Migration, distribution and population (stock) structure of shallow-water hake (Merluccius capensis) in the Benguela Current Large Marine Ecosystem inferred using a geostatistical population model

Jansen, Teunis; Kristensen, Kasper; Kainge, Paulus Inekela; Durholtz, Deon; Strømme, Tore; Thygesen, Uffe Høgsbro; Wilhelm,; Kathena, John; Fairweather, Tracey P.; Paulus, Sarah; Degel, Henrik; Lipiński, M.; Beyer, Jan

doi:10.1016/j.fishres.2016.02.026

Cited by 19 publications

(30 citation statements)

References 29 publications

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“…Spatial and temporal changes in the sex, size and age structure of the population is an important factor in abundance indexes because blue sharks show evidence of size (Nakano & Nagasawa, ) and sex segregation (ratio of BSH, male:female, 1.00 : 0.34) (Mucientes, Queiroz, Sousa, Tarroso, & Sims, ). Several previous studies (Jansen et al., ; Kai, Thorson, Piner, & Maunder, ; Kristensen et al., ; Nielsen, Kristensen, Lewy, & Bastardie, ; Thorson, Ianelli, Munch, Ono, & Spencer, ) developed the spatio‐temporal dynamics modeling incorporating the size‐structured populations. In this study, however, we did not explicitly account for the age or length in the estimated species distribution function.…”

Section: Discussionmentioning

confidence: 99%

Predicting the spatio‐temporal distributions of pelagic sharks in the western and central North Pacific

Kai

Thorson

Piner

et al. 2017

Fisheries Oceanography

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Spatio‐temporal modeling estimates a species distribution function that represents variation in population density over space and time. Recent studies show that the approach may precisely identify spatial hotspots in species distribution, but have not addressed whether seasonal hotspots are identifiable using commonly available fishery data. In this study, we analyzed the seasonal spatio‐temporal distribution of pelagic sharks in the western and central North Pacific using fishery catch rates and a generalized linear mixed model with spatio‐temporal effects. Different spatial distribution patterns were observed between two shark species. The hotspots of shortfin mako (SFM) appeared in the vicinity of the coastal and offshore waters of Japan and the Kuroshio‐Oyashio transition zone (TZ), whereas the hotspots of blue shark (BSH) were widely distributed in the areas from the TZ to the waters of the Emperor Seamount Chain. Shortfin mako distribution changes seasonally with clear north‐south movement, which follows higher sea surface temperatures (SST). However, preferred spring and summer water temperature was still colder than those in fall and winter, but not as cold as for BSH, which did not show seasonal north‐south movement. BSH exhibits seasonal east‐west movement apparently unrelated to temperature. The spatial fishing effort by season generally follows the seasonal movement of temperature possibly making SFM more vulnerable to the fishery than BSH. These findings could be used to reduce the capture risk of bycatch sharks and to better manage the spatial distribution of fishing for targeted sharks.

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Section: Discussionmentioning

confidence: 99%

Predicting the spatio‐temporal distributions of pelagic sharks in the western and central North Pacific

Kai

Thorson

Piner

et al. 2017

Fisheries Oceanography

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“…It has been hypothesized that hake and its prey use this Northern Benguela habitat feature to their advantage at various stages of their life history. The deep‐water Cape hake is not exposed to the hypoxic inner shelf water as the shallow‐water Cape hake is (Monteiro et al., ), since it is distributed further offshore and deeper (Burmeister, ; Jansen et al., ), and temperatures at these depths are also cooler and salinities slightly lower (Monteiro et al., ). The distribution and abundance of the species on the Namibian shelf would certainly depend on the density of the two species, but also on the environmental parameters that shape their habitat such as temperature, salinity and dissolved oxygen.…”

Section: Introductionmentioning

confidence: 99%

“…According to Gordoa and Hightower (), highest catchability for M. capensis was observed during lowest abundance and “below‐average” temperatures, although that was sea surface temperature (SST) and not the temperature in the depth range where the two hake species live. Furthermore, the distribution of hake may change in relation to their age and size (Jansen et al., ).…”

Section: Introductionmentioning

confidence: 99%

Effects of environmental variables on survey catch rates and distribution by size of shallow‐ and deep‐water Cape hakes, Merluccius capensis and Merluccius paradoxus off Namibia

Kainge

Plas²,

Bartholomae³

et al. 2017

Fisheries Oceanography

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In order to study the effects of temperature, oxygen, salinity and time of day on survey trawl catches, we modeled observed catches of juvenile, small, medium and large hakes per station as functions of zenith angle of the sun, geographical position, year, temperature, salinity, oxygen and depth. We used data from summer demersal surveys conducted during the period 2002–2015, together with a computation of the corresponding light level data from which the solar zenith angles were obtained, and fitted the generalized additive models to these data. Based on best model results, important covariates were oxygen, depth, geographical position and temperature. The best models explained 70%, 69%, 57% and 57% of the variability in catches of juvenile, small, medium and large Merluccius capensis, respectively, and 71%, 68%, 81% and 70% of juvenile, small, medium and large Merluccius paradoxus, respectively. The significant effects of temperature, oxygen, depth and geographical position on survey catches of hake of different size groups indicate that survey size structure may be affected by the behavior of both species towards environmental conditions. Greater care should therefore be taken when interpreting hake survey biomass estimates, based on swept area method, especially those that were collected during exceptional unfavourable environmental conditions. It would also be highly desirable if the oceanographic conditions are collected on each trawl station in order to improve understanding of the linkage between resources and environmental conditions.

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“…Recent biological and ecological surveys have reported the presence of up to four M. capensis spawning grounds, with alongshore transboundary migratory (Jansen et al . , ; Wilhelm et al . ).…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, our results support the hypothesis of homing behaviour in M. capensis (Jansen et al . , ; Wilhelm et al . ).…”

Section: Discussionmentioning

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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Migration, distribution and population (stock) structure of shallow-water hake (Merluccius capensis) in the Benguela Current Large Marine Ecosystem inferred using a geostatistical population model

Cited by 19 publications

References 29 publications

Predicting the spatio‐temporal distributions of pelagic sharks in the western and central North Pacific

Predicting the spatio‐temporal distributions of pelagic sharks in the western and central North Pacific

Effects of environmental variables on survey catch rates and distribution by size of shallow‐ and deep‐water Cape hakes, Merluccius capensis and Merluccius paradoxus off Namibia

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

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