Protecting Kenya’s dolphin habitat

Marine protected areas (MPAs) are pretty nifty tools for marine conservation. You take an area, you give it a designations and (hopefully… but the reality can be quite different) you attach some regulations/legislation to remove harmful activities to whatever it is you are trying to protect inside the MPA and make efforts to rebuild and conserve this spot. The situation of picking an area to designate can become trickier when dealing with ocean wanderers – species that move around a lot, and over great distances. It is safe to say that it is politically unfeasible to designate one area big enough to encompass, for example the movement of sea turtles. Instead, sea turtles may find critical habitat – feeding areas or nesting beaches for instance, covered by an MPA. We can’t protect them everywhere, but we can build a case to protect them where we know they hang out in large numbers.

Some species are a little less predictable – or we simply don’t know where their critical habitats are. Take southern Kenya’s populations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) for instance. Apparently these critters are the most abundant of the marine mammals in Kenya’s Kisite-Mpunguti MPA. Abundance does not mean we know much about them though. The species is listed as data deficient on the IUCN Red List. We don’t know the status of the Kenyan population – if it is significantly under threat, or even doing very well, but we do know that globally top marine predators – especially mobile species, are showing signs of trouble. Can the Kisite-Mpunguti MPA play a role in looking after these predators key habitats? That’s what Sergi Pérez-Jorge of Global Vision International Kenya/Mediterranean Institute for Advanced Studies (IMEDEA) and fellow researchers set to find out.

What we need to know If we want to see where MPAs for our dolphins should be we need to identify their key habitats. To do that, we start with sightings data, which was acquired via vessel-based surveys conducted between 2006 and 2009 both inside and outside the MPA. Take that information, plot it on a map and you can see where they have been (have a look at the paper for some maps – link below).

They’re over here! But why? We could just say ‘put the MPAs where the dolphins were seen a lot before’, but there is a problem. We only have data for when the survey-boats encountered the dolphins. The dolphins probably have a great deal more habitat than that so when we want to identify key habitat, we also want to understand why they are somewhere, so we can make predictions as to where else they may like to be. The researchers took 10 different environmental variables (5 dynamic – like sea surface temperature, and 5 static – like distance to the nearest reef) to ‘describe’ the areas the dolphins were sighted in. Not all of these variables play vital roles in explaining the dolphin’s preference for area, so the researchers did some fancy modelling to work out which were and which weren’t key predictors of dolphin presence in an area.

Where do the dolphins like to go? The researchers combined the sightings data with the environmental data, and grouped the dolphin’s distribution into three different categories – recurrent areas (dolphins are seen frequently there every year), occasional areas (dolphins visit, but their presence varies year to year), and unfavourable areas (where dolphins are almost never seen). The team’s analysis found that the dolphins frequently used several key places including near reefs inside the MPA and on the east side of Wasini Island, which lies to the north of the MPA. They also liked to hang out around nearshore oceanographic fronts.

Is the MPA also good for dolphins? Some of the key dolphin areas was indeed inside the existing MPA but 53% of the recurrent and 43% of the occasional areas were found to be outside MPA. What is more 65% of the whole study area (not just the MPA) was classed as unfavourable habitat. The researchers recognise that a giant MPA covering the dolphin’s movement year-on-year is unrealistic, but they do point out that the MPA does not appear to contain enough critical habitat for the species. With threats increasing in magnitude and frequency, this, the researchers believe, is concerning news.

MPAs aren’t the only thing needed to secure the long-term sustainability of these dolphins. Some of the areas outside the MPA that dolphins favour fall under areas proposed for collaborated co-management of fisheries. If these areas prove to be effective in increasing and maintaining a suitable biomass of fish, the dolphins may have a few less areas where they are being out-competed for food by humans.

The original paper The paper was published in the open access journal PLOS ONE. The authors have paid for the paper to be open access, so why not have a read of it yourself

The Image Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) in the Red Sea. Credit Serguei S. Dukachev/Wikimedia (CC BY-SA 3.0)