Fisheries, ecology and markets of South African hake

Durholtz, M. D.; Singh, Larvika; Fairweather, T. P.; Leslie, R. W.; Lingen, Carl D. van der; Bross, C. A. R.; Hutchings, L.; Rademeyer, RA; Butterworth, Doug S; Payne, A. I.

doi:10.1002/9781118568262.ch2

Cited by 18 publications

(14 citation statements)

References 32 publications

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“…In the case of adult M. paradoxus, response curves and graphs depicting the relative importance of various factors in defining the sizes of distribution areas (Figures 2, 5 and 9) do not indicate any particular temperature or oxygen niche, except that temperature is important in defining large areas of adult distribution (Figure 8), which is already well known (e.g. Durholtz et al 2015). Such broad ranges of occurrence justify consideration of other sources of variability as potentially being more critical than temperature and oxygen in determining where adult M. paradoxus occur.…”

Section: Biological Interpretation Of the Environmental Relationshipsmentioning

confidence: 80%

Oxygen and temperature influence the distribution of deepwater Cape hake Merluccius paradoxus in the southern Benguela: a GAM analysis of a 10-year time-series

Mbatha

Yemane

Ostrowski

et al. 2019

African Journal of Marine Science

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Generalised additive models (GAMs) were applied to survey data to assess the influence of dissolved oxygen, water temperature and year of sampling upon the presence/absence of small (≤15 cm TL), medium (16-34 cm TL) and large (≥35 cm TL) size classes of deepwater Cape hake Merluccius paradoxus captured off the west coast of South Africa. Data were obtained from surveys using the RV Dr Fridtjof Nansen conducted in 2003 and from 2005 to 2013 during summer (January-February). Among the variables investigated, oxygen was the most important for the small size class (juveniles), with both low and high constraints (two-sided, 'just right' option), whereas for the medium and large size classes the oxygen effects were one-sided (avoiding lows). This finding, in combination with other published information, suggests that the Orange Banks is a nursery ground for juvenile M. paradoxus and that the area covered by this nursery ground can vary with the optimal oxygen concentration. The temperature constraint was generally wider and weaker than that for oxygen, being two-sided for the small and medium hake and one-sided (avoiding highs) for the large hake. The medium hake displayed the greatest tolerance to the investigated variables, which resulted in the widest distribution for this size class. Temperature, oxygen and sampling year play an important role in determining the distribution of M. paradoxus, but details of the biology (life cycle) of the species, such as its pelagic-demersal transition and associated movements, are no less important. . The list of models considered and the performance measures of each of the models, considered for the three size classes of Merluccius paradoxus, are presented in Tables S1 and S2. The climatologies of bottom temperature and dissolved oxygen are shown in Figure S1. Additional model diagnostics (e.g. calibration plots and residual variograms) are shown in Figures S2 and S3.

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Section: Biological Interpretation Of the Environmental Relationshipsmentioning

confidence: 80%

Oxygen and temperature influence the distribution of deepwater Cape hake Merluccius paradoxus in the southern Benguela: a GAM analysis of a 10-year time-series

Mbatha

Yemane

Ostrowski

et al. 2019

African Journal of Marine Science

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“…Furthermore, between À80 and À350 m, there is a permanent cold-water body located at 28°S (in the region of the Orange River mouth), which disappears with depth (Shillington et al 2004). As M. paradoxus distribution ranges from À110 to À1000 m, and M. capensis is commonly found between À30 and À500 m (Durholtz et al 2015), the species should broadly be exposed to different environmental conditions across the system and throughout their life cycle. A similar pattern was observed in two co-occurring demersal fishes from the genus Coryphaenoides, where the abyssal species did not show signs of genetic differentiation across a thermal front, while the 'shallower' species had two populations on either side of the barrier (White et al 2011).…”

Section: Temporal and Spatial Substructuring Across A Depth Gradient mentioning

confidence: 99%

“…The Cape hakes (Merluccius paradoxus and M. capensis) are offshore, demersal species co-occurring from southern Angola to southern South Africa (Botha 1985). Distribution and abundance varies between taxa, with adult M. paradoxus considered a slope species, occurring mainly in deeper waters (200-800 m), and M. capensis considered a shelf species, with higher abundance at shallower depths (100-300 m; Payne & Punt 1995;Durholtz et al 2015). Therefore, the distribution of the two species is thought to be associated with local bathymetry and continental shelf width, with both moving to deeper waters as they mature (Jansen et al 2015;Stromme et al 2015;Wilhelm et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Spatio‐temporal genetic structure and the effects of long‐term fishing in two partially sympatric offshore demersal fishes

et al. 2016

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Environmental gradients have been shown to disrupt gene flow in marine species, yet their influence in structuring populations at depth remains poorly understood. The Cape hakes (Merluccius paradoxus and M. capensis) are demersal species co-occurring in the Benguela Current system, where decades of intense fishing resulted in severely depleted stocks in the past. Previous studies identified conflicting mtDNA genetic substructuring patterns and thus contrasting evolutionary trajectories for both species. Using 10 microsatellite loci, the control region of mtDNA and employing a seascape genetics approach, we investigated genetic connectivity and the impact of prolonged exploitation in the two species, which are characterized by different patterns of fishing pressure. Three consecutive years were sampled covering the entire distribution (N = 2100 fishes). Despite large estimated population sizes, both species exhibited low levels of contemporary genetic diversity (0.581 < H < 0.692), implying that fishing has had a significant impact on their genetic composition and evolutionary trajectories. Further, for M. paradoxus, significant temporal, but not spatial, divergence points to the presence of genetic chaotic patchiness. In contrast, M. capensis exhibited a clear latitudinal cline in genetic differentiation between Namibia and South Africa (F = 0.063, P < 0.05), with low (0.2% per generation) estimates of contemporary gene flow. Seascape analyses reveal an association with bathymetry and upwelling events, suggesting that adaptation to local environmental conditions may drive genetic differentiation in M. capensis. Importantly, our results highlight the need for temporal sampling in disentangling the complex factors that impact population divergence in marine fishes.

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“…Studies have shown that M. paradoxus spawns in both Namibian and South African waters, while M. capensis spawns only in South African waters (Burmeister, 2005; Kainge et al 2007). Furthermore, M. capensis show morphological variation (colour of the anal fin and iris) between these two regions (Durholtz et al 2014). Yet, recent genetic analyses (von der Heyden et al 2007, 2010) have not successfully clarified the current perceptions of stock structure of these fishes by showing no differences in mitochondrial DNA between M. capensis from Namibia and South Africa, but showing significant genetic differentiation between adult M. paradoxus from these two regions.…”

Section: Southern Africa (Angola Namibia South Africa Mozambique mentioning

confidence: 99%

“…Yet, recent genetic analyses (von der Heyden et al 2007, 2010) have not successfully clarified the current perceptions of stock structure of these fishes by showing no differences in mitochondrial DNA between M. capensis from Namibia and South Africa, but showing significant genetic differentiation between adult M. paradoxus from these two regions. Currently both species are managed separately in South Africa and Namibia (Durholtz et al 2014), but were it the case that the M. paradoxus population is shared between these countries, serious re-evaluation of management strategies should be considered.…”

Section: Southern Africa (Angola Namibia South Africa Mozambique mentioning

confidence: 99%

A review of parasite studies of commercially important marine fishes in sub-Saharan Africa

Reed

2014

Parasitology

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Scattered records of parasitic species infecting commercially important marine fishes in sub-Saharan Africa are known from just a few countries where concerted efforts have been made by local parasitologists (e.g. Senegal, Nigeria, South Africa). Most of these consist of taxonomic records or general surveys of parasite faunas associated with marine hosts, which may or may not have been of commercial value. Little to no multi-disciplinary research is conducted in most parts of sub-Saharan Africa and hence parasitological data are not commonly used to advise fisheries management procedures. This review summarizes current knowledge on all parasitological research associated with commercially important marine fish species in sub-Saharan Africa.

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Fisheries, ecology and markets of South African hake

Cited by 18 publications

References 32 publications

Oxygen and temperature influence the distribution of deepwater Cape hake Merluccius paradoxus in the southern Benguela: a GAM analysis of a 10-year time-series

Oxygen and temperature influence the distribution of deepwater Cape hake Merluccius paradoxus in the southern Benguela: a GAM analysis of a 10-year time-series

Spatio‐temporal genetic structure and the effects of long‐term fishing in two partially sympatric offshore demersal fishes

A review of parasite studies of commercially important marine fishes in sub-Saharan Africa

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