The interactive effects of anthropogenic impacts on coastal fisheries

Felicity E Osborne

doi:10.25907/00945

Direct anthropogenic impacts (e.g., habitat loss and overharvesting), combine with global-scale modifications (e.g., climate change) to change the distribution, condition and structure of both plant and animal assemblages in marine ecosystems. The degree to which these differing scales of anthropogenic impacts interact to change the value of ecosystem services (e.g., food provision), remains poorly understood in many settings and almost never understood over continental scales and beyond for marine ecosystems. Establishing the drivers of fisheries biomass globally is vital to identify the attributes that are most associated with change of fisheries biomass and how to mitigate the effects of climate change and overfishing. Testing these attributes on both broad and fine scales using climate sentinel species can help identify patterns of species distribution in response to climate change in Australia and inform management on future sustainable climate mitigation strategies for pelagic species. In this thesis I undertook a comprehensive systematic global review of published literature to identify the key drivers that increase fisheries biomass globally. Here, open water ecosystems had the highest identified increase of fisheries biomass globally (35% of studies), while overfishing contributed most to declines (37%) in fisheries biomass. The variables most responsible for increasing fisheries biomass were water quality (16%), fisheries management (15%), physical attributes (15%), vegetation (12%) and seasonal influence (11%). Climate drivers like sea surface temperature concurrently increased (34%) and decreased (17%) fisheries biomass. I applied these findings of climate change and water quality effects in open water environments to investigate shifts in net latitudinal capture records of dolphinfish Coryphaena hippurus over eighteen years in response to variation in ocean characteristics in the southwest Pacific. Conventional tagging data collected by fishers as part of the New South Wales (NSW) Department of Primary Industries (DPI) Game Fish Tagging Program identified poleward shifts in captures between 2002 and 2020 and increased seasonal poleward shifts particularly in the austral summer and autumn months. Dolphinfish tended to be cause more polewards when negative sea level anomaly, more west geostrophic currents, greater surface current velocity, lower concentrations of net primary productivity and chlorophyll-a and waters between 500 – 2200 m depth were observed. There was a restricted thermal range of smaller dolphinfish (50 to 60 cm) to waters between 18 to 24°C and broader thermal range of larger dolphinfish (60 to 100 cm) to waters between 13 to 33° C. I then used acoustic telemetry to assess the use of fish aggregating devices (FADs) by dolphinfish and understanding the role of climate and ocean attributes in determining dolphinfish movement and FAD connectivity. Acoustic telemetry of 43 out of 60 tagged dolphinfish (resulting in over 220,000 detections) established the residency times of dolphinfish at FADs and ascertained the ocean attributes driving the movements between stations. Detections ranged from Double Island Point, Queensland to Wollongong, New South Wales. Residency at stations varied between one to nine days (mean = 2.18, median = 0). Two of the tagged dolphinfish remained at FAD locations for large periods of time, including one at Sunshine Coast FAD 7B for 404 days over 748 days at liberty and another at Brisbane FAD 6 periodically for 439 days over 550 days at liberty. Detections on acoustic stations across NSW were only in Austral summer and autumn, while detections on acoustic stations in QLD were across all seasons. Network analysis identified FAD 12C, FAD 2 and Byron Bay FAD as key stations in the acoustic network, with New South Wales FADs showing less interconnectedness that FADs in Queensland. I identified an increased probability of north or south movements when temperatures were between 24°C to 28°C, while there was a greater probability of fish moving in a northerly direction when currents were moving north. Southerly movements were more likely when mixed layer depth is shallower. Combining fisheries management and jurisdictional collaboration can help to mitigate the effects of fishing pressure and climate change on marine ecosystems and fisheries biomass, thereby potentially increasing fishing opportunities for fishers.

The interactive effects of anthropogenic impacts on coastal fisheries

Files and links (1)

Abstract

Details

Metrics