Arxiu de la categoria: Impact of fishing

Cetaceans and fishing: a dangerous relationship

The cetaceans are creatures that live in the seas and oceans of the Earth. Like other animals, not only must they cope with natural threats to their environment, such as predation or disease, but they also interact with human activities, such as fishing. Here we will see how fishing threatens the populations of these marine mammals. 


According to a recently report published by Ecologists in Action, the main threats of anthropic origin that cetaceans have to overcome are fishing, aquaculture, submarine noise, collisions with boats, marine litter, chemical pollution, sighting tourism , research, climate change and dolphinariums.

amenazas cetaceos
Cetaceans have to face several anthropic threats and they might beach at coast (Picture: Bahnfrend, Creative Commons)


During the last century, whaling activity captured more than three million individuals worldwide, especially in the southern hemisphere, where according to the IWC, about 750,000 individuals of fin whales (Balaenoptera physalus) and 400,000 specimens of sperm whales (Physeter macrocephalus) were captured, among others.

It is known that until the 1960s, hundreds of thousands of blue whales were captured, the largest animal that inhabits the Earth. Despite conservation efforts, currently only between 10,000 and 20,000 individuals survive, a small part compared to those that inhabited the Earth before the boom in the whaling industry.

industria ballenera, relacion cetáceos pesca
Picture showing whaling (Picture: Creative Commons)

In fact, according to a study by Tulloch et al. (2017), although there is currently an international moratorium and major conservation efforts are being made, in the year 2100 the populations of cetaceans that were the object of catches will reach, at most, by half of its original size.

Contrary to the prohibitions established in 1986, there are countries that continue to catch whales and dolphins. These countries are mainly Japan, Norway and Iceland. It is believed that they capture some 1,500 whales annually together, although the demand for meat from these marine mammals is low. In fact, since the ban, it is estimated that some 30,000 whales have been captured.

In Spain, the capture of cetaceans is also prohibited, although it is believed that there is a small illegal activity.


We must bear in mind the impact of accidental catches, one of the main causes of mortality in cetaceans. It consists in the capture of species that are not the target of fishing.

Bycatch can cause a conservation problem when there are endangered species affected, such as the vaquita (Phocoena sinus), a critically endangered porpoise (there are only about 30 animals left around the world), according to the IUCN. mainly due to gillnets.

Bycatch is one of the main causes of mortality, although at European level some measures have been taken, such as Regulation 812/2004. Accidental capture with the use of driftnets was especially important, but this practice is currently prohibited throughout the Mediterranean. In any case, other fishing gears, such as gillnets, purse seines or trawls, are particularly harmful.

In the 1960s, the tuna purse seine fishery in the Eastern Pacific had a significant impact on dolphin populations. The reason is that the fishermen knew that under the groups of dolphins that swam on the surface there are schools of tuna that followed them to take directionality. Thus, knowing this relationship, they surrounded the cetaceans (and therefore the tuna) with the purse seines, killing the former. It is estimated that in 1986 alone, about 133,000 dolphins were captured. To stop this situation, the pressure of the society was fundamental to take the appropriate measures. In fact, currently less than 0.1% of individuals are captured.

relacion pesca cetáceos, pesca accidental delfines
Fishers related dolphins with tuna, so that purse seine affected them (Picture: Wally Gobetz, Creative Commons)

Now we will focus on a case of gillnets. Gillnets kill many different species of cetaceans, both dolphins and whales. Although whales often survive, they often have traces of fishing gear attached to the body, such as nets. Small cetaceans do not suffer the same fate and often die. We have already seen the case of the vaquita , but another porpoise, the harbour porpoise (Phocoena phocoena) is the cetacean that suffers most deaths from gillnets.

Finally, we will see the relationship between cetaceans and trawling. Many species of cetaceans, both dolphins and small whales, feed on the target species of trawling, so they are caught while they are feeding on their prey. In fact, 16 cetacean species have been reported worldwide that feed in association with trawling. The catches are much greater when nets are left at a medium depth than when fishing is done on the seabed.

Despite all conservation efforts, according to an estimate by Read and collaborators, about 300,000 marine mammals are accidentally caught around the world each year due to fishing operations.


Finally, we cannot forget that cetaceans and fishermen compete for the same resources. Therefore, we must bear in mind that some cetaceans also interact with fishing to get food. Sperm whales, bottlenose dolphins and killer whales have learned to “steal” food from fishermen.

In fact, they take captures from longline, gillnets and trawl nets, running the risk of being trapped.

In any case, some measures have been taken, such as installing devices that emit annoying sounds for animals. Despite the attempts, they have adapted to it and, in fact, in some cases interpret them as an indication of the presence of fishermen in the area.


  • López López, L (2017). Cetáceos: los mamíferos más salaos. Informe sobre las interacciones entre cetáceos y actividades humanas. Ecologistas en acción.
  • Hall, MA; Alverson, DL & Metuzals, KI (2000). Bycatch: Problems and solutions. Marine Pollution Bulletin Vol. 41, N 1-6, pp. 204-219.
  • Northridge, S (2009). Bycatch. In Perrin, WF; Würsig, B & Thewissen, JGM (Eds). Encyclopedia of Marine Mammals (pp.167-169). Academic Press (2 ed).
  • Whale and Dolphin Conservation: Stop Whaling
  • World Wildlife Foundation: The Vaquita
  • Cover picture: Omar Vidal (source)

Farm fishing: the solution to overfishing?

We have heard many times that fishing grounds are being depleted due to the overexploitation of species. It is also widely said that farm fishing could solve this problem. But, are farms the solution to overfishing?


In general terms, the status of wild fish stocks has not improved. By 2013, 58.1% of fish stocks were fully exploited, 10.5% were under-exploited and 31.4% were overexploited (FAO, 2016). Thus, 30% of the populations suffered from overfishing.

This is due to the increasing consumption of fish. According to a report published by FAO, in 2014 each person ate on average about 20 kg of fish, twice as much as in 1960.

On the other hand, since the 1980s, wild catches have remained stable. However, the supply of fish for human consumption has increased considerably. So, if consumption has increased and fishing has remained stable, where does the rest of the fish come from?

The explanation for this fact is in aquaculture: in 2014, catch production was 93.4 million tonnes, while aquaculture production amounted to 73.8 million tonnes. In other words, 44% of the fish came from aquaculture.

Evolution of capture production and aquaculture production (Source: FAO, 2016).

Looking at this scenario, it does not seem far-fetched to think that farm fishing could solve the problem of overfishing.


According to the UN World Population Prospects report, by 2050, the world population will have risen to 9.7 billion people.

Given these figures, we can think that the increase in fish consumption will grow well above the production capacity of the oceans and seas. Aquaculture could therefore respond to this increase in the demand of fish for human consumption, in order to meet protein requirements.

Wild populations, therefore, will not be subject to greater pressure than they are now.

Another advantage of fish farms is that production is constant because they have more control over them, that is, there are few fluctuations during the year. This is not true for wild populations, either because of their biological cycle or because they are overexploited.

Finally, farms could reduce the environmental impact caused by fishing: there would be no incidental catches of non-interest species, seabed would not be eroded by trawling…

If you want to know more about aquaculture, I recommend you to watch this video (in this case is about river fishes):

Despite all these advantages, not only are not farms a solution, they also increase the problem of overfishing and cause many other problems.


Half of the cultivated species (including both animals and algae) in aquaculture do not require food from outside, because they feed by filtration. Anyway, it is true that this is not the case for carnivorous species.

Without going any further, according to FAO (2016), in 2014, 21 million tons of fish were destined for non-food products, three quarters of which were used to produce fishmeal or fish oil, the main component of feed for carnivorous species of the fish farms.

piscifacotrias solucion sobreexplotacion
Fish from farm fishing is feed by feed based on wild fish (Picture: Yousuf Tushr, Creative Commons).

In other words, to feed fish from fish farms, wild fish have to be caught, which exacerbates the problem of overfishing. According to FAADA, between 3 and 5 tons of wild fish are needed to feed a ton of farm fish.


We have already seen that aquaculture needs to catch wild fish in order to feed the species under cultivation. Now we are going to see other problems for the animals themselves and the environment.

Due to the fact that the cages are installed at fixed points, in the surrounding waters and on the seabed there is a significant accumulation of nutrients and chemicals from feces and uneaten food. This can cause a bloom of algae, which deplete oxygen and, depending on the species, can cause the production of toxic substances.

However, in some cases some measures have been implemented, such as changing the position of cages every year or placing them in areas with strong currents.

The use of antibiotics and vaccines is frequent to prevent or treat diseases as the stress makes them more susceptible. In fact, in the cages the mortality is around 10 to 30%.

impactos ambientales piscifactorias
Diseases and parasites, such as sea lice, are a common problem in farmed fish (Picture: 7Barrym0re, Creative Commons).

Another important problem is that genetically modified fishes are often used. If by accident or by the effect of predators, these organisms escape and mate with their wild relatives, a significant change in the genetic composition of the species can occur (genetic pollution). In fact, between 1992 and 1996, about 1.3 million salmons escaped each year from farms in Norway. Another effect of the leaks is the transmission of diseases and parasites to the wild organisms.

Another disadvantage of farms is that non-native species are often cultivated, that is, species that do not belong to the area in which they are caged. Their escape may involve competition for resources (both food and habitat) with native species. We have already seen that exotic species are a problem for biodiversity.

As we have said, predators can be a problem for companies engaged in fish farming. The solution to this threat is their control or killing, thus affecting their populations.



We have seen that farms have a number of advantages to solving the problem of overfishing. In any case, feeding farmed fish with wild animals further increases the problem of overfishing; in addition to the other existing problems.

What do you think: are the advantages of fish farms more important than their drawbacks? Leave your opinion in the comments of this article.


You can save bluefin tuna!

Bluefin tuna is an endangered predator fish. Last week, we explained that other species like sardines and mackerel are also endangered due to overfishing. This week, we will focus on this species and we will explain its biology and distribution, in addition to the reasons why it is under threat. 


Bluefin tuna (Thunnus thynnus) is the biggest species of the Scombridae family and one of the biggest bony fishes. Despite they can achieve a length of 3 meters, they usually range between 0.4 and 2 meters. Moreover, they weight between 140 and 680 kilos, but it is difficult to find an organism that exceed 450 kilos. It is a migratory animal with a high economical value for its red and dusky meat. The body is fusiform and can be distinguished from the rest of tunas by pectoral fins: they are rather short and reach the 11th or 12th dorsal spine.

Tonyina vermella (Thunnus thynnus) (Foto de Club de la Mar).
Bluefin tuna (Thunnus thynnus) (Picture from Club de la Mar).

Back and upper sides are dark blue to black, with a grey or green iridescence. Inferior sides are silvery with grey spots and bands. Anal in is dark and yellow.

Diet of bluefin tuna includes squids, eels and crustaceans, but also schooling fishes like herrings and mackerels.


Bluefin tuna lives in subtropical and temperate waters of North Pacific, Atlantic, Mediterranean and Black Sea. Despite bluefin tuna can be found along the year in the Mediterranean, they are present mainly in June and July.

Tonyina vermella en llibertat (Foto de Animals on Earth).
Free bluefin tuna (Picture from Animals on Earth).


According to IUCN, bluefin tuna is endangered and its population is in decline. Due to overfishing, being the most important the illegal fishing, it is estimated that Western Atlantic population has decreased in an 87% since 1970. Anyway, other references indicates that this drop has been between 29 to 51%. In 1996, scientist alarmed that worldwide catch quotas must be reduced an 80% to recover populations in 20 years, but in fact they were increased. Nevertheless, it seems like the reduction of captures recently has produced an increase of populations.

Because they achieve maturity in an advanced age, they are specially vulnerable to overexplotation. Despite catch quotas have been established, the measure have not had always success for several reasons: disembark of small fishes (and big) has continued, the lack of regulations in some areas, fishermen ignore restrictions in some countries and the lack of fines when breaking the lows.

Between 2000 and 2004, it had been captured about 32,000 – 35,000 tonnes per year in the Eastern Atlantic and Mediterranean, achieving 50,000-60,000 tonnes in 2006, so the stock status is overexploited. Nowadays, the catch quota is restricted to 13,500 annual tonnes, but 3,000 tones are for Spain.

This tuna is captured with different types of fishing: purse-seine, longline and tramps. The reason of its fishing is to meet demand of Japanese market of sashimi (just one piece of tuna can be sold for 90,000€), what caused its overfishing. In addition, it is a goal species in recreational fishing of United States and Canada.

Sashimi de atún rojo (Foto de TripAdvisor).
Bluefin tuna sashimi (Picture from TripAdvisor).

So, fisheries are being reduced and, at the moment, neither European Union nor other countries have acted to save it. In addition, governments have ignored experts.


Bluefin tuna is a predator of jellyfishes. Its reduction, together with the rise of sea temperature, is causing a rising of jellyfishes. Moreover, its disappearance would produce an imbalance of food webs.

If you are worried about the status of bluefin tuna and the oceans, when you go to a fish market, don’t buy it and also when you go to a Japanese restaurant, refuse to eat any dish with tuna. Only reducing the demand, we will be able to stop its fishing. 


Eat less sardines to eat more sardines

A recent study published in November 2014 in Proceedings of the National Academy of Sciences of the United States of America (PNAS) demonstrates the effect of fishing in forage fish population collapses. In this article, we are going to do a review of it.


Forage fish is important in two ways: in the first one, they support the largest fisheries in the world; and in the second one, they transfer energy from plankton to predators, like large fish, seabirds and marine mammals. So, if fishing depletes foraging fish, the consequences can be catastrophic in both the ecological and the economical way. When a fish population collapses, there are three additive reasons:

  1. High fishing pressure for several years before collapse.
  2. A sharp drop in natural population productivity.
  3. A delayed response to reduce fishing pressure.
Forage fish: The vital link of the ocean food webs (Picture from Grist)
Forage fish: The vital link of the ocean food webs (Picture from Grist)


Forage fish are small fishes that eat plankton (phytoplankton or zooplankton) and are eaten by larger predators that are higher on the food web. They play a key role in marine ecosystems by transfering energy through the food chain. So, the collapse of theses species can produce widespread ecological effects. They include sardines, capelin, herrings, anchovies, mackerels, sand eels and menhaden. Further information here.

Some examples of forage fish (Picture from The Pew Charitable Trust).
Some examples of forage fish (Picture from The Pew Charitable Trust).

They also provide benefits to people since these species support the 30% of the worldwide fisheries by weight, as well benefiting aquaculture and livestock industries.

It is important to know that these species, naturally, suffer large cyclical fluctuations in abundance. For this reason, the fishing pressure on these species can aggravate the situation.


Almost one-half of the forage fish studied populations collapsed at a limit of 25% of the average population biomass and almost one-third do it at a limit of 15%. Severe depletions of these populations have commonly occurred and the reasons of this population collapses are a combination of three elements: rapid decline in natural productivity (average population productivity dropped 2-3 years before collapse), continuous high fishing rate (50-200% higher that average annual fishing rates) and retarded response of the fishery to low productivity.

Fishing rate is an important factor that contribute to collapse of populations because it was higher in collapsed populations (1/0.44 vs. 1/0.26 years), while the mean natural productivity was similar in both cases. Models predict that only 4 of the 15 studied populations would have collapsed due to a decline in natural productivity. Moreover, the average minimum biomass levels would have been six times greater if fishing had not occurred during the years immediately leading up to collapse. So, it can be concluded that high fishing rates promotes population collapse.


There are two managements tools to protect predators that feed on forage fish. The first case consist on developing early warning indicators of changing stock productivity, but it has been successful in some particular cases. The second one overcome the limitations of the first and consist on a risk-based approach, when fishing is restricted during the high-risk periods.

It is important to emphasise that reducing fishing when forage fish are moderately limited would have small effect on fishery catches while providing substantial ecological benefits. 



Recreational fishing in marine reserves: is it compatible?

This week, the topic of the article is recreational fishing in marine protected areas. In concrete, it is explained what recreational fishing is, which are the impacts and a list of recommendations is given to reduce the impacts. This article has been written together with Guillem Santamaria, for the subject Marine Reserves of the Master in Oceanography and Marine Environment Management. 


Recreational fishing has an important impact in Marine Protected Areas (MPA), being one of the most common activities in all the coasts worldwide (Font et al. 2012).

We understand recreational fishing as that non-commercial fishing done with leisure or sports purposes and in which captures, which is forbidden its sale, are used for personal consumption (Font et al. 2012). Despite several definitions have been proposed, this includes most of the disciplines.

Recreational fishing has a great importance worldwide. In 1995, worldwide total captures were about 2 million tonnes and, in 2004, 47.000 million fishes were caught, of which two thirds were returned into sea (Cooke et al. 2006). In European perspective, in 1998 there were about 21.3 million recreational fishers from 22 countries, of which 10 invest 10 million dollars (Cooke et al. 2006). A study from 2004 estimates that this investment increase to 25.000 millions of euros in Europe, with more than 10 millions of fishers, exceeding 5.000 millions of euros of benefits the commercial captures of the state members in 1998 (Pawson et al. 2007).

La pesca recreativa té una gran importància a nivell mundial (Foto extreta de Magic1059).
Recreational fishing is important worldwide (Picture from Magic1059).

Despite recreational fishing is not well studied than traditional fishing, several studies suggest that both can suppose a similar impact in fish stocks and aquatic ecosystems (Cooke et al. 2006). In the Mediterranean, recreational fishing represents more than 10% of the total fishing production (EU, 2004).


Fishing from boats is the one that includes more techniques, followed by fishing from shore (Font et al. 2012). Moreover, fishing from kayak is increasing and uses GPS and deep sensors. According to Font et al. (2012), the most used types of fishing from boats are: bottom fishing with rod, handline and trolling. In the case of fishing from shore, it is important bottom fishing with rod cork buoy to capture species from rocks, and spinning to capture pelagic species and some Sparidae. Spearfishing uses harpoons.


In the last decades, it is increasing the number of recreational fishers that do their activity in Marine Protected Areas and, for this reason, impacts in resources and marine ecosystems are increasing (Cooke et al. 2006). In general, it reduces the potential benefits of the reserve effect and spillover (the fact that organisms go out the protected zone) (Font et al. 20012). Some studies have show that no-take zones are effective in conservationist terms (Denny & Babcock, 2004).


Font et al. (2012) determine that the type of fishing that capture, in average, the biggest number of different species is fishing from boats (38 species), followed by shore fishing (28) and spearfishing (25). Spearfishing is more selective and, as a consequence, captures less species  (Jozami et al. 2011).

Sparidae, Serranidae and, with less extend, Labridae families has been the most capture. About species, comber (Serranus cabrilla) and Mediterranean rainbow wrasse (Coris julis) are the most captured species in both fishing from boat and shore fishing. On the other hand, in spearfishing the main captures are: white seabream (Diplodus sargus), common two-banded seabream (Diplodus vulgaris), European seabass (Dicentrarchus labrax) and common octopus (Octopus vulgaris) (Cuvier, 1797).

Sard (Serranus cabrilla) (Foto extreta de Asturnatura).
Comber (Serranus cabrilla) (Picture from Asturnatura).
Donzella (Coris julis) (Foto extreta de Ictioterm).
Mediterranean rainbow wrasse (Coris julis) (Picture from Ictioterm).

In the 31 Mediterranean MPA studied by Font et al. (2012), it has been found that recreational fishing captures 41 vulnerable species. The average ratio of vulnerable species in the capture is about 30%. The biggest impact in vulnerable species is produced by fishing from boat (39 vulnerable species) because it uses more techniques, captures are bigger and they can move to different habitats. Spearfishing fishing goals are generally vulnerable species because they have a long life and a slow growth. These species have a reproductive potential that increases with age, so when fishers captures the biggest animals, it is drastically reduced the reproductive potential of the population (Jozami et al. 2011).


Capture and freeing 

Although capture and freeing is widespread, in the Mediterranean it is not because what is taken usually is eat. This practice is not free of negative impacts on the organisms. Some actions in the manipulation of the animals can cause many stress and death. Minimizing the time of manipulation and the exposure to air, and using devices to reduce the injury, stress and mortality; many of the negative effects can be eliminated (Arlinghaus et al. 2007).

Mètode d'extracció de l'ham de la boca del peix (Foto extreta de WikiHow).
Method to remove hook from the mouth of a fish (Picture from WikiHow).

Accidental captures

Elasmobranchii are the most important accidental captures in recreational fishing (Font et al. 2012).

Ecological impact of bait

In the 93.3% of the MPA studied by Font et al. (2012), worms are used as bait. The use of exotic species (80% of the cases (Font et al. 2012)) can be a threat for ecosystems (Di Stefano et al. 2009). Moreover, we have to have into account that these baits usually are sell alive and to do that they have a substrate of exotic algae, where small crustaceans, other worms and snails can be present. If this substrate is thrown to the water, the consequences can be horrible because new viruses can affect fishes (Goodwin et al. 2004).

Ghost fishing 

Ghost fishing is the negative effects of devices lost and abandoned into the sea, like lead weights, lines and hooks.

The loose of lead weights affects seabirds because they confuse them with stones (that are digestive for them) and cause lethal effects. When another bird (eagle, falcon…) feeds on them, it happens the bioaccumulation, what can cause morphological, physiological and behavioural disorders. Nevertheless, the impact is less important than the caused by the atmospheric lead. (Font et al. 2012)

Fishing lines abandon sessile organisms, causing abrasion, strangulation and the reduction of the light.

Plastics produce the plugging of the digestive tracts and reduce the reproductive capacity.


Anchoring can affect marine environment, specially seagrasses, with a huge ecological importance.


És important presentar unes bones pràctiques de pesca per tal de minimitzar l'impacte en les poblacions marines (Foto extreta de NSW Government).
It is important to know the good practices to minimize the impact of marine populations (Picture from NSW Government).


  • To regulate the fishing effort with the limitation of the number of rods, hooks (number and size) and licences.
  • To increase the vigilance and control in MPAs, assuring the compliance of laws, specially in no-take zones.
  • To forbid and control the use of exotic bait.
  • To implement cleaning programmes of fishing devices to reduce ghost fishing.
  • To control and penalize the sale of captures.
  • To increase the capture and freeing practice in a good way: minimizing the time that the animal is out of the water and that is being manipulated, minimize the injury using devices to free the hook and avoid the unnecessary manipulation.
  • To limit the fishing of concrete species in reproductive periods.
  • To apply measures that stablish a minimum size over the size of sexual maturity.
  • To forbid or limit the fishing of vulnerable species.
  • To reduce the use of lead weights.
  • To include recreational fishing in the management programmes of marine resources exploitation.
  • To stablish educational programmes.
  • To do specific researches about the impact of recreational fishing in the communities inside the MPAs.

Fishing from boats

  • To control the captures through observers in the boats (minimum size, vulnerability of the species, accidental captures, number and biomass of captures…) and to do the capture and freeing practice in a good way.
  • To stablish anchoring systems that don’t destroy the seafloor, like buoys.
  • To minimize movements and noise inside MPAs to avoid bother and injury in animal and plant communities.

Shore fishing

  • To stablish controlled zones and limit the practise.


  • To direct spearfishing with guides and/or observers that indicate which are the animals that can be fished.
  • To control the use of scuba sets.


  • Arlinghaus R., Cooke S. J., Schwab A. & Ian G. Cowx.2007. Fish welfare: a challenge to the feelings-based approach, with implications for recreational fishing. Fish and Fisheries 2007, 8, 57–71.
  • Cooke S. J., Ian G. Cowx. 2006 .Contrasting recreational and commercial fishing: Searching for common issues to promote unified conservation of fisheries resources and aquatic environments. Biological Conservation 128 : 93-108.
  • Denny C.M., R.C. Babcock. 2004. Do partial marine reserves protect reef fish assemblages? Biological Conservation 116 (2004) 119–129.
  • Di Stefano R.J., Litvan, M.E., Horner, P.T. 2009. The Bait Industry as a Potential Vector for Alien Crayfish Introductions: Problem Recognition by Fisheries Agencies and a Missouri Evaluation. Fisheries 34(12): 586-597.
  • EU. 2004. Mediterranean: guaranteeing sustainable fisheries. Fishing in Europe 21: 12.
  • Font T., Lloret J., Piante C. 2012. Recreational fishing within Marine Protected Areas in the Mediterranean. MedPAN North Project. WWF-France. 168 pages.
  • Gaudin C. & De Young C. 2007. Recreational fisheries in the Mediterranean countries: a review of
  • existing legal frameworks. General Fisheries Commission for the Mediterranean. Studies and Reviews No. 81. ISSN 1020-9549.
  • Goodwin A.E., Peterson, J.E., Meyers, T. R, Money, D.J., 2004. Transmission of exotic fish viruses: the relative risks of wild and cultured baits. Fisheries, 29: 19–23.
  • Jozami S.I., Lorente A., Hereu B. 2011. Área marina protegida del parque natural del Montgrí, las Islas Medes y el Baix Ter. Análisis de los usos y recomendaciones de gestión. Tesis de Màster. Universitat de Barcelona.
  • Lau W. 1995. Importation of baitworms and shipping seaweed: vectors for introduced species? In Environmental Issues: From a Local to a Global Perspective, Sloan DM, Christensen KD (eds). Environmental Sciences Group Major, University of California: Berkeley, CA; 21–38.
  • Pawson M.G., D. Tingley, G. Padda, H. Glenn. 2007. EU contract FISH/2004/011 on Sport Fisheries (or Marine Recreational Fisheries) in the EU. Prepared for The European Commission Directorate-General for Fisheries.


How can we save marine turtles from longline fishing?

This week, in this article we discuss how can we save marine turtles from longline fishing, since many species of marine turtles are endangered due to accidental captures. 


Loggerhead sea turtle (Caretta caretta) and leatherback sea turtle (Dermochelys coriacea) are the marine turtles most captured with superficial longline fishing (Gilman et al. 2006), but are also captured the other species (Polovina et al. 2003).  Despite accidental captures of this species are strange, the worldwide whole has an important effect (Lewison et al. 2004). Here, we are focusing in the measure to reduce these accidental captures in the loggerhead sea turtle for the huge available bibliography.

Caretta_Caretta_by_kailorLoggerhead sea turtle (Caretta caretta) (Picture from DeviantArt).


Longline fishing is a type of fishing that consists on a main line from which puts up hooks with bait. It’s one of the most ancient fishing systems that are known. The main line can measure between some hundreds of meters to 50-60 km, with a distance between hooks from 1 meter to 50 m. Despite of being considered the most selection fishing, because depending on the bait and the hook size it is possible to catch one type of fish or another, it is not free from accidental captures, among which we can find sea birds and marine turtles.

longline-fishing-animationLongline fishing, despite of being very selection, captures marine turtles (Picture from Sea Turtle Conservancy).


Reduction of the fishing time

If fishers reduced the time in which the longline is in the water, it would be reduced the accidental captures of loggerhead sea turtle, but this doesn’t happen with leatherback sea turtle (Watson et al. 2005). The problem is that is not economically possible for the reduction in the goal species captures.

Change of the hook

Changes in the hooks are the most effective. Wider hooks reduce turtle’s captures and the proportion of the animals that swallows the hook without compromising the commercial viability the swordfish in the North Atlantic (Gilman et al. 2006), but these doesn’t happen in other fisheries. The shape determines the place where the hook gets hooked: while circular hooks gets hooked in the mandible or in the mouth, J hooks gets hooked internally. The change to a circular hook reduces the captures and the mortality after the freeing (post-release death) in the loggerhead sea turtle because they usually are captured with they bite the bait and this get hooked more externally and it is easier to free them (Gilman et al. 2006; Bolten & Bjorndal 2005; Watson et al. 2003). The change in the shape is effective in certain fisheries and areas, like for example in the swordfish (maintaining the captures (Piovano et al. 2009)) an the blue shark in Azores (Bolten & Bjorndal 2005). For this reason, circular hooks don’t reduce the captures of goal species and suppose a low-cost investment, but complicate their removal and they usually are more breakable than J hooks (Gilman et al. 2006). In conclusion, the use of circular hooks in the swordfish fishery in the Mediterranean and the Northwest Atlantic can suppose an easy and cheap technique to reduce marine turtle captures (Piovano et al. 2009; Watson et al. 2005; Gilman et al. 2006, 2007). The direct mortality produced for the hooks is reduced, so the 80% of the freed turtles are alive, but the post-release death depends on the position of the hook (Camiñas & Valeiras, 2001).

bas09_n02_ac_01Hook types. (A) Circular hook and (B) J hook(Picture from Cicmar).

Change of the bait 

Bait is another important factor. When the bait is fish, the captures of loggerhead turtles are reduced compared to the use of squid, and the captures of swordfish become bigger (Watson et al. 2005). The reason is that they feed on fish doing small bites and this prevent from being swallowed, while squid is more resistant and they swallow the bait completely (Watson et al. 2003, 2004). In the Mediterranean and Northwest Atlantic, using mackerel maintains the swordfish’s captures and reduces the captures of loggerhead sea turtles (Alessandro & Antonello 2010; Watson et al. 2005; Gilman et al. 2006, 2007), but reduces the captures of the Atlantic bluefin tuna (Rueda et al. 2006; Rueda & Sagaraminaga 2008). Using baits with different colours don’t seem to be a good measure because don’t prevent from capturing them (Swimmer et al. 2005; Watson et al. 2002).

Change of the depth of fishing and the distance to the coast 

Loggerhead sea turtles usually dive over the 40 m deep, maximum until 100 m (Polovina et al. 2003). For this reason, if the longline was placed under the depth of more abundance, the captures would be reduced (Rueda & Sagarminaga 2008). The problem is that the goal species captures would be reduced too depending on the fishery (Gilman et al. 2006) and, moreover, if they got hooked, they wouldn’t be able to breath in the surface and they would die. According to fishers, the hooks closer to the buoys capture more turtles because they are in swallower depths (Watson et al. 2002). So, these secondary lines should be longer. The turtle captures also depend on the distance to the coast (Báez et al. 2007), and the longline should be place further than 35 nautical miles and the captures of swordfish captures don’t be affected (Alessandro & Antonello 2010).

Elimination of light sticks 

Light sticks should be banned because increase their capture (Alessandro & Antonello 2010).

Change of the fishing areas 

Marine turtles gather in areas, so one capture increases a lot the probability of capturing more. For this reason, a good measure should be the communication between ships and the shift in the areas (100 km away) during a period of time (for example, one week) (Gilman et al. 2007). This would be very effective, but suppose an extra gas expense and the reduction of the time that fishers are fishing due to the journeys. Another measure could be the permanent or seasonal closure of areas, but this is economically infeasible.

Sea temperature monitoring

The capture rate of loggerhead sea turtles increases when the temperature is over 22ºC, while the capture of swordfish increases under 20ºC. For this reason, it should be better to fish in waters under 20ºC (Watson et al. 2005). However, in this case the fishing pressure on the swordfish should be controlled.

Fisher observers 

A good manage tool is the presence of observers on board a ship, like in the longline swordfish fleet in Hawaii (Gilman et al. 2007). Fisher observers record the number of fishing devices, the fishing days, the fishing position and the number of captured turtles (Álvarez de Quevedo et al. 2010).

JPE_TurtleA good manage tool is the presence of observers on board a ship (Picture from Journal of Applied Ecology).


Turtles have to be freed using the right device to remove the hook and, in the case that it is not possible, the line has to be cut as closer to the hook as possible because this reduces the mortality because the line can affect the intestines (Casale et al. 2007).

Activists Free a TurtleTo free the turtles, the line has to be cut as closer to the hook as possible (Picture from Greenpeace).


The effectiveness and the commercial viability of the strategies to avoid the capture of loggerhead turtles depend on the fishery, the size of the animal, the goal species and other differences between fleets (Gilman et al. 2006, 2007). The combination of circular hooks and fish like a bait is very effective in reducing the captures of turtles without affecting the goal species. This changes, together with tools to remove the hooks and the lines, reduce the accidental captures and the post-release deaths.


  • Alessandro L,  Antonello S (2010) An overview of loggerhead sea turtle (Caretta caretta) bycatch and technical mitigation measures in Mediterranean Sea. Rev. Fish Biol. Fisheries 20: 141-161
  • Álvarez de Quevedo I, Cardona L, De Haro A, Pubill E, Aguilar A (2010) Sources of bycatch of loggerhead sea turtles in the western Mediterranean other than drifting longlines. ICES Journal of Marine Science, 67: 000-000
  • Báez JC, Real R, García-Soto C, De la Serna JM, Macías D, Camiñas JA (2007) Loggerhead sea turtle bycatch depends on distance to the coast, independent of fishing effort: implications for conservation and fisheries management. Mar Ecol Prog Ser 338:249–256
  • Bolten A, Bjorndal K (2005) Experiment to evaluate gear modification on rates of sea turtle bycatch in the swordfish longline fishery in the Azores – Phase 4. Final Project Report submitted to the National Marine Fisheries Service. Archie Carr Center for Sea Turtle Research, University of Florida, Gainesville, Florida, USA.
  • Camiñas JA, Valeiras J (2001) Marine turtles, mammals and sea birds captured incidentally by the Spanish surface longline fisheries in the Mediterranean Sea. Rapp Comm Int Mer Medit 36:248
  • Casale P, Freggi D, Rocco M (2007) Mortality induced by drifting longline hooks and branchlines in loggerhead sea turtles, estimated through observation in captivity. Aquatic Conserv: Mar Freshw Ecosyst doi: 10.1002/acq. 894
  • Gilman E, Kobayashi D, Swenarton T, Brothers N, Dalzell P, Kinan-Kelly I (2007) Reducing sea turtle interactions in the Hawaii-based longline swordfish fishery. Biol Cons 139:19–28
  • Gilman E, Zollet E, Beverly S, Nakano H, Davis K, Shiode D, Dalzell P, Kinan I (2006) Reducing sea turtle bycatch in pelagic longline fisheries. Fish Fish 7:2–23
  • Lewison RL, Freeman SA, Crowder LB (2004) Quantifying the effects of fisheries on threatened species: the impact of pelagic longlines on loggerhead and leatherback sea turtles. Ecol Lett 7(3):221–231
  • Piovano S, Swimmer Y, Giacoma C (2009) Are circle hooks effective in reducing incidental captures of loggerhead sea turtles in a Mediterranean longline fishery? Aquatic conservation: marine and freshwater ecosystems. Published online in Wiley InterScience
  • Polovina JJ, Howell EA, Parker DM, Balazs GH (2003) Dive depth distribution of loggerhead (Caretta caretta) and olive ridley (Lepidochelys olivacea) turtles in the central North Pacific: Might deep longline sets catch fewer turtles? Fish Bull (Wash DC) 101:189–193
  • Rueda L, Sagarminaga R (2008) Reducing bycatch of loggerhead sea turtles in the southwest Mediterranean via collaborative research with fishermen. Poster presented to the 28th international sea turtle symposium Loreto, Baja California Sur, Mexico, 19–26 January 2008
  • Rueda L, Sagarminaga RJ, Báez JC, Camiñas JA, Eckert SA, Boggs C (2006) Testing mackerel bait as a possible bycatch mitigation measure for the Spanish Mediterranean swordfish longlining fleet. In: Frick M, Panagopoulou A, Rees A, Williams K (eds) Book of abstracts of the 26th annual symposium on sea turtle biology and conservation. Island of Crete, Greece, 3–8 April 2006
  • Swimmer Y, Arauz R, Higgins B, McNaughton L, McCracken M, Ballestero J, Brill R (2005) Food color and marine turtle feeding behaviour: Can blue bait reduce turtle bycatch in commercial fisheries? Mar Ecol Prog Ser 295: 273–278
  • Watson J, Foster D, Epperly S, Shah A (2002) Experiments in the Western Atlantic Northeast Distant Waters to Evaluate Sea Turtle Mitigation Measures in the Pelagic Longline Fishery. Report on Experiments Conducted in 2001. US National Marine Fisheries Service, Pascagoula, MS, USA
  • Watson JW, Epperly SP, Shah AK, Foster DG (2005) Fishing methods to reduce sea turtle mortality associated with pelagic longlines. Can J Fish Aquat Sci 62:965–981
  • Watson JW, Foster DG, Epperly S, Shah A (2004) Experiments in the western Atlantic Northeast Distant Waters to evaluate sea turtle mitigation measures in the pelagic longline fishery. Report on experiments conducted in 2001, pp 135
  • Watson JW, Hataway BD, Bergmann CE (2003) Effect of hook size on ingestion of hooks by loggerhead sea turtles. Report of NOAA National Maritime Fisheries Service, Pascagoula, MS, USA

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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. 


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.


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:


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.


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).


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.


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.



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.

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How much fish do we eat?

This article is included in the fishing section, so we will talk about how much fish do we eat worldwide. To do it, we focused on a 2014 FAO report (Food and Agriculture Organization of the United Nations). 

The global production of fish and other aquatic organisms includes two types of activities: on the one hand, the capture or fishing of wild organisms and, on the other hand, their production in aquaculture. This production has increased steadily in the last five decades. The reason is an increase on the demand of fish to be feed: in the 1960s, each person ate 9.9 kg on average every year, while in 2012 this value was about 19.2 kg.

In 50 years it has been doubled the average consumption of fish, achieving 20 kg per person on 2012.

There are some reasons that explain this increase: the worldwide population growth, rising incomes and urbanization, a large expansion of fish production and an improvement on the distribution channels.

EnglishThis picture shows the evolution of the world population from 1800 to 2015 and the increase of the fish consumption for person in the 1960s (9.9 kg) and in the 2014 (19.2 kg). Picture done by Marc Arenas Camps.

China has been the most responsible country of the growth in the availability of fish due to its big rise of the fish production, mainly in aquaculture. Its consumption for person grew in an annual rate of 6% between 1990 and 2010 till 35.1 kg in 2010.

Although developing countries have increased the annual consumption of fish for person, developed countries are still which have the highest levels of consumption, but both are being more equal. An important part of the eaten fish in the developed countries is imported, what explain that the demand in this countries is equal despite its production has decreased.

On the other hand, in the developing countries fish comes from local fisheries and they eat seasonal fish. Nevertheless, these countries are presenting a diversification of the species because it has increased the incomes and wealth.

CapeVerde_16Feb_195In developing countries, the consumption of fish comes from local fisheries and they eat seasonal species. Picture from Greenpeace.

In 1996 there were a maximum in the captures, achieving 93.3 million tonnes, followed by 2011 with 93,7 million tones. In addition, excluding anchoveta (Engraulis ringens) captures, 2012 gets another production maximum (86.6 million tonnes). Concerning fish production in marine waters, this was about 82.6 million tonnes in 2011 and 79.7 million tonnes in 2012. In these years, 18 countries (11 in Asia) were responsible of 76% of total marine captures.

18 countries were responsible of 76% of total marine captures.

Captures in inland waters were about 11.6 million tones in 2012, what represents a 13% of total captures. Finally, production in aquaculture was about 90.4 million tonnes in 2012, including 66.6 million tonnes of fish (43.5 were produced only for China) and 23.8 million tonnes of seaweed (China represents 13.5 million tonnes).

ConsumENGFish consumption during 2012 (in million tonnes) according to FAO. Picture done by Marc Arenas Camps.

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Fishing and general state of fisheries

This is the first post in the topic Impacts of the fishing, whose goal is to expose the impact of fisheries in the sea populations and them ecosystems.


Fishing consists on the exploitation of the aquatic populations that exsists naturaly. Since 1950, it has been observed an increase of the natural captures until 1990 due to the incorporation of motors and sonars in the ships. As of 1990, the capture are around 90 million tonnes. Nowadays, the fishing pressure is so high that the fisheries tend to collapse because the adults cannot produce enough juvenile fishes. The following picture shows the evolution of the natural captures (blue) and the evolution of aquaculture production (green) (FAO).

evolució pesca

The captures of the fisheries have different components. On one side, the capture of the species of interest (goal species) and, on the other side, the other species with no interest (bycatch). Bycatch can be divided into species with low value or discards. Discards consists on species captured unintentionally because they economic value is non-existent, species legally protect or with a bad appearance. Fishing by trawling discards 40% of the captures.

A fishing stock consists on a population or a piece of it that is exploited as a whole. Depending on the exploitation of the stocks, these can be non-fully exploited (blue), when the fishing pressure don’t affect the population; overexploited (red), when the juvenile fishes aren’t enough to recover the adult population; or fully exploited (green), when the stock tends to collapse.


A 10-times reduction on the fishing resources of the continental shelf in just a century has been reported (Christensen et al. 2004), and a reduction too in the resources of the abyssal plain (Devine et al. 2006) and the open sea.

The climate change and the fishing are the main factors that impact the sea. The effects of the fishing take place in the organisms and ecosystems.


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