Ray

PROJECT TITLE: Estuarine use and ecological impacts of two stingray families (Dasyatidae and Urolophidae)

RESEARCHERS: Matt Taylor and Teagan Marzullo
LOCATION: Batemans Bay Marine Park (more specifically Clyde River) and Jervis Bay Marine Park

OVERVIEW

In Australia, stingrays are comprised of two distinct families; these are the large-bodied Dasyatid species (whip-tail stingrays) and smaller Urolophid species (round stingrays). In this project researchers explore the influence of environmental variables such as temperature on their movement and estuary fidelity (loyalty) of three abundant coastal species, smooth stingray (Dasyatis brevicaudata), estuary stingray (D. fluviorum) and common stingaree (Trygonoptera testacea).

These stingrays were tagged using acoustic transmitting devices that are capable of being picked up by a network of acoustic receiver stations (listening stations).

Acoustic data show that temperature and salinity appear to be important in driving movement and behaviour in these species, but the degree of influence varies between species, with the estuary stingray and the common stingaree both primarily affected by temperature and salinity. This highlights that we need to consider species-specific responses to environmental change, as opposed to species groups or complexes.

Smooth stingray
– In Jervis Bay, smooth stingray movements could only partially be related to rainfall events with movements largely influenced by food provisioning (by locals and fishermen).

Common stingarees
– Activity levels increase with temperature until its thermal optimum of 23.9°C, thereafter activity decreased.
– Common stingarees changed habitat so that their surrounding environmental conditions such as salinity were close to ideal for species. They also appear to use behavioural thermoregulation to deal with varying water temperatures.

Estuary stingray
– Similar to the common stingaree they chase warm water during cooler periods, however they continue to move further upstream towards warmer waters during warmer periods.
– Lower salinities (associated with rainfall events) also caused this species to move downstream towards the mouth. Despite the changes in movement in less saline conditions, the estuary stingray appears to be more tolerant of salinity changes than the common stingaree.

DEFINITION:

Behavioural thermoregulation – The maintenance of a constant body temperature by means of movement/behaviour of an individual. For example Common stingarees chase warmer waters upstream during cooler periods, and moved towards cooler waters downstream during warmer periods.