Annual Statewide Spotlight Surveys Tasmania 2020/2021 Regional Summary: Priority Harvested Species May 2021 Wildlife Management Department of Primary Industries Parks Water and Environment Cite as: DPIPWE (2021). Annual Statewide Spotlight Surveys, Tasmania 2020/2021. Nature Conservation Report 21/2 ISSN: 1838-7403 2020 Annual Statewide Spotlight Surveys 2 Summary The Department of Primary Industries, Parks, Water and Environment has been carrying out annual nocturnal spotlight surveys in Tasmania since 1975. The surveys were originally designed to monitor the harvested populations of Bennett’s wallabies, Tasmanian pademelons and brushtail possums, however all observations of wild native and non-native mammal species are recorded. Surveys are conducted by vehicle across five management regions on mainland Tasmania and also on King and Flinders Islands. Each survey route follows an existing road and is 10 km long. The results of these surveys provide a long-term time-series of data for detecting population trends. This report summarises the survey results for the three main target species, the Bennett’s wallaby, Tasmanian pademelon and the brushtail possum from the 2020 surveys. Encounter rates are also provided for a range of other species. 2020 Annual Statewide Spotlight Surveys 1 Table of Contents SUMMARY................................................................................................................................ 1 OVERVIEW .............................................................................................................................. 3 PRIORITY SPECIES ................................................................................................................. 4 BRUSHTAIL POSSUM ............................................................................................................ 5 BENNETT’S WALLABY ......................................................................................................... 8 TASMANIAN PADEMELON ................................................................................................ 11 NON-HARVESTED SPECIES ............................................................................................... 14 APPENDIX 1: Statewide average densities ......................................................................... 17 APPENDIX 2: Raw counts of significant other species ...................................................... 19 APPENDIX 3: Management regions and survey routes ..................................................... 21 2020 Annual Statewide Spotlight Surveys 2 Overview The Department of Primary Industries, Parks, Water and Environment have been carrying out annual nocturnal spotlight surveys in Tasmania since 1975. The surveys were established to monitor the harvested populations of Bennett’s wallabies, Tasmanian pademelons and brushtail possums, however all observations of wild native and non-native mammal species are recorded (see Appendix 1 for summary). Surveys are undertaken across five management regions on mainland Tasmania and also on King and Flinders Islands. The results of these surveys provide a long-term time-series of data for detecting population trends. Surveys were originally undertaken along fifty-one survey routes, however following a review by Southwell (1985), the number of survey routes was increased to 132 and the methodology standardised for all surveys. Further survey routes were added between 1985 and 1990, resulting in 150 transects surveyed annually since 1990. In 2002 a change in methodology was made whereby the distance an animal was sighted from the survey route was noted, allowing the calculation of density indexes for the three most abundant species. Further surveys were also added in 2002. In 2006, the system was further changed to record the age class (immature, juvenile, adult) and exact location of particular species including the eastern quoll and Tasmanian devil. As of 2009, there have been 190 survey routes spread across Tasmania: 172 on mainland Tasmania, 8 on Flinders Island and 10 on King Island. Appendix 2 gives an overview of the establishment of new survey routes since surveys began. Each survey route follows an existing road and is 10 km long. Surveys are conducted by vehicle at a steady speed of 20 km/h, with the driver operating a hand-held spotlight. The driver relays their observations to a passenger for recording. The distance of each animal from the roadside is estimated, allowing a detection function to be modelled, and an estimate of species density is produced. Population trends are analysed on a regional basis. Due to the inherent biases of surveying from roads, this estimate is intended as an index of density to monitor population trends. It is used to provide an indication of changes in relative abundance but should not be used for calculating estimates of population size. A more detailed description of survey methodology can be found in the Tasmanian Spotlight Survey Manual. This report summarises the survey results for the three abundant harvested species, the Bennett’s wallaby, Tasmanian pademelon and the brushtail possum from the 2020 surveys. Population trends are also shown since distance sampling methodology was first used in 2002. 2020 Surveys The 2020 surveys were carried out by a number of staff from the Natural and Cultural Heritage Division, DPIPWE, primarily between late November 2020 and early January 2021. Surveys on King and Flinders islands were conducted in March. Data analysis and report writing was undertaken by staff from Wildlife Management, Natural and Cultural Heritage Division. Climatic conditions leading up to the survey period were variable across the state, particularly during spring. Mean temperatures were warmer than average across Tasmania from September to November with November being ‘very much above average’ for both minimum and maximum temperatures (BOM 2021). October and December were very wet in the east with average or above average rainfall elsewhere. However, November was the 9th driest on record for the 2020 Annual Statewide Spotlight Surveys 3 state, resulting in a drier than average spring for the west and south, and close to average seasonal rainfall for the east. These combined environmental conditions resulted in extensive grass growth, particularly along roadside verges which consequently lowered observation rates and detectability of animals. Priority Species In accordance with methods established by Dr Tony Pople, DPIPWE, has reviewed the 2020 spotlight survey data for Tasmania and calculated Density Index estimates in the five mainland management regions and Flinders Island for the three abundant harvested species: the Bennett’s wallaby; Tasmanian pademelon; and the brushtail possum. Statewide (mainland) average density estimates are provided for each of these species in Appendix 1 Counts of other mammal species observed during the surveys are given in Appendix 2. Regional Surveys Table 1 gives details of the number of surveys carried out in each region during 2020 and the numbers of animals sighted. Table 1: Number of survey routes undertaken and mammals sighted 2020 Survey Brushtail Tasmanian Region Bennett’s Other Possum Pademelon Non- Native Routes Wallaby Native Central 27 261 321 113 89 567 Flinders Island 8 35 682 137 111 3 King Island 10 122 446 30 0 6 North East 59 154 262 704 70 105 North West 30 62 124 489 55 11 South East 44 308 424 430 82 102 South West 12 33 28 189 13 0 Total 190 975 2287 2092 420 794 2020 Annual Statewide Spotlight Surveys 4 Brushtail Possums A summary of 2020 regional density indexes for the brushtail possum is given in Table 2. The density indexes from 2011 to 2020 are given in Table 3 and Figure 1 depicts the density index for the period 2002 to 2020. The results for density estimates for brushtail possum for 2020 surveys were essentially stable in the Central, South East and South West when compared with recent years. Results were slightly up for the North East and slightly down for Flinders Island but the long-term trend for density estimates have remained stable since 2002 (when estimates were initially calculated). Density estimates declined substantially in the North West region to the lowest level since 2002, however the long-term trend is stable. On King Island the density of brushtail possums has substantially increased since 2018 (when surveys were last conducted) and were recorded at levels (113 animals per km2) nearly twice the previous highest level (59 animals per km2) in 2005. The statewide average density index for brushtail possum in 2020 was 28.1 animals per km2 which is less than recorded for 2019 (33.2 animals per km2) but similar to the period 2014- 2018. It is speculated that the lower figure for 2020 may be caused by lower detection of animals due to higher grass levels. The long-term average statewide density trend is shown in Appendix 1. Table 2: Regional Density Index Summary 2020: Brushtail Possum (BP) Length Enc. Rate Detection Density (n/km2) %CV No. BPs (km) (n/km) Probability Central 49.9 21.87 261 270 0.97 0.097 Flinders Is. 16.9 44.95 35 80 0.44 0.130 King Island 113.0 21,63 122 100 1.22 0.054 North East 19.40 18.41 154 590 0.26 0.071 North West 11.44 36.17 62 300 0.21 0.090 South East 31.52 17.23 308 440 0.7 0.111 South West 23.62 29.92 33 120 0.275 0.058 Table 3: Regional Density Index results 2010 – 2020: Brushtail Possum 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Central 30.7 69.6 74.0 51.9 37.1 56.3 48.7 29.9 50.4 49.9 Flinders Is. 12.63 24.9