Climate-growth relationships of Argyrosomus spp. found along the Namibian coast
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Date
2024
Authors
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Journal ISSN
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Publisher
University of Namibia
Abstract
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
Description
A thesis submitted in fulfilment of the requirements for the degree of master of science (Fisheries and Aquatic sciences)
Keywords
Otoliths, Ocean warming, Argyrosomus, Benguela, Biochronology