Browsing by Author "van der Lingen, Carl D"

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    Developing dynamic energy budget (DEB) models for small pelagic fishes in the Southern Benguela
    (2021) Groenewald, Grea; Moloney, Coleen L; van der Lingen, Carl D
    Dynamic energy budget models are useful for describing energy flow in individual organisms as functions of their state (e.g., age, size, and energetic reserves) and environment (e.g., food and temperature). Anchovy (Engraulis encrasicolus), redeye round herring (Etrumeus whiteheadi) and sardine (Sardinops sagax) are short-lived fish species co-occurring in the Southern Benguela upwelling system, where they experience marked environmental variability. This study developed full life cycle dynamic energy budget models of these species in the Southern Benguela, which could be compared to the same or similar species in other ecosystems and investigated trade-offs between temperature and feeding conditions in influencing the growth and reproductive outputs of the three species. The key hypothesis was that there would be niche differences among bioenergetic factors for the three species that allow them to cooccur. Models were created and calibrated using published information and survey data (recruitment, biomass, weight-at-length) from 2012-2016. Best visual fit values were estimated for five parameters, using von Bertalanffy growth models and length-weight relationships of each species. Results indicated that redeye round herring invested less than anchovy and sardine in reproductive storage capacity (larger maintenance ratio) and had lower assimilation rates. Sardine had higher structural growth costs than anchovy and redeye round herring. Larval redeye round herring took longer to reach metamorphosis than anchovy and sardine. In all three species, decreased growth rates of larvae in cool waters were mitigated by increased growth from good food availability. Good feeding condition associated with cooler temperatures halved the time spent as recruits in all three species. Thus, increased growth rates from good food availability outweighed decreased growth rates from cool temperatures and resulted in higher egg batch production in adults. Comparisons of Southern Benguela anchovy and sardine to similar species in other ecosystems showed differences in core parameters between regions because of the influence of environmental inputs and species differences, indicating that model parameters may not be species-specific or transferable between ecosystems. Differential responses of small pelagic fish species to environmental factors help in understanding the variable population dynamics of these species and can help predict the impacts of climate change.
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    Progress report on recommendations from the International review panel report for the 2013 International Fisheries Stock assessment workshop:sardine
    (2014) de Moor, Carryn L; Butterworth, Doug S; Coetzee, Janet C; van der Lingen, Carl D
    The international review panel report (MARAM/IWS/DEC13/General/4 Final Report) contained the following recommendations pertinent to sardine in response to key questions put to them at the annual stock assessment review meeting held at UCT from 2-6 December 2013. Comments on any progress in response to these recommendations are inserted in italics. As a general point of background information, the Small Pelagic Scientific Working Group agreed earlier in 2014 to finalise OMP-14 based on a single sardine stock operating model only, but coupled with some spatial management, the spirit of which is to be a “warm up period” with the expectation that the next OMP will quite likely require spatial management components. The development of new operating models and a new OMP is to be brought forward, commencing in early 2015 with the aim of being finalised before the end of 2016.
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    The quantitative use of parasite data in multistock modelling of South African sardine (Sardinops sagax) 1
    (NRC Research Press, 2017) de Moor, Carryn L; Butterworth, Doug S; van der Lingen, Carl D
    Differences in parasite infection have previously been used to distinguish between fish stocks. We demonstrate a novel use of parasite prevalence-by-length data to inform quantitatively on stock mixing. An initial two mixing stock hypothesis proved consistent with biological and survey data, suggesting that there are different stocks of sardine off the west and south coasts of South Africa. That hypothesis assumed that only recruits moved from the west to the south stock. However, new “tetracotyle”-type metacercarian parasite bio-tag data indicate a need to allow older fish to move between the stocks as well. We demonstrate extension of bio-tagging to inform on the plausibility of population structure hypotheses by including parasite prevalence-by-length data in the model’s likelihood. Our method enables the estimation of the magnitude of mixing between semidiscrete stocks, providing more precise estimates of annual movement. Such improved precision may be important in better informing future movement hypotheses and thereby management. Our research provides a framework to use to inform quantitatively on stock structure and movement hypotheses for other fish species with bio-tagging data.