The effect of different logging regimes on the ecomorphological structure of stream fish assemblages in the Brazilian Amazon

Abstract

We evaluated the effects of changes in habitat structure resulting from conventional logging (CL) and reduced-impact logging (RIL) on the ecomorphological structure of stream fish assemblages in the eastern Brazilian Amazon, investigating (1) which habitat characteristics are influenced by different logging methods, (2) the differences in the ecomorphological structure of fish assemblages between two logging methods and undisturbed forest (UF), and (3) the relationships between ecomorphological traits of fish assemblages and habitat variables. We measured 13 habitat variables and characterized 11 ecomorphological traits of 55 fish species collected in 34 sampling sites (stream stretches) located in CL, RIL, and UF. In logged areas, the streams present a fine sediment increase and reduced vegetation cover, while in the UF a greater amount of natural shelter and more cover vegetation were observed. These environmental changes selected ecomorphological traits of stream fish assemblages, recording a greater relative width of the mouth in UF, higher ventral flattening index in RIL, or greater relative head length, and higher caudal peduncle compression index in CL. In this sense, we recommend that logging practices, including RIL, should be reviewed as a means of adopting better strategies to minimize human disturbances in streams.

Effects of human disturbance on habitat and fish diversity in Neotropical streams

“…Environmental heterogeneity and microhabitat diversity are fundamental to the availability of shelter and food resources for fish species [19]. These conditions facilitate the existence of diverse species in these streams through utilization of resources in different microhabitats [20,21]. The increased input of nutrients in the water column resulting from urban and agricultural land use causes changes not only in water physic-chemical conditions but also in terms of primary productivity and aquatic biota [22][23][24].…”

The drivers and impacts of Amazon forest degradation

“…In fragmented landscapes, patch area is an important determinant of species persistence; conserving the full suite of forest birds requires maintaining large patches (e.g., >10,000 ha) of good-condition forest (71). The impacts of forest disturbance extend to aquatic biota, and even reduced-impact logging affects the composition and functional traits of stream fishes (72). Disturbance also disrupts multi-trophic processes such as pollination, decomposition, seed dispersal and herbivory (73), and drives sub-lethal changes in the morphology or physiology of birds (74) and dung beetles (70).…”

“…4B) and reduce availability of preferred game species (93). Forest degradation can impact fish abundance in streams, rivers and floodplains, with implications for the nutritional diversity and food security of local communities (72). Some of the material changes extend beyond local communities, as reductions in forest resources can affect peri-urban households that maintain strong links with forests (89), compounding existing vulnerabilities associated with structural marginalization (94).…”

The identification of logging roads in Point Reyes National Seashore

“…These are anadromous fish who depend entirely on gravely freshwater stream beds for habitat and breeding success [18]. Logging roads are known to affect the spawning rates and habitat suitability in anadromous fish populations [21], primarily because logging roads increase fine sediment loads to stream channels and decrease amounts of available gravel [3]. Increased sediment flow into stream beds from logging roads can persist up to 80 years past the logging event [8],…”

“…Decommissioning roads has been found to return sediment loads to their natural levels [1,10]. Identifying and removing sources of high sediment loads should be a priority for any habitat remediation project for these sensitive species [18,21].…”