Spawning on the edge: spawning grounds and nursery areas around the southern African coastline

Abstract

The southern African coastline is dominated by strong currents. Along the eastern seaboard, the warm western boundary Agulhas Current sweeps close inshore along the shelf edge before diverging from the coast on the Agulhas Bank and retroflecting back into the Indian Ocean. On the western seaboard, strong jet currents develop in the southern Benguela, associated with the strong thermal gradients induced by upwelling and Agulhas Current intrusions and eddies. There is, in general, northward drift of surface waters in the Benguela Current with strong offshore losses in the vicinity of an exceptionally active upwelling region off Lüderitz. Several potent mechanisms exist for offshore dispersal and loss from the productive shelf waters, such as eddies, filaments, retroflections and offshore Ekman drift, which pose special problems for successful retention of planktonic eggs and larvae from broadcast spawners. Most fish species in southern Africa have evolved highly selective reproductive patterns, which ensure that sufficient progeny are retained or can enter the nursery grounds along the coastline. Four important reproductive habitats, comprising spawning areas, transport mechanisms and nursery grounds, occur between Moçambique and Angola. These are used by a wide variety of pelagic, demersal and inshore-dwelling fish species.

No Population Genetic Structure of Skipjack Tuna (Katsuwonus pelamis) in the Tropical Western and Central Pacific Assessed Using Single Nucleotide Polymorphisms

“…However, mating dynamics in the ocean are very different to those in terrestrial environments. While a majority of genetically assessed terrestrial species utilize internal fertilization (Baur, 1994), skipjack and other pelagic species rely on broadcast spawning (Hutchings et al, 2002). Among other implications for marine species' life history, broadcast spawning can produce a distinctive pattern of variable reproductive success described as sweepstakes reproduction (Waples, 2016).…”

Exploring the spatial distribution patterns of South African Cape hakes using generalised additive models

“…However, fisheries catch data suggest that M. capensis is more numerous on the west coast than on the south coast (Payne and Punt 1995). Only a few Cape hakes live east of 25° E (Payne 1989).Based on current evidence, M. capensis and M. paradoxus have relatively different recruitment areas both on the west and south coasts of South Africa (Crawford et al 1987;Hutchings et al 2002;Stenevik et al 2008). The main recruitment areas of M. capensis are thought to be located in shallow waters (<100 m) on the West Coast, between St Helena Bay and Hondeklip Bay, and north of Port Nolloth, and on the South Coast, between Hermanus and Plettenberg Bay.…”

Combining microvolume isotope analysis and numerical simulation to reproduce fish migration history

“…Warm streamers are also spread intermittently from the KE (Sainz-Trápaga & Sugimoto, 2000) and quasi-stationary jets extend northeastward in the transitional area between the KE and the Oyashio fronts (Isoguchi, Kawamura, & Oka, 2006), probably providing conditions for longitudinal selection. Although these processes seem unique for the KE, similar processes may occur in other regions as many fish larvae depend on regional flows, such as the coastal jets in the Benguela Current (Hutchings et al, 2002) or the eddies in the California Current (Logerwell, Lavaniegos, & Smith, 2001), to effectively reach food-rich feeding grounds.…”