Clupeidae: D II A1
Etrumeus teres (De Kay, 1842) and E. whiteheadi Wongratana, 1983.
East coast roundherring (locally known as redeye), and redeye roundherring
Egg diameter in µm |
Number of oil globules |
Diameter of oil globule in µm |
Yolk texture |
Perivitelline space |
Position of oil globule at hatch |
Gut length at eye- pigment stage |
Myomeres |
1160-1320 |
0 |
n/a |
segmented |
narrow |
n/a |
78% of NL |
ca50 |
Egg: The size, fine segmentation of the yolk, and lack of an oil globule (A & B), set this egg apart from all others found in the area, except for DIIA2 and HIIA4 (see notes below). The developing embryo does not have any conspicuous pigmentation (B). Incubation time is about 50 hours (21°C).
Larva: The 1-day larva is elongate, with unpigmented eyes, an undeveloped mouth, and just a faint line of black pigment spots ventrally along the notochord (C). C: 1 day, D: 3 days, E: 10 days, F: 15.8mm E. whiteheadi juvenile from plankton net, 26 June 2014.
No attempt was made to rear this egg, as it was easily identifiable, from the literature. Brownells (1979) reference to this species is probably Etrumeus whiteheadi, which was only recognised as different from E. teres in 1983 (Wongratana 1983, in Whitehead and Wongratana 1986). Ikeda and Mito (1988) gives the size of E. teres eggs as 1230-1440 µm, which matches local eggs. Brownell (1979) recorded whiteheadi eggs as 1330 -1450µm.
During the course of this study, numerous specimens of Etrumeus have been collected using yazuri lures, in the vicinity of the shark nets (removed permanently in 2014), about 500m offshore at Park Rynie. All these adult fish keyed out to E. teres (Whitehead and Wongratana 1986). But, of the 11 larvae barcoded (hatched from eggs), only two match 5 locally collected adult E. teres (BOLD); the other 9 larvae matched 5 adult E whiteheadi from the Agulhas Bank. While this confirms that both species occur, and spawn, off Park Rynie, the dominance of E. teres in yazuri lure catches at the shark nets off Park Rynie is curious, possibly indicating that E. whiteheadi remains further offshore. I have not been able to separate the eggs of the two species by eye.
This was the third most abundant egg in Park Rynie samples (Introductory notes: Section 7, Table 3, and Connell, 2001). The species shows a June to December spawning period, with a maximum in September to November (blue graph). The egg was seen in the DHM samples on only 6 occasions (green graph). There was a progressive drop in eggs collected through the early 1990s, the arrest of which coincided with good rains in 1995/96 (white graph). Below average rainfall from 2003 to 2006, which saw St Lucia Lake dwindle to its lowest level in living memory (May 2006),coincided with another drop in spawning intensity (white graph). See also Introductory Notes, Section 6: Rainfall and Spawning Intensity, and notes on EIIIA6, FIIA1 and LIIA7. In the Park Rynie linked samples, only 69% of these eggs were in offshore samples, indicating that the majority of spawning occurs on the shallow shelf, inshore the 50m depth contour. See Section 7.3 and Table 1 of the Introductory Notes, for more information on the linked samples.
linked samples |
Offshore |
Inshore |
Eggs |
45537 |
20380 |
Hits |
339 |
277 |