Pregnant rays and babies pay a price after ‘catch and release’ from fishing trawlers

This article is co-authored by Leonardo Guida and Richard Reina. 

Rays are among the species most vulnerable to overfishing and are often caught incidentally in commercial trawlers and released as unwanted bycatch.

Unfortunately, we’re probably underestimating the impact that fishing is having on ray populations. Although some will survive capture, we know little about the non-lethal and long-term effects of that stressful experience.

Included in those unknowns are questions relating to reproduction. In particular, what if the captured ray was pregnant? Would she still give birth? If she did, would her offspring survive?

Our latest research shows capture stress can reduce a mother ray’s body condition, and also affects the health of her offspring – in much the same way that stress during pregnancy can affect humans.

This research focused on the southern fiddler ray (Trygonorrhina dumerilii), also known as the “banjo shark”, a species common in the coastal waters of southern Australia.

Beyond just this species, our results suggest it’s possible that other ray and shark species that have live-birth (including most large sharks) could be similarly affected.

All rays give birth to live young. For many species pregnancy lasts about a year, making them more likely to be captured during reproduction compared to egg-laying species.

A makeshift maternity ward

Pregnant southern fiddler rays were collected by hand in Swan Bay, Victoria, Australia, using SCUBA to minimise stress during collection. They were transported and housed in our “maternity ward” – a large outdoor research facility located nearby.

Our maternity ward included a large tank equipped with a giant paddle that pushed water past stationary nets, thereby simulating a trawl net being dragged by a boat. Rays were placed in these nets and trawled, followed immediately by 30 minutes of air exposure to replicate the process of sorting the catch on board a boat. A similar number of control females were kept in a separate tank and were not subjected to trawling or air-exposure.

Over the next three months, pregnancy and the health of each mother was regularly monitored via ultrasounds, blood-sampling and weighing. At birth, their pups were also measured for length, weight and had their blood sampled. Mothers carried and gave birth to an average of two pups.

It’s tough out there for the little guy

Pups from trawled mothers were 12% shorter and 27% lighter than those from untrawled mothers.

A baby southern fiddler ray is released. Leonardo Guida,  CC BY-NC-ND

A baby southern fiddler ray is released. Leonardo Guida, CC BY-NC-ND

In most animals undersized offspring generally have a lower chance of survival. Marine predators are often restricted in their options of potential prey by the size of their mouth, with smaller animals more easily consumed.

Lower body mass may mean pups have fewer energy reserves - in the form of an internal yolk sac - to rely on. An increased risk of starvation is possible during the early stages of life when inexperience can make catching prey difficult.

Pups from trawled mothers also showed signs of a stress response in their immune system, and increased vulnerability to infection and disease is possible. The increased energy needed to maintain a healthy immune system may also limit growth rates. This is important for female fertility because larger females tend to carry more offspring.

Mum feels the stress too

Trawled mothers showed indicators of stress for 28 days after trawling, exhibiting elevated immune responses and 9-15% lower body weights compared to their unstressed counterparts.

Southern fiddler ray mother and offspring in tank. Leonardo Guida

Southern fiddler ray mother and offspring in tank. Leonardo Guida

Reduced body condition after giving birth could mean that the next mating event may be delayed or missed in order to rebuild sufficient energy stores for a successful pregnancy.

Delaying or missing mating opportunities could be particularly important for other live-bearing species like the scalloped hammerhead (Sphyrna lewini) and sharpnose sharks (Rhizoprionodon taylori), which mate again shortly after giving birth.

The bigger picture - fishing for the future

By examining the non-lethal responses to capture stress, we’re working towards more efficient fishing practices that improve conservation outcomes for marine species.

Regarding reproduction, it may mean that we can better assess and manage fishing practices in areas where sharks and rays are known to congregate and breed. Fishing techniques that reduce the amount of accidental capture of rays and sharks will benefit both fishermen and conservation efforts, especially during vulnerable breeding periods.

For example, “turtle exclusion devices” in trawl nets (originally designed to prevent the capture of sea turtles) allow animals that are much bigger than the target catch to escape through a chute. Such a device may be suitable for reducing shark and ray bycatch too.

Our study into how capture affected pregnancy in rays is part of a larger research program led by Monash University in collaboration with Flinders University, University of Tasmania and the Victorian Marine Science Consortium. The research program’s results on both lethal and non-lethal outcomes of capture have helped inform the Australian Fisheries Management Authority (AFMA) how to fish for the future and improve the conservation of sharks and rays.

This article originally appeared on The Conversation. Read the original article here.


Leonardo Guida

Following a childhood love for sharks, Leo recently completed his PhD at Monash University investigating the effects of fishing on shark and ray populations. He is Director of Community Operations for Wild Melbourne.

You can find him on Twitter at @ElasmoBro.

Our tiny ally: How fleas are helping us protect nature from rabbits

Rabbits are a major problem for our plants and animals across Australia, as well as our agriculture. They breed quickly, and are able to substantially change vegetation as their numbers grow. Because of this, they are a major threat to over 300 of Australia's threatened species

In our latest video, we interview Mackenzie Kwak, a parasitologist from the Centre for AgriBioscience in Melbourne about how fleas are helping us to reduce the impacts of rabbits on nature, and us. 

The Little Things That Run The City

This is a guest post by Luis Mata. 

…let me say a word on behalf of these little things that run the world.

This quote was part of an address given by E.O. Wilson on the occasion of the 1997 opening of the invertebrate exhibit of the National Zoological Park in Washington D.C. The ultimate objective of Wilson’s address was to stress the urgent need to recognise the importance of insects and other invertebrates for humanity. He was keen to see that efforts aimed at the conservation of biodiversity were beginning to include non-vertebrate animals. In his words:

‘A hundred years ago few people thought of saving any kind of animal or plant. The circle of concern has expanded steadily since, and it is just now beginning to encompass the invertebrates.’

With The Little Things that Run the City - a close research collaboration between the City of Melbourne’s Urban Sustainability Branch, RMIT University’s Interdisciplinary Conservation Science Research Group and nine other academic and government organisations - we sought to expand this circle so that it may also encompass the conservation of insects in urban environments. We were driven by the motivation to ‘say a word on behalf of the little things that run the city’. 

The Little Things that Run the City, Mata et al. 2016.  Artwork: Kate Cranney

The Little Things that Run the City, Mata et al. 2016. Artwork: Kate Cranney

How many insect species live in your city? How are they distributed amongst the city’s green spaces and habitats? What are the ecological processes they perform and ecosystem services they deliver? What are their most frequent ecological interactions?

The Little Things that Run the City project is addressing these and other questions within the boundaries of the City of Melbourne. Here are some of our key findings:

We found that at least 560 insect species occur within the City of Melbourne’s public green spaces. These included species of ants, bees, beetles, cicadas, flies, heteropteran bugs, jumping plant lice, leafhoppers, treehoppers, planthoppers, parasitoid and stinging wasps, and sawflies. The insect group with the highest diversity was beetles, followed by parasitoid wasps and flies.

The most common species was a ‘Minute brown scavenger beetle’ in genus Cortinicara. Minute brown scavenger beetles are tiny and dark, and measure about 2 mm in length. Truly ubiquitous in the City of Melbourne, the species was collected in all studied sites and habitats, and in association with 102 different plant species – that’s 94% of all surveyed plant species!

The European honey bee Apis mellifera was the most common bee species. We also recorded many Australian native bees, including chequered cuckoo, leafcutter, and blue-banded bees.

A blue-banded bee ( Amegilla asserta ) flying towards a black-anther flax-lily.  Image: Luis Mata

A blue-banded bee (Amegilla asserta) flying towards a black-anther flax-lily. Image: Luis Mata

We have recorded at least four new species to science. These include an ant in genus Turneria, a lacebug in genus Tingis, and two jumping plant lice: Mycopsylla sp. nov. and Acanthocasuarina sp. nov..

As many as 97% of all recorded species were native to Australia. The most common non-native species was the Argentine ant Linepithema humile, an aggressive invasive species known to displace native ants and capable of disrupting ant-mediated seed dispersal interactions.

Mid-storey was the habitat type with the highest insect diversity. As many as 337 species were recorded in association with mid-storey plants. The second most diverse habitat type was tree, followed by grassland and lawn.  

The tussock-grass Poa labillardierei was the plant species with the highest associated insect diversity. As many as 103 insect species were associated with this native grass. The native wallaby grass Rytidosperma sp. and kangaroo grass Themeda triandra also had large numbers of associated insect species. The shrub with the highest associated insect diversity was the fragrant saltbush Chenopodium parabolicum, followed by sweet bursaria Bursaria spinosa, gold-dust wattle Acacia acinacea and hop goodenia Goodenia ovata.

There were over 60% more insect species in native than non-native tree species. Interestingly, however, the tree species with the highest associated insect diversity were both the native spotted gum Corymbia maculata and the non-native pepper tree Schinus molle.

We documented approximately 2,200 associations between insect and plant species. On average, each insect species was associated with 3.3 plant species. For example, the most generalist herbivore recorded in the study, a tiny green leafhopper, was recorded in association with 57 plant species, which is more than 50% of all surveyed plant species. This is assuming of course that it actually feeds on every plant species that we found it on!

A dingy swallowtail ( Papilio anactus ) in Carlton Gardens.  Image: Luis Mata

A dingy swallowtail (Papilio anactus) in Carlton Gardens. Image: Luis Mata

Half of all adult insect species recorded in the study were herbivores. Of these, as many as 68% were folivores, a guild in which species specialise to eat leaves.

We don’t know how many species were pollinators! What we do know is that as many as 25% of all recorded species are known to visit flowers to collect nectar and/or pollen – that is almost 150 species of beetles, parasitoid and stinging wasps, flies, heteropteran bugs, ants, and, of course, bees.

Over 40% of all recorded insect species were predators or parasitoids. These species are therefore capable of regulating the populations of potential insect pests.

The insects recorded in the study may supply at least two types of food: honey and lerps. We documented only one species of honey-producing bee, namely the non-native European honey bee. Lerps are crystallised protective structures made out of the sugar-rich liquid honeydew exudated by the immature stages of jumping plant lice.

The Little Things that Run the City project illustrates the importance of insect biodiversity conservation to the City of Melbourne, and by extension, to other cities worldwide. Our findings are being applied to identify where to prioritise conservation activities, guide the design and maintenance of green spaces, and assist decision-makers considering insects in broader biodiversity plans and strategies. The study is providing valuable baseline data that can be integrated into the council’s planned research agendas; for example, in future iterations of the City of Melbourne’s BioBlitz and in the future development of monitoring programs.

Our findings are also providing data to The shared urban habitat, one of the five main research lines of the National Environmental Science Programme – Clean Air and Urban Landscapes Hub, and to the recently awarded Australian Research Council Linkage Project Designing green spaces for biodiversity and human well-being.

Insects are the most diversified animal group on our planet - and in our city! From a functional perspective they are arguably the most important as well. The ‘little things that run the city’ spread seeds, eat rubbish, pollinate food crops and flowers, produce honey, keep soils healthy, help control weeds and pests, and are a food source for some of our other most dear animals, such as lizards, bats and birds. Keeping them safe and healthy within our city should be one of our top urban conservation priorities!

Dr Luis Mata is a postdoctoral researcher at RMIT University’s Interdisciplinary Conservation Science Research Group. You can discover more about Luis and his research on his research blog. 

Banner image of a shield bug from genus Cuspicona courtesy of Luis Mata.  

Review: The Red Kangaroo in Central Australia

The Book: The Red Kangaroo in Central Australia - An Early Account by Alan E. Newsome
The Authors: Alan & Thomas Newsome

When first looking through The Red Kangaroo by Alan & Thomas Newsome, my first thoughts were something along the lines of wishing there were more books like it. The late Alan Newsome was one of Australia's most respected ecologists, known for pioneering countless research projects in Central Australia and integrating Indigenous knowledge with ecological insight. Indeed, throughout my brief scientific career, I’ve encountered and cited much of Alan's work.

In itself, the history behind the compilation of this text is fantastic. The story goes that Alan's son, Tom, found Alan's original notes and manuscript in the family garage several years ago, meekly labelled 'Red Kangaroo Book.' Along with the manuscript were notes from a potential publisher expecting it ready for publication in 1975. Thirty years later, after Tom happened across the box of notes, the work contained in The Red Kangaroo remains every bit as relevant.

The period in which this work was conducted represented an exciting time to be a desert ecologist in Australia. Alan's work contributed to much of our basic understanding of the region and its fauna, particularly the red kangaroo Osphranter rufous. Logically set out, this text showcases much of Alan's early work on the red kangaroo's ecology and life history, supported with data and images collected from those early field trips. Not only does this offer an insight into fundamental aspects of an iconic Australian species, but it also showcases how field ecology was conducted half a century ago.

The view was magnificent, and the ride, an armchair, we were just above the trees... there was no margin for error.
— Alan's description of an aerial kangaroo survey

Of particular interest is the chapter describing red kangaroo 'Ecomythology': the communication of red kangaroo ecology through Indigenous culture. Alan's research and conversations with traditional owners uncovered chants and songs detailing much of the red kangaroo's ecology, from its diet to its habitat preferences. Given this work occurred over fifty years ago, Alan was somewhat of a pioneer in integrating science and Indigenous knowledge, and his documentation of that process is fascinating.

Where The Red Kangaroo succeeds, however, is through Newsome's ability to marry scientific discovery with naturalism. Written from the perspective of a young scientist (Alan conducted this research as a 25- to 30-year-old in the 1950s and 60s), Alan's prose exudes a flair and love of his subject rarely seen in modern scientific writing. It's refreshing to come across a book not only steeped with data, but also language that reflects the sheer amount of knowledge of the landscape the author was working in. Consequently, The Red Kangaroo makes for an incredible read, regardless of the reader's background, whilst also standing out as an important contribution to Australian natural history and science.

This book belongs on your bookshelf if... you're at all interested in natural history and science, or the reasons why the red kangaroo is so adept at persisting in the harsh Australian desert. 

Billy Geary
Billy is the Science & Conservation Editor at Wild Melbourne. He is a wildlife ecologist interested in predator-prey interactions and invasive species management.

You can find him on Twitter at: @billy_geary