Fine-Scale Habitat Selection of Chilean Dolphins (Cephalorhynchus Eutropia): Interactions with Aquaculture Activities in Southern Chiloé Island, Chile
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J. Mar. Biol. Ass. U.K. (2007), 87, 119–128 doi: 10.1017/S0025315407051594 Printed in the United Kingdom Fine-scale habitat selection of Chilean dolphins (Cephalorhynchus eutropia): interactions with aquaculture activities in southern Chiloé Island, Chile Sandra Ribeiro*¶, Francisco A. Viddi†‡, José Luís Cordeiro*∫ and Thales R.O. Freitas*§ *Programa de Pós-Graduação em Ecologia, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500, Caixa Postal 15007 CEP 91540-000, Porto Alegre, RS, Brazil. †Marine Mammal Research Group, Graduate School of the Environment, Macquarie University, Sydney, NSW 2109, Australia. ‡Centro Ballena Azul (CBA/BWC), Carlos Anwandter 624, Casa 4, Valdivia, Chile. ∫Laboratório de Geoprocessamento, Centro de Ecologia, UFRGS, RS, Brazil. §Laboratório de Genética Molecular, Departamento de Genética, UFRGS, RS, Brazil. ¶Corresponding author, e-mail: [email protected] Fine-scale habitat selection of Chilean dolphins was studied between January and April 2002 through shore- based theodolite tracking in order to investigate the environmental and behavioural determinants of habitat use, and to evaluate the interactions between this species and aquaculture activities in Yaldad Bay, southern Chile. During 293.5 h of effort, movement and habitat selection patterns of dolphins exhibited a significantly concentrated use of only 21% of the entire study area. Correspondence analysis showed that shallow waters (5–10 m), proximity to coast and rivers were the most significant environmental parameters determining fine- scale dolphin distribution patterns, with foraging the most frequently observed activity. Aquaculture activities in the area were observed to affect dolphin habitat use patterns by restricting space available for biologically important dolphin behaviours. INTRODUCTION environment, such as modification of benthic community and local biodiversity (Buschmann et al., 1996; Naylor The Chilean dolphin, Cephalorhynchus eutropia, is the et al., 2000). Furthermore, mussel farming takes up three only cetacean species endemic to Chile, distributed from dimensional space in near-shore waters and can restrict Valparaiso (33°S) to Navarino Island, Cape Horn (55°S). animals, such as dolphins, from using the available space, It is a coastal species, inhabiting sheltered bays, channels, reducing the extent of areas used for potentially important fjords and exposed coast (Goodall, 1994). Basic knowledge biological and social activities (Würsig & Gailey, 2002; about its biology and ecology are still very limited and there Kemper et al., 2003). are no data available on abundance, population dynamics, Interactions between aquaculture activities and marine home range size and movement patterns, a consequence of mammals are generally thought to be negative (Würsig which is that its current conservation status still corresponds & Gailey, 2002; Kemper et al., 2003). Marine mammals to Data Deficient as listed by the IUCN (IUCN, 2004). might be affected by shooting, netting, and due to the use The main concern for the conservation of Chilean of acoustic devices to prevent the animals approaching, dolphins is the incidental catch in local fisheries and the area abandonment and even subsequent death might occur progressive destruction of potentially critical areas mainly (Würsig & Gailey, 2002). due to aquaculture activities (for mussel and salmon), which The main purpose of this study is to describe habitat have expanded rapidly in the sheltered bays, channels and selection patterns of Chilean dolphins, while identifying fjords of southern Chile (Buschmann et al., 1996). potential environmental features responsible for fine-scale Since its implementation in Chilean waters in 1980, the habitat use and to assess the interactions between this species aquaculture industry has increased more than 140-fold in and aquaculture activities in Yaldad Bay, Chiloé Island. its initial production, especially in the Tenth Administrative Region of Chile, which is responsible for more than 90% of MATERIALS AND METHODS the national aquaculture production (Claude et al., 2000). Given that mussels and salmon are cultivated on a massive Study area scale, they can generate intense organic enrichment and Yaldad Bay is located in southern Chiloé Island, Chile reduce the amount of oxygen available on the sea-floor and (43°08'S 73°44'W) (Figure 1) and has an area of ~22 km2. in the water column through high bio-deposition rates (from The bay’s average depth is about 13.4 m, with a maximum faeces and pseudofaeces), frequent detachment of individual of 32 m. Average slope is 2.3% and the maximum 12%. The mussels from suspended systems and external supplementary tidal cycle is semidiurnal, with amplitudes ranging from 3 feeding (rich in phosphorus and nitrogen) for salmon, all to 5 m. The bay receives freshwater input from four rivers of which cause significant and potential impacts on the (~25 m wide) and 17 streams (Figure 1). An extensive area Journal of the Marine Biological Association of the United Kingdom (2007) 120 S. Ribeiro et al. Fine-scale habitat selection of Chilean dolphins Figure 1. Study area in Yaldad bay, southern Chile. Theodolite station (⊕) and field of view ( ). of the bay is used for cultivating the mussel Mytilus edulis in the study area, it was necessary to continuously correct chilensis, which has progressively extended since the late the theodolite height in relation to sea level during the 1980s. Salmon farming is also carried out in the bay to grow observation period. By using a Correction Tide Table from Atlantic salmon, Salmo salar. the Chilean Navy available for the region, the tide height was calculated at ten-min intervals. We estimated that a 50 cm Data collection error in theodolite height (the maximum believed possible Between January and April 2002, land-based observations in this study) would cause a position error of approximately were performed from a fixed vantage point 102.78 m above 15 m at a range of 3000 m (Würsig et al., 1991). This error is sea level (Figure 1). The geographical positions of dolphins considered not to have affected the results of this study. were determined using a digital theodolite ‘Pentax ETH- Two to three observers, using binoculars (10×50) and a 10D’ (precision ±10" of arc and magnification 30×), which tripod-mounted spotting scope with 60× magnification, measures horizontal and vertical angles that can then be scanned the study area to locate a dolphin group, which converted into x/y map coordinates (see Würsig et al., 1991 was then tracked throughout the entire observation period for details). For this particular study, this procedure was until it was lost (group follow protocol, after Mann, 1999a). performed by using the software PYTHAGORAS© (G. A group of dolphins was defined as any aggregation of one Gailey, Texas A&M University). or more dolphins (including all age-classes) observed close to The precision of the theodolite fixes is proportional to each other within 100 m, in apparent association and often the instrument’s elevation above sea level and inversely engaged in similar activities. proportional to the distance of the acquired fix. Furthermore, Theodolite fixes were taken at the centre of the dolphin the greatest source of position error is inaccuracy in theodolite group approximately every 60 seconds. In addition, every height (Würsig et al., 1991). Considering the tide amplitude fix point included information on time (hour, minute and Journal of the Marine Biological Association of the United Kingdom (2007) Fine-scale habitat selection of Chilean dolphins S. Ribeiro et al. 121 Table 1. Variables used in the correspondence analysis. Intensity of and aerial behaviours such as leaping and breaching. Sexual habitat use of Cephalorhynchus eutropia was classified into four and aggressive behaviours were also included within this categories (according to dolphin permanence time in each cell); and category. environmental variables were classified into 25 categories identified –Travelling: directional and persistent movement at speed. with a numerical code. Observation effort and tracking sessions varied and were limited to favourable environmental conditions. When Variable Category possible, observations started at 0800 h through to 1900 h, Intensity of habitat use (min.) 0 Absent and were restricted to good visibility conditions, no rain and 1–10 Little sea states of Beaufort 2 or less. 11–25 Intermediate In order to evaluate the habitat use patterns in relation ≥25 High to aquaculture activities in the bay, fixes from the vertex of each structure (such as salmon cages and mussel long lines) Environmental variables Numerical code were obtained with the theodolite. These fixes were then Distance to coast (m) 0–250 1 plotted and mapped resulting in the spatial distribution of 251–500 2 polygons of areas occupied by mussel and salmon farms 501–1000 3 (Figure 1). The unobservable areas obscured by islands ≥1000 4 were estimated by taking fixes of the treetops on the islands, Depth (m) 0–5 5 which represented geographical positions on the water surface, 6–10 6 delineating the unseen area (Figure 1). 11–15 7 Considering only that area within the field of view and 16–20 8 excluding the zone obscured by the islands, 16 km2 were ≥20 9 effectively searched, which represents 73% of the entire bay Declivity (% ) 0 10 1–5 11 area. ≥5 12 Distance to rivers (m) 0–500 13 Spatial analysis 501–1000 14 By performing a spatial analysis with Geographic ≥1000 15 Information Systems (IDRISI 3.2®), independent variables Distance to streams (m) 0–350 16 such as depth, slope, distance to the coast, rivers, streams 351–700 17 (small rivers) and aquaculture structures were extracted for ≥700 18 correlation of dolphin habitat use patterns. Thematic maps Distance to salmon farms (m) 0–250 19 were constructed for each of these variables in a raster format 251–500 20 of 1×1 m cell resolution. Water depth was estimated from ≥ 500 21 bathymetry maps (Winter et al., 1982) and complemented with Mussel farm coverage (%) 0 22 bathymetry profiles obtained using a handheld Hondex 1–30 23 Depth Sounder.