Crocodilians and fisheries in the Philippines: revisiting Fittkau’s hypothesis

Abstract

Crocodilians have been assumed to influence aquatic primary productivity and fishery yield. However, strong empirical evidence to support such claims is lacking. The long-standing assumption first hypothesized by Fittkau (1970), is that local fisheries (secondary productivity) in areas inhabited by crocodilians would be expected to improve. We tested this hypothesis at two locations in the Philippines, inhabited by the Philippine Crocodile (Crocodylus mindorensis) in Paghungawan Marsh in Siargao Island Protected Landscape & Seascape (SIPLAS), Jaboy, Pilar, Surigao Del Norte, and the Indo-Pacific Crocodile (Crocodylus porosus) in the Rio Tuba River, Bataraza, southern Palawan Island. Water chemistry parameters, with emphasis on nutrient (nitrate and phosphate) levels, were determined using using standard protocols. Catch-per-Unit Effort (CPUE) of gillnets in sites with crocodiles was compared with corresponding control sites without crocodiles. CPUE was higher in areas inhabited by crocodiles, but appeared not to be directly influenced by nutrient levels. Increased fish catches in areas inhabited by crocodiles might be attributed to several factors, such as reduced fishing pressure due to the presence of crocodiles which discouraged the local fishermen to fish intensively. Overall, while fish catch was higher in areas inhabited by crocodiles, it is too early to attribute this to the nutrient output from crocodiles due to several confounding factors. KEYWORDS: estuarine, fish catch, freshwater, nutrient