Using Pooled Local Expert Opinions (PLEO) to Discern Patterns in Sightings of Live and Dead Manatees (Trichechus senegalensis, Link 1785) in Lower Sanaga Basin, Cameroon

Abstract

We aimed at unveiling patterns in live and dead manatee sightings in the Lower Sanaga Basin, Cameroon. For this purpose, the expert opinions of 133 local fishers were collected during in-person interviews, distilled using categorical data analysis, and checked against scientific literature. The five main results are as follows: manatees were sighted averagely once a week in lakes, rivers, and the coast & estuaries, mostly in group sizes of 2-3; the odds of sighting live manatees (respectively dead manatees) decreased (respectively increased) from inland lakes to estuaries and the coast, via rivers; manatee carcasses were reported in all habitats, albeit more frequently in rivers; a distribution map based on fishers’ reports show two manatee concentration areas: Lake Ossa and the Malimba-Mbiako section of River Sanaga; the number of manatees was perceived as increasing despite incidental and directed catches. Thus, our findings corroborate earlier assessments of the Lower Sanaga Basin as being a major manatee conservation area. Additionally, from these results and the literature, we identified three hypotheses about local manatee persistence: deep pools such as lakes offer year round sanctuaries, not just dry-season refugia; seasonality of specific habitat variables determine manatee occurrence patterns; and local variability in habitat encroachment mediate the meta-population dynamics of manatee in the Lower Sanaga Basin. Finally, we examine the implications for data requirements in light of the small ecological scale at which the surveyed fishers ply their trade. Thus, consonant with the Malawi principles for the ecosystem approach to management (www.cbd.int/ecosystem), we recommend collecting data preferably at landscape scale, through a participatory monitoring program that fully integrates scientific and traditional knowledge systems. This program should include, amongst others, a standardised necropsy protocol for collecting mortality and biological data together with sonar and radio-telemetry technology to discern manatee use and movements between critical habitat components.

Occurrence patterns of African manatees, conflicts with humans, and local perception in the Southern Korup Area, Cameroon

“…Accordingly, the following recommendations are made for improving manatee conservation locally, with respect to two main issues: manatee occurrence and human – manatee conflicts. The successful implementation of these recommendations depends upon enabling a co‐management framework (for which, see Mayaka, ; Mayaka et al, , ).…”

“…This recommendation is particularly relevant given the strong association between negative perceptions of manatees and support for their poaching. Mayaka, 2002;Mayaka et al, 2013Mayaka et al, , 2015.…”

“…Two previous surveys in the lower Sanaga River basin in Cameroon reported that more than half of the fishers interviewed sighted manatees once every week on average, whereas Lake Ossa and other deep pools appear to be year‐round sanctuaries for manatees (Mayaka et al, ; Takoukam, ). In these studies, fishers perceived an increase in manatee numbers based on the growing frequency of net destruction and fish theft from nets (Mayaka et al, ). Conflicts also include crop raiding, as has been reported elsewhere in Cameroon (Awah, ; Takoukam, ).…”

“…African manatees are difficult to study as they are not only elusive (exacerbated by hunting pressure) but generally prefer murky and remote waterways (Marsh et al, 2012;Reynolds & Odell, 1991) (Figure 1). These challenges are further compounded by the dearth of resources in the least developed countries, with frequent recourse to the traditional ecological knowledge of fishers and short-term studies (Grigione, 1996;Mayaka, Awah, & Ajonina, 2013;Mayaka, Takoukam, & Self-Sullivan, 2015; Moore et al, 2010;Mouyakan, 2015;Nishiwaki, Yamaguchi, Shokita, Uchida, & Kataoka, 1982;Powell, 1996;Rodas-Trejo, Romero-Berny, & Estrada, 2008;Silva & Araújo, 2001).…”

“…Manatees in coastal habitats, such as estuaries and river mouths (Fertl et al, 2005), generally spend the dry season in coastal regions and move upstream in the wet season, owing to increased water depth, access to bank vegetation, and flooded forests and savannahs (Akoi, 2004;Auil, 2004;Keith-Diagne, 2015;Mayaka et al, 2015;Powell, 1996;Rodas-Trejo et al, 2008;Siaffa & Jalloh, 2006;Silva & Araújo, 2001). Depending upon the time of year, nocturnal sightings of African manatees are more frequent in some estuarine areas compared with the rivers upstream (Akoi, 2004;Takoukam, 2012), although some manatees are found upstream all year round.…”