Fishing in the Anthropocene

David Freudenberger looks to the future in an unprecedented era of human influence on our environment.

When trout were first introduced to Australia in the 1860s there were only 1.5 billion people scattered about the globe, now there are 7.7 billion. In my father’s lifetime (he’s now 90) the world’s population has nearly quadrupled in size. In just this short period of time, humans have come to so dominate the biosphere that we have now entered a new geological age — the Anthropocene. Our collective impact is so great that we’ve even managed to alter the chemistry of the atmosphere. The air we now breathe has more carbon dioxide and methane than at any other time in human history. The ripple effects of this unprecedented increase in humanity are vast and profound, and our recreational fisheries are not immune. Heating up Our climates are now on steroids. The 50% increase in greenhouse gases that has occurred since 1750 is capturing more heat and heat is energy. This increase in atmospheric energy is driving more frequent and severe extremes of drought and flooding rain. It’s also led to higher temperatures. On average, the earth’s surfaces are now 1–1.5°C warmer than 200 years ago. But averages rarely tell the full story. Sure, Bureau of Meteorology (BoM) data shows there were some above average hot years in Australia during the early 1900s, but 36 of the past 40 years have been hotter than average. For Australia, the challenging reality is a recent and dramatic increase in extremely hot days. BoM data shows that back in the 1960s there were usually about five days of extremely high temperatures. This has increased to an average of 12 days of extreme heat per year as we witnessed across Australia last summer. Such days are often linked to high winds, low humidity and the reality of massive wildfires, even burning parts of the usually wet Tasmanian highlands during February 2019. Climate change is making extreme events even more severe, resulting in unprecedented conditions that are rewriting local and global histories. New Zealand’s changes have been on average less extreme, but the summer of 2017/18 may be a harbinger of conditions to come. The ocean and land surface heatwave was the most intense in 150 years of temperature records. There was a huge loss of snow and ice in the Southern Alps including the loss of 3.8 cubic kilometres of glacial ice, the largest annual loss on record. In southern New Zealand, extensive canopies of habitat-forming sea kelp were unusually absent that summer — the 19°C temperature tolerance threshold for this kelp was breached three times. Significant deaths of farmed salmon were reported in the Marlborough Sounds, the country’s most important salmon aquaculture area. Sightings of marine life not usually present were noted around the country that summer, including kingfish in Dunedin Harbour and Queensland groupers in the Bay of Islands. Back across the Tasman, warm and nutrient poor eddies of the East Australian Current are frequently stationed off the east coast of Tasmania. This has caused the kelp forests of eastern Tasmania to silently disappear along with the vast marine life they support. The problem with warmer water is that it contains less oxygen. Most of our sport fish are highly active predators with high oxygen requirements. Freshwater species like trout avoid warm deoxygenated water, so during a summer heatwave they are often excluded from shallow and food-rich water. Deep water in lakes and rivers are refuges of cold water, but often not ideal feeding grounds. Shallow lakes in Tasmania are highly productive because they are shallow enough to support vast fields of aquatic plants, but such shallows have fewer deep and cool refuges. Even Australian native fish, particularly Murray cod, are sensitive to rapidly warming water. Cod are a territorial ambush feeder, reluctant to move out of their lies under fallen timber and undercut banks. Recent cod deaths in otherwise clear, high-quality waters appear to be due to oxygen deprivation rather than disease or water pollution. Drying out Not surprisingly we’re also experiencing changing rainfall patterns. The BoM reports that there has been a 20% decrease in May–July rainfall in southwestern Australia since 1970. There has been an 11% decline in April–October rainfall in southeast Australia since the late 1990s. This is linked to measured declines in stream flow during the periods in which both rainbow and brown trout spawn. In contrast, Northern Australian seasonal stream flow has increased with annual rainfall, but the start of the monsoon has become more variable. New Zealand’s meteorological service, NIWA, has recently identified a long lasting ‘shift’ in climate that occurred around 1977. The shift was characterised by more persistent westerlies, resulting in the west and south of the South Island being about 10% wetter and 5% cloudier with more damaging floods. The north and east of the North Island have on average been 10% drier and 5% sunnier, compared to 1951–76 data. Pretty good news for trout, but NIWA suggests that increasing future rainfall extremes, which often result in flooding, should be assumed everywhere. Winners and losers One of the striking features of us humans is that we love to travel with lots of baggage. Wherever we’ve gone, we’ve brought our favourite species along with us. The European brown trout and the North American rainbow trout are now found in every suitable habitat, from the foothills of the Andes and the highlands of Ethiopia to the antipodes of New Zealand and Australia. So too for warm-water species like carp and tilapia that now have global distributions. Hitching a ride in our baggage are thousands of weeds and pest animal species that now have global distributions. This includes our coastal waters where 129 invasive marine species have been found, many of them coming in via bilge water discharged by ships. The losers in this globalization of biota are those often-unseen aquatic creatures like native minnows that can’t compete or are eaten out by our introduced baggage. But iconic fish like the Murray cod have also done it tough as we’ve built dams and irrigation systems to feed our growing population, whilst starving warm-water wetlands that cod and native golden perch need for spawning. But mud marlin (carp) thrive in the down-river reaches of these human dominated waterways and trout thrive in the upper impoundments. Our marine fisheries are no different. Some species thrive; others suffer from increasing water temperatures. As mentioned, the East Australian Current has shifted south killing kelp ecosystems dependent on cold water, but this warm current is bringing tropical game fish further south. There are now more kingfish showing up in Tasmanian waters, but declining in their northern distribution around Lord Howe Island. The losers are temperate fish like snotty trevalla, barracouta and some baitfish species that can no longer tolerate warmer shallow waters around Tassie. Stressed land & seascapes Angling in the Anthropocene is not just hotter and drier; we fish in universally disturbed water catchments. There is no such place as wilderness undisturbed by us and our baggage. In every remote backcountry river in New Zealand there are disturbing signs of North American deer, Australian possums, globally ubiquitous mice and rats, and a plethora of weedy plants. Australian alpine waters, particularly wetland bogs and headwater creeks are being churned into mud by the heavy hooves of feral horses. There has been an explosion of deer right across the Australian Alps to add to the stressors. Lowland waters have been chronically affected by over-clearing of native woodlands and subsequent erosion. Coastal estuaries are under stress from sedimentation and nutrient enrichment from cleared landscapes and urban encroachment. Sediments from over-grazed slopes and burned out catchments dump vast amounts of carbon into our waterways. This carbon feeds bacteria, which rapidly consume the water’s oxygen. Many of Australia’s waterbugs — the keystone of river and stream food webs — feed on the algae, fungi and bacteria in the slime covering on the surface of rocks and snags. When sediment is suspended in the water, light can’t penetrate as effectively, so there’s less opportunity for these slimes to photosynthesise (turning sunshine into energy). After the 2003 alpine fires a sediment slug penetrated the Ovens River in the northeast Murray catchment causing trout losses in the upper catchment and cod deaths in the lower reaches. It was so bad in places even freshwater crayfish crawled out of the river. Sediment slugs, exacerbated by agricultural land uses, are also a major cause of coral reef losses in northern Australia. Plumes of sediment reduce light, smother coral and over-fertilise this delicate ecosystem. Similar problems occur in southern coasts and estuaries. Rising ocean temperatures are a further stress. Making the most of a changed world Us two legged apes are remarkably adaptable. We’re really good at making the most of changed situations. I like to hone my trout-stalking skills by flicking flies to carp down stream of Canberra’s sewage treatment plant. I helped my kids learn to fish by finding schools of redfin perch in Lake Burley Griffin. I enjoy catching silver perch and cod released into my mate’s farm dams. As we see in every issue of FlyLife, the incredible expansion of road and air travel infrastructure now allows us to get to most of the world’s remote and exotic fishing locations, often in less than 24 hours. Us flyin-flyout fly flickers are part of the massive increase in air travel that has risen from 500 million passengers per year to 5 billion in just 40 years. Remoteness is a state of mind, rarely physical reality. Fishing in the Anthropocene is not all doom and gloom. It’s not like it used to be, but there is much to still enjoy. The opportunity and challenge is to protect what we can. We can start with how we fish. Catch and release was pretty well unheard of when I was a kid, it was all about a heavy string of fish and bragging rights. Boasting about a big kill is no longer socially acceptable in most networks of mates. A sun bleached marlin or mako shark hanging by its tail at the wharf weigh-in is now disgusting to many of us. At one point in NSW, the government promised to abolish recreational fishing licences, but instead grass roots lobbying kept them and increased the price. Now much of our fees go to buy back inshore commercial fishing licences, fund fresh and marine habitat enhancement projects, and support educational programs. New Zealand and Australia have been pioneers in establishing marine conservation reserves. They are still controversial to some, but research and fishing experience shows they work. Our sport fish are becoming more abundant and larger outside the reserves. The struggle to release more water for environmental flows below our dams will always require hard work and tough compromises. After 30 years of lobbying there is now a big spring release from Jindabyne Dam into the lower Snowy River. But this is water that no longer provides hydro-power, nor irrigation for peaches and grapes growing in the Riverina. Similar compromises are being worked out in New Zealand. They are never perfect, but with diligence and continuous fine-tuning, a reasonable balance can be achieved between water for fisheries and other legitimate uses. Our seasonal fishing practices will need to continue to change and adapt to the inevitable surprises of climate change. We’re accustomed to closed seasons to let our sport fish spawn. We need to consider closed fishing afternoons or even whole days during summer heatwaves. The lethal threshold for brown and rainbow trout is about 24ºC, but they seek out temperatures much lower than that wherever they can. Adding the additional stress of landing and releasing fish when they are already near their thermal limits likely leads to higher mortality. A reasonable rule of thumb is to quit fishing for trout when most of the stream or river has reached 20ºC. So include a thermometer in your vest. As antipodean summers have increasing heatwaves, we need to think about postponing beloved fishing trips until our favourite lake, river or stream cools off. Part of the solution We’re all a part of the problem, and therefore need to be part of a wide range of solutions. The energy we consume matters. Is a 3-tonne ute really needed for fanging down the highway to the coast for a fish, or will a little buzz-box get you there just as well? Can we put off spending big bucks on an overseas fishing trip, instead investing in some solar panels? Do we just grizzle about the way it used to be, or join forces with a group to restore shade trees along an over-cleared stream bank? Do we stay home and wait for a heat wave to pass, or fish-on to mortally stress our beloved trout? As a species we’re remarkably good at creating all sorts of social and environmental messes, but we’re also really talented at fixing problems. Living and fishing in a human dominated biosphere simply means we have some big problems to fix, but plenty of solutions too. Live and fish as gently as you can. The research papers used to prepare this article can be obtained from [email protected]

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