Evaluating the effects of catch-and-release angling on Cape stumpnose Rhabdosargus holubi in a South African estuary
- Authors: Arkert, N K , Childs, Amber-Robyn , Parkinson, Matthew C , Winkler, Alexander C , Butler, Edward C , Mannheim, Samantha L , Potts, Warren M
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124439 , vital:35613 , https://doi.10.2989/1814232x.2018.1494041
- Description: Fisheries managers are increasingly promoting catch and release (C&R) as a means to manage recreational fish stocks. Several commonly used output regulations, including bag and size limits, require the mandatory release of captured fishes by anglers. In addition to mandatory C&R, conservation-conscious anglers have adopted voluntary C&R behaviour as a result of the noticeable declines in the populations of many fishery species and this behaviour is becoming increasingly popular among recreational anglers (Cooke et al. 2013a). The combination of mandatory and voluntary C&R behaviour is substantial, as Raby et al. (2014) estimated that 60% of fish captured in global recreational fisheries are released. In South Africa, Cowley et al. (2013) found that a large proportion (mean 74% [SD 7.3]) of the five most-dominant fishery species captured in the Sundays Estuary recreational fishery were released.
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Evidence for protandry in Polydactylus quadrifilis in the Kwanza Estuary, Angola, and its implications for local fisheries
- Authors: Butler, Edward C , Childs, Amber-Robyn , Winkler, Alexander C , Milner, Marianne V , Potts, Warren M
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124451 , vital:35614 , https://doi.10.1007/s10641-017-0699-6
- Description: A total of 141 Polydactylus quadrifilis were sampled from the Kwanza Estuary in Angola ranging in size from 436 to 1360 mm fork-length (FL). Of these, 124 were male, six intersex and 11 female. Female fish were significantly longer (mm, FL) and heavier (kg) than males and had significantly higher gonadosomatic indices (GSI’s) than those of males and intersex fish. Transitional (intersex) gonads were delimited, with testicular and ovarian regions separated by connective tissue. The first signs of ovarian tissue appeared on the outer ventral surface of the gonad. A second layer of ovarian tissue was first noticeable at either end of the initial ovarian region and developed back towards the centre of the ventral wall to form a luminal space. Early-stage oocytes were commonly found in the outer area of male regions and residual late-stage spermatids and spermatozoa were found in the luminal space of ovarian regions, suggesting a process of sex change from the outside inwards. A loss of male function was noted with increased ovarian prevalence. Based on this evidence it is suggested that P. quadrifilis in the Kwanza Estuary are protandrous. Owing to the reliance of P. quadrifilis on large highly fecund females for egg production, it is likely that they will be sensitive to fishing practices that target larger individuals within the population.
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