fish habitats

Innovative fish habitat reef modules

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A state of steady decline

Structurally complex fish habitats and coral reefs are in a state of steady decline, with much of the damage to high-quality habitat caused by human activity. Along the east coast of Australia, hard, vertical relief habitats such as oyster reefs, sub-tidal coral reefs and rocky outcrop reefs have been severely impacted by intensive land use practices, to the detriment of both fisheries resources and coral reef habitats.

More about artificial reefs

In order to address the declining quality of hard, vertical fish habitat and to provide opportunities for coral reef growth, Fisheries Ecologists at Catchment Solutions set about designing artificial fish habitat structures, which also specifically incorporate features to promote and facilitate coral growth. Through consultation with recreational fishing experts, spearfisherman, divers, coral reef experts and fisheries biologists with experience in tropical Queensland waters, two key fish habitat designs were devised. Importantly, the fish habitat structures were designed specifically to;

  • Provide habitat to predatory, target species of central Queensland such as barramundi, coral trout, fingermark and black jewfish,
  • Provide refuge and shelter for juvenile species, and
  • Provide conditions for the rapid settlement and colonisation of hard and soft corals, polychaetes, molluscs and other sessile marine organisms.

‘Ledge and Cave’ habitat reef module

The first design, termed the ‘Ledge and Cave’ habitat reef module, is constructed from pre-fabricated concrete components. This reef unit features a large central cave, with two smaller cave-like habitats attached along the outside walls providing additional surface area contact with the substrate to increase stability and reduce subsidence. Two large, round ‘table top’ plates are located above the central cave, providing overhanging shade and refuge over a large surface area. They also provide vertical habitat designed to manipulate tidal currents, creating eddies which attract bait fish and schooling pelagic fish species such as trevally and queenfish.

‘Pyramid’ habitat reef module

The second design termed the ‘Pyramid’ habitat reef module, is constructed from concrete cast into a large, steel mold of the reef module. The ‘Pyramid’ reef module features a central cave located within the bottom of the unit and an enclosed chamber in the top of the unit, only accessible through a series of small holes. It is anticipated that larger predatory species will utilise the lower cave, while juveniles and smaller species such as bream, mangrove jack, and baitfish will seek refuge within the enclosed chamber.

The habitat reef modules also incorporate design features critical to promoting coral colonisation, including high surface area, roughened external surfaces, small grooves throughout the roughened surfaces, and vertical and horizontal complexity in the form of underhangs and ledges. The calcium bicarbonate used in the concrete is also biologically suited to promoting and facilitating coral settlement and growth.

It is anticipated that the greatest benefit can be achieved by arranging four ‘Pyramid’ modules around a single ‘Ledge and Cave’ module as a ‘set’, and by placing a number of sets within close proximity to achieve maximum utilisation by fish, and coral recruitment. The habitat reef modules are suitable for a range of projects, including fish habitat improvement works at land-based recreational fishing access points, coral reef restoration activities, eco-tourism ventures for snorkeling and diving sites, and also through utilisation as fish-friendly mooring systems.

 

Habitat Importance of Urbanised Estuaries in Central Queensland

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Globally, estuarine habitats rank in the most modified of all marine ecosystems, driven primarily by coastal development. The urbanisation and infrastructure associated with population growth concentrate impacts on ecological communities of coastal regions, with anthropogenic advancement constantly recognised in the deterioration of estuarine process zones. Despite this, Queensland’s estuaries provide habitat to a range of species of significant commercial and recreational fisheries value, with many of these species having been documented to utilise highly urbanised marine fish habitats.

In Queensland, urban marine habitats are generally maintained by landholders, local councils and infrastructure management departments. Maintenance works can be routine (e.g. trimming marine plants on access tracks) or as required (e.g. repair of stormwater outlets) and involve varying levels of disturbance. While most maintenance works are required, there are potential risks to fisheries resources and marine plants, particularly when works procedures do not comply with legislative guidelines.

Figure 1. Example of an urban estuarine site showing signs of marine plant vegetation clearing and degradation, with inset of juvenile sea mullet (M. cephalus), barramundi (L. calcarifer) and mangrove jack (L. argentimaculatus) surveyed from the site.

For the purpose of guiding improvements to the management of urban marine fish habitats, Catchment Solutions conducted a 2-year project investigating and comparing the habitat utilisation by fish and crustacean species of urban, peri-urban and non-urban estuarine sites throughout central Queensland. Particular attention was paid to habitat usage of these areas by species of value to commercial and recreational fisheries. The primary objective was to show the critical habitat role that areas thought primarily of as urban ‘drains’ play in providing refuge for juveniles of important species. Furthermore, densities of marine plant vegetation such as mangroves were also surveyed to evaluate the role marine plants play in providing habitat for these species.

These objectives were achieved by carrying out a range of fish community sampling techniques across a number of different urbanised coastal fish habitat sites including tidal creek habitats (lower, mid and upper tidal sites) and supralittoral wetland habitats in the Rockhampton and Gladstone regions. Sampling techniques included a combination of seine netting, fyke netting, cast netting and the use of baited box traps to sample for fish and crustacean species.

In total, 78 species were recorded from 13 sites over five rounds of monitoring, demonstrating the exceptional diversity that can be found at such sites. This comprised 27 species recognised to be of socioeconomic importance to commercial and recreational fisheries. Analyses comparing overall species presence/absence between urban versus non-urban sites showed no significant difference between assemblages, which provides evidence that the highly urbanised sites surveyed are being utilised by identical aquatic assemblages to non-urban sites. Results also showed that for the species of 27 species of socioeconomic importance to commercial and recreational fisheries, the majority of the catch comprised post-larval and juvenile life stages. This highlights the role that coastal estuarine habitats (urban and non-urban) play in providing important nursery grounds to a high number of valuable inshore species, including barramundi, mangrove jack, sea mullet, mud crabs and banana prawns. Peaks in urban habitat utilisation by post-larval and juvenile individuals of species of socioeconomic importance were found between April and September, and numbers were at their lowest between November and December.

Figure 2. Species surveyed during the monitoring (top to bottom, left to right); 1) yellowfin bream (A. australis), 2) giant herring (E. hawaiensis), 3) barramundi (L. calcarifer), 4) Moses perch (L. russelli), 5) endeavour prawns (M. endeavouri), 6) northern whiting (S. sihama), 7) mud crab (S. serrata) and 8) giant queenfish (S. commersonnianus).

Correlations were identified between tidal connection, marine plant composition and the composition of fish/crustacean communities. There was insufficient data to determine whether any of these links were causal, however it is a reasonable assumption that both tidal connection and plant species composition (i.e. mangroves) play a role in the diversity and abundance of fish that utilise urban marine habitats. Review of marine plants surveyed across all sites identified a period of reduced reproductive activity (i.e. flowering and fruiting) between September and October.

Key conclusions from this research suggest that any maintenance works of urban marine habitats in central Queensland should be undertaken late in the dry season. This is to avoid peak periods of utilisation of these habitats by post-larvae and juvenile fish of socioeconomic importance and to avoid peak reproductive periods of marine plants. Where possible, a minimum 2m vegetation strip should be provided along all urban marine habitats to provide refuge habitat for aquatic communities utilising these areas.

It is anticipated that the outcomes of this work will guide future best management practices of urban fish habitats, such as frequency and timings of routine maintenance works adopted by local governments and land holders of the region. The study also provides a framework for similar research into the field of urban marine habitat utilisation and could be replicated to guide appropriate management of urban marine habitats in other regions of Queensland. Building on the dataset would also provide the opportunity to perform more detailed analysis on the causal links between tidal connection, marine plant composition and fish/crustacean diversity and abundance. Knowledge gained through this study could also be built on by investigating the contribution of urban marine habitats to the commercial and recreational catches.