We’re back in the land of Trauco, Truchas, and of course Toninas! – that is in the mythical northern Patagonian waters (Trauco is a famous fabled figure on Chiloé) where salmon farming and flyfishing (for trout = Truchas) abound along with our study subjects, the Toninas or dolphins. This is my 16th summer field season looking for Chilean dolphins (and other small cetaceans) around Isla Chiloé, but this year is very different. Usually we are based at the south-eastern tip of Isla Chiloé Grande and survey familiar waters looking for well-known individual dolphins.
Chilean dolphin in front of Patagonia´s volcanos (photo: Sonja).
This year we’re embarking on a new challenge – to survey new areas looking specifically for Chilean dolphins to estimate their local population sizes. As a bonus, we also record all other marine mammals and birds that pop up in our way. Over the next two years we’re aiming to survey at least 6 different areas in the wider Ecoregion Chiloense which extends from Puerto Montt to Laguna San Rafael and from Chiloé to the mainland fjords of northern Patagonia. To estimate the population size of a 1.6m long, elusive and coast-hugging dolphin that never seems to be numerous anywhere in an area the size of the Netherlands is a pretty mad idea!!! Especially if you’re doing so with 4 observers in a 4m inflatable boat! Needle in a haystack springs to mind, only our tool for going through the hay is a toothpick! But, fear not, there is some reason to this madness. Chilean dolphins are, by all accounts of observations from all available sources across their distributional range, almost always seen very close to shore (<1km), in shallow water (<30m deep), often in estuaries or close to river mouths. We have used our long-term observations at Chiloé to predict where good Chilean dolphin habitat might be located in the Ecoregion Chiloense using a relatively simple geo-spatial modelling approach (see here for more info, publications in progress). That has narrowed the search area considerably! The additional catch with Chilean dolphins is that they prefer waters that are usually not (easily) accessible by larger survey vessels. This elusive, site-selective behaviour and the very high costs of renting ships or aircraft rule out using traditional, well established distance sampling line-transect survey methodology. But if you know of a friendly donor willing to invest some decent US dollars/Euros/GB pounds into renting a vessel that can accommodate our field team (or someone willing to offer a vessel free of charge use of our four observers)– we have ideas how this could be used very sensibly in one of the most spectacular parts of the planet...!!! ……
1, 2, 3 - Chilean dolphin calf (left) surfaces with two adults (the right fin bears subtle identification marks) (photo: Sonja).
For now, we’ve opted to break down the haystack into smallish chunks with an educated guess of where our little grey needles (aka Chilean dolphins) might most likely be found. We’ve chosen six promising areas in the Ecoregion Chiloense to estimate local population sizes of Chilean dolphins using mark-recapture methods. That is: identify individual dolphins based on natural markings on their dorsal fins, and apply a simple mathematical ratio using re-sighted known and newly identified individuals to estimate how many dolphins are using a particular study area.
This summer we’re hoping to work in at least two areas – one in northern Chiloé (Quemchi) and one on the Chilean mainland near Calbuco. I had visited both areas in December (among others) keeping a lookout for dolphins from land, and indeed had spotted their little round dorsal fins then. And – spoiler alert-…. We’ve also found Chilean dolphins now .….But those are different blog entries….
THANK YOU to the IWC Voluntary Fund for Small Cetaceans, the University of St Andrews and yaqupachae.V. Germany for supporting our needle in haystack efforts with Chilean dolphins!