Endpoint of overfishing is now in sight: Firth of Clyde

Diagram showinig a dredge behind a diesel-powered ship. (Credit: Greenpeace)

Seems like any time I read about ecology studies lately, its tales of waste and wanton destruction. And a recent paper in PLoS-One about “Ecological Meltdown in the Firth of Clyde, Scotland” was no different. Sigh. May as well have titled this post “Why we need Hands-Off conservation approaches.”

The paper describes commercial fishing in the Firth of Clyde, a small near-shore marine ecosystem nearly due west of Glasgow on the western coast of Scotland, from the 1800s to modern day. The researchers use the Firth of Clyde’s history as a mini-model to  assert that the collapse of fisheries there, and poor policies regulating bottom-trawling, provide a snapshot of what is happening globally to the world’s oceans.

Species that were once caught in the Firth of Clyde in the 1800s, like herring, cod, haddock and turbot are now extirpated. Today, fishers target invertebrate bottom-dwellers like Norway lobster, nephrops and and scallops – all of which are caught using trawls and dredges dragged along the seabed. (Honestly, to me this reads like a tale of biblical waste. Not only are species locally extinct, but now people are tearing up the seafloor too.) The researchers say that these destructive and invasive fishing practices are causing a restructuring of marine communities in the area and that commercially-sought after fish have declined in both abundance and diversity. “The endpoint of overfishing,” they caution, “is now in sight.” (Italics are mine.)

By surveying archival catch landings (government landings data, as well as anecdotal and qualitative sources) from the 1700s and 1800s, the researchers established that this area was once teeming with abundant and diverse fish. They describe the era before commercial fishing like this:

The productive waters and shallow banks attracted shoals of herring which migrated to spawn and feed within the Firth, and these in turn attracted a diverse array of predators such as seabirds, whales, porpoises, and dogfish (Squalus spp., Squalidae). The productive waters regularly attracted other visitors such as basking sharks (Cetorhinus maximus,  Cetorhinidae), which were numerous enough to support local fisheries for their oil.

But all that yummy marine goodness attracted fishers. While herring was the most economically important fish, others were sought too, including: skate, ling, cod, flatfish, mackerel, turbot, haddock, flounder and whiting, to name a few. The authors discuss who was fishing with what kinds of equipment over time, painting a picture of the growth of the fisheries and the technological developments along the way. This nifty little timeline sums up major fishing advancements with a summary of its affect on fish (click for larger image, if needed):

In the 1880s came a huge break through: steam powered vessels, which replaced the older sailing vessels. But perhaps nothing changed fishing more here than the combination of trawl nets and the introduction of rail networks leading inland in the 1900s. Indiscriminate bottom trawling allowed fishers to catch more, which could then be shipped as refrigerated railroad cargo to satisfy growing demand in inland cities. Excessive trawl fishing ensued, quickly leading to a closure of the Firth to trawl fishing within three nautical miles of shore because it was evident to fisheries scientists that the practice was decimating fish populations. More than a century ago, the inverse relationship between improved catching technologies (including ship speed) and nose-diving fish populations was apparent.

Next came diesel motorboats and otter trawls (more efficient than prior beam trawls) in the first half of the 20^th century. By the 1950s and 60s, the herring population was crashing hard and fishers argued loudly that the bottom trawl ban should be lifted so they could diversify into bottom-dwelling invertebrates, the authors write. What ensued was a boom and bust in the fisheries of the Firth of Clyde. This graph sums it up:

Graph of total landings, in tons, after trawl ban removed.

At the same time as the decline shown in the graph, fishing effort was rising. The paper gives detailed decline charts for cod, whiting, haddock, hake, flounder and plaice. As a result, many fish that were once fished in the Firth of Clyde are no longer there. The authors conclude that the trawl closure had helped to maintain the fisheries through to the 1960s, and its removal led to the collapse of bottomfish populations. The intensive trawling for bottom species that ensued then prevented the recovery of other species by destroying seabed habitat needed for spawning.  They write:

This once diverse and highly productive environment will only be restored if trawl closures or other protected areas are re-introduced. The Firth of Clyde represents at a small scale a process that is occurring ocean-wide today, and its experience serves as a warning to others.

NOTES:
Thurstan, R., & Roberts, C. (2010). Ecological Meltdown in the Firth of Clyde, Scotland: Two Centuries of Change in a Coastal Marine Ecosystem PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011767

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