Earlier this year the IUCN (International Union for Conservation of Nature) Shark Specialist Group took a close look at the status of chondrichthyes -that’s sharks, rays, skates, and chimaeras. Their findings did not make for happy reading. Just 23% of the species that make up this group were classified as ‘Least Concern’. But that doesn’t mean the remaining 77% of sharks are threatened, because the research also revealed that around 46% of the species that make up the chondrichthyes are classed as ‘data deficient’ – meaning we really don’t have enough information to figure out what their population status is. Given that many chondrichthyes are in bad shape, it is important that we rectify this data deficiency so we can better direct conservation management. The trouble is, data doesn’t come cheap – especially when it involves marine species.
One of the methods used for studying shark populations is to use acoustic telemetry. The exact details vary, but the general process is to 1) catch a shark 2) attach an acoustic tag to it 3) deploy acoustic receivers 4) collect ‘ping’ data (when a tagged shark comes in range of a receiver) from the acoustic receiver 5) analyse data to figure out which sharks have been where and when. Of course this method only tells us when a shark has come across a receiving station, so if a shark happens to spend a lot of time out of the range of a station, we wouldn’t get a ‘ping’ to analyse. There are other methods of monitoring shark movements that get around this problem but they are costly – more costly than acoustic monitoring which doesn’t come cheap. This isn’t to say that acoustic monitoring isn’t useful. If you have an area that is known to have resident sharks, or frequented by visiting sharks, deploying acoustic monitoring in those areas can act as a population monitoring point.
With limited funds for research and conservation, there is always a balance between collecting the best data technology can provide, with collecting the best data that we can afford. Perhaps monitoring doesn’t always have to involve high-tech gadgets at all. After all, there are many parts of the world where scuba diving and snorkelling occurs regularly. Can these human eyes act as reliable data collectors?
To answer this question Gabriel Vianna from The University of Western Australia and fellow researchers headed out to Palau in the Western Pacific - home to several species of reef shark. Palau also has some great scuba diving opportunities, with some 41,000 human visitors to Palau going scuba diving in 2010. That’s a lot of eyes in the water but for the data to be robust, those eyes need to belong to people who are familiar with the species. For this reason, the researchers only questioned dive guides. That didn’t mean that they were short of data. Over a 5-year period, 62 guides recorded some 2,360 dives across 52 different sites. Among other questions about the dive site and conditions, the guides were asked some fairly simple questions about the sharks they saw: what species, and how many. This data was then compared with some acoustic telemetry data obtained from four of the key dive sites known to be home to resident grey reef sharks (Carcharhinus amblyrhynchos) . Some fancy stats later and we can see just how well the dive guides did against the acoustic telemetry.
Actually the dive guides did pretty well. The final dataset used for analysis filtered out some of the returned questionnaires, and focused on just five dive sites – the four sites where the acoustic telemetry was deployed, and an additional site well known for being a hotspot for reef sharks. Grey reef sharks and the whitetip shark(Triaenodon obesus) were the most commonly observed of all the shark species spotted. What is really nice is that the relative abundance of the sharks recorded by the guides was consistent with data obtained from the telemetry, both on daily comparisons and monthly comparisons (which is useful for looking at more general changes over time).
Utilizing dive guides as citizen scientists is all well and good but as the researchers note, who these citizen scientists are, and how the monitoring is undertaken is key. The guides were all experienced, and familiar with the biodiversity at their dive sites. Remember that dive guides tend to take tourists on pre-determined and often repeated routes to give the best dive experience as well as take into account health and safety. Even though the guides were experienced, the questionnaires they filled in and instructions provided helped to ensure that data was collected in a consistent fashion. Less experienced guides – and certainly tourists – may have produced more unreliable data that was not as consistent with the telemetry. The researchers also note that there are a few peculiarities to Palau that may have helped to produce such consistent results. First, the sharks are largely habituated divers in the water. In other areas, sharks may scatter when divers are present resulting in the guides counting less sharks that the telemetry records when divers are absent. Another point they raise is the clarity of the water in Palau, which allows guides to clearly see and identify sharks over a fairly long distance. In more murky conditions, visual counting may not work so well.
This paper was published in the open access journal PLoS ONE - follow this link to have a read of it yourself: www.dx.doi.org/10.1371/journal.pone.0095565
Image: Blacktip Reef Sharks (and remoras and needlefish). Credit Doug Finney/Flickr (CC BY-NC 2.0)