**1. Introduction**

422 Modern Telemetry

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The South African chokka squid*, Loligo reynaudii* is found along the coast of South Africa, from Southern Namibia in the west to Port Alfred in the east (Augustyn, 1991). Inshore spawning, however, is limited to the South Coast between Plettenberg Bay and Port Alfred (Figure 1) (Augustyn, 1990). As it is these inshore spawning aggregations that are targeted by the squid jigging fishery (Sauer et al., 1992), an in depth knowledge of the spawning process is essential to the development of effective management strategies for this fishery. In addition squid catches are determined to a large extent by the successful formation and size of these aggregations. As a result, the majority of research on the chokka squid has focused on inshore spawning, i.e. environmental effects on spawning (Augustyn, 1990, Roberts, 1998, 2005; Roberts & Sauer, 1994; Roberts & van den Berg, 2002, 2005; Sauer et al. 1991, 1992), the impact of fishing on spawning concentrations (Hanlon et al., 2002; Oosthuizen et al., 2002a; Sauer, 1995; Schön et al. 2002), biological studies (Augustyn 1990; Lipinski & Underhill, 1995; Melo & Sauer, 1999; Olyott et al., 2006; Roel et al., 2000; Sauer & Lipinski, 1990; Sauer, 1995; Sauer et al., 1992, 1999), life cycle (Augustyn, 1990, 1991; Olyott et al. 2007; Roberts & Sauer, 1994), feeding on the spawning grounds (Augustyn, 1990; Sauer & Lipinski, 1991; Sauer & Smale, 1991, 1993; Sauer et al., 1992), spawning behaviour (Hanlon et al, 1994, 2002; Sauer, 1995; Sauer & Smale, 1993; Sauer et al. 1992, 1993, 1997; Shaw & Sauer, 2004), the inshore spawning environment (Augustyn, 1990; Roberts, 1998, 2002; Roberts & Sauer, 1994; Roberts and van den Berg, 2002; Sauer et al. 1991, 1992), the location of spawning grounds (Augustyn, 1990; Roberts, 1995; Roberts & Sauer, 1994; Sauer, 1995; Sauer et al., 1992, 1993), predation on spawning grounds (Hanlon et al. 2002; Roberts, 1998; Sauer & Smale, 1991, 1993; Smale et al., 1995, 2001), migration / movement on spawning grounds (Augustyn, 1990, 1991; Lipinski et al. 1998; Roberts & Sauer, 1994; Sauer & Smale, 1993) and paralarval development (Oosthuizen & Roberts, 2009; Oosthuizen et al. 2002b; Roberts & van den Berg, 2002; Vidal et al. 2005).

A number of these studies have, however, been limited by certain factors. The inshore spawning grounds extend from ~20 to 70 m. Diving observations are only possible up to a depth of 30 m, are limited in terms of the amount of time that can be spent underwater and are highly dependent on water visibility. Many of these limitations can be overcome by the use of underwater cameras, however, the issue of water visibility remains. Not only has the

The Use of Acoustic Telemetry in South African Squid Research (2003-2010) 425

Passive tracking involves the use of stationary or fixed receivers to monitor the movement of acoustically tagged animals in a particular area. South African researchers made use of two such systems, namely VR2 receiver arrays and the VRAP system. All acoustic telemetry equipment mentioned throughout this section and following sections was purchased from

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

The VRAP (Vemco Radio-linked Acoustic Positioning) system (Figure 3) is comprised of three buoys and a computer base station. The three buoys are controlled from the base station by way of line-of-sight radio modems. Each buoy has a hydrophone which receives acoustic transmitter signals. The information received is then transmitted to the base station where a VRAP computer software programme calculates the position of the transmitter, based on the arrival time of the signal at each buoy. Each detected signal, as well as the position of the three buoys, is plotted in real-time on the computer monitor and stored in a

**3. Passive tracking telemetry systems** 

Fig. 2. VR2 receiver deployed in Kromme Bay

Vemco, Ltd, Canada.

**3.1 VR2 receivers** 

(Singh et al., 2009).

**3.2 VRAP system** 

development of acoustic telemetry systems allowed researchers to overcome many limitations, it has also opened up new avenues of research.

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 studies aimed to:


Also described are the types of transmitters used and the various transmitter attachment techniques developed, which are dependent on the species being tagged.

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

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 aggregations, are avoided.

Fig. 1. Maps of (a) the study site, Kromme Bay, (b) the main spawning grounds (shaded area) between Plettenberg Bay and Port Alfred
