Ragged-tooth Shark Movement Patterns

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Ragged-tooth Shark Movement Patterns

This project falls under SHARKLIFE MAIN OBJECTIVE: Through scientific research, education and awareness bring about positive change to the current destructive trends of ocean exploitation. Identifying key conservation areas and movement patterns of pregnant Carcharias taurus in the iSimangaliso Wetland Park.

raggie sodwana bay

Project Overview:

Every year between December and March pregnant Spotted Ragged-tooth Sharks C. taurus migrate into the iSimangaliso Wetland Park Marine Protected Area (MPA) where they spend most of their nine month gestation period.

The 3 year study aims to identify key congregation areas and movement patterns of the pregnant sharks. Understanding the sharks’ spatial and temporal abundance is key to protecting important congregation sites and migratory corridors.

Research Aim:

Define the movement patterns of pregnant female ragged-tooth sharks within the Park and determine the importance of known congregation sites.

Research Objectives:

Build a Photo-ID database of pregnant ragged-tooth sharks seasonally using the Park to estimate population abundance.
Record the pre-caudal length of individual sharks using paired laser photogrammetry to support Photo ID database.
Survey nearby similar reef habitats to identify additional congregation sites, if any.
Conduct Photo-ID surveys at all known congregation sites, as permitted, to determine movement patterns and site philopatry.
Record shark-diver interactions at the Quarter-mile congregation site to document disturbance levels.

Significance of Research:

Population Abundance Assessment

Recently, there have been indications of declining numbers of ragged-tooth sharks on Quarter-mile reef. By utilising the unique spot patterns found on ragged-tooth sharks it is possible to determine the number of individuals at Quarter-Mile reef during a given gestation season. This method can be undertaken without causing disturbance to the animals or altering their natural behaviour. This Capture-Mark-Recapture (CMR) method is widely used to estimate population abundance for shark species with unique makings, including white sharks (Carcharodon carcharias) (Domeier & Nasby-Lucas, 2007), whale sharks (Rhincodon typus) (Holmberg et al. 2009) and nurse sharks (Ginglymostoma cirratum) (Castro & Rosa, 2005). The systematic long-term monitoring of mature females will be a good indication of overall population health and recruitment rates of the globally important South African ragged-tooth shark population.

Movement Patterns

Former studies conducted by KZN Sharks Board and Port Elizabeth Museum used acoustic tags to track 11 gestating females in the KZN range during the 2003/4 and 2007/8 seasons, with receivers deployed at Raggie reef, Seven-Mile reef, Quarter-Mile reef and Island Rock. Results from this study highlighted the need to better understand movement patterns within the iSimangaliso Wetland Park in order to improve management.

Site Philopatry

It is widely recognized that pregnant female ragged-tooth sharks show high site philopatry, with a study at Wolf Rock, Australia, reporting 78-90% of their time was spent within 500m of the aggregation site (Bansemer & Bennett, 2009). However, it remains unclear why these sites are preferable to surrounding areas despite having similar physical characteristics (Dicken et al. 2006).

Given the species’ high susceptibility to over-exploitation, evidence for site philopatry is of direct importance to the management and conservation of ragged-tooth sharks, not only in the iSimangaliso Wetland Park, but worldwide. This may warrant the creation of protected areas, temporal-spatial closures, prohibiting exploitation activities during the gestation season, or firmer management and regulations of ragged-tooth shark related activities like SCUBA diving (Klein et al. 2016).