SUMMARY
*Corresponding autorFeeding habits of Lontra longicaudis were compared in two periods at Río Zimatan, Oaxaca. Two transects were explored monthly in the years 1998 and 2002. We collected 1,188 scats; there were crustaceans (66.6%), fish (29.5%), insects (2.4%), birds (1.06%) and plants (0.44 %). Significant differences were found (F = 0.05, (7, 25) 3.94) Tukey’s test, these differences between groups were also found by dry or rainy seasons (q = 0.05, 8,118) and between the two periods. Shannon-Wiener Diversity index didn’t show significant differences for 1998 between transects and seasons, with the exception of comparing the “Zimatan” transect in dry season, vs “La escalera” transect in rainy season (t(.o5(2),5) > 2,57). Also when comparing between years at the total of each transect (t(.05(2), 54)>2). Three species obtained the 73 % of scats during 1998 Atya ormanioides, Macrobrachium americanum yGobiexus mexicanus influencing on the low levels of Diversity found (0.9 bits/ind). The second period showed higher values (2.4bits/ind). Human activities such as eco-tourism increased in the area during the second period, causing changes in the foraging strategies of otters. Levin’s index (5 to 11.9) showed convenient opportunistic habits, similar to equitativity (0.33 a 0.91). Variation in these indexes indicate niche amplitude is related to three or four species of crustaceans, mainly of the genera Macrobrachium and Atya.