Ross Maclennan, Department of Tourism and Renewable Resources, RegIna Saskatchewan s4p 3Nl

Transcription

1 Reasons For The Decline In Moose Populations In Saskatchewan Ross Maclennan, Department of Tourism and Renewable Resources, RegIna Saskatchewan s4p 3Nl ABSTRACT Moose (AZaes azaes) populations in Saskatchewan increased throughout the 1960's to a high point in 1968 and By 1973, however, aerial surveys showed very low populations. Decreases in harvest totals and bull to cow ratios in the kill of less than one, indicated that over hunting may have contributed to the decline of moose in some zones, but other major factors also appeard to be involved. Aerial surveys from a non-hunted area, an. abnormal age structure in harvested moose and high snow depth indices indicated that a large die-off of moose occurred during the winter of This loss lowered the population to the point that even though the hunting pressure in 1972 was r~duced overhunting occurred in much of the moose range. These two factors combined to substantially lower the moose population.

2 INTRODUCTION The moose population in Saskatche~an has varied considerably in past years. In the early 1950's, the season was closed because of reported low populations, but since 1953, an either sex moose season has beel held. Since 1956 the season has been divided up into an early (calling) season and a regular (snow) season. Throughout the 1960's the early season was three weeks in length and the regular season four weeks. As moose hunting beca~e more. popular during the 1950's and 196P's, research and management programs relating to moose expanded considerably. Aerial surveys were started in 1954, expanded in 1958 and again in Big game checking stations were established in 1963 and by 1965 covered most of the province. Hunter questionnaire surveys were standardized by 1959 and expanded through the sixties. The results of these studies were incorporated into a moose management program along with the usual smattering of "gut feelings" and public pressure which are common to most game management schemes. Generally speaking, moose populations increased gradually to a peak in 1968 and 1969 then began decreasing slowly until when a sharp decrease was noticed in most of the areas of the province. Hunter numbers also increased gradually reaching a peak of about 18,000 in The combination of decreasing moose populations and increasing hunting pressure created considerable public reaction in 1971 and this combined with concern by Department of Natural Resources field staff resulted in a partial restriction of hunting in north-eastern Saskatchewan in 1972 and further restrictions in This paper analyzes some of the management data collected since 1963 and attempts to determine the reasons for the apparent decline in moose populations. METHODS The transect method of aerial surveys was used throughout the province. Survey blocks were set up to sample most of the moose range. The number of survey blocks flown reached a high of 25 in 1959 but after 1959 some of the smaller blocks were discarded so that by 1968, 19 blocks comprising almost 4,000 miles of transects were flown. In 1970, severe budget cuts reduced the survey to its present size of 11 blocks totalling 2,700 miles of transects (Fig. 1). 64

3 ~. "~ l,\ \ l>')o "- i? i22z! AERIAl. SlJRIIEY!LOCKS Ileoi' \..ClIt % A:mCo!ne 1'"IaII 3~- 4~IOnd.Gemral!SpnS!\.iff 61b'd'1RIWI' TCcrtle\.dltEast S()arft"aleSaltt'l 9WO~ K'ft1rt [0 CcId Ulle II00vidt *Q<ECK1NO STATlONS A~ B'Sq..rJWFQ:ltis C~tcI'Il..ckr o Candle l,qkt E ElOinc' Lalit> F~LQIra G_I.<'- N.,'bwg r.... to!or'f 13 Fig:1 Aerial survey blocks and big game checking stations in relation 10 Game Management zones.

4 A total of six Big Game Checking Stations were operated until 1971 when another one was added. These stations were set up on main acceds routes leading into popular moose hunting areas and were operated on a 24 hour basis throughout the season. Hunters were asked to stop in on the way into the hunting area and leave their name and hunting location in case of emergencies. After their hunt, they were asked to stop and give success rates, location of kill, sex and age data and to bring in jaws or incisors. In the last two years, hunters have been asked to supply biological samples such as reproductive tracts and kidneys. The transects were flown in late January and February at an altitude of 600 feet and counts were made for 1/4 mile on each side of the p~ane. Two observers were used and the pilot navigated and plotted observations on a map. Pilot and observers were kept constant from year to year when possible. From 1966 to 1973 the same pilot and observers were used. All aircraft used were top-winged models particularly Dehaviland Beaver and more recently Cessna 185. Air speed on transect approximated 90 to 100 miles per hour. The hunter questionnaire was sent out to a sample of hunters near the end of ' the season. If no reply was received, a reminder was mailed but there was no other followup. Questionnaires were sent out to 20% of all moose hunters. This sample was drawn from a list of licence holders from the previous year. RESULTS AND DISCUSSION Moose densities obtained from aerial surveys are given in Table 1. A gradual increase in moose densities occurred until 1969, followed by a sharp decrease. The 1973 surveys showed the lowest density in the 11 year period. In 1972, all 10 survey blocks had lower than average densities but many of the 1972 densities were only slightly below average. In 1973, 10 of 11 blocks had densities below the long term average and many of the 1973 densities were 30 to 50% below average. 66

5 Table 1 Aerial Survey Results 1963 to 1973,urvey Block Leaf Lake P orcup i rie"p"lai n Cumberland South Cumberland Central Pine Bluff Torch River Candle Lake East Dore Lake South Waterhen-Keeley Cold Lake Divide Number of 59,. Miles Surveyed lp Moose Per Square Mile Ave ~ t 1.lt ; l t t o ' o o Weighted Average t '\ ~

6 While these figures gave rise for concern, biologists could not put absolute faith in the transect surveys because of the findings of the Alaska Moose Research Station (LaResche and Davis 1971). Studies on penned moose ~howed high variation in counts depending on experience of observers and flight conditions. An attempt was made to overcome the problem by making the statistical assumption that between 1963 and 1971 the moose population of Saskatchewan had not changed and therefore any changes in survey results were due solely to changes from year to year in observers, flight conditions, snow depths, etc. A 1963 to 1971 mean and standard errol' was found for eac,1 survey block. The standard error was then multiplied by the t(n-l) value. Using this value the 95% confidence limit for each block was calculated (Sokal and Rohlf 1969). This method placed limits on the errors in survey results caused by annual changes in techniques. Thus if a survey density fell below the lower 95% confidence level, it indicated a lower population. Using this theory, densities of 1972 and 1973 were compared to the lower confidence limits of the mean densities. This informatiori is summarized in Table 2. Table 2 Hoose Per Square Mile From 1963 to 1971 Aerial Surveys and Lower 95~ Confidence Limits Block No Lower 95% Confidence Limit Densities Survey Block Mean+SE x t(n-l) [mean-se {t(n-l)] 1972 Leaf Lake Porcupine Plain Cumberland South Cumberland Central Pine Bluff Torch River Candle Lake East Dore Lake South '7 Waterhen-Keeley O.BO Cold Lake Divide ,

7 In 1972, three of 10 survey blocks had lower densities than the 95% confidence level. These blocks were all located in north-eastern Saskatchewan. In 1973 seven survey blocks of eleven showed lower densities than the '95% confidence level. Vegetation differences between survey blocks should be considered before conclusion3 on population trends are made. Survey blocks 3, 'I, and 5 are predominately willow (Salix sp.) flats intermixed with stands of aspen (Populus tremuloides) 'and balsalm poplar [Populus balsamifera}. Blocks 1, 2, 9, 10, 11, have large stands of aspen with smaller stands of conifers intermixed. The other three blocks are principally conifers with lesser amounts of aspen. In areas of willow and aspen cover, observability of moose is quite good compared to blocks comprised mainly of conifers. Thus changes in survey results in willow or aspen areas more likely reflect true changes in populations than do surveys in coniferous areas. If the results of the aerial surveys are credible, then some explanation for the decrease in population must be found. One possible reason for decreasing populations is excess hunting. Cummings (1973) found that in a small area of Ontario where overhunting was purposely allowed, two harvest statistics reflected overhunting. As the population decreased, kill totals declined and bull to cow ratios dropped below 1.0. Table 4 gives the Saskatchewan kill by zones tabulated from hunter questionnaire surveys. Table 3 Moose kill by zone from hunter questionnaire survey Zone A 34B B 181'" 645 6, * B9 98 1: '" ISS !l 'l B Blil {' TOTAL 3'iiO' 'i6O """"6iiOl I: These zones put on a draw system in A sizeable reduction in kill occurred in the 1971 survey in Zones 23, 30 and 34B with Zone 34A showing some drop. Reduced harvest occurred in Zones 27, 31, 34A in 1972 but 69 the kill rose somewhat in Zone 30. Zones 23 and 34B along

8 with other zones in northern Saskatchewan were put on a draw licence system in 1972 and the kill was greatly reduced. Bull to. cow ratios were obtained from checking stations and from hunter questionnaires, however, sample sizes on the questionnaire data were too small to be reliable. Tables 4 and 5 give bull to cow ratios in the harvest. Table 4 Bull to cow ratio in harvest from checking stations Average Station Sample Size Otosquen ~98'" 341 Squaw Candle-Hanson Dore Lake Meadow Elaine Lake '" 1972 sample size at Otosquen was only 87 animals. The checking station data did not indicate any areas where more cows than bulls were shot until 1971 when the Squaw Rapids area had a ratio of However, in 1972, four stations showed ratios of less than one. Table 5 Bull to cow ratio in harvest from hunter questionnaire survex Zone Averase Sample Size A 34B 35J : 'I"':"' Not sufficient data Great caution must be used in making conclusions on Table 5. Sample sizes are very small and bull to cow ratios vary from year to year without showing a definite pattern. A few zones bear mentioning because low bull to cow ratios correspond to decreases in kill in Table 3. Zones 23 and 34B are two zones which show signs of overhunting and zones such 70

9 as 30 and 31 show varying ratios that switch from below one to above and then below again. Combining data from Tables 3, 4, and 5, overhunting appears to have occurred in Zones 23 and 34B and possibly 34A by In 1972, overhunting appears to have occurred in most parts of the province except the western and northern areas. Only Meadow Lake and Elaine Lake checking stations had bull to cow ratios of ~.Iore than one. If overhunting occurred throughout much of the province in 1972, it would be expected that hunting pressure increased. Table 6. however, shows that the opposite occurred with both hunter numbers and success rates decreasing. Because of these figures, it is difficult to conclude that hunting was the major cause of the moose decline. Table 6 Number of hunting licences and success rates Year Success Rate Success Rate No. of Licences From Questionnaire From Checking Stations ,204 9,459 9,414 10,066 11,845 14,295 13,643 17,363 18,080 12, Winter mortality can be a major factor in decreases of ungulate populations. Three factors indicate that the winter of was a worse than average winter and likely caused a substantial reduction in moose. Prince Albert National Park is situated in the centre of the Saskatchewan moose range. Because no hunting is allowed iri the park, it can be used as a control area to determine whether hunting or some other factor was responsible for the decline. Table 7 gives the results of aerial surveys conducted in the park (Young, Millard and Leader, 1973). Table 7 Aerial Surveys Prince Albert National Park Ungulate Density Per Square Mile Species % Ch ange Moose Elk

10 -----: AVERAGE I VI UJ ~ 15 ~ 11. o I Z UJ U ~ AGE CLASS ~ Fig.2 Age strucfl!re of moose harvested from compared with 1972.

11 ~1600 o ~ :t: 15OO h: UJ ~ ~ 1300 BOO!! );:; rO l w Fig.3 Snow depth indices for eastern 3/4 of Saskatchewan moose range.

12 The 40% decrease in moose populations 'and 44% in elk populations cannot be attributed to hunting within the park. A large winter loss of animals must have occurred., If a large loss of moose occurred in the winter of , the calf segment of the populatio~ would be hardest hit because they have the lowest fat reserves (McGillis 1972) and being smaller cannot cope with deep snow as well as adults. The normal age structure in the harvest for years and the 1972 age structure is shown in Figure 2. The age structure of 1972 strongly indicates a large loss of calf moose, and perhaps yearling animals between the 1971 and 1972 hunting seasons. The 1971 calf kill was close.to normal at 13.6%. However, in 1972 the yearling segment formed only 12.1% of the kill comp~red with over 25% normally. ihe most likely cause of the low yearling segment in 1972 is a large loss of calves during the, previous winter. Several factors combine to cause severe winters. Snow depth, snow densii1 and crusting are important as is the length of winter. Gasaway and Coady (1973) found that moose existed in, a state of negative energy balance throughout the fall, winter and early spring and the length 6f time an animal had to exist on its fat reserves could be a critical component of winter ~urvival., At the time of writing, the only winter severity data available was snow depths recorded by Atmospheric Services of'environ~ent Canada. Snow depths were taken at the end o~ eadh month, at major weather stations. These snow depths were analyzed s~milar to the method of Coady (1973). which plots snow depth from fall to spring and uses the area under the curve as,~ snow index. Figure 3 summarizes snow depths indices from most'bf the moose range in Saskatchewan except for the extreme western area. The winter of , and had the highest snow depth indices. In both and 71-72, reports of dead moose and deer were received from regional staff of the Dept. of Natural Resources, trappers and Indians. However, few if any reports were received in 66~67. Factors other than snow, depth must be analyzed to furthe'r classify the severity of winters. Considering all data given in this paper, we can conclude that moose harvest levels increased throughout the 1960's but were,:in balance with populations and reproduction. In 1971 both harvest totals and bull to cow ratios indicated that overhuriting had occurred in at least two game management zones in north-eastern Saskatchewan,. To remedy this, five zones were placed on a compulsory draw system. In 1972 both total hunters and hunting success decreased substantialiy from previous years. Despite this, overhunting appeared to take, place in many parts of the moose range. '

13 The only logical explanation for the widespread overhunting in 1972 was that moose populations in the fall of 1972 had to be substantially lower than the previous winter's aerial surveys had indicated. The most likely reas~n for a reduced herd was a severe winter-kill after the surveys were flown. A reduced yearling segment in the 1972 harvest strongly indicates a large loss of calf moose during the winter of Snow depth i~dices showed that the winter in question did have deep snow conditions comparable with only two other winters since Aerial surveys in Prince Albert National Park also suggest a sizeable drop in ungulate populations during the same period even trough hunting is not permitted. Thus the most likely explanation for the reduced moose populations in much of Saskatchewan is that after a fairly heavy harvest in 1971 a winter los~ occurred which substantially lowered the moose p~pulations. Since these losses occurred after the winter aerial surveys, game managers did not appreciate the extent of these losses and allowed a normal hunting season in all but fiv~ game management zones. Overhunting likely occurred in much of the province in 1972 reducing the population still further. In order to avoid a similar situation in the future, reliable indices of winter severity must be developed. Data needed include snow depths, density and crusting factors and a measurement of the period of negative energy balance. These factors should be correlated with animal condition and mortality to provide game managers with suitable assessments of winter severity and game losses before the following hunting season is legislated. 75