Document ID: chunk:federal_register_of_legislation:F2016L00300:body:0:p14
Version: federal_register_of_legislation:F2016L00300
Segment Type: other
Provision Reference: 
Character Range: 38645–41595

reduced abundance and distribution of benthic organisms suitable for egg mass attachment (DPIWE, 2002). This reduction in the availability of suitable spawning substrate was found to limit the reproductive success of spotted handfish in the Derwent Estuary (DPIWE, 2002). All three species of handfish rely on semi-rigid vertical structures, such as stalked ascidians, sponges and fleshy alga, on which to attach their egg masses (DEH, 2005). When spawning substrate is absent handfish are unable to secure and guard their egg masses, which often results in any eggs laid being swept away in the current. Anecdotal reports suggest there has been a significant decline in abundance of the preferred spawning substrate for spotted handfish in recent years (Flukes, pers comm., 2014).
While reports indicate that handfish may use alternative forms of substrate, such as filamentous alga, this strategy may not be reproductively viable. Red handfish at Frederick Henry Bay were observed attaching egg masses to filamentous alga but all egg masses failed as the algae was washed away (Jacques, 2014). Furthermore, blooms of filamentous alga may smother the egg masses and possibly restrict the movement of handfish. Several species of unidentified red and brown filamentous algae have been recorded in the Derwent Estuary (Barrett et al., 2010) and Frederick Henry Bay (Jacques, unpublished). Filamentous algae cover varies in space and time and often appears in seasonal flushes. Anecdotal evidence indicates that warm summers and increasing water temperatures favour the growth of filamentous algae, which appears to outcompete other algae such as branching Caulerpa species (Flukes, pers comm., 2014). In spring and summer 2010 high covers of filamentous red and brown algae (unidentified species) were recorded at sites across the Derwent Estuary (Barrett et al., 2010). Divers have reported that they have not observed spotted handfish at sites in the Derwent Estuary where high covers of filamentous algae were present (Flukes, pers comm., 2014).
Other native species that have increased in abundance as a result of human activity may also impact on the availability of spawning substrate and interfere with the recruitment of juvenile handfish. The common butterfly-shell oyster (Electroma georgiana) is a rapidly growing species which experiences population explosions that result in the formation of large, smothering accumulations on the sea floor; these leave behind extensive swathes of decomposing matter when they die off (Green, pers comm., 2014). This species tends to proliferate under high nutrient conditions (Aquenal Pty Ltd, 2008), such as those found in the Derwent Estuary where high sediment and nutrient loads are associated with urban and industrial development and changes in catchment use (Australian Government Land and Coasts, 2010). A high abundance of these oysters was observed at a site in the Derwent Estuary in the late