Browsing by Author "Jagger, Charmaine Eleonora"

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    Climate-growth relationships of Argyrosomus spp. found along the Namibian coast
    (University of Namibia, 2024) Jagger, Charmaine Eleonora
    Understanding how fish growth responds to changing environments is critical for monitoring and predicting the impacts of climate change on fish populations. The ocean warming hotspot in the northern part of the northern Benguela provides an excellent opportunity to examine the responses of fishes to rapid environmental change. This research focused on the congeneric Argyrosomus inodorus and Argyrosomus coronus as these are commercially and recreationally important fishery species in Namibia. Standard otolith age determination techniques were used to determine if the age and growth of A. inodorus had changed from the 1990s to 2019. The results showed that there was a significant difference (Likelihood-ratio chi square test, χ 2 = 33.36, df = 4, p < 0.001) for the historical (1994-1996) and contemporary (2018-2019) period, thus indicating that A. inodorus stock used to grow older and faster in the historical period when compared to the contemporary. Kruskal Wallis test showed that there was a significant difference between A. inodorus and A. coronus lengths at age 4 (H (1) = 8.264, p = 0.004 < 0.05). The linear mixed-effects models fitted to the A. inodorus otolith biochronology indicated that a best linear unbiased predictor (BLUP) of growth was significantly positively correlated (r = 0.580, n = 25, p < 0.05) with mean SSTs (July, year of formation) and significantly negatively correlated (r = -0.473, n = 25, p < 0.05) with mean spring-summer SSTs (October y-1 to December y-1) in the area 20-24◦S, 12-14◦E. Thus, faster annual growth was observed during cooler periods (above 15℃) and slower growth was noted when exposed to warmer temperatures >17℃. These findings suggest that changes in A. inodorus growth was associated with a change in temperature and that its growth and productivity will be negatively affected with the increasing frequency of extreme climate events and ocean warming