Climate change and the collapse of fisheries

This is the thiFishing down foodwebsrd article in the series that I’m writing for a Chinese magazine targeting wildlife conservation. As you may guess, they started with Panda conservation, so the magazine is called Giant Panda, but they are running a series on exploitation of natural resources. So far I have covered overfishing, trawling and longline fishing. In this current article we discuss the interaction between fishing and climate change. I say we, because this article was led by Charlee Corra, a postgraduate student of mine. Charlee really deserves the credit for this one!

The first article in this series discussed the effects of overfishing and how it causes degradation to the environment. However, changes to the environment also affect fisheries and their sustainability. In any ecosystem, the survival of a species is dependent on its ability to grow to maturity and reproduce, which is in turn dependent on many factors such as environmental conditions that support healthy physiological functioning. Temperature, salinity, and water quality are all examples of integral abiotic factors that can have the power to support life or pose a serious threat. Global climate change is rapidly altering these environmental conditions, and thus altering marine communities in a way that scientists, fishermen, fisheries managers, and policy makers must understand in order to predict future stocks and improve sustainable practices

How the environment affects plants and animals
Physiology:  Marine organisms differ widely in their tolerance of environmental conditions. Some animals can survive better under stress than others. These differences in biological responses determine where an organism can live. For example, in the intertidal zone temperature sets the upper limits of species distributions such that barnacles, mussels or oysters with a greater heat tolerance live higher on the shore than those with a lower tolerance. While almost every organism has the ability to withstand heat stress to varying degrees, most organisms are also adapted to the temperatures in their particular habitat. Thus, many species, and even populations, have different thermal limits beyond which survival is brought into question. As an extreme example, imagine that you grew up in the polar regions and summer for you only gets as hot as, say, 10°C and you were put in the desert in summer – you would be above your thermal tolerance and likely would die.

The water chemistry of our oceans also heavily affects physiological functions. Calcifying organisms, such as corals, oysters, mussels, and some crustaceans, rely on specific levels of CO2 (usually low) and several other chemical compounds (usually high) in order to induce the chemical reaction that allows them to make their skeletons and shells. Changes to the water’s chemistry can compromise the structural integrity of these essential parts. Of particular concern is that constant and increasing CO2 emissions are causing more CO2 to dissolve into the ocean, causing Ocean Acidification (OA). OA is already making it difficult for shelled organisms to make their shells in some parts of the ocean! You can do a small experiment to demonstrate this effect: put a small seashell or piece of egg shell into a glass of an acidic liquid like Cola or vinegar and watch it slowly dissolve (this can take a day or two).

Climate change and long-term climate shifts: Climate fluctuates and changes naturally across many different time scales from seasonal to multi-decadal and millennial. However, in the last two centuries industrial activity has begun to influence these cycles, mostly because of emissions of greenhouse gases such as CO2 into the atmosphere. Of particular concern is that in addition to causing OA this CO2 also causes the earth’s atmosphere to warm, in turn warming the ocean. Unless something is done to change this trajectory, CO2 levels will continue to rise, negative effects on the environment will become stronger, and the impacts on marine habitats and communities will become more visible.

Shifts in distribution of plants and animals: As environmental conditions change, and especially as oceans warm up, many species are predicted to move poleward to higher latitudes to live in more optimal conditions. These range shifts are not always consistent or predictable among organisms or across regions due to complex ecological interactions with other physical and biological factors such as currents and larval dispersal, competitors and predators. Importantly, as the distributions of different species change, the balance of ecosystems is upset and their function is degraded.

Just as with other species, climate change will invariably impact fish populations and dynamics. For example, fish populations may either get smaller where they currently are or move to a new area. Adjusting fishing practices and quotas to these changes is essential for the future of sustainable fisheries.

Trawler

Photo courtesy of the NOAA photo library (www.photolib.noaa.gov) Photographer: Robert K. Brigham

Effects of climate change on fisheries
Range shifts represent a huge threat to the productivity and success of fisheries, especially when they occur to economically and socially important species. In addition to losing an important species as its range shifts poleward, fisheries may be further affected by the opening of a gap in the ecosystem that can become occupied by a new species. This ultimately changes the structure and function of the ecosystem, potentially reducing the productivity of not only that single fishery but also the ecosystem overall.

In addition to range shifts, decreases in abundance of fish may also occur simultaneously. For example, warming has already caused decreases in populations of Norwegian Cod, leading to a less sustainable fishery. In such cases, the fishermen must either change to another fishery or risk damage to the fishery, degradation of the ecosystem and going out of business.

Together, the combination of range shifts and declining abundance has the potential to be devastating to fisheries if vulnerable fish stocks are fished at the same intensity.  Particularly sensitive fish stocks could easily collapse under these combined pressures. Considering that over 80% of the world’s fisheries are either already fully fished or over-exploited, collapses will become more likely under future conditions. However, armed with more accurate knowledge of how fished populations will be impacted, fishing regulations could be fine-tuned to protect the viability of fished species and avoid such a bleak future.

Predicting future stocks
Knowing that these issues exist, a lot of research is currently being done to predict the trajectory of future fish stocks and assist in managing fisheries in a more sustainable way. Because we are trying to predict what will happen in the future, one of the common techniques is to use computer-generated models which use complex calculations based on as many environmental and biological variables as possible to predict the effects of climate change on fish populations. These models take into account the physiological effects of climate change (mentioned above) on the targeted species to predict parameters such as growth, survival, and reproductive output to determine the future supply of adults. Then, in combination with experiments to test the outputs of these models, managers and policy makers decide how many and what type of fish can be caught annually to avoid depleting populations but also to maximize profits and food security. Importantly, these models can, if used properly, help managers prepare for the future of fisheries and to hopefully avoid more fisheries collapsing. However, it is extremely important to remember that predictions are not certainties and models, while very powerful tools, are far from perfect. There will always be variability across regions and habitats due to the interaction of many different factors and projections might represent some outcomes but not all.

It is important to remember that we can formulate all the regulations that want, but unless we are also simultaneously making an effort to decrease or mitigate the impacts of a changing climate on the ocean and its ecosystems, fisheries will continue to decline. The ocean is an important source of food for humans. In many countries seafood is a way of life. Many smaller communities rely exclusively on fish and other marine organisms for protein.  Therefore, it is important for everyone to understand how climate change will impact on the ability of marine organisms to survive because our fate is inextricably intertwined with that of the marine environment.

Top predators are essential to ecosystems: wolves revisited

In a recent post I explained how top predators are essential for healthy ecosystem function. Being a marine ecologist I obviously focused on sharks. I did, however, use the example of wolves in Yellowstone National Park in the USA and how their reintroduction lead to the reestablishment of the forest ecosystem.

Last night I discovered a video that tells the wolf story much more eloquently than I can. I have been an ecologist for nearly 20 years, I know this “story”, and I was still left amazed at the extent to which the presence of wolves improved the ecosystem and the landscape. Even more stunning to me was the multitude of pathways that this improvement takes; from direct control of deer populations to behavioural change which means that deer don’t graze in certain areas.

Not only is the video based on good quality ecology but the visuals are stunning. A must watch. Enjoy!

Scariest part of climate change isn’t what we know, but what we don’t

A good colleague of mine at The University of Adelaide, Corey Bradshaw, recently posted a blog on what we don’t know about climate change….. and the answer is scary. It is such a poignant article that I thought I would share it again here.

ConservationBytes.com

image-20150731-18728-1ntffbr © Nick Kim

My good friend and tropical conservation rockstar, Bill Laurancejust emailed me and asked if I could repost his recent The Conversationarticle here on ConservationBytes.com.

He said:

It’s going completely viral (26,000 reads so far) in just three days. It’s been republished in The Ecologist, I Fucking Love Science, and several other big media outlets.

Several non-scientists have said it really helped them to understand what’s known versus unknown in climate-change research—which was helpful because they feel pummelled by all the research and draconian stuff that gets reported and have problems parsing out what’s likely versus speculative.

With an introduction like that, you’ll just have to read it!

“It’s tough to make predictions, especially about the future”: so goes a Danish proverb attributed variously to baseball coach Yogi Berra and physicist Niels Bohr. Yet some things are so important — such as…

View original post 1,360 more words

Top predators are essential to the oceans

Source: www.photolib.noaa.gov/htmls/reef1373.htm Photographer: David Burdick

Gray Reef Shark (Carcharinus amblyrhynchos) Source: http://www.photolib.noaa.gov/htmls/reef1373.htm
Photographer: David Burdick

The global media was recently full of reports about the interaction that Australian pro-surfer Mick Fanning had with a shark during a competition in South Africa (see the video here). There is no doubt that the experience would have been terrifying and I’m very happy that Mick was not injured. The reactions across media and social media have been broad and varied. Many reports have reasonably pointed out that the rate of shark attacks is less than other more frequent dangers (like being killed by a cow) while some have, unreasonably in my opinion, postulated that we should “clear the ocean of sharks”.

There is no doubt that shark attacks are an emotionally charged event and that they sometimes have tragic outcomes. This has, in some instances, been used as an excuse to have shark culls. Rather than add to the chorus of voices stating how ridiculous this approach is (which it certainly is), I thought I would state something that seems to get forgotten: sharks are essential to the health of marine ecosystems and therefore essential to human life.

Why should we care about marine ecosystems? This seems like an inane question, but many people either don’t care or don’t understand how important healthy oceans are to our lives. Approximately 50% of the oxygen we breathe is produced in the ocean – can you skip every second breath? Over one billion people worldwide rely on seafood as their primary source of protein. Much of our food and pharmaceuticals relies on marine-based products. Basically, we can’t live without healthy marine ecosystems.

Why should I mention that? Because ecosystems rely on balance. When they are out of balance, they are unhealthy and become less productive. One of the services that top predators such as sharks provide to marine ecosystems is this balance. They control the species which would otherwise rapidly expand and dominate systems, lowering species diversity and productivity. A very good example of this in a terrestrial ecosystem is wolves in Yellowstone National Park in the USA. Wolves were hunted to local extinction in the area because they were thought to prey on livestock in the surrounding farmlands. In the absence of the wolves, however, elk populations expanded to the point where massive ecological damage was being done to the forests by grazing elk. Since reintroduction of the wolves, the forests have once again become healthy.

Another of the services that sharks perform is to “clean-up” marine ecosystem. Again, a terrestrial example that most people would be familiar with is lions in Africa catching the sick, diseased or old animals from herds. By removing these weaker individuals the lions are strengthening the herd as well as increasing the per capita resources available to the herd (by reducing its size).

Indeed, there is now a plethora of information on the benefits of top predators to the health and function of different ecosystems. We don’t seem to doubt this information for terrestrial systems, but our fear of sharks makes us irrational when it comes to marine systems. If one person is attacked by a shark the media goes crazy and we hear phrases like “shark cull”. If someone is killed by a cow…….. well, you’d never hear about it.

The reality is that in marine ecosystems the top predators are often sharks and these ecosystems cannot function properly without them. Humans need marine ecosystems to survive. Ergo, without sharks we can’t live as we currently do. While interactions with sharks can be terrifying and even tragic, we need to accept that the oceans are their habitat and we humans need them.

Environmental impacts of trawling and longline fishing

This is the second article in a series that I’m writing for a Chinese magazine targeting wildlife conservation. As you may

Photo courtesy of the NOAA photo library (www.photolib.noaa.gov) Photographer: Robert K. Brigham

Photo courtesy of the NOAA photo library (www.photolib.noaa.gov)
Photographer: Robert K. Brigham

guess, they started with Panda conservation, so the magazine is called Giant Panda, but they are running a series on exploitation of natural resources. In the first I covered overfishing. This current article delves a bit deeper into some of the bigger impacts (certainly not all of them!) of trawling and longline fishing. This is an abridged version.

In the previous article I discussed why overfishing is such a harmful and global issue and how it is leading to negative changes in marine ecosystems. It is not only this overall effect that we should be concerned about, however, because some fishing practices can have large negative impacts on other species, such as sea birds and turtles, or the environment, even if they are not overfished.

What many people don’t realise is that many fishing techniques have some level of unintended negative impacts. The two biggest impacts are 1) the destruction of benthic habitats and 2) bycatch. Benthic habitats are the habitats on the sea floor such as kelp forests or coral reefs which support many other species and are essential to functioning of the ecosystem. Bycatch is the unintentional catch of species that are not of commercial value, not of interest to the fishermen, cannot be sold under their fishing licence or because it is a protected species. It is estimated that approximately 40% of the global fisheries catch is bycatch and discarded back into the ocean. The major issues with bycatch are that it is discarded back into the water, usually dead, contributing to the decline of the ecosystem. Below, I discuss two globally common fishing techniques and some of their impacts.

Longline fishing

Longline fishing is a technique where long fishing lines, up to 10 km long, and containing thousands of baited fishing hooks, are floated along the surface of the ocean to catch pelagic fish species such as tuna or marlin. These lines are set in place for many hours to days and left to drift on the ocean to catch their prey. Over this time, however, many other species are both exposed to and attracted to the baited hooks, meaning that longline fisheries are responsible for a large amount of unwanted bycatch. Unlike trawl fisheries which catch big and small species (explained below), longline fisheries have the dubious record of killing larger animals such as seabirds, turtles, sharks and whales. For example, it has been estimated that global longline fisheries kill somewhere between 160,000 – 320,000 seabirds annually. Unfortunately, many of these species are protected or endangered and such bycatch only serves to increase the pace at which their populations decline.

Another impact that some fisheries, including longline fisheries, have on marine ecosystems is a phenomenon known as ghost fishing. This is when the fishing gear is lost and not collected by the fishermen, allowing it to float around the world’s oceans indiscriminately catching and killing marine life. For longlines it is easy to see how this can occur, as the lines are kilometres long and can be lost when other ships run over the lines, cutting them and separating them from the marker buoys so the fishermen cannot find them again. Unlike bycatch which is pulled from the ocean within a matter of hours, however, such “ghost gear” will continue to kill animals until it degrades and breaks up, usually several years after it is lost.

Trawl fishing

Much of the world’s seafood is caught by trawling, where fishing vessels (trawlers) drag large nets through the water to catch the target species. There are broadly two main types of trawling, pelagic, where the net is dragged through the water column, and benthic, where the net is dragged along the bottom. While a common practice and quite cost-effective for the fishing industry, trawling has two large negatives, 1) a very large bycatch and, 2) for benthic trawls, damage to the seabed.

While effective in catching the target species, the nets used for trawling are not selective and catch many of the animals which are in their path. Imagine a net that can be as much as 100 m wide at the mouth, travelling faster than most fish can swim and it is easy to see that most organisms cannot escape the net, becoming bycatch. The extent of this bycatch can be astonishing. In some regions of the world up to 64 % of the catch is discarded back into the ocean, dead. In the trawl fisheries of the Gulf of Mexico alone, for example, bycatch is estimated to be the equivalent of 1 billion meals a year3! In addition to this wastage, large species such as dolphins, sharks, turtles and seals are often caught in the nets and drown, severely impacting their populations and causing them great suffering. For example, a single prawn fishery that does not employ Turtle Exclusion Devices (TEDs) can catch more than 50,000 turtles per year. Not only are some of these species in decline and protected by law but, as discussed in my previous article, they perform important roles in regulating the function of marine ecosystems on which we depend.

The other major negative impact of trawling is damage to the seabed. When nets are dragged along the seabed they not only catch the species that is being targeted, but they also rip up the seabed itself. Indeed, many fisheries, such as prawn or shrimp trawl fisheries, use chains on the bottom of the net to drag along the seabed and scare the prawns up into the net to be caught. Unfortunately, this type of trawling is now very common and in some regions the seabed is highly impacted. An example is the North Sea, much of which is turned over every year, some areas up to three times per year. Such intense disturbance corresponds with a decline in faunal abundance and species diversity, meaning that over 100 years of intense trawl activity in the North Sea has led to marked declines in species diversity.

This type of physical disturbance of the seabed also, leads to dramatic changes in benthic habitats – larger structures are gradually removed or broken leading to homogenous habitats which are less suitable for most species. Biological habitats such as seagrasses or deep sea sponge beds are destroyed. Unfortunately, many of these types of biological habitats are extremely slow-growing and can take 100’s – 1000’s of years to regrow, assuming that they are not disturbed again in that time.

Are there solutions?

Bycatch is a problem of massive scale which requires a global effort to improve. Thankfully, there are emerging fishing techniques, practices and gear which will start the process of limiting some bycatch. One of the best examples for trawl nets is the inclusion of a device known as a Turtle Exclusion Device, or TED, which also work for excluding other large animals like dolphins and sharks. These devices are large metal bars which cross the opening of the net allowing small species, like prawns or shrimp, into the net so they are caught but larger animals, like turtles, are allowed to escape and are free to swim away. In fisheries where TEDs are now compulsory the bycatch of turtles has deceased by up to 100 %. But this is only one species being excluded.

There are also changes to longline fisheries that can be implemented to reduce bycatch, in particular of seabirds. For instance, setting the baited hooks deeper in the water rather than on the surface and only setting lines at night when the birds aren’t feeding have shown to be effective to some degree.

Limiting the damage of benthic habitats by trawling is more difficult. Changing some practices, such as not using chain on the bottom of the net, can reduce the impact a little, but it is unlikely that these techniques will be broadly implemented as they also reduce the catch. As such, one way to limit damage to benthic habitats is to reduce the frequency with which an area is trawled to allow habitats to recover, but even this will not be effective when geological features or long-lived biological habitats are destroyed. This means that the only truly effective way to ensure the protection of these habitats is by implementing systems of Marine Protected Areas in international waters, currently a very difficult task.

As with all fishing activities, however, regulating and policing these techniques is extremely difficult, especially in international waters. In addition, some fishermen, especially in developing nations, incorrectly think that using these techniques (such as TEDs) will reduce their catch. These people are often already poor and desperate to feed their families and therefore afraid to make any changes that could further harm their families’ health. Until we move towards complete implementation of these techniques, or even improvements on them, the impact of fishing will go beyond what we see on the target fish stock and continue to degrade marine ecosystems. One effective way that you can help towards implementing these changes is by only eating or purchasing seafood from restaurants and shops that support sustainably managed fisheries. Making this choice is becoming more and more viable (see and example guidebook here) and by doing so this will only continue to improve, meaning that you too can help improve the health of our oceans.

When global warming and shifting-baselines syndrome collide

We are having a strange summer in South Australia. First it was mild, then it was late, now it’s hot. So, the weather is a hot topic (pardon the pun) in every conversation. Invariably, conversation then leads onto climate and global warming. And that’s where things get interesting because, as I’ve discussed before, humans and all other organisms experience weather, not climate. In one such conversation with a friend I brought up an excellent article published recently in The Conversation. The article outlines a scary truth; by the end of February 2015 the global temperature has been above the long-term average for 30 years (see the second figure from NOAA, below). My friend said to me, in a very tongue-in-cheek way, “well, I’m 30-ish, which means that they ARE average temperatures to me!”

And that is part of the problem with climate change. It is now easy to demonstrate that temperatures are warming. In Australia, we’re starting to get used to hot summers and bush fires. Even amongst normal inter-annual variation, it’s certainly not difficult to see where the temperature trend is going from the temperature records:

This pattern is repeated globally:

But why can’t we seem to accept the data to all agree that the earth is warming and that we’re the cause?

The problem is three-fold. First, there is the shifting-baselines syndrome. Basically, the idea behind this syndrome is that what you experience in your lifetime is “normal” to you. As with my friend, if you’re only 30 years old (or younger!) then these current temperatures are “normal”. But that doesn’t mean that they ARE normal; the data clearly show that we’re warming outside pre-industrial climatic patterns.

Second, and related to the first, is that we only experience weather. If it rains, we get wet. If it’s winter, we put on a jacket. If it’s summer, we go swimming. We don’t experience “averages.” Some colleagues and I recently published a paper explaining the different effects of climate and weather, noting that without understanding these differences we will not be able to predict what will happen to our marine ecosystems. Yet, policy-makers generally conflate climate with weather, and so we continue to hold to bad policy.

The third, and possibly worst reason, is that in an attempt to “sell the story” the global media still pretends to provide a balanced report. What this means for them is that one person who speaks out against the science underpinning our understanding of climate change gets equal voice to the thousands of scientists who recognise the rigor of this science. That is not only unbalanced, but simply confuses the public into thinking that there is some debate. There is not. To paraphrase the start of the Conversation article, let’s call it, the climate has changed and we’re the cause.

Can nature compensate for human impacts?

Algal turfs dominating under acidified conditions at cold-water (temperate) CO2 seeps, which we use at "natural experiments". You can just see the fronds of a solitary kelp plant in the right of the photo, otherwise they are rare at the site (when they should be 8 - 10 plants per metre!).

Algal turfs dominating under acidified conditions at cold-water (temperate) CO2 vents, which we use at “natural experiments” to try and understand the effects of carbon emissions on our oceans. You can just see the fronds of a solitary kelp plant in the right of the photo, otherwise they are rare at the site (when they should be 8 – 10 plants per metre!). This is a system that has been pushed past its ability to resist or compensate for human activities.

One thing that humans are really good at is having an impact on the environment through their activities. The problem is that we generally don’t realise that we’re having an impact until something changes in a drastic way. We talk about things called phase-shifts, where the environment changes from one “phase” to another. Good (and unfortunately common) examples are the loss of kelp forests for bare reef, seagrass meadows for bare sand, or coral reefs for algal habitats. In all of these cases, the environment has been degraded to the point where it no longer functions as it should, meaning that biodiversity and productivity are massively reduced.

There are two questions to ask here, (1) why don’t we see these phase-shifts coming, and (2) does nature have any resistance to them? A new paper by one of my PhD students, Giulia Ghedini, shows that nature may actually try to resist human-caused stressors (such as increased nutrient pollution, ocean acidification, warming) by increasing the strength of compensation. In this case, Giulia found that the compounding effects of multiple disturbances increasingly promoted the expansion of weedy algal turfs (which replace kelp forests), but that this response was countered by a proportional increase in grazing of those same turfs by gastropods. This is a natural compensatory mechanism, but it has limits.

What does this mean for our understanding of phase-shifts? First, it means that nature is stronger at resisting than we realised. BUT, because it is extremely difficult to either see or quantify this resistance we generally don’t realise it is happening…. until it stops. Then, once we push the systems past their ability to compensate for the increased pressure we place on them we see a sudden shift. It’s like watching a duck on a river – it may look extremely calm on the surface, seemingly stationary, but underneath it is paddling extremely hard. At some point the current strengthens too much and it can’t paddle harder and so, seemingly suddenly, the duck begins to float down the river.

Unfortunately, when put together, this means that more systems may be more stressed than we realise, and the only way to stop detrimental phase-shifts is to take the conservative approach and start to reduce our impacts on these systems. For example, we know that nutrient pollution, carbon emissions, overfishing and many other activities have damaged marine ecosystems, why not begin to reduce our impacts before we add more systems to the list of those we didn’t realise were at breaking point?