This not so small ocean critter is an angelshark (Squatina squatina) – also known as a monkfish. Back in the 19th and early 20th century the angelshark had a pretty wide distribution across Europe, and was particularly common around the coasts of the UK, Ireland, and Atlantic Iberia. A nocturnal feeder, these guys bury themselves in sediment and lies in wait for a tasty morsel which, for the angelshark, includes skates, flatfish, and (as once recorded) cormorants. Unfortunately, being a demersal species (living on or near the seabed) they are quite vulnerable to being caught as bycatch in fishing gear like trawls, and bottom lines. Even more unfortunate for the angelshark, they are also quite a tasty species, so they have also been deliberately targeted by fishers.
Slow growing, and producing relatively few offspring, angelshark numbers plummeted, and today it is largely absent from many of the waters it once inhabited. The numbers of angelshark is now so low that the species is listed as critically endangered on the International Union for Conservation of Nature Red List. There seems to be a somewhat predictable pattern to fisheries exploitation. First, as catches declined and technology improved, we responded by moving further out to sea, into deeper grounds, and targeting new species. Second, we tend to target predators first then, as the catch of those guys decline, move our focus onto different species lower down the food web.
The concept of “fishing down marine food webs” was first introduced by Daniel Pauly back in 1998. Daniel used global catch data to infer that a decline in the mean trophic level of the species (an average of how far up the food chain a species is) being caught directly related to what was actually in the oceans. In other words we are catching fewer predators because there are fewer in the oceans. Of course the situation is much more complex than that, and there may be other reasons for changes in trophic catch levels such as regulation changes, as highlighted in a later paper by Trevor A Branch of the University of Washington and a team of collaborators. Whatever the reasons for the declines, Pauly’s findings have been mirrored by many other papers that focus on commercial fishery catches at regional scales. Most recently, Carlotta Molfese and Janson Hall-Spence of Plymouth University, and Doug Beare of WorldFishhave cast an eye over commercial fisheries data from the English Channel, and assessed how catches from the area have declined since the early 20th century.
Spanning some 75,000 square kilometres, the English Channel has a long history of fishing, primarily by French and English fishers. The area has been intensively fished, and unfortunately some species - like the angelshark - are now considered commercially extinct (there are still some there, but the numbers are so few there is little point in fishers specifically targeting them). For their analysis into the changing face of fishery catch from the English Channel, the team used datasets spanning some 90 years from 1920 through to 2010, obtained from the intergovernmental science organization ICES - the International Council for the Exploration of the Sea. This data, which spans a range of different species - from finfish though to molluscs, tells us an interesting if not necessarily all together unsurprising tale of fishing in the Channel.
First to fisheries landings, which is measured in tons. Between 1920 and 1970 there was a gradual increase in the weight of species being landed, from 9,146 t up to 50,924 t, after which landings soared to 177,793 t in 1982. Then came a swift decline and by 1985, landings had fell to just under 97,000 t. Catches did increase again and from 2000 onwards seemed to stabilize between 130,000 – 150,000 t. So what is going on here? Did the populations rebuild back? If we look at the species that make up these catches, we can see that they have dramatically changed since the 1920's. For example, back in 1920 cod, haddock, and hake species made up 48% of the catch. By 2010 they made just 14% of the catch. Catches of sharks, rays, and chimeras have declined from 34% in 1926 down to just 6% in 2010. But remember, the landing tonnage tells us that landings have stabilized somewhat – and at a level much higher than the low point in 1985. This is because whilst many species declined, some species – especially invertebrate species, like the European lobster and Great Atlantic scallop have increased over the years. Since the 1970s, almost half of the landings are made up of squid, octopus, and cuttlefish, and ‘miscellaneous aquatic invertebrates’, a pattern seen in other regions of the world too. If we translate the catches to mean trophic level, this has decreased by 0.1 unit per decade since 1920, making it one of the fastest rates reported in heavily fished areas so far. It’s not all increase and decrease though. Catches of some species like flounders and soles didn’t really changed that much over the 90 year period.
What we are seeing, suggest the researchers, is that landings between 1925 and 1970 were only maintained because we increased fishing effort – heading out into new waters and improving technology to increasing the efficiency of fishing. There are also environmental factors to consider. Between 1980 and 2010 they note that in the Northeast Atlantic sea temperature as well as productivity in the region was on the increase. Warmer seas might be nice for us to swim in, but for cold-water species like haddocks and cod, warm isn’t so great. The warmer temperatures coincide with the decline in the number of those species being landed. Incidentally, landings of demersal species like cod, hake, and haddock increased after the first and second World Wars, but declined quickly thereafter. During both wars, fishing effort declined significantly throughout Europe, particularly the English Channel. This relief from fishing allowed the populations to rebuild slightly and so when the fishers returned to the sea after the wars they were rewarded with large catches. Unfortunately overfishing quickly followed, and demersal fisheries went from boom to bust.
But does all this mean that higher trophic level species have really declined in the English Channel? The researchers certainly think it likely. In particular they highlight the price of species, noting that as a resource becomes scarcer, its price tends to increase. High trophic level species have indeed increased in price, and the UK is importing large numbers of demersal fish to meet demand. Focusing on the UK, they also note that although the UK has imposed quota restrictions on these species this hasn’t really been a reason for the reduction of high trophic level species being landed, as the level of catches haven’t even reached UK quota limits.
If indeed there has been a decline in predators and there isn’t some other reason for our failure to catch them in the English Channel then there will invariably be ecosystem wide impacts, primarily through two routes. The first is the trophic cascade – when a predator population reduces, allowing its prey population to grow, which then reduces whatever it preys on… and so forth. The second is through competitive release – freeing up shared resources for other species. And whilst our ability to adapt to the changing ecosystem to exploit different species is in the short-term good for the fishing industry, we are failing to learn from our past mistakes. We are continuing the same pattern of boom and bust, and now with our focus on species like scallops and prawns, we are using highly destructive bottom trawling gear. There is a chance to redeem ourselves, point out the researchers. We need a plan; we need a holistic, ecosystem based plan. Crucial to that plan, the researchers emphasise, is effective conservation zones in which destructive fishing practices – like bottom trawling – are banned.
The paper is published in the open access journal PLoS ONE so why not check out the original yourself http://www.dx.doi.org/10.1371/journal.pone.0101506
Image: Angelsharks in Tenerife. Credit Philippe Guillaume/Flickr (CC BY 2.0)