Editors’ Choice for CJZ, CJFAS, and CGJ – July 2016

July 20, 2016

By Jeremiah Yarmie

Each month, the Editors of many of our journals highlight noteworthy articles with an Editors’ Choice selection. These selections often include the best papers of a specific issue or highlight novel approaches. Editors’ Choice articles are also made freely accessible for the month. We invite you to check out a selection of Editors’ Choice papers featured in July 2016. 

Canadian Journal of Fisheries and Aquatic Science

Transboundary movements, unmonitored fishing mortality, and ineffective international fisheries management pose risks for pelagic sharks in the Northwest Atlantic” by Steven E. Campana

This perspective article by Steven Campana looks at how the shortfin mako (Isurus oxyrinchus), porbeagle (Lamna nasus), and blue shark (Prionace glauca) have been neglected and abused in the fishing industry.

A shortfin mako shark in the ocean.

Sharks have more reasons to be scared of us than we do of them. They are sensitive to a range of risk factors, including fishing pressure, and many shark and ray species are now at-risk at a global scale.

Sharks have unique reproductive biology, which at times resembles mammalian rather than fish life history. This can be seen in their internal mode of fertilization, live birthing, and small number of young per year. As a consequence, they are extremely vulnerable to fisheries exploitation, including bycatch—the capture of non-target species by fisheries.

All three shark species range across many national boundaries in the Northwest Atlantic, but spend more than 90% of their time out at sea.

As a result, no country claims ownership over these fish and the subsequent assessment and management that these few populations so desperately need is left in limbo. The sharks end up being managed by regional fisheries management organizations that care more about commercial fish like swordfish and tuna. Ultimately, the responsibility for these sharks washes away in the waves.

Illustration of a porbeagle. Image via the Biodiversity Heritage Library.

Sharks swim a lot. Their migratory behaviour is due to the fact that they must swim to stay afloat and not sink to the depths of the ocean. 

Because of this, alongside the fact that they often hunt commercially valuable fish, sharks are more likely to encounter fisheries. 

What happens to the sharks from there depends on the kind of shark that is caught and the fishing crew. 

Shortfin makos have some commercial value, so about two-thirds of all bycatch sharks are retained for the market. Porbeagles are less valuable, and more than 80% of these sharks are discarded after capture. Blue sharks have no commercial value, and all 3 million annually captured sharks are released.

The back of a swimming blue shark.

Unfortunately, it is a common practice for caught sharks to be killed and discarded without record. These mortalities are not included in population assessments, muddling the data.

The numbers of North American shark fins that are sold in Asian markets exceed the number of illegally caught sharks, indicating that shark finning is still a serious problem in North American fisheries, despite being illegal.

Sharks also die while snagged on longline fishing hooks, as well as shortly after being released from fishing hauls.

Campana concludes his paper by discussing how to better manage these fish. He discusses what sustainable levels would be for discarded sharks, how to allocate responsibility for monitoring and assessing these at-risk species, and how to better protect shortfin makos, porbeagles, and Blue sharks.

He suggests initial steps of developing a better monitoring system of sharks and catches, establishing shark quotas, and disrupting the illegal shark finning network.

Canadian Journal of Zoology

Testing for predicted decrease in body size in brown bears (Ursus arctos) based on historical shift in diet” by Jun Matsubayashi, Ichiro Tayasu, Junko O. Morimoto, and Tsutomu Mano

In a previous study, lead author Jun Matsubayashi presented data showing a historical decline in the amount of meat consumed by brown bears (Ursa arctos) on the Hokkaido Islands in the northern part of Japan.

This decline in meat eating was presented in relation to human activities—the data showed that consumption of Sika deer, as well as Pacific salmon on the eastern side of Hokkaido, began to decrease about 200 years ago when humans began to modernize the region.

This shift from an omnivorous diet to an almost herbivorous one has not been seen in animals in any other study so far.

A brown bear eating salmon. Image via Chrisoph Strässler.

In this current study, Matsubayashi and colleagues investigated if this shift away from carnivorous eating affected the size of these bears. Feeding habits are closely related with animal body size—larger bears have a better time competing for food and mates.

It has been previously shown that meat intake is positively correlated with brown bear body size, so the authors hypothesized that this herbivorous shift would be associated with smaller bears.

Using fully grown bear samples collected between 1996 and 2011, the researchers determined total body size by using femur length and analyzed the diets of these bears with carbon and nitrogen stable isotopes in collagen samples taken from these bones.

They found that in the analyzed subpopulations, femur lengths was positively correlated with nitrogen isotope values, and that the association was stronger for males than females. However, they found no predictive ability for skeletal size of individual bears, indicating that body size changes due to nutrition occur over several generations but not within a single one.

Based on this data they estimated that brown bear size decreased by 10-18% for males and 8-9% for females in this time period, suggesting that this dietary shift influenced a decrease in body size.

Canadian Geotechnical Journal

Capillary water retention curve and shear strength of unsaturated soils” by Annan Zhou, Ruiqiu Huang, and Daichao Sheng

Authors Zhou, Huang, and Sheng present a new water retention model for unsaturated soils that better describes the adsorbing of water. The shear strength of unsaturated soils must be known in the design of foundations, slopes, pavements, and other civil engineering tasks. The shear strength of soil is closely related to its water saturation.

The water found in soil pores contributes different to shear strength and can be divided into capillary condensation, which describes water that exists in suspension between soil particles, and adsorbed water, which simply coats the outer surface of soil particles. While capillary condensation affects shear strength, adsorbed water does not.

Currently used models for soil shear strength are lacking since all pore water is assumed to be capillary water, a drastic oversimplification considering the two-state model of unsaturated soil. The results of this are significant overestimations of shear strength, which can increase the likelihood of structures built on these soils to fail, for example, through a landslide on a slope.

A section of a road was washed away during an overnight storm—a mudslide off the shoulder wore away the foundation and caused the failure. Image from the N.C. Department of Transportation.

In this newly proposed model, only capillary water is considered when determining sheer strength, providing a more accurate calculation of this measurement.

Jeremiah Yarmie is a writer from Winnipeg, Manitoba. While completing a BSc at the University of Manitoba, he realized that he enjoys talking about science much more than he enjoys doing it. When he isn't telling stories about science and the people who make it happen, he can be found on stage making stories up as an improviser. You can find some of his writing on his website. You can tweet at him @jeremiahyarmie

Filed Under: Editors Choice Jeremiah Yarmie CJFAS

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