Mariculture activities abound in the central and southern Chiloé Archipelago and most bays and channels are occupied by at least one farm. Locations without mariculture activities are used for shellfish extraction, fishing or constitute shipping routes. Although no direct interactions between cetaceans and any of these activities were observed the multitude and intensity of anthropogenic activities are bound to impact, singly or synergistically, on the local ecosystem and potentially the cetaceans inhabiting these nearshore waters.
2.5.6.1. Mussel farms
Mussel farms have been shown to affect dolphins directly by displacing them from potentially important habitat (Kemper et al. 2003, Markowitz et al. 2004, Watson- Capps and Mann 2005). Alterations of the local food web due to mussel farms have been documented (Grange and Cole 1997, Mirto et al. 2000), but cascading effects reaching apex predators like dolphins have yet to be investigated. Some of the largest
Crovetto and Medina 1991). Recent observations suggest that dolphins could be excluded from large parts of Yaldad bay due to the extensive mussel farm coverage (this study, Ribeiro 2003). Structural components, such as floats and lines, suspended at the surface and extending vertically into the water column (often reaching close to the bottom), could impede dolphin movements and impact on foraging behaviour by acting as visual or acoustic obstructions (Figure 2-15). Field observations of dolphins (this study, Ribeiro 2003, Watson-Capps and Mann 2005) and captive studies of harbour porpoises (Kastelein et al. 1995) suggest that small cetaceans are reluctant to swim through ropes. A better understanding of Chilean dolphin movements and habitat use is required before conclusions about exclusion from vital habitat and impacts on foraging efficiency can be drawn.
2.5.6.2. Salmon farms
Ecological effects of fish farming (e.g. salmonids, tuna, and other fin fish) on the surrounding ecosystem are numerous and varied and have received much attention in recent years (Bushmann et al. 1996, Naylor et al. 2000, Tovar et al. 2000, Holmer et al. 2001). Cetaceans can be impacted directly by becoming entangled and drowned in the netting from fish cages or anti-predator nets (Kemper and Gibbs 2001, Kemper et al. 2003). Predatory attacks on caged fish, as is common for pinnipeds (Nash et al. 2000, Kemper et al. 2003), have yet to be reported for any cetacean species. Bottlenose dolphins in the Mediterranean have learnt to exploit the abundant wild fish assemblages attracted to the outside of the fish cages by an over-abundance of fish feed (Bearzi et al. 2004b). Most fatal entanglements of dolphins appear to occur accidentally when dolphins feed on wild fish associated with the fish cages (Kemper and Gibbs 2001). An unknown number of Peale’s dolphins are thought to have died in anti-predator nets at salmon farms around Chiloé (Perrin et al. 1994, Claude and Oporto 2000). Foraging behaviour around or direct interactions with salmon farms were not observed during this study, neither for the two dolphin species nor the porpoise.
Dolphins and porpoises alike have been excluded from potentially important habitat by loud aversive sounds intended to deter pinnipeds from predating on caged fish (Johnston and Woodley 1998, Morton and Symonds 2002, Olesiuk et al. 2002). These acoustic harassment devices (AHDs) were trialled unsuccessfully by salmon farmers in
during this study (M. Sepúlveda, pers. communication; S. Heinrich, unpublished acoustic data).
As for mussel farms, indirect effects on cetaceans via impacts on and alteration of the local food web are difficult to determine. Consequently, relevant information is lacking. The intensity with which salmon and mussel farming occur in the Chiloé Archipelago generate additional, untargeted and yet potentially serious impacts. Boat traffic has increased due to mariculture activities (e.g. for harvest, supply and maintenance of farms) and has increased noise levels that could disrupt or interfere with normal behaviours of cetaceans (Richardson et al. 1995). Chilean dolphins tend to avoid boats and alter their behaviour (at least short-term) in response to passing boats (Crovetto and Medina 1991, Ribeiro et al. 2005). Although such traffic is usually not targeted at the dolphins, effects of boats and behavioural changes might be similar to those caused by whale- and dolphin watching activities (Hastie et al. 2003, Lemon et al. 2005, Lusseau 2005). Salmon farming introduces large quantities of contaminating substances such as antifouling chemicals, antibiotics and solid marine debris into the coastal waters (Haya et al. 2001, Miranda and Zemelman 2002). Millions of farmed salmon have escaped accidentally (or been released intentionally) from salmon farms in southern Chile and constitute a threat to the native fish fauna (Soto et al. 2001).
2.5.6.3. Entanglement in fishing nets
Entanglement in fishing nets or bycatch constitutes the largest and most imminent global threat to small cetaceans (Read et al. 2006). Peale’s dolphins, Chilean dolphins and particularly Burmeister’s porpoises have been subject to bycatch in Chile (Oporto and Brieva 1990) and in other parts of their range (Reyes and Oporto 1994, Goodall et al. 1997b, Majluf et al. 2002). Information on bycatch of small cetaceans in the fisheries of Chile has never been assessed nationally and has not been documented locally anywhere in the last 20 years.
The ports of Quellon, Dalcahue and Ancud on Isla Chiloé support small artisanal fishing fleets (mainly for hake, silversides, anchovies, conger eel) that fish locally and out into the Golfo Corcovado. An adult male Burmeister’s porpoise washed ashore
material of the specimen was made available to verify species identification and determine clear net entanglement marks around the snout and head of the animal (photographs courtesy of C. Maturina, Gobernación Maritíma, Castro).
Given that members of the genus Cephalorhynchus and the Phocoenoidae (porpoises) are particularly prone to entanglement in fishing gear (Read and Gaskin 1988, Dawson 1991, Reyes and Oporto 1994, Crespo et al. 1997, van Waerebeek et al. 1997, d'Agrosa et al. 2000) it is reasonable (but currently unsubstantiated) to assume some ongoing bycatch of Chilean dolphins and Burmeister’s porpoises (and possibly Peale’s dolphins) off Chiloé.
One of the ecological challenges generated by salmon farming in Chile is the unintended (or intended) release of millions of farmed salmon which act as exotic predators and competitors to the native fish fauna. Soto et al. (2001) suggest that artisanal fishing constitutes the best way of controlling and removing escaped farm fish from the wild. Escaped salmon have become a lucrative alternative target for the struggling artisanal fishing industry (Soto et al. 2001), and are caught in increasing numbers in shorebased gillnets. Shorebased gillnets are the “poor man’s ticket” to the salmon bonanza and escaped farmed salmon have become a lucrative product on the larger local markets2 (Heinrich, pers. observation). Nets are placed in the shallow intertidal zone perpendicular to shore and are left unattended. They only fish around high tide, which coincides with regular foraging activities of Chilean dolphins in the same area (Heinrich, pers. observation, Ribeiro 2003). Chilean dolphins purportedly have been caught in these nets but were released alive (G. Burgos, pers. communication). Whether entanglement occurs regularly or in substantial numbers is unknown at present. The fact that congeneric Commerson’s dolphins are subject to high levels of bycatch in the same type of intertidal gillnet (Iniguez et al. 2003) should be reason for concern.