Project

Baby sharks sharing space

Description

Sharks don’t look after their babies, but they do choose a safe place to give birth. Ornella’s studies young blacktip reef and sicklefin lemon sharks in St Joseph’s lagoon to see how they get along while growing up together.

Baby sharks sharing space

Ornella Weideli

Project leader
About the project leader


While a humpback whale and her calf surface for air, majestic killer whales chase their prey, a pod of dolphins plays in front of a stunning sunset and several shark fins mysteriously break the surface of the waves.
No, this is not a gaudy daydream, but an image of the ocean my young self created while growing up in landlocked Switzerland. Countless drawings like this from my childhood depict my early fascination for marine life, especially the large mammals. Years later, I am a doctoral student working passionately with sharks and I wonder why...

PROJECT LOCATION : St Joseph Atoll, Seychelles
All news about this project
By Ornella Weideli, 7th December 2016
Brothers from another Ocean Mother
Individual sharks that belong to one species but occur in different locations can vary significantly in size, growth rate and life-history traits. Some species, such as the abundant and well-studied reef species, the blacktip reef shark Carcharhinus melanopterus, even show variations of up to 20…
By Ornella Weideli, 3rd May 2016
Sharks, sharks, sharks
It was 5 pm on a Friday, the train station in Bern, Switzerland, was crowded with people rushing home from work and I was standing there waiting for a seven-year-old boy called Adrián and Zaira, his mother. Zaira had contacted me and asked me to…
By Ornella Weideli, 7th January 2016
Getting to know our sharks
The blacktip reef shark Carcharhinus melanopterus is a commonly seen shark species with a large distribution in the Western Pacific and Indian oceans and the eastern Mediterranean (via the Suez Canal). Due to the fact that it is quite common and occurs in shallow coastal…
By Ornella Weideli, 5th October 2015
A change of scenery
The months of June and July saw a complete change in my working routine. Instead of going to work in a small kayak equipped with shark work-up equipment and huge water bottles to keep us hydrated, I drove a small red Toyota through the busy…
By Ornella Weideli, 25th June 2015
How bats help me to better understand a shark’s diet
After eight weeks of running and paddling around St Joseph Atoll to catch juvenile blacktip reef sharks and sicklefin lemon sharks, it’s time for me to analyse the samples I’ve obtained. As part of my PhD, I’m aiming to better understand what these two shark…
By Ornella Weideli, 13th May 2015
Unforgettable St Joseph Atoll
It is time for us, the atoll refugees, to go home! Our eight weeks at St Joseph Atoll in the Seychelles have passed so quickly, but we have all learnt so much and experienced so many once-in-a-lifetime moments. We think it fitting for our last…
By Ornella Weideli, 24th April 2015
Dancing with the devil
Words by Bridgette Rademakers Manta rays are a true spectacle to behold. While the gracefulness and ease with which they fly through the water charms any diver who encounters them, it is also their sheer size, dynamic shape and unique belly markings that make diving…
By Ornella Weideli, 20th April 2015
DNA samples
We use the presence of an umbilical scar as an indication of each shark’s age (as described in my previous blog), and therefore, we are able to guess the approximate sizes of sharks at birth. Additionally, the presence or absence of open umbilical scars helps…
By Ornella Weideli, 20th April 2015
Disguised paradise
Words by Morgan Gueuning Despite the idyllic appearance of St Joseph Atoll, one must never forget the roughness and inhospitably of this environment. If you think – as we naively did – that sampling on tropical islands is an easy thing, you’ve got it wrong.…
By Ornella Weideli, 2nd April 2015
Umbilical scars
Written by Ornella Weideli The life history of sharks is remarkably different to that of bony fishes in that only about 40% of shark species lay eggs (are oviparous). The majority of sharks are viviparous. Viviparity means that fertilised eggs are retained inside the female’s…
By Ornella Weideli, 2nd April 2015
Atoll neighbours
Written by James Guilder As you all know by now, we are working with juvenile sharks – sicklefin lemon and blacktip reef sharks. And on their own, they would be more than enough for us. However, this is only the tip of the iceberg, and…
By Ornella Weideli, 24th March 2015
Photo Identification
We are able to identify a recaptured shark by the PIT tag that has been inserted into it. These tags are coded with a unique number (see previous blog). However, in case a shark loses its PIT tag or the PIT tag does not work,…
By Ornella Weideli, 24th March 2015
A day in the life of an ‘atoll refugee’
Written by Bridgette Rademarkers Those of us working on St Joseph atoll are affectionately referred to as ‘atoll refugees’, because usually by the time we leave the atoll we’re a bit worse for wear and smelling rather fragrant. We come bearing tons of gear, which…
By Ornella Weideli, 17th March 2015
First recaptures
It’s been exactly three months since the end of the first sampling season at the St Joseph Atoll and now we’re back to catch more juvenile sharks as part of the shark nursery study. Juvenile sharks usually suffer from high mortality rates mainly due to…
By Ornella Weideli, 17th March 2015
Ready or not St Joseph, here we are!
Written by Bridgette Rademakers, James Guilder and Morgan Gueuning We are the volunteers that have been fortunate enough to assist in this season’s shark nursery project. The three of us (Bridgette, James and Morgan) feel extremely lucky to be here and would like to share…
By Ornella Weideli, 7th January 2015
Internship at the SOSF-D’Arros Research Centre – Shark Nursery Project
The Save Our Seas Foundation D’Arros Research Centre (SOSF–DRC) is looking for research assistants to help with a shark nursery project at St Joseph Atoll, a remote atoll adjacent to D’Arros Island, one of the tropical Outer Islands of the Seychelles. The project will run…
By Ornella Weideli, 6th January 2015
A real field experience
Field work is… ‘Practical work conducted by a researcher in the natural environment, rather than in a laboratory or office.’ This is what you find if you look up the definition of ‘field work’. In most cases, researchers return to their laboratories after a successful…
By Ornella Weideli, 28th November 2014
First insights into an unexplored shark nursery
Until the beginning of November 2014, the populations of juvenile blacktip reef sharks and sicklefin lemon sharks at St Joseph Atoll in the Seychelles had never been scientifically assessed. Now, however, my field team and I are catching these young sharks in order to discover…
By Ornella Weideli, 4th November 2014
Getting ready for the field
Preparing to undertake field work for the first time in a new location is no mean task and it’s made even more intimidating when that location is a remote coral speck in the immense Indian Ocean; once you’re there, you can’t go out and buy…
Project details

Habitat and resource partitioning of juvenile sharks and their roles in remote coastal ecosystems

Key objective

To conduct an initial assessment of populations of sicklefin lemon and the blacktip reef sharks in a remote coastal ecosystem and investigate how natural resources are partitioned between and within these species. These findings will be crucial for general management and conservation strategies of juvenile predators in this and other nursery habitats.

Why is this important

Global increases in fishing pressure, habitat loss and biological vulnerability of sharks has resulted in steady population decline. Many shark populations lack baseline data, hampering their management and conservation. This research will add to our understanding of sharks in remote coastal ecosystems.

Background

The sicklefin lemon Negaprion acutidens and blacktip reef shark Carcharhinus melanopterus are both known to live in coastal habitats and atoll lagoons throughout their lives; juveniles of both species show a high degree of site-fidelity to only a restricted portion of these habitats, known as nurseries. Juvenile sharks benefit from the protection and food provided by these nurseries until they reach a certain age when they disperse from their natal home.
For a long time it was believed that young sharks living in undisturbed nursery habitats were able to feed and grow with little to no competition, because it was assumed that the nurseries provided more than enough food for the inhabiting species. But more recently, studies in coastal nurseries have demonstrated that juvenile sharks have high mortality rates coupled with slow growth rates, which is most likely at least partially attributable to an uninvestigated lack of food. Aiming to validate this assumption, various studies have demonstrated that a coexistence of shark species in limited coastal habitats relies on the successful partitioning of naturally occurring food resources or spatial segregation.
Furthermore, resource and niche partitioning is not necessarily restricted to the population level, but can also occur among individuals within a population. This intraspecific variation facilitates the successful coexistence of individuals of one species.
The lack of studies originating from the Seychelles to date, coupled with the rising interest in the roles and importance of predators in coastal nurseries for management and conservation strategies, prompts research with multidisciplinary methods. Such research should include movement data and dietary investigations (of stable isotopes and stomach contents) in order to fully understand the ecology and biology of these predators.

Aims & objectives

The aims and objectives of this project are to:

  • Assess population structure, abundance, life history traits, survival rate, growth rate, reproductive growth and genetic relatedness (60 samples) of the sicklefin lemon Negaprion acutidens and blacktip reef shark Carcharhinus melanopterus.
  • Determine home range size, degree of site fidelity and spatio-temporal movement patterns.
  • Examine stomach contents and take tissue samples to determine resource partitioning between species and whether intraspecific variation exists.