Northland Lakes Ecological Status 2010
Hornwort is one of the greatest threats to Northland lakes with tall (5m) dense weed beds displacing native communities, and affecting sediments and water quality.
NIWA Client Report: HAM2010-058 May 2010
NIWA Project: NRC10202
Northland Lakes Ecological Status 2010
Rohan Wells Paul Champion
Prepared for Northland Regional Council
NIWA Client Report: HAM2010-058 May 2010
NIWA Project: NRC10202
National Institute of Water & Atmospheric Research Ltd Gate 10, Silverdale Road, Hamilton P O Box 11-115, Hamilton, New Zealand Phone +64-7-856 7026, Fax +64-7-856 0151 www.niwa.co.nz
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Contents
Executive Summary iv 1. Introduction 1 2. Methods 3 2.1 Lake description 3 2.2 Wetland vegetation 3 2.3 Submerged vegetation 3 2.4 Prioritisation of lakes 6 2.5 Water birds 8 2.6 Fish 8 2.7 Aquatic invertebrates 8 2.8 Changes in indicators 9 2.9 Threats 9 2.10 Management recommendations 9 2.11 Summary 9 2.12 Biosecurity – managing the spread of aquatic weeds in Northland lakes 9 3. Inventory of Lakes in Northland 10 3.1 Lake Austria (Aupouri), NRC Lake No. 22; surveyed in 2005. 10 3.2 Lake Bulrush (Aupouri), NRC Lake No. 49; surveyed in 2005. 14 3.3 Lake Carrot or Ngakapua West (Aupouri), NRC Lake No. 118; surveyed in 2005 and 2010 16 3.4 Forest Lake or Deans Swamp (Aupouri), NRC Lake No. 114; surveyed in 2005 and one profile sampled in 2010 20 3.5 Half Mile Lagoon (Aupouri), NRC Lake No. 62; surveyed in 2005. 23 3.6 Lake Heather (Aupouri), NRC Lake No. 125; surveyed in 2005 and 2008; rapid assessment in 2009 and two profiles surveyed in 2010 25 3.7 Katavich Lake - west of Lake Waiparera (Aupouri), NRC Lake No. 103; surveyed in 2005 31 3.8 Lake Kihona (Aupouri), NRC Lake No. 31; surveyed in 2005 33 3.9 Lake Little Gem, near Ngatu (Aupouri) NRC Lake No. 123; surveyed in 2007 and 2010 36 3.10 Mini Lake (Split Lake) (Aupouri), NRC Lake No. 130; surveyed in 2005 40 3.11 Lake Morehurehu (Aupouri), NRC Lake No. 32; surveyed in 2006 and 2009 43 3.12 Lake Morehurehu South 1 (Aupouri), NRC Lake No.(33); reconnaissance 2010 47 3.13 Lake Morehurehu South 2 (Aupouri), NRC Lake No. 36; surveyed in 2006 49 3.14 Lake Ngakapua (Aupouri), NRC Lake No. 115 (South Basin) and 117 (North Basin); surveyed in 2005 and 2010 52 3.15 Lake Ngakeketa (Aupouri), NRC Lake No. 14; surveyed in 2005 57 3.16 Lake north of Ngakeketa, Te Paki Lake (Aupouri), NRC Lake No. 13; surveyed in 2004 and 2009 60 3.17 Lake Ngatu, (Aupouri) NRC Lake No. 120; surveyed in 2004, and 2010 64 3.18 Lake Ngatuwhete (Aupouri), NRC Lake No. 23; surveyed in 2005 70
3.19 Lake Pretty (Aupouri), NRC Lake No. 24; surveyed in 2005 73 3.20 Lake Rotokawau (Aupouri), NRC Lake No. 116; surveyed in 2005 and 2009 76 3.21 Lake Rotoroa (Aupouri), NRC Lake No. 126; surveyed in 2005 and visited in 2010 79 3.22 Salt Lake (Aupouri), NRC Lake No. 48; surveyed in 2005 83 3.23 Lake Taeore (Aupouri), NRC Lake No. 38 reconnaissance in 2010 86 3.24 Te Arai Ephemeral Wetland and Pond (Aupouri), NRC Lake No. 46; surveyed in 2005 88 3.25 Te Arai Lake (Aupouri), NRC Lake No. 47; surveyed in 2006 90 3.26 Lake Te Kahika (Aupouri), NRC Lake No. 29; surveyed in 2006 and 2009 94 3.27 Te Kahika Sth (Aupouri), NRC Lake No.(30); reconnaissance 2010 98 3.28 Te Paki Dune Lake (Aupouri), NRC Lake No. 15; surveyed in 2005 and 2007 100 3.29 Te Werahi Lagoon (Aupouri), NRC Lake No. 6; surveyed in 2005 105 3.30 Lake Wahakari (Aupouri), NRC Lake No. 35; surveyed in 2005 and 2008 109 3.31 Lake Waihopo (Aupouri), NRC Lake No. 78; surveyed in 2006 and 2009 114 3.32 Lake Waimimiha North (Aupouri), NRC Lake No. 136; surveyed in 2005 118 3.33 Lake Waimimiha South (Aupouri), NRC Lake No. 137; surveyed in 2005 121 3.34 Lake Waipara / Dead Lake (Aupouri), NRC Lake No. 25; surveyed in 2005 124 3.35 Lake Waiparera (Aupouri), NRC Lake No. 102; surveyed in 2005 and 2010 127 3.36 Waitahora Lagoon (Aupouri) NRC Lake No. 4; surveyed in 2007 and 2009 131 3.37 Waitahora Lakes (Aupouri) NRC Lake No. 3; surveyed in 2007 and 2009 134 3.38 West Coast Road (Aupouri), NRC Lake No. 121; surveyed in 2005, visited in 2007 and 2010 137 3.39 Lake Yelavich (Aupouri), NRC Lake No. 105; surveyed in 2008 and 2010 140 4. Karikari Peninsula, central and east 143 4.1 Horahora Dune lake (central and east Northland), NRC Lake No. 199A; visited in 2008 143 4.2 Jack’s lake (Central Northland), NRC Lake No. 180; surveyed in 2005 145 4.3 Roadside pond, Matai (Karikari), no NRC Lake No.; surveyed in 2005 148 4.4 Lake Manuwai (Central Northland), NRC Lake No. 146 149 4.5 Lake Omapere (Central Northland), NRC Lake No. 173; surveyed in 2005 151 4.6 Lake Owhareiti (Central Northland), NRC Lake No. 177; surveyed in 2006 154 4.7 Lake Ora (Whangarei / Kamo), NRC Lake No. 205; surveyed in 2006 157 4.8 Lake Rotokawau East (Karikari), NRC Lake No. 96; surveyed in 2005 159
4.9 Lake Rotokawau West (Karikari), NRC Lake No. 95; surveyed in 2005 162 4.10 Lake Rotopokaka or Coca Cola (Karikari), NRC Lake No. 104; surveyed in 2005 165 4.11 Lake Sands Lake at Mangawhai, (central and east Northland), NRC Lake No. 309A; first surveyed in 2008 167 4.12 Smith’s Dam Hikurangi (central and east Northland) NRC Lake No. 199B; visited in 2008 170 4.13 Stanners Road Dam, Kerikeri (central and east Northland) NRC Lake No. 148A; visited in 2008 172 4.14 Tapui Rd Quarry Lake (central and east Northland) NRC Lake No. 199C; visited in 2008 174 4.15 Lake Waingaro (Central Northland), NRC Lake No. 167; surveyed in 2005 176 4.16 Lake Waiporohita (Karikari), NRC Lake No. 99; surveyed in 2005, surveillance 2010 178 4.17 Lake Waro (Hikurangi) Lake No. 410; surveyed in 2006 182 4.18 The Whau Dam (central and east Northland) NRC No. 206; first visit 2008 186 5. Kai-Iwi and north Dargaville lakes 188 5.1 Freidrich’s Lake (north Dargaville), NRC Lake No. 282; surveyed in 2005 188 5.2 Lake Kai-iwi (Kai-iwi Lakes) NRC Lake No. 236; surveyed in 2005 and 2007 191 5.3 McEvoy’s Lake (north Dargaville) NRC Lake No. 277; surveyed in 2005 195 5.4 Midgley’s Lake (north Dargaville), NRC Lake No. 257; surveyed in 2005 197 5.5 Shag Lake (Kai-Iwi), NRC Lake No. 221; surveyed in 2005 and 2010 200 5.6 Lake Taharoa (Kai-iwi) NRC Lake No. 229; surveyed in 2005 and 2007 204 5.7 Te Riu (Waipuoa), NRC Lake No. 409; surveyed in 2006 208 5.8 Waikere (Kai-iwi Lakes) NRC Lake No. 227; surveyed in 2005 and 2007 211 5.9 Lake Waingata (Waipoua) NRC Lake No. 200; surveyed in 2006 215 6. Pouto Peninsula 218 6.1 Grevilles Lagoon, the lake north of Kapoai (Pouto), NRC Lake No. 295; surveyed in 2005 218 6.2 Lake Humuhumu, Pouto, NRC Lake No. 350; surveyed in 2005 and 2007 221 6.3 Lake Kahuparere (Pouto), NRC Lake No. 384; surveyed in 2005 and 2007 225 6.4 Lake Kanono (Pouto), NRC Lake No. 377; surveyed in 2005 and 2007 229 6.5 Lake Kapoai (Pouto), NRC Lake No. 296; surveyed in 2005, visited in 2007 233 6.6 Lake Karaka (Pouto), NRC Lake No. 347; surveyed in 2005 and 2007 236 6.7 Lake Mokeno (Pouto), NRC Lake No. 356; surveyed in 2005, and 2007 240
6.8 Lake Parawanui (Pouto), NRC Lake No. 297; surveyed in 2005 244 6.9 Phoebe’s Lake (Pouto), NRC No. 346; surveyed in 2001, re-visited in 2008 247 6.10 Lake Rotokawau (Pouto), NRC Lake No. 364; surveyed in 1985, 1988, 2001, 2005 and 2007 250 6.11 Lake Roto-otuauru / Swan, (Pouto), NRC Lake No. 355; surveyed in 2005, 2009 and 2010 254 6.12 Lake Rotopouua (Pouto), NRC Lake No. 348; first surveyed in 2008 263 6.13 Lake Rototuna (Pouto), NRC Lake No. 328; surveyed in 1988, 2001, 2005 and 2007 266 6.14 Lake Waingata (Pouto), NRC Lake No. 371; surveyed in 2005 and visited in 2010 270 6.15 Lake Wainui (Pouto), NRC Lake No. 305; surveyed in 2001, 2005 and 2007. 273 6.16 Lake Wairere (Pouto), NRC Lake No. 339; surveyed in 2005 277 6.17 Lake Whakaneke (Pouto), NRC Lake No. 390; surveyed in 2005 and 2007 280 7. Biosecurity – minimising the spread of aquatic weeds in Northland lakes 283 7.1 Introduction 283 7.2 Weed status of Northland lakes 283 7.3 Aquatic weed risk 290 7.4 Aquatic weed distribution and potential impacts 290 7.4.1 Submerged species 290 7.4.2 Emergent and wetland species 293 7.5 Prioritisation of lakes 295 7.6 Introduction pathways, risks and targeted surveillance 296 7.6.1 Natural dispersal 297 7.6.2 Deliberate dispersal 297 7.6.3 Accidental dispersal 297 7.6.4 Targeted surveillance 298 7.7 Threat evaluation and management implications 298 7.8 Contingency planning 302 8. Weed surveillance programme 2010 303 8.1 Introduction 303 8.2 Methods 303 8.3 Results and discussion 304 9. Acknowledgements 307 10. References 308 ______
Reviewed by: Approved for release by:
Kerry Bodmin Dave Roper
Formatting checked:
Executive Summary Northland Regional Council (NRC) engaged NIWA to assist achievement of its goal “to prevent deterioration in water quality and loss of biodiversity value in Northland lakes”.
This report presents a summary of information on native biodiversity value gathered on 84 Northland lakes and wetland margins. The core information in this report is a ‘living’ document to be added to and modified to incorporate changes in lake values as they change. This information is key for the NRC Lakes Strategy as it is essential for managers to know what they are managing and monitor responses to management initiatives.
The report was updated in April 2010 by:
Lake native biodiversity value monitoring for Lakes Yelavich, Carrot, Ngakapua N & S, Ngatu, Little Gem, West Coast Road, Waiparera (high ranking Waipapakauri lakes) and Shag (Kai-Iwi Lakes) with vegetation descriptions, and ecological observations.
LakeSPI surveys (assessment of submerged plant indicators) for Lakes Yelavich, Carrot Ngakapua (north and south), Ngatu, Shag, Heather and Waiparera.
Weed surveillance monitoring of Lakes Ngatu, Waiporohita, Kai-Iwi, Taharoa, Waikere, Humuhumu and Rotokawau (Pouto).
Reconnaissance of the water bodies adjacent to Te Kahika and Morehurehu (Te Kahika South, Morehurehu South 1), Lake Taeore, Forest Lake, Lake Rotoroa (all Aupouri) and Lake Waingata (Pouto).
Sampling for fish in Lake Ngatu to confirm the presence of the pest fish perch.
Re-survey Lake Swan and assess effectiveness of grass carp since the May 2009 release.
Re-survey and photograph submerged vegetation in Lake Heather for a baseline prior to grass carp release.
Updating the Methods and Biosecurity sections.
Lakes Yelavich, Shag and Waiparera had more abundant and deeper submerged native vegetation since last surveyed; Lakes Ngakapua North and South, Ngatu had changed little; but Lakes Heather, Carrot, Little Gem and West Coast Road had decreased and their native biodiversity value ranking has been changed accordingly. Egeria densa was found in Lake Carrot for the first time but, as only a few plants were found, we attempted to remove them by hand (follow-up hand weeding as an attempt to eradicate it is recommended). Lake Little Gem’s submerged vegetation had receded from 3.3 (in 2007) to 2.6 m in 2010, and was restricted to within the emergent’s zone. West Coast Road Lake now has no open water with the spread of Eleocharis sphacelata and so was not assessed for lake biodiversity value monitoring.
Northland Lakes Ecological Status 2010 iv
Weed surveillance monitoring found no new invasions of pest plants, but E. densa was found in Lake Carrot during lake ecological condition monitoring. We hand-weeded what we found and a full lake search and follow-up control measures (hand-weeding and / or compression screens) are recommended. The discovery of E. densa in Lake Carrot has increased the likelihood of E. densa invading Ngakapua Sth so annual surveillance is now recommended.
Utricularia gibba, noted in previous surveillance reports as becoming increasingly more widespread and abundant in Northland lakes, was found in all surveillance lakes. Unfortunately little can be done to prevent the spread of this weed as waterfowl are likely to be dispersing it. Access to Lake Rotokawau (Pouto) has become more restricted due to changing farm practices and it is recommended that annual weed surveillance is discontinued.
Te Kahika South was found to be a small, remote ‘high’ ranked lake with endangered Todea barbara and Utricularia australis present. Along with Te Kahika this lake had a low pH (< 5) and the invasive U. gibba was absent. Lake Morehurehu South 1 was ranked ‘low to moderate’ as it had only the odd submerged plant but large amounts of the invasive U. gibba, although was surrounded by good wetland habitat. Lake Taeore at the time of survey was dry so was ranked ‘low’. The lake bed however was moist and supported a range of wetland herbs and tall emergent species including the rare annual species Fimbristylis velata (northern most record in NZ), Alternanthera nahui and Centipeda aoteorana. Submerged vegetation had re-established in Forest Lake, comprised of Chara australis, Nitella leonhardii and Potamogeton cheesemanii, along with dense mats of U. gibba. Water clarity was poor in Lakes Rotoroa and Waingata and vegetation in these lakes was similar to previous surveys.
A combination of Gee minnow traps, siene and gill nets were deployed in Lake Ngatu in 2010 as a response to the possible sighting of perch during the 2009 surveillance survey, but only inanga, bullies, gambusia and a goldfish were caught.
In Lake Swan grass carp had removed virtually all the E. densa and about half the Ceratophyllum demersum since introduced nearly a year ago in May 2009.
Lake Heather had further significant invasion by tall-growing beds of C. demersum leaving little native submerged vegetation and a heightened risk of lake-wide de-oxygenation. Baseline profiles were recorded as a reference for lake vegetation present prior to grass carp release scheduled for later in 2010.
All lakes are ranked (summarised in table form below) based on assessment of ecological significance, and this information is intended to facilitate prioritisation of lakes for monitoring and assist managers to make decisions that could preserve, protect or enhance lake condition and ecological values.
Assessment of biosecurity risks posed by the freshwater pest plants are presented and updated, with recommendations for monitoring and control. This work is part of the NRC Regional Surveillance Strategy for management of freshwater pests within Northland Region. This approach is justified as native aquatic flora and fauna are highly susceptible to displacement by invasive species, and freshwater systems are much more vulnerable than forest and other terrestrial ecosystems. Northland Northland Lakes Ecological Status 2010 v
Region has some of New Zealand’s highest ranked examples of intact natural aquatic ecosystems. They are being lost at an alarmingly rapid rate as new invasive species continue to be spread as a result of human activities. Most pristine lakes are now situated in remote areas with difficult access. With community support and active protection, such exceptional lakes could be maintained in a pristine state for perpetuity. Protection requires that no introductions occur via accidental means. Fishing nets, non-resident boats, boat trailers and drainage machinery need to be prohibited or strictly controlled from the highest ranking water bodies including any inflows and outflows within the catchment.
Recommendations
Delimit the distribution of E. densa in Lake Carrot. If feasible consider eradication options such as hand-weeding and / or compression screens which may work at this early stage of invasion.
Annual pest surveillance is now recommended for Ngakapua Sth. The discovery of E. densa in adjacent Lake Carrot has increased the likelihood of E. densa being introduced into Lake Ngakapua.
Advocate maintaining an area of open water in West Coast Road Lake with localised glyphosate spraying. This will maintain habitat for the endangered Myriophyllum robustum.
Reduce biomass of C. demersum and E. densa in Lake Heather, one month prior to grass carp release, by applying 100L diquat. This will markedly reduce pest plant biomass and assist the effectiveness of grass carp.
Trial the use of endothall to control L. major in Lake Ngatu. Use of curtains to temporarily section off target areas will increase contact times and efficacy.
Erect signage at Lakes Ngatu and Waiparera to encourage checking and removal of pest plants on entering and leaving the lake.
Advocate fencing the margins of Lake Shag and consider additional ways of reducing nutrient inputs. This lake is finely balanced between supporting submerged vegetation versus algal blooms; a small change in nutrients could make a big difference.
Northland Lakes Ecological Status 2010 vi
Table 1: Northland lakes ranked for native biodiversity value and summary of monitoring recommendations. Lakes are listed alphabetically within four geographic areas, with a Northland Regional Council lake number and rankings colour-coded (by colours of the rainbow) as outstanding (red), high (orange), moderate-high (yellow), moderate (green), moderate-low (blue), low (violet):
Lake NRC Lake Pest Plant Rank Biodiversity Name Number Surveillance Monitoring
Aupouri
Austria 22 Moderate
Bulrush 49 Low
Carrot or Ngakapua West 118 Moderate I yr
Forest Lake or Deans Swamp 14 Low
Half Mile Lagoon 62 Low
Heather 125 Moderate-low 5 yrs 1 yr
Katavich 103 Low
Kihona 31 Low
Little Gem 123 Moderate-high 5 yrs
Mini (Split) 130 Low
Morehurehu 32 Outstanding 5 yrs
Morehurehu South 1 33 Moderate-low
Morehurehu South 2 36 Moderate-high 5 yrs
Ngakapua 115 & 117 Moderate-high 5 yrs 1 yr
Ngakaketa 14 Low
Ngakaketa North (Te Paki) 13 Moderate-high 5 yrs
Ngatu 120 Outstanding 5 yrs 1 yr
Ngatuwhete 23 Low
Northland Lakes Ecological Status 2010 vii
NRC Lake Rank Lake Pest Plant Name Number Biodiversity Surveillance Monitoring
Pretty 24 Moderate
Rotokawau 116 High 5 yrs
Rotoroa 126 High 5 yrs
Salt 48 Low
Taeore 38 Low
Te Arai Ephemeral Wetland 46 Moderate & Pond
Te Arai Lake 47 Low
Te Kahika 29 Outstanding 5 yrs
Te Kahika South 30 High 5 yrs
Te Paki dune 15 High 5 yrs
Te Werahi Lagoon 6 Low
Wahakari 35 Outstanding 5 yrs
Waihopo 78 Outstanding 5 yrs
Waimimiha North 136 Low
Waimimiha South 137 Low
Waipara/Dead 25 Moderate
Waiparera 102 Moderate-high 5 yrs
Waitahora lagoon 2 Outstanding 10 yrs
Waitahora lakes 3 & 4 Outstanding 10 yrs
West Coast Rd 121 Low 5 yrs
105 5 yrs Yelavich High Northland Lakes Ecological Status 2010 iv
NRC Lake Rank Lake Pest Plant Name Number Biodiversity Surveillance Monitoring Karikari Peninsula,
central and east
Horahora Dune 199A Moderate 180
Jacks Low
Roadside pond, Matai Low
Manuwai 146 Low
Omapere 173 Low
Ora 205 Low
Owhareiti 177 Low
Rotokawau East 96 Moderate
Rotokawau West 95 Moderate
Rotopokaka 104 Moderate
Sand’s Lake 309A Moderate
Smith’s Dam 199B Low
Stanner’s Rd Dam 148A Low
Tapui Rd Quarry Lake 199C Low
Waingaro 167 Low
Waiporohita 99 Outstanding 5 yrs 1 yr
Waro 410 Moderate-high
Whau Dam 206 Low Kai Iwi lakes & north Dargaville
Freidrich’s 282 Low
Kai-Iwi 236 Outstanding 5 yrs 1 yr
McEvoy 277 Low
Northland Lakes Ecological Status 2010 v
NRC Lake Rank Lake Pest Plant Name Number Biodiversity Surveillance Monitoring
Midgeley 257 Moderate-high 5 to 10 yrs
Shag 221 Moderate
Taharoa 229 Outstanding 5 yrs 1 yr
Te Riu 201 High 5 yrs
Waikere 227 Outstanding 5 yrs 1 yr
Waingata 200A High 10 yrs
Pouto Peninsula
Grevilles Lagoon 295 Moderate
Humuhumu 350 Outstanding 5 yrs 1 yr
Kahuparere 384 High 5 yrs
Kanono 377 Outstanding 5 yrs 3-5 yrs
Kapoai 296 Moderate-low 5 yrs
Karaka 347 High 10 yrs 5-10 yrs
Mokeno 356 Outstanding 5 yrs 5 yrs
Parawanui 297 Low
Phoebe’s 346 Low
Rotokawau 364 High 5 yrs
Roto-otuauru (Swan) 355 Moderate 1 yr
Rotopouua 348 Outstanding 5 yrs
Rototuna 328 High 5 yrs
Northland Lakes Ecological Status 2010 vi
NRC Lake Rank Lake Pest Plant Name Number Biodiversity Surveillance Monitoring
Waingata 371 Low
Wainui 305 Moderate-high 5 yrs
Wairere 339 Moderate-high 10 yrs
Whakaneke 390 High 5 yrs
Northland Lakes Ecological Status 2010 vii
1. Introduction Northland Regional Council (NRC) engaged NIWA to assist in achieving its goal “to prevent deterioration in water quality and loss of biodiversity value in Northland lakes”. The baseline report (Champion et al. 2005) has been updated annually and this is the 2010 update.
The report was updated in April 2010 by:
Lake native biodiversity value monitoring for Lakes Yelavich, Carrot, Ngakapua N & S, Ngatu, Little Gem, West Coast Road, Waiparera (high ranking Waipapakauri lakes) and Shag (Kai-Iwi Lakes) and with vegetation descriptions, ecological observations and LakeSPI.
LakeSPI surveys (assessment of submerged plant indicators) for Lakes Yelavich, Carrot Ngakapua (north and south), Ngatu, Shag, Heather and Waiparera.
Weed surveillance monitoring of Lakes Ngatu, Waiporohita, Kai-Iwi, Taharoa, Waikere, Humuhumu and Rotokawau (Pouto).
Reconnaissance of the water bodies adjacent to Te Kahika and Morehurehu (Te Kahika South, Morehurehu South 1), Lake Taeore, Forest Lake, Lake Rotoroa (all Aupouri) and Lake Waingata (Pouto).
Sampling for fish in Lake Ngatu to confirm the presence of the pest fish perch.
Re-survey Lake Swan and assess effectiveness of grass carp since the May 2009 release.
Re-survey and photograph submerged vegetation in Lake Heather for a baseline prior to grass carp release.
Updating the Methods and Biosecurity sections.
This report presents a summary of information gathered on each of the 84 lakes surveyed up to and including April 2010. The region is divided into 4 geographical areas: Aupouri; Karikari \ Central & East Northland; Kai-iwi lakes & North Dargaville; and Pouto Peninsula. Information includes vegetation descriptions (submerged and wetland), the LakeSPI method of assessing submerged plant indicators, records of water birds, fish and macroinvertebrates. Ecological and lake condition changes were identified by comparison with previous surveys and major
Northland Lakes Ecological Status 2010 1
threats to the current lake condition are identified. Finally, management recommendations are presented for each lake.
Assessment of biosecurity risks posed by freshwater pest plants is discussed, with recommendations for monitoring and control.
This report presents a ranked inventory of lakes of high ecological value based on available ecological and water quality data. Data gathered on the lakes was analysed and used to prioritise the lakes for future monitoring, and to make recommendations on which lakes need to be monitored, for what purpose and what frequency, to assist managers aiming to preserve, protect and enhance water quality and ecological values.
The core information in this report is a living document to be further added to and modified as further information comes to hand, or if lake values change. This information is key for the NRC Lakes Strategy as it is essential for managers to rapidly respond to new incursions or other identified threats and monitor responses to past management initiatives.
Northland Lakes Ecological Status 2010 2
2. Methods An inventory of Northland lakes was assembled. The following information was gathered for each lake and is presented in Section 3 of this report.
2.1 Lake description Lakes were referenced according to assigned lake number and location (NZTM Easting and Northing) in the NRC lakes database. In addition, water bodies were photographed and lake size, observations of catchment features and ease of access were noted.
2.2 Wetland vegetation The extent of emergent vegetation (percentage of shoreline, width of beds and depth range), species present at profiles and elsewhere around the lake, and wetlands associated with the lake were described.
Presence of endangered species (de Lange et al. 2009; Forester and Townsend 2004 and discussion with DOC and NRC staff) and pest plants were reported along with an estimate of population size.
2.3 Submerged vegetation The submerged vegetation was surveyed by divers using a method similar to Clayton (1983). Divers swam perpendicular to shore recording plant species present, their depth ranges, average and maximum heights and covers. These and other details were recorded on data sheets (Fig. 1). LakeSPI (Clayton & Edwards 2002; Clayton & Edwards 2006; http://lakespi.niwa.co.nz/index.do) information was extracted from this data, and by recording the following additional information: the maximum depth of native and invasive species with cover >10%, and the maximum depth of charophyte meadows with >75% cover. A sketch was made of the profile relief and spatial distribution of vegetation with notes on height and cover. Lakes were sampled at five localities where practical (less when small or de-vegetated) and the profile locations were selected as representative of the underwater vegetation and the range of plant communities present in the lake.
Presence of endangered species (de Lange et al. 2009; Forester and Townsend 2004 and discussion with DOC and NRC staff) and pest plants were reported along with an estimate of population size.
Vegetation survey data was entered into the NIWA Freshwater Biodata Information System (FBIS). Raw data can be viewed using spatial and textural searches at the web-site, fbis.niwa.co.nz. Tables that summarise the vegetation surveys can be extracted from the ‘reports’ menu, as ‘Lake Vegetation Summary Reports’, by first
Northland Lakes Ecological Status 2010 3
selecting the lake of interest, and then selecting a survey date. Note that access to reports requires log-in; a username and password are provided upon request to [email protected].
Figure 1: Survey sheet for submerged vegetation surveys.
LakeSPI data was entered into the NIWA LakeSPI database, to calculate three ecological indices. The Native Condition Index provides a measure (score) of the diversity, quality and abundance of indigenous submerged vegetation. The Invasive
Northland Lakes Ecological Status 2010 4
Impact Index scores the impact by any of ten invasive alien plant species that may be present. A high Invasive Impact Index indicates large impacts by invasive alien plants. The LakeSPI Index integrates components of the previous indices, together with additional ecological information. The specific features that are assessed to generate each score are detailed on the web-reporting pages (lakespi.niwa.co.nz). In this report the indices are expressed as a percentage of their maximum potential score to enable direct comparisons between different types of lake. The LakeSPI Index provides a
measure of how close a water body is to its potential or unimpacted (by human) state, and can be used to detect changes in lake condition over time and make comparisons between lakes. LakeSPI is not suitable for lakes where a factor such as salinity or pH restricts submerged vegetation communities, or where submerged plant growth is less than 10% cover.
This method should not be confused with the ‘Lake Native Biodiversity Value Assessment’ covered in Section 2.4.
LakeSPI results presented in this report are also available on NIWA’s web-reporting pages (lakespi.niwa.co.nz), where a report can be generated for any lake, summarising all available assessments.
To place Northland’s lakes in a national context, a comparison of regions and lakes nationally was made (Fig. 2) from national Lake SPI results to 2010. More than 50% of Northland’s 46 lakes were in the High and Excellent categories. Only Otago and Southland (with only 6 records for each region) had a higher % (only a few lakes in Fiordland have been surveyed due to difficult access). Compared with other regions nationally, Northland has a large number of excellent and high ranked lakes using the LakeSPI ranking.
Northland Lakes Ecological Status 2010 5
0% 20% 40% 60% 80% 100%
Northland (46) Auckland (30) Bay of Plenty (13) Waikato (53)
Hawkes Bay (6) Manawatu-Wanganui (3) West Coast (17) Canterbury (20) Otago (6) Southland (6) National (200)
Figure 2: LakeSPI results for lakes regionally and nationally (number of lakes in brackets) with LakeSPI scores grouped into 5 colour coded categories:
LakeSPI score Category >75 Excellent >50-75 High >20-50 Moderate >0-20 Poor 0 Non-vegetated*
*non-vegetated lakes have a submerged vegetation at <10% average cover and by default are scored as zero.
2.4 Prioritisation of lakes
The lakes were prioritised for ecological value based on three components: Indigenous biota, endangered species and habitat availability.
1. Indigenous biota
For native species or indigenous biota we assessed the value of what species were present at the time and the metrics scored were: species richness, abundance and representativeness:
Northland Lakes Ecological Status 2010 6
‘Species Richness’ was the total number of indigenous macroscopic species (fauna and flora) in the lake and wetland margins.
‘Abundance’ was for native flora present and was assessed on the basis of area and cover, and for fauna it was population size.
‘Representativeness’ of the species assemblage was obtained by assessing the significance of the communities present (not species rarity) in regional and national context.
2. Endangered species
Endangered species were scored on the basis of the ‘New Zealand Threat Classification System lists’ (R. Hitchmough; L. Bull; P. Cromarty (Comp.) 2002; -- 2007) and also using de Lange et al. (2009). The categories are ‘acute’, ‘chronic’ and ‘at risk’:
Within ‘acute’ there are four categories:
‘Extinct in the wild’ (e.g., Isoetes ‘flabellata’, Omapere) but was not used in this evaluation, as we were assessing what species were present at the time, not past species or potential;
‘Critical’ e.g., the white heron which is a casual visitor to Northland;
‘Endangered’ e.g., brown teal, grey duck, bittern, Northland mudfish, native bladderwort; and
‘Vulnerable’ e.g., Trithuria inconspicua.
‘Chronic’ has two sub-categories:
‘Serious decline’ e.g., dune lakes galaxias (dwarf inanga), Myriophyllum robustum, and black-billed gull.
‘Gradual decline’ e.g., longfin eel, giant kokopu, black mudfish, kakahi, koura, marsh fern, and red-billed gull.
The ‘At-risk’ category are for those naturally uncommon, relict (sparse) species such as NI fernbird, dabchick, crakes, freshwater crab, Centipeda aotearana, Mimulus repens, and Sporodanthus ferruginea.
Northland Lakes Ecological Status 2010 7
3. Habitat availability
The extent \ area of indigenous vegetation (wetland, emergents and submerged vegetation) was quantified as it is a measure of habitat availability for native biota.
Each of the parameters was subjectively scored on a 1-6 metric and these metrics used to obtain rankings (from best to worst) of: outstanding; high; moderate-high; moderate; low-moderate; and low. Outstanding lakes are nationally important, containing a diverse indigenous biota, with sustainable populations of endangered species. Conversely, low ranked lakes are either de-vegetated with poor water quality, or severely impacted by exotic pest species.
Rankings for the lakes to date are presented in Table 1.
2.5 Water birds Habitat suitability for birds was assessed during the field visit, with bird species presence and abundance observed with binoculars. Results were compared with previous records from OSNZ and DoC SSBI surveys, with any nationally or regionally threatened species noted. The combination of scuba divers and various water craft involved in this survey was not conducive to observing water birds, with many flying away before their identity was ascertained. However, some secretive species such as the nationally endangered bittern (Botaurus poiciloptilus) were often disturbed and flew allowing their detection, whereas shore-based observation would probably not detect such species.
2.6 Fish Fish records for the Northland Region extracted from NIWA FBIS comprised 295 records since 1980. These records were assessed to identify lakes containing species of regional or national significance (Hitchmough et al. 2007) and those containing pest fish. While sampling plants, divers also recorded observations of fish but these were not specifically sampled for or quantified.
2.7 Aquatic invertebrates
Large aquatic invertebrates such as freshwater mussels (Hyridella menziesi), koura (Paranephrops planifrons) and snails were noted by divers in the course of macrophyte surveys. Mussels and koura are potentially important indicators of lake condition and are likely to be incorporated into LakeSPI methodology in the future.
Northland Lakes Ecological Status 2010 8
2.8 Changes in indicators Any significant changes in biota and lake condition compared with previous surveys were reported; for example new species records, and / or change in species dominance, or vegetation depth range.
2.9 Threats
Biosecurity threats (current pest plant and fish impacts, potential impacts and risk of introduction) and other threats to water quality or ecological condition (e.g., nutrient sources, livestock access and decreasing water levels) were considered for each lake based on the surveys and discussion with landowners, NRC and DoC staff. Water quality monitoring is carried out by NRC.
2.10 Management recommendations Monitoring strategies for the highest ranked of the lakes were made (Section 3 and Executive Summary) including recommending:
Lake native biodiversity value monitoring – LakeSPI protocol with additional assessment of nationally or regionally significant biota and assessment of any new threats to ecological condition.
Pest plant surveillance – targeted monitoring of lake access and anchoring sites to detect early incursions of weed species.
2.11 Summary A summary of overall ranking, identified threats and recommendations is presented for each lake in the inventory.
2.12 Biosecurity – managing the spread of aquatic weeds in Northland lakes An evaluation of the risks posed by aquatic weeds to Northland lakes is presented in Section 4. Problem species were identified, current and potential impacts for each species, mechanisms and likelihood of spread, evaluation of threat posed by aquatic weed species and management implications are discussed. For selected water bodies prioritised for monitoring, the monitoring methods, areas searched, and results for the 2007 surveillance are reported.
Northland Lakes Ecological Status 2010 9