Sharks in trouble?

It might be a surprise that in the ICES area we have over 100 recorded species of sharks and their relatives. Sharks and their relatives are called elasmobranchs.

Sharks have been around for more than 400 million years.

The term elasmobranch encompasses the group of fishes that is characterised by having skeletons composed entirely of cartilage. These fish have been around for a very long time, more than 400 million years. Though they appear to have evolved slowly since then, they have some remarkable features that we, as marine scientists, need to be aware of.

To begin with the diversity of reproductive modes is most surprising. Unlike most other fish, all elasmobranchs copulate and have internal fertilisation. Some, such as skates, produce eggs, but others, such as most sharks, give birth to live young. Most fish that we work with in ICES produce large numbers of progeny that are at the mercy of the environment. In contrast, elasmobranchs produce small numbers of young, better able to survive predation in the sea.

Elasmobranchs are very well adapted to their environment. Although they have low reproductive output, populations are quite stable. The theory is that they have evolved such that growth/reproduction and mortality are balanced and their populations exist at the level their environment can support.

Of course this is an oversimplification as all populations are subject to fluctuations. But because of their more predictable life cycle, we can assume more stable populations. Their slow and steady life strategy seems to have served elasmobranchs well, for millions of years.

But then humans enter the equation and when we start to remove them at a rate that is greater than their ability to replace themselves, their populations are not able to respond.

Fishing for sharks

From the wide diversity of European elasmobranchs, only a few have supported fisheries.

Basking sharks
There have been targeted fisheries for centuries for the basking shark. But the last of these, by Norwegian harpoon vessels, has ceased in recent years.

Porbeagle
Our other widespread big shark, the porbeagle, has been targeted in most countries along its migratory route, with a target fishery by Faroese vessels in earlier years. Though targeting has mostly ceased, there are sporadic targeted fisheries from time to time.

The porbeagle is a valuable species and its flesh is highly prized. Like other large sharks, a lucrative market for its fins has developed in recent times in SE Asia.

Spurdog
Perhaps the largest fishery has been for the spurdog. This is a very widespread small pelagic shark that is found in many parts of the world. ICES area landings peaked at almost 70,000 t in the 1960s when UK and Norwegian vessels targeted the species.

Perhaps the largest fishery has been for the spurdog, a widespread small pelagic shark

The landings declined from then until the 1980s when targeting began in Ireland, England, and Wales. This species is still valuable, and targeted fisheries will continue to be lucrative, even though the once plentiful schools of spurdogs have become difficult to locate as the stock has become depleted.

Skates and rays
skates and rays have always been fished in demersal gears in various areas and this continues. Some inshore specialist fishermen target them, but most are taken in mixed fisheries for gadoids, flatfish, anglerfish, and hake.

Deepwater sharks
The newest development in elasmobranch fishing in the ICES area is for deepwater sharks. These sharks are not highly valuable.

They are caught in large numbers by fleets that diversified into deepwater fishing in the 1990s as an alternative to traditional fisheries. The main fleets catching deepwater sharks are French and UK trawlers, UK and German gill netters, and Portuguese artisanal longliners.

Other countries that have become involved are Spain, Ireland, and Norway. The diversity and widespread nature of deepwater sharks means that fishers in deepwater areas cannot avoid catching them.

What effect have these fisheries had on shark populations?

Spurdog
Starting with the spurdog, a variety of models within the ICES Working Group on Elasmobranch Fisheries (WGEF) have been used to estimate the population and the results show that the NE Atlantic stock is depleted – possibly down to as little as 5% of its initial biomass.

The NE Atlantic spurdog stock is depleted - possibly down to 5% of its initial biomass.

These results are sensitive to data quality, and because up-to-date biological data for the species are incomplete, they should be treated with caution. But we have recently run another model and again declines were demonstrated.

Although we are still unable to calculate the absolute stock size, the evidence of a strong decline of spurdog cannot be ignored and urgent measures are likely to be needed to prevent a collapse of the stock. Landings have reached their lowest levels since WW2.

ICES WGEF estimate of landings of spurdogs in the entire ICES area since 1905.

This species is still valuable, and targeted fisheries will continue to be lucrative, even though the once plentiful schools of spurdogs have become difficult to locate, further evidence indicates that the stock is depleted.

In fact some EC nations have now taken to importing spurdog from the Northwest Atlantic fisheries to make up for the lack of landings in the Northeast Atlantic.

For basking shark, porbeagle, and other pelagic sharks, very few data exist for assessment.

Basking shark
At present there are no directed fisheries for basking shark in the ICES area; the main catch is as bycatch in other fisheries and more data is needed on the size of this bycatch.

Porbeagle
While the catch data for basking shark are available for the period when fisheries operated, for porbeagle even these data are not complete. Porbeagle-directed fishing in the ICES area is thought to have ceased by the 1970s, as the fishery became unprofitable, indicating that the stock was depleted - at least to uneconomic levels.

As scientists, we are left with a strand of evidence of stock decline and no evidence that it has since recovered. Having considered the problem, ICES WGEF concluded that no fisheries should be allowed to proceed unless new information is presented that could be used to calculate sustainable catch levels.

Blue, mako and thresher sharks
Catches of other pelagic sharks such as blue, mako, and thresher shark are mainly as a bycatch in tuna and billfisheries where blue sharks, for instance, can comprise up to 70% of the total catch. Little has been done to assess the impact of bycatch on pelagic shark populations.

Deepwater sharks
The effects of fishing on deepwater sharks are a particular concern because of their slow reproductive rates. The rapid development of fisheries for deepwater sharks has also made it difficult for scientists to collect data and perform stock assessments.

Two leafscale gulper sharks in foreground, one Portuguese dogfish at the back.

The main species taken in these fisheries are the leafscale gulper shark (Centrophorus squamosus) and the Portuguese dogfish (Centrophorus coelolepis). The first assessment, in 2000 by the ICES SGDEEP in 2000, was based on catch per unit effort in kg per hour fished from French deepwater trawlers. The results suggested that in 1998, the combined stocks of Portuguese dogfish and leafscale gulper shark were below 50% of their initial biomass.

Unfortunately, this assessment could not give information on the status of either of these shark species separately, so WGEF has recently tried to address this problem. All available CPUE data from France, UK, Ireland, and Norway were pulled together by WGEF and a stark trend was confirmed: there has been an extreme decline, particularly in Portuguese dogfish, a species that was once an abundant shark in deepwater catches.

The low reproductive output of the Portuguese dogfish, coupled with the fact that females—including pregnant females dominate the catches, explains this decline.

Not having species-specific catch data disguised an extreme decline of a vulnerable species. Landings of these species have peaked at about 11,000 t in 2003. Although it is difficult to advise on a sustainable catch with so little information, the current fishing effort is clearly too high.

Lesser spotted dogfish seem to be increasing in numbers...

Lesser spotted dogfish on the increase
But not all elasmobranchs are showing declines in the ICES area. The recent EU DELASS project suggested that the lesser spotted dogfish on the north Spanish coast has increased its biomass. North Sea IBTS (International Bottom Trawl Survey) data shows increasing abundance of this species from 1990 to 2004.

This trend appears in other areas too, and will be further investigated by WGEF in 2006. The question is whether the increase in dogfish populations is because it is mainly discarded alive from fishing boats (so lives to see another day), or due to the removal of its competitors, or increased availability of food (it scavenges on discarded fish). Or is it something to do with changing environmental conditions?

WGEF estimated landings of rays in the North Sea area

Other demersal elasmobranchs in the North Sea have not been doing as well as the dogfish. The thornback ray (Raja clavata) displayed a strong decline in abundance and distribution from 1990 to 2004. One hundred years ago this species was found all over the North Sea : today it is in small patches in the North Sea with a stock concentrated in the southern North Sea.

Also the once widespread common skate (Dipturis batis) has been reduced, primarily by fishing, to very low levels in the North Sea and now occurs only sporadically. While these two species have declined, a third species, the spotted ray (Raja montagui), appears to have fared better and its population has been stable over the same period.

Getting better data

WGEF has made a lot of progress in many areas. But perhaps the most important development has been the disentanglement of landings data for elasmobranchs. Official ICES area landings have amounted to over 5 million tonnes of elasmobranchs since 1953, but about 2.5 million t of this has often been recorded in group categories that are not species-specific – such as “various sharks”.

Obviously, this means that we can’t track which species has been landed and unfortunately this practice continues in many ICES member countries. It is difficult to comprehend how the ICES community, having ambitions towards excellence in fisheries science and management, could accept such shoddy practices. The lack of even the most basic information on removals of vulnerable species from our seas surely cannot continue.

Patchy management of shark fishing

Total Allowable Catches (TACs) and quotas are in place for only a few elasmobranchs, mainly those in the North Sea . Elsewhere, there are some regulations in some areas, but no overall management regime exists. In 2005, for the first time, ACFM has been asked to produce fisheries management advice for elasmobranchs which is a positive move.

Conclusion: sharks face uncertain future

Overall, the picture seems to be that most pelagic shark stocks (spurdog, porbeagle etc) in the ICES area have been depleted.

Demersal elasmobranchs are displaying mixed fortunes, with increases and declines.

The European fishing industry is also going through a difficult period. Its future, however, cannot depend on such depleted and low-productivity stocks and their vulnerability means that we must be precautionary in our scientific advice.

For more information please contact:

Maurice Clark
Chair of the ICES Working Group on Elasmobranch Fisheries
Marine Institue, GTP, Parkmore,
Galway , Ireland
Tel: + 353 91 730 400
E-mail: Maurice.Clarke@marine.ie

Useful websites

ICES Working Group on Elasmobranch Fisheries

Information on shark bycatches

http://www.iccat.es/Documents/SCRS/DetRep/DET_shk.pdf.

ICES
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