Essential Ocean Variables: Marine Turtle, Bird and Mammal Abundance and Distribution

Jordan van Stavel

Marine turtle, bird and mammal species are wide-ranging, large-bodied, long-lived animals that play a key role in structuring marine ecosystems. Also known as ecosystem engineers these megafauna interact and influence the population dynamics and distribution of important prey species as well as directly impacting their environment through nutrient exchange and transport. In this Essential Ocean Variable (EOV ) category, abundance refers to the number of individuals within a population while the distribution refers to the geographic or spatial extent of habitats used by individuals within the population. As they are at or near the top of the food web, marine turtle, bird and mammals are threatened by, and particularly vulnerable to anthropogenic contaminants that bio-accumulate up the food chain. Humans also face these threats as they share a similar trophic position and often consume the same marine resources. Marine turtle, bird and mammals are long-lived with life histories that are characterised by low reproductive rates, which when depleted may take many years to recovery. Therefore, these organisms are quite sensitive to human activities such as fisheries, and climate change, which makes them an excellent indicator of long term ecosystem health. 

As “charismatic megafauna” marine turtle, bird and mammals have intrinsically high societal value. Given the societal importance of these organisms and their importance to marine ecosystems, it is crucial to monitor and evaluate the interactions and their variability by understanding the abundance and distribution of the turtles, birds and mammals. Such data will be used managers for stock assessments and to assess long term trends in marine ecosystems. This EOV is of critical importance for ensuring that the appropriate marine management measures are in place and their effectiveness is monitored, and also as marine turtles, birds and mammals can act as sentinels for human health risks.  

In order to monitor this EOV, various methods have been implemented. The main methods are indicated below and the observing networks associated with this at a global level are SWOT, SOOS/CCAMLR-CEMP and ORNITHOECO. 
•    Species presence/absence
•    Population Density
•    Population structure; Age, sex, reproductive status
•    Reproductive rate (natality or fecundity)
•    Count Data
•    Repeated individual presence (tracking/re-sights)

More information regarding the Best Practices associated with this EOV can be found on the Ocean Best Practice repository, as well as the GOOS specification sheet