Freshwater browning threatens growth and populations of economically important fish

Smallmouth bass
Image Credit: Scientific Frontline / stock image

Scientific Frontline: "At a Glance" Summary

• Main Discovery: Freshwater browning stunts the growth of specific fish species and alters community composition by favoring distinct traits, ultimately shifting population dynamics in north-temperate lakes.
• Methodology: Researchers synthesized data from 871 lakes across North America and Europe to analyze population trends and further examined a subset of 303 lakes to assess functional traits, such as eye size, in relation to water color gradients.
• Key Data: Browner waters correlated with increased abundance of northern pike and walleye but declines in lake trout, brook trout, yellow perch, largemouth and smallmouth bass, and whitefish; communities in darker waters were significantly more likely to feature species with large eyes.
• Significance: This phenomenon, driven by climate change and land use, disrupts aquatic food webs and creates cascading ecological effects that extend to terrestrial systems, such as altering the diets of birds dependent on specific fish populations.
• Future Application: These findings enable improved forecasting models for fisheries management, allowing for better prediction of ecosystem shifts and biodiversity loss under continuing browning scenarios.
• Branch of Science: Ecology and Limnology
• Additional Detail: The study confirms that freshwater browning is a widespread, transcontinental issue affecting biodiversity across North America and Europe, rather than a localized anomaly.

Counting salmon is a breeze with airborne eDNA

A male Coho salmon, featuring the characteristic hooked nose, returns to spawn from the Oregon Coast.
Photo Credit: NOAA Fisheries

During the annual salmon run last fall, University of Washington researchers pulled salmon DNA out of thin air and used it to estimate the number of fish that passed through the adjacent river. Aden Yincheong Ip, a UW research scientist of marine and environmental affairs, began formulating the driving hypothesis for the study while hiking on the Olympic Peninsula.

“I saw the fish jumping and the water splashing and I started thinking — could we recover their genetic material from the air?,” he said.

The researchers placed air filters at several sites on Issaquah Creek, near the Issaquah Salmon Hatchery in Washington. To their amazement, the filters captured Coho salmon DNA, even 10 to 12 feet from the river. Scientists collect environmental DNA, or eDNA, to identify species living in or passing through an area, but few have attempted to track aquatic species by sampling air.

Ichthyology: In-Depth Description

Image Credit: Scientific Frontline / AI generated

Ichthyology is the specialized branch of zoology devoted to the scientific study of fish, encompassing all three major groups: jawless fish (Agnatha), cartilaginous fish (Chondrichthyes), and bony fish (Osteichthyes). This discipline investigates the biology, morphology, taxonomy, evolution, and behavioral patterns of the most diverse group of vertebrates on Earth, ranging from microscopic species to massive biological entities like whale sharks.

Lessons from Ascension’s shark troubles could help boost conservation

Sharks at the coast of Ascension Island.
Photo Credit Kate Downes

Understanding people’s attitudes to interactions with sharks could help halt the global decline of shark numbers, according to new research carried out on Ascension Island.  

In 2017, there were two non-fatal shark attacks at Ascension – a UK territory in the South Atlantic with a population of about 800 people.

Large numbers of sharks – mostly silky and Galapagos sharks – have affected the island’s recreational fishers, who often lose tackle and hooked fish before they can be landed.

The research team, led by the University of Exeter and ZSL, interviewed 34 islanders to assess perceptions of sharks.

“We found that human-shark conflict is driven by lots of different factors beyond just attacks – and understanding this is vital if we want shark conservation to work,” said Dr Claire Collins, from ZSL and the University of Exeter.

Captivity makes salmon less symmetrical

Photo Credit: Courtesy of Cardiff University

The stress of captivity is likely to be causing reared salmon to be less symmetrical in appearance, according to a new study.

Research by the University of Eastern Finland, Natural Resources Institute Finland, and Cardiff University has found that salmon reared in captivity are more asymmetrical in appearance compared to wild salmon, suggesting that captive fish are more stressed, and their appearance might have impacts on salmon in the wild.

Currently, hatcheries are used in some countries to help boost wild populations with captive reared salmon. Global sales of aquatic species reared in captivity for food are also worth over $300 billion annually, with the Atlantic salmon being the most valuable of these species.

Range-shifting fishes are climate-change losers, according to new research

Pouting (Trisopterus luscus)
Photo Credit: Diego Delso
(CC BY-SA 4.0 DEED)

The warming of the Earth’s oceans due to climate change is affecting where the world’s fishes live, eat and spawn — and often in ways that can negatively impact their populations. That’s according to a new paper in the journal Nature Ecology and Evolution.

The researchers write that populations that experience rapid-range shift decline noticeably, up to 50 per cent over a decade. The populations affected most are those living on the northern poleward edges of their species’ range.

“There is a conventional wisdom among many climate-change biologists that species that shift their ranges quickly by moving northward should provide a mechanism to sustain healthy populations — that shifting species should be climate-change winners. Our results show the exact opposite,” says paper co-author Jean-Philippe Lessard, a professor in the Department of Biology.

“Species that are shifting their range quickly experience little change in their population size in their core range. But some of them experience a major collapse in their populations at the northern edges.

“In fact, the population collapse is mostly driven by the northern poleward populations,” he adds. “We were expecting that many individuals from the core of the range would be moving up north due to climate change and maintain these northern populations. But the northern-edge populations are the ones most likely to collapse.”

Study of slowly evolving ‘living fossils’ reveals key genetic insights

The alligator gar, and other gar species, are “living fossils” that it shows little species diversity or physical differences from ancestors that lived tens of millions of years ago.
Photo Credit: David Solomon

In 1859, Charles Darwin coined the term “living fossils” to describe organisms that show little species diversity or physical differences from their ancestors in the fossil record. In a new study, Yale researchers provide the first evidence of a biological mechanism that explains how living fossils occur in nature.

The study, published in the journal Evolution, shows that gars — an ancient group of ray-finned fishes that fit the definition of a living fossil — have the slowest rate of molecular evolution among all jawed vertebrates, meaning their genome changes more slowly than those of other animals.

By linking this finding to the process of hybridization — when two different species produce viable offspring — of gar species in the wild that last shared common ancestry during the age of the dinosaurs, the researchers demonstrate that slow evolution rate of their genome drives their low species diversity.

“We show that gars’ slow rate of molecular evolution has stymied their rate of speciation,” said Thomas J. Near, professor of Ecology and Evolutionary Biology in Yale’s Faculty of Arts and Sciences and the paper’s senior author. “Fundamentally, this is the first instance where science is showing that a lineage, through an intrinsic aspect of its biology, fits the criteria of living fossils.”