27-Mar-01 156 32 54 17 19-Nov-01 49 11 22 8 12-Mar-02 100 21 26 14 17-Apr-02 88 9 28 7 27-Mar-06 119 12 51 8 Recent Population Declines Year Survey Count Pop Estimate Trend Poor lamb survival appears to be a common denominator in each case of declining sheep numbers in the Fraser River herds; however, the underlying causes of low recruitment are unclear, as are other factors that may be contributing to these declines. During the past several years, the Management Plan for California Bighorn Sheep in the Fraser River Basin, has directed work to shed some light on the reason(s) for seemingly chronic poor lamb survival in several of the Fraser River herds. 7
Harvest Strategy and Ram Harvest Management Unit 3-17 California bighorn ram harvest and hunter effort in MU 3-17 have been, in general, proportional (Figure 4). An increase in effort and harvest from 1998 through 2000 followed a 1996 regulation change where a ¾-curl LEH replaced a full-curl general open season (GOS). This increased harvest attended a growing proportion of Class III rams in the population (Figure 5). Toweill (1999), addressing California bighorn harvest specifically, has suggested a sustainable harvest level of 8% of the total ram component of a herd. With this herd currently estimated at 125 animals, approximately 32 of which would be rams (assuming herd composition of 15 rams:100 ewes:40 lambs; see Table 9), an annual harvest of 2.6 rams should be sustainable. The 3-year average harvest is currently 4.3. With all signs pointing to a population in trouble, ram classification data and harvests must be carefully monitored to ensure that mature rams are always present in a population. Toweill and Geist (1999) suggest that old rams are essential to pass along traditions of seasonal habitat use and travel/migration corridors between critical habitats, without which parts of their range may be permanently abandoned. These patriarchal individuals also guide the social behaviour of the ram population; for example, luring young rams away from females immediately following the rut to reduce competition for food on ewe winter ranges. 700 600 500 400 300 200 100 Hunter-days Harvest 8 7 6 5 4 3 2 1 0 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Figure 4. Estimated hunter effort and California bighorn ram harvest, MU 3-17, 1994 2004. 8
100% 90% 80% 70% 60% IV III II I 50% 40% 30% 20% 10% 0% 1989 1990 1992 1993 1994 1995 1996 1999 2001 2002 2006 Figure 5. Proportion of rams observed in age/horn curl classes, MU 3-17, 1988 2006. Management Unit 3-31 Hunter effort and ram harvest in MU 3-31 increased through the early 1990s, followed by a sharp decline in both beginning in the 1996 season and continuing through the present time (Figure 6). Significant regulation changes occurred for the 1996 hunting season; a full-curl GOS replaced a ¾-curl GOS and an Any Male 1+ LEH draw was offered. The Any Male 1+ LEH was terminated the following year and a ¾-curl LEH joined the fullcurl GOS. A continuing decline in total counts, poor recruitment and low ram:ewe ratios are cause for concern. With a current population for the MU estimated at 250 animals, 59, or 24%, would be rams (based on average herd composition of 40 rams:100 ewes:30 lambs; see Table 10). An annual allowable ram harvest (AAH) under the suggested 8% sustainable level proposed by Toweill (1999) would be 4.7. Therefore, the recent low harvest (3-year average of 4.3) should certainly be sustainable, while still maintaining hunting opportunities. Live ram and harvest composition must be carefully tracked to ensure adequate mature rams are present for social and breeding purposes. 9
1200 1000 800 600 400 200 Hunter-days Harvest 45 40 35 30 25 20 15 10 5 0 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Figure 6. Estimated hunter effort and California bighorn ram harvest, MU 3-31, 1994 2004. 100% 80% 60% IV III II I 40% 20% 0% 1989 1990 1992 1993 1994 1995 1996 1999 2001 2002 2006 Figure 7. Proportion of rams observed in age/horn curl classes, MU 3-31, 1988 2006. 10
Management Unit 3-32 Hunter effort in MU 3-32 was on the increase in the late 1980s and early 1990s, while harvest was quite variable. Both variables began a precipitous decline in 1995 (Figure 8) The same regulation changes as were applied to MU 3-31 were instituted in MU 3-32, beginning in 1996. The number of animals observed in the 2006 survey was gratifying and the adult sex ratio appears strong; however, recruitment remains poor. There is considerable concern that this herd is heading towards a decline similar those observed in MUs 3-17 and 3-31. The bighorn population in MU 3-32 appears stable at approximately 200 animals (Figure 3, above). Assuming herd composition ratios of 50 rams:100 ewes:20 lambs, 29% or 59 animals should be rams. Again using the 8% sustainable harvest of rams suggested by Toweill (1999), the AAH for this MU would be 4.7. As in MU 3-31, current annual ram harvests (average 3.3 over the past 3 years) shouldn t negatively impact the mature ram component of the herd. Indeed, indications are that the proportion of older rams is increasing (Figure 9). 1000 900 800 700 600 500 400 300 200 100 Hunter-days Harvest 18 16 14 12 10 8 6 4 2 0 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Figure 8. Estimated hunter effort and California bighorn ram harvest, MU 3-32, 1994 2004. 11
100% 80% IV III II I 60% 40% 20% 0% 1988 1992 1994 1996 2001 2002 2006 Figure 9. Proportion of rams observed in age/horn curl classes, MU 3-32, 1988 2006. RECOMMENDATIONS 1) Consider reducing ram harvests in MU 3-17. Current population inventory, herd composition and harvest levels indicate that recent ram harvests may not be sustainable. Ram classification data and harvests must continue to be carefully monitored to ensure adequate mature rams are present for social and breeding purposes. The following management objectives from the Management Plan for California Bighorn Sheep in the Fraser River Basin (2004) are especially applicable to the herds discussed in this inventory report, and have been identified as imperative: 2) Document changes in bighorn sheep subpopulation distribution, size and demographics through frequent population inventory work, particularly in those herds experiencing declines and poor lamb survival. 3) Determine factors responsible for changes in bighorn sheep population distribution, size and demographics, using adaptive management methods, where possible. i. Investigate causes of bighorn sheep lamb mortality. ii. Assess predator impacts on bighorn sheep populations. iii. Investigate trace mineral cycles. iv. Investigate the interaction between bighorn sheep and agricultural production. 4) Maintain and enhance existing bighorn sheep migration corridors. 5) Inform domestic sheep and goat producers about domestic/wild sheep disease issue. 12
6) Monitor Fraser River Basin bighorn sheep health on an ongoing basis, through supporting and co-ordination of ongoing fecal, tissue, blood and forage sampling in Fraser bighorn sheep herds. 7) Secure funding to support applied research and long-term management programs. 13
REFERENCES Demarchi, R.A., C.L. Hartwig and Donald A. Demarchi. 2000. Status of Rocky Mountain bighorn sheep in British Columbia. BC Ministry of Environment, Lands and Parks, Wildlife Branch, Victoria BC. Wildlife Bulletin No. B-99. 56pp. Fraser River California Bighorn Sheep Advisory Committee. 2004. Management Plan for California Bighorn Sheep in the Fraser River Basin, British Columbia, including the Spences Bridge Rocky Mountain Bighorn Herd. Prepared for BC Ministry of Water, Land and Air Protection, Victoria, BC. 124 pp. Geist, V. 1971. Mountain sheep: a study in behaviour and evolution. University of Chicago Press, Chicago, IL. 383 pp. Halladay, D. R. and R. A. Demarchi. 1996. Wildlife Harvest Strategy: Improving British Columbia s Wildlife Harvest Regulations. British Columbia, Ministry of Environment, Lands and Parks, Wildlife Program. Victoria, BC. 73 pp. Harper, F. E. 2001. A Wildlife Inventory Strategy for Ungulate Game Species within the Southern Interior Region. Ministry of Environment, Lands & Parks, Kamloops, BC. 38pp. Hatter, I. W. and Wendy A. Bergerud. 1991. Moose recruitment, adult mortality and rate of change. Alces 27:65-73. Toweill, D.E. 1999. A Working Hypothesis for California Bighorn Sheep Management. Foundation For North American Wild Sheep Annual General Meeting, Reno, NV. Toweill, D.E. and V. Geist. 1999. Return of Royalty: Wild Sheep of North America. Boone and Crockett Club. Missoula, MT. Wegge, P. 1997. Guidelines for sustainable use of wild caprins. - Pp 365-370 in: Shackleton, D. (ed.). Action plan for wild caprins. - IUCN publication, Gland, Switzerland. 14