26th International Congress for Conservation Biology
July 21-25, 2013
Mark Bond: “Southern stingrays concentrate on shallow flats inside marine reserves: response to top-down or bottom-up processes?”
Marine reserves release fished species from harvest pressure but their effect on unfished species is unpredictable and may even be negative. Southern stingrays (Dasyatis americana) are not commercially targeted in Belize, Central America, but nonetheless are potentially important ecotourism attractions and bioturbators. We used Baited Remote Underwater Video (BRUV©) to survey southern stingrays in two distinct habitats (flats and fore-reef) at four sites (N=90 deployments per site, 50 on the forereef and 40 on the flats). Two of the sites were marine reserves and two were otherwise similar fished reefs. A generalized linear model (GLM) is being used to explain the effect of the factors “marine reserve,” “habitat,” “reef type” (atoll or barrier reef), and a range of environmental variables on the presence of southern stingrays on BRUVs. Preliminary analysis of BRUV deployments within one marine reserve and one fished reef found that stingray presence was significantly influenced by “habitat,” but only at the marine reserve site. Specifically, stingrays were more commonly observed on BRUVs deployed in shallow flats than on the deeper forereef habitats inside the reserve. In contrast, there was no significant effect of habitat on stingray presence at the fished site. We will present the full results from all four sites to see if this pattern holds for another marine reserve and fished site. We will also discuss the potential drivers of this pattern. “Top down” possibilities include avoidance of deeper habitats due to intimidation by sharks, which we have shown are much more common at the reserve sites. “Bottom up” possibilities include habitat or prey differences between sites. Understanding how marine reserves influence unfished species is intrinsically important given the burgeoning use of this strategy for marine conservation, but can also provide insights into ecological interactions that are otherwise difficult to study.