Fishing Down the Food Chain

Fishing down the food chain (also known as fishing down the food web) is a concept used to describe the process of moving away from catching large fish (because they have become too scarce) and instead targeting progressively smaller and smaller fish until eventually non-fish species are targeted when all of the fish species have been completely removed. In these days of depleted fish stocks fishing down the food chain is a concept which has become increasingly relevant across the world. The phrase ‘fishing down the food web’ has been credited to the world-renowned French fisheries scientist Professor Daniel Pauly, whose co-authored paper Fishing Down Marine Food Webs coined this phrase when it was first published in 1998.

Tsukiji Fish Market in Central Tokyo handles 600,000 tons of fish a year. The overfishing of large predatory fish such as tuna is a major issue in fishing down the food chain.

Tsukiji Fish Market in Central Tokyo handles 600,000 tons of fish a year. The overfishing of large predatory fish such as tuna is a major issue in fishing down the food chain.

The basic idea behind fishing down the food chain is simple. In an unexploited (pristine) marine ecosystem there will be a balance between large, long lived predatory fish such as sharks and tuna, medium sized fish such as grouper and cod and smaller species which the large and medium fish prey on such as mackerel and squid. There will also be even smaller species forage species such as sandeels, herring, sprats and anchovy (which the mackerel prey on), as well as crustacean and shellfish species on the seabed. Fishing down the food chain happens when species are removed from this ecosystem in the order shown below.

Fishing down the food chain

  1. In the first stage the very largest predators such as shark and tuna are targeted by commercial fisheries as these are the most valuable species. However, as the majority of these species are slow growing and long-lived they can be reduced in number in a very short amount of time.
  2. Once the shark and tuna species become too low to fish commercially the attention will shift to fish on the next stage of the food chain which are medium sized species such as cod and grouper. These too will be exploited until they are reduced in number to such an extent that it is no longer commercially viable to target them.
  3. The fish next targeted are the smaller species which the cod and grouper used to prey on such as mackerel and squid.
  4. Once the mackerel and similar species have been exhausted (or reduced to such as small number that it is no longer economical to fish for them) then commercial fisheries will switch to catching the forage fish which were once prey for the mackerel – small species such as herring, anchovy and sandeels.
  5. As forage fish are the smallest species of fish which are caught commercially then once they are exhausted the commercial fishing operations must switch their attention to non-fish species. These are generally crustacean species such as crabs, shrimps and prawns as well as shellfish species, all of which are likely to have boomed in numbers due to all of their natural predators being removed from the ecosystem. Since crab, prawn and shellfish are all commercially valuable the fishery may still be able to provide employment and profit and successfully disguise the fact that the ecosystem has been stripped of fish and is now only capable of supporting crustacean and shellfish species.
  6. In some places crabs and shellfish have been fished out, leaving commercial fishermen no choice other than to scrape the final stage of the food chain and attempt to catch creatures such as starfish, sea cucumbers and jellyfish.

In total the volume (by weight) of large predatory sea fish has reduced by 67% across the world in the last century, while the volume of smaller prey-fish has increased by 130% over the time scale (source). This removal of large fish and the booming numbers of small fish leads to the concept of fishing down the food chain being put into practice, as the examples below show.

Example of Fishing Down the Food Chain 1:The Firth of Clyde, Scotland

Main article: The Decline of the Firth of Clyde

Firth of Clyde nephrops

Crustaceans such nephrops are now the only species which are commercially caught in the Firth of Clyde.

The Firth of Clyde on the west coast of Scotland was once one of the most productive fisheries in western Europe and possibly the world. The relatively sheltered waters attracted a multitude of species, but it was the herring fishery which formed the backbone of the fishing industry and provided plentiful employment for those living in and around the Clyde. A ban on bottom trawling introduced all the way back in the 1800s meant that the marine environment was protected from over-exploitation and the stocks of all species remained healthy. However, the increasing efficiency of fish-catching vessels meant that fish stocks in the Clyde were starting to show signs of depletion by the middle of the twentieth century. While this should have seen fish stocks given greater protection and signalled a reduction in fishing intensity it was instead agreed in the 1960s that the bottom trawling ban would be lifted, meaning that demersal fish such as cod, haddock and flatfish could now be fully exploited. While a ban on trawling within three miles of the shore was originally put in place this was lifted shortly after, and the entire Firth of Clyde was open to commercial fishing.

This had the effect of wiping out the remaining large demersal fish, while numbers of the pelagic (mid-water) herring also dropped dramatically, meaning that it soon became impossible for the Clyde to support a fishery which relied on catching finfish. While the number of fishermen employed in the area shrank dramatically those who remained did were forced to begin fishing down the food chain. They switched from targeting fish and instead began catching crustaceans – mostly nephrops (a lobster species also known as Dublin bay prawn or scampi) and crabs and lobsters. However, this type of fishing requires heavy gear and fine mesh nets to be dragged along the seabed, further damaging the marine environment and reducing the chances of the cod, haddock and plaice from returning. Today 98% of the commercial catch in the Firth of Clyde is made up of crabs, lobsters and nephrops, and the only finfish found in the area in any meaningful numbers are small, immature whiting as well as a brief run of summer mackerel. The Firth of Clyde is a perfect example of intensive commercial fishing operations completely changing an ecosystem and commercial fishermen being forced to fish down the food chain in order to continue catching anything. One has to wonder what the commercial fishermen will attempt to catch once the stocks of crustaceans begin to run out.

Examples of Fishing Down the Food Chain 2: The Grand Banks, Canada

Main article: The Collapse of the Grand Banks Cod Fishery

The Grand Banks off the coast of Newfoundland, Canada was, for hundreds of years the most productive cod fishery on planet earth. Scientists now estimate that in the 1500s when explorers first arrived there was a spawning cod biomass of 4,000,000 tons. By the late 1990s the fishery had been intensively trawled by a growing number of vessels which were increasingly effective at hunting down and catching the remaining cod stocks. By the mid-1990s catch rates had collapsed and scientific surveys showed that the remaining biomass was somewhere around the 2,000 ton mark. This led to the entire cod fishery being closed in an attempt to rebuild the stocks, leading to mass unemployment and huge social and economic upheaval across the entire region. Twenty years on – with cod fishing banned – the Grand Banks have yet to return to a fraction of their former productivity.

Commercially caught snow crabs.

Crustacean species such as snow crab have replaced cod as the commercial catch in the Grand Banks.

While the complete collapse of cod stocks has been an economic and ecological disaster some fishermen are making as much money – and in some cases even more money – than they were in the heyday of the cod era. These fishermen target crab, shellfish and shrimp and have seen numbers of these species boom as cod, their natural predators, have been eliminated from the area. With growing demand for shellfish across the world crab and prawn species have increased in value, meaning that a proportion of Grand Banks fishermen (i.e. those who target crabs, prawn and shellfish) are in a better position than they were before the crash in cod stocks. Indeed, the Canadian authorities appear to have learned from the mistakes made with cod and seem determined to stop the same thing from happening with the now abundant crustacean and shellfish stocks, as crab have been caught within very strict limits, and the Newfoundland and Labrador snow crab fishery has even been awarded MSC (Marine Stewardship Council) certification.

Despite this there are still concerns that a fishery dominated by shellfish and bottom dwelling crustaceans can never be healthy, and were the crab fishery to collapse than the region would again be plunged into economic and social turmoil. There are also issues cultural and social issues with fishermen who previously caught cod being cast aside while those set up to catch crab and shellfish continuing to make a living. While the Grand Banks continues to operate as a commercial fishery its nature has changed dramatically since the cod days of the past, and the switch for catching cod to catching the species cod used to prey on is a perfect example of fishing down the food chain.

Deep Sea Fish

Orange roughy caught for research expedition.

Orange roughy caught as part of a scientific research expedition to check on stock levels in 2000. The equipment seen to the right of the picture is used to accurately measure the fish.

In a different example of fishing down the food chain a range of deep sea fish have become important commercial fish relatively recently. These species live and feed at immense depths of around 1000 to 3000 metres, meaning that the commercial operations to catch these fish is extremely expensive. However, the reduction in shallower water fish (such as cod and haddock) and hugely generous subsidies (mostly provided by taxpayers via the European Union) to keep fishermen in work mean that previously unheard of species are now regularly caught and consumed. An example of this is a species once known as slimehead. In the late 1970s enterprising commercial fishermen realised that if this species was renamed as something more appealing (the name orange roughy was chosen) and marketed correctly than people across the world would buy it. Catches rose until the early-1990s when stocks of this slow-growing and extremely late-maturing species began to show clear signs of depletion. Today stocks of orange roughy are thought to be at around 10% of pre-1970s levels. Similarly, other deep-sea species such as rat-tail have been renamed as roundnose grenadier and also fished down to a fraction of previous levels. Indeed, some scientists have even advocated the intensive fishing of the deep seas in order to feed the world’s population with fish which are directly edible, and process others into fishmeal to feed livestock. With the continued reduction of shallow water fish stocks the pressure to expand commercial fishing into deep water environments is only going to increase.

UK and European Species

While it is fairly common to see whiting on sale in fishmongers and supermarkets now it is not that long ago that they held very little commercial value and were either discarded at sea or only retained to be either reduced down to fishmeal or used in pet food. Now, however the lack of premium whitefish such as cod and haddock has seen whiting acquire a new reputation and a growing value as a table fish. The same is true of pouting – a fish which just a few short years ago was practically worthless but is now increasingly common both on both wet fish counters and as the fish used in ready meals and other fish products. Gurnard is a species which has had its reputation utterly transformed. Once a species which was discarded at sea or used as bait in crab and lobster pots it could only raise a price of around 25p a kilo as recently as 2007. A year or so later gurnard were finding their way into supermarkets and fishmongers as a food fish. This was quickly followed by celebrity chefs featuring gurnard on TV shows and in recipes in cookbooks and by the end of 2007 the price of gurnard had reached £4 per kilo and sales were up 1000%, showing the speed at which the reputation of a fish as a food can be turned around. Even the most unattractive species can be re-branded to sell in place of more traditional food fish. In February 2016 Norwegian fish exporting company the Lerøy Seafood Group stated that they were investing money in re-branding lumpsucker fish so they could be exported and sent to Asia as a food fish, while Irish fishmongers have attempted to sell the unusual greater forkbeard species to consumers under the somewhat unappetising name of ‘Sweaty Betty.’

Sea Angling and Fishing Down the Food Chain

Evidence of fishing down the food chain can be seen in sea angling. LRF (Light Rock Fishing) is a development in sea angling where anglers use small, light rods that can cast lures weighing less than one gram to catch mini species such as rockling, blennies, gobies and sea scorpions.

Mini Species

Mini species which were once ignored by anglers are now caught using LRF methods – a case of anglers fishing down the food chain.

While this type of fishing is both fun and highly enjoyable it has developed due to the declining numbers of larger fish which anglers traditionally targeted such as cod, bass and ray species. While many anglers continue to go fishing for larger species (and intersperse this with LRF sessions) there can be no doubt that the huge expansion of Light Rock Fishing is a form of fishing down the food chain whereby anglers are having to turn their attention to smaller species due to the lack of larger fish which they originally targeted.

The Future: Jellyfish Sandwiches?

Fishing down the food chain has led to some previously unthinkable species being targeted for human consumption. Once the big fish, medium fish, forage fish and crustaceans and shellfish have been removed from an ecosystem commercial fishermen must move even further down the food chain and catch some weird and wonderful sea creatures. Daniel Pauly himself states that people in poor nations have seen their seas emptied by commercial fishing operations from rich nations and have therefore been reduced to eating sea creatures such as sea urchins and sea cucumbers.

Worldwide jellyfish catchHowever, western nations have also been forced to look for new non-fish species to catch in their own waters in order to keep their own fishermen in employment. As predatory fish have been removed from the sea the number of jellyfish has skyrocketed. This has led to some fishermen in both Europe and America targeting jellyfish. There is now a fishery in the US state of Georgia where a jellyfish are caught and then processed at a specially converted plant on shore.

Jellyfish and noodles

Cannonball jellyfish (Stomolophus meleagris), left, is caught in US waters and turned into a noodle like food, right.

The vast majority of jellyfish are dried and exported to Asia where they are used in soups and salads, or can be rehydrated and eaten as a noodle-type food. It remains a real possibility that jellyfish fisheries could expand and jellyfish could become an increasingly common food in developed nations in Europe and North America. This is not as unlikely as it sounds with scientists warning in 2008 that Europe’s declining fish stocks mean that jellyfish could be the only marine species on the menu relatively soon unless commercial fishing is reigned in. Also consider that many of the species which are now completely accepted as perfectly normal to eat were once considered weird and unusual species unfit for human consumption. The same transformation in reputation could easily happen to jellyfish, indeed, it may have to if there are no other fish species to eat.

Prof. Daniel Pauly

Prof. Daniel Pauly

The only answer is to reduce commercial fishing to sustainable levels and allow the all of the species which make up marine ecosystems to rebuild their numbers back to something approaching the levels they were at before industrialised commercial fishing began in the 1950s. Anglers must also play their part by protecting the marine environment and returning endangered species and those fish which are not being kept to eat. In many parts of the world fishermen have already fished so far down the food chain that they are approaching the end point where soon there will be absolutely nothing left to catch.

As Daniel Pauly states:

When we first presented this, it was a joke – you’re going to have a jellyfish sandwich … It was a joke, but now it’s real … We really are headed for trouble.”

Share this page: