Using volunteer anglers to survey Murray Cod : what's the catch?

  • Patrick Ross-Magee

Student thesis: Master's Thesis


Diminishing biodiversity is a global ecological problem, and as the human population continues to
grow and climate change continues to worsen, biodiversity conservation is of vital importance.
Freshwater ecosystems are particularly imperilled, as the linear and unidirectional flow
characteristics of rivers and streams make them overly sensitive to human impacts. Competing
demands from agriculture, domestic, and industrial use are a major threat to freshwater
ecosystems. Despite freshwater habitats comprising less than 0.02 % of the planet’s water, they
contain around 40% of the world’s fish species – with 30 to 40% of these thought to be threatened.
Freshwater fish in Australia are facing growing threats from modified land use, increasingly
regulated rivers, and competition, predation, and ecosystem alterations from alien fish species and
in the Murray-Darling Basin (MDB) Australia native fish abundance has declined to around 10% of
the level of pre-European settlement.
Murray cod (Maccullochella peelii), endemic to the MDB, is Australia’s largest obligate freshwater
fish. It is an iconic species that plays an important role ecologically, culturally, and economically.
Murray cod are aggressive sit-and-wait ambush predators that are relatively sedentary outside of
breeding season, maintaining close association within a stream section. They are usually closely
associated with structure, such as submerged timber or rocks, undercut banks and overhanging
vegetation. This means that Murray cod are difficult to sample using traditional fish survey methods
like netting and electrofishing. Murray cod are simultaneously a nationally listed threatened species,
while remaining a prized recreational fishing target. For these reasons, the species requires
management attention.
Population assessments are an important early step in any threatened species management
programs, and while Murray cod are well studied in lowland reaches of the MDB, little is known
about upland populations. Boat electrofishing has been used extensively in lowland monitoring
programs and, as a survey technique, it lends itself well to lowland riverine environments.
Conversely, the characteristics of upland rivers of the MDB make access for a boat electrofisher
impossible for large stretches of river. Furthermore, boat electrofishing is a costly process and
because of strict licensing and legislative requirements, it largely precludes stakeholder involvement.
The high costs and limitations of current standard sampling methods (netting and boat
electrofishing) resulted in the commencement in 2013 of a MDB-wide project to investigate the use
of volunteer angler-based surveys for Murray cod. This thesis is part of that Basin-wide project. Growing interest in participatory citizen science initiatives, as well as a strong cohort of conservation motivated anglers, provide an opportunity to develop an alternative angler-based survey method. A volunteer-based participatory research approach not only allows stakeholder involvement, but could substantially reduce the costs and increase the scope of monitoring programs. In this thesis, I report on three key aspects of Murray cod monitoring: (1) a comparison of the effectiveness of different capture techniques, including using volunteer anglers and boat electrofishing, (2) an analysis of the motivations of anglers to inform participatory fishery management study designs and limit volunteer attrition, and (3) an analysis of mark recapture data from the two different electrofishing survey methods, as well as angling surveys to quantify Murray cod populations in upland rivers. To determine the effectiveness of capture techniques, I compared (i) standardised volunteer angler-based surveys for Murray cod, (ii) standard (SRA) boat electrofishing surveys and (iii) targeted habitat boat electrofishing surveys in a mark-recapture study. Six sites on the upper Murrumbidgee River were first surveyed by angling and then by boat electrofishing during three sampling campaigns in 2015-2016. A total of 48 fish were captured in 724 angler-hours by anglers, and 149 fish were captured in 10.6 hours by boat electrofishing. A total of 11 marked fish were recaptured, all of which were captured during electrofishing surveys. Angling was shown to capture larger fish (median = 633 mm TL) than electrofishing (median = 349 mm TL). Although angling is a less efficient capture method in terms of catch per unit effort, it provides a cost-effective sampling method that can be employed across a much greater spatial extent in a short period of time. The mark recapture data was also fitted into a Bayesian framework using Markov Chain Monte Carlo (MCMC) methods to estimate per-site Murray cod populations. Acknowledging the large uncertainties stemming from a relatively low recapture rate, I was able to extrapolate local per-site population estimates to include all pool habitat within the Murrumbidgee River in the ACT. This resulted in an estimate for total post-juvenile Murray cod abundance in the Murrumbidgee River in the ACT of 1710 fish. Although these estimates should be treated with caution, they are the first attempt to quantify Murray cod populations in an upland system. To determine their motivations for initial and continuing participation in fishery science, a series of semi-structured interviews were conducted with 16 volunteer anglers who participated in the angling surveys. The interviews were analysed using an adaptive theory approach. Participant’s motivation for initial involvement stemmed largely from a strong interest in both freshwater angling for native species, and from the conservation of a valued fish species. Participants motivations changed as participation continued, shifting to a desire to continue achieving benefits such as improved angling knowledge/skills, networking opportunities, and greater understanding of
scientific processes. Key factors impacting a volunteer’s ability to maintain participation were other commitments affecting availability at specific times, together with concern about whether angler and researcher goals were complementary or might conflict in future, particularly if data on fish locations were published. This underlines the need to tailor study design to enable participants to
continue achieving benefits from engaging in citizen science over the longer-term, as well as to ensure shared objectives are built between citizen scientists and professional researchers engaged in using citizen data.
This study provides the basis for building a cost-effective and angler-inclusive Murray cod monitoring program for upland systems where traditional survey methods are supplemented by structured angler surveys. Some small adjustments to study design, such as the use of longer-term tags and more frequent angling surveys, should result in a higher recapture rate, and reduce the uncertainties of this study. Additionally, design of future participatory fishery monitoring programs should take
into account factors that allow volunteers to achieve benefits from being involved in the research process, as well as limit factors that are likely to result in volunteer attrition.
Date of Award2018
Original languageEnglish
SupervisorMark Lintermans (Supervisor), Jacki Schirmer (Supervisor), Ben Broadhurst (Supervisor) & Fiona Dyer (Supervisor)

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