Seabed features such as canyons, seamounts, banks
and shoals provide aggregation points for ocean (pelagic) predators such as tunas and mackerels.
Predictions of pelagic fish abundance
ABOVE: Modelled predictions of pelagic fish abundance, showing three main regional-scale hotspots (red areas): one in the north, one in the south-west and one along the southern coast. Submarine canyons are shown in black. Image: Phil Bouchet, UWA.
Learning more about this relationship can offer insight into the distribution patterns of these wide-ranging species, and may present opportunities for monitoring programs and the assessment of management initiatives such as Commonwealth Marine Reserves (CMRs). This research sought to identify relationships between pelagic predators and seabed geomorphology to support the management and monitoring of conservation values inside and outside the CMR network.
A literature review assessed knowledge of predator dynamics in relation to seabed geomorphology. Of particular interest were relationships between predator species and seabed features and methods used to quantify these relationships, as well as the use of landscape metrics (standard measures) by ecologists.
Model simulations determined which metrics best captured seabed complexity and showed promise for monitoring the responses of predators to seabed features. The distribution of oceanic predators such as tunas and mackerels was modelled in relation to seabed geomorphology such as canyons to find continental-scale patterns in marine biodiversity.
The study of long-term commercial catch data off Western Australia found geomorphology to be a key predictor of the distributions of tunas, marlins and mackerels. Data for other pelagic predators including marine mammals and sharks were less available (no fishery data, or poor bycatch data). Many areas of predicted high pelagic fish diversity fell outside the CMR network, particularly those in the Gascoyne Coast, South and West Coast bioregions. Where predicted areas did fall within in CMRs, they often fell within multiple use zones, indicating the importance of how these multiple use zones are managed.
Historical, global fisheries datasets – such as those produced by the Sea Around Us Project – are among the most extensive information sources available for many marine organisms. They can be a useful avenue for identifying important biological processes, and a continental-scale view of predatory dynamics, in the data-deficient pelagic ocean. With careful treatment, they can act as a foundation for determining conservation priorities on scales much broader than local surveys could capture. Identified hotspots can then be refined and further studied on local scales.
New knowledge and opportunities
A new understanding of relationships between geomorphology and pelagic fish assemblages can support the effective design, internal zoning, management and monitoring of CMRs in the open ocean.
Fisheries-derived data relating to large fish such as tunas provide a valuable tool to support marine conservation and ecology and further analyses of these data across Australia’s Exclusive Economic Zone (EEZ) would help to identify opportunities for conserving pelagic megafauna inside and outside CMRs. (Similarities between the predicted hotspots of tunas and those of other large predators such as blue whales and tiger sharks have been observed in other studies, suggesting tunas can be used as proxies for pelagic diversity.)
Outputs and outcomes
This project has contributed an increased understanding of the relationship between geomorphology and pelagic fish that can be applied to CMR monitoring and assessment, environmental impact assessments for offshore oil and gas, and fisheries management. A pelagic fish and sharks dataset linked to an environmental dataset including static (geomorphometric) and dynamic data is now available for the EEZ adjacent to Western Australia.
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