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There be giants! The importance of taxonomic clarity of the large ocean sunfishes (genus Mola, Family Molidae) for assessing sunfish vulnerability to anthropogenic pressures.

Nyegaard, Marianne (2018) There be giants! The importance of taxonomic clarity of the large ocean sunfishes (genus Mola, Family Molidae) for assessing sunfish vulnerability to anthropogenic pressures. PhD thesis, Murdoch University.

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The study of ocean sunfishes has for decades been practically synonymous with the study of Mola mola, recently listed as ‘vulnerable’ on a global scale by the International Union for Conservation of Nature. The concerns are high levels of fisheries bycatch worldwide, however sunfish bycatch is rarely identified to species level anywhere, perhaps as a long legacy of taxonomic confusion in the sunfish taxonomy has rendered identification to species level challenging. This includes the Australian and New Zealand longline fisheries, where sunfishes are listed at “High Risk” due to data deficiency. In the popular sunfish SCUBA dive tourism off Bali, Indonesia, another type of anthropogenic pressure is manifested through diver crowding, preventing sunfish from interacting with cleaner-fish on the local reefs. The consequences are difficult to gauge due to a paucity of information on this highly seasonal phenomenon, but have motivated discussions of sunfish protection by Indonesian authorities.

In this study, the species identities and zoogeographies of the little studied sunfishes in Australia and New Zealand were explored through biopsy sampling in the longline fisheries, and by reviewing museum collections across both countries. Specimen IDs were established phylogenetically and/or morphologically. Combined, the results revealed a new species of ocean sunfish, Mola tecta, which was diagnosed and described. Furthermore, the results showed that three large species of sunfish dominate the tropical, subtropical/warmtemperate and cold-temperate waters of Australia and New Zealand; Masturus lanceolatus, Mola alexandrini and Mola tecta, respectively. Mola mola appears to be rare. These results imply that the long-term fisheries observer sunfish bycatch data from both countries consists of a mix of species. Bycatch rate analyses within four fishing grounds sub-areas, each presumably dominated by one species of sunfish, did not reveal downwards trends over the 10 - 12 year periods, for which data were available.

In the Bali tourism industry, the sunfish species identity was confirmed molecularly and morphologically as Mola alexandrini. The strong seasonality in diver sightings was documented through sunfish encounter rates based on operator logs. The results revealed that the 2015 sunfish season (August – October/November) lagged by ~1 month the seasonal change in intensity of two major oceanographic features of the area, established from in situ and satellite sea surface temperature data. Data from eight satellite tagged sunfish revealed a high affinity by four fish to the dynamic Lombok Straight during the sunfish season, however, at least one other fish left the area. Overall, temperature emerged as an unlikely main driver of the sunfish seasonality, which is instead presumably driven by an increase in sunfish prey availability, associated with the seasonal cold-water upwelling.

Overall, these findings have provided much needed clarity to the taxonomy and phylogenetic relationships of the genus Mola, and demonstrated the need for species-level investigations of fisheries bycatch globally to inform fisheries risk assessments. Furthermore, the results provided important information on the sunfish seasonality off Bali to inform tourism management decisions.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
United Nations SDGs: Goal 14: Life Below Water
Supervisor(s): Loneragan, Neil, Warren, Carol and Bejder, Lars
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