Quantifying commercial catch and effort of monkfish Lophius vomerinus and L. vaillanti off Namibia
- Authors: Maartens, Lima , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125786 , vital:35817 , https://doi.10.2989/025776101784528999
- Description: Mark-recapture models do not distinguish how ‘‘deaths’’ accrue to marked animals in the population. If animals lose their tags, then recaptures will be fewer than expected and estimates of survival will be underestimated (Arnason and Mills, 1981; McDonald et al., 2003). Similarly, if the non-reporting rate is unknown and assumed to be negligible, as is the case in some tagging studies (e.g. Cliff et al., 1996, for white sharks Carcharodon carcharias), the probability of capture can be underestimated. The effects of both these problems, inherent in cooperative tagging programmes, lead to too few tagged fish being recovered, with a positive bias on the estimation of population size. These effects are most pronounced when capture probability is low and fewer tags are available for recapture (McDonald et al., 2003).
- Full Text:
- Date Issued: 2010
On the life history of the lesser gurnard (Scorpaeniformes: Triglidae) inhabiting the Agulhas Bank, South Africa
- Authors: Booth, Anthony J
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125434 , vital:35782 , https://doi.10.1111/j.1095-8649.1997.tb01133.x
- Description: Fishes of the genus Labeo are widely distributed throughout Africa and consist of at least 80 species which comprise 16.4% of the African cyprinid ichthyofauna (Reid 1985). Most labeo species are also commercially important throughout the African continent, having contributed significantly to various fisheries. Their roe (sensu caviar) is often harvested as an additional bycatch (Skelton et al. 1991). Despite their obvious importance, the few studies that have investigated aspects of their life history have been conducted on the larger commercial species (Lowe 1952, Mulder 1973, Balon et al. 1974, Potgieter 1974, Baird 1976, Tomasson et al. 1984, van Zyl et al. 1995).
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- Date Issued: 1997
Age validation, growth, mortality, and demographic modeling of spotted gully shark (Triakis megalopterus) from the southeast coast of South Africa
- Authors: Booth, Anthony J , Foulis, Alan J , Smale, Malcolm J
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123630 , vital:35466 , https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/2011/1091/booth.pdf
- Description: This study documents validation of vertebral band-pair formation in spotted gully shark (Triakis megalopterus) with the use of f luorochrome injection and tagging of captive and wild sharks over a 21-year period. Growth and mortality rates of T. megalopterus were also estimated and a demographic analysis of the species was conducted. Of the 23 OTC (oxytetracycline) -marked vertebrae examined (12 from captive and 11 from wild sharks), seven vertebrae (three from captive and four from wild sharks) exhibited chelation of the OTC and f luoresced under ultraviolet light. It was concluded that a single opaque and translucent band pair was deposited annually up to at least 25 years of age, the maximum age recorded. Reader precision was assessed by using an index of average percent error calculated at 5%. No significant differences were found between male and female growth patterns (P>0.05), and von Bertalanffy growth model parameters for combined sexes were estimated to be L∞=1711.07 mm TL, k=0.11/yr and t0= –2.43 yr (n=86). Natural mortality was estimated at 0.17/yr. Age at maturity was estimated at 11 years for males and 15 years for females. Results of the demographic analysis showed that the population, in the absence of fishing mortality, was stable and not significantly different from zero and particularly sensitive to overfishing. At the current age at first capture and natural mortality rate, the fishing mortality rate required to result in negative population growth was low at F>0.004/ yr. Elasticity analysis revealed that juvenile survival was the principal factor in explaining variability in population growth rate.
- Full Text:
- Date Issued: 2011
Effect of water temperature on the biogeography of South African estuarine fishes associated with the subtropical/warm temperate subtraction zone
- Authors: Maree, R C , Booth, Anthony J , Whitfield, A K
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6766 , http://hdl.handle.net/10962/d1008043
- Description: Estuarine biogeographical regions along the southeastern coast of South Africa were investigated in terms of fish distribution and abundance patterns, with particular emphasis on the role of water temperature in influencing these patterns. Qualitative and quantitative analyses were conducted upon the ichthyofaunal assemblages to determine whether the location of the subtropical/warm temperate boundary corresponds to that proposed by Whitfield.(n1) Analyses included the distribution ranges of species associated with estuaries according to presence/absence data, cluster analysis of gill net catches in eight estuaries along the southeastern coast and the relative proportion of tropical to temperate marine species within these eight systems. Quantitative analysis indicated that the ichthyofaunal biogeographical regions are indeed a reflection of water temperature regimes and that the subtropical/warm temperate boundary is located between the Great Kei and Mbashe estuaries. A strong negative correlation was found between the number of temperate fish species and the mean of the minimum monthly temperatures recorded in the systems studied. Qualitative analysis revealed that a barrier appears to exist in the vicinity of the Swartkops estuary, which prevents the westward migration of tropical 'vagrants'. The influence of the Agulhas Current along the east coast and its divergence from the coastline in the Algoa Bay region, as well as upwelling phenomena on the southeast and south coasts are identified as major factors that influence marine and estuarine temperature regimes and therefore the ichythyofauna of this region.
- Full Text: false
- Date Issued: 2000
Ocean warming affects the distribution and abundance of resident fishes by changing their reproductive scope
- Authors: Potts, Warren M , Booth, Anthony J , Richardson, Timothy J , Sauer, Warwick H H
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125352 , vital:35775 , https://doi.10.1007/s11160-013-9329-3
- Description: With ocean warming predicted globally, one of the mechanisms driving distributional shifts and changes in the abundance of resident fishes is reproductive output. The relationship between sea surface temperature and the reproductive activity of a eurythermic, resident coastal species, blacktail seabream Diplodus sargus capensis, was examined in the ‘‘ocean warming’’ hotspot of the northern Benguela. Reproductive activity was found to be restricted to periods when the water temperature dropped below 20 _C. A metadata analysis conducted on the D. sargus sub-species complex similarly showed that reproductive activity was restricted to temperatures between 15 and 20 _C, regardless of the range in ambient water temperature. Based on these findings and using satellite derived SST information, we examined D. s. capensis’s total and seasonal ‘‘reproductive scope’’ that is defined as either the area suitable for spawning each year or the duration of its potential spawning season at a fixed geographical locality, respectively. Trends were examined over the last three decades. Reproductive scope by area was found to be shrinking at a rate of 7 % per decade in southern Angola and expanding at a rate of 6 % per decade in northern Namibia. Reproductive scope by season decreased by 1.05 months per decade in Namibe, southern Angola and increased by 0.76 months per decade in Hentiesbaai, northern Namibia. Changes in reproductive scope may be a driving mechanism of distributional shifts in resident fishes, although the rate of the shifts is likely to be slow. More importantly, changes in reproductive scope will not be uniform throughout fish distributions and will most likely result in heterogeneous variations in fish abundance.
- Full Text:
- Date Issued: 2014
Life history and population dynamics of invasive common carp, Cyprinus carpio, within a large turbid African impoundment
- Authors: Winker, A Henning , Weyl, Olaf L F , Booth, Anthony J , Ellender, Bruce R
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124898 , vital:35708 , https://doi.10.1071/MF11054
- Description: Common carp (Cyprinus carpio) is one of the world’s most widely introduced and established freshwater fishes (Casal 2006). The species is considered to be one of the eight most invasive freshwater fishes (Lowe et al. 2000) and worldwide, it accounts for most of the records of successful establishments and adverse ecological effects (Casal 2006; Kulhanek et al. 2011). This invasive success suggests that feral C. carpio is equipped with a set of adaptable life history attributes that allow it to successfully colonise a wide range of habitats (Koehn 2004; Zambrano et al. 2006; Britton et al. 2007). Where feral C. carpio occurs in high densities, it is often perceived as an invasive pest species (Sivakumaran et al. 2003; Brown and Walker 2004; Koehn 2004) because it can have severe impacts on habitat heterogeneity and biodiversity by increasing water turbidity through its bottom feeding behaviour, increasing nutrient availability, decreasing benthic and macrophyte density and diversity, altering zooplankton assemblages and decreasing endemic fish abundance (Zambrano et al. 2001; Khan 2003; Kulhanek et al. 2011). Within south-east Australia, for example, C. carpio comprises the largest proportion of the ichthyobiomass in the continent’s largest river system – the Murray–Darling Basin (Gehrke et al. 1995). As a consequence, serious concerns about its threat to endemic freshwater species (Koehn 2004) have prompted several of the most recent investigations into its life history (e.g. Sivakumaran et al. 2003; Smith and Walker 2004; Brown et al. 2005). Other potential threats posed also include competition with indigenous species and the spread of diseases and parasites (Dudgeon et al. 2006). In South Africa, for example, Asian tapeworm Bothriocephalus acheilognathi is now widely distributed in seven river systems and has infected eight novel cyprinid hosts due to the translocation of infected by C. carpio from a centralized aquaculture facility (Stadtlander et al. 2011).
- Full Text:
- Date Issued: 2011
Ocean warming, a rapid distributional shift, and the hybridization of a coastal fish species
- Authors: Potts, Warren M , Henriques, Romina , Santos, Carmen V D , Munnik, Kate , Ansorge, Isabelle J , Dufois, Francois , Sauer, Warwick H H , Booth, Anthony J , Kirchner, Carola , Sauer, Warwick , Shaw, Paul W
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125375 , vital:35777 , https://doi.10.1111/gcb.12612
- Description: Despite increasing awareness of large-scale climate-driven distribution shifts in the marine environment, no study has linked rapid ocean warming to a shift in distribution and consequent hybridization of a marine fish species. This study describes rapid warming (0.8 °C per decade) in the coastal waters of the Angola-Benguela Frontal Zone over the last three decades and a concomitant shift by a temperature sensitive coastal fish species (Argyrosomus coronus) southward from Angola into Namibia. In this context, rapid shifts in distribution across Economic Exclusive Zones will complicate the management of fishes, particularly when there is a lack of congruence in the fisheries policy between nations. Evidence for recent hybridization between A. coronus and a congener, A. inodorus, indicate that the rapid shift in distribution of A. coronus has placed adults of the two species in contact during their spawning events. Ocean warming may therefore revert established species isolation mechanisms and alter the evolutionary history of fishes. While the consequences of the hybridization on the production of the resource remain unclear, this will most likely introduce additional layers of complexity to their management.
- Full Text:
- Date Issued: 2014
Reproductive biology of a riverine cyprinid, Labeo umbratus (Teleostei: Cyprinidae), in small South African reservoirs
- Authors: Potts, Warren M , Booth, Anthony J , Hecht, Thomas , Andrew, Timothy G
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125854 , vital:35826 , https://doi.10.2989/16085910509503849
- Description: The reproductive and recruitment characteristics of moggel, Labeo umbratus, populations were examined in four small South African reservoirs. Reproduction, characterised by an extended spawning season, high fecundity, short incubation time and rapid larval development, appears to be ideally suited to the highly variable environment of small reservoirs. Evidence suggested that L. umbratus spawns in the reservoirs. In two reservoirs where samples were conducted monthly, GSI (gonado-somatic index) was positively correlated with both water temperature and day length, whilst the CPUE (catch per unit effort) of juveniles was not related to any environmental variable. The success of moggel spawning appeared to increase when there was early spring and consistent summer rainfall.
- Full Text:
- Date Issued: 2010
An endangered seahorse selectively chooses an artificial structure
- Authors: Claassens, Louw , Booth, Anthony J , Hodgson, Alan N
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123718 , vital:35486 , https://doi.10.1007/s10641-018-0732-4
- Description: The development of a residential marina estate within the Knysna estuary, South Africa, introduced Reno mattresses (horizontal wire cages filled with rocks) as a novel habitat for the endangered Knysna seahorse Hippocampus capensis. Consistently high seahorse densities on these artificial structures, despite the availability of seagrass habitat, begged the question of whether this habitat was chosen by the seahorse in preference to natural vegetation. An in situ habitat choice experiment was conducted which focused on the choice made by adult H. capensis between natural vegetation (Zostera capensis) and artificial (Reno mattress) habitat within a choice chamber. Seahorses were significantly more likely to move away from Z. capensis onto a Reno mattress structure or remain on this structure. This study concludes that higher H. capensis densities on Reno mattresses within Thesen Islands Marina are owing to some positive feature of this habitat and the underlying processes responsible for the choice made by this species (additional food, holdfasts, protection) can now be investigated.
- Full Text:
- Date Issued: 2018
An assessment of a light-attraction fishery in southern Lake Malawi
- Authors: Weyl, Olaf L F , Kazembe, Jacqueline , Booth, Anthony J , Mandere, D S
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123683 , vital:35472 , https://doi.org/10.2989/16085910409503787
- Description: This study provides the first quantitative assessment of the light-attraction component of a small-scale purse seine, locally known as a chilimira net, fishery in two areas of southern Lake Malawi. For monitoring purposes the shoreline of Lake Malawi is divided into a number of statistical strata. Two strata (‘2.1’ in the southeast arm and ‘3.1’ in the southwest arm of the lake) were selected for this study. Catch per unit effort in stratum 2.1 was generally lower than that recorded in stratum 3.1 but nets in stratum 2.1 fished more frequently, leading to similar annual catches in the two strata. Annual catch was estimated as 19.4 (CI = 15.9–23.5) tons net–1 year–1 in stratum 2.1 and 23.5 (CI = 19.5–28.1) tons net–1 year–1 in stratum 3.1 respectively. A total of 62 species from 28 cichlid genera, and 13 species from nine non-cichlid genera, were identified from the samples. Of the 37 genera identified, only five; Copadichromis, Dimidiochromis, Engraulicypris, Oreochromis and Rhamphochromis, contributed more than 5% to the total annual catch in either stratum. Their combined contribution to the annual catch was in excess of 85% in both strata. Comparisons showed that catch-composition was dependent on area. Length-frequency distributions of major target species in the catch showed that the fishery targeted juveniles in stratum 2.1, while in stratum 3.1 most individuals were harvested after reaching their lengthat-maturity. The dependence of catch-composition and size-selection on area indicates that management interventions for this fishery need to be area-specific. Since the fishery targets a diverse species assemblage, effort limitation or area closure may be the only viable management options, until such time as additional biological and fisheries data are available for the application of stock assessment models.
- Full Text:
- Date Issued: 2010
Do environmental factors influence the movement of estuarine fish? A case study using acoustic telemetry
- Authors: Childs, Amber-Robyn , Cowley, Paul D , Næsje, T F , Booth, Anthony J , Thorstad, Eva B , Økland, F
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6772 , http://hdl.handle.net/10962/d1008070
- Description: Telemetry methods were used to investigate the influence of selected environmental variables on the position and movement of an estuarine-dependent haemulid, the spotted grunter Pomadasys commersonnii (Lacepède 1801), in the Great Fish Estuary, South Africa. Forty individuals (263–698 mm TL) were surgically implanted with acoustic coded transmitters and manually tracked during two periods (7 February to 24 March 2003; n = 20 and 29 September to 15 November 2003; n = 20). Real-time data revealed that spotted grunter are euryhaline (0–37) and are able to tolerate large variations in turbidity (4–356 FTU) and temperature (16–30 °C). However, the fish altered their position in response to large fluctuations in salinity, temperature and turbidity, which are characteristic of tidal estuarine environments. Furthermore, tidal phase had a strong influence on the position of spotted grunter in the estuary.
- Full Text:
- Date Issued: 2008
Retrospective stock assessment of the Emperor red snapper (Lutjanus sebae) on the Seychelles Bank between 1977 and 2006
- Authors: Grandcourt, E M , Hecht, Thomas , Booth, Anthony J , Robinson, J
- Date: 2008
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125887 , vital:35829 , https://doi.10.1093/icesjms/fsn064
- Description: The Emperor red snapper, Lutjanus sebae, known as “Bourzwa” in the Seychelles, is distributed throughout the Indo-West Pacific from the southern Red Sea and East Africa to New Caledonia, north to Japan and south to Australia. It occurs near coral or rocky reefs and also over adjacent sand flats and gravel patches between 5 and 180 m deep (Allen, 1985; Anderson, 1986). Juveniles are frequently commensal with sea urchins (Kuiter and Tonozuka, 2001), and are found in nearshore, turbid waters (Williams and Russ, 1992), mangrove areas (Allen, 1985), and around coastal and offshore reefs (Williams and Russ, 1992). Larger L. sebae are generally found deeper, although they are also known to move into shallower water during winter (McPherson et al., 1988; Williams and Russ, 1992). Prey items include fish, crabs, other benthic crustaceans, and cephalopods. Lutjanus sebae is a large, long-lived species, attaining a maximum size of 116 cm fork length (McPherson and Squire, 1992) and maximum age of 34 years (Newman and Dunk, 2002). Despite an absence of data on its population structure, mixing, and identity, the population on the Seychelles Bank has been considered to be a unit stock for assessment purposes because of its remote location (e.g. Lablache and Carrara, 1988; Mees, 1992).
- Full Text:
- Date Issued: 2008
Factors affecting recapture rates of raggedtooth sharks Carcharias taurus tagged off the east coast of South Africa
- Authors: Dicken, Matthew L , Booth, Anthony J , Smale, Malcolm J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124493 , vital:35618 , https://doi.10.2989/AJMS.2009.31.3.9.997
- Description: Understanding differences in the recapture rate between different tags (A-, B- and C-types), capture methods (rock-and-surf anglers, scientific divers and Natal Sharks Board protection nets) and life-history stages (juvenile and adult) is critical in evaluating the results obtained from cooperative tagging programmes (CTPs). A generalised linear modelling approach, using a log-linear model, was used to determine significant differences in the probability of recapture between these various factors using data from the Oceanographic Research Institute and Port Elizabeth Museum CTPs. Between 1984 and 2004, a total of 3 385 raggedtooth sharks Carcharias taurus was tagged by volunteers from both programmes along the east coast of South Africa. A likelihood ratio test indicated significant differences in the probability of recapture between A- and C-type and B- and C-type tags (p < 0.01), between different capture methods (p < 0.05) and between juvenile and adult sharks (p < 0.01). A comparison of recapture rates between members of the CTPs also indicated a marked variability in the performance of individual taggers. The study highlights important data-quality issues inherent in large CTPs.
- Full Text:
- Date Issued: 2010
A description of gametogenesis in the panga Pterogymnus laniarius (Pisces: Sparidae) with comments on changes in maturity patterns over the past two decades
- Authors: Booth, Anthony J , Hecht, Thomas
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123542 , vital:35452 , https://doi.org/10.1080/02541858.1997.11448428
- Description: A description of gametogenesis in the panga Pferogymnus laniarius, a common endemic seabream species inhabiting the Agulhas Bank, South Africa, is presented. After sexual maturity, oogenesis and spermatogenesis continued throughout the year and were found to be similar to these processes in other seabream species and teleosts in general. Analysis of maturity data over the past two decades revealed a significant change in both age and size-at-maturity, a response to fishing pressure.
- Full Text:
- Date Issued: 2015
Long-term catch and effort trends in Eastern Cape Angling Week competitions
- Authors: Dicken, Matthew L , Smale, Malcolm J , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124931 , vital:35711 , https://doi.org/10.2989/1814232X.2012.709961
- Description: Recreational shore-based angling is one of the most popular sport and outdoor activity pastimes in South Africa with an estimated 412 000 fishers (McGrath et al. 1997). It is a form of linefishing where fish are caught using a hook and line and comprises a social as well as a more formal organized competitive sector (van der Elst 1989). Similar to other components of the linefishery, which include the subsistence as well as boat-based commercial sectors, excessive shore-fishing effort along the Eastern Cape has resulted not only in declining catches (Bennett 1991, Griffiths 1997, Brouwer and Buxton 2002, Pradervand and Govender 2003) but also changes in the species composition of catches (Bennett et al. 1994, Brouwer et al. 1997, Attwood and Farquhar 1999). Stock assessments indicate that many important linefish species are severely overexploited (Griffiths 1997, Hutchings 2000, Mann 2000) and that continued fishing pressure threatens endemic linefish populations. In 1996, shore-anglers alone were responsible for an annual catch of approximately 4.5 million fish, weighing around 3 000 tonnes (Brouwer et al. 1997).
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- Date Issued: 2012
Growth and longevity of Exosphaeroma hylocoetes (Isopoda) under varying conditions of salinity and temperature
- Authors: Henninger, Tony O , Froneman, P William , Booth, Anthony J , Hodgson, Alan N
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124571 , vital:35630 , https://doi.org/10.3377/004.045.0118
- Description: Numerous studies have documented the importance of both temperature and salinity in influencing aquatic crustacean metabolic processes such as respiration and growth. For example, increased water temperatures have been shown to increase respiration rates in various species of shrimp (Chen & Nan 1993; Spanonopoulos-Hernándeza et al. 2005; Allan et al. 2006), and copepods (Isla & Perissinotto 2004). The response of invertebrates to changes in salinity is more complex, largely reflecting their evolutionary origins (Kinne 1966). For example, juvenile blue swimming crabs, Portunus pelagicus, displayed significantly faster growth and higher survival in response to increasingsalinity (Romano & Zeng 2006). Additional factors that may influence the growth rates of crustaceans include photoperiod (Gambardella et al. 1997), food availability (Shuster & Guthrie 1999) and sex (Newman et al. 2007).
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- Date Issued: 2010
A qualitative ecological risk assessment of the invasive Nile tilapia, Oreochromis niloticus in a sub-tropical African river system (Limpopo River, South Africa)
- Authors: Zengeya, Tsungai A , Robertson, Mark P , Booth, Anthony J , Chimimba, Christian T
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123575 , vital:35457 , https://doi.10.1002/aqc.2258
- Description: 1. This study outlines the development of a qualitative risk assessment method and its application as a screening tool for determining the risk of establishment and spread of the invasive Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), within the central sub-catchment of the Limpopo River basin in northern South Africa. 2. The assessment used known physiological tolerance limits of O. niloticus in relation to minimum water temperature, presence or absence of dams, seasonality of river flows, and the presence of indigenous fish species of concern to identify river systems that would be suitable for O. niloticus establishment. 3. River sections along the Limpopo main river channel and the immediate reaches of its associated tributaries east of the Limpopo/Lephalala river confluence along the Botswana–South Africa–Zimbabwe border were identified as being highly vulnerable to O. niloticus invasion. Rivers in the upper Bushveld catchment (Upper Limpopo, Mogalakwena, Lephalala, Mokolo, Matlabas and Crocodile rivers) were categorized as of medium ecological risk, while headwater streams were considered to be of low ecological risk. The decrease in vulnerability between lowveld and highveld river sections was mainly a function of low water temperatures (8–12˚C) associated with increasing altitude. 4. Oreochromis niloticus is already established in the lower catchment of the Limpopo River basin where indigenous congenerics are at an extinction risk through hybridization and competition exclusion. Oreochromis niloticus, therefore, poses an ecologically unacceptable risk to river systems in the upper catchment where it is yet to establish. The current risk assessment model provides a useful preliminary framework for the identification of river systems that are vulnerable to an O. niloticus invasion where conservation measures should be directed and implemented to prevent its introduction and spread within the Limpopo river system.
- Full Text:
- Date Issued: 2013
Effect of turbidity on the foraging success of Glossogobius callidus (Teleostei: Gobiidae)
- Authors: Parkinson, Matthew C , Booth, Anthony J
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124375 , vital:35600 , https://doi.org/10.2989/16085914.2011.589120
- Description: Particles suspended in water attenuate the light that passes through it via absorption or scattering (Utne-Palm 2002). For example, whereas algae absorb specific wavelengths of light necessary for photosynthesis, inorganic suspensoids tend to scatter light (Radke and Gaupisch 2005). This results in lowered ambient light levels and reduces the visual acuity of aquatic organisms. From a fish’s perspective, an increase in water turbidity has the potential to alter visually-mediated reproductive behaviours (Järvenpää and Lindström 2004), predator avoidance (Meager et al. 2006) and foraging success negatively (Utne-Palm 2002, Rowe et al. 2003, Sweka and Hartman 2003, Stuart-Smith et al. 2004). The foraging success of various fish species was affected by increased turbidity through decreasing predator–prey encounter rates (Sweka and Hartman 2003) and through decreasing visual acuity whereby the distance at which prey are visually detected is reduced (Utne-Palm 2002).
- Full Text:
- Date Issued: 2011
Assessment of the monkfish Lophius vomerinus resource off Namibia
- Authors: Maartens, Lima , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123863 , vital:35509 , https://doi.10.2989/025776101784528926
- Description: Monkfish (Lophius vomerinus and L. vaillanti) constitute a commercially important resource off Namibia. During 1998, the Lophius resource was the fourth most important commercial resource in terms of landed mass (c. 17 000 tons) and the fifth most important commercial resource in terms of export value (U$19.8 million) of the Namibian fishing sector (Ministry of Fisheries and Marine Resources, Namibia, unpublished data). Historically, monkfish constituted an important bycatch in the trawl fishery directed at hake (Merluccius spp.), but due to increasing market demand since the early 1990s, a fishery directed at monkfish and sole (Austroglossus microlepis) has developed. The Namibian Ministry of Fisheries and Marine Resources has identified the need to develop a management plan to ensure the resource’s medium and longterm sustainability (Maartens et al. 1999). Long-term resource management plans include the identification of an assessment model to represent reality so that the implications of managing the resource in future under a range of assumptions about its present status and its future dynamics (Cochrane et al. 1998) can be examined. The aim of this study was, therefore, to assess the status of at least part of the monkfish resource using a length-based cohort assessment (Jones 1979, 1984, Sparre and Venema 1998) and an age structured production model (Punt 1994, Punt and Japp 1994, Booth and Punt 1998).
- Full Text:
- Date Issued: 2010
Environmental niche patterns of native and non-native fishes within an invaded African river system
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124407 , vital:35605 , https://doi.10.1111/jfb.13988
- Description: To test ecological niche theory, this study investigated the spatial patterns and the environmental niches of native and non-native fishes within the invaded Great Fish River system, South Africa. For the native fishes, there were contrasting environmental niche breadths that varied from being small to being large and overlapped for most species, except minnows that were restricted to headwater tributaries. In addition, there was high niche overlap in habitat association among fishes with similar distribution. It was therefore inferred that habitat filtering-driven spatial organization was important in explaining native species distribution patterns. In comparison, most non-native fishes were found to have broad environmental niches and these fishes showed high tolerance to environmental conditions, which generally supported the niche opportunity hypothesis. The proliferation of multiple non-native fishes in the mainstem section suggest that they form a functional assemblage that is probably facilitated by the anthropogenic modification of flow regimes through inter-basin water transfer. Based on the distribution patterns observed in the study, it was inferred that there was a likelihood of negative interactions between native and nonnative fishes. Such effects are likely to be exacerbated by altered flow regime that was likely to have negative implications for native ichthyofauna.
- Full Text:
- Date Issued: 2019