**3.1 VR2 receivers**

424 Modern Telemetry

development of acoustic telemetry systems allowed researchers to overcome many

Initial telemetry experiments, conducted in 1993 and 1994 (Sauer et al., 1997), made use of a four buoy radio-linked acoustic positioning system and simple acoustic transmitters. The use of this then "unorthodox technique" (Sauer et al., 1997) led to the discovery that the formation of spawning aggregations and mating behaviours is well organized in time and space. The advancement of telemetry systems has enabled researchers to apply this technique to many different areas of research. This chapter describes and compares the various telemetry systems used in South African squid research from 2003 to date. These

5. monitor the presence and movement of predators on the inshore spawning grounds

Also described are the types of transmitters used and the various transmitter attachment

Kromme Bay (St Francis Bay, South Africa, Figure 1) forms part of the main squid spawning grounds on the south coast of South Africa, and is a commonly used spawning area. Relatively sheltered from south-westerly swells and winds, with a gentle-sloping seabed (Birch, 1981) consisting mainly of rippled coarse sand (Roberts, 1998), this area is an ideal study site for squid acoustic telemetry experiments. The annual November squid fishery closed season provides an ideal opportunity to conduct such studies, as the potential impact of boat anchors on instrumentation, as well as intense commercial fishing on spawning

Fig. 1. Maps of (a) the study site, Kromme Bay, (b) the main spawning grounds (shaded

limitations, it has also opened up new avenues of research.

1. further our knowledge of inshore (20-70 m) spawning behaviour 2. determine the effect of upwelling and turbidity events on spawning

6. investigate movement on the deep spawning grounds (71-130 m)

techniques developed, which are dependent on the species being tagged.

**2. The chosen study site for acoustic telemetry squid research** 

3. investigate movement on the inshore spawning grounds

studies aimed to:

4. investigate nocturnal behaviour

aggregations, are avoided.

area) between Plettenberg Bay and Port Alfred

VR2 receivers (Figure 2) are single frequency autonomous omnidirectional underwater units. Transmitters send out a series of pings, known as a 'pulse train', which are detected by the receivers. When all the pings are recognised in sequence, the 'pulse train' is then recorded as a signal detection by the VR2. The transmitter ID code, date and time of detection as well as any other received information (depth/temperature) are stored in the internal memory. Once the receiver has been recovered the data is downloaded using a VR PC interface and a computer running VR2PC software. Receiver ranges vary depending on the power output of the transmitters as well as local factors and environmental conditions (Singh et al., 2009).

Fig. 2. VR2 receiver deployed in Kromme Bay
