Fine‐scale habitat partitioning of Chilean and Peale's dolphins and their overlap with aquaculture

Abstract

1. Predictive species distribution models (SDMs) have become powerful tools to determine habitat use patterns of mobile marine predators and their spatial overlap with potentially impacting anthropogenic activities.2. This study used SDMs to investigate fine-scale habitat use patterns of two poorly known and broadly sympatric coastal delphinids, Chilean dolphins (Cephalorhynchus eutropia) and Peale's dolphins (Lagenorhynchus australis), and their spatial interactions with intense aquaculture farming activities in the Chiloé archipelago, southern Chile. A long-term dataset (2002-2012) of boat-based dolphin sightings and concur-rently in situ collected environmental and anthropogenic variables was analysed using binomial Generalized Additive Models to investigate ecological drivers of each species' fine-scale distribution and to predict dolphin occurrence spatially.4. Chilean dolphins preferred shallow (<30 m deep), turbid waters, close to shore (<500 m) and river mouths which often placed them in sheltered bays and channels used intensively by shellfish farms. Peale's dolphins were also found in shallow waters but occurred over a wider range of conditions along more open or exposed coastlines. Both species had to navigate extensive salmon and shellfish farming sites to transit between areas of important habitat.5. Sightings and predicted occurrence maps showed a clear pattern of spatial habitat partitioning between species, which remained stable across the 11 year study period. The identification of important habitat for Chilean dolphins warrants the consideration of spatially explicit conservation measures to limit the potential effects of overlapping salmon and shellfish farming.6. The observed differences in ecological plasticity of the two sympatric species should be considered when evaluating and mitigating the effects of environmental change and ongoing anthropogenic pressures on their nearshore habitat. The estimated species-environment relationships could also be used to predict where dolphin habitat and anthropogenic activities are most likely to overlap in other parts of the species' ranges.

Predicting suitable coastal habitat for sei whales, southern right whales and dolphins around the Falkland Islands

“…Concurrently, the GAM results explained between 34.7 and 41.1% of the total deviance for those species, which is similar to, or better than, the values achieved for cetacean species in many other studies [e.g. 8,35,36]. The MaxEnt models for those three species had moderate discriminatory power with AUC values of 0.60 to 0.69, although those values are lower than those achieved for MaxEnt modelling of cetacean species in some other studies [e.g.…”

“…They estimate the statistical relationships between spatial and temporal species presence and environmental factors, and generate models with some level of predictive power [4]. Model outputs have conservation applications including predicting species occurrence in areas of unsurveyed habitat [5], predicting where species may overlap with anthropogenic activities [6][7][8], and predicting changes in species distribution range in response to environmental factors [9]. Cetacean occurrence is usually modelled against a range of topographic (e.g.…”

“…seabed substrate type, proximity to river mouths), and oceanographic (e.g. sea surface temperature, chlorophyll, fronts) variables [7,8,[10][11][12]. Since cetacean distributions may primarily be driven by those of their prey, it is likely that such factors serve as proxies for spatio-temporal variation in prey density [13]; information on the latter is only rarely directly obtainable [14].…”

First Abundance Estimates of Heaviside’s (Cephalorhynchus heavisidii) and Dusky (Lagenorhynchus obscurus) Dolphins Off Namibia Using a Novel Visual and Acoustic Line Transect Survey

“…Combined, these findings provide insight into how these sympatric species may use different depth gradients to avoid competition for resources within the coastal environment of the Benguela Current ecosystem (Elwen et al, 2010;Heinrich et al, 2010). A similar pattern in habitat partitioning has been reported off Chile between Chilean and Peale's dolphins (Lagenorhynchus australis), another sympatric Cephalorhynchus and Lagenorhynchus combination (Heinrich et al, 2010(Heinrich et al, , 2019.…”

“…Heaviside's dolphins are facing increasing anthropogenic impacts in both the coastal and shelf regions of their habitat as both Namibian ports (Walvis Bay and Lüderitz) are undergoing or planning major expansion, and there is continued exploration and mining for hydrocarbons, diamonds and marine phosphates at sea. The strong site fidelity of Heaviside's dolphins (Elwen et al, 2006;Davis et al, 2014) makes them more vulnerable to localized impacts compared to a more widely ranging species like dusky dolphins, and this needs to be considered for effective population management (Heinrich et al, 2019). Studies of satellite tagged Heaviside's dolphins off South Africa show that the home ranges of individuals lie adjacent to the coast, with maximum recorded offshore distances up to 33 km (Elwen et al, 2006;Davis et al, 2014).…”