Fear of fishers: anti-predator behaviour of coral reef fish and its relevance to fisheries management and conservation

Responding appropriately to predators is essential for prey animals to maximise fitness and survival. Non-lethal predator-prey dynamics can have large effects on how animals use and perceive their environment. The understanding of predator escape behaviour in animals can play an important role in conservation and management, with implications for human/wildlife interactions, particularly hunting and tourism. In this thesis I use coral reef fish as model organisms to examine our existing knowledge of factors influencing prey flight response in the context of marine ecosystems. I go on to examine how fishing and protection from fishing influences the flight behaviour of fishery target coral reef fishes through the use of no-take reserves (NTRs) and periodically harvested closures (PHCs). Flight initiation distance (FID - how close a predator can get to an animal before it flees) is widely used when investigating how prey animals respond to predation, and has been utilised in systems where humans are predators or otherwise disturb wildlife (e.g., through tourism such as bird watching). However, the use of FID in the marine realm prior to this thesis was limited. Studies investigating FID vary in methodology and many of the potential confounding effects inherent to in-water estimation of FID have yet to be investigated. In Chapter 2, I compared the relative effects of spear guns, dive gear (SCUBA vs. free diving), observer bias and protection from fishing on estimates of FID. FID in areas protected from fishing was, on average, 141 cm lower than in fished areas, with no difference found between treatments for either dive gear or speargun. Management status explained 60% of the variation in FID estimates, while differences between observers only accounted for 4%. Size was highly significant, with larger fishes being associated with greater FID in every treatment. These findings imply that fishes use only limited predator attributes as cues for flight, and that the response of fishes to these attributes is amplified in areas of higher predation risk. In Chapter 3 I examined how FID changed across a range of families and fishing pressures on coral reefs in Papua New Guinea. I surveyed FID, fish size, group size and pre-flight behaviour of two families commonly targeted by spearfishers - Acanthuridae and Scaridae - and four families that were less common in the spearfish catch – Balistidae, Lutjanidae, Mullidae and Serranidae (groupers) across four levels of fishing pressure. Increases in fishing pressure were associated with increases in FID for Acanthuridae, Balistidae, Mullidae, and Scaridae, while FID of Lutjanidae and Serranidae showed no relationship with fishing pressure. Notably, mean FID of Lutjanids was greater than the mean effective range (MER) of spear guns, while the mean FID of Serranids was lower than other families. Larger individuals tended to flee earlier, particularly at moderate or high fishing pressures, while group size and pre-flight behaviour differed between families, but showed low concordance with fishing pressure. These findings indicate that the relationship between size and FID of coral reef fishes is more complex than has previously been presented, and that an interaction between predation experienced by fish families and traits such as territoriality or trophic level, may be important in determining FID. One of the benefits expected from NTRs is spillover of adult biomass to adjacent fishery grounds, through density dependent export or random movement of fishes across NTR borders. Fishes with little experience of predation may transport non-wary behaviours across the borders of marine reserves, resulting in a gradient of increasing FID with distance from the reserve border. In Chapter 4 I examined FID and biomass of Acanthuridae and Scaridae, and one non-target family (Chaetodontidae) across the borders of three NTRs and three control borders within fished areas in the Philippines. FID only increased significantly with distance from the NTR centre for the two fishery families at NTRs, and remained below FID recorded in fished areas until 140 m outside the NTR, significantly further than spillover of biomass. These reductions in FID are likely to lead to increased catchability of fishes near NTRs. While this may increase local support for management, changes in catchability may give rise to inaccurate estimates of NTR effects on fish biomass and abundance. Across the South Pacific, PHCs are often utilised in place of NTRs, with the specific aim of taming fishes to increase catchability and produce high yields during harvests. Using a before-after-control-impact-pair design, in Chapter 5 I investigated whether PHCs in Vanuatu had similar effects on fish FID and biomass as NTRs, and the effects of a single harvest. Catch per unit effort was higher during the harvest than for regular fishing, and this was linked to FID of Acanthuridae being lower than MER of spear guns in PHCs. Acanthuridae also increased as a proportion of the catch, and showed substantially lower biomass in PHCs than NTRs, even with no detectable effect of the harvest on UVC estimates of biomass. The effects of PHCs are attuned to the expectations of local communities. However, differences in the magnitude of behavioural changes between fishery-target families may result in contrasting outcomes of PHC management regimes. In Chapter 6 I tested whether predictions of increased FID with increased predation risk, size of individual and availability of refuge were consistent across a broad range of fishing pressures around protected areas and inside fished areas. I included FID of fishes from the Chagos Archipelago, which is a completely unfished population, and FID from areas in Vanuatu, Philippines and Papua New Guinea. FID in fished areas was consistently higher than protected areas across the spectrum of fishing pressure. Both in fished areas and protected areas, fishing pressure had the most support explaining FID, followed by fish size then refuge availability. Life-history stage was not a significant predictor. These results show that fishing effects such as increases in wariness can be imported into marine reserves, and supports predictions of increases in FID with increased predation risk and size (as a loose proxy for reproductive values). Previous studies have shown increases in FID with hunting, a result confirmed here for coral reef fishes. Experience of predation and some prey conditional and environmental factors can all have significant influences on FID. In contrast, little evidence was found for other factors such as predator attributes or group size. In general, I found that the level of predation risk in the environment tends to have the largest effect on FID (Chapters 2), while fish family, prey size and environmental variables had small but significant effects (Chapters 3, 6). These results have important implications for management, showing that changes in fish behaviour can positively influence fishing on during the harvest of PHCs (Chapter 5), and around the borders of NTRs (Chapter 6), both of which may help increase stakeholder support for management. Temporary changes in behaviour caused by management may increase the susceptibility of fishes to fishing gears, and reduce the impacts of protection. Furthermore, borders of NTRs are porous to behaviour, and fishery mediated behavioural changes may be ubiquitous within smaller NTRS within heavily fished seascapes (Chapter 6)