Denham Parker

Denham Parker
The Commonwealth Scientific and Industrial Research Organisation | CSIRO

PhD

About

88
Publications
33,434
Reads
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549
Citations
Introduction
Broad interests in marine ecology, but a fisheries scientist generally researching population dynamics, stock assessment and the overall effects of marine resource use. Research focusses on tuna, billfish, sharks and coastal teleost species. I also study interactions with vulnerable bycatch species such as sea turtles and sea birds in an attempt to improve mitigation measures.
Additional affiliations
February 2019 - present
University of Cape Town
Position
  • Research Associate
November 2016 - present
Department of Agriculture, Forestry and Fisheries
Position
  • Researcher
September 2015 - October 2016
University of Cape Town
Position
  • PostDoc Position
Education
April 2012 - April 2015
Rhodes University
Field of study
  • Ichthyology and Fisheries Science

Publications

Publications (88)
Article
Full-text available
The declaration of a state of emergency in the South African linefishery in 2000 has had a positive impact on a few overexploited endemic seabreams (Family Sparidae). However, the population of the reef-dwelling dageraad Chrysoblephus cristiceps has been unresponsive to progressively stricter management regulations. After decades of unsustainable f...
Article
Full-text available
For most rare marine species abundance trends are poorly estimated. This uncertainty often translates into disagreement on managment regulations, impeding conservation efforts when they are most urgently required. The world’s largest sea bream, the red steenbras (Petrus rupestris), has been subject to a substantial and widely acknowledged decline d...
Article
Full-text available
White stumpnose Rhabdosargus globiceps is the main target of the linefishery in Saldanha Bay. Increased fishing pressure over the last three decades, particularly by the recreational sector, has led to concerns regarding sustainability of the local white stumpnose stock. The fishery was exceptionally productive between 2006 and 2008, with an estima...
Article
Knowledge of the spatiotemporal behavior and interactions with fishing gear of bycatch species is essential to improve conservation and fisheries management strategies. We analyze fine-scale data from onboard observers, covering 25 fishing fleets from 2002 through 2018, to assess temporal trends and spatial variation in sea turtle bycatch in longli...
Article
Yellowfin tuna (Thunnus albacares) supports the second largest tuna fishery worldwide, and in the Indian Ocean, it is overfished and subject to overfishing. This situation presents a significant challenge to fisheries management, requiring effective measures to rebuild and then maintain the stock at sustainable levels. A single stock of yel-lowfin...
Article
Crustacean fisheries, which are influenced by environmental drivers, can benefit from spatial management solutions. More size limit zones or other controls afford finer tuning of management solutions, but can also increase complexity in fishing operations. Defining management boundaries, and the feasibility of that compliance can be a balancing act...
Technical Report
Full-text available
This report presents the most up-to-date information and analyses of the status of marine fishery resources in South Africa at the time of compilation. The number of fish stocks covered has increased steadily from 43 in 2012 to 77 in the current report (Figure I). Among the species included for the first time are a further six sharks (bronze whaler...
Article
Full-text available
To clarify potential trans-oceanic connectivity and variation in the natal origin of albacore tuna (Thunnus alalunga) from the southwest Indian Ocean (SWI) and the southeast Atlantic (SA), lifetime otolith elemental signatures were assessed from 46 adults sampled from Reunion Island, and 26 juveniles(group 2+) sampled from two locations along the A...
Article
Full-text available
Managing fisheries to achieve ecological, economic and social sustainability is complex. The use of dynamic bioeconomic models can be and have been used to assist in determining management targets. However, optimizing profits over time can result in large reductions in fishing effort in the short term with adverse social consequences. There exist o...
Article
Temperate mesophotic ecosystems are generally poorly understood and in South Africa, few studies have analysed imagery from benthic assemblages in this depth range. This study used a remotely operated vehicle (ROV) to survey and describe benthic communities off the Kei River in the Amathole Region of South Africa's Indian Ocean. The CATAMI classifi...
Article
Full-text available
Manta rays (Mobula alfredi and M. birostris) are poorly understood in South Africa, despite their ecological importance and charismatic appeal. This study analyzed a 41-year dataset from the KwaZulu-Natal bather protection program to investigate catch per unit effort between 1981-2021. We used Generalized Additive Models and the probability of enco...
Article
Full-text available
The blue shark Prionace glauca is a top predator with one of the widest geographic distributions of any shark species. It is classified as Critically Endangered in the Mediterranean Sea, and Near Threatened globally. Previous genetic studies did not reject the null hypothesis of a single global population. The blue shark was proposed as a possible...
Article
Full-text available
Billfish species (families Istiophoridae and Xiphiidae) are caught in artisanal, recreational, and commercial fisheries throughout the Western Indian Ocean region. However, data and information on the interactions among these fisheries and the ecology of billfish in the WIO are not well understood. Using an in-depth analysis of peer-reviewed articl...
Article
Full-text available
We present some preliminary closed-loop simulations for South Atlantic swordfish. We condition an Operating Model using OpenMSE's Rapid Conditioning Model and using a joint multivariate prior for steepness derived from maturity, growth and natural mortality information from northern swordfish to integrate across the uncertainty in these quantities...
Preprint
The blue shark Prionace glauca is a top predator with one of the widest geographic distributions of any shark species, yet classified as critically endangered in the Mediterranean Sea, and Near Threatened globally. Previous genetic studies did not reject the null hypothesis of a single global population across the worldwide species range. Blue shar...
Article
The diamond ray Gymnura natalensis is endemic to southern Africa where its preference for shallow coastal habitats makes it vulnerable to recreational shore-based angling. Although it makes up approximately 1% of the shore-based tag numbers, little is known about its movements, reproduction or population status in South Africa. This study used thre...
Article
Full-text available
Originating from the Second International Indian Ocean Expedition (IIOE-2), the main goal of the Western Indian Ocean (WIO) Regional Benthic Imagery Workshop, was to provide information and training on the use of various underwater imagery platforms in benthic research. To date, attempts made to explore the bottom of the ocean range from simple div...
Article
The present study aimed to determine the abundance index of blue marlin, Makaira nigricans (Lacepède, 1802) utilizing fishery-independent data, i.e., scientific observer, and attempted to bridge the research's gap for low coverage information in the north eastern Indian Ocean. A total of 2,984 set-by-set observer data from 2006-2018, spatially disa...
Technical Report
Full-text available
JABBA Models were fitted to South Atlantic swordfish (Xiphias gladius) data. This document presents details on the model diagnostics and stock status estimates for three preliminary models (S1-S3). In general, our results suggest that all candidate models are stable and provide robust fits to the data as judged by the presented model diagnostic res...
Article
Full-text available
Understanding how fish associate with habitats across marine landscapes is crucial to developing effective marine spatial planning (MSP) in an expanding and diversifying ocean economy. Globally, anthropogenic pressures impact the barely understood temperate mesophotic ecosystems and South Africa’s remote Amathole shelf is no exception. The Kei and...
Technical Report
Full-text available
This report presents the most up-to-date information and analyses of the status of marine fishery resources in South Africa at the time of compilation. The number of fish stocks covered has increased steadily from 43 in 2012 to 61 in the current report (Figure I). Among the species included for the first time are a number of linefish species (black...
Chapter
Marine animal forests, although among the most diverse ecosystems worldwide, remain obscure in terms of their diversity and functioning. Their spatial extent, diversity and function within the larger marine ecosystems remain poorly known; mainly due to a lack of traditional taxonomic expertise and the challenges associated with non-destructive samp...
Article
Sixteen species of Latrunculiidae Topsent, 1922, belonging to the genera Latrunculia du Bocage, 1869, Strongylodesma Lévi, 1969, Cyclacanthia Samaai & Kelly, 2004, Samaai & Kelly, 2002, are currently known from the temperate waters of South Africa. Extensive new sponge collections from the Amathole region of South Africa revealed the existence of t...
Article
• The white‐spotted wedgefish (Rhynchobatus djiddensis) is a Critically Endangered shark‐like ray in the family Rhinidae. Throughout its Western Indian Ocean distribution, it is targeted for its valuable meat and fins and is reported to have undergone major population declines. However, there remains a need for species specific time‐series data to...
Technical Report
Full-text available
Soupfin sharks (Galeorhinus galeus), globally referred to as tope, are medium sized sharks that are globally distributed in temperate waters. Soupfin sharks were the first shark species to be commercially harvested in South Africa and remains one of the top five most commercially valuable shark species. The species is currently caught in the demers...
Article
Full-text available
Managing coastal fisheries is challenging as the status of many fish stocks caught in these fisheries remains unknown. In the South African linefishery, regular comprehensive assessments of the status of most linefish stocks are unattainable owing to a scarcity of reliable long-term data. Length-based analysis remains the only option to determine s...
Article
Full-text available
To further implement an ecosystem approach to management of the small pelagic fishery in South Africa, we attempted to develop functional relationships between spatialised time-series of the biomass of three small pelagic fish species and the catch per unit effort (CPUE) of four linefish species (i.e. species caught on hook and line, excluding long...
Conference Paper
Full-text available
The blue shark Prionace glauca is a cosmopolitan species that inhabits all oceans worldwide except the poles. Several IUCN regional assessments have classified it as Near Threatened, mostly due to overfishing. Previous genetic studies that have used classical genetic markers failed to reject the hypothesis that the species is a single worldwide pop...
Technical Report
Full-text available
Swordfish, Xiphias gladius, is a target species in the South African pelagic longline fleet operating along the west and east coast of South Africa. A standardization of the CPUE of the South African swordfish directed longline fleet for the time series 2004-2019 was carried out with a Generalized Additive Mixed Model (GAMM) with a Tweedie distribu...
Technical Report
Full-text available
Albacore, Thunnus alalunga, is the main target of the South African tuna pole-line (baitboat) fleet operating along the west and south west coast of South Africa. The South African catch is the second largest in the region with annual landings of around 4000 t. A standardization of the CPUE of the South African baitboat fleet for the time series 20...
Technical Report
Full-text available
The blue shark Prionace glauca is a cosmopolitan species that inhabits all oceans worldwide except the poles. Several IUCN regional assessments have classified it as Near Threatened, mostly due to overfishing. Previous genetic studies that have used classical genetic markers failed to reject the hypothesis that the species is a single worldwide pop...
Technical Report
Full-text available
Bayesian State-Space Surplus Production Models were fitted to Indian Ocean swordfish (Xiphias gladius) catch and CPUE data using the 'JABBA' R package. This document presents details on the model diagnostics and stock status estimates for a single 'Reference' model with a prior distribution for r of log(r) ~ N(log(0.42),0.4) and a fixed input value...
Technical Report
Full-text available
Bayesian State-Space Surplus Production Models were fitted to South Atlantic albacore (Thunnus alalunga) catch and CPUE data using the 'JABBA' R package. In accordance with the 2019 SCRS work plan (update of the 2016 assessment), this document presents four preliminary scenarios that explore two production functions (Schaefer or Fox) as well as two...
Article
Full-text available
Rapid urbanisation has led to major landscape alterations, affecting aquatic ecosystems’ hydrological and biogeochemical cycles, and biodiversity. Thus, habitat alteration is considered a major driver of aquatic biodiversity loss and related aquatic ecosystem goods and services. This study aimed to investigate and compare aquatic macroinvertebrate...
Article
Full-text available
Rhodolith beds have not previously been recorded in South Africa. A multidisciplinary research effort used remote sampling tools to survey the historically unexplored continental shelf off the Eastern Cape coast of South Africa. A rhodolith bed, bearing both living and dead non-geniculate coralline red algae, was discovered in the 30–65 m depth ran...
Article
Full-text available
A Sustainability Assessment for Fishing Effects (SAFE) was conducted for the porbeagle shark in the North and South Atlantic oceans. The SAFE approach is a quantitative assessment that computes a proxy for fishing mortality rate as the product of four susceptibility components: availability of the species to the fleets, encounterability of the gear...
Technical Report
Full-text available
Common smoothhound shark (Mustelus mustelus) are medium sized sharks distributed from the Mediterranean down to the SouthWest Indian Ocean. Commercially it is one of the top five most valuable shark species mainly caught as target or by-catch by the demersal shark longline fishery, commercial linefishery and the inshore trawl fishery. Total catches...
Article
Full-text available
The southern mullet Chelon richardsonii (Mugilidae) is the main target species of the inshore net fishery (gillnet and beach-seine) on the west coast of South Africa. The stock has displayed symptoms of overfishing, with a 28% reduction in the standardised catch per unit effort (CPUE) between 2008 and 2016, and a 36.5-mm reduction in mean total len...
Article
International trade in vulnerable marine species is regulated once they are listed in CITES Appendices (the Convention on International Trade in Endangered Species of Wild Fauna and Flora). Parties to the Convention submit proposal(s) 150 days prior to the CITES Conference for voting on the inclusion of new species in Appendices I and II, making a...
Presentation
(website: http://dehoopfishmonitoring.uct.ac.za) Broad communication of scientific findings is challenging. Scientific jargon, restricted access journals and a tendency for scientists to follow traditional formats inhibits the natural flow of information to the general public. This problem is particularly troublesome for so called ‘citizen scienc...
Article
Fire is an important environmental disturbance in Mediterranean‐climate regions; however, its intensity and frequency are predicted to increase under climate change scenarios with unknown implications for ecosystems in these regions. Temporary wetlands, with their periodic wet and dry phases, are considered one of the most productive systems in the...
Article
Full-text available
Spatial dependence can obscure relationships between response and explanatory variables because of structuring within the residuals reducing variance and biasing coefficient estimates. Here, we highlight the influence of the spatial component, in the presence of spatial dependence, on abundance trends. This is illustrated using abundance data for a...
Technical Report
Full-text available
South Africa has one of the most diverse shark faunas in the world and many species are caught in appreciable quantities in directed and non-directed shark fisheries. South Africa has well developed fisheries management systems for most of its fisheries and many challenges with regard to the sustainable management and conservation of sharks have al...
Technical Report
Full-text available
An initial assessment of the Indian Ocean black marlin (Makaira indica) was run using Bayesian State-Space Surplus Production Models in the open-source stock assessment tool JABBA. Four scenarios were selected based on alternative specifications of the Pella-Tomlinson model type that incorporated two differing nominal catch data time-series, three...
Technical Report
Full-text available
Five scenarios were run using Bayesian State-Space Surplus Production Models to assess the Indian Ocean striped marlin (Tetrapturus audax) using the open-source stock assessment tool JABBA. A 'drop one' sensitivity analysis indicated that omitting any of the CPUE time-series would not significantly alter the stock status. Similarly, a retrospective...
Technical Report
Full-text available
Yellowtail (Seriola lalandi) are large, schooling, fast growing fish that undergo unpredictable seasonal migrations. They have a high fertility and reach sexual maturity after 2-3 years, making them resilient to fishing pressure. Yellowtail are one of the most important target species of the South African linefishery, and their total catch is only...
Technical Report
Full-text available
Hottentot (Pachymetopon blochii) are small bodied sea bream that have a core distribution on the West and SouthWest Coast of South Africa. They are abundant on reefs and are typically associated with nearshore kelp beds, but are also found on deeper reefs from Namibia to Cape Agulhas. Hottentot are an important component of the commercial linefishe...
Technical Report
Full-text available
Snoek (Thyrsites atun) are nomadic, circumglobally distributed, meso-pelagic predators found in both shallow water and along the coastal shelf to depths exceeding 500 m. In South Africa, snoek are distributed along the West and South Coast, including the Agulhas Banks. It is the most important species targeted by the commercial linefishery in terms...
Technical Report
Full-text available
Santer (Cheimerius nufar) are medium-sized sea bream that are targeted by the commercial boat-based linefisheries of southern Mozambique, KwaZulu-Natal (KZN), the Eastern Cape (EC) and to a lesser extent in the Western Cape. Recent catches in the KZN commercial sector averaged approximately 70 t per annum. Santer are also of notable importance in t...
Technical Report
Full-text available
Slinger (Chrysoblephus puniceus) are medium-sized sea bream that are distributed from Coffee Bay in the Eastern Cape of South Africa to Ponta Zavora in southern Mozambique. Slinger are the most important species in the commercial linefishery of KwaZulu-Natal (KZN) and southern Mozambique. They are also of notable importance in the recreational boat...