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.

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Relevant experimental scales for Ocean Acidification

Degraded reef where kelp have been replaced by algal turfs

Degraded reef where kelp have been replaced by algal turfs

In a few of my posts have discussed the potential effects of ocean acidification (OA), caused by the dissolution of CO2 into seawater, on marine ecosystems. What I haven’t really discussed yet is how we make these predictions, because quite frankly attempting to predict the effects of OA is a difficult prospect. There are a couple of different ways that you can make such predictions, but for me one of the most obvious and effective ways is to identify the key species’ in a particular marine ecosystem and then experimentally expose them to elevated CO2 based on the various emissions scenarios. On the surface that sounds simple…… but it turns out to be quite hard. The most simple way to do it is to bring organisms back into the lab and do the experiments there. True, it’s easier to manipulate the CO2 by bubbling mixed air with elevated concentrations of CO2 under lab conditions, but invariably you end up with a situation where you’re looking at the physiological responses of organisms. This is a very valid thing to do, but you can also be in for some surprises when you try to scale up to identify ecological effects. For example, based on

laboratory based experiments we have predicted that algal turfs will replace kelp forests and corals under

Healthy forest of the kelp Ecklonia radiata

Healthy forest of the kelp Ecklonia radiata

future OA conditions (picture to the right; link to the kelp study) because these algal turfs use the extra CO2 as a resource and grow faster. This conclusion, based on physiological changes, was and still is quite valid. HOWEVER, when we scaled up our experiments to mesocosms (literally “medium” experimental environment or ecosystem) and included the kelp we discovered that the kelp were able to resist a lot of this effect by suppressing the growth of the turfs. But, realising that this mesocosm study was also limited because it only occurred over one generation of kelp, and you may need to study multiple generations because the adults may not be the “weak point”, we took this work up to the next scale, field experiments at naturally occurring CO2 vents – currently our best “ecosystem” approach to understanding OA.

But we were interested in not only the larger, system response, but also how well our other experiments may predict ecosystem outcomes. We tested this thought by combining laboratory and field CO2 experiments (which is difficult but possible) and data from ‘natural’ volcanic CO2 vents. Interestingly, and to our great

Coral reefs are structurally complex and "cemented" together by Crustose Coralline Algae.

Coral reefs are structurally complex and “cemented” together by Crustose Coralline Algae.

relief, we found that algal mats showed the same direction of response to elevated CO2 (i.e. they grew more) across all scales of experiments but that the strength of response was modified by the ecosystem complexity. Basically, the things that either eat or suppress the growth of algal turfs slow the rate at which they will come to dominate the systems. BUT, we did find that these turfs have enhanced productivity and more expansive covers in situ under projected near-future CO2 conditions both in temperate and tropical conditions.; that is, our original predictions from the laboratory experiments that these weedy turfs could come to replace kelps and corals seems to hold up, it’s just that the rate of change will be a bit slower.

 

Digital library links for:
Lab based kelp study (Russell et al. 2009)
Kelp resisting turfs (Falkenberg et al. 2012)
Need to study multiple life stages (Russell et al. 2012)
Field manipulations of CO2 (Kline et al. 2012)
Ecological outcomes across different experimental scales (Connell et al. 2013)

Ocean acidification: will there be ecosystem effects?

Turfs overgrowing coral

Algal turfs overgrowing corals under acidified conditions at CO2 seeps, which we use at “natural experiments”. Note that the seagrass in the middle of the photo also grow well under these conditions.

It has been a while since my last post, for which I apologise, but I have just emerged from a particularly busy period. I was lucky enough to be invited to an ocean acidification round table at the Peter Wall Institute in Vancouver late last year and we have been madly working on multiple papers since then (and I also had a short break over the Christmas week because of sheer exhaustion!). Why are we working so madly to get the papers written? Because the topic of the meeting is both topical and imminently important: how do we predict the ecosystem-level impacts of ocean acidification, and what can we do about it?

Why is this such an important question? The simple answer is that ocean acidification is a direct consequence of increasing CO2 in the atmosphere. It’s simple, indisputable chemistry. As CO2 dissolves into seawater it forms carbonic acid, finally reducing the amount of carbonate in the water (a good diagram of this reaction can be found here). The early research into this field (only 10 years ago now!) focussed entirely on calcifying species, such as gastropods and corals, because they use this carbonate to form their hard structures (calcium carbonate). What we’ve realised more recently, and a big part of my research program, is tha t the extra Carbon in the system (in the form of CO2) is also a resource for some algae and plants, potentially causing a change in the dominant species in ecosystems (see my photo of a “future” coral reef and kelp forest in this post).

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 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!).

I’m happy to say that we made real progress in trying to understand what the likely ecosystem effects are globally, and more importantly the things that we need to know into the future. I won’t pre-empt our publications, but the synopsis is that ecosystems will change, and for the worse. This has been highlighted before, including for Australia, but for the first time I think we’re starting to get at understanding the ecological mechanisms (which is essential if we are to help the systems resist this change!).

Lead by Prof. Chris Harley, and including an amazing group of contributors, I’d say it was the most successful round-table that I’ve been involved with and we’ll have some good papers coming out soon (I’ll be sure to post about them!). If you’re interested in the topic and want more information, I strongly suggest that you watch this video of the public event we held as part of the week’s activities.

 

Digitial library links for:Falkenberg et al. 2013
Russell et al. 2013

Mediation of global change by local biotic and abiotic interactions

Dr Laura FalkenbergThis post is basically a short synopsis of the work done by one of my (now ex-) Ph.D. students, Dr Laura Falkenberg. Laura’s work has turned much of what we thought we knew about the effect of increased CO2 and nutrients on its head; we found synergies where we didn’t expect them (reviewed in a book chapter) and system resilience and resistance to change beyond what we hoped (via strong competitive interaction and trophic links; published in Oecologia, PLoS One and Marine Ecology Progress Series). Laura has certainly helped us look at things in new ways and given us hope that in marine systems where synergies between stressors exist that management of local conditions could potentially buy us some time in mitigating climate change (e.g. reducing nutrient flows into the marine environment, in Journal of Applied Ecology).

Ph.D. thesis: Mediation of global change by local biotic and abiotic interactions
by Dr Laura Falkenberg.

Throughout my Ph.D., I assessed the conceptual model that while cross-scale abiotic stressors can combine to synergistically favour shifts in marine habitats from kelp forests to mats of turfing algae, management of local conditions can counter this change. My experimental manipulations found broad support for the hypotheses that; 1) cross-scale factors (i.e. local and global) can have interactive effects which increase the probability of expansion of turfs but not kelp and, 2) management of local conditions (e.g. maintaining intact forests, limiting nutrient enrichment) can dampen the effects of global change (e.g. forecasted carbon dioxide). I published the results from my thesis in four papers. In the first, I showed that experimental enrichment of CO2 and nutrients influence the biomass accumulation of turf and kelp differently, with turf responding positively to enrichment of both resources while kelp responded to enrichment of nutrients but not CO2. Given that such direct responses could be mediated by interactions with other taxa, in the second paper I considered a key competitive interaction and revealed that the presence of kelp can inhibit the synergistic positive effect of resource enrichment (i.e. CO2 and nutrients) on their turf competitors. Similarly, in the third paper I highlighted the importance of herbivory by showing that under enriched CO2 conditions rates of this process were increased to counter the expansion of turfs. Finally, in the fourth paper, I considered a scenario in which these biotic controls were absent and identified that where multiple resources had been enriched and prompted a synergistic response (i.e. the expansion of turf where CO2 and nutrients are modified), subsequent reduction of the locally-determined factor alone (i.e. nutrients) substantially slowed further expansion of turf algae, but that the legacy of nutrient enrichment was not entirely eradicated. Together, these results represent progress in ecological tests of hypotheses regarding global climate change as they incorporate comprehensive sets of abiotic and biotic community drivers.

You can access all of Laura’s publications from the University of Adelaide’s digital library, or email her for a copy.