Download
1 / 34
340 likes | 459 Views
A seminar celebrating the launch of. 120 years of change in fishing power of English North Sea trawlers. Georg H. Engelhard 23 April 2008. Anecdote: the ‘sailing smack’ experiment. 1990s Cefas scientists boarded sailing smack Excelsior and fished off Lowestoft for a week
E N D
A seminar celebrating the launch of 120 years of change in fishing powerof English North Sea trawlers Georg H. Engelhard 23 April 2008
Anecdote: the ‘sailing smack’ experiment • 1990s Cefas scientists boarded sailing smack Excelsior and fished off Lowestoft for a week • Aim: compare current with ‘virgin’ state of North Sea, using fishing methods of 120 years ago—beam trawling by sail • 1880s sailing trawlers were responsible for ~100,000 tonnes fish landed in UK
Lack of skills by scientists and crew (despite hard labour)? Has North Sea become so scarce of fish resources? Lack of fishing power? Lack of fish? Results of the ‘sailing smack’ experiment Few dab and dragonet, otherwise near-zero catch—WHY?
Fishing power • Expresses differences in cpuebetween fishing vessels if fishing at same time and location • General trend of increasing fishing power over time • Typically, fishing power studies limited to 1–2 decades • What about long-term trends?
How has fishing power changed over 120 years of trawling the North Sea?
Overview‘Time travel’ through 5 “fishing power ERAS” • 1400s–1890s Sail to early steam trawlers • 1900s–50s Golden Age steam trawlers • 1950s–60s Steam gives way to diesel • 1960s–80s Rise of modern beam trawlers • 1980s–now Recent changes fishing power
Origin of trawl • 14th Century, Thames: “wondyrchoun”— primitive beam trawl • Already hated by other fishermen Michael Graham (1956): “Opposition against the trawl has continued throughout history, but never halted its development.”
Dutch coast Barking (Thames) Brixham (Devon) Trawling taken to open sea • Historians disagree; 3 views: 1821
19th Century expansion trawling North Sea • Quick spread throughout North Sea • Causes: • Industrial revolution • Population growth, demand and markets • Railway allowing fast transport fresh fish from port to market
First ‘leap’ in fishing power • Trawling by sail peaked in 1870s, then declined • Decline caused by first major jump in fishing power — introduction of steam
Advantages of steam trawlers • Not subject to mercies of wind • Range further from port • Trawl faster and deeper • High trawl speed allowed switch from beam to otter trawl • Iron, later steel hulls • Garstang (1900): • 1881: first steam beam trawlers had 4x higher fishing power than sailing beam trawlers • 1898: steam otter trawlers already had 8x higher fishing power
Era 2. 1900s–1950sGolden Age of steam trawling Great Yarmouth, 1930s
Turn of century: steam trawlers built rapidly Both World Wars: significant reductions effort, but steam trawling quickly recovered afterwards 1890s-1950s: ‘Golden Age’, steam trawlers landed 50-80% of North Sea demersal landings UK Rise, rule, and decline of steam trawling
Sailing trawlers only survived until 1930s, in IVc • Co-occurrence allowed fishing power comparison Extensiveness of steam trawling • 1900s-1950s: British steam trawlers fished throughout North Sea • More extensive spatial distribution than British fisheries nowadays • British steam trawlers caught 25-70% of international North Sea demersal catch
...about 4x higher plaice fishing power... ...about 10-20x higher cod fishing power! Fishing power of steam trawlersexpressed in ‘sailing smack units’ Steam trawlers, fishing in the same rectangle at the same time as sailing trawlers, had...
Post-WWII decades • Steam trawl fleet now mainly old vessels—fishing power probably equal to pre-WWII • during war, best trawlers requisitioned by Navy as minesweepers, and many destroyed • Change within steam trawlers: from coal burners to oil burners(but still driven by steam) • Could not halt decline steam trawlers: competition with motor trawlers • had already existed from WWI, but only as sailing trawlers with small petrol/paraffin motors installed • 1946: first purpose-built diesel-driven motor trawler
...about equal cod fishing power and... ...only marginally higher plaice fishing power, but... Fishing power of motor (diesel) trawlersexpressed in ‘steam trawler units’ 1950s–1960s motor trawlers, fishing in the same rectangle at the same time as steam trawlers, had...
...this was despite far greater average tonnage of steam trawlers! 1950s and 1960s: large steam trawlers were gradually outcompeted by on average smaller but equally or increasingly efficient motor trawlers
Trends in North Sea fishing effortin British sailing, steam and motor trawlers
Rise of modern (twin) beam trawlers • Two large beam trawls lowered mechanically from side of ship, often with tickler chains, very effective for catching sole and plaice • Developed by Dutch and Belgian fisheries in 1960s • UK slow to follow in North Sea—only in 1980s • UK beam trawling peaked 1990s, then declined, and now almost gone from North Sea (but strong in SW) • However, international effort in North Sea high, arguably most invasive fishing method here
First success Dutch beam trawlers linked to strong 1958 sole year-class Note decrease mean tonnage English otter trawlers in southern North Sea Strong 1963 year-class leads to Dutch ‘wave’ of new large beam trawlers rapidly built Rise of Netherlands beam trawl fleet
...initially ~2x, later ~8x higher plaice fishing power... ...initially lower, later on ~equal cod fishing power... Fishing power of Dutch beam trawlers 1960s–1970s: Dutch beam trawlers, compared to English otter trawlers fishing in IVc, had... ...but were actually targeting sole
Era 5. 1980s–nowRecent changes fishing power RV Corystes, 2004
1980s–present: recent changes fishing power • From 1977 on, we have consistent North Sea survey data: IBTS, EGFS • Compared fishing power English commercial otter and beam trawlers, with that of EGFS • Based on commercial and survey cpue in same rectangles, same month
...in 1980s have ~5–10x higher, later only ~1–3x higher plaice fishing power... ...and in most years about equalcod fishing power as the EGFS (but in some years ~3–6x higher). Fishing power of commercial otter trawlers expressed in ‘EGFS units’ Compared to EGFS survey, commercial otter trawlers...
...in most years, have roughly half thecod fishing power... ...and have decreasing, but always far higher (~20–50x!) plaice fishing power, confirming efficiency beam trawl for flatfish Fishing power of commercial beam trawlers expressed in ‘EGFS units’ Compared to EGFS survey, commercial beam trawlers...
Conclusions • Past 120 years: fishing power has increased substantially • Trend has not been gradual: • FP has sometimes “leapt forward” in few years • FP has also “stagnated” for decades • Combined all estimated FP changes: • Estimated total change over 120 years (plaice and cod)
...beam trawlers in 2000 have ~10x higher cod FP and ~100x higher plaice FP... ...otter trawlers in 2005 have ~50x higher cod FP and ~4x higher plaice FP... Total change fishing power over 120 years Compared to 1880s sailing beam trawlers... However, fisheries have not necessarily become more profitable!
Comparison historical and modern plaice cpue and fishing power Rijnsdorp & Millner (1996): North Sea plaice was about equally abundant in 1920s and ~2000
Modern beam trawlers have 100x higher FP than 1920s sailing trawlers, but only 5x higher plaice cpue Modern otter trawlers have lower plaice cpue than old sailing trawlers, and far lower than old steam otter trawlers Comparison historical and modern plaice cpue and fishing power
Implications for capacity EU trawler fleet • Marked discrepancies between long-term changes plaice fishing power and cpue • In spite of similar biomasses 1920s and 2000s! • Limited nature of North Sea marine living resources • Implication: much reduced international fleet probably capable of catching the same quantities of fish!
