The contribution by phytoplankton, bacteria and detritus to a rocky shore ecosystem

An investigation has been carried out on the particulate organic matter (IU-1) in suspension over the large inter-- and subtidal reef at Dalebrook in False Bay, standing stocks of hytoplankton, bacteria and detritus were monitored for 13 months, at three localities on the reef, on incoming and outgoing tides. A number of seasonal trends recharge, despite day-to-day variation in t."'1ese stocks. In spring and summer chlorophyll levels were la, 1 - 2 µg/1. Due to the extrerrely lcw nitrate concentrations ( < 2 µg at/1) and to a lesser extent, silicates ( < 6 µg at/1) , little autochthonous phytoplankton production was recorded over this period. Concentrations of nitrates, silicates and chlorcphyll a were highest at the offshore edge of the reef in incoming water. After a strong south-easterly win:i, chlorophyll concentrations of 19 µg/1 were rerorded O, 5 km offshore. Chlorophy 11 concentrations were in the region of 5 µg/1 in winter. Detritus accounted for aln'Ost 80% of the Pa1 and never dropped bela, O, 5 :rrg/1. There were no marked spatial and tidal influences on the mass of detritus in suspension. However, considerable import and export of material is believed to be associated with the strong water m,vements over the reef. Most of the detritus was in advanced stages of deconposition, making it extremely difficult to determine its origin. A Coulter Counter provided particle size spectra over the range 5 - 112 µm. It was found that particles with apparent diameters of 10 - 30 iirn contributed the highest volurre. Bacterial densities ranged fran 4 x 105 to 16 x 105 cells/ml; nurrbers were highest in late surmer and autumn. 95% of the cells were not attached to particles but were free in suspension. These results are canpared with those fran other inshore envirorurents

Weak population structure of the Spot-tail shark Carcharhinus sorrah and the Blacktip shark C. limbatus along the coasts of the Arabian Peninsula, Pakistan, and South Africa.

The increase in demand for shark meat and fins has placed shark populations worldwide under high fishing pressure. In the Arabian region, the spot-tail shark Carcharhinus sorrah and the Blacktip shark Carcharhinus limbatus are among the most exploited species. In this study, we investigated the population genetic structure of C. sorrah (n = 327) along the coasts of the Arabian Peninsula and of C. limbatus (n = 525) along the Arabian coasts, Pakistan, and KwaZulu-Natal, South Africa, using microsatellite markers (15 and 11 loci, respectively). Our findings support weak population structure in both species. Carcharhinus sorrah exhibited a fine structure, subdividing the area into three groups. The first group comprises all samples from Bahrain, the second from the UAE and Yemen, and the third from Oman. Similarly, C. limbatus exhibited population subdivision into three groups. The first group, comprising samples from Bahrain and Kuwait, was highly differentiated from the second and third groups, comprising samples from Oman, Pakistan, the UAE, and Yemen; and South Africa and the Saudi Arabian Red Sea, respectively. Population divisions were supported by pairwise F ST values and discriminant analysis of principal components (DAPC), but not by STRUCTURE. We suggest that the mostly low but significant pairwise F ST values in our study are suggestive of fine population structure, which is possibly attributable to behavioral traits such as residency in C. sorrah and site fidelity and philopatry in C. limbatus. However, for all samples obtained from the northern parts of the Gulf (Bahrain and/or Kuwait) in both species, the higher but significant pairwise F ST values could possibly be a result of founder effects during the Tethys Sea closure. Based on DAPC and F ST results, we suggest each population to be treated as independent management unit, as conservation concerns emerge

Book Reviews

Book Review 1Book Title: Sharks and Rays of AustraliaBook Authors: P.R. Last &amp; J.D. StevensPrinted and distributed by CSIRO, P.O. Box 89 East Melbourne. 3002 Australia, 1994. 612 pages and 84 colour plates.Book Review 2Book Title: The Ecology of Mangrove and Related Ecosystems.  Proceedings of the International Symposium held at Mombasa, Kenya 24-30 September 1990Book Authors: Edited by Victor Jaccarini &amp; Els MartensKluwer Academic Publishers, Dordrecht 1993. 272 pages. Hardbound. ISBN 0-7923-2049-2.Book Review 3Book Title: Rotifer Symposium VI. Proceedings of the Sixth International Rotifer Symposium, held in Banyoles, Spain, June 3-8, 1991Book Authors: Edited by J.J. Gilbert, E. Lubzens &amp; M.R. MiracleReprinted from Hydrobiologia, vols 255-256, as Developments in Hydrobiology 83Kluwer Academic Publishers, Dordrecht /Boston /London. 572 pagesBook Review 4Book Title: Identification Guide to the Ant Genera of the WorldBook Author: Barry BoltonHarvard University Press, 1994. 224 pages, 522 SEM photographs. ISBN 0-674-44280-

The extinct shark Otodus megalodon was a transoceanic superpredator: Inferences from 3D modeling

Although shark teeth are abundant in the fossil record, their bodies are rarely preserved. Thus, our understanding of the anatomy of the extinct Otodus megalodon remains rudimentary. We used an exceptionally well-preserved fossil to create the first three-dimensional model of the body of this giant shark and used it to infer its movement and feeding ecology. We estimate that an adult O. megalodon could cruise at faster absolute speeds than any shark species today and fully consume prey the size of modern apex predators. A dietary preference for large prey potentially enabled O. megalodon to minimize competition and provided a constant source of energy to fuel prolonged migrations without further feeding. Together, our results suggest that O. megalodon played an important ecological role as a transoceanic superpredator. Hence, its extinction likely had large impacts on global nutrient transfer and trophic food webs

Mortalities of southern right whales (Eubalaena australis) and related anthropogenic factors in South African waters, 1999–2019

The southern right whale (Eubalaena australis; SRW) population in South Africa’s coastal waters has experienced marked changes since 2009, including altered feeding and migration behaviour, and decreased calving success. At the same time, anthropogenic activities in the area have increased. Based on this, an update on SRW mortalities and related anthropogenic factors is warranted. Building on the published information of Best et al. (2001a), data were collated on all SRW mortalities as well as non‐fatal ship‐strikes and entanglements along the South African coast between 1999 and 2019. A total of 97 SRW mortalities were recorded, including three that did not result in a stranding, of which the majority were classified as calves of the year. Most of these occurred on the Western Cape coast between the months of July to November, coinciding with the seasonal presence of the species in South African coastal waters. Eleven of these mortalities could be attributed to ship‐strikes whereas three mortalities related to entanglements. A total of 98 non‐fatal incidents, including 16 ship‐strikes and 82 entanglements with SRWs, were recorded in South Africa between 1999 and 2019. Ship‐strikes occurred mainly around the area of Cape Town harbour. Entanglements occurred mainly in rock‐lobster gear and bather‐protection nets in the Western Cape and KwaZulu‐Natal provinces respectively, although the latter did not occur between 2015–2019 attributable to the replacement of over 70% of the nets by drumlines, and the removal of the remaining nets during whale season. In general, the incidence of SRW mortalities and entanglements decreased post‐2007, coinciding with the decreased presence of SRWs along the South African coast. Available data show a relatively low rate of fatal entanglements and ship‐strikes, although this may be underestimated due to the opportunistic nature of the collated data. In view of the population growth rate and the increased anthropogenic activities in South African coastal waters, continued and improved monitoring (e.g. through a more systematic reporting system) of these incidents is crucial to ensure accurate knowledge‐based management decisions in the future. Possible mitigation measures aimed at reducing anthropogenic interactions are mooted.https://journal.iwc.int/index.php/jcrmam2023Mammal Research InstituteZoology and Entomolog

The extinct shark Otodus megalodon was a transoceanic superpredator: Inferences from 3D modeling

Although shark teeth are abundant in the fossil record, their bodies are rarely preserved. Thus, our understanding of the anatomy of the extinct Otodus megalodon remains rudimentary. We used an exceptionally well-preserved fossil to create the first three-dimensional model of the body of this giant shark and used it to infer its movement and feeding ecology. We estimate that an adult O. megalodon could cruise at faster absolute speeds than any shark species today and fully consume prey the size of modern apex predators. A dietary preference for large prey potentially enabled O. megalodon to minimize competition and provided a constant source of energy to fuel prolonged migrations without further feeding. Together, our results suggest that O. megalodon played an important ecological role as a transoceanic superpredator. Hence, its extinction likely had large impacts on global nutrient transfer and trophic food webs

Pessimistic assessment of white shark population status in South Africa: comment on Andreotti et al.(2016)

Andreotti et al. (2016; Mar Ecol Prog Ser 552:241−253) estimate an abundance (N) of 438 white sharks Carcharodon carcharias and a contemporary effective population size (CNe) of 333 individuals along the South African coast. N was estimated by using a mark-recapture analysis of photographic identification records from a single aggregation site (Gansbaai). CNe was calculated based on the levels of pairwise linkage disequilibrium of genetic material collected from 4 aggregation sites across approximately 965 km of South African coastline. However, due to the complex stock structure of white sharks and the model assumptions made by Andreotti et al. (2016), the conclusions drawn cannot be supported by their methods and data

Population Connectivity of the Highly Migratory Shortfin Mako (Isurus oxyrinchus Rafinesque 1810) and Implications for Management in the Southern Hemisphere

Copyright © 2018 Corrigan, Lowther, Beheregaray, Bruce, Cliff, Duffy, Foulis, Francis, Goldsworthy, Hyde, Jabado, Kacev, Marshall, Mucientes, Naylor, Pepperell, Queiroz, White, Wintner and Rogers. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.In this paper we combine analyses of satellite telemetry and molecular data to investigate spatial connectivity and genetic structure among populations of shortfin mako (Isurus oxyrinchus) in and around Australian waters, where this species is taken in recreational and commercial fisheries. Mitochondrial DNA data suggest matrilineal substructure across hemispheres, while nuclear DNA data indicate shortfin mako may constitute a globally panmictic population. There was generally high genetic connectivity within Australian waters. Assessing genetic connectivity across the Indian Ocean basin, as well as the extent that shortfin mako exhibit sex biases in dispersal patterns would benefit from future improved sampling of adult size classes, particularly of individuals from the eastern Indian Ocean. Telemetry data indicated that Australasian mako are indeed highly migratory and frequently make long-distance movements. However, individuals also exhibit fidelity to relatively small geographic areas for extended periods. Together these patterns suggest that shortfin mako populations may be genetically homogenous across large geographical areas as a consequence of few reproductively active migrants, although spatial partitioning exists. Given that connectivity appears to occur at different scales, management at both the national and regional levels seems most appropriate

Future research directions on the "elusive" white shark

White sharks, Carcharodon carcharias, are often described as elusive, with little information available due to the logistical difficulties of studying large marine predators that make long-distance migrations across ocean basins. Increased understanding of aggregation patterns, combined with recent advances in technology have, however, facilitated a new breadth of studies revealing fresh insights into the biology and ecology of white sharks. Although we may no longer be able to refer to the white shark as a little-known, elusive species, there remain numerous key questions that warrant investigation and research focus. Although white sharks have separate populations, they seemingly share similar biological and ecological traits across their global distribution. Yet, white shark’s behavior and migratory patterns can widely differ, which makes formalizing similarities across its distribution challenging. Prioritization of research questions is important to maximize limited resources because white sharks are naturally low in abundance and play important regulatory roles in the ecosystem. Here, we consulted 43 white shark experts to identify these issues. The questions listed and developed here provide a global road map for future research on white sharks to advance progress toward key goals that are informed by the needs of the research community and resource managers

White sharks and cephalopod prey : indicators of habitat use?

The stomach contents of White Sharks (Carcharodon carcharias) caught in large mesh gillnets off the KwaZulu-Natal coast of South Africa were examined for prey remains during routine biological necropsies. Of 220 White Sharks with prey remains in their stomachs sampled between 1983 and 2008, cephalopod beaks, which are highly digestion resistant, were found in 24. This sample was split according to predator size to investigate whether these prey remains could be used to test the hypothesis that smaller individuals [2.5 m TL), which may be a proxy for habitat use. These preliminary results supported the hypothesis in that the cephalopods from small sharks were composed almost exclusively of coastal and benthic species typical of the continental shelf, such as octopods and sepiids, and coastal pelagic prey, such as loliginid squids. Cephalopod prey of large sharks were dominated by mesopelagic and oceanic prey (e.g. Ancistrocheirus, Octopoteuthis, and Ommastrephidae), with few coastal taxa. This suggests that larger sharks are using deeper offshore waters to a greater extent than smaller individuals, supporting the ¢ndings from tagging research on these apex predators. This study has shown the potential of stomach content analyses to provide an alternative approach to studying habitat use by large predators, although there are some potential pitfalls of such investigations