Bait collecting by subsistence and recreational fishers in Knysna Estuary may impact management and conservation

Simon, Carol A.; Toit, A. du; Smith, M. Kyle S.; Claassens, Louw; Smith, F.; Smith, Peter C.

doi:10.1080/15627020.2019.1608862

Cited by 21 publications

(24 citation statements)

References 31 publications

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“…It has not, however, been designated a Marine Protected Area, notwithstanding that it is ranked South Africa's premier estuary in terms of its biodiversity and overall conservation importance (Turpie and Clark 2007;Van Niekerk et al 2019). Seagrasses are subject to many pressures (Gubbay 2016;Mvungi and Pillay 2019;Unsworth et al 2019) and at Knysna two of the main ones are green-algal blooms (Human et al 2016;Barnes 2019a;Pollard et al 2019) and heavy exploitation for bait largely for subsistence and recreational fishing (Hodgson et al 2000a;Napier et al 2009;Simon et al 2019;Claassens et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Do beds of subtidal estuarine seagrass constitute a refuge for macrobenthic biodiversity threatened intertidally?

Barnes

Claassens

2020

Biodivers Conserv

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Biodiversity differentials between macrobenthic assemblages associated with adjacent intertidal and subtidal areas of a single seagrass system were investigated for the first time. Assemblage metrics of conservation relevance—faunal abundance and its patchiness, faunal richness, and beta diversity—were examined at four contrasting dwarf-eelgrass localities in the Knysna estuarine bay, part of South Africa's Garden Route National Park but a system whose intertidal areas are heavily impacted anthropogenically. Faunal assemblages were significantly different across all localities and between subtidal and intertidal levels at each locality although their taxonomic distinctness was effectively constant. Although, as would be expected, there were clear trends for increases in overall numbers of species towards the mouth at all levels, few generalities relating to the relative importance of the subtidal seagrass habitat were evident across the whole system—magnitude and direction of differentials were contingent on locality. Shore-height related differences in assemblage metrics were minor in the estuarine and lagoonal zones but major in the marine compartment, although the much greater subtidal faunal abundance there was largely consequent on the superabundance of a single species (the microgastropod Alaba pinnae), intertidal zones then displaying the greater species diversity due to greater equitability of species densities. Along its axial channel, the Knysna subtidal seagrass does not support richer versions of the intertidal polychaete-dominated assemblages fringing it; instead, it supports different and more patchily dispersed gastropod-dominated ones. At Knysna at least, the subtidal hardly constitutes a reservoir of the seagrass biodiversity present intertidally.

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Section: Introductionmentioning

confidence: 99%

Do beds of subtidal estuarine seagrass constitute a refuge for macrobenthic biodiversity threatened intertidally?

Barnes

Claassens

2020

Biodivers Conserv

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“…The development of Thesen Islands Marina with artificial habitat in the form of Reno mattress combined with the alga C. tenue has provided much needed additional habitat to H. capensis . The utilisation of additional habitat by Knysna seahorse is particularly important for the conservation of this species because the seagrass beds ( Zostera capensis ) in the Knysna estuary are increasingly threatened by eutrophication (Human et al ., ) and disturbance by bait collectors (Simon et al ., ; Claassens pers. obs.).…”

Section: Discussionmentioning

confidence: 99%

Conservation value of Codium tenue habitat for the endangered Knysna seahorse Hippocampus capensis

Villiers

Barker

Claassens

et al. 2019

Journal of Fish Biology

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We investigated the density and size structure of the endangered Knysna seahorse Hippocampus capensis in the macroalga Codium tenue at three sites in a residential marina estate in the Knysna Estuary, South Africa, over an 18 month period from March 2017 to August 2018. Seahorses were present in C. tenue throughout the year. Average (± SE) densities of 0.33 (± 0.03) and 0.23 (± 0.03) seahorses per kg of C. tenue were found for 2017 and 2018 respectively. Density did not vary across sites but varied significantly across months with a decreasing trend from summer to spring. The average (± SE) adult seahorse height was 75.16 mm (± 0.63 mm) and 69.09 mm (± 0.64 mm) and mass was 2.05 g (± 0.04 g) and 1.65 g (± 0.04 g) for males and females, respectively, and an even sex ratio was observed throughout the sampling period. Height varied across months, with significantly smaller seahorses found in June and August of 2017. Tail length was highly correlated with height and therefore can serve as a potential proxy for determining the height of H. capensis. This study showed that C. tenue is consistently utilised by Knysna seahorse and should therefore be considered an important habitat to protect and facilitate the ongoing conservation of this endangered seahorse species.

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“…We sampled 18 sites ( Figure 2) from the mouth of the estuary to about 14 km upstream, covering most of the estuary. The sampled sites included those surveyed by Day et al (1951) and Allanson et al (2000b) and popular bait collecting sites (Hodgson et al, 2000;Napier et al, 2009;Simon et al, 2019). Thirteen sites were in the low intertidal zone (i.e.…”

Section: Distribution Density and Population Estimatementioning

confidence: 99%

“…D. neapolitana: Macnae, 1956;Macnae, 1957;Day, 1960;Day, 1967;van der Westhuizen & Marais, 1977;McLachlan et al, 1984;Branch et al, 2016 Diopatra sp. : Napier et al, 2009;Allanson et al, 2016;Simon et al, 2019 Material examined 16 specimens (MB-A090376-MB-A090391), incomplete, Knysna Estuary (34°04 ′ 17.6 ′′ S 23°03 ′ 30.5 ′′ E), Knysna, Western Cape, South Africa, coll. H. van Rensburg, 20 February 2017; 15 specimens (MB-A090394-MB-A090408), incomplete, Swartkops Estuary (33°52 ′ 00.7 ′′ S 25°36 ′ 42.5 ′′ E), Port Elizabeth, Western Cape, South Africa, coll.…”

Section: Taxonomymentioning

confidence: 99%

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Moonshine worms (Diopatra aciculata: Onuphidae, Annelida) in the Knysna Estuary, South Africa; taxonomy and distribution

2020

Self Cite

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Moonshine worms are a popular bait species used for fishing. The taxon was not detected during surveys of the macrobenthos conducted in Knysna in the 1940s and 1990s, and was first reported as a harvested bait species in the mid-2000s, suggesting that it appeared for the first time in the estuary in the last three decades. A previous molecular analysis identified the worms as Diopatra aciculata, a species first described from Australia. This study provides an updated detailed morphological description of D. aciculata in South Africa to facilitate future identifications and also investigates the species' distribution and population size in the Knysna Estuary. Specimens were examined by scanning electron, stereo- and compound microscopes. Diopatra aciculata has tubes that protrude from the sediment in sandy areas, often decorated with algae and shell fragments; a large body size, up to 600 mm long and 11.5 mm wide. It has 10–18 rings on ceratophores; 5–10 teeth on pectinate chaetae; uni- and bidentate pseudo-compound falcigers and dorsal cirri approximately as long as branchiae. Diopatra aciculata was detected up to 12 km from the mouth of the Knysna Estuary with densities measured at 18 sampled sites. Statistical analysis retrieved high and low density groups that were significantly different from one another (Kruskal-Wallis H(14, 800) = 376.55; P = 0.01), but distribution of high density sites was patchy. We estimate that the population comprises 20–24 million individuals. Given the size of individual worms and the population estimate, this species can be expected to have significant ecological impacts in the estuary.

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Bait collecting by subsistence and recreational fishers in Knysna Estuary may impact management and conservation

Cited by 21 publications

References 31 publications

Do beds of subtidal estuarine seagrass constitute a refuge for macrobenthic biodiversity threatened intertidally?

Do beds of subtidal estuarine seagrass constitute a refuge for macrobenthic biodiversity threatened intertidally?

Conservation value of Codium tenue habitat for the endangered Knysna seahorse Hippocampus capensis

Moonshine worms (Diopatra aciculata: Onuphidae, Annelida) in the Knysna Estuary, South Africa; taxonomy and distribution

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