Abundance of larval and 0+ juvenile marine fishes in the lower reaches of three southern African estuaries with differing freshwater inputs

Abstract

Although numerous studies have been conducted on the biology and ecology of larval and juvenile marine fishes in estuaries, information on the factors influencing abundance, which in turn reflects the magnitude of immigration into these systems, is generally lacking. In an effort to provide some insight into the posslble role of freshwater discharge on the abundance of marine larval and juvenile fishes, 3 permanently open eastern Cape Province estuaries with similar tidal prisms and mouth dimensions, but differing riverine inputs and turbidity characteristics, were selected as study sites. The Great Fish system can be characterized as a turbid estuary (>50 NTU) with a moderate axial salinity gradient (> 20 g kg-'), the Sundays as a semi-turbid estuary (> 10 NTU) with a strong axial salinity gradient (>30 g kg-'), and the Kariega as a relatively clear estuary (< 10 NTU) with a weak axial salinity gradient (< 10 g kg-'). Although the number of marine fish taxa entering the 3 estuaries was similar (18 to 20 species), Littoral densities of larvae and 0+ juveniles in the lower reaches of the Great Fish (280 ind. 100 m-2) and Sundays (290 ind. 100 m-2) estuaries were significantly (p < 0.01) greater than those in the Kariega system (50 ind. 100 m-'). lchthyoplankton densities in the lower reaches of the 3 estuaries were highest in the Great Fish estuary (13 ind. 100 m-3), followed by the Sundays Estuary (7 ind. 100 m-3) and Kariega Estuary (4 ind. 100 m-3). Regression analyses indicated that several factors were associated wlth the abundance of the early life stages at the ichthyonekton study sites, the most important of which were estuarine axial salinity gradient, water temperature and axial turbidity gradient. The possible significance of these and other associated variables in influencing migration processes into eastern Cape estuaries is discussed.

Plasticity of European flounder life history patterns discloses alternatives to catadromy

“…These factors are among the main factors influencing the structure of estuarine fish assemblages (Nicolas et al 2010) and flounder juvenile recruitment (Martinho et al 2009). The inter-annual variability of river discharge may be an indirect driver of flounder life history plasticity, probably due to its control in setting estuarine productivity (Whitfield 1994, Loneragan & Bunn 1999 and in influencing the rate of direct and indirect recruitment of fishes in estuaries (Chícharo et al 2001). The management of European flounder estuarine fisheries relies on accurate, multidisciplinary scientific data.…”

Distribution of Fin-fish Eggs and Larvae from Point Calimere and Muthupettai, South East Coast of India

“…The response to environmental variables has however been shown to be species specific [22], the spatial distribution of fish larvae was greatly influenced by hydrobiology [23], salinity and turbidity are important factors associated with larval fish abundance [24,25]. Meteorological and oceanographic conditions influence the feeding of organisms and currents can transport eggs and larvae by [26].…”

Recruitment of juvenile fishes into a small temperate choked lagoon (Argentina) and the influence of environmental factors during the process

“…5). Though salinity has been categorized as an important factor in detecting estuaries during the recruitment process of juveniles (Blaber andBlaber 1980, Martino andAble 2003), olfactory cues associated with riverine inputs, and hence estuarine outflow, stimulate the immigration of euryhaline fishes into estuaries and not salinity per se (Whitfield 1994).…”

“…The recruitment process into estuaries is presumably in response to certain environmental cues (odours, turbidity and/or salinity gradients) transported into the marine environment from either estuarine or freshwater sources (Whitfield 1994, Strydom 2003 and/or to tidal currents, particularly in sufficiently deep estuaries where vertical movements of young fishes exploiting flood and/or ebb currents have been proposed (Boehlert andMundy 1988, Harris et al 2001). These findings also explain why fish larvae and juveniles congregate in the surf zones adjacent to estuaries before colonizing them (e.g.…”