available evidence Justin Irvine Evidence based decision making - PowerPoint PPT Presentation

Using sound science and best available evidence Justin Irvine

Evidence based decision making  Approaches to monitoring for decision making  Research findings: making use of these.  Tools

Deer management plans: what do you need to put these into practice? Sustainable deer management means ensuring that the resource base can support the deer density.  i.e. that the deer are in good condition because the habitats they depend on are in good condition. The harvest (stags, venison) from the population is therefore linked to the habitats  Local knowledge is invaluable  But decisions need to be transparent: Qu. “What information is used to decide and act on the numbers to be culled, or the target densities? “

Adaptive Management  We don’t know exactly how the system (habitat, deer numbers) will respond to management actions – other factors beyond our control.  Therefore we need to learn from our actions to see if they are achieving what we want or expect.

Wetter summers by 2050 Wetter winter by 2050 = increased fecundity = increased mortality? UK Climate Projections UKCP18 http://ukclimateprojections.metoffice.gov.uk/

Changes in sheep stocks across the Highlands and Islands (1969 – 2014).

4. Overall Trends – Sheep versus deer 20 Replacement of 18 Parish deer density (km2) sheep by deer? 16 (NW Highlands) 14 12 10 8 6 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 Sheep density (Nat Log) Redrawn from Clutton-Brock and Albon (1989)

So planning takes place under uncertainty. Typical deer management plan aims to: …..maintain the habitats, forage and shelter required to sustain a healthy, resilient and productive deer herd,  …..capable of supporting an ongoing stag cull  …..in keeping with the main natural heritage objectives (public interest)

Deer management based on habitat: Habitat condition guides managed by Deer culling density Density dependence Stag off- take

Adaptive Management: Building knowledge Stag numbers, Objectives habitat condition Deer density, stag Options/ evidence population size, Cull, fence, methods habitat condition • grazing impact, Number (or %) Monitor Action • deer numbers to cull. • calf:hind

Monitoring to better support management decisions: What type of data do you need? 1. Habitat condition, grazing impact. 2. Counts: Deer density & calf:hind ratio 3. Cull numbers,

1. Habitat condition  Assessment of grazing and trampling impacts by larger herbivores: not just deer

Recording impacts over time Work involved – random selection, marking of plots, training of staff, recording baseline measurement

Recording impacts over time  Recording of baseline height data from heath/grass mosaic plot

For example: dwarf-shrub heath MAIN INDICATORS Grazing and Trampling Impact Dwarf-shrub heath Heavy Moderate Light % of heather Calluna vulgaris or blaeberry >66% 33-66% <33% Vaccinium myrtillus shoots browsed Browsing of cross-leaved heath Erica tetralix , cowberry Vaccinium vitis-idaea , bearberry Extensive Local None Arctostaphylos uva-ursi or crowberry Empetrum nigrum Grazing-induced growth forms ; drumstick, topiary, or Widespread Local Scarce carpet Stem and branch breakage of heather Conspicuous Inconspic. Inconspic. Red deer/sheep scars Frequent V. local Scarce % flowering and fruit of heather or blaeberry (summer Sparse Patchy Abundant browsing) Herbivore dung, sheep and/or deer V conspic. Moderate Low After Macdonald et al (1998)

Impacts over time  Approx. 50 km 2  88 plots (2-3 per km 2 ) Resource input:  6-8 plots per day (stalker – 1-2 weeks)

Tools to help?  In the pipeline  SWARD ( S upporting W ide A rea R ange management for D eer)

2. Deer density: Counting deer  Counts do not give absolute numbers  Need to be repeatable to identify trends (up or down) – (one-off counts can be misleading)  Use counts as density estimates: more useful for linking to habitat condition  Recruitment rate (calf:hind ratio) influences population growth

Population dynamics External factors (climate & sheep) Calf recruitment Increasing when Stable when recruitment > (mortality+cull) recruitment=mortality+cull Population size decreasing when recruitment < (mortality+cull) Natural mortality Numbers culled

Example (using SNH pop model available on web) Starting with 500 stags and 500 hinds  Calf:hind ratio 30% = 150 calves (75 male)  17% cull Population after 4 years will have declined to about 370 hinds and 370 stags . Same regime with calf:hind ratio 40% = 180 calves (90 male) Population after 4 years = 437 hinds, 437 stags Importance of using actual estimates of recruitment

Density dependence: Results from Rum North Block per km 2 1972 Present day Density 6.5 12.8 Stag density 8.2 2.7 As hind density increases,  Calving dates get later and overwinter mortality of calves increases but more so in males.  Fecundity declines  Birth weight declines  Sex ratio becomes more female biased  Stag antlers decline  Stag emigration increases

3. Cull The percentage of the estimated population culled varied markedly across the red deer range  10% to 30% Historically, a 1/6 th (17%) cull was advocated to maintain a stable population  based on a calf:hind ratio of around 33 per 100 hinds.  However, across Scotland the calf-hind ratio has been around 40% (recent small decline since populations have been relatively high is consistent with density dependence)

SWARD: deer population modelling allows variable recruitment and mortality rates

Count and cull: What cull is needed to reach target density? Plan for deer counts: once every 5 years - translate into density:  Use population model to estimate change in numbers under different cull levels to achieve required density  Confirm with count 5 years later (and modify cull if necessary) Recruitment counts = Calf:hind ratio  To ensure that the right estimate of fecundity is used in the model = big influence on outcome

Cull data can reveal population performance: Example from Norway  As density increases, size of animals and reproductive rate declines.  Kvinnherad municipality, Hordaland County, West Coast Norway  Density estimate has increased from around 4.3 in 1991 to about 11.4 in 2012 (526km 2 )  [Cf North West Sutherland = 5 deer per km over 1700km 2 ]

Deer culled km -2 Year Prop hinds calving Deer culled km- 2

Stag yearlings & calves Hinds yearlings & calves Slaughter weight (kg) Slaughter weight (kg)

Deer management based on habitat: Habitat condition guides managed by Deer culling density Density dependence Stag off- take

Tools  B est P ractice G uidance on habitat monitoring  Tools on SNH website for population modelling SWARD (under test):  Manages your data for habitat condition, count and cull data  Produces maps of habitat condition  Guidance on culling to achieve density or stag numbers DeerMAP: illustrates deer distribution and density as a result of changes such as culling and fencing

Discussion sessions  What are the barriers to putting this into practice? i.e. You have a plan: what is stopping you providing the evidence to demonstrate that it is being implemented?

Justin.irvine@hutton.ac.uk