Abstract
We investigated population parameters using the capture-mark-recapture method (Ituglanis passensis and I. bambui) and visual censuses (I. epikasrticus and I. ramiroi). The four species are regionally threatened (Brazilian Red List) and occur in caves of Terra Ronca State Park, São Domingos region, Central Brazil. We conducted seven fieldtrips across three years of dry seasons. For the capture-mark-recapture method, a 400 m long stream inside Passa Três cave, where I. passensis occurs and a 300 m long reach of an upper tributary where I. bambui occurs inside Angélica cave were divided into 20 and 17 study sections, respectively. Catfishes were hand-netted, measured (standard length), weighed, marked by subcutaneous injection of biocompatible pigments, and released. The four species show medium-to-low mean population densities (0.03 ind/m2 0.7 ind/m2). Capture-mark-recapture data pointed to a relatively small population size for I. passensis, restricted to a 1600 m long stream inside Passa Três cave (N = 719) and for I. bambui (N = 246; 300 m of epikarstic drainage). Ituglanis passensis and I. bambui move along relatively small areas with a restricted home range. We observed recruitment patterns and a trend of decrease in condition factor during the dry seasons for I. bambui but not for I. passensis, suggesting that epikarstic waters are probably more limiting concerning food input. Ituglanis passensis and I. bambui showed low growth and consequently high longevity, corroborated by captivity data (20 years). We suggest urgent actions and long-term monitoring projects to effectively protect this unique and endemic ichthyofauna.
Highlights
Troglobites, characterized by exclusively subterranean species [1], show, in general, small population size [2]
The low rates of recapture observed for I. passensis and I. bambui are probably related to the loss of marks
For I. bambui, which occurs in an upper vadose tributary of Angélica cave, recapture rates were markedly lower than rates recorded for I. passensis, which occurs in a base level stream
Summary
Troglobites, characterized by exclusively subterranean species [1], show, in general, small population size [2]. Available data for subterranean fish show that population densities may vary considerably, from very low to very high, and are sometimes higher than their relatives from epigean (surface) environments [3]. This variation can be partly related to the methods of study since the lowest densities are usually recorded in studies that used the visual census method [3]. We do not know the full extent of habitats occupied by the species, and the characteristics of the subterranean realm, which is largely inaccessible, prevent accurate studies [3]
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