Tuesday, September 3, 2019

The Overfishing Problem, by Don Orth

When did our overfishing problems begin?  Hugo Grotius, a Dutch philosopher and jurist, proposed that in times of peace, high seas are open to all nations and may not be subjected to national sovereignty.  This “freedom of the seas” doctrine, first proposed as early as 1609, was eventually accepted among international freedoms, particularly laissez-faire economics in the 19thcentury.  The doctrine was vigorously supported by dominant powers at the time, especially Great Britain. In the late 19thcentury, fishermen and some fisheries biologists argued strongly against all restrictive measures on the basis of the inexhaustible nature of the fishery resources of the sea.  In 1883, Thomas Henry Huxley extended the thinking of the freedom of the seas to fisheries.   

 “I believe then, that the cod fishery, the herring fishery, the pilchard fishery, the mackerel fishery, and probably all the great sea fisheries, are inexhaustible… and any attempt to regulate these fisheries seems consequently, from the nature of the case, to be useless.”  Thomas Henry Huxley 1883. 

If the overfishing problem did not exist, there would be no need for fisheries science to develop.   However, steam-powered trawling in the 1880's and improvements in trawling technology in the early 20thcentury had an enormous, unappreciated effect on the fishing capacity. Many fish stocks were in decline, and more boats and more fisherman were fishing harder for fewer and fewer fish.    North Sea government commissions began to collect fisheries data to deal with the overfishing problem by providing better numbers. Petersen (1900-1903) first developed an approach to estimate overfishing, which eventually led to important developments in fisheries science.  The first empirical evidence to support the overfishing problem was collected during World War I, during which fishing was sharply curtailed in European waters and exploited fish populations increased dramatically. Fish marking experiments initiated by Danish biologist C. G. J. Petersen and others further showed that fishing was a major cause of fish mortality in developed fisheries. At the same time, Heincke (1913) developed the first catch-curve approach to estimate mortality.  Huntsman (1944) defined the overfishing problem as the point “Where the take in proportion to the effort fails to yield a satisfactory living to the fisherman.” Eventually, fisheries scientists proposed a Great Law of Fishing -- “Fisheries that are unlimited become unprofitable.” Graham (1943). 

Russian professor, Fedor Baranov, the “Grandfather of fisheries population dynamics”, Quinn (2003), first explained the problem in economic terms. 

“As we see, a picture is obtained which diverges radically from the hypothesis which has been favoured almost down to the present time, namely that the natural reserve of fish is an inviolable capital, of which the fishing industry must use only the interest, not touching the capital at all. Our theory says, on the contrary, that a fishery and a natural reserve of fish are incompatible, and that the exploitable stock of fish is a changeable quantity, which depends on the intensity of the fishery. The more fish we take from a body of water, the smaller is the basic stock remaining in it; and the less fish we take, the greater is the basic stock, approximating to the natural stock when the fishery approaches zero. Such is the nature of the matter.” Baranov, F. (1918, translated by W.E. Ricker 1945, mimeograph, cited in Gordon 1954).

Baranov’s seminal contribution was the solution to the catch equation.  

Baranov's catch equation, where C is catch, F is fishing mortality, M is natural mortality, T is time, N0 is cohort number at time zero, and e is Euler's constant.
Where C is annual catch, N is abundance, F is fishing mortality, and M is natural mortality.  Quinn (2003), in a review of fisheries models, writes that Baranov’s catch equation is “probably the most used in all of fisheries modeling.”

Russell (1931, 1942) developed a simple algebraic equation S2= S1+ (A + G) – (C + M) to account for changes in total weight of the catchable stock of a particular size. Here S1is the weight of the catchable stock at the beginning of year, Sis weight of the catchable stock at end of the year, and A represents additions to the catchable stock, G is growth of individuals that survive, C is catch, and M is non-fishing mortality. Russell’s theoretical contributions could now be incorporated in practical determinations of overfishing.  During the period after World War I and the acceptance of overfishing, many scientists made important development of fisheries models for fish population dynamics. Read Quinn’s (2003) review -- it will answer students' questions about where all these population dynamics equations came from. Getting better numbers for these models remains a high priority for solving the overfishing problem.

Unfortunately, what happened when we defined the overfishing problem and the Great Law of Fishing was not an end to overfishing.  Governments did initiate better data collection,  and scientists developed improved mathematical and statistical analysis. Many debates ensued over the relative importance of fishing and the environment in controlling population dynamics. The Thompson-Burkenroad debate on the Pacific Halibut is well documented (Skud 1975).  This career-time debate was eventually called a draw.  Skud's (1975) concluding sentence was “Until unknowns, particularly about growth and recruitment, are determined, one cannot properly credit the increase in abundance to either the management program or to fishery induced changes or to environmental effects.”  On the  Altantic coast, a similar debate ensured after the declines in Striped Bass in the 1970s and 1980s. Today, the Striped Bass stock is overfished and overfishing is occurring;  emergency regulations were imposed this summer. 

 "The trail of fishery science is strewn with the opinions of those who, while partly right, were wholly wrong."  Michael Graham, The Fish Gate (1943, p 129).

While managers were collected better data and scientists were debating, many governments made concerted efforts to increase fishing capacity. Catches rose from the 1950s to 1996 as fishing fleets expanded and discovered new fish stocks to exploit.  

Trends in world capture fisheries and aquaculture.  Source: FAO. 
The rise in fishery yields did not continue and recent trends suggest we’ve maxed out global fishery yields. The increase in fishery yields is due to growth of aquaculture, which is now responsible for much of the world’s fishery yields.  In the last two decades, aquaculture was China’s fastest growing food sector  (Cao et al. 2015).  Many aquacultured species require formulated feeds, which include fishmeal from wild capture fisheries.  Today’s major debate is over the effect of the burgeoning aquaculture industry on wild fisheries. Are we overfishing forage fish to feed salmon, bass, and tuna in captivity? In 2016, 88 percent of the total fish production (151 million out of 171 million tonnes) was for direct human consumption. Overfishing is a direct threat to our capacity to feed ourselves. Plenty of problems may be added to overfishing problems, and they include many issues related to the poor numbers: unreported and illegal catches, bycatch, and inland fisheries (Pauly and Zeller 2016).  There will be no shortage of opportunities for those committed to studying the overfishing problems.  

Fishers display a day's catch in Manteo, North Carolina, before limits were imposed in 1979. Striped bass were in decline in virtually every drainage area from Maine to Florida.  CC-BY-2.0 Source.

Cao, L., R. Naylor, P. Henriksson, D. Leadbitter, M. Metian, M. Troell, and W. Zhang. 2015.  China’s  aquaculture and the world’s wild fisheries. Science 347(6218):133-135.
Gordon, H. S. 1954.  The economic theory of a common-property resource: the fishery.  The Journal of Political Economy 62(2):124-142.
Graham, M. 1943. The Fish Gate. London.  
Heincke, F. 1913. Investigations on the plaice—general report: 1. plaice fishery and protective measures, preliminary brief summary of the most important points of the report. Rapports et Procés-Verbaux des Réunions, Conseil International pour l’Exploration de la Mer16.
Huntsman, A.G. 1944. Fishery depletion.  ScienceXCIX, 534.
Pauly, D., and D. Zeller. 2016. Catch reconstructions reveal that global marine fisheries catches are higher than reported and declining. Nature Communications 7: 10244. 
Petersen, C.G.J.  1900-1903. What Is overfishing? Journal of the Marine Biological Association 6:587-595.      
Quinn, Terrance J. II  2003. Ruminations on the development and future of population dynamics models in fisheries. Natural Resource Modeling16 (4): 341–392. 
Russell, E.S. 1931. Some theoretical Considerations on the “Overfishing” Problem.  ICES Journal of Marine Science6:3-20.
Russell, E.S. 1942.  The Overfishing Problem.  Cambridge, United Kingdom.  130 pp. 

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