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An unexpected journey (of eels)

29 05 2023

The way that eels migrate along rivers and seas is mesmerising. There has been scientific agreement since the turn of the 20^th Century that the Sargasso Sea is the breeding home to the sole European species. But it has taken more than two centuries since Carl Linnaeus gave this snake-shaped fish its scientific name before an adult was discovered in the area where they mate and spawn.

Even among nomadic people, the average human walks no more than a few dozen kilometres in a single trip. In comparison, the animal kingdom is rife with migratory species that traverse continents, oceans, and even the entire planet (1).

The European eel (Anguilla anguilla) is an outstanding example. Adults migrate up to 5000 km from the rivers and coastal wetlands of Europe and northern Africa to reproduce, lay their eggs, and die in the Sargasso Sea — an algae-covered sea delimited by oceanic currents in the North Atlantic.

_{The European eel (Anguilla Anguilla) is an omnivorous fish that migrates from European and North African rivers to the Sargasso Sea to mate and die (18). Each individual experiences 4 distinct developmental phases, which look so different that they have been described as three distinct species (19): A planktonic, leaf-like larva (i lecocephalus phase) emerges from each egg and takes up to 3 years to cross the Atlantic. Off the Afro-European coasts, the larva transforms into a semi-transparent tiny eel (ii glass phase) that enters wetlands and estuaries, and travels up the rivers as it gains weight and pigment (iii yellow phase). They remain there for up to 20 years, rarely growing larger than 1 m in length and 4 kg in weight (females are larger than males) — see underwater footage here and here. Sexual maturity ultimately begins to adjust to the migration to the sea: a darker, saltier, and deeper environment than the river. Their back and belly turn bronze and silver (iv silver phase), respectively, the eyes increase in size and the number of photoreceptors multiplies (function = submarine vision), the stomach shrinks and loses its digestive function, the walls of the swim bladder thicken (function = floating in the water column), and the fat content of tissues increases by up to 30% of body weight (function = fuel for transoceanic travelling). And finally, the reproductive system will gradually develop while eels navigate to the Sargasso Sea — a trip during which they fast. Photos courtesy of Sune Riis Sørensen (2-day embryo raised at www.eel-hatch.dk and leptocephalus from the Sargasso Sea) and Lluís Zamora (Ter River, Girona, Spain: glass eels in Torroella de Montgrí, 70 cm yellow female in Bonmatí, and 40 cm silver male showing eye enlargement in Bescanó). Eggs and sperm are only known from in vitro fertilisation in laboratories and fish farms (20).}

As larvae emerge, they drift with the prevailing marine currents over the Atlantic to the European and African coasts (2). The location of the breeding area was unveiled in the early 20^th Century as a result of the observation that the size of the larvae caught in research surveys gradually decreased from Afro-European land towards the Sargasso Sea (3, 4). Adult eels had been tracked by telemetry in their migration route converging on the Azores Archipelago (5), but none had been recorded beyond until recently.

Crossing the Atlantic

To complete this piece of the puzzle, Rosalind Wright and collaborators placed transmitters in 21 silver females and released them in the Azores (6). These individuals travelled between 300 and 2300 km, averaging 7 km each day. Five arrived in the Sargasso Sea, and one of them, after a swim of 243 days (from November 2019 to July 2020), reached what for many years had been the hypothetical core of the breeding area (3, 4). It is the first direct record of a European eel ending its reproductive journey.

Eels use the magnetic fields in their way back to the Sargasso Sea and rely on an internal compass that records the route they made as larvae (7). The speed of navigation recorded by Wright is slower than in many long-distance migratory vertebrates like birds, yet it is consistent across the 16 known eel species (8).

_{Telemetry (6) and fisheries (14) of European eel (Anguilla anguilla). Eel silhouettes indicate the release point of 21 silver females in Azores in 2018 (orange) and 2019 (yellow), the circles show the position where their transmitters stopped sending signals, and the grey background darkens with water depth. The diagrams display the distance travelled and the speed per eel, where the circle with bold border represents the female that reached the centre of the hypothetical spawning area in the Sargasso Sea (dashed lines in the map) (3). Blue, green and pink symbols indicate the final location of eels equipped with teletransmitters in previous studies, finding no individual giving location signals beyond the Azores Archipelago (6). The barplot shows commercial catches (1978-2021) of yellow+silver eels in those European countries with historical landings exceeding 30,000 t (no data available for France prior to 1986), plus Spain (6120 t from 1951) — excluding recreational fishery and farming which, in 2020, totalled 300 and 4600 t, respectively (14). Red circles represent glass-eel catches added up for France (> 90% of all-country landings), Great Britain, Portugal, and Spain. Catches have kept declining since the 1980s. One kg of glass eels contains some 3000 individuals, so the glass-eel fishery has a far greater impact on stocks than the adult fishery.}

Wright claimed that, instead of swiftly migrating for early spawning, eels engage in a protracted migration at depth. This behaviour serves to conserve their energy and minimises the risk of dying (6). The delay also allows them to reach full reproductive potential since, during migration, eels stop eating and mobilise all their resources to swim and reproduce (9).

Other studies have revealed that adults move in deep waters in daylight but in shallow waters at night, and that some individuals are faster than others (3 to 47 km per day) (5). Considering that (i) this fish departs Europe and Africa between August and December and (ii) spawning occurs in the Sargasso Sea from December to May, it is unknown whether different individuals might breed 1 or 2 years after they begin their oceanic migration.

Management as complex as life itself

The European eel started showing the first signs of decline at the end of the 19^th Century (10, 11). In 2008, the species was listed as Critically Endangered by the IUCN, and its conservation status has since remained in that category — worse than that of the giant panda (Ailuropoda melanoleuca) or the Iberian lynx (Lynx pardinus).

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Tags: Anguilla, CITES, European Union, fish migration, hydroelectric dams, ICES, migration, Overfishing, Sargasso Sea
Categories : aquaculture, connectivity, conservation, decline, ecology, environmental policy, Europe, exploitation, fish, fisheries, food, habitat loss, harvest, illegal fishing, impact, IUU fishing, management, marine, metapopulation, recovery, threatened species

A cascade of otters

4 04 2022

Carnivores are essential components of trophic webs, and ecosystem functions crumble with their loss. Novel data show the connection between calcareous reefs and sea otters under climate change.

Trophic cascade on the Aleutian Islands (Alaska, USA) linking sea otters (*Enhydra lutris*) with sea urchins (*Strongylocentrotus polyacanthus*) and calcareous reefs (*Clathromorphum nereostratum*). With males weighting up to 50 kg, sea otters have been IUCN-catalogued as *Endangered* since 2000. The top photo shows a male in a typical, belly-up floating position. The bottom photo shows live (pinkish) and dead (whitish) tissue on the reef surface as a result of grazing of sea urchins at a depth of 10 m. Sea otters are mesopredators, typically foraging on small prey like sea urchins, but their historical decline due to overhunting unleashed the proliferation of the echinoderms. At the same time, acidification and sea-water warming have softened the skeleton of the reefs, allowing for deeper grazing by sea urchins that eliminate the growth layer of living tissue that give the reefs their pinkish hue. Large extents of dead reefs stop fixing the excess in carbonic acid, whose carbon atoms sea water sequesters from the atmosphere enriched in carbon by our burning of fossil fuels. Photos courtesy of Joe Tomoleoni taken in Moss Landing – California, USA (otter), and on the Near Islands – Aleutian Archipelago, Alaska (reef).

For most, the decisions made by people we have never met affect our daily lives. Other species experience the same phenomenon because they are linked to one another through a trophic cascade.

A trophic cascade occurs when a predator limits the abundance or behaviour of its prey, in turn affecting the survival of a third species in lower trophic levels that have nothing directly to do with the predator in question (1).

Sea otters (Enhydra lutris) represent a text-book example of a trophic cascade. These mustelids (see video footage here and here) hunt and control the populations of sea urchins (Strongylocentrotus polyacanthus), hence favouring kelp forests — the fronds of which are eaten by the sea urchins.

Removing the predator from the equation should lead to more sea urchins and less kelp, and this chain of events is exactly what happened along the coasts of the North Pacific (2, 3). The historical distribution of sea otters once ranged from Japan to Baja California through the Aleutian Islands (see NASA’s photo from space, and documentary on the island of Unimak), a sub-Arctic, arc-shaped archipelago including > 300 islands between Alaska (USA) and the Kamchatka Peninsula (Russia), extending ~ 2000 kilometres, and having a land area of ~ 18,000 km².

But the fur trade during the 18^th and 19^th centuries brought the species to the brink of extinction, down to < 2000 surviving individuals (4). Without otters, sea urchins boomed and deforested kelp ecosystems during the 20^th Century (5). Now we also know that this trophic cascade has climate-related implications in other parts of the marine ecosystem.

Underwater bites

Doug Rasher and collaborators have studied the phenomenon on the Aleutian Islands (6). The seabed of this archipelago is a mix of sandy beds, kelp forests, and calcareous reefs made up of calcium and magnesium carbonates fixed by the red algae Clathromorphum nereostratum. These reefs have grown at a rate of 3 cm annually for centuries as the fine film of living tissue covering the reef takes the carbonates from the seawater (7).

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Tags: Alaska, cascade, fisheries, kelp, mesopredator release, otter, Pacific Ocean, sea otter, sea urchins, Trophic cascade, urchins
Categories : biodiversity, biosequestration, carbon, climate change, community ecology, conservation, conservation biology, decline, ecology, ecosystem function, ecosystem services, environmental policy, environmental science, exploitation, extinction, fisheries, harvest, human-wildlife conflict, investment, kelp, mammal, management, marine, meso-predator release, predation, predator, recovery, threatened species, top-down ecology

Influential conservation papers of 2021

5 01 2022

Following my annual tradition, I present the retrospective list of the ‘top’ 20 influential papers of 2021 as assessed by experts in Faculty Opinions (formerly known as F1000). These are in no particular order. See previous years’ lists here: 2020, 2019, 2018, 2017, 2016, 2015, 2014, and 2013.

Amazonia as a carbon source linked to deforestation and climate change — “… confirms what the sparse forest inventory has suggested, that climate change and land-use change is driving Amazonian ecosystems toward carbon sinks. … the research team provides a robust estimate of the carbon dynamics of one of the world’s most important ecosystems and provides insights into the role of land use change and potentials for mitigating direct carbon losses in the future.“

Organic and conservation agriculture promote ecosystem multifunctionality — “… a very clear insight into the trade-offs between the different ecosystem services and indicate that yield and product quality are lower in organic systems compared to conventional systems, yet organic systems have higher economic performance due to higher product prices and subsidies.“

Biodiversity of coral reef cryptobiota shuffles but does not decline under the combined stressors of ocean warming and acidification — “… even with similar richness, community function is very likely to be perturbed by ocean warming/acidification with unpredictable impacts on economically important species such as fish and corals.“

Local conditions magnify coral loss after marine heatwaves — “… show that climate-induced coral loss is greater in areas with elevated seaweed abundance and elevated sea urchin densities, both of which commonly result from local overfishing … effective local management can synergize with global efforts to mitigate climate change and help coral reefs survive the Anthropocene.“

Large ecosystem-scale effects of restoration fail to mitigate impacts of land-use legacies in longleaf pine savannas — “… while restoration can have major benefits in longleaf savannas, land-use legacies have clear effects on many aspects of the ecosystem.“

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Tags: biodiversity, conservation, conservation biology, ecological function, ecology, Ecosystem, function, restoration, top 20
Categories : agriculture, alien species, biodiversity, carbon, climate change, conservation, coral reefs, deforestation, economics, ecosystem, ecosystem function, ecosystem services, evolution, extinction, fish, fisheries, food, fragmentation, habitat loss, invasive species, protected area, reforestation, restoration

Remote areas not necessarily safe havens for biodiversity

16 12 2021

The intensity of threats to biodiversity from human endeavour becomes weaker as the distance to them increases.

As you move away from the big city to enjoy the countryside, you’ll notice the obvious increase in biodiversity. Even the data strongly support this otherwise subjective perception — there is a positive correlation between the degree we destroy habitat, harvest species, and pollute the environment, and the distance from big cities.

Remote locations are therefore usually considered safe havens and potential reservoirs for biodiversity. But our new study published recently in Nature Communications shows how this obvious pattern depicts only half of the story, and that global conservation management and actions might benefit from learning more about the missing part.

Communities are not just lists of individual species. Instead, they consist of complex networks of ecological interactions linking interdependent species. The structure of such networks is a fundamental determinant of biodiversity emergence and maintenance. However, it also plays an essential role in the processes of biodiversity loss. The decline or disappearance of some species might have detrimental —often fatal — effects on their associates. For example, a parasite cannot survive without its hosts, as much as a predator will starve without prey, or a plant will not reproduce without pollinators.

Events where a species disappears following the loss of other species on which it depends are known as co-extinctions, and they are now recognised as a primary driver of the ongoing global biodiversity crisis. The potential risk stemming from ecological dependencies is a major concern for all ecological systems.

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Tags: climate change, coral reefs, coral-reef fishes, ecological networks, Fish, Giovanni Strona, Trophic cascade
Categories : biodiversity, bottom-up ecology, climate change, community ecology, connectivity, conservation, conservation biology, coral reefs, ecology, extinction, fish, fisheries, marine, marine protected area, modelling, planning, predation, predator, top-down ecology, tropical

… some (models) are useful

8 06 2021

As someone who writes a lot of models — many for applied questions in conservation management (e.g., harvest quotas, eradication targets, minimum viable population sizes, etc.), and supervises people writing even more of them, I’ve had many different experiences with their uptake and implementation by management authorities.

Some of those experiences have involved catastrophic failures to influence any management or policy. One particularly painful memory relates to a model we wrote to assist with optimising approaches to eradicate (or at least, reduce the densities of) feral animals in Kakadu National Park. We even wrote the bloody thing in Visual Basic (horrible coding language) so people could run the module in Excel. As far as I’m aware, no one ever used it.

Others have been accepted more readily, such as a shark-harvest model, which (I think, but have no evidence to support) has been used to justify fishing quotas, and one we’ve done recently for the eradication of feral pigs on Kangaroo Island (as yet unpublished) has led directly to increased funding to the agency responsible for the programme.

According to Altmetrics (and the online tool I developed to get paper-level Altmetric information quickly), only 3 of the 16 of what I’d call my most ‘applied modelling’ papers have been cited in policy documents:

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Tags: conservation, ecology, environment, extinction, mathematics, modelling, science
Categories : conservation, conservation biology, ecology, economics, environmental economics, environmental policy, exploitation, extinction, fisheries, harvest, invasive species, investment, management, mathematics, minimum viable population, modelling, mvp, planning, population dynamics, population viability analysis, PVA, research, science, species distribution model

Influential conservation papers of 2020

19 12 2020

Following my late-December tradition, I present — in no particular order — a retrospective list of the ‘top’ 20 influential papers of 2020 as assessed by experts in Faculty Opinions (formerly known as F1000). See previous years’ lists here: 2019, 2018, 2017, 2016, 2015, 2014, and 2013.

Life in fluctuating environments — “… it tackles a fundamental problem of bio-ecology (how living beings cope with the fluctuations of the environment) with a narrative that does not make use of the cumbersome formulas and complicated graphs that so often decorate articles of this kind. Instead, the narrative and the illustrations are user-friendly and easy to understand, while being highly informative.“

Forest carbon sink neutralized by pervasive growth-lifespan trade-offs — “… deals with a key process in the global carbon cycle: whether climate change (CC) is enhancing the natural sink capacity of ecosystems or not.“

Bending the curve of terrestrial biodiversity needs an integrated strategy — “… explores different scenarios about the consequences of habitat conversion on terrestrial biodiversity.“

Rebuilding marine life — “The logic is: leave nature alone, and it will come back. Not necessarily as it was before, but it will come back.“

Towards a taxonomically unbiased European Union biodiversity strategy for 2030 — “… states that the emperor has no clothes, providing an estimate of the money dedicated to biodiversity conservation (a lot of money) and then stating that the bulk of biodiversity remains unstudied and unprotected, while efforts are biased towards just a few “popular” species.“

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Tags: agriculture, ammonium, bioecology, carbon cycle, Climate, climate disruption, CO2, diversification, environmental variation., European Union, farming, food, food security, Forest, genetic rescue, Global warming, governance, MPA, nitrate, outbreeding, Soil, soil biodiversity, synchrony, topoclimates, weather, weathering
Categories : agriculture, anthropocene, biodiversity, birds, cattle, climate change, conservation, conservation biology, deforestation, ecosystem function, ecosystem services, environmental policy, exploitation, extinction, fisheries, habitat loss, marine, marine protected area, protected area, research, science, sustainability

The state of global biodiversity — it’s worse than you probably think

24 01 2020

Chefurka biomass slide

I often find myself in a position explaining to non-professionals just how bad the state of global biodiversity really is. It turns out too that even quite a few ecologists seem to lack an appreciation of the sheer magnitude of damage we’ve done to the planet.

The loss of biodiversity that has occurred over the course of our species’ time on Earth is staggering. This loss is now truly planetary in scale and caused by human actions, albeit the severity of which is unequally distributed across the globe¹. While Sandra Díaz and company recently summarised the the extent of the biodiversity crisis unfolding¹ well in their recent synopsis of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES)² report, I’m going to repeat some of the salient summary statements here, and add a few others. Read the rest of this entry »

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Tags: Anthropocene, biodiversity, decline, extinction, Sixth Mass Extinction, threatened species
Categories : agriculture, anthropocene, biodiversity, biowealth, conservation, conservation biology, coral reefs, decline, deforestation, extinction, fisheries, food, habitat loss, harvest, kelp, threatened species

Influential conservation ecology papers of 2019

24 12 2019

As I’ve done for the last six years, I am publishing a retrospective list of the ‘top’ 20 influential papers of 2019 as assessed by experts in F1000 Prime (in no particular order). See previous years’ lists here: 2018, 2017, 2016, 2015, 2014, and 2013.

Decline of the North American avifauna — … the first comprehensive assessment of population change in the North American avifauna.

Scientists’ warning to humanity: microorganisms and climate change — … [highlights] the crucial role of microbial transformations in determining set points for sea temperature, pH and ocean productivity … [identifies] microbial activity as the “life support system of the biosphere”.

(Note: Lots of people hated this one, basically because it appears to be severely flawed; nonetheless, it received several recommendations on F1000): The global tree restoration potential — … illustrates the substantial potential of capturing some of the excess carbon dioxide present in the earth’s atmosphere by planting trees.

Managing the middle: a shift in conservation priorities based on the global human modification gradient — … probably the best global assessment of spatial extent of human modification of natural terrestrial environments published to date.

Five decades of northern land carbon uptake revealed by the interhemispheric CO₂ gradient — … [concludes] that northern hemisphere [sic] vegetation and soil account for the majority of the terrestrial carbon sink, rather than tropical forests (not trying to display too many sour grapes here, but we’ve already reported this for the boreal forest, and they didn’t even bother to cite us — sad panda)

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Tags: agriculture, biodiversity, birds, carbon, carbon uptake, climate change, climate emergency, CO2, conservation, declines, drought, extinction, Fish, fisheries, forests, insects, marine ecology, microorganisms, pesticides, range edges, trees, urban biodiversity, wilderness
Categories : agriculture, anthropocene, biodiversity, biogeography, biowealth, birds, carbon, climate change, climate shift, community ecology, connectivity, conservation, conservation biology, conservation ecology, decline, deforestation, demography, ecology, economics, ecosystem, ecosystem function, ecosystem services, environmental policy, environmental science, exploitation, extinction, extinction debt, fish, fisheries, function, habitat loss, harvest, marine, planning, pollution, protected area

“Overabundant” wildlife usually isn’t

12 07 2019

koalacrosshairs Late last year (10 December) I was invited to front up to the ‘Overabundant and Pest Species Inquiry’ at the South Australian Parliament to give evidence regarding so-called ‘overabundant’ and ‘pest’ species.

There were the usual five to six Ministers and various aides on the Natural Resources Committee (warning here: the SA Parliament website is one of the most confusing, archaic, badly organised, and generally shitty government sites I’ve yet to visit, so things require a bit of nuanced searching) to whom I addressed on issues ranging from kangaroos, to dingoes, to koalas, to corellas. The other submissions I listened to that day were (mostly) in favour of not taking drastic measures for most of the human-wildlife conflicts that were being investigated.

Forward seven months and the Natural Resources Committee has been reported to have requested the SA Minister for Environment to allow mass culling of any species (wildlife or feral) that they deem to be ‘overabundant’ or a ‘pest’.

So, the first problem is terminological in nature. If you try to wade through the subjectivity, bullshit, vested interests, and general ignorance, you’ll quickly realise that there is no working definition or accepted meaning for the words ‘overabundant’ or ‘pest’ in any legislation. Basically, it comes down to a handful of lobbyists and other squeaky wheels defining anything they deem to be a nuisance as ‘overabundant’, irrespective of its threat status, ecological role, or purported impacts. It is, therefore, entirely subjective, and boils down to this: “If I don’t like it, it’s an overabundant pest”. Read the rest of this entry »

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Tags: dingo, environment, fur seals, Government of South Australia, Kangaroo, koala, little corella, Natural Resources Committee, South Australia
Categories : alien species, animal welfare, Australia, biodiversity, climate change, community ecology, conservation, decline, dingo, ecology, ecosystem, ecosystem function, environmental policy, exploitation, fish, fisheries, harvest, human-wildlife conflict, impact, invasive species, kangaroo, management, meso-predator release, predation, predator, science, South Australia, sustainability, threatened species, top-down ecology

How to fix a broken river

5 04 2019

murraycod

It seems that most of what I do these days is measure, model, or otherwise quantify environmental damage. While I dabble in restoration, occasionally I’m involved in a project that really can make a positive difference.

If you’re an Australian, you’ll know a thing or two about just how much of a clusterfuck our biggest river system has turned into. From mismanagement, to outright theft, to lobbyist-driven over-exploitation, to climate change itself, the Murray-Darling system is now in a right mess.

So, I’ll pretext this post with a caveat — no amount of ecological restoration can ‘fix’ a compromised river if there’s no water in it. Goes without saying, really.

But, if you do have water, then there are things one can do to promote populations of various creatures living in it, like fish.

Dubbed the ‘honeypot effect’ — we have just shown that providing woody habitat, or ‘snags’, for native fish in the Murray River increases population size. Read the rest of this entry »

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Tags: aquatic, ecological restoration, ecology, golden perch, Murray cod, Murray-Darling, rehabilitation, restoration, snags
Categories : Australia, conservation, conservation ecology, fish, fisheries, Murray cod, Murray River, Murray-Darling, restoration, River Murray, South Australia, southern Australia, water

Influential conservation ecology papers of 2018

17 12 2018

For the last five years I’ve published a retrospective list of the ‘top’ 20 influential papers of the year as assessed by experts in F1000 Prime — so, I’m doing so again for 2018 (interesting side note: six of the twenty papers highlighted here for 2018 appear in Science magazine). See previous years’ posts here: 2017, 2016, 2015, 2014, and 2013.

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Tags: biodiversity hotspots, biodiversity loss, climate breakdown, climate change, cognition, coral reefs, disease, fieldwork, Fish, fisheries, fishing impacts, Great Barrier Reef, killer whales, mammals, nuisance species, plastics, predators, productivity, richness-productivity relationship, sharks, Species richness, wild areas
Categories : anthropocene, aquaculture, Australia, biodiversity, biowealth, carbon, climate change, climate shift, community ecology, connectivity, conservation, conservation biology, conservation ecology, coral reefs, decline, deforestation, demography, ecology, economics, ecosystem, ecosystem function, ecosystem services, environmental policy, environmental science, exploitation, extinction, extinction debt, fish, fisheries, food, fragmentation, function, habitat loss, harvest, human overpopulation, invasive species, management, marine, marine protected area, modelling, pollination, pollution

Predicting sustainable shark harvests when stock assessments are lacking

26 03 2018

I love it when a good collaboration bears fruit, and our latest paper is a good demonstration of that principle.

It all started a few years ago with an ARC Linkage Project grant we received to examine how the whaler shark fishing industry in Australia might manage its stocks better.

As I’m sure many are aware, sharks around the world aren’t doing terribly well (surprise, surprise — yet another taxon suffering at the hands of humankind). And while some populations (‘stocks’, in the dissociative parlance of the fishing industry) are doing better than others, and some countries have a better track record in managing these stocks than others, the overall outlook is grim.

One of the main reasons sharks tend to fair worse than bony fishes (teleosts) for the same fishing effort is their ‘slow’ life histories. It doesn’t take an advanced quantitative ecology degree to understand that growing slowly, breeding late, and producing few offspring is a good indication that a species can’t handle too much killing before populations start to dwindle. As is the case for most large shark species, I tend to think of them in a life-history sense as similar to large terrestrial mammals.

Now, you’d figure that a taxon with intrinsic susceptibility to fishing would have heaps of good data with which managers could monitor catches and quotas so that declines could be avoided. However, the reality is generally the inverse, with many populations having poor information regarding vital rates (e.g., survival, fertility), age structure, density feedback characteristics, and even simple estimates of abundance. Without such key information, management tends to be ad hoc and often not very effective. Read the rest of this entry »

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Tags: bronze whaler sharks, bronze whalers, bronzies, Carchcarinus brachyurus, chondrichthyan, commercial fishing, copper shark, demographic model, fishing, global sensitivity analysis, Latin hypercube, sustainable fisheries
Categories : Australia, conservation, environmental policy, exploitation, fish, fisheries, genetics, harvest, management, marine, ocean, population dynamics, population viability analysis, shark

Penguins cheated by ecosystem change

13 03 2018

Jorge Drexler sings “… I was committed not to see what I saw, but sometimes life is more complex than what it looks like …”*. This excerpt by the Oscar-winning Uruguayan singer seems to foretell the theme of this blog: how the ecological complexity of marine ecosystems can elicit false signals to their predators. Indeed, the fidelity of marine predators to certain feeding areas can turn demographically detrimental to themselves when the amount of available food shrinks. A study of jackass penguins illustrates the phenomenon in a context of overfishing and ocean warming.

Adult of jackass penguin (Spheniscus demersus) from Robben Island (South Africa) — in the inset, one of the first juveniles released with a satellite transmitter on its back. The species is ‘Endangered’ under IUCN’s criteria (28), following a recent halving of the total population currently estimated at ~ 80,000 adults. Jackass penguins are the only penguins living in Africa, and owe their common name to their vocalisations (you can hear their braying sounds here); adults are ~ 50 cm tall and weigh ~ 3 kg. Photos courtesy of Richard Sherley.

Surface temperature, dissolved oxygen, acidity and primary productivity are, by and large, the top four environmental factors driving the functionality of marine ecosystems (1). Growing scientific evidence supports the idea that anthropogenic warming of the atmosphere and the oceans correlates with this quartet (2). For instance, marine primary productivity is enhanced by increased temperatures (3), but a warmer sea surface intensifies stratification, i.e., stacked layers of seawater with contrasting physical and chemical properties.

In coastal areas experiencing ‘upwelling’ (where winds displace surface water, allowing deep water laden with nutrients to reach the euphotic zone where plankton communities feast), stratification weakens upwelling currents and, in turn, limits the growth of plankton (4) that fuels the entire trophic web, including our fisheries. The study of these complex trophic cascades is particularly cumbersome from the perspective of large marine predators because of their capacity to move long distances, from hundreds to thousands of kilometres (5), with strong implications for their conservation (6).

With those caveats in mind, Richard Sherley and colleagues satellite-tracked the movement of 54 post-fledged, juvenile jackass penguins (Spheniscus demersus) for 2-3 years (7). All individuals had been hatched in eight colonies (accounting for 80% of the global population), and were equipped with platform terminal transmitters. Jackass penguins currently nest in 28 island and mainland locations between South Africa and Namibia. Juveniles swim up to 2000 km in search of food and, when approaching adulthood, return to their native colonies where they reproduce and reside for the remainder of their lives (watch individuals swimming here).

The natural history of this species is linked to the Southern Hemisphere’s trade winds (‘alisios’ for Spanish speakers), which blow from the southeast to the tropics. In the South Atlantic, trade winds sustain the Benguela Current, the waters of which surface from some 300 m of depth and fertilise the marine ecosystems stretching from the Western coasts of South Africa to Angola (8). Read the rest of this entry »

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Tags: anchovy, Benguela, climate change, fisheries, food web, Global warming, jellies, jellyfication, Namibia, Overfishing, penguin, penguins, pilchard, South Africa, upwelling
Categories : Africa, behaviour, birds, climate change, climate shift, coasts, decline, ecology, ecosystem, ecosystem function, fish, fisheries, food, function, harvest, impact, research, science, trophic cascades

Offshore Energy & Marine Spatial Planning

22 02 2018

I have the pleasure (and relief) of announcing a new book that’s nearly ready to buy, and I think many readers of CB.com might be interested in what it describes. I know it might be a bit premature to announce it, but given that we’ve just finished the last few details (e.g., and index) and the book is ready to pre-order online, I don’t think it’s too precocious to advertise now.

A little history is in order. The brilliant and hard-working Katherine Yates (now at the University of Salford in Manchester, UK) approached me back in 2014 to assist her with co-editing the volume that she wanted to propose for the Routledge Earthscan Ocean series. I admit that I reluctantly agreed at the time, knowing full well what was in store (anyone who has already edited a book will know what I mean). Being an active researcher in energy and biodiversity (perhaps not so much on the ‘planning’ side per se) certainly helped in my decision.

And yes, there were ups and downs, and sometimes it was a helluva lot of work, but Katherine certainly made my life easier, and she has finally driven the whole thing to completion. She deserves most of the credit.

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Tags: acoustic, aquaculture, benthic communities, benthos, biodiversity, birds, buffer zones, cables, climate change, co-location, collision, conflict, earthquake, ecosystem services, energy, energy extraction, energy security, entanglement, epifauna, eutrophication, exclusion, exclusive economic zone, Fish, fisheries, fishing, food security, gas leak, impact, infauna, intertidal, invasive species, Law of the Sea, local knowledge, marine, marine mammals, marine spatial planning, mooring lines, noise, objective function, oil and gas, oil platforms, oil spill, OSPAR, partnerships, pile-driving, pipelines, planning, platforms, pollution, portfolio theory, production, productivity, Renewable energy, renewables, resilience, resuspension, sediments, social licence, spatial planning, stakeholder engagement, stakeholders, tidal energy, trade-offs, values, wave energy, wind farms
Categories : acidification, alien species, aquaculture, biodiversity, biowealth, birds, book, carbon, climate change, climate shift, community ecology, connectivity, conservation, development, economics, ecosystem function, ecosystem services, environmental economics, environmental policy, eutrophication, exploitation, fish, fisheries, food, habitat loss, harvest, invasive species, investment, management, marine protected area, modelling, monitoring, MPA, ocean, planning, pollution, prioritisation, research, seagrass, sustainability, toxicology, toxification

Limited nursery replenishment in coral reefs

27 03 2017

blue-striped grunt (Haemulon sciurus)

Coral reef fishes are wonderfully diverse in size, form, and function, as well as their need for different habitats throughout the life cycle. Some species spend all of their life in the same kind of coral habitat, while others need different places to breed and feed.

Fishes requiring different habitats as they progress through life often have what we call ‘nurseries’ in which adults lay eggs and the subsequent juveniles remain, and these places are often dominated by mangroves or seagrasses (i.e., they are not part of the coral reef).

While we’ve known for quite some time that when these nursery habitats are not around, adjacent coral reefs have few, if any, of these nursery-dependent species. What we haven’t known until now is just how far the influence of nurseries extends along a coral reef.

In other words, if a nursery is present, just how many new recruits do different areas of a reef receive from it? Read the rest of this entry »

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Tags: connectivity, coral reefs, coral-reef fishes, Fish, mangroves, nurseries, replenishment
Categories : biodiversity, community ecology, connectivity, conservation, conservation biology, coral reefs, demography, ecology, ecosystem function, exploitation, fish, fisheries, fragmentation, management, marine, marine protected area, seagrass, tropical

Biowealth

24 02 2016

While I’ve blogged about this before in general terms (here and here), I thought it wise to reproduce the (open-access) chapter of the same name published in late 2013 in the unfortunately rather obscure book The Curious Country produced by the Office of the Chief Scientist of Australia. I think it deserves a little more limelight.

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As I stepped off the helicopter’s pontoon and into the swamp’s chest-deep, tepid and opaque water, I experienced for the first time what it must feel like to be some other life form’s dinner. As the helicopter flittered away, the last vestiges of that protective blanket of human technological innovation flew away with it.

Two other similarly susceptible, hairless, clawless and fangless Homo sapiens and I were now in the middle of one of the Northern Territory’s largest swamps at the height of the crocodile-nesting season. We were there to collect crocodile eggs for a local crocodile farm that, ironically, has assisted the amazing recovery of the species since its near-extinction in the 1960s. Removing the commercial incentive to hunt wild crocodiles by flooding the international market with scar-free, farmed skins gave the dwindling population a chance to recover.

Conservation scientists like me rejoice at these rare recoveries, while many of our fellow humans ponder why we want to encourage the proliferation of animals that can easily kill and eat us. The problem is, once people put a value on a species, it is usually consigned to one of two states. It either flourishes as do domestic crops, dogs, cats and livestock, or dwindles towards or to extinction. Consider bison, passenger pigeons, crocodiles and caviar sturgeon.

As a conservation scientist, it’s my job not only to document these declines, but to find ways to prevent them. Through careful measurement and experiments, we provide evidence to support smart policy decisions on land and in the sea. We advise on the best way to protect species in reserves, inform hunters and fishers on how to avoid over-harvesting, and demonstrate the ways in which humans benefit from maintaining healthy ecosystems. Read the rest of this entry »

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Tags: Anthropocene, biodiversity, biowealth, ecosystem services, extinction
Categories : alien species, anthropocene, Australia, biodiversity, biosequestration, biowealth, carbon, cattle, caviar, climate change, conservation, conservation biology, decline, deforestation, ecology, ecosystem, ecosystem function, ecosystem services, environmental economics, environmental policy, extinction, fish, fisheries, food, function, habitat loss, human overpopulation, invasive species, mammal, meso-predator release, predation, predator, research, trophic cascades, water

It’s not always best to be the big fish

3 02 2016

Loosely following the theme of last week’s post, it’s now fairly well established that humans tend to pick on the big species first.

From fewer big trees, declines of big carnivores, elephant & rhino poaching, to fishing down the web, big species tend to cop it hardest when it comes to human-caused ecological disturbance.

While there are a lot of different combinations of traits that make some species more vulnerable to extinction than others (see examples for legumes, amphibians, sharks & teleosts, and mammals), one of the main ones is species size.

Generally speaking, larger species tend to produce fewer offspring and breed later in life than smaller species. This means that despite larger species tending to live longer than their smaller counterparts, their ‘slow’ reproductive output means that they are generally more susceptible to rapid environmental change (mainly via human intervention). In other words, their capacity for self-replacement is often too low to counteract the offtake from direct exploitation or habitat loss.

Despite a reasonable scientific understanding of this extinction-risk principle, the degree to which human disturbance affects species’ distributions is much less well quantified, and this is especially true for marine species.

I’m proud to announce another fascinating paper led by my postdoc, Camille Mellin, that has just come out online in Nature Communications: Humans and seasonal climate variability threaten large-bodied coral reef fish with small ranges.

With the world’s largest combined dataset of coral reef fish surveys for the entire Indo-Pacific (including the coral reef fish biodiversity hotspot — the Coral Triangle), we examined which conditions best described the distribution of fishes over a range of body sizes. Read the rest of this entry »

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Tags: biodiversity, Biogeography, coral reef, distribution, energy, exploitation, Fish, fishes, human disturbance, Overfishing, range, richness, species' range
Categories : biodiversity, conservation, conservation biology, coral reefs, exploitation, extinction, fish, fisheries, habitat loss, harvest, hotspot, human overpopulation, management, marine protected area, predation, predator

Grim tale of global shark declines

25 06 2015

Please don’t eat me

How do you prevent declines of species you cannot even see? This is (and has always been) the dilemma for fisheries because, well, humans don’t live underwater. Even when we strap on a metal tank full of air and a pair of fins, we’re still more or less like wounded astronauts peering through a narrow window of glass at the huge, largely empty, ocean space. It’s little wonder then that we have a fairly crap system of estimating fish abundance, and an even worse track record of managing them sustainably.

But humans love to eat fish – the total world estimate of legal fisheries landings is something in the vicinity of 190 million tonnes in 2013, up from 18 million tonnes in 1950 (according to FAO). We’re probably familiar with some of the losers of that massive harvest, with species like tunas, bill fishes and orange roughy making the news for catastrophic declines in abundance over the last 30-40 years. And we’re not even talking about the estimated tragedy that is illegal, unreported and unregulated (IUU) fishing.

Back in 1999, the FAO started to report that sharks – the new-ish target of many world fisheries resulting from the commercial extinction of many other fin fish fisheries – we’re starting to take the hit. Once generally ignored by fishing industries, sharks soon became popular target species. Then in 2003, Julia Baum and colleagues famously (and somewhat controversially) sounded the alarm for sharks in the Gulf of Mexico by some claims of major and catastrophic declines of large, predatory sharks. While some of the subsequent to-ing and fro-ing in the literature challenged these claims, Baum’s excellent work was ultimately vindicated.

Since then, more and more evidence that sharks are in trouble has surfaced, including the assessment of the reported (again, only legal) catch indicated heavy depletion of coastal sharks even by 1975, and the estimate that 25% of all shark and ray species have an elevated extinction risk, mainly resulting from overfishing. Now even the direct fisheries landings statistics are confirming this grim tale. Read the rest of this entry »

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Tags: chondrichthyans, declines, extinction, FAO, fisheries, fishing, management, rays, sharks
Categories : coasts, fish, fisheries, marine, ocean

Western Australia’s moronic shark cull

4 07 2014

A major media release today coordinated by Jessica Meeuwig in Western Australia makes the (obvious) point that there’s no biological justification to cull sharks.

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301 Australian and International Scientists experts have today provided their submission to the Western Australia Environmental Protection Authority (EPA), rejecting the scientific grounds for the proposed three-year drum-line programme.

Coordinating scientist, Professor Jessica Meeuwig from the University of Western Australia said:

“To have over 300 researchers, including some of the world’s top shark specialists and marine ecologists, all strongly agreeing that there is no scientific basis for the lethal drum-line programme, tells you how unjustified the government’s proposal is. If the EPA and the Federal Minister for the Environment are using science for decisions, the drum-line proposal should not be approved.”

The experts agree that the proposal presents no evidence that the lethal drum-line programme, as implemented, will improve ocean safety. It ignores evidence from other hook-based programs in Hawaii and Queensland that have been shown to be ineffective in reducing shark attacks on humans.

Dr. Christopher Neff from the University of Sydney stated:

“There is no evidence that drum lines reduce shark bites. The Western Australia EPA now faces a question of science versus politics with global implications because it is considering establishing a new international norm that would allow for the killing of protected white sharks.”

The drum lines are ineffective and indiscriminate, with 78% of the sharks captured not considered ‘threatening’ to humans. Yet, scientifically supported, non-lethal alternatives such as the South African ‘Shark Spotter’ and Brazil’s ‘Tag and Remove’ programmes are not adequately assessed as viable options for Western Australia. Read the rest of this entry »

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Tags: Apex predator, culling, environment, human-wildlife conflict, lethal, marine, policy, shark, top predator, WA, Western Australia
Categories : Australia, biodiversity, coasts, connectivity, conservation, decline, demography, environmental policy, extinction, fish, fisheries, harvest, impact, management, marine, minimum viable population, modelling, population dynamics

Biodiversity needs more than just unwanted leftovers

28 02 2014

The real measure of conservation progress, on land or in the sea, is how much biodiversity we save from threatening processes.

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A new paper co-authored by Memorial University’s Dr Rodolphe Devillers and an international group of researchers argues that established global marine protected areas are too often a case of all show with no substance and do not adequately protect the most vulnerable areas of the world’s oceans.

“There is a big pressure internationally to expand global MPA coverage from around 3 % of the oceans to 10 %, resulting in a race from countries to protect large and often unused portions of their territorial waters for a minimal political cost,” said Mr. Devillers. “Marine protected areas are the cornerstone of marine conservation, but we are asking whether picking low-hanging fruit really makes a difference in the long-term, or if smaller areas currently under threat should be protected before, or at the same time as, those larger areas that are relatively inaccessible and therefore less used by people.

“We need to stop measuring conservation success in terms of square kilometres,” he added. “The real measure of conservation progress, on land or in the sea, is how much biodiversity we save from threatening processes. Metrics such as square kilometres or percentages of jurisdictions are notoriously unreliable in telling us about the true purpose of protected areas.” Read the rest of this entry »