Mortality Estimation

Mortality is an essential parameter in understanding the dynamics of any population and sharks are no exception. Without knowledge of how fast individuals are removed from a population it is impossible to model the population dynamics or estimate sustainable rates of exploitation or other useful management parameters.https://scholarworks.wm.edu/vimsbooks/1024/thumbnail.jp

Shark Research: emerging technologies and applications for the field and laboratory

Over the last decade, the study of shark biology has benefited from the development, refinement, and rapid expansion of novel techniques and advances in technology. These have given new insight into the fields of shark genetics, feeding, foraging, bioenergetics, imaging, age and growth, movement, migration, habitat preference, and habitat use. This pioneering book, written by experts in shark biology, examines technologies such as autonomous vehicle tracking, underwater video approaches, molecular genetics techniques, and accelerometry, among many others. Each detailed chapter offers new insights and promises for future studies of elasmobranch biology, provides an overview of appropriate uses of each technique, and can be readily extended to other aquatic fish and marine mammals and reptiles

Dietary overlap of carcharhinid sharks in the Gulf of Papua

Assessing the feeding patterns of sharks provides insight into ecological interactions. Three coastal sharks are common by-catch in the Gulf of Papua prawn fishery in Papua New Guinea. The diets of Carcharhinus coatesi (n = 122), Rhizoprionodon acutus (n = 83) and Rhizoprionodon taylori (n = 177) were assessed using stomach content analysis. Teleosts, crustaceans and molluscs were the main prey. Percentage frequency of occurrence (%FO) and percentage frequency by number (%N) were computed to describe dietary compositions. Non-metric multidimensional scaling and Morisita Index determined the level of feeding overlap. Rhizoprionodon taylori was a generalist feeder having the broadest diet, R. acutus was the most selective feeder, preying predominantly on teleosts and C. coatesi consumed the greatest proportion of crustaceans that increased with size. The pairwise ANOSIM tests showed significant difference in dietary compositions of R. acutus and R. taylori (P = 0.1%, R = 0.318) and R. acutus and C. coatesi (P = 0.1%, R = 0.589), which indicate potential resource partitioning. Further work should aim to adequately characterise diets, improve prey identification and investigate spatial and temporal resource use patterns. Understanding ecological processes informs ecosystem approaches fisheries management

Sex-based differences in movement and space use of the blacktip reef shark, Carcharhinus melanopterus

Information on the spatial ecology of reef sharks is critical to understanding life-history patterns, yet gaps remain in our knowledge of how these species move and occupy space. Previous studies have focused on offshore reefs and atolls with little information available on the movement and space use of sharks utilising reef habitats closer to shore. Cross-shelf differences in physical and biological properties of reefs can alter regional ecosystem processes resulting in different movement patterns for resident sharks. Passive acoustic telemetry was used to examine residency, space use and depth use of 40 blacktip reef sharks, Carcharhinus melanopterus, on an inshore reef in Queensland, Australia, and assess temporal or biological influences. All sharks showed strong site-attachment to inshore reefs with residency highest among adult females. Sharks exhibited a sex-based, seasonal pattern in space use where males moved more, occupied more space and explored new areas during the reproductive season, while females utilised the same amount of space throughout the year, but shifted the location of the space used. A positive relationship was also observed between space use and size. There was evidence of seasonal site fidelity and long-distance movement with the coordinated, annual migration of two adult males to the study site during the mating season. Depth use was segregated with some small sharks occupying shallower depths than adults throughout the day and year, most likely as refuge from predation. Results highlight the importance of inshore reef habitats to blacktip reef sharks and provide evidence of connectivity with offshore reefs, at least for adult males

Nearshore movement ecology of a medium-bodied shark, the creek whaler Carcharhinus fitzroyensis

Background: The movement and habitat use patterns of medium-bodied nearshore sharks are poorly understood. However, these species face some of the highest levels of exposure to anthropogenic development. The habitat and space use strategies species exhibit affect their role within communities and how they respond to environmental change. The present study used passive acoustic telemetry to evaluate the residency, space use, and habitat use patterns of the creek whaler Carcharhinus fitzroyensis in a nearshore embayment in Queensland, Australia. Results: Individuals were monitored for approximately 18 months. Half of the monitored population were highly resident to the bay. In contrast, several individuals spent less than 2 weeks in the bay, suggesting that broader movements may occur in a portion of the population. Size had no effect on residency. Activity space size varied between months and time of day but was also not affected by animal size. All C. fitzroyensis spent the majority of time in seagrass habitat (70%) and deep water (>5 m) mud substrate (20%). Shallow mudflat, sandy inshore, and reef habitats were rarely used (7%). Although the sample size of immature individuals was relatively small, results indicated immature and mature C. fitzroyensis shared space and habitats. Conclusions: Overall, C. fitzroyensis used a combination of nearshore movement patterns typically exhibited by small- and large-bodied species. The movement patterns exhibited by C. fitzroyensis suggest that this species has a moderately high degree of seagrass habitat specialisation. Seagrass habitat is typically highly productive and may be an important foraging habitat for this species. Given the consistent use of seagrass habitat, C. fitzroyensis are likely vulnerable to population decline as a result of seagrass habitat loss. Future research should continue to investigate the unique movements of medium-bodied sharks

Population productivity of shovelnose rays: inferring the potential for recovery

Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. There is recent evidence of widespread declines of shovelnose ray populations (Order Rhinopristiformes) in heavily fished regions. These declines, which are likely driven by high demand for their fins in Asian markets, raises concern about their risk of over-exploitation and extinction. Using life-history theory and incorporating uncertainty into a modified Euler-Lotka model, the maximum intrinsic rates of population increase (rmax) were estimated for nine species from four families of Rhinopristiformes, using four different natural mortality estimators. Estimates of mean rmax, across the different natural mortality methods, varied from 0.03 to 0.59 year-1 among the nine species, but generally increased with increasing maximum size. Comparing these estimates to rmax values for other species of chondrichthyans, the species Rhynchobatus australiae, Glaucostegus typus, and Glaucostegus cemiculus were relatively productive, while most species from Rhinobatidae and Trygonorrhinidae had relatively low rmax values. If the demand for their high-value products can be addressed then population recovery for some species is likely possible, but will vary depending on the species

Ανάπτυξη και χαρακτηρισμός ικριωμάτων νανοϋδροξυαπατίτη με την τεχνική της λυοφιλίωσης

Post-trawl survival (PTS) is an important metric used in determining the ecological risk posed by prawn (shrimp) trawling on discarded elasmobranchs. Despite this, PTS of elasmobranchs is poorly understood. The present study quantified the PTS of two small batoids caught incidentally by prawn trawlers in southern Queensland, Australia, namely the common stingaree (Trygonoptera testacea) and the eastern shovelnose ray (Aptychotrema rostrata). Field studies using on-board tanks revealed that A. rostrata were more resilient to trawl capture and release than T. testacea. For both species, survival was found to increase with size, whereas increasing time on deck resulted in lower survival. Female T. testacea were found to be more resilient than males, and increased tow duration resulted in lower survival for A. rostrata. The mean (+/- s.e.m.) PTS for female and male T. testacea was 33.5 +/- 6.0 and 17.3 +/- 5.5% respectively, compared with a mean PTS for A. rostrata of 86.8 +/- 3.2%. The survival estimates derived in the present study provide an insight into the effects of trawling on these species and will improve their ecological risk assessment and management

Movements and space use of giant trevally in coral reef habitats and the importance of environmental drivers

Background: Effective conservation of large predators requires a broad understanding of their ecology. Caranx ignobilis is a large marine predator well represented in coral reef environments, yet they are poorly studied. Passive acoustic monitoring was used to track the movements of 20 C. ignobilis at offshore reefs in the central Great Barrier Reef from 2012 to 2014. Using a modelling approach, temporal changes in movement patterns of C. ignobilis were explored to determine if individuals exhibited predictable movement patterns. The effects of biological and environmental variables on monthly space use, daily presence and hourly depth use were investigated to define any response to environmental changes. Results: Caranx ignobilis typically remained at their capture reef with 98.8% of detections recorded at these locations. Individuals were recorded in the study site for periods from 9 to 335 days (mean = 125.9) with a mean residency index of 0.53, indicating movements away from the reef or out of detection range occurred on the scale of days. Inter-reef movements from only three individuals were recorded which coincided with the summer full moon so may have been related to spawning behaviour. Environmental drivers were correlated with daily presence and hourly depth use of C. ignobilis but had little influence on monthly space use. There was little or no effect of fish size on space use, presence and depth use. Conclusion: By improving the current understanding of movement patterns of this large teleost among individual coral reefs, the results of this study reveal that site attachment may be present and that environmental parameters play a role in observed movement patterns related to depth and presence. These data provide useful information for the development of management plans, particularly in relation to space-based protection