ARGOS USER STORIES
Simon Pierce & Chris Rohner
Marine Megafauna Foundation
We first started researching whale sharks in Mozambique in 2005. Over the first few years of work we quickly identified over 600 whale sharks frequenting the coastal waters of Inhambane province in southern Mozambique. Recognition of this region as a global whale shark hotspot helped precipitate rapid growth in the marine tourism sector, assisting local development within one of the world’s poorest countries.
Unfortunately, after a few years we started noticing that less whale sharks were turning up each year. While whale shark movements are often linked to sea surface temperature and other variables, even when these factors were incorporated into time-series models we still documented a 79% decline in whale shark sightings between 2005 and 2011, which have continued to the present.
What had happened to the Mozambican sharks? We turned to satellite tags to help us learn more about the movements of whale sharks in the region. As part of Chris’s PhD thesis at The University of Queensland, we used the ARGOS satellite network to track 15 juvenile whale sharks with SPOT5 tethered tags designed by Wildlife Computers.
These tags transmitted positions and temperature data for up to 87 days following deployment on the sharks, with individual sharks travelling up to 2, 700 km. Some of the sharks moved south into South African waters, and several moved offshore into international waters in the Mozambique Channel. However, most spent the bulk of their time in a clear coastal movement corridor within Inhambane province, often in shallow waters within a few hundred metres of the shore.
Modelling their movements in relation to remotely-sensed chlorophyll-a concentration showed that the sharks were targeting productive waters, presumably to feed. Unfortunately, declining fisheries catches in these same waters have led to local communities turning to indiscriminate large-mesh gillnets to ensure a continued supply of fish protein. These gillnets are being placed right across the whale shark freeway.
With the shark movement data in hand, we turned to aerial surveys, funded by the Rufford Small Grant Foundation and flown by Janneman Conradie, to help us identify the communities where gillnets are most likely to inadvertently catch whale sharks. Citizen science data on gillnet locations within the main whale shark hotspot, collected by All Out Africa volunteers, showed a dramatic increase in gillnet use over 2012-15.
Our conservation team at MMF is now gearing up to work with the communities that are most likely to interact with whale sharks. The MMF team have developed a highly successful community engagement program in Mozambique over the past few years, culminating in a gillnet ban and short-term fisheries closure within a portion of the main area used by the sharks, along with a new alternative livelihood development program. We hope to scale these initiatives to other coastal communities that have been driven by poverty to use unsustainable fishing methods that threaten local marine megafauna.
Ultimately, our use of the ARGOS network has informed us that highly localised conservation efforts could make a genuine difference to the regional conservation of this endangered species. These data will shortly be published. For ongoing updates, check out Simon’s shark biology and underwater photography website (link to https://www.simonjpierce.com) and the Marine Megafauna Foundation site (link to ).