A recent update introduced to the CMSY methodology used to assess the status of fish stocks has proven to more accurately predict the catch that a population can support than highly valued data-intensive models.
In a paper published in the journal Acta Ichthyologica et Piscatoria, the international team of researchers that shaped the improved CMSY++ model noted that its results better correspond with what is, in reality, the highest catch that a fish stock can support in the long-term, given that environmental conditions do not change much.
Now powered by an artificial neural network that has been trained with catch and biomass data of 400 stocks to identify plausible ranges of the initial and final state of the stocks being assessed, CMSY++ allows managers and scientists to input only catch data to estimate how much fish is left in a given stock and how much fishing pressure can be applied.
Maximum sustainable catches or yield (MSY) is a concept developed in the 1950s by US fisheries scientist M.B. Schaefer who proposed that if fishers left in the water a biomass equivalent to at least 50 per cent of the unexploited fish population, that is, of the biomass it had before being commercially exploited, then the highest possible catches could be sustained over time.
“By comparing the results of CMSY++ to models that are considered superior because they require large amounts of initial data inputs, such as the Fox surplus-production model and the Stock Synthesis (SS3) age-structured model, we noticed that these models badly overpredicted the catch that a population can support when previous overfishing has reduced it to a small fraction of its natural size, as is the case with most exploited fish populations in the world.”
Dr. Rainer Froese, lead author of the study and a senior scientist at the GEOMAR Helmholtz Centre for Ocean Research.
In other words, the model underlying the CMSY++ method fitted the observed data, while the predictions of the ‘gold standard’ models were too optimistic in estimating sustainable catches.
“These models tend to estimate the biomass required to produce maximum sustainable yields as less than half of unexploited biomass, which is lower than M.B. Schaefer originally proposed based on the widely observed S-shaped growth curve of unexploited populations or population size that the ecosystem would normally accommodate.
“This finding could explain the often-observed failure of fisheries managers to maintain or rebuild depleted stocks even when the predictions of the gold standard models were followed.”
Daniel Pauly, co-author of the study and principal investigator of the Sea Around Us initiative at the University of British Columbia.
Froese R, Winker H, Coro G, Palomares MLD, Tsikliras AC, Dimarchopoulou D, Touloumis K, Demirel N, Vianna GMS, Scarcella G, Schijns R, Liang C, Pauly D (2023) New developments in the analysis of catch time series as the basis for fish stock assessments: The CMSY++ method. Acta Ichthyologica et Piscatoria 53: 173-189. https://doi.org/10.3897/aiep.53.e105910
Guest blog post by Dr Gregory Barord, marine biology instructor at Central Campus and conservation biologist at the conservation organization Save the Nautilus
Nautiloids were once quite plentiful throughout the oceans, based upon the fossil record. Today, they are represented by just a handful of species, including the newly described Nautilus vitiensis of Fiji, Nautilus samoaensis of American Samoa, and Nautilus vanuatuensis of Vanuatu. These descriptions highlight the concept of allopatric speciation, or biogeographic isolation, where populations are geographically separated from other populations, resulting in a barrier to gene flow. Over time, these populations may eventually evolve into distinct species.
But what does it take to be able to collect the evidence needed to determine if three different populations of nautiluses are in fact three different species? For me, this is the best/worst part of the overall process, because nautilus fishing is not easy. For our team, it starts with building large, steel traps that are about a meter cubed. Then, we wrap the steel frame (ouch), with chicken wire (ouch) mesh (ouch), create an entry hole (ouch), attach it to a surface buoy with about 300 meters of fishing line, and bait it with (ouch) raw meat, usually chicken! Trap construction may take place on a nice beach or a bit inland in the rain or in a warm warehouse. Wherever it takes place, you will have some memories, I mean little scars, on your hands from working with the chicken wire. Looking down at my hands right now, I can remember where I was by looking at each of those scars… worth it!
Tossing the traps into the sea at dusk is the easy part. Load them on the boat, find the right depth, and tip them over the side of the boat. The hard part is retrieving the traps the next day, after about 12 hours of the raw chicken scent moving through the currents. There are a number of methods we’ve used to pull the traps up, from mechanical winches, hand-powered winches, float systems, boat pulls, and of course, just pulling with one hand at a time. Invariably, something happens in each location where we are just pulling the trap up from 300 meters one meter at a time, which takes a good half hour at least. But, at least you are getting a VERY good work-out. Eventually, you see the trap and these white little orbs in it and you know you’ve caught some nautiluses and the pulling is almost done, for now.
The next step might be my favorite. One of us jumps in the water and free dives about 5 meters to carefully (ouch, that chicken wire) reach for the nautiluses in the trap and bring them to the surface. You are face to face with these uniquely, misunderstood organisms who seem like this is just another day for them. For me, this is exhilarating! Once on the boat, they are placed in chilled seawater and from then on, the data collection happens fast. With the living organism in hand, you can start to glean even more of the differences between the species, examining the hood ornaments, or lack thereof. After some photos, measurements, and non-lethal tissue samples, the nautiluses are released and burped.
Maybe nautilus burping is my favorite part. To do this, we either dive with SCUBA or free dive with the nautiluses, and ensure there are no air bubbles trapped in the shell that may cause them to be positively buoyant. Imagine, you have one nautilus in each hand and you start swimming down, your feet and the nautilus tentacles pointed toward the surface. At a sufficient depth, you release them and observe their buoyancy. As the nautiluses compose themselves and jet back down to their nektobenthic habitat 300 meters below, you realize you may never see that individual nautilus again, and that nautilus may never see another human, well, maybe they will…
For me, the impetus for this publication in ZooKeysis rooted in nautilus conservation efforts. Over the last 20 years, I have studied nautiluses from many angles and for over 10 years now, have worked with an international team of folks to address nautilus conservation issues. For many nautiluses, probably millions, they were caught in much the same way that our team collected nautiluses. However, their first meeting with humans was their last as they were pulled from the trap, ripped from their protective shell, and tossed back in the ocean, used as bait, or, rarely, consumed. The shell is the attractive piece for shell traders and the living body has no value. It is like shark finning in that sense. As a direct result of these unregulated fisheries, populations of nautiluses have crashed, some have reportedly gone extinct, and international and country level legislation and regulations has been enacted.
Currently, there are no known fisheries in Fiji, American Samoa, or Vanuatu so the risk of these populations decreasing from fisheries is low, at the moment. Now, what is the risk to these same populations from ocean acidification, increased sedimentation, eutrophication, warming seas, and over-fishing of other species connected to the ecosystem nautiluses reside in? Right now, we simply do not know. Our conservation efforts started with simply counting how many nautiluses were left in different areas across the Indo-Pacific, then recording them in their natural habitat, then tracking their migrations, and now describing new species. There are still many questions to address regarding where they lay eggs, what they eat, and how they behave.
All nautiluses have long been grouped together when describing their natural history, but as we continue to uncover the nautilus story, it is increasingly obvious that each population of nautiluses is different, as exemplified by these three new species descriptions. This is certainly an exciting time for nautilus research, as we uncover more and more information about the secret life of nautiluses. I just hope that this is also an exciting time for nautiluses as well, and they continue doing their nautilus thing as they have done for millions of years.
Invasive crayfish have the potential to cause high economic cost to artisanal fisheries in southern Africa through scavenging behaviour and destroying fish fry habitat.
A recent study by C∙I∙B Research Associate Josie South (University of Leeds, UK) with scientists from the South African Institute for Aquatic Biodiversity (SAIAB) quantified the damage caused by two invasive crayfish compared to native crab species, at two temperatures, on tilapia catch and macrophytes.
Economic costs of invasive species are vital to prioritise and incentivise management spending to reduce and restrict invasive species. No economic costs have been published for the global invader – the redclaw crayfish (Cherax quadricarinatus), and none for the entire continent of Africa. Another prolifically invasive crayfish, the red swamp crayfish (Procambarus clarkii) is also invasive in various countries of southern Africa. Anecdotal reports of crayfish scavenging from artisanal gillnet fisheries are abundant across the invasive ranges but lacked quantification. Similarly anecdotal information about macrophyte stands being destroyed by crayfish has been reported.
For their study, Josie and colleagues compared the feeding rates per gram of crayfish to that of the native Potamonautid crabs at 19°C and 28°C on simulated fisheries catch and macrophytes to identify how much damage may be caused.
The red swamp crayfish consumed the most macrophytes regardless of temperature, at a higher rate than the redclaw crayfish or crabs. In contrast, redclaw crayfish consumed the most tilapia regardless of temperature, and targeted the tail, abdomen, and fins whereas the crab only consumed the head of the fish. The damage rates of redclaw crayfish were then combined with average mass of crayfish in three invasion cores in Zambia and Zimbabwe. It was found that the damage one crayfish may cause annual fishery losses from $6.15 (Kafue River); $5.42 (Lake Kariba); and $3.62 (Barotse floodplain).
Inland fisheries contribute substantially to the livelihoods and quality of life in Africa. The two invasive crayfish have different capacities for ecological and socio-economic impact depending on the resource and the temperature which means that impact assessments should not be generalised across species.
Redclaw crayfish capacity to damage fish catch was substantial but this should be caveated with two over/under estimation issues: 1) the potential for fisher behavioural change which may reduce crayfish damage and 2) small damage to the fish may render the catch unsaleable and therefore the cost of the whole fish is lost.
Dr Josie South states that while these data are a crucial first step in filling knowledge gaps in crayfish impacts in Africa, it also stresses the need to derive observed costs from fisheries dependent data to avoid misleading estimates.
Also of concern, is the capacity for ecological and socio-economic damage from the red swamp crayfish, which was recently removed from the NEM:BA regulations of prohibited species due to lack of impact evidence.
The scholarly publisher and technology provider Pensoft welcomes the latest addition to its diverse portfolio of scholarly outlets – the open-access, peer-reviewed journal Acta Ichthyologica et Piscatoria (AIeP), which publishes research in the fields of ichthyology and fisheries.
AIeP is an international scientific journal publishing articles in any aspect of ichthyology and fisheries concerning true fishes (fin-fishes), including taxonomy, biology, morphology, anatomy, physiology, pathology, parasitology, reproduction and zoogeography. The academic outlet, which was launched in 1970, favours research based on original experimental data or experimental methods, or new analyses of already existing data. AIeP is indexed by all major indexers, including Web of Science and Scopus. The journal’s first Impact Factor was released in 2010, and currently stands at 0.629 (2019).
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Even though the short-neck clam is the major resource and export coming from Ashtamudi Lake in Kerala, India – the first fishery to be awarded with a a Marine Stewardship Council certification for sustainability in the country, a recent study found out that the mollusc had been subject to mistaken identity.
Further, this is not the first time when the species and genus name of this clam has been changed. At first, the species was identified as Paphia malabarica, which is also the name one could read in all hitherto published reports, including the Marine Stewardship Council’s register. Later on, as the name was proved to not be compliant with the current nomenclature, the Ashtamudi short-neck clam began to be referred to as Protapes gallus.
However, the latest in-depth taxonomic study points to the clam having been misidentified from the very beginning. According to the finding of the team of A. Arathi, R. Ravinesh and A. Biju Kumar of the Department of Aquatic Biology and Fisheries, University of Kerala, and Graham Oliver of National Museum Wales, United Kingdom, the Ashtamudi short-neck clam belongs to a totally different genus, while its rightful scientific name actually is Marcia recens. Their paper was published in the open access journal ZooKeys.
During their research, the scientists identified another edible species from Ashtamudi Lake that belongs to the Marcia genus: Marcia opima. While it could easily be mistaken for its commercially important relative thanks to a multitude of colour variations, it does not appear to contribute significantly to the export. Meanwhile, the actual species identified as Paphia malabarica (Protapes gallus) can be found in shallow coastal waters in the south of the country, but not in the studied brackishwater lake.
“No deleterious effects on the viability of the fishery have resulted from this error in identification, but from a legislative perspective applying the incorrect name to the exploited species could undermine its certification and protection,” comment the researchers.
“On the basis of this study, the species involved in the Marine Stewardship Council certification would be better considered at the generic level of Marcia or at the species level for Marcia recens, the most dominant species in the Ashtamudi Lake clam fishery zone.”
In conclusion, the authors of the study say that, “misidentification can undermine comparative biological studies and conservation, while more molecular studies are required to resolve the taxonomy of all clams involved in fishery.”
Arathi AR, Oliver PG, Ravinesh R, Kumar AB (2018) The Ashtamudi Lake short-neck clam: re-assigned to the genus Marcia H. Adams & A. Adams, 1857 (Bivalvia, Veneridae). ZooKeys 799: 1-20. https://doi.org/10.3897/zookeys.799.25829
While people tend to describe tropical oceanic islands as ‘paradises on Earth’ and associate them with calm beaches, transparent warm waters and marvellous landscapes, archipelagos are often the product of a fierce natural force – volcanoes which erupt at the bottom of the sea.
Because of their origin, these islands have never been connected to the mainland, thereby it is extremely difficult for species to cross the ocean and populate them.
One such species – the South American guppy (Poecilia vivipara) – is a small freshwater fish which looks nowhere equipped to cross the distance between the mainland and the Fernando de Noronha oceanic archipelago in Northeast Brazil.
To answer these questions, the scientists sequenced a gene of the guppies’ DNA to analyze potential signatures of the island colonization left in the fish DNA. As a result, they concluded that the isolated population was in fact closely related to the fish inhabiting the closest continental drainages.
However, this evidence was not enough to explain how the species turned up on the island in the first place. Was it natural colonization, or rather human introduction?
The most likely scenario, according to the team, leads back to about 60 years ago when the American military had their WWII bases positioned at both Fernando de Noronha and Natal – the closest continental city. Indeed, the soldiers suggested to bring guppies to the island in an attempt to control mosquito population (in this region, guppies are commonly placed in water reservoirs to eat mosquito larvae).
On the other hand, natural dispersion cannot be completely excluded. The biologists remind that, apart for their exuberant colours and shapes, the guppies are well known for their capacity to resist to a wide range of environmental conditions. It could be that a set of circumstances occurring together, such as a favourable sea current, physiological adaptation and a bit of luck, might have brought the guppies to the archipelago.
“Regardless of their means of transportation,” argue the authors, “this guppy population represents a valuable lesson on how small populations manage to colonize and thrive in isolated environments.”
“Despite being visited by thousands of people every year, some of the most intriguing secrets of tropical islands may still be hidden in the DNA of their inhabitants,” they conclude. “These ‘paradises on Earth’ are capable of simultaneously filling our hearts with beauty and our minds – with knowledge.”
Berbel-Filho WM, Barros-Neto LF, Dias RM, Mendes LF, Figueiredo CAA, Torres RA, Lima SMQ (2018) Poecilia vivipara Bloch & Schneider, 1801 (Cyprinodontiformes, Poeciliidae), a guppy in an oceanic archipelago: from where did it come? ZooKeys 746: 91-104. https://doi.org/10.3897/zookeys.746.20960