Arxiu d'etiquetes: shark

Symbiosis: relationships between living beings

Predation, parasitism, competition… all living beings, besides interacting with the environment, we relate to other living beings. What types of relationships in addition to those you know? Do you feel like to know them?

INTRODUCTION

The group of all living beings in an ecosystem is called biocenosis or community. The biocenosis is formed in turn by different populations, which would be the set of individuals of the same species occupying an area. For survival, it is imperative that relations between them are established, sometimes beneficial and sometimes harmful.

INTERESPECIFIC RELATIONSHIPS

They are those that occur between individuals of different species. This interaction it is called symbiosis. Symbiotic relationships can be beneficial to a species, both, or harmful to one of the two.

Detrimental to all the species involved:

Competition: occurs when one or more resources are limiting (food, land, light, soil …). This relationship is very important in evolution, as it allows natural selection acts by promoting the survival and reproduction of the most successful species according to their physiology, behavior …

Las selvas son un claro ejemplo de competencia de los vegetales en busca de la luz. Selva de Kuranda, Australia. Foto de Mireia Querol
Rainforests are a clear example of competition between vegetals in the search for light. Kuranda rainforest, Australia. Photo by Mireia Querol

One species has benefits and the other is detrimented:
  • Predation: occurs when one species (predator) feeds on another (prey). This is the case of cats, wolves, sharks

foca, león marino,
Great white shark (Carcharodon carcharias) jumping to depretade a marine mamal, maybe a sea lion. Photo taken from HQ images.

  • Parasitism: one species (parasite) lives at the expense of other (host) and causes it injury. Fleas, ticks, pathogenic bacteria are the best known, but there are also vertebrate parasites, like the cuckoo that lay their eggs in the nests of other birds, which will raise their chicks (brood parasitism). Especially interesting are the “zombie parasites”, which modify the behavior of the host. Read this post to learn more!

    Carricero (Acrocephalus scirpaceus) alimentando una cría de cuco (Cuculus canorus). Foto de Harald Olsen
    Reed warbler (Acrocephalus scirpaceus) feeding a cuckoo’s chick (Cuculus canorus). Photo by Harald Olsen

    Parasites that live inside the host’s body are called endoparasites (such as tapeworms), and those who live outside ectoparasites (lice). Parasitism is considered a special type of predation, where predator is smaller than prey, although in most cases does not cause the death of the host. When a parasite causes illness or death of the host, it is called pathogen.

    Cymothoa exigua es un parásito que acaba sustituyendo la lengua de los peces por su propio cuerpo. Foto de Marcello Di Francesco.
    Cymothoa exigua is a parasite that replaces the tongue of fish with their own body. Picture by Marcello Di Francesco.

Kleptoparasitism is stealing food that other species has caught, harvested or prepared. This is the case of some raptors, whose name literally means “thief.” See in this video a case of kleptoparasitism on an owl:


Kleptoparasitism can also occur between individuals of the same species.

One species has benefits and the other is not affected:
  • Commensalism: one species (commensal) uses the remains of food from another species, which does not benefit or harm. This is the case of bearded vultures. It is also commensalism the use as transportation from one species over another (phoresy), as barnacles attached to the body of whales. The inquilinism is a type of commensalism in which a species lives in or on another. This would apply to the woodpeckers and squirrels that nest in trees or barnacles living above mussels. Finally, metabiosis is the use of the remains of a species for protection (like hermit crabs) or to use them as tools.

    El pinzón carpintero (Camarhynchus pallidus) utiliza espinas de cactus o pequeñas ramas para extraer invertebrados de los árboles. Foto de
    The woodpecker finch (Camarhynchus pallidus) uses cactus spines or small branches to remove invertebrates from the trees. Picture by Dusan Brinkhuizen.

    Both species have benefits:
  • Mutualism: the two species cooperate or are benefited. This is the case of pollinating insects, which get nectar from the flower and the plant is pollinated. Clownfish and anemones would be another typical example, where clown fish gets protection and food scraps while keeps predators away and clean parasites of the sea anemonae. Mutualism can be optional (a species do not need each other to survive) or forced (the species can not live separately). This is the case of mycorrhizae, an association of fungi and roots of certain plants, lichens (mutualism of fungus and algae), leafcutter ants

    Las hormigas Atta y Acromyrmex (hormigas cortadoras de hogas) establecen mutualismo con un hongo (Leucocoprinus gongylophorus), en las que recolectan hojas para proporcionarle nutrientes, y ellas se alimentan de él. Se trata de un mutualismo obligado. Foto tomada de Ants kalytta.
    Atta and Acromyrmex ants (leafcutter ants) establish mutualism with a fungus (Leucocoprinus gongylophorus), in which they gather leaves to provide nutrients to the fungus, and they feed on it. It is an obligate mutualism. Photo taken from Ants kalytta.

INTRAESPECIFIC RELATIONSHIPS

They are those that occur between individuals of the same species. They are most beneficial or collaborative:

  • Familiars: grouped individuals have some sort of relationship. Some examples of species we have discussed in the blog are elephants, some primates, many birds, cetaceans In such relationships there are different types of families.
  • Gregariousness: groups are usually of many unrelated individuals over a permanent period or seasonal time. The most typical examples would be the flocks of migratory birds, migration of the monarch butterfly, herds of large herbivores like wildebeest, shoal of fish

    El gregarismo de estas cebras, junto con su pelaje, les permite confundir a los depredadores. Foto tomada de Telegraph
    Gregariousness of these zebras, along with their fur, allow them to confuse predators. Photo taken from Telegraph
  • Colonies: groups of individuals that have been reproduced asexually and share common structures. The best known case is coral, which is sometimes referred to as the world’s largest living being (Australian Great Barrier Reef), but is actually a colony of polyps (and its calcareous skeletons), not single individual.
  • Society: they are individuals who live together in an organized and hierarchical manner, where there is a division of tasks and they are usually physically different from each other according to their function in society. Typical examples are social insects such as ants, bees, termites

Intraspecific relations of competition are:

  • Territorialityconfrontation or competition for access to the territory, light, females, food can cause direct clashes, as in the case of deer, and/or develop other strategies, such as marking odor (cats, bears), vocalization

    Tigres peleando por el territorio. Captura de vídeo de John Varty
    Tiger figthing for territory. Video caption by John Varty
  • Cannibalism: predation of one individual over another of the same species.

And you, as a human, have you ever thought how do you relate with individuals of your species and other species?

MIREIA QUEROL ALL YOU NEED IS BIOLOGY

REFERENCES

Sharks: predators as prey

Today we will talk about a sensitive topic. This topic is shark finning, an unsustainable and macabre practise that happen in our waters. 

INTRODUCTION

Sharks, together with rays, are included in the elasmobranchii group. They are characterized by a cartilaginous skeleton and several teeth rows, which are continuously renovated. Sharks are predators because they are in the top of food chains. It means that they devour but they aren’t devoured. Nevertheless, we will see that is not completely true, as there is a species that has the ability to capture them, cut their fins and then to throw them to the sea.

WHAT IS SHARK FINNING?

Shark finning consists on cutting and saving shark fins and discard the rest of the body.

4145Fisher cutting a shark fin (Foto: Gary Stokes; Sea Shepherd, Hong Kong).

The animal usually is still alive when is thrown into the water, so it can swim and sink slowly to the deep sea; where, still alive, will be food for other animals. Fishers only save the fins because its economical value is much bigger than the meat of the animal so, discarding the body, they have more space in the ship for fins. In the next video, which is very hard to see, we can watch this activity:

IS THAT ILLEGAL?

Shark finning is a forbidden activity around Europe since 2003, with the passing of the Council Regulation (EC) No 1185/2003 of 26 June 2003 on the removal of fins of sharks on board vessels, but this law allowed to discharge fins without its body, with a permission, and in the case that the fin weight was lower than 5% of the total weight of the animal. This means that, despite the law, finning was taking place. This regulation had some legal vacuums, thanks to 4th article, that allowed to give special permissions to cut fins on board of the vessels and discharge these fins and the rest of the body in different harbours, what meant a big difficulty to control finning.

For all this reasons, in 2011, European Commission proposed the obligatory nature to discharge fins together with the shark body, what was well received by conservationist organisations, most of the scientific community, general public, Committee of Ministers of EU and the Environment Committee of EU. Nevertheless, Spain and Portugal, whose shark fisheries are by far the most important in EU, express their opposition to this reform. Both countries have a fishing line fleet in the North Atlantic.

Finally, in June 2013, it is approved the reform of the European reform about finning, Regulation (EU) Nº 605/2013 of the European Parliement and of the Council (of 12 June 2013), amending Council Regulation (EC) No 1185/2003 on the removal of fins of sharks on board vessels. In this regulation, it is mandatory to discharge sharks with their fins. This measure has been successfully to fight against finning in other parts of the world. Portugal and Spain were put up it because it reduces their benefits, so holds are full sooner.

WHY IS THAT HAPPENING?

This practise was expanded due to the high price of shark fins in the Asiatic market to do shark fin soup and in traditional cures. Every single kilo of fresh or frozen fin costs 20 €, while in the case of meat the value is just 1€. EU captures sharks in the Mediterranean and the Atlantic, Indian and Pacific oceans. It is the first worldwide power in shark fishing, with a 17% of declared captures in 2009, and the biggest fin exporter at Hong Kong and China.

_MG_7002Shark fins spread in the ground to be dried (Gary Stokes; Sea Shepherd, Hong Kong).
_MG_7411Shark fins spread in the ground to be dried (Gary Stokes; Sea Shepherd, Hong Kong).

WHICH SPECIES ARE THE TARGET?

Nowadays, many species are target of fishing because, despite 28% of the species are considered threatened by IUCN, just some of them are protected. In Spain and Europe, there are just 9 protected species. In addition, catch shares don’t exist and, for this reason, fishers can fish till extinction. Why do not exist catch shares? The reason is that fishing regulation in EU is conditioned by Spain and Portugal. However, specialists estimates that every year are killed 100 million sharks for their fins.

Blue shark is the main species in the Atlantic fishing line feet. If we have a look in the capture statistics of this shark in Vigo harbour (Spain) (2468 tones and more than 3 million euro of benefit, according to Puerto de Vigo), we can observer that is a great benefit: is legal, there aren’t catch shares and fins are well-paid in Hong Kong market.

WHICH IS THE IMPACT OF SHARK FINNING?

Shark finning has the following impacts:

  • Loss and devastation of shark populations around the world. Experts estimate that within a decade, most species of sharks will be lost because of longlining.
  • Unsustainable fishery. The massive quantity of sharks harvested and lack of selection deplete shark populations faster than their reproductive abilities can replenish populations.
  • Threatens the stability of marine ecosystems.
  • Obstructs the collection of species-specific data that are essential for monitoring catches and implementing sustainable fisheries management.
  • Wasteful of protein and other shark-based products. Up to 95 per cent of the shark is thrown away.

REFERENCES

ACKNOWLEDGEMENT

I wouldn’t finish this article without give thanks for her help and patient to Mónica Alonso Ruiz, who is communication responsible and Madrid responsible of Alianza Tiburones Canarias, who informed me and give me most of the information and data present here.

If you find this article interesting, you can share it in Social Networks to dissiminate this problem. The goal of this blog is to inform people about science. 

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