Long-term trends and a risk analysis of cetacean entanglements and bycatch in fisheries gear in Australian waters

Tulloch, Vivitskaia; Pirotta, Vanessa; Grech, Alana; Crocetti, S.; Double, Michael C.; How, Jason; Kemper, Catherine M.; Meager, Justin J.; Peddemors, Victor M.; Waples, Kelly; Watson, Mandy; Harcourt, Robert

doi:10.1007/s10531-019-01881-x

Cited by 36 publications

(25 citation statements)

References 76 publications

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“…Bycatch in fisheries poses the biggest threat to small cetaceans globally (Mannocchi et al, 2012;Brownell et al, 2019;Tulloch et al, 2019;Hines et al, 2020;Omeyer et al, 2020), including the Indian Ocean (Anderson et al, 2020), increasingly highlighting unsustainable levels (Peltier et al, 2016). Incidental bycatch of dolphins in bather protection nets off the East Coast of South Africa has been a cause for concern for a number of decades (Cockcroft and Ross, 1990b;Peddemors et al, 1990;Cockcroft, 1994).…”

Section: Introductionmentioning

confidence: 99%

Long-Term Demographic and Spatio-Temporal Trends of Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) Bycatch in Bather Protection Nets off KwaZulu-Natal, South Africa

2020

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Bather protection nets have been in place off the coast of KwaZulu-Natal (KZN), South Africa, since the 1950’s. Besides sharks, they also catch a number of other marine vertebrates, including dolphins, the majority of which are Indo-Pacific bottlenose dolphins Tursiops aduncus. Previous analyses of dolphin bycatch in the nets indicated the potential impacts on the local populations, but a lack of information on population structure has to-date hindered a more detailed assessment. A recent re-assessment of the status and population delineations of T. aduncus off South Africa prompted a re-examination of demographic, spatial, and temporal patterns of its catches in bather protection nets over a 36-year period (January 1980 to December 2015). In total, 1169 dolphins were caught, including a slightly greater number of females and juveniles than other sex-classes, raising concern about the potential long-term effects on population demographics. More dolphins were caught off the North than the South coast. Temporal trends indicate that the bycatch during June and July every year (peak Sardine Run period) as a percentage of overall dolphin bycatch has been steadily decreasing from 39.8% in 1980 to 13% in 2015. A large inter-annual fluctuation can be seen, probably as a result of the inter-annual intensity of the Sardine Run. Although our results do not indicate a long-term decline of the individual populations as previously predicted, revised abundance estimates and data on the demographics and movement patterns of the animals are urgently required to accurately assess the impact of bycatch on the Indo-Pacific bottlenose dolphin populations off KZN and to advise conservation and management decisions going forward.

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Section: Introductionmentioning

confidence: 99%

Long-Term Demographic and Spatio-Temporal Trends of Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) Bycatch in Bather Protection Nets off KwaZulu-Natal, South Africa

2020

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“…However, obtaining robust and unbiased estimates of abundance of marine mammals remains challenging due to the large geographic expanses that often characterize their distribution and the many factors that introduce detection bias (Marsh and Sinclair, 1989;Taylor et al, 2007;Buckland et al, 2015). Furthermore, bycatch of marine mammals is not evenly distributed across a population or species geographical range but concentrated in particular hotspots (Lewison et al, 2014;Tulloch et al, 2020). Such concentrated mortality can lead to the fragmentation of populations, reduction in annual survival and population growth rates, genetic diversity and gene flow among fragments; local extinctions of detected or undetected populations; and cascading ecological changes on the structure and function of marine ecosystems (Pichler and Baker, 2000;Lewison et al, 2004;Heppell et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Abundance and Potential Biological Removal of Common Dolphins Subject to Fishery Impacts in South Australian Waters

et al. 2021

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Conservation management of wildlife species should be underpinned by knowledge of their distribution and abundance, as well as impacts of human activities on their populations and habitats. Common dolphins (Delphinus delphis) are subject to incidental capture in a range of Australia’s commercial fisheries including gill netting, purse seining and mid-water trawling. The impact these fishery interactions have on common dolphin populations is uncertain, as estimates of abundance are lacking, particularly for the segments of the populations at risk of bycatch and in greater need of protection. Here we used double-observer platform aerial surveys and mark-recapture distance sampling methods to estimate the abundance of common dolphins in 2011 over an area of 42,438 km2 in central South Australia, where incidental mortality of common dolphins due to fisheries bycatch is the highest. We also used the potential biological removal (PBR) method to estimate sustainable levels of human-caused mortality for this segment of the population. The estimated abundance of common dolphins was 21,733 (CV = 0.25; 95% CI = 13,809–34,203) in austral summer/autumn and 26,504 in winter/spring (CV = 0.19; 95% CI = 19,488–36,046). Annual PBR estimates, assuming a conservative maximum population growth rate of Rmax = 0.02 and a recovery factor of Fr = 0.5 for species of unknown conservation status, ranged from 189 (summer/autumn) to 239 dolphins (winter/spring), and from 378 (summer/autumn) to 478 dolphins (winter/spring) with an Rmax = 0.04. Our results indicate that common dolphins are an abundant dolphin species in waters over the central South Australian continental shelf (up to 100 m deep). Based on the 2011 abundance estimates of this species, the highest estimated bycatch of common dolphins (423 mortalities in 2004/05) in the southern Australian region exceeded the precautionary PBR estimates for this population segment. Recent bycatch levels appear to be below PBR estimates, but low observer coverage and underreporting of dolphin mortalities by fishers means that estimates of dolphin bycatch rates are not robust. The effects of cumulative human impacts on common dolphins are not well understood, and thus we recommend a precautionary management approach to manage common dolphin bycatch based on local abundance estimates.

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“…Through leveraging global systems and regional seafood ratings programs that compile small-scale fisheries knowledge [ 9 , 93 ], multi-species risk assessment can be applied to disentangle the human dimension of fisheries bycatch and integrate locally-relevant criteria, such as set height or mesh strength of nets, that embrace the conceptual complexity of marine megafauna conservation research [ 79 ]. After risk baselines have been developed [ 94 , 95 ], it is possible to compare feasible management and policy interventions. Finally, GIS-based scenarios that capture inter-annual variability and modifications of fishing gears [ 52 ] could be incorporated into ByRA to examine how the location and timing of risk is likely to change in the future, and anticipate at-risk areas in need of further monitoring and evaluation.…”

Section: Discussionmentioning

confidence: 99%

Using GIS and stakeholder involvement to innovate marine mammal bycatch risk assessment in data-limited fisheries

et al. 2020

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Fisheries bycatch has been identified as the greatest threat to marine mammals worldwide. Characterizing the impacts of bycatch on marine mammals is challenging because it is difficult to both observe and quantify, particularly in small-scale fisheries where data on fishing effort and marine mammal abundance and distribution are often limited. The lack of risk frameworks that can integrate and visualize existing data have hindered the ability to describe and quantify bycatch risk. Here, we describe the design of a new geographic information systems tool built specifically for the analysis of bycatch in small-scale fisheries, called Bycatch Risk Assessment (ByRA). Using marine mammals in Malaysia and Vietnam as a test case, we applied ByRA to assess the risks posed to Irrawaddy dolphins (Orcaella brevirostris) and dugongs (Dugong dugon) by five small-scale fishing gear types (hook and line, nets, longlines, pots and traps, and trawls). ByRA leverages existing data on animal distributions, fisheries effort, and estimates of interaction rates by combining expert knowledge and spatial analyses of existing data to visualize and characterize bycatch risk. By identifying areas of bycatch concern while accounting for uncertainty using graphics, maps and summary tables, we demonstrate the importance of integrating available geospatial data in an accessible format that taps into local knowledge and can be corroborated by and communicated to stakeholders of data-limited fisheries. Our methodological approach aims to meet a critical need of fisheries managers: to identify emergent interaction patterns between fishing gears and marine mammals and support the development of management actions that can lead to sustainable fisheries and mitigate bycatch risk for species of conservation concern.

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Long-term trends and a risk analysis of cetacean entanglements and bycatch in fisheries gear in Australian waters

Abstract: Long-term trends and a risk analysis of cetacean entanglements and bycatch in fisheries gear inAustralian waters. Biodiversity and Conservation, 29 pp. 251-282.

Cited by 36 publications

References 76 publications

Long-Term Demographic and Spatio-Temporal Trends of Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) Bycatch in Bather Protection Nets off KwaZulu-Natal, South Africa

Long-Term Demographic and Spatio-Temporal Trends of Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) Bycatch in Bather Protection Nets off KwaZulu-Natal, South Africa

Abundance and Potential Biological Removal of Common Dolphins Subject to Fishery Impacts in South Australian Waters

Using GIS and stakeholder involvement to innovate marine mammal bycatch risk assessment in data-limited fisheries

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