The effects of instream barriers on the distribution of migratory marine-spawned fishes in the lower reaches of the Sundays River, South Africa

Abstract

The distribution and abundance of migratory marine-spawned fish species was investigated in the lower reaches of the warm temperate Sundays River, Eastern Cape, South Africa. Fish were collected above and below manmade instream barriers using multi-meshed gill net fleets, 12 mm mesh fyke nets and 1 mm mesh fyke nets. Sampling was undertaken twice in the winter and twice in the summer of 2009. Of the 2 764 fish caught, marine-spawned species contributed 42.3%. Freshwater mullet Myxus capensis and Cape moony Monodactylus falciformis were the dominant marine-spawned species at most sites and were capable of surmounting almost all instream barriers. The longitudinal distribution of these species did, however, vary by size class, with the largest individuals being recorded the furthest upstream. The longfin eel Anguilla mossambica was the only species sampled above all instream barriers, including the 4 m high Cleveland Weir. The giant mottled eel Anguilla marmorata was found in low numbers at sites closer to the estuary headwaters. Other marine-spawned species, including Liza tricuspidens and Mugil cephalus (Mugilidae), Argyrosomus japonicus (Sciaenidae), Lithognathus lithognathus and Rhabdosargus holubi (Sparidae), were sampled in low numbers from the site directly below the first instream barrier only, suggesting that this first barrier restricted the access of these species to upstream environments. Freshwater non-native fishes contributed 41.7% to the total catch by numbers. The potential impact of the non-native species as predators and competitors on marine-spawned species in the study area is discussed.

The future of fish passage science, engineering, and practice

“…Some successes have been reported (Barrett & Mallen-Cooper, 2006;Baumgartner, Zampatti, Jones, Stuart, & Mallen-Cooper, 2014;Parsley et al, 2007), especially at sites where solutions were specifically developed to meet target species and hydrology. But the precarious conservation status of native population reduction of migratory species in South America (Agostinho, Gomes, Fernandes, & Suzuki, 2002;Agostinho, Gomes, & Latini, 2004), and the disrupted river connectivity throughout Africa (Jewitt, Goodman, Erasmus, O'Connor, & Witkowski, 2015;Nel et al, 2007;Wasserman, Weyl, & Strydom, 2011) and Asia (Dudgeon, 2005), clearly indicates that these strategies cannot be applied everywhere. Understanding the reason of this failure is critical, as the world's most biodiverse river basins (the Amazon, Congo, and Mekong) are experiencing an unprecedented boom in construction of hydropower dams (Winemiller et al, 2016), and their effects on biodiversity and fisheries are potentially enormous.…”

Regional variation in otolith Sr:Ca ratios of African longfinned eel Anguilla mossambica and mottled eel Anguilla marmorata: a challenge to the classic tool for reconstructing migratory histories of fishes

“…He hypothesized that the elvers might enter one estuary and if the freshwater flow in this river was insufficient to make river migration possible, they might leave and travel along the coast searching for favourable conditions. In addition to the erratic rainfall and periodic droughts, man‐made obstructions such as dams and excessive abstraction of fresh water create at least partial barriers for the upstream and downstream migration of elvers (Whitfield & Cowley, 2010; Wassermann et al , 2011). The upstream migration of the elvers might be less restricted in some rivers, such as the Nahoon River where none of the sampled A. mossambica and A. marmorata showed early experience in saltwater habitats.…”

Assessment of a vertical slot fishway in south‐eastern Australia designed to pass numerous species and size classes of fish

“…Barriers can have the greatest impact upon diadromous species as migration between freshwater and marine environments is an obligate component of their life cycle. Barriers located in the lower reaches of rivers, such as tidal barrages often have the biggest impact on fish (Wasserman et al 2011) yet have received less attention than riverine barriers in regard to refinement of fish passage (Bice et al 2017). Barriers located in the lower reaches of rivers, such as tidal barrages often have the biggest impact on fish (Wasserman et al 2011) yet have received less attention than riverine barriers in regard to refinement of fish passage (Bice et al 2017).…”

“…This group not only include fish, but also snails and some species of shrimp (Pyron & Covich 2003;Weerts et al 2014) with migrations also important for promoting the import of productivity from marine to freshwater habitats (Bauer 2013). Barriers located in the lower reaches of rivers, such as tidal barrages often have the biggest impact on fish (Wasserman et al 2011) yet have received less attention than riverine barriers in regard to refinement of fish passage (Bice et al 2017).…”