Monitoring and mitigating interactions between small pelagic fisheries and dolphins: literature review and analysis of fishery data.

Rationale and scope 

This review compares approaches taken to monitor and mitigate common dolphin (Delphinus delphis) interactions with the South Australian Sardine Fishery (SASF) with those taken for protected species interactions with other fisheries for small pelagic species, including Australia’s Commonwealth Small Pelagic Fishery (SPF). The review informs ongoing refinement of approaches in the SASF and supports the SASF’s commitment to a “continuous process of review and improvement”. This is one of the main elements of the fishery’s Code of Practice (CoP) for mitigating interactions with wildlife (SASIA 2021). 

This study was also needed to ensure that approaches taken in the SASF are “reviewed with consideration to international standards for mitigating interactions with marine mammals” (Commonwealth of Australia 2016), which is a requirement of the accreditation of the management regime for the SASF under Part 13 of the Commonwealth Environment Protection and Biodiversity Conservation Act 1999.  

Context 

The SASF’s Wildlife Interaction CoP was first implemented in September 2005, in response to a seven-month independent observer program estimating 377 dolphin mortalities (484 dolphins for the 200405 financial year), and discrepancies between logbook records and observer data in dolphin interaction rates. The CoP documents avoidance and release procedures aimed at minimising dolphin encirclements and mortalities. Annual analyses of observer data show that adherence to the CoP is effective in mitigating these interactions. Estimates of common dolphin abundance in Spencer Gulf and its adjacent shelf in 2011 and 2021, and potential biological removal analysis, suggest that current mortality levels recorded by the observers are unlikely to be having major impacts on the conservation status of common dolphins in southern Spencer Gulf. The main unresolved issue is whether observed mortality rates reflect overall mortality rates in the fishery. Fisher behaviour appears to differ in the absence of observers and logbook mortality rates are ten-times lower than observed rates, providing uncertainty in the estimated number of mortalities and accuracy of TEPS interaction and mortality recording in the absence of observers.  

Approaches to monitor interactions between small pelagic fisheries and dolphins  

Programs for monitoring interactions between fisheries and cetaceans typically involve a mix of logbook and observer data and, in recent years, electronic monitoring (fixed cameras, e.g., Cornwall purse-seine fishery). Knowledge of the population status of marine mammals impacted by fisheries is needed to inform the design of monitoring programs, because different approaches should be applied to species with different conservation status (e.g., protected, threatened, endangered, critically endangered species). 

Logbooks are used in most fisheries and often include records of interactions with marine mammals. The interaction information may be biased though, with under-reporting occurring when interactions are not recognised, or reporting is additional to requirements or perceived to have negative consequences.   Independent observer programs provide independent estimates of bycatch rates of marine mammals in many fisheries. Observer coverage is usually limited to a proportion of fishing effort and findings are extrapolated across the entire fishery. Observer coverage rates in purse-seine fisheries worldwide vary between 0 to 100% of effort, but most are <10%. Observer coverage in the SASF is 10% of net-sets. Twice it has increased temporarily, to 20 and 30%, following higher-than-normal observed mortality rates and discrepancies between observer and fisher-reported data. Observer coverage will not accurately measure interaction rates if, in the presence of observers, fishing behaviour is different compared to when an observer is absent.   Electronic monitoring has been used to augment observer programs in pelagic fisheries worldwide, including a night-time purse seine fishery in the UK, and can improve the accuracy of reporting rates of interactions with protected species.   Assessments of dolphin abundances are typically conducted by aerial- or ship-based, distance sampling methods. These can incorporate methods to account for individuals underwater at the time of passing. A limitation to abundance estimates is that they provide a single point estimate whereas local dolphin abundances can change rapidly in response to environmental conditions. Also, estimates typically have large confidence limits meaning only substantial changes over time can be detected.   Best practice for monitoring interactions of pelagic fisheries with marine mammals and impacts on the population status of bycatch species involves clear management objectives, a frequency of population assessments suitable for detecting change, accurate recording of bycatch mortality, biological performance indicators and reference points for management. Different jurisdictions have taken a range of approaches.  

Approaches to mitigate interactions between small pelagic fisheries and dolphins 

Effective mitigation of interactions between fisheries and cetaceans usually requires the implementation of an inter-related suite of monitoring (to detect and quantify rates), management (to direct the need to mitigate), and mitigation measures, which need to be refined over time using an adaptive approach. Approaches taken to mitigating interactions can be specified in documents published by fisheries management agencies (e.g., the Commonwealth Small Pelagic Fishery, SPF, Dolphin Mitigation Strategy), industry CoPs, (e.g., the SASF and the Commonwealth Blue Grenadier (Macruronus novaezelandiae) Fishery, and management plans for specific vessels (e.g., SPF Vessel Management Plan, FV Geelong Star). 

The avoidance (search for dolphins and delaying fishing if they are detected) and release (opening the front of the net, and/or aborting the net-set) procedures used in the CoP for the SASF are effective in mitigating dolphin mortalities. Elsewhere, purse-seine fisheries for small pelagic species do not appear to have frequent dolphin encirclements, but when they occur, use similar procedures to avoid dolphin encirclement and release encircled dolphins. The SASF has the added difficulty of using large nets and operating at night.   Acoustic deterrents are reasonably effective in alerting dolphins to the presence of set nets, such as gillnets, but are less effective in preventing dolphins being encircled by purse-seine nets or entering trawl nets. Devices trialled in the SASF did not reduce encirclement rates. Net pingers have also been trialled in a purse-seine fishery in the UK, but are not in routine use as dolphin interactions are infrequent.  Enhanced methods for detecting dolphins (e.g., night vision goggles, thermal imaging, hydrophones) may help to reduce encirclement and mortality rates by increasing the effectiveness of pre-fishing searches and reducing the time taken to detect the presence of encircled or entangled dolphins.   Dolphin Mitigation Strategies (e.g., SPF Dolphin Mitigation Strategy) that include objectives, performance indicators, reference points (criterion) and defined management responses are valuable for informing monitoring and mitigation programs.   In the SASF, management responses to temporal increases in rates of observed mortality and large discrepancies between mortality rates recorded in logbooks and by observers, have been implemented across the entire fishery (e.g., increased observer coverage). An alternative is to apply management responses to individual vessels where reference levels are breached (e.g., SPF Dolphin Mitigation Strategy). 

Options for maintaining and improving monitoring and mitigation of interactions with dolphins in the SASF include: 

Maintain, regularly review and improve (as required) the industry CoP and the ‘real-time’ monitoring program run by the South Australian Sardine Industry Association (SASIA). Maintain SASIA/PIRSA pre-season briefings/ training to skippers and crew.   Conducting trials to assess the potential for using electronic monitoring to evaluate fishing behaviour and application of the CoP when an observer is not present.   Conducting trials to assess the potential benefits of using new technologies (e.g., night vision goggles, thermal imaging (infra-red), hydrophones) to enhance the searches for dolphins prior to and after setting the net.  Evaluating the benefits of applying management responses to increased mortality rates and/or discrepancies between logbook and observer data to individual fishers/vessels rather than across the fishery.   Repeating the aerial surveys and population assessments of common dolphins at a frequency that reflects the conservation status of the population.  Establishing a SASF Dolphin Mitigation Strategy, ideally informed by an overarching bycatch strategy for South Australia, that includes quantitative objectives, performance indicators, reference points and decision rules. 

Broader implications 

This review compares the approach used to monitor and mitigate dolphin interactions in the SASF with other small pelagic fisheries worldwide. It highlights advances made in the SASF as well as opportunities to enhance the current program and will help industry and managers to evaluate future refinements. Limitations and differences in the approaches used to monitor and mitigate interactions with dolphins in the SASF and SPF highlight the potential benefits of establi