News Article | September 7, 2016
On the dock in Buenaventura, Colombia, the fisherman needed help identifying his catch. “I don’t have any clue what this is,” he said, holding a roughly 50-centimeter-long, grayish-brown fish. Gustavo Castellanos-Galindo, a fish ecologist, recalls the conversation from last October. “I said, ‘Well, this is a cobia, and it shouldn’t be here.’ ” The juvenile cobia had probably escaped from a farm off the coast of Ecuador that began operating earlier in 2015, Castellanos-Galindo and colleagues at the World Wildlife Fund in Cali, Colombia, reported in March in BioInvasions Records. Intruders had probably cut a net cage, perhaps intending to catch and sell the fish. Roughly 1,500 cobia fled, according to the aquaculture company Ocean Farm in Manta, Ecuador, which runs the farm. Cobia are fast-swimming predators that can migrate long distances and grow to about 2 meters long. The species is not native to the eastern Pacific, but since the escape, the fugitives have been spotted from Panama to Peru. The cobia getaway is not an isolated incident. Aquaculture, the farming of fish and other aquatic species, is rapidly expanding — both in marine and inland farms. It has begun to overtake wild-catch fishing as the main source of seafood for the dinner table. Fish farmed in the ocean, such as salmon, sea bass, sea bream and other species, are raised in giant offshore pens that can be breached by storms, predators, fish that nibble the nets, employee error and thieves. Global numbers for escapes are hard to come by, but one study of six European countries over three years found that nearly 9 million fish escaped from sea cages, according to a report published in Aquaculture in 2015. Researchers worry that these releases could harm wildlife, but they don’t have a lot of data to measure long-term effects. Many questions remain. A study out of Norway published in July suggests that some domesticated escapees have mated extensively with wild fish of the same species, which could weaken the wild population. Scientists also are investigating whether escaped fish could gobble up or displace native fish. Worst-case scenario: Escaped fish spread over large areas and wreak havoc on other species. From toxic toads overrunning Australia and Madagascar (SN Online: 2/22/16) to red imported fire ants in the United States, invasive species are one of the planet’s biggest threats to biodiversity, and they cost billions of dollars in damage and management expenses. Not every introduced species has such drastic effects, but invasives can be tough to eliminate. While researchers try to get a handle on the impact of farm escapes, farmers are working to better contain the fish and reduce the ecological impact of the runaways. Some countries have tightened their aquaculture regulations. Researchers are proposing strategies ranging from new farm designs to altering fish genetics. As aquaculture becomes a widespread means to feed the planet’s protein-hungry people, the ecological effects are getting more attention. If escapees weaken native wildlife, “we’re solving a food issue globally and creating another problem,” says population geneticist Kevin Glover of Norway’s Institute of Marine Research in Bergen. Norway, a top producer of marine fish, has done much of the research on farm escapes. Fish farming is big business. In 2014, the industry churned out 73.8 million metric tons of aquatic animals worth about $160 billion, according to a report in July from the Food and Agriculture Organization of the United Nations in Rome. Nearly two-thirds of this food comes from inland freshwater farms such as ponds, used in Asia for thousands of years. The rest is grown on marine and coastal farms, where farmed fish live in brackish ponds, lagoons or cages in the ocean. Freshwater fish can escape from pond farms during events such as floods. Some escapees, such as tilapia, have hurt native species by competing with and eating wild fish. But sea farming has its own set of problems. The physical environment is harsh and cages are exposed to damaging ocean waves and wind, plus boats and predator attacks. Salmon is one of the most heavily farmed marine fish. In some areas, the number of farmed salmon dwarfs wild populations. Norway’s marine farms hold about 380 million Atlantic salmon, while the country’s rivers are home to only about 500,000 wild spawning Atlantic salmon. In the four decades that farmers have been cultivating Atlantic salmon, farmed strains have diverged from their wild cousins. When both are raised in standard hatchery conditions, farm-raised salmon can grow about three to five times heavier than wild salmon in the first year of life. Salmon raised in farms also tend to be less careful; for instance, after being exposed to an artificial predator, they emerge more quickly from hiding places than wild fish. This risky behavior may have arisen partly because the fish haven’t faced the harsh challenges of nature. “The whole idea of a hatchery is that everything gets to survive,” says Philip McGinnity, a molecular ecologist at University College Cork in Ireland. Farmed fish don’t know better. These differences are bad news for hybrid offspring and wild fish. In early experiments, hybrid offspring of farmed and wild salmon tended to fare poorly in the wild. In the 1990s, McGinnity’s team measured these fish’s “lifetime success” in spawning rivers and the ocean. Compared with wild salmon, hybrid offspring had a lifetime success rate about a fourth to a half as high. Around the same time, a team in Norway found that when wild fish swam with farmed fish in their midst, the number of wild offspring that survived long enough to leave the river to head to the ocean was about one-third lower than expected, perhaps because the fast-growing farmed offspring gobbled a lot of food or claimed territory. “There was truly reason to be concerned,” says Ian Fleming, an evolutionary ecologist at Memorial University of Newfoundland in St. John’s, Canada, who was part of the Norway team. Recent work supports the idea that farmed fish could crowd out wild fish by hogging territory in a river. In a study published last year in the Journal of Fish Biology, researchers found that the survival rate of young wild salmon dropped from 74 to 53 percent when the fish were raised in the same confined stream channels as young farmed salmon rather than on their own. When the channels had an exit, more wild fish departed the stream when raised with farmed salmon than when raised alone. “These are fish that give up the territory and have to leave,” says study coauthor Kjetil Hindar, a salmon biologist at the Norwegian Institute for Nature Research in Trondheim. To find out how much escaped fish had genetically mingled with wild fish, Glover’s team obtained historical samples of salmon scales collected from 20 rivers in Norway before aquaculture became common. The researchers compared the DNA in the scales with that of wild salmon caught from 2001 to 2010 in those rivers. Wild salmon in five of the 20 rivers had become more genetically similar to farmed fish over about one to four decades, the team reported in 2013 in BMC Genetics. In the most affected population, 47 percent of the wild fish’s genome originated from farmed strains. “We’re talking about more or less a complete swamping of the natural gene pool,” Glover says. Imagine buckets of paint — red, blue, green — representing each river, he says, and pouring gray paint into each one. Interbreeding was less of an issue where wild fish were plentiful. The farmed fish aren’t good at spawning, so they won’t mate much if a lot of wild competitors are present. But in sparse populations, the farm-raised salmon may be able to “muscle in,” Glover says. A larger study by Hindar’s team, published in July in the ICES Journal of Marine Science, showed that genetic mixing between wild and farmed salmon is happening on a large scale in Norway. Among 109 wild salmon populations, about half had significant amounts of genetic material from farmed strains that had escaped. In 27 populations, more than 10 percent of the fish’s DNA came from farmed fish. What does that mean for the offspring? Each salmon population has adapted to survive in its habitat — a certain river, at a specific temperature range or acidity level. When farmed fish mate with wild fish, the resulting offspring may not be as well-suited to live in that environment. Over generations, as the wild population becomes more similar to farmed salmon, scientists worry that the fish’s survival could drop. Scientists at several institutions in Norway are exploring whether genetic mixing changes the wild salmon’s survival rates, growth and other traits. Making a definitive link will be difficult. Other threats such as climate change and pollution also are putting stress on the fish. If escapes can be stopped, wild salmon may rebound. Natural selection will weed out the weakest fish and leave the strongest, fish that got a lucky combination of hardy traits from their parents. But Glover worries that, just as a beach can’t recover if oil is spilled every year, the wild population can’t rally if farmed fish are continually pumped in: “Mother Nature cannot clean up if you constantly pollute.” In places where the species being farmed is not naturally abundant, researchers are taking a look at whether escapes could upset native ecosystems. For instance, European sea bass sometimes slip away from farms in the Canary Islands, where (except for a few small populations on the eastern end) the species doesn’t normally live. In February 2010, storms battered cages at the island of La Palma, “like a giant tore up all the nets,” says Kilian Toledo-Guedes, a marine ecologist at the University of Alicante in Spain. About 1.5 million fish — mostly sea bass — reportedly swam free. A couple of weeks later, the number of sea bass in nearby waters was “astounding,” he says. “I couldn’t see the bottom.” Sea bass density in waters near the farm was 162 times higher than it had been at the same time the previous year, his team reported in 2014 in Fisheries Management and Ecology. Fisheries data showing a spike in catches of sea bass by local fishermen that January also suggested that large unreported escapes had occurred before the storm. Despite being raised in captivity, where they are fed pellets, some of the farmed fish learn to hunt. The researchers found that escaped sea bass caught four months after the 2010 farm breakdown had eaten mostly crabs. Sea bass from earlier escapes that had been living in the wild for several years had eaten plenty of fish as well. The results, reported in 2014 in Marine Environmental Research, suggest that escapees start by catching easy targets such as crustaceans and then learn to nab faster-moving fish. So far, though, scientists have not seen clear signs that the escapees damaged the ecosystem. The density of sea bass around La Palma had fallen drastically by October 2010 and continued to decline the next year, probably because some fish couldn’t find enough to eat, while others were caught by fishermen or predators, according to a 2015 study by another team in the Journal of Aquaculture Research & Development. Catches of small fish that sea bass eat, such as parrot fish, did not drop significantly after the 2010 escape or after a similar large escape in 1999, says study coauthor Ricardo Haroun, a marine conservation researcher at the University of Las Palmas de Gran Canaria in Spain. While he agrees that the industry should try to prevent escapes, he sees no evidence that the runaways are suppressing wild species. If the escaped fish can breed and multiply, the risk of harming native species rises. In a study published in Marine Ecology in 2012, Toledo-Guedes and colleagues reported finding sexually mature sea bass around the central island of Tenerife. But Haroun says the water is too warm and salty for the fish to reproduce, and his team did not see any juveniles during their surveys of La Palma, nor have they heard any reports of juveniles in the area. Toledo-Guedes says that more extensive studies, such as efforts to catch larvae, are needed before reproduction can be ruled out. Similarly, researchers can’t predict the consequences of the cobia escape in Ecuador. The water is the right temperature for reproduction, and these predators eat everything from crabs to squid. Castellanos-Galindo believes that farming cobia in the area is a mistake because escapes will probably continue, and the fish may eventually form a stable population in the wild that could have unpredictable effects on native prey and other parts of the ecosystem. He points to invasive lionfish as a cautionary tale: These predators, probably released from personal aquariums in Florida, have exploded across the Caribbean, Gulf of Mexico and western Atlantic and are devouring small reef fish. The situation for cobia may be different. Local sharks and other predators will probably eat the escapees, whereas lionfish have few natural predators in their new territory, argues Diego Ardila, production manager at Ocean Farm. Milton Love, a marine fish ecologist at the University of California, Santa Barbara, also notes that lionfish settle in one small area, but cobia keep moving, so prey populations might recover after the cobia have moved on. Not all introduced species become established or invasive, and it can take decades for the effects to become apparent. “Time will tell what happens,” says Andrew Sellers, a marine ecologist at the Smithsonian Tropical Research Institute in Panama City. “Basically, it’s just up to the fish.” Once fish have fled, farmers sometimes enlist fishermen to help capture the escapees. Professional fishermen caught nearly one-quarter of the sea bass and sea bream that escaped after the Canary Islands breach. On average, though, only 8 percent of fish are recaptured after an escape, according to a study published in June in Reviews in Aquaculture. Given the recapture failures, farmers and policy makers should focus on preventing escapes and maintaining no-fishing zones around farms to create a “wall of mouths,” local predators that can eat runaway fish, says coauthor Tim Dempster, a sustainable aquaculture researcher at the University of Melbourne in Australia. Technical improvements could help. The Norwegian government rolled out a marine aquaculture standard in 2004 that required improvements, such as engineering nets, moorings and other equipment to withstand unusually strong storms. Compared with the period 2001–2006, the average number of Atlantic salmon escaping annually from 2007–2009 dropped by more than half. Ocean Farm in Ecuador has tightened security, increased cage inspections and switched to stronger net materials; no cobia have escaped since last year’s break-in, says Samir Kuri, the company’s operations manager. Some companies raise fish in contained tanks on land to avoid polluting marine waters, reduce exposure to diseases and control growth conditions. But the industry is largely reluctant to adopt this option until costs come down. The money saved from reducing escapes probably wouldn’t make up for the current start-up expense of moving to land. The 242 escape events analyzed in the 2015 Aquaculture study cost farmers about $160 million. By one estimate, establishing a land-based closed-containment farm producing about 4,000 metric tons of salmon annually — a small haul by industry standards — would cost $54 million; setting up a similar-sized sea-cage farm costs $30 million. Another solution is to raise fish that have three sets of chromosomes. These triploid fish, produced by subjecting fertilized eggs to a pressure shock, can’t reproduce and therefore wouldn’t proliferate or pollute the wild gene pool. “The only ultimate solution is sterility,” Norway’s Glover says. “Accidents happen.” Escaped triploid salmon are less likely to disrupt mating by distracting females from wild males, the researchers wrote in Biological Invasions in May. But triploid fish don’t grow as well when the water is warmer than about 15° Celsius, and consumers might be reluctant to accept these altered salmon. Although the ecological effects of fish farm escapes may take a long time to play out, most researchers agree that we shouldn’t take chances with the health of the oceans, which already face threats such as climate change, pollution and overfishing. With the aquaculture industry expanding at about 6 percent per year, farmers will have to keep improving their practices if they are to stay ahead of the runaway fish. This story appears in the September 17, 2016, issue of Science News with the headline, "Runaway fish: Escapes from marine farms raise concerns about native wildlife."
News Article | March 4, 2016
For a few weeks in early fall, Georges Bank — a vast North Atlantic fishery off the coast of Cape Cod — teems with billions of herring that take over the region to spawn. The seasonal arrival of the herring also attracts predators to the shallow banks, including many species of whales. Now researchers from MIT, Northeastern University, the Institute of Marine Research in Norway, and the National Oceanic and Atmospheric Administration, have found that as multiple species of whales feast on herring, they tend to stick with their own kind, establishing species-specific feeding centers along the 150-mile length of Georges Bank. The team’s results are published today in the journal Nature. Based on acoustic data they collected in the region in 2006, the researchers identified and mapped the calls of various whales, and discovered a clear grouping of species within the dense herring shoals: Humpback whales congregated in two main clusters, at either end of the spawning grounds, while minke, fin, and blue whales set up feeding territories in the space in between. In general, calls from each whale species increased dramatically at nighttime, when herring tended to form extremely dense shoals. During the day, these whale calls dissipated, as herring scattered throughout the seafloor. These results represent the first time that scientists have observed such predator and prey interactions over a large marine region. “It’s known that different marine mammal species will eat fish, but no one has mapped their simultaneous feeding distributions over these huge scales,” says Purnima Ratilal PhD ’02, associate professor of electrical and computer engineering at Northeastern University. “Maybe there is some territorialism going on, or maybe they are preferentially selecting these locations based on their different foraging mechanisms. That’s material for new research.” Ratilal and her husband, Nicholas Makris, professor of mechanical engineering at MIT, along with their students, are co-authors of the paper. In 2006, Makris and Ratilal led a two-week cruise to Georges Bank, initially to track and study the behavior of populations of herring, which can number in the billions within a single shoal. The team had developed a remote-sensing system that uses acoustics to instantaneously image and continuously monitor fish populations over tens of thousands of square kilometers. Unlike conventional technologies, their system uses the ocean as a waveguide through which acoustic waves can travel over much greater distances, to sense the marine environment. To get a much wider, more detailed view of the herring populations, Makris and Ratilal deployed 160 hydrophones during their 2006 cruise, towing the array, like a “big acoustic antenna,” in and around Georges Bank. Using their ocean acoustic waveguide sensing technique, they mapped the evolving shoals over the two-week period in October. During that cruise, the group remembers hearing distinct sounds coming through the ship’s hull. “We were hearing these strange haunting sounds in the galley, like an upsweep, then a down-sweep,” Makris recalls. “Purnima recognized these were whale calls, and had all the characteristics of a classic humpback song. At that point she started the research that led to the current paper in Nature, which she spearheaded.” Makris notes that such whale calls have been heard through the hulls of ships for thousands of years. “The Patogonian Indians even had a name for them: 'Yakta,’” Makris says. “People had been listening to these sounds for a very long time, and it’s really this century that we’re starting to localize and observe their behavior.” The group continued looking through the data, even after they had analyzed them for herring signals, to look this time for whale calls. The team developed a technique to sift through the acoustic data for interesting signals — a method called passive ocean acoustic waveguide remote sensing (POAWRS). Through the years, the team gathered research on the characteristics of certain whale species’ calls and looked for these characteristics in their acoustic data. They eventually identified several hundred thousand calls, mostly along the northern edge of Georges Bank. “Different marine mammals in the ocean produce different sounds, sort of related to their size,” Ratilal says. “Humpbacks have a distinct song, while some species of tooth whales can sound like birds chirping.” “Fin whale calls, on the other hand, are in the register of a bass guitar,” Makris adds. The researchers located the source of each call by triangulation and other methods unique to waveguides, and found that the call rates of four main species of whales observed — humpback, sei, minke, and blue — tended to go up significantly at night, possibly in response to the increasing number of herring. “Spawning herring typically don't form big shoals during daytime because it’s too risky they can get caught more easily,” Makris notes. “So they form just as the sun goes down. That’s when the whale calls start going wild and begin to come from on top of the shoals.” These calls were concentrated in species-specific “hotspots,” with humpback whale calls bookending the other three species, all along the northern length of Georges Bank. The group found that humpbacks in particular emitted a distinct pattern of calls that may indicate a cooperative feeding ritual, which others have observed. “The whales will circle the herring, and then one will blow a bubble to contain the fish group, and another will scream and scare the fish into a tight ball,” Ratilal says. “Then another will give a signal, and they’ll all come up with their jaws open.” Jeff Simmen executive director of the Applied Physics Laboratory at the University of Washington, says that for the most part, technologies used to observe marine ecosystems are unable to localize fish and marine mammals at the same time. In contrast, Makris and Ratilal’s approach “provides unusual insight into the macroscopic behavior of marine populations.” “In short, the methodology provides a new and grand view of marine populations that will lead to completely new perspectives about the marine ecosystem, perhaps in a similar way that the enhanced views from the Hubble Space Telescope have changed our perspectives on the universe,” Simmen says. Going forward, the team hopes to tease out more marine behaviors in their dataset. “With this technology, you can really sense a lot of things,” Makris says. “Fish and marine mammals are just two examples.” Ratilal adds, “There are quite a few other interesting phenomena in our dataset.” This research was supported, in part, by the Ocean Acoustics Program of the Office of Naval Research, the National Science Foundation, the National Oceanographic Partnership Program, the Alfred P. Sloan Foundation, and is a contribution to the Census of Marine Life.
News Article | December 15, 2015
For a second straight year, the Arctic is warming faster than any other place in the world, and walrus populations in the area’s Pacific and Atlantic ocean regions are thinning along with the ice sheets that are critical for their survival, researchers reported Tuesday. Overall, the outlook for the frozen top of the world is bleak, according to the annual Arctic Report Card: 2015 Update released by the federal National Oceanic and Atmospheric Administration. Since the turn of the last century, it said, the Arctic’s air temperature has increased by more than 5 degrees due to global warming. Warmer air and sea temperatures melt ice that in turn expands oceans and causes sea-level rise, which scientists say presents a danger to cities along the entire Atlantic coast, from Miami to Washington to Boston. Walrus and other arctic mammals that give birth on ice sheets are struggling with the change, and fish such as cod and Greenland halibut are swimming north from fishermen and animals that feed on them in pursuit of colder waters. [The Arctic keeps warming. And polar bears are feeling the heat] NOAA chief scientist Richard Spinrad said changes in the Arctic portend changes that are likely to spread to the wider world — higher air temperatures, longer hot seasons, anomalous weather spikes and fish fleeing north only to be replaced by new species swimming from areas south. “The conclusion that comes to my mind is these report cards are trailing indicators of what’s happening in the Arctic. They can turn out to be leading indicators for the rest of the globe,” Spinrad said. The annual average surface-air temperature over the period of the report, between October 2014 and September 2015, was nearly 2.5 degrees higher than the time period scientists use as a baseline to compare temperatures, 1981 to 2010. As a result, Alaska was warmer in fall 2014 and winter this year, when the snow pack that usually melts to replenish rivers and moisten the earth was extremely low. Lightning strikes on dry land sparked that state’s second-worst wildfire season in its history. According to the NOAA report card, “the 2015 spring melt season provided evidence of earlier snow melt across the Arctic” because of the increased warmth. As of early July, the Arctic melt included more than half of the region’s ice sheet for the first time “since the exceptional melt of 2012.” The length of the melt season was up to 4o days longer than that of the average northwestern, northeastern and western regions, the report said. This year’s findings are largely consistent with the dire findings last year. Dozens of scientists from across the world contribute to the report card, including those from U.S. Naval Research and the Army Corps of Engineers, the Institute of Marine Research in Norway, Knipovich Polar Research Institute of Marine Fisheries and Oceanography in Russia and University of Victoria in Canada. [A stunning five million acres have burned in Alaskan wildfires this year] The report cards’ year-to-year consistency will help scientists establish whether they are watching a weather anomaly in a key part of the world or an established trend. “What you see here is stronger confirmation,” Spinrad said. A separate study focusing on Alaska’s North Slope, which was presented late Tuesday at the fall meeting of the American Geophysical Union, estimates that the permafrost there will decline rapidly over time because of rising temperatures. Vladimir Romanovsky, head of the Permafrost Laboratory at the University of Alaska Fairbanks, said thinning permafrost is already causing roads and houses built on it to crumble. “Under these conditions, the permafrost will become unstable beneath any infrastructure such as roads, pipelines and buildings,” Romanovsky said. “The result will be dramatic effects on infrastructure and ecosystems.” Another researcher at the university, Santosh Panda, said permafrost that covers virtually all of five national parks as large collectively as South Carolina could decline by 10 percent within the next 35 years. “Permafrost degradation is going to touch the whole landscape through changes in water distribution, slope failures and changes in vegetation that will affect wildlife habitat and the aesthetic value of the parks,” Panda said. In the Arctic, the age of ice generally defines the region’s health. Older ice is thicker, more resilient and resistant to atmospheric changes, and better at supporting mammals. Younger ice is thin and vulnerable to collapse. Yet in nearly all Arctic regions, sea ice is decreasing, the report said. In 1985, 85 percent of the region’s ice qualified as old. In March, that fell to 30 percent. “This is the first year that first-year ice dominated the ice cover,” it notes. “Sea ice cover has transformed from a strong, thick pack in the 1980s to a more fragile, thin and younger pack in recent years.” [The collapse of the Antarctic ice sheet is underway and unstoppable, but will take centuries] Walruses are starting to teem on land as the ice fades, exposing their young to frequent trampling events. Walruses mate on the edges of ice, and females prefer giving birth and raising pups on old ice, which they use as a base to reach feeding grounds. Now many are on land, and the long path to the feeding areas are filled with animals that prey on them, such as sharks and orcas. That is further reducing walrus numbers, the U.S. Fish and Wildlife Service concluded in its section of the report. Ice melt “is already a pervasive threat” to walrus, the agency’s researchers said, but how much of a threat depends on the ability of animals to adapt to change, tolerate it or flee it for more suitable habitat. Scientists estimate that Pacific walrus populations have fallen by half as a result of declining sea ice and hunting. The Atlantic stock, reduced by 80 percent through unregulated hunting between 1900 and 1960, is unknown, but estimates put the population at 25,000. The world just adopted a tough new climate goal. Here’s how hard it will be to meet Holding warming under two degrees Celsius is the goal. But is it really attainable? For more, you can sign up for our weekly newsletter here, and follow us on Twitter here.
Cardinale M.,Institute of Marine Research |
Nugroho D.,Agency for Marine and Fisheries Research |
Jonson P.,Institute of Marine Research
Fisheries Research | Year: 2011
Pelagic fish stocks in the Java Sea have declined since the beginning of the 1990s and are nowadays at the lowest observed level. The fishery exploiting those stocks has essentially been unregulated and historically driven by market demands. This constitutes an ideal example to test the hypothesis of serial depletion of fishing grounds in an open-access fishery. Here we show that different fishing grounds were successively depleted depending on the distance from the harbor and the commercial importance of the species. Closest fishing grounds were depleted first, while the most distant ones where the last to be affected. The spatio-temporal trend in effort showed a decrease for the closest fishing grounds and an increase for the most distant ones over time. To our knowledge, this is the first data driven example of the " serial depletion phenomenon" in harvesting marine resources, where the harvesters successively exploit, deplete and finally abandon traditional fishing grounds with increasing distance from the harbor and economical importance of the species. © 2010 Elsevier B.V.
Polgar G.,University of Malaya |
Bartolino V.,Institute of Marine Research
Marine Ecology Progress Series | Year: 2010
Reduction in size from sea to land is a common trend of many fish species and communities, at both the intraspecific and interspecific level. Within the intertidal zone, similar trends have been described at the intraspecific level in several transient and resident fish species. Oxudercines are a group of intertidal gobies (Gobiidae: Oxudercinae) including several species, which exhibit extreme adaptations to an amphibious lifestyle. Ecomorphological and ecophysiological considerations suggest that size reduction in this group may have facilitated the adaptation to semi-terrestrial conditions. To test this hypothesis, the spatial ecology and the presence of an intra- and interspecific size gradient was investigated in an oxudercine community of a Malayan intertidal ecosystem (6 species included in 3 genera). A random stratified sampling design was adopted, and ANOVA and cluster analysis performed to describe this variation. Multivariate analyses of the quantity of environmental water were also conducted to investigate the correspondence between size and habitat terrestriality. Larger species were found in more aquatic conditions at lower topographical levels along the vertical intertidal gradient, supporting the hypothesis of an adaptive value of smaller size in more terrestrial habitats. Intraspecific variation showed more complex patterns, even if in several species smaller individuals were found in more terrestrial conditions. © Inter-Research 2010.
Casini M.,Institute of Marine Research |
Bartolino V.,Institute of Marine Research |
Molinero J.C.,Leibniz Institute of Marine Science |
Kornilovs G.,Latvian Fish Resources Agency
Marine Ecology Progress Series | Year: 2010
How multiple stressors influence fish stock dynamics is a crucial question in ecology in general and in fisheries science in particular. Using time-series covering a 30 yr period, we show that the body growth of the central Baltic Sea herring Clupea harengus, both in terms of condition and weight-at-age (WAA), has shifted from being mainly driven by hydro-climatic forces to an interspecific density-dependent control. The shift in the mechanisms of regulation of herring growth is triggered by the abundance of sprat, the main food competitor for herring. Abundances of sprat above the threshold of ̃18 × 10 10 ind. decouple herring growth from hydro-climatic factors (i.e. salinity), and become the main driver of herring growth variations. At high sprat densities, herring growth is considerably lower than at low sprat levels, regardless of the salinity conditions, indicative of hysteresis in the response of herring growth to salinity changes. The threshold dynamic accurately explains the changes in herring growth during the past 3 decades and in turn contributes to elucidate the parallel drastic drop in herring spawning stock biomass. Studying the interplay between different stressors can provide fundamental information for the management of exploited resources. The management of the central Baltic herring stock should be adaptive and take into consideration the dual response of herring growth to hydro-climatic forces and food-web structure for a sound ecosystem approach to fisheries. © Inter-Research 2010.
Svedang H.,Institute of Marine Research |
Stal J.,Gothenburg University |
Sterner T.,Gothenburg University |
Cardinale M.,Institute of Marine Research
Reviews in Fisheries Science | Year: 2010
This study shows how cod subpopulations may have been eradicated as a consequence of the use of imperfect models for assessing stock assessment, depleting what was formerly a productive sea. The Kattegat and Öresund (North Sea) were chosen as study objects due to the combination of different exploitation patterns and the possible existence of separate stock units. The scenario was further elaborated by simulating the potential harvest of fishing for different long-run levels of fishing effort as well as stock size. The study clearly indicated that new policy instruments are needed but these instruments need to be carefully fine-tuned to take into account real biological as well as social factors. © Taylor and Francis Group, LLC.
Petchey O.L.,University of Sheffield |
Belgrano A.,Institute of Marine Research
Biology Letters | Year: 2010
The sizes of individual organisms, rather than their taxonomy, are used to inform management and conservation in some aquatic ecosystems. The European Science Foundation Research Network, SIZEMIC, facilitates integration of such approaches with the more taxonomic approaches used in terrestrial ecology. During its 4-year tenure, the Network is bringing together researchers from disciplines including theorists, empiricists, government employees, and practitioners, via a series of meetings, working groups and research visits. The research conducted suggests that organismal size, with a generous helping of taxonomy, provides the most probable route to universal indicators of ecological status. © 2010 The Royal Society.
Cardinale M.,Institute of Marine Research |
Svedang H.,Swedish Institute for the Marine Environment
Marine Ecology Progress Series | Year: 2011
The Baltic Sea ecosystem is hypothesized to have undergone a regime shift during the last 3 decades, altering its functioning and the composition of its zooplankton and fish communities. The new stable state has been considered as 'cod hostile' due to reduced spawning success in cod, as well as increased predation on and declining food sources for cod larvae. Nonetheless, the eastern Baltic cod stock has recently recovered after more than 2 decades of low biomass and productivity. The recovery was mainly driven by a sudden reduction in fishing mortality and occurred in the absence of any exceptionally large year classes. The recovery of the cod stock during a 'cod-hostile' ecological regime indicates that fisheries are the main regulator of cod population dynamics in the Baltic Sea. © Inter-Research 2011.
Madsen N.,Technical University of Denmark |
Valentinsson D.,Institute of Marine Research
ICES Journal of Marine Science | Year: 2010
The spawning-stock biomass of cod (Gadus morhua) in the Kattegat area is at a historically low level. Throughout the past decade considerable efforts have been devoted to research on improving both species and size selectivity of the trawls used in the mixed demersal fishery in the area, because this provides a valuable management tool for reducing the bycatch of cod and reducing mortality, and thus helping to rebuild the depleted stock. Gear research in the area has been focused on devices that allow for continued exploitation of the Norway lobster (Nephrops norvegicus) and flatfish, but minimizing the bycatch. We review the results of previous and continuing experiments with various codend mesh sizes, mesh configurations, escape windows, sorting grids, sorting frames, and separator panels, but also changes in whole-trawl designs. Based on our review, we compare and discuss the gear-related technical measures and their effectiveness in maintaining a commercial fishery on viable stocks, yet protecting cod. We discuss the results in relation to changes in legislation and experience with implementation of new selective devices in recent years. We also discuss ways to create stronger incentives for fishers to participate in gear research and to increase acceptance of more selective gears. © 2010 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.