Drift Modelling of Hector’s and Māui Dolphins to Improve At-Sea Mortality Estimates
This is a suggestion for a Degree Project for Bachelor's and Master's levels at the Department of Marine Sciences. Degree projects at the Department of Marine Sciences are done independently and must be written and assessed individually.
Ämne: Oceanografi
Level: Master
Contact: Johan Svenson, Cawthron, Pierre de Wit, Göteborgs universitet
Location: Cawthron Institute, Nelson, New Zealand
Background
Māui and Hector’s dolphins are the world’s rarest and smallest dolphin species, endemic to New Zealand’s coastal waters. Despite decades of management, fisheries bycatch and Toxoplasmosis remain the main causes of mortality.
Bycatch in set net and trawl fisheries continues to impact populations, while toxoplasmosis, caused by Toxoplasma gondii from land-based runoff, leads to fatal infections affecting the brain and organs.
However, the relative importance and spatial distribution of these threats remain poorly understood. Stranding data provide critical insight into mortality but only represent a fraction of deaths and are strongly biased by ocean transport. Carcasses may drift tens to hundreds of kilometres before reaching shore. International studies have shown that combining stranding data with drift modelling can reconstruct mortality locations and improve understanding of offshore threats.
Project description
This project will apply drift modelling for the first time to Māui and Hector’s dolphin conservation to improve estimates of at-sea mortality. Using OceanTracker (a Lagrangian model in Python), the student will simulate carcass drift under realistic ocean conditions through two complementary approaches:
- Backtracking trajectories from known stranding locations to estimate likely mortality areas and identify links with fishing activity or high-risk environments.
- Simulating drift forward from dolphin habitats to estimate the probability of carcass stranding versus loss at sea, allowing quantification of detection bias and total mortality.
The model will be informed and evaluated using New Zealand’s long-term marine mammal stranding dataset. By linking observed strandings with simulated drift pathways, the project will estimate both mortality locations and the proportion of undetected deaths.
This work will generate spatially explicit mortality estimates and improve understanding of where, how, and how many dolphins die at sea, supporting conservation decisions by the New Zealand Department of Conservation.
Tasks and duties
- Run and analyse Lagrangian drift simulations using Python-based tools
- Work with historical marine mammal stranding datasets from New Zealand
- Validate model outputs against observed strandings
- Collaborate with oceanographers and marine mammal experts
- Communicate findings to stakeholders
Contacts
Romain Chaput: romain.chaput@cawthron.org.nz
Deanna Clement: deanna.clement@cawthron.org.nz
Johan Svenson: Johan.Svenson@cawthron.org.nz
More about Cawthron
Cawthron Institute is New Zealand’s largest and oldest independent research organisation with a 100-year history of delivering practical research solutions that benefit New Zealand and the rest of the world.
The majority of the research undertaken at Cawthron is focused on the marine and freshwater environment. Cawthron’s purpose is to deliver world class science for a better future. We partner with Māori, industry, academia, international stakeholders and government to deliver on our outcomes of healthy ecosystems, a prospering blue economy, thriving people and communities and our five impact pathways:
- Turning the tide on climate change
- Protecting and enhancing aquatic environments
- Securing safe and sustainable food
- Realising the potential of algae
- Supporting resilient communities in the Pacific
Project resources
During the New Zealand-based phase of the project, Cawthron will provide full host support, including:
- Access to necessary practical research facilities and materials
- Supervision, training, mentoring and technical support, as required
- Personal desk space and access to internal network and internet
- Incorporation into Cawthron staff, student and early career researcher networking groups
Support costs (including Cawthron staff time) will be covered by Cawthron.