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.


Photo courtesy of the NOAA photo library ( 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 the oceans

Source: Photographer: David Burdick

Gray Reef Shark (Carcharinus amblyrhynchos) Source:
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 ( Photographer: Robert K. Brigham

Photo courtesy of the NOAA photo library (
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.

Overfishing: a problem for everyone

I am currently writing a series of articles for a Chinese produced magazine which targets 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 over exploitation of natural resources. Which is where I come in, contributing a series on fisheries. Over the next few months I will post abridged versions of these articles here. The first, as the title suggests, is about overfishing.


It shouldn’t be a surprise to most people that many of the world’s fisheries are overexploited. Most of the world’s population eats seafood. In fact, the amount of seafood that each person eats, on average, has risen to 19.2 kg per person per year, with over 1 billion people relying on seafood for their primary source of protein. This means that seafood is an extremely important part of our lives. The problem is that over 90% of the world’s fisheries are either fully exploited or overfished (FAO 2014 report on the global fisheries), meaning that if we take any more from those fish stocks they will collapse, perhaps forever.


Over fishing and fisheries collapse

Overfishing has a long history. One of the best documented cases of a fish stock collapse is that of the Atlantic Cod. When the fishery was discovered in the late 1400’s the cod were so plentiful that it was assumed that the stock was unending. There are stories of people dipping a basket into the ocean and pulling it out full of cod! Catches of cod steadily increased from the early 1500’s, supplying a major proportion of the world’s protein, but were relatively small until industrialisation meant that catches increased dramatically. In the late 1960’s the annual catch peaked at over 1.5 million tonnes, an unsustainable catch. Years of overfishing caused the stock to collapse, and despite ever-improving fishing technology and manpower, the catches continued to decline until the fishery was forced closed in 1992. By that time, the total biomass of cod remaining in the Atlantic was estimated to be less than 1% of the original stock, and still has not and may never recover.  (for a great read on this topic pick up the book “Cod: A biography of the fish that changed the world” by Mark Kurlansky).

The most important lesson to learn from the Atlantic Cod fishery is that any fishery which is overfished can and will collapse. In the last decade alone, many important fisheries have been listed as overfished, including the Largehead hairtail (Trichiurus lepturus), of which over 1 million tons is caught in Asian waters annually, the Mediterranean hake (Merluccius merluccius) and red mullet (Mullus barbatus), Cunene Horse Mackerel (Trachurus trecae), White Grouper (Epinephelus aenus), a number of shrimp species, the list is extensive, and most countries in the world feature at least one fishery. As mentioned above, over 90% of the world’s fisheries are already heading in the direction of being overfished and without good management they too will collapse. Unfortunately, the true frequency with which fisheries collapse can be masked by catch statistics. Global annual fisheries production has been relatively stable since the 1990’s. On the surface, it would appear that fisheries are well-managed and sustainable. What happens in reality, however, is that as we overfish one stock and it becomes unviable, either economically or biologically, so it is replaced by another, new fishery. So, the overall global catch stays the same but we have simply shifted the damage. Usually this means that we are doing something known as “fishing down food webs”, whereby we overfish one stock and then move on to fish a different species further down the food web, often the food of the species that is now over fished! This leads to a situation where the productivity of the oceans as a whole has reduced because the catch is now coming from a previously unfished source. Over time, this continual overfishing causes not only a decline in fish abundance but also massive damage to the ocean ecosystems (which will be topics of future articles in this series).

Fishing down foodwebs

Ecosystem Impacts

Overfishing doesn’t only impact the particular fish species that is over exploited; it is not simply a matter of thinking “it is only one fish species, we will do better next time”. Removing a species from an ecosystem is like removing one cog from a finely tuned machine – it stops working properly. This is especially the case because many of the species that we prize play critical roles in regulating the function of ecosystems. When these species are removed from the ecosystem it begins to become unwell, not providing all of the ecosystem services that we take for granted. Then, as we fish down the food web and remove more species, the ecosystem degrades further.  A very good example of this is shark fishing. Sharks are usually the top predators in ecosystems and control how it functions. To be healthy and function properly, marine ecosystems need these top predators. However, nearly all shark fisheries in the world are over fished, with some species of shark becoming extremely rare. As most species of shark are long-lived they tend to be particularly susceptible to over fishing, and the only way that their populations will recover is by not fishing them.

Indeed, some of the most dramatic changes we see in ecosystems are because of over fishing. A good example from colder oceans would be the overfishing of large predatory fish such as snapper, which are prized by humans to eat, allowing species like sea urchins to become overly abundant because normally the predatory fish would keep their numbers in balance. While sea urchins are a natural part of the ecosystem, in large numbers they completely consume kelp forests, which are the base of the food chain and removing them causes the loss of hundreds of species. Unfortunately, these are not isolated examples, and every country in the world has examples of ecosystems which are degraded by overfishing.


Why aren’t fisheries sustainable?

The answer to this question is that they actually are sustainable, as long as we do not take too much. In fact, the goal of fisheries managers is to maintain catches at the Maximum Sustainable Yield (MSY), or the catch that you can take from a particular fishery forever. In its simplest form, the MSY is an easy concept – you just need to harvest slightly less than the total number of fish which recruit to the fishery each year. It is, however, exceptionally hard to calculate the MSY for a fishery for a number of reasons, in particular that (1) we cannot know how many fish there actually are because we cannot actually count them all, (2) the number of fish which recruit into a fishery, the number we need to know so that we can set catch limits, is dependent not only on how many fish are in the stock, but also a myriad of environmental factors, and (3) we don’t really know how many fish are being taken from a stock because of unmonitored recreational and illegal fishing. This third pressure can be very problematic as people often take fish that are too small, and taking fish before they are able to reproduce (that is, they are immature) means that they cannot contribute young to the next generation before they are caught. In addition to these factors, governments, businesses and the public in many countries often place immense pressure on fisheries managers and fishermen to take more fish to keep supply high. Ultimately, this proves to be counterproductive as when a fishery becomes fully exploited, catches begin to decline and prices rise. Increasing fishing effort at this point leads to overfishing and extremely high prices, making that particular species unavailable to everyone, from the consumer who can’t afford to buy it to the fisherman who can no longer make a living and also the forgotten victim – the ecosystem itself.


What’s the solution?

Contrary to what we used to believe, the oceans are not an endless supply of resources; the ocean has a limited productivity budget. But, this doesn’t mean that we cannot sustainably harvest seafood from the oceans, we just need to ensure we don’t take too much.

What does this mean for the future? At a time when the consumption of seafood is increasing, 90% of the world’s fisheries cannot produce any more, meaning that we need to look to other ways to produce our seafood and reduce consumption. The logical way to do this is through environmentally sustainable aquaculture, or farming of seafood. Aquaculture is already common around the world, making up over 40% of total seafood production, but there is still a lot of room for sustainable expansion.

How can you help? The best way to help is to be a discerning consumer. Rather than not eating seafood, ask where it comes from. Is it from a wild fishery? If so, is it sustainably managed? Is the fish you’re eating grown in aquaculture in a sustainable manner? While it may be hard to get the answers to these questions, if you ask at restaurants or where you buy your seafood you will then force the suppliers to ask the same questions. This will then force industries to become more responsible and manage fisheries in a sustainable manner. In some countries, this public pressure has shown to be an effective way to change fishing practices.


Next time

In the next article I will discuss two different types of fishing, trawling and long-line fishing, and the damage that they cause to marine ecosystems.

What’s in a little noise?

Image source:

Different sources of noise in the marine environment. Image source:

Everyone has seen some sort of human impact in the ocean, from plastic washed up on the beach, to a plankton bloom driven by nutrient pollution, possibly even something as confronting as a fish kill (or even dolphins!). But what about the things you can’t see, say some noise?

Marine noise pollution has again become topical in South Australia, with the announcement that seismic surveys in the waters south and west of Kangaroo Island will begin in 2015. But this raises the question, what do we know about the effects of seismic surveys? The answer is…. not much. There is obviously immense community concern, and I was lucky enough to talk about it on ABC radio today.

For those of you who don’t know, the most common method of seismic surveys in marine waters is to use an array of air guns that are towed below the surface (at say, 8 m depth) behind a ship, firing in a sequence at intervals from seconds to minutes. The sound that is reflected back is then analysed to tell you what is on and under the sea floor, important information if you’re looking to extract resources. These surveys can span hundreds of square kilometres and run for months.

There is some literature on the effect of these surveys, but woefully little, and none in this region. The little information that we do have suggests that the effects will be variable, depending on taxa. Whales and dolphins seem to alter the way they communicate and potentially migration routes or residency patterns, at least in the short term, which is concerning because of the seasonal Blue Whale and Southern Right Whale populations in this region. Fish may become stressed and migrate away from the testing area, which includes important fisheries for species such as the Southern Bluefin Tuna. In contrast, it seems that at least some invertebrates may not be affected. I would reiterate, however, that the evidence in either direction is extremely sparse, which concerns me because this region (South Australia) is a global hotspot for species diversity and endemism.

This is where the discussion collides with another topical issue in Australia – how much information do we need to properly assess applications to develop marine resources, and which activities should we allow in our marine (and terrestrial) environments in the name of “progress”? Although some development and an increase in productivity is good, there is more and more support from the scientific community to make sure we don’t damage our environment beyond repair. I won’t go into detail on this, however, as others have written about this topic in much more depth. But, I note that other countries are taking the issue of marine noise seriously, and discussing it, so why aren’t we?

How to track the environment with fish

Clockwise from right – Juvenile Murray cod after calcein marking; Juvenile silver perch during the experiment; An adult golden perch. Credit: Zoe Doubleday

Clockwise from right – Juvenile Murray cod after calcein marking; Juvenile silver perch during the experiment; An adult golden perch. Credit: Zoe Doubleday

Following up on an earlier post about how hard body parts can be used to reconstruct environmental signatures, Dr Zoe Doubleday and her team have identified the relative contribution of water (that the fish are swimming in) and diet to otolith (fish ear bones) chemistry in freshwater fish. Now I know that this isn’t strictly a study about oceans, but the techniques and findings of this paper are extremely useful if you want to do this in the ocean as well! See her report below.

Otolith chemistry is used extensively around the world to address key questions relating to fish ecology and fisheries management, particularly in marine systems. Nevertheless, there is limited research on the relative contribution of water and food to elements within otoliths.
Using a controlled lab experiment, researchers at the University of Adelaide sought to address this gap by explicitly testing the relative contribution of water and food in three iconic Australian freshwater fish species — silver perch, golden perch and Murray cod.  Water was found to be the key, but not sole, contributor to otolith chemistry in all fish species. This research will improve interpretation of otolith chemistry data in freshwater fish and will help to build a more accurate picture of their movements and the environments they inhabit.
Read journal article here:

Aquatic body parts reveal all

This post is written by guest blogger Dr Zoë Doubleday, who is a Post-doctoral Fellow in the Marine Biology Program at The University of Adelaide. She has a particular interest in the utilisation of hard calcified tissues found in aquatic organisms as tools for answering critical questions in aquatic ecology. What interests me about Zoe’s work is how you can apply the techniques below to understanding past environmental conditions in the ocean and what that can tell us about the future…..


When you look at a tree stump what do you see? That’s right, rings, rings radiating out from the center to the edge; rings that represent the growth history of the tree.  Aquatic species also have rings laid down like this, year after year, decade after decade, in all kinds of body parts.  Fish and squid ear bones, shark vertebrae, coral skeletons, marine mammal teeth, bivalve and gastropod shells, cuttlefish bones. . .and the list goes on.  The beauty of hard calcified tissues is that many form growth rings with a precise periodicity (e.g. daily or annual), providing a time-calibrated archive of biological and environmental information.  To extract information from these natural chronometers we can analyse their chemical composition (such as trace elements and isotopes) and examine their growth ring

The otolith (ear bone) of a Murray Cod showing annual growth rings. Photo: Zoe Doubleday

The otolith (ear bone) of a Murray Cod showing annual growth rings. Photo: Zoe Doubleday

patterns (such as number and width) in relation to the temporal context of ring formation.  From here we can examine both the biological history (e.g. age, growth, diet, and movement) and environmental history (e.g. temperature and salinity) of an individual from birth to death.  This type of data can additionally tell us two important things: how the environment is changing and what biological impact that environmental change is having.

Another valuable attribute of calcified tissues is that they can hang around long after the organism has died.  This allows us to compare information derived from modern-day samples with information derived from historical (e.g. 19th and 20th Century), archeological and even paleontological samples.  Such comparisons are very powerful and can provide a rare and crucial insight into past biological baselines and what aquatic environments may have been like, say, prior to industrial-scale fishing or European colonization. This in turn can help us make a more realistic assessment of how much humans have impacted, and are impacting, the environment and about what environmental changes might happen in the future.

In the Marine Biology Program, we have a number of biochronologists working away on a range

Red Gurnard Perch (deep-water marine fish) ear bone with growth ring measurements. Photo: Gretchen Grammer

Red Gurnard Perch (deep-water marine fish) ear bone with growth ring measurements. Photo: Gretchen Grammer

of calcified tissues collected from freshwater to oceanic environments.  From here we are linking chemical and growth pattern data to various climatic and oceanographic variables, tracking movement patterns of individuals over large spatial and temporal scales, and seeing how biological indices, such as growth rate, age, and diet are changing.  However, there is still much to discover and uncover in calcified tissues and, in my opinion, is a mu ch underutilized resource of historical data, particularly in Australia.  As we continue to dig up long forgotten sample archives, find novel body parts with chronological properties, and work with constantly evolving analytical technology, who knows what we will find next…

Vertebra of Port Jackson Shark. Photo: Chris Izzo

Vertebra of Port Jackson Shark. Photo: Chris Izzo