Social Media and citizen science provide valuable data for behavioural ecology research: Are cuttlefish using pursuit-deterrent signals during hunting?

Obtaining robust, analysable data sets from wild marine animals is fraught with difficulties, dangers, expense, often without success. Scientists are becoming increasingly reliant on citizen scientists to help fill in gaps where they exist, especially in the area of biodiversity. Here, uniquely, we use social media and citizen science videos to investigate the behavioural ecology of hunting in five cuttlefish species – Metasepia pfefferi (N = 24), Sepia apama (N = 13), Sepia latimanus (N = 8), Sepia officinalis (N = 17), and Sepia pharaonis (N = 23). We find that hunting strategies and prey type differ between species as do the types of behaviours used by the five species studied here. We also use kinematic permutation analysis to elucidate chains of behaviours, finding that cuttlefish significantly use a mixture of predator behaviours but also prey-like behaviours, such as warning signals and possibly even a ‘pursuit-deterrent signal’ during the final moments of hunting. We also show and discuss significant intraspecific differences.

Predictable spatiotemporal dynamics of a dense cuttlefish spawning aggregation increases its vulnerability to exploitation

The giant Australian cuttlefish, Sepia apama, forms a dense spawning aggregation at a single known location across its wide southern Australian distribution. After a rapid increase in fishing pressure on the aggregation in the late 1990s, a series of fishing closures were introduced before any biological information could be collected. We surveyed the habitats, timing, and spatial distribution of the spawning aggregation over 4 years, using underwater visual transects and passive tagging, to assess the suitability of the closures. We found that the annual aggregation was both temporally (April–August) and spatially (over 8 km of coastline) localized and predictable, with a consistent peak in abundances in late May–early June. Cuttlefish densities were generally highest over the shallow, broken bedrock habitat, which was more extensive in several sites left open to fishing. Although the original closure covered about 43% of the hard substrate, it accounted for only 23–37% of the total cuttlefish abundance. The extremely high densities recorded during this study verified that this is a massive spawning aggregation for cuttlefish species worldwide, and that it could be highly vulnerable to overexploitation in the absence of adequate protection, because it is so spatiotemporally predictable and localized.

Seasonal feeding on giant cuttlefish (Sepia apama) by Indo-Pacific bottlenose dolphins (Tursiops aduncus) in south-western Australia

We report on observations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) feeding on giant cuttlefish (Sepia apama) from March 2007 to April 2013 in the temperate waters off Bunbury, south-western Australia. Seventeen feeding events were observed during the cooler months between July and September in relatively shallow coastal waters, with 12 dolphins identified as adult females. We observed behavioural sequences of complex prey-handling of cuttlefish where dolphins’ used multiple steps to remove the cuttlefish head, ink and cuttlebone before consuming the flesh of the cuttlefish mantle. Our study provides valuable information to the limited knowledge on the complex prey-handling by T. aduncus on cuttlefish in Australia, and is complementary to other known specialised foraging behaviours of bottlenose dolphins. This study also details a different behavioural sequence of cuttlefish prey-handling to that of the bottlenose dolphins in the Sado estuary, Portugal, where only the head is consumed, and to the Spencer Gulf, Australia, in that the dolphins in Bunbury carry the cuttlefish mantle over their rostrum before removing the cuttlebone. Information on S. apama in Bunbury is scarce, therefore studies on abundance, distribution and egg-laying sites are recommended in order to enable informed decision making and to understand the importance of S. apama to the diet of T. aduncus.

Evidence for a broad-scale decline in giant Australian cuttlefish (Sepia apama) abundance from non-targeted survey data

Little is known about the population trajectory and dynamics of many marine invertebrates because of a lack of robust observational data. The giant Australian cuttlefish (Sepia apama) is IUCN-listed as Near Threatened because the largest known breeding aggregation of this species in northern Spencer Gulf, South Australia, has declined markedly since the turn of the century. We used by-catch records from long-term trawl surveys to derive abundance data for S. apama and commercial cuttlefish harvest data as a measure of exploitation. Using Bayesian hierarchical models to account for zero-inflation and spatial dependence in these abundance counts, we demonstrated a high probability of broad-scale declines in the density of S. apama, particularly surrounding the primary aggregation site, which supports the recent closure of the entire S. apama fishery in northern Spencer Gulf. Historical harvest data were positively correlated with S. apama density estimated from the trawl surveys, suggesting that the commercial cuttlefish catch tracks the species abundance. Our results also indicated the possibility that the known S. apama breeding grounds might be supplemented by individuals that were spawned elsewhere in northern Spencer Gulf.

Using the giant Australian cuttlefish (Sepia apama) mass breeding aggregation to explore the life cycle of dicyemid parasites

Dicyemid mesozoan parasites, microscopic organisms found with high intensities in the renal appendages of benthic cephalopods, have a complex, partially unknown life cycle. It is uncertain at which host life cycle stage (i.e. eggs, juvenile, adult) new infection by the dispersive infusoriform embryo occurs. As adult cephalopods have a short lifespan and die shortly after reproducing only once, and juveniles are fast-moving, we hypothesize that the eggs are the life cycle stage where new infection occurs. Eggs are abundant and sessile, allowing a huge number of new individuals to be infected with low energy costs, and they also provide dicyemids with the maximum amount of time for survival compared with infection of juvenile and adult stages. In our study we collected giant Australian cuttlefish (Sepia apama) eggs at different stages of development and filtered seawater samples from the S. apama mass breeding aggregation area in South Australia, Australia, and tested these samples for the presence of dicyemid DNA. We did not recover dicyemid parasite cytochrome c oxidase subunit I (COI) nucleotide sequences from any of the samples, suggesting eggs are not the stage where new infection occurs. To resolve this unknown in the dicyemid life cycle, we believe experimental infection is needed.