Monitoring and Assessment of North Island Tuna

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1 Monitoring and Assessment of North Island Tuna Marc Griffiths Taxonomy Longfins prefer faster flowing water and rocky river beds, and their distribution generally extends further inland Shortfins prefer slower moving water and often inhabit lakes and swamps and the lower reaches of rivers. Not all individuals follow the rules and the two species often co-occur. Longfinned tuna (Anguilla dieffenbachii) Maximum size: 2.0 m, 25 kg Shortfinned tuna (A. australis) Maximum size: 1.1 m, 3 kg Australian longfin tuna (A. reinhardtii) Maximum size: 2.0 m, 21 kg Drawings courtesy of R. M. McDowall 1

2 Life-cycle Maturity Tuna are semelparous: which means they have only one spawning season, after which they die. Mature tuna have developed gonads and are silvery with larger eyes They mature at relatively large age. Longfin Shortfin Age at maturity M 25 yrs 14 yrs Age at maturity F 40 yrs (max >100yrs) 25 yrs Length at Maturity M 62 cm (48-74) 44 (38-55) Length at Maturity F 115 cm (75-180) 74 (50-110) 2

3 Spawning Grounds Mature longfin tuna migrate downstream to the ocean in late Autumn They then make their way to marine spawning grounds After spawning they die Glass Eels Eggs and larvae travel to New Zealand via a combination of passive transport on prevailing currents and active swimming. When leptocephalus larvae approach the coast they transform into glass eels and then enter rivers (in Spring). Glass eels are typically 9-12 months old and 6-7cm long They become pigmented, thus transforming into elvers, within a week or two of entering freshwater 3

4 Elvers Elvers are pigmented tuna <15cm long (1-5yrs old), and are capable of using surface tension to climb moist rock faces. They spend most of the time buried within the substrate/gravel (to at least 50cm) For a period of two or three months each year in late summer they migrate upstream (which is when they accumulate at dams). The further from the sea, in a particular system, the older the elvers are. However they appear to migrate more quickly up some rivers than others. Sub-Adults Sub-adults are tuna >15cm long that are not yet mature These are sometimes referred to as yellow eels (other parts of the world) or adult tuna. However, since they are not mature adult is not really appropriate. The commercial fishery targets sub-adult tuna of around 300g - 4kg (<2kg in the Waikato). Although the MLS is 220g, legislated 31mm escape tubes exclude fish < 300g. Tuna >Max legal size are returned alive. Commercial fishers voluntarily avoid migrating silver tuna (i.e. Adults) 4

5 Eel QMAs MPI Tuna Monitoring Research contracted by the Ministry for Primary Industries (MPI) is largely focused on monitoring trends in: 1. the recruitment of elvers and 2. the relative abundance of larger exploited tuna (300g to 4kg). Elver recruitment is monitored by counting the number of elvers arriving at several dams, throughout the country, during the elver migration season in late summer. Abundance of exploitable tuna is monitored using standardised catch rates of commercial fishers (based on statutory catch and effort data). 5

6 Commercial CPUE Catch per day is modelled as a function of the following key variables: year, permit holder, number of nets, target species, month and river flow. Standardised catch per unit effort (CPUE) trends are produced for each Eel Statistical Area (ESA), and the series for each species is updated on a three-year cycle North Island ESAs 6

7 % Longfin Habitat Fished Commercially Standardised commercial CPUE monitors the abundance of tuna of legal size in the part of each ESA that is fished commercially. But not all of the habitat is fished commercially In 2014 MPI commissioned a research project to determine the proportion of habitat in each ESA that was fished commercially and also impacted by hydro dams. This work was done by NIWA with input from the EEL WG. The area fished in each ESA was determined from face to face interviews with fishermen, using maps. The area not fished included: DoC Estate; areas closed by MPI to commercial fishing, e.g. Whanganui, Motu, and Mohaka Rivers Inaccessible areas and streams too small to be commercially viable The proportion of longfin habitat was determined using models based on presence absence data on the NZFWFDB and environmental predictors on the REC2 Data Base. % Longfin Habitat Fished Commercially Percent (%) QMA Eel Statistical Area Current habitat fished Max. impacted area LFE 20 AA LFE 20 AB LFE 21 AC LFE 21 AD LFE 21 AE LFE 21 AF LFE 22 AG LFE 23 AH LFE 23 AJ LFE 22 AK LFE 22 AL LFE 22 AM All NI All NI

8 North Island CPUE Trends North Island ESAs 8

9 9

10 Limitations of Long Fin CPUE Series They apply only to the areas commercially fished in each ESA (3-50% of habitat). CPUE after 2005 is biased low for the following reasons: 1. An increase in escape tube dia. from 25 mm to 31 mm in Some eels previously retained are no longer caught also applies to shortfins 2. Failure of some fishers to record on ECE returns all legal sized tuna caught, not just those retained. Due to limitations in ACE for longfins, a substantial portion of the catch is often returned to the water. Not recording this results in underestimated CPUE/abundance. ACE became limiting after longfin TACCs were severely cut in 2005, and even more so during the last few years when many Iwi, concerned with LFE sustainability, shelved their quota. 3. Unrecorded release of > 4kg tuna ( >2kg in Waikato co-management area). The 4kg maximum legal size was introduced in , with no statutory requirement to record the weight of returned eels. CPUE before includes eels >4kg, but after this date does not. A voluntary logbook programme on the SI showed that large numbers of large eels are returned. The new electronic monitoring system planned to begin in 1 October 2017 does include recording of eels over the maximum legal size Elver monitoring at dam sites The purpose of this programme is to monitor recruitment of longfin and shortfin eels - to ensure there are enough adults escaping to spawn. It is not the intention to measure recruitment to as many rivers as possible, but rather to monitor those rivers deemed to be representative of recruitment to North and South Islands 10

11 Trap and Transfer sites - North Island Wairua Falls (WRU) Karāpiro Dam (KAR) 17 Watercare Reservoirs Wairere Falls & Mokauiti Upper Whanganui Motukawa Mangorei Matahina Dam (MAT) Patea Dam (PAT) Turitea Dam 20 Piripaua (PIR) (Waikaremoana) Elver ageing Median Age (yrs) Karapiro Patea Matahina Piripaua LFE SFE

12 Longfin Tuna Recruitment Shortfin Tuna Recruitment 12

13 STOCK ASSESSMENT OF NORTH ISLAND TUNA Reference Points for each ESA 1. Target: 40%B0 2. Soft Limit: 20%B0 3. Hard Limit: 10%B0 4. Overfishing threshold: Fmsy = F40%B0 13

14 Longfin Assessment Method The LFE population in each ESA was assessed by taking into account: 1. Proportion of habitat impacted by hydro dams and commercial fishing 2. The CPUE trend in the fished area 3. Relative exploitation rate in the fished area 4. Trends in elver recruitment at dams Relative Exploitation Rate Historical Stock Status Trajectory and Current Status Standardised CPUE for longfin eels in Northland (AA) from to (from Beentjes & McKenzie in prep). Also shown is the total estimated core fisher longfin catch in AA from ECERs. Error bars are 95% confidence intervals. Vertical dashed line indicates when the 4 kg maximum size was introduced in after which longfin eels 4 kg and over are not recorded on ECERs. Before 2001, 37% of the catch was recorded as EEU (unidentified) and these catches are omitted. Annual relative exploitation rate for longfin eels in the Northland (AA). Because some catch of longfin was reported as EEU (unidentified) and has not been allocated to species, the exploitation rate is likely to have been higher than shown before

15 ESA % Imp. (F+D) Status in relation to Target Status in relation to limits Over-fishing AA 40.2 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AB 38.2 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AC 55.0 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AD 55.7 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AE 23.9 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AF 13.6 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AG 24.7 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AH 29.9 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AJ 23.6 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AK 40.6 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AL 5.0 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below AM 7.4 Likely (> 60%) at or above Soft Limit: Very Unlikely (< 10%) below Stock Status of NI Shortfin Tuna No negative trends in recruitment Shortfin CPUE is increasing in most ESAs Relative exploitation rate below long-term average in most ESAs But no information on the proportion of habitat fished or impacted by dams. Therefore not possible assess status of populations in each ESA against reference points. 15

16 North Island TACC Review Step Eel stock assessment reviewed by Working Group and Plenary Pre-consultation with industry and iwi on North Island eel TACs Public consultation Implementation of decisions on North Island eel stocks Timing Completed June - October 2017 February/March 2018 Late 2018 Contact for Review: Duncan Petrie Senior Analyst, Inshore Fisheries Duncan.petrie@mpi.govt.nz Acknowledgments Shannan Crow, Mike Martin, Mike Beentjes (NIWA) for figures used in this presentation. The Eel Working Group members for their contribution to the work and to the assessment. Iwi involved with elver trap and transfer programmes at dams. A big thank you to Te Wai Maori for the opportunity to speak at this conference 16

17 Data Not Used in the 2017 Assessment In early 2013 the Parliamentary Commissioner for the Environment (PCE) completed a review of the stock status of longfin eels. One of the conclusions of the PCE s report was that the information used by MPI to monitor eels had limited value and that greater emphasis should be placed on the following alternative data: New Zealand Freshwater Fish Database (NZFWFDB): This is a voluntary database containing a substantial quantity of research data, beginning in 1960, that could potentially be used to monitor eel abundance. It is mostly presence/absence data collected using electric fishing by a variety of organisations including NIWA, the Department of Conservation (DOC) and Regional Councils. Electric Fishing Size Composition Data: Regional Councils and NIWA have a substantial quantity of length frequency data for both longfin and shortfin eels collected by electric fishing in wadeable streams. International Panel Review The PCE s report also recommended the establishment of a fully-independent peer review panel to assess the full range of information available on the status of the longfin eel population. In November 2013 a panel of international experts was convened by MPI to review information available on the status of longfin and shortfin eels. The Panel endorsed methods currently used by MPI to monitor New Zealand eels and while it shared MPIs views on the limitations of existing analyses using NZFWFDB and electric fishing size composition data, it did support MPI initiatives to investigate the use of more sophisticated analyses to produce reliable trends from these data. 17

18 NZFFDB Two types of data on the database Presence/absence Catch per Unit Effort. NZFFDB Presence/absence (unstandardized) 18

19 NZFWFDB Presence/absence (standardized) Limitations of Presence/Absence data Year Catch (No.) CPUE (n/ hour) P/A Yes Y Y Y Y Y Y Y Y Y Same site fished for three hours each year. N = numbers of eels 19

20 7/17/17 NZFWFFB - CPUE Few reliable records of catch and effort data Mostly because effort not consistently recorded Not possible to generate CPUE series Electric Fishing Length Frequencies sample sites 20

21 Electric Fishing Length Frequencies Add Conor s Chart New MPI Projects Research in addition to regular monitoring (CPUE, elver recruitment, % habitat fished) Using the WRC data-set to develop standardised series of abundance for size categories of longfin eels. 1. Main aim is to look at generating an alternative index of recruitment for rivers not affected by dams. 2. This project will also investigate environmental factors influencing catches of each size category, e.g. distance from sea, substrate type etc. Feasibility and data requirements for a spatially integrated statistical stock assessment. 1. Develop a suitable spatial model 2. Identify what data we need, in addition to what we already have 3. How much will it cost to collect the shortfall. 21

22 DoC Risk Assessment DoC recently classified Longfin eels as At risk and declining This does not necessarily mean they are in danger of becoming extinct For a population as large as that for LFE, the classification system asks whether the population is likely to decline by 10-70% in the next two generations. For LFE the generation time is around 40yrs Although MPI will endeavour to maintain or increase abundance in fished areas, by adjusting TACCs, current rates of habitat loss suggest at least 10% of current LFE habitat will be lost over the next 80yrs. Shortfin eels were classified as Not Threatened Reference Points Stock Status Reference Points For ESA, Interim Target is 40% B 0 For commercially fished area, Target is B MSY proxy based on CPUE; not determined Default Soft Limit: 20% B 0 Default Hard Limit: 10% B 0 For ESA, Overfishing threshold is F MSY For commercially fished area, Overfishing threshold is F MSY proxy based on relative exploitation rate; not determined Status in relation to Target Status in relation to Limits Status in relation to Overfishing For total ESA: Likely (> 60%) to be at or above For fished area: Unknown For ESA, Soft Limit: Very Unlikely (< 10%) to be below For ESA, Hard Limit: Very Unlikely (< 10%) to be below For ESA: to be overfishing For fished area: Unknown 22