The distribution of gamefish, particularly marlin, is dependent on oceanic features such as shelf breaks, cold water upwellings (the process of deep water rising to the surface and replacing surface water often caused by wind blowing parallel to a coastline) and eddies (circular currents formed by nutrient-rich deep water that can rise to the surface). Upwellings and eddies can be unpredictable meaning the distribution of gamefish varies from week to week and year to year. Gamefishers have long known about the connection between oceanographic features and gamefish catch rates. This article will explore what impacts oceanographic conditions have on gamefishing, both in the short term, but also the effects of longer-term climate change.

East Australian Current

Gamefishing on the east coast is largely driven by the East Australian Current (EAC), which was featured as a ‘super highway’ in the popular Disney animated movie Finding Nemo. The EAC brings warm, although nutrient poor, water down Australia’s east coast allowing striped marlin to be caught in autumn months at 36°S, off Montague Island.  It also enables the seasonal movement of fish, such as young black marlin down the Queensland coast.

When flowing strongly, the EAC is one of the fastest ocean currents in our region, sometimes flowing faster than 2 knots. The warm tropical waters of the EAC are generally nutrient poor. However, the current can create cold water upwellings and eddies, where warm water and cold nutrient rich water mix to form favourable oceanographic conditions for primary production. Primary production of phytoplankton is the basis for the entire marine ecosystem that gamefish rely on. Zooplankton, baitfish and eventually large pelagic predators are drawn to areas of the ocean where phytoplankton can thrive. Therefore, the oceanographic conditions necessary for phytoplankton are key in understanding where gamefish will be.

In recent years, the EAC has been observed to flow stronger and further south. A stronger EAC is predicted by just about all climate models and the stronger current flow in recent years has been attributed to climate change. Many climate models predict the south east coast of Australia to be the most highly impacted area by climate change through a stronger EAC.  

Warming sea temperatures

The United States National Oceanic and Atmospheric Administration (NOAA) forecasts high sea surface temperatures off south-eastern Australia for February to April 2019 with waters south of Sydney predicted to be at least 2°C higher than average. The increase in warm water off southern NSW is predicted to be caused by one of the strongest EAC’s on record and this could have consequences for gamefishing.

The stronger current may also mean eddies are less likely to form, or are formed further south than usual. This could be an issue for gamefishing tournaments held through the year, such as Bermagui (26-28 January 2019) and Port Stephens (15-17 February 2019). At these ports, warm water could arrive earlier than a normal year and gamefish may pass through earlier and head further south.

As always, bigger boats will be able to venture further to have a better chance at finding ideal conditions and good strike rates, but smaller boats may be restricted to areas closer to the shelf, where NOAA predict the highest temperature anomalies will be.

Warmer water is not all bad news though. A strong EAC means new species are likely to turn up where they have not been seen before. For example, striped marlin are more likely to venture to the Tasmanian coast and many tropical species may start being caught off NSW.

Meteorological and fisheries agencies will monitor this summer’s oceanographic conditions closely. An interesting question is; will these conditions become the new normal as climate change continues? The south east coast of Australia is expected to be one of the earth’s most rapidly impacted areas. The Australian Fisheries Management Authority (AFMA) is assessing how resilient current management arrangements are to climate change and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) have predicted the likely impacts of climate change on various species.

Climate change and longer term implications

Climate change is already having significant impacts on marine ecosystems and fisheries worldwide and these impacts will continue to grow into the future. These may include wide ranging negative and positive impacts for Australian fish resources.

A variety of oceanographic changes are predicted to occur which will impact pelagic systems. These include temperature, pH, oxygenation, and mixed layer depths/thermoclines. Whatever the cause of the changing climate, fisheries management needs to be both adaptive and resilient to the potential impacts, noting the significant costs and effort often associated with any action.

Impacts on tuna and billfish will be varied. Abundance (both increases and decreases) of stocks are predicted to vary spatially and temporally, and effects will be species specific, including changes in range, depth and life history. It will become increasingly difficult to work out if stock declines are due to climate effects or too much fishing effort.

Changes in weather, especially extremes of weather for greater periods of time, may restrict fishing access for both commercial and recreational anglers. This may also result in increased workplace safety issues and risk-taking by crews. Fisheries compliance may also need to change as a result of fishers targeting stocks that move as a result of climate change.

A recent project by CSIRO and AFMA used decadal scaling models to predict impacts of climate change on tuna and billfish fisheries. The focus of the models was primarily oceanographic temperature change. The increases in temperature are predicted to drive pelagic fish further south and lead to changes in abundance. Southern bluefin tuna abundance is predicted to remain constant or increase. Bigeye and yellowfin tuna, marlin and swordfish are generally predicted to decrease in abundance, although this is less certain as there is disagreement among models. Baitfish, such as small mackerel and scad (also known as also known as slimies and yakkas), are generally predicted to fare well with climate change, especially in southern waters. Other oceanographic factors, such as decreased pH, decreased oxygenation or the impacts of changing temperatures on thermoclines, are not clearly understood in terms of their impacts on pelagic fish and will be factored into future modelling as knowledge improves.

Preparing Commonwealth fisheries for climate change

As the regulator of Australia’s Commonwealth fisheries, AFMA wants to better understand how the anticipated effects of climate change on fish stocks will impact the fishing industry, the adaptation strategies that industry may use to adjust to on-the-water changes and how AFMA can support this. The main focus of fisheries management to date has been on fishing mortality as a key driver of stock status based on the assumption that natural mortality was fairly stable over time. That paradigm is now known to be incomplete with climate effects causing fisheries to fluctuate in abundance.

Over the last decade, the Fisheries Research and Development Corporation (FRDC) has invested in a considerable amount of research on the anticipated impacts of climate change on fisheries. The research has wide-ranging implications for fish species all around Australia including those managed by the states and territory and the recreational and indigenous fishing sectors. Furthermore, the changes are anticipated to give rise to ecological, economic and social challenges for Australian fisheries that will require the fishing sectors and fisheries management agencies to respond. This has prompted the question as to whether the fisheries regulatory framework is in a good position to deal with the expected changes.

 

Through the project Adaptation of Commonwealth Fisheries Management to Climate Change (FRDC 2016-059), AFMA, the CSIRO and others are working together to develop a risk assessment framework and methodology as a tool to evaluate, prioritise and address climate-driven ecological, economic and social risks that may arise in Commonwealth fisheries.

 

The project’s first stakeholder workshop was held in Melbourne in November 2018 and attended by a wide range of stakeholders from the commercial, recreational and indigenous fishing sectors, scientists from Australia, New Zealand, the United States of America and Canada, environmental non-government organisations, and state and federal government departments. The workshop identified some key challenges and opportunities that each sector faced because of climate change including the ecological, economic and social risks.

The outcome of this project has the potential for national and global relevance, as it will aim to synthesize the outcomes of the risk assessment, and any existing and potential adaptation strategies, into a useable, plain English manual for fisheries managers and industry alike. This would support the implementation of outcomes from this project and has the potential to be transferable across other fisheries sectors and jurisdictions.

The future

Along with commercial and recreational fishers, consumers will need to learn how to adapt to climate change too, by eating seafood species that become more abundant and reducing their intake of species that are less so. Collection of more environmental data is already underway and this should help fishery managers improve our knowledge of climate impacts on large pelagic species over time.

The projects run by AFMA, CSIRO and other partner agencies are making significant steps towards ensuring fisheries management will be resilient in the face of climate change, and highlight the commitment of the fishing industry and Australian government authorities to maintaining a sustainable and economically viable industry.

View the article printed in issue 136 of BlueWater Magazine.