Beaver Population Analysis and Research Proposal

8/14/2019 Beaver Population Analysis and Research Proposal

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Beaver Population Analysis

And

An Assessment of 1995-2004 Harvest Trends

Prepared byPaul Saunders

Wildlife Division

Corner Brook

Newfoundland and Labrador

Canada


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Beaver Population Analysis

Issue:

Concerns about current and historical beaver populations has been raised in previous

Furbearer Management plans. These concerns were brought forth primarily by trapperson the Northern Peninsula, Zone 11, and indicated that populations in this area haddeclined to a point where it became uneconomical to pursue further trapping activities.An investigation as to the causes for observed declines has been initiated.

Review of Existing Beaver Data:

To facilitate the evaluation of beaver populations and the identification of possiblereasons for declines a review of existing beaver data was conducted. The initial reviewof this data set revealed that the period from 19952004 included sufficient informationfor the analysis of trends for all beaver management zones on the island of

Newfoundland. Data for the period prior to this period currently exists but was in a formthat did not allow for inclusion in subsequent analysis.

Analysis of Existing Beaver Data:

Existing data for the period of 1995-2004 was collected and organized using MicrosoftExcel. This information consisted of the average price for beavers by year, the number ofbeavers captured by zone per year and the number of active traplines. To standardize thedata, due to the size difference in beaver management zones, harvest data was convertedto the catch rate per square kilometer for each zone by year. This was accomplished byaccessing data from the WIMS system, identifying active traplines by zone per year and

calculating associated areas of active traplines by zone using acrgis.

This data was then plotted using excel and the result can be seen in figure 1. To make iteasier to see any trends apparent in the data, trendlines using forth order polynomials forbest fit, were constructed and plotted using excel. The result of this exercise can be seenin figure 2.

It was hypothesized that the observed trends in catch rates could be explained by changesin the average beaver price paid by year. To evaluate this possibility a regressionanalysis was conducted comparing observed catch rates to changes in the average pricepaid for beaver pelts for the period 1995 - 2004. The results of this analysis can be seen

in Table 1. The average price for a beaver pelt by year can be seen in figure 3. Forreference purposes the historical annual harvest of beavers can be seen in figure 4.


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Fig. 1 Catch Rate of Beaver per km2

of Active Traplines by Zone

Catch /KM2 Active Traplines

0

0.05

0.1

0.15

0.2

0.25

1995-96 1996-97 1997-98 1998-99 1999-00 2000-01 2001-02 2002-03 2003-04 2004-05

Year

CatchRate/KM2

Zone 11 Active KM2 Zone 10 Active KM2 Zone 9 Active KM2 Zone 8 Active KM2

Zone 7 Active KM2 Zone 6 Active KM2 Zone 5 Active KM2 Zone 4 Active KM@

Zone 3 Active KM2 Zone 2 Active KM2 Zone 1 Active KM2

Fig. 2 Trendlines for the Catch Rate per km2

of Active Traplines by Zone.

Catch /KM2 Active Trendlines

R2

= 0.8844

R2

= 0.9557

R2

= 0.9119

R2

= 0.8168

R2

= 0.5814R

2= 0.8504

R2

= 0.6421

R2

= 0.7054

R2

= 0.5321

R2

= 0.7229

R2

= 0.2119

0

0.05

0.1

0.15

0.2

0.25

1995-96 1996-97 1997-98 1998-99 1999-00 2000-01 2001-02 2002-03 2003-04 2004-05

Year

CatchRate/KM2

Poly. (Zone 11 Active KM2) Poly. (Zone 10 Ac tive KM2) Poly. (Zone 9 Ac tive KM2) Poly. (Zone 8 Ac tive KM2)

Poly. (Zone 7 Active KM2) Poly. (Zone 6 Active KM2) Poly. (Zone 5 Active KM2) Poly. (Zone 4 Active KM@)

Poly. (Zone 3 Ac tive KM2) Poly. (Zone 2 Ac tive KM2) Poly. (Zone 1 Ac tive KM2)


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Table 1 Regression Analysis Catch Rate km2

and Annual Beaver Pelt Price

Regression Analysis

1995-2002 1995-2004

Zone R Square P-ValueR

Square P-Value

1 0.13856 0.363847 0.003244 0.875788

2 0.459559 0.064656 0.129894 0.306279

3 0.192984 0.276149 0.220607 0.170792

4 0.404221 0.090195 0.392131 0.052748

5 0.241301 0.216394 0.069794 0.460766

6 0.332128 0.134846 0.112165 0.344172

7 0.531048 0.040302 0.185927 0.213441

8 0.440591 0.072675 0.064902 0.477497

9 0.6712 0.012831 0.285175 0.111836

10 0.573787 0.029486 0.182625 0.218006

11 0.650475 0.015581 0.188432 0.210038

AllNF 0.574724 0.029275 0.192732 0.204326

Discussion of Results:

It is apparent from figure 2 that all beaver management zones on the island ofNewfoundland have experienced a decline in catch rates since 1995. The trends for allzones also show that the pattern of decline was the same throughout the island. From thisthe conclusion can be reached that the factor driving this decline must be of the samemagnitude and widespread.

To evaluate the impact of average beaver pelt price on catch rates per km2

a regressionanalysis was completed. For the period of 19952004 catch rate was positively relatedto price (r2 = 0.19, P = 0.20) but the analysis did not show a significant relationship.When the period 1995 -2002 is considered a strong positive relationship becomesapparent (r2 = 0.57, P = 0.029). This is similar to results obtain for beaver in Alberta (r2 =0.66, P < 0.001) (Poole, et al, 2001). The reason for the breakdown in relationshipbetween price and catch rate after 2002 could be explained if existing populationsdeclined to the point where harvest could not be increased even with a substantialincrease in price. This seems to have occurred on the island since the average price forbeaver was the highest in 2003, $32.33, than for any other year for the period beingconsidered. Even though we did see a slight increase in catch rates for 2003 (Fig. 2) it

did not approach the catch rates seen in 1995 and 1996 when the average price waslower.

When harvest is considered by zone, all zones on the island showed a positiverelationship to price. This relationship was significant for 8 zones for the period 1995 -2002 but for only 1 zone when data for 2003 and 2004 was added (Table 1).


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Another factor that supports the hypothesis that current catch rates are being influence bypopulation size is the fact that the total area trapped on the island has increased since1995 (r2 = 0.63, P = 0.005) (Fig. 5). This increase in area did not translate into acorresponding increase in the total number of beaver caught, which would be expected ifpopulation numbers had remained constant during this period. The corresponding catch

rate per km

2

for this period declined, (r

2

= 0.61, P = 0.007), as can be seen in figure 6.

The underlying reason for the decline in catch rates for the period 1995 -2002 is in partrelated to the average price for beaver. The continuation of low catch rates into 2003 and2004 suggests that some other factor have an influence which overrides the impactcaused by pelt price. Two factors that may cause this continued decline could be lowpopulation numbers or a reduction in effort of trappers. The rise in the total area trapfrom 1995 -2004 does not seem to support the conclusion that trapping effort declinedenough to account for the observed declines in catch rates. At this point in time we donot have sufficient data on beaver densities to state that low catch rates are be controlledby low populations in all zones. The rate of decline in all areas does suggest that

increased trapping effort may have had a negative impact on beaver densities and mayhave pushed population to a point where recovery is not possible at the current level oftrapping effort. Further research is proposed below which is designed to answer thisquestion.

Fig. 5 Total Area of Beaver Taplines Trapped on the Island 1995 2004

Total Area Trapped km2

All Zones

R2 = 0.6389

47000

48000

49000

50000

51000

52000

53000

54000

55000

56000

1995-96 1996-97 1997-98 1998-99 1999-00 2000-01 2001-02 2002-03 2003-04 2004-05

Year

km2

Total Area Trapped km2

Linear (Total Area Trapped km2)


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Fig. 6 Catch Rate per km2

Island of Newfoundland, 1995 -2004

Catch Rate per km2

Island of Newfoundland

R2

= 0.6188

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

1995-96 1996-97 1997-98 1998-99 1999-00 2000-01 2001-02 2002-03 2003-04 2004-05

Year

NumberCaughtperkm2

Catch Rate km2

Linear (Catch Rate km2)

Proposed Research:

To answer questions concerning current beaver population densities on its relationship toobserved catch rates basic research on beaver abundance and distribution needs to be

conducted. Due to the large area involved funding required for a complete census wouldbe prohibitive. This creates the need for the development of a protocol that could besupported with limited funds and utilizes the input of trappers to estimate current beaverdensities for all zones in the province. To achieve this it is proposed that a combinationof individual trapline surveys coupled with personal interviews with associated trappersbe conducted. Since this process was initiated by complaints from trappers in zone 11 inis suggested that this area be include in upcoming field activities. The following researchis proposed as a trial to determine if population parameters can be estimated using thisapproach.

2 traplines from 2 zones will be surveyed using helicopter.

Zone 11Trapline # 568 (80.9 km2) and 334 (101.1 km2)

Zone 10Trapline# 598 (88.8 km2) and 287 (80.2 km2)


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A complete survey of all 4 traplines is to be conducted. All activite lodges are to beidentified and gps locations recorded in UTMs (NAD 83). This information is then to be

transferred to arcgis. Density maps for all traplines are to be created and the density ofbeavers lodges per square km calculated.

To determine if trapper interviews can be used to provide a similar estimate of beaverlodge densities it is proposed that the trappers from the 4 traplines surveyed beinterviewed. The following information to be obtained:

- a plot of area trapped- a plot of all activitive lodges

From this information the percentage of the trapline covered by the trapper can becalculated and the density of beaver lodges in that area estimated. This number will beextrapolated to the complete trapline giving an overall density estimate for each trapline.A comparison between this estimate will then be conducted to determine its accuracy and

develop a correction factor if deemed necessary.

The cost for this phase of the study is as follows:

Helicopter flying time (12 hrs @ $1500.00/hr) $18000.00Trapper Interviews $ 1000.00

Total $19000.00

If it is determined that trapper interviews provide a reasonable estimate of beaverpopulation densities this program will be expanded to all zones in the province withhelicopter surveys to be completed only as needed to verify the accuracy of data.

To translate the density of beaver lodges into the actual density of beavers an evaluationof the number of beavers per active lodge is proposed for the coming year. This workwill be coupled with an evaluation of associated habitat parameters.


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Beaver survey flights and analysis of data:

The study area in both zone 11 (181 km2) and zone 10 (168.89 km2) was conducted onNovember14 and 16, 2005. Conditions during the flights were clear with noprecipitation. Some of the smaller ponds were covered with ice, and snow cover was nil

or trace amounts. Due to travel time, the zone 11 study area required 7.5 hours tocomplete and the zone 10 study area required 5.5 hours. The total cost of surveyactivities was $17,618.48. Flight lines and lodge locations can be seen in figures 7, 8 and9.

Figure 7:


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Figure 8:

Figure 9:


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Survey Results:

Population Status for each trapline was derived according to Bergerud et. al., 1961.

2 inactive lodges/active lodgesdeclining

Population density for each trapline was derived according to Bergerud et. al., 1961.

Low .4 active lodges Km2

The results for both study zones have been summarized in Table 2.

Table 2: Survey Results and Associated Population Parameters.

Results obtained were compared to historical data which is shown in Table 3 (Bergerudet. al., 1961, Miller 1961, Payne 1970).

Table 3: Historical Beaver Population Data for Study Areas in Zone 11 and 10.

Zone Year Location Active/Km2 Ratio inactive/active Density Status

11 1961 Salmon River 1.16 1.70 High Stable

11 1969 Ten Mile Lake 0.08 1.90 Low Stable

11 1969 Main Brook 0.23 1.30 Medium Stable

10 1961 Deer Lake 0.08 1.60 Low Stable

10 1969 Silver Mountain 0.04 1.00 Low Stable

10 1969 Sandy Lake 0.08 1.00 Low Stable

As can be seen in tables 2 and 3 the status of beaver in both study areas has changed fromstable in all areas surveyed in the 1960s to declining, except for a portion of zone 10

covered by trapline #287. When this area is combined with trapline #598, zone 10, theoverall total indicates a declining population. When density is considered we see that thezone 11 study area has experienced a decline ranging from 2595 %. For the zone 10study area density has increased by 6080 %.

Zone Trapline Area Active Active/km2 Inactive Ratio inactive/active Density Status

11 568 80.9 2 0.02 11 5.50 low declining

11 334 101.1 9 0.09 21 2.33 low declining

11 Total 182 11 0.06 32 2.91 low declining

10 598 88.8 17 0.19 57 3.35 low declining

10 287 80.2 18 0.22 22 1.22 medium stable

10 Total 169 35 0.21 79 2.26 medium declining


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The change in beaver density over time can be seen in Figure 10.

Figure 10: Historical and Current Beaver Densities for Zone 10 and 11.

Beaver Km2

Zone 10 and Zone 11

0

0.2

0.4

0.6

0.8

1

1.2

1.4

10 11

Fur Zone

BeaverKm2

1938

1940

1941

1961

1969

2005

Habitat Characteristics:

During the beaver survey flights the general habitat characteristics within 50 m of thelodge was recorded. Species composition was divided in five broad categories;coniferous, deciduous, cutover, shrub, and grasses. Observers were required to estimatethe percentage coverage of each category which was then recorded on data sheets. Theresults of this exercise can be seen in Figure 11.


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Figure 12: Available Browse Species on Surveyed Traplines

Beaver Survey 2005

0

10

20

30

40

50

60

fir spruce alder birch aspen popular other

Main Browse Species

NumberofLodges

Zone 11 334

Zone 11 568

Zone 10 598

Zone 10 287

Figure 13: Aquatic Habitat Associated with Individual Lodge Locations

Beaver Survey 2005

0

5

10

15

20

25

30

35

40

45

50

stream pond bog barren

Lodge Locaion

NumberofLodges

Zone 11 334

Zone 11 568

Zone 10 598

Zone 10 287


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Figure 14: Historical Beaver Harvest for Surveyed Trapline

The historical catch of beaver on the traplines surveyed can be se in Figure 14.

Discussion:

The objective of this exercise was to determine if there was actually a reduction in beaverabundance in Zone 11 as compared to Zone 10 and the identification of possible causesfor any differences found. Our preliminary analysis does show a difference betweenbeaver densities between zones and has documented a decline in Zone 11 when comparedto historical data.

When possible causes are considered, the observed differences in habitat between thetraplines surveyed in Zone 10 and 11 may provide a possible explanation. The absenceof a deciduous component in the riparian areas in Zone 11 was evident throughout allareas flown. This conclusion was supported by our preliminary analysis (Figure 11).The absence of a deciduous component was also brought forth by trappers in the area asthe cause for the observed beaver decline and they claim that browsing by moose wasresponsible. Such a scenario could be possible in Zone 11, since this area now has someof the highest densities of moose on the island.

Beaver Catch by Trapline

0

5

10

15

20

25

30

35

40

1997 1998 1999 2000 2001 2002 2003 2004

Year

NumberofBeavers

Zone 11 334

Zone 11 568

Zone 10 287

Zone 10 598


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Historical evidence of beaver habitat utilization was found throughout the two traplinessurveyed in Zone 11. Old dams and beaver meadows were dispersed throughout bothtraplines and provided evidence that beaver densities were much higher in the past. Thelack of forest regeneration was also apparent in existing beaver meadows and supportsclaims made by local trappers that high moose populations are inhibiting normal forest

succession of these areas. This would be similar to the situation observed by Northcott,1963, in central Newfoundland where it was discovered that moose browsing hadrestricted the growth of birch seedling to such an extent that 8-13 year old trees were lessthan 30 cm in height.

In Zone 11 we have beaver lodges in small ponds located in the center of bogs: whereas alarge number of lodges in Zone 10 are located on streams (Figure13). This would not bepossible in Zone 11 where most stream banks have become meadows. The movement ofbeaver into bogs in Zone 11 could be related to the lack of deciduous vegetation,requiring beavers to access the limited supply of aquatic vegetation available inunutilized bogs.

The number of beaver taken in on Zone 10 traplines are does not reflex lodge density:whereas, the number of beaver taken on Zone 11 traplines appears to be a function oflodge density (Figure 14).

Conclusions:

To verify observed differences in habitat characteristics between Zones 10 and 11 an, onthe ground habitat survey, should be conducted on the traplines surveyed. The lack ofdeciduous trees in Zone 11 should also be quantified and a determination made as towhether there absence is related to lack normal forest succession patterns or the activitiesof large herbivores such as moose and caribou.

An evaluation of beaver parturition rates in both Zones should be conducted and links toavailable foods resources evaluated.

References:

Bergerud, A. T. and Manuel, F. 1961, Beaver Management Report. WildlifeDivision, Nfld. Dept. of Mines, Agric. and Resources, 40pp.

Miller, D., 1960, Beaver Research in Newfoundland. Unpubl. Report, Dept. Mines,Agric. and Res. 209pp.

Northcott, T. H. A., 1963, AnEvaluation of the Factors Affecting Carrying Capacityof Selected Areas in Newfoundland for the Beaver, Castor canadensis caecator(Bangs), MSc. Thesis, Memorial University of Newfoundland, 133pp.

Payne, N. F., 1970, Newfoundland Aerial Beaver Census, Fall 1969. Internal Report,Government of Newfoundland and Labrador, Wildlife Division, 19pp.

Documents

Beaver Population Analysis and Research Proposal