In a world’s first, a mating pair of anglerfish is observed in the wild, evoking awe in SAFS professor Ted Pietsch, who comments in UW Today on the video footage by researchers Kirsten and Joachim Jakobsen aboard a submersible run by the Rebikoff-Nigeler Foundation. Only 14 females (and no males) of this species have ever been recorded, all collected in jars and none observed alive in the ocean. Anglerfish males are tiny compared to females: females may be 60 times longer and half a million times heavier than males. Males have enormous eyes and huge nostrils to detect the specific chemicals exuded by females. When a male finds a female, they bite onto and fuse with the female, relying entirely on the female to feed them, while supplying sperm in return. The species observed in the video is the Fanfin Seadevil (Caulophryne jordani) which has enormously elongated fin rays that look a bit like an array of tentacles, each laced with blinking lights, perhaps to attract unwary prey closer to the “fishing lure” hanging above the mouth of the female anglerfish.
Old-growth fishes are going missing through fishing
In 2011, National Marine Fisheries Service announced the end of overfishing in the U.S. This achievement was considered an important milestone for fishery management. Six years later, a study in Current Biology by Dr. Lewis Barnett (previous postdoctoral researcher) and Prof. Trevor Branch from School of Aquatic and Fishery Sciences revealed a significant decline of old-growth fishes around globe, including the U.S. Their findings revealed some potential risks in marine ecology and sustainable fisheries. Old age is not something fish can avoid, any more than people. In fact, many marine fish species exhibit extremely long-life spans. Just imagine a 100-year-old white sturgeon and a 150-year-old rougheye rockfish swimming through the sea together, beguiling the twilight time of their lives.
Increasing body sizes of many fish species have been associated with lower risks of predation. The size-dependent processes result in decreasing natural mortality as fish grow older and larger. Fishing, however, generally selects for larger, older fish, imposing a selection pressure that works opposite to natural mortality. As Branch explains, “the young fishes are reduced mainly through natural mortality, but the older groups are more likely to be jeopardized under both natural and fishing mortality.” Because of cumulative mortality sources throughout their lives, the number of older fishes may suffer a rapid decrease even at a moderate level of fishing, that would usually be considered to be sustainable.
The study examined 63 fished populations across five ocean regions, and reported that the portion of fish in the oldest age groups has declined significantly. Compared to historical data, almost 80% of the population have lost their old cohorts; the rate went up to 97% in comparison to unfished values. In terms of the magnitude of decline, close to half of the populations suffered a 90% decrease of their old-growth members. As the study pointed out, the widespread removal of old fishes via fishing may put the long-term community stability and sustainable fishery at risk.
- Reduce productivity
The decrease of old fishes may cause declines in birth rate and offspring survival rate. This is due to the crucial differences in reproductive ability between the old and young spawning females. Larger (and presumably older) fishes can produce higher quality and quantity eggs than their younger counterparts. In addition, their offspring may have a higher survive rate related to the fecundity of their mothers. Finally, because older fishes generally spawn earlier than younger ones, elimination of older age classes through fishing will effectively shorten the spawning season and reduce productivity.
- Cause sensitivity to environmental variability
The missing old-growth fish will cause the population to be more sensitive to future environmental change. “It’s like an insurance policy,” explains Branch, “the existence of old growth fish allow the population to persist during adverse climate conditions, when regular recruitment is essentially absent.” Also, because the offspring of older fish are more likely to survive, they can compensate the population under bad and extreme environmental conditions. Missing old fishes may destroy both “storage insurance” and “recruitment compensation”, and thereby hurt the stability and persistence of a population in bad or extreme situations.
- Reduce life-history diversity
Scarcity of old fish would also reduce the life-history diversity, which is often related to the age and size of individual species. For example, there are age-related differences in the timing and location of spawning, movements and migration. These varieties spread the population out so that it can cope with variable environmental conditions, thereby reducing the probability that all individuals in the species encounter unfavorable conditions. Meanwhile, some fish may eat differently as they grow age, and these diet shifts would benefit the stabilization of the food webs. The diversity within the species can decrease their risk of extinction. Missing old fish narrows the range of age structure and will inevitably jeopardize the diversity and stability of the fish community.
Current fisheries management is based on maintaining spawning biomass. But as the study implies, we may need to do more to help save older fishes. One option is to limit harvesting to specific size and weight ranges, so that extremely young and old fishes could be protected from commercial fisheries. But this approach has its limitations in practice. For many fish species living in deep waters, even though fishers can pick them out of each haul and throw back to the sea, they may die when brought up to the ocean surface.
For the species with limited mobility, like oysters and clams, or some fishes that live near coral reefs, rotational harvests are another option. By rotating through a small number of fishing grounds each year, fish will always have the opportunity to grow larger and older. “For some specific species, like geoduck, people bid auctions for the harvesting,” as Branch recalls, “this can also help us better monitor and manage the rotational harvest.”
Another suggestion is to establish marine reserves, preventing fish harvest for certain regions. This may help boost population and bring back old cohorts effectively.
Limits to overfishing are certainly worth celebrating. However, it is also worth noting that the stock assessments might not be adequate to represent the true situation for fishes that exhibit complex age structure. The scarcity of old-growth fishes is not a good sign, and the fight for sustainable fisheries is not over.
This post was written by Zhengxin Lang out of the FISH 507 course on science blogging, instructed by SAFS Professors Julian Olden and Steven Roberts.
Why do some species associate together? Habitat is the key, not randomness
The species found in a particular place (“species assemblages”) differ from those found in other places, and figuring out why this is so has occupied the minds of ecologists since the mid-20th century. Currently two theories dominate: the niche theory, and the neutral theory. The niche theory holds that species assemblages result from species migrating into a particular place, and then either thriving or leaving based on how good of a match they are to the habitat and other living organisms (the “niche”) in that place. In contrast, neutral theory predictions of species assemblages assume that each species has similar fitness and purely random processes determine which species end up in a particular place. In a new paper, assemblages of small, cryptic fish species in the Indo-Pacific were examined to test whether niche theory or neutral theory best explains patterns in species association. The results strongly support niche theory: species in each broad region contribute to the assemblages, but the distinct microhabitat preferred by individual species has a strong influence on species assemblages. The research is published in the journal Coral Reefs by Gabby Ahmadia, SAFS professor Luke Tornabene, David Smith, and Frank Pezold.
To reduce human infections, control the snails
Schistosomiasis (also known as billharzia) is a parasitic flatworm that infects a quarter of a billion people worldwide, mostly in tropical countries. If left untreated, it causes chronic pain and diseases of the liver and kidney, and kills up to 200,000 people annually. In recent years, control of the disease has focused on mass-treating humans with a drug called praziquantel, instead of reducing the prevalence of snails that are a required part of the parasite’s life cycle. A new study now shows a strong relation between elimination of schistosomiasis and control of the snails, instead of using drug treatments that are unable to prevent reinfection when people enter streams and lakes containing the parasite-infested snails. For example, in 1994 Japan completely eliminated schistosomiasis from their entire country through a sustained snail control effort, while some countries relying purely on drug treatment of humans have seen little reduction in disease prevalence. The scientists authoring the study, which include SAFS professor Chelsea Wood, urge a rethink in global strategy that focuses more on snail control to reduce the disease burden of schistosomiasis. The work appears in the journal Trends in Parasitology.
Fewer big and old Chinook salmon in the Pacific
Chinook salmon (king salmon) are the most prized salmon in the Pacific because of their large size. But now an analysis shows that the oldest Chinook salmon are disappearing, and their size is also declining, and these patterns are seen from California to western Alaska and in both wild and hatchery Chinook salmon. The research by SAFS researchers Jan Ohlberger and Daniel Schindler, and their coauthors Eric Ward and Bert Lewis, appears in the journal Fish and Fisheries, and was highlighted in UW News.
An overlooked carbon source to an important freshwater fishery may be under threat
By Ben Miller, SAFS student
When you first arrive at the community of Kampong Phluk, your neck cranes up bamboo stilts to meet the chatter of families in houses high above. From the top of what guidebooks call “bamboo skyscrapers,” locals gaze over the tops of submerged trees, a glittering, island Buddhist temple, and clusters of floating fishing villages in the distance. This is the shoreline of Tonlé Sap Lake, or “The Great Lake,” a landscape in which the boundaries between land and water are constantly shifting.
Located in the center of Cambodia, Tonlé Sap Lake is part of a much larger lower Mekong watershed. Each year, the monsoon increases water levels in the Mekong by up to 15 meters. This increases discharge from six Olympic-sized swimming pools to 16. Per second. As all of that water flows downriver, past Laos, Thailand, Cambodia, and the delta in Vietnam, it backs up at the edge of the South China Sea. This causes flows in one tributary, Tonlé Sap River, to change course. Instead of flowing south, from Tonlé Sap Lake into the Mekong, the Tonlé Sap River begins to flow north, from the Mekong into Tonlé Sap Lake. Over the next several months, the lake expands to four times its normal surface area over the surrounding floodplain and under the bamboo stilts of Kampong Phhluk, carrying with it fish, people, and floating villages. Where children walked to school yesterday, they paddle in dugout canoes and even giant rice bowls today.
Fish catches skyrocket during this annual flood pulse. Markets at the water’s edge receive a steady stream of boat traffic starting at 5:00 a.m. as fishermen unload catches from a variety of ingenious traps and mazes deployed overnight and designed to funnel fish on the floodplain into nets. It is estimated that 60 million people in Cambodia and the surrounding countries rely on protein from the Tonlé Sap Lake fish catch each day. These markets provide a unique opportunity for scientists in SAFS’s Holtgrieve Ecosystem Ecology Lab to sample a variety of species and size classes of fish without ever leaving the shore.
The Holtgrieve lab looks at chemical signatures within fish muscle and bone to determine their role in local food webs, how they migrate, and where their carbon—which is the building block of all life—ultimately originates. Conventional wisdom says that most carbon in lake food webs originates from plants. However, scientists analyzing samples from Tonlé Sap Lake noticed that carbon in several fish species is low in one of two stable isotopes of carbon. This is an unequivocal sign that some of the carbon within fish comes from methane.
Methane is produced by bacteria in water-logged soils. As bacteria that thrive on oxygen metabolize carbon in soils, oxygen begins to run out. Eventually, a group of bacteria known as methanogens take over and slowly but steadily metabolize carbon into methane gas. As methane gas rises out of soils and into floodplain waters, it encounters yet another group of bacteria that metabolize methane, known as methanotrophs. Methanotrophs are consumed by protozoans, rotifers, and zooplankton in the water column, which are in turn consumed by fish. This makes methane a potentially important carbon source to the Tonlé Sap food web. And for a fishery that happens to expand with monsoonal flooding each year, when 9,000 square kilometers of floodplain soils become water-logged.
To determine how much carbon from methane becomes available to the fishery when waters rise in Tonlé Sap Lake, scientists in the Holtgrieve Lab are leaving the shore on long, wooden fishing boats with fellow researchers from the Cambodian Ministry of Agriculture’s Inland Fisheries Research and Development Institute in order to sample water and mud on the floodplain. Production of methane by methanogens and consumption by methanotrophs is being measured at different flood stages in hopes of associating these rates with the lake’s flood pulse. Alteration of this flood pulse and the amount of carbon from methane available to the fishery is imminent as the lower Mekong is dammed.
Until recently, the Mekong remained one of the world’s wildest rivers. But three dams have been built on the upper Mekong in China, with a fourth—Xayaburi—under construction along the Laos-Cambodia border. These hydropower development projects are undertaken with Chinese funding, and will primarily benefit power consumers in that country rather than the riverside nations of Laos and Cambodia. Such hydropower is projected to tightly control future flooding downstream. Modeling suggests that, under current scenarios of hydropower development, Tonlé Sap Lake will experience shorter periods of maximal flooding. If predictions by scientists in the Holtgrieve Lab are correct, this means that the amount of carbon from methane available to the Tonlé Sap fishery, and perhaps the region’s food security, will be threatened by the dams.
Hydropower is set to increase globally by 56% over the next 20 years, with the majority of new dams built in the tropical, developing countries of Southeast Asia, South America, and Africa. What happens in the lower Mekong, Tonlé Sap Lake, and communities like Kampong Phhluk therefore has far reaching implications. Many large, tropical rivers such as the Irrawaddy, Amazon, and Congo follow the same pattern of predictable, annual flooding long known to the scientific literature. In countries along these rivers, freshwater fish is a crucial, easily available protein source for the poor. If the flood pulse is an important ecosystem service that maintains fisheries, communities, and traditional cultures, this service should be evaluated against the hydropower boom occurring throughout the developing world today.
SAFS professor Chelsea Wood receives prestigious Sloan Fellowship
SAFS Professor Chelsea Wood was awarded a Sloan Fellowship, awarded to early-career researchers in recognition of distinguished performance and a unique potential to make substantial contributions to their field. Prof. Wood is a prolific researcher who uses parasites and pathogens (both human and fish-based) to uncover fundamental ecological truths about the natural world. She will receive $65,000 to further her research initiatives, which includes using museum fish specimens as “parasite time capsules”, as reported in UW News.
Baby salmon use the earth’s magnetic field to figure out which way is up
Salmon are capable of using the Earth’s magnetic field as a part of their built-in navigating skills to home back to their streams of birth. Now it has been discovered that young salmon emerging from the gravel also use the Earth’s magnetic field to figure out which way is up. Salmon eggs are laid in gravel nests, and the young salmon remain in the gravel until all of the attached yolk reserves are finished, then they emerge to live out in the open water. In lab experiments, scientists were able to determine that the direction of emergence from the gravel depended on the Earth’s magnetic field: when this was disrupted or reversed in the laboratory, the young salmon were much less likely to move upwards and out of the gravel beds. The new work was coauthored by SAFS Professor Tom Quinn, who first had the idea decades previously during his PhD studies, and appears in the journal Biology Letters.
With sea ice loss, beluga whales make longer and deeper feeding dives in the same places
Satellite tracking devices on beluga whales in the Arctic show how they reacted to far lower sea ice concentrations in recent years. Instead of shifting where they feed, as might have been expected, beluga whales continued to feed in similar (but now largely ice-free) places. However, where dive data were available, their dives were significantly longer and deeper than in years with higher ice concentrations. The research, led by former SAFS graduate student Donna Hauser and Prof. Kristin Laidre, were unable to tell whether the deeper, more prolonged, dives were bad for the belugas (because deeper dives use up more energy), or good for belugas (because they can access new feeding habitat in the absence of sea ice). The research appears in the journal Diversity and Distributions and is highlighted on UW News.
Narwhals prefer serene glaciers over rambunctious glaciers
Combining data from glaciers with tracking devices on narwhals, reveals that these elusive marine mammals prefer glaciers that calve infrequently over active calving glaciers. The research, to be presented by SAFS professor Kristin Laidre at the Ocean Sciences Meeting next week, shows narwhals congregating at the outlets of serene glaciers in Greenland’s Melville Bay. Prof. Laidre speculates that the cold fresh water melting off the glacier may stun fish, making them easy prey for the hunting narwhals, while active glaciers produce more silt-filled waters that are harder to hunt in. The research is highlighted in UW Today.