Critical knowledge gaps: estimating potential maximum cumulative anthropogenic mortality limits of key marine mammal species to inform management
South Australian Research and Development Institute
Principle investigator: Alice Mackay, Simon Goldsworthy, and Peter Harrison - South Australian Research and Development Institute (Aquatic Sciences)
Key words: Marine mammal, Small Pelagic Fishery, population estimate, elicitation review, Australian fur seal, bottlenose dolphin, Indian Ocean bottlenose dolphin, Fraser’s dolphin, hourglass dolphin, Risso’s dolphin, southern right whale dolphin, striped dolphin, Potential Biological Removal .
The Commonwealth Small Pelagic Fishery (SPF) has attracted significant public attention as a result of marine mammal bycatch (common dolphins and fur seals) in mid-water trawl operations by the FV Geelong Star since it commenced fishing in April 2015. The Australian Fisheries Management Authority (AFMA) currently has a number of management measures in place to minimise further interactions between marine mammals and the fishery. These include spatial and temporal closures based on bycatch trigger limits.
A two day workshop funded by the Fisheries Research and Development Corporation (FRDC) held in June 2015 explored further mitigation options to reduce interaction rates with marine mammals. An outcome of this meeting recommended that an expert group be established to review available information used to establish trigger limits for key marine mammal species in the area of the SPF.
The FRDC established this project to follow up on recommendations and achieve the following:
Potential Biological Removal calculates the maximum number of anthropogenic mortalities a population can sustain while still allowing that population to reach or maintain its optimum sustainable population. In other words, the limit that the population can bear before there are adverse impacts on the population. The calculation of PBR is relatively simple but requires data on the abundance of a given population and an understanding of the range or spatial distribution of that population.
A two day workshop was convened at SARDI Aquatic Sciences, Adelaide on 19-20 October 2015: The first day of the workshop provided stakeholders from Commonwealth and State fisheries, environment agencies, industry and environmental organisations with a summary of currently available information on the abundance and distribution of key marine mammal species in the area of the SPF.
On the second day, a Closed Technical Workshop (CTW) of invited scientists was held. During the Closed Technical Workshop a process of expert elicitation was used to elicit estimates of population size for each marine mammal species relative to different spatial zones. Estimates were based on available data on marine mammal abundance and were not provided for those species or zones where there was no data.
Estimates obtained through CTW and Expert Elicitation process were used, where possible, to calculate Potential Biological Removal (PBR) for the species considered. The outputs of the Expert Elicitation were used where possible to calculate PBR for species and management zones. While recent abundance data were available for the seal species considered, available data on dolphin population structure and size were extremely limited.
Key Project Results:
1. Collate and synthesise all available data on the distribution, abundance and population structure of key marine mammal species that overlap with the area of the SPF.
2. Convene an Expert workshop to “review current information available to inform the establishment of trigger limits for key marine mammal species (especially the short-beaked common dolphin, Australian fur seals and long-nosed fur seal).”
3. Report on the outcomes of this workshop and present the results of PBR analysis for short-beaked common dolphins and seals , based on available data, expert opinion and a precautionary approach.
4. Identify knowledge gaps and research needs to improve quantitative robustness of PBR of each species.