Mesh Size and the New England Groundfishery 

 Applications and Implications 



RONALD JOEL SMOLOWITZ 1 



ABSTRACT 



Mesh size control bas been advocated from the earliest days of the otter trawl fishery in the United States. 

 Researchers determined that larger meshes in the cod end of a trawl reduce discarding by allowing small fish to 

 escape; a process known as size-selection. This selectivity is measured by the selection factor — tbe relationship 

 between the 50% retention length and the stretched length of the mesh. Selection factors vary by species, net 

 materia], duration of tow, speed of tow, size of catch, and with variations in mesh size. 



Cod end mesh size experiments were conducted aboard eight New England otter trawlers during the period 

 December 1977 to October 1978 to examine the possible effects of increasing the mesh size in that fishery. Selec- 

 tion factors were determined for Atlantic cod, Gadus morhua (3.33-3.80), haddock, Melanogrammus aeglefinus 

 (3.04-3.47), yellowtail flounder, Limanda ferruginea (2.16-2.29), pollock, Pollachius virens (3.26-3.33), winter 

 flounder, Pseudopleuronectes americanus (2.04-2.27), and American plaice, Hippoglossoides platessoides 

 (2.25-2.41). For Atlantic cod, haddock, and winter flounder, there was a reduction of discards, up to 93%, and 

 an increase in landings, by as much as 44%, with the larger mesh (133-138 mm). For yellowtail flounder, there 

 was a reduction of discards and of landings. 



Mesh size regulation as a management tool first requires tbe determination of the objectives in order to 

 choose the size mesh. Enforcement difficulty, especially in the New England mixed fishery, is the greatest 

 obstacle to overcome. Tbe implications of mesh management reach beyond the fishery into the processing and 

 financial sectors of the industry. 



HISTORICAL PERSPECTIVE 



For hundreds of years men have been harvesting groundfish 

 off of New England, but until 1905 this fishery consisted 

 almost entirely of sailing vessels using hand lines and bottom 

 longlines. In 1905 the Bay State Fishing Co. of Boston built 

 the first American steam otter trawler at Quincy, Mass., the 

 steamer Spray. By 1912 there were 11 steam-driven otter 

 trawlers from New England fishing groundfish. 



With the rapid rise of this new fishing method, the line 

 fishermen grew apprehensive about the conservation of their 

 fishery. This resulted in a government act, approved 24 August 

 1912, making appropriations as follows: "To enable the Com- 

 missioner of Fisheries to investigate the method of fishing 

 known as beam or otter trawling and to report to Congress 

 whether or not this method of fishing is destructive to the fish 

 species or is otherwise harmful or undesirable, $5,000, or so 

 much thereof as may be necessary." 



Alexander et al. (1915) began the work that year. Some of 

 their tasks were to determine: 1) The general effects of trawl 

 nets and hook gear on the fish populations. 2) The nature and 

 extent of the destruction of juvenile fish. 3) The waste of "edi- 

 ble fishes that have no present market value." 4) The extent 

 that trawl nets catch fish not taken by other gear. 5) Any 

 evidence of depletion of fish stocks by trawl nets. 6) The extent 

 of any gear conflicts. 7) The necessity of international 

 agreements to regulate the fisheries. 



Results of this study indicated that average mesh sizes 

 (stretched mesh measured between knots) used by otter 

 trawlers were 6 in in the forward parts of the net, 3 in in the 



'Northeast Fisheries Center Woods Hole Laboratory, National Marine 

 Fisheries Service, NOAA, Woods Hole, MA 02543. 



bellies, and 2.5 in in the cod end. Between 30 and 40% of the 

 cod and haddock caught by these nets were too small to 

 market, and it was concluded that not only does the otter trawl 

 destroy more undersized fish than line trawls, but it was also 

 more destructive to the fish stocks because of the smaller 

 average size of the landings. 



The study's recommendations noted that certain European 

 authorities had proposed increasing the size of the meshes of 

 the net to let the small fish escape. The American authors felt 

 this would not be a feasible approach because they believed 

 that 1) the meshes tend to close as the trawl catches fish, 2) the 

 fish in the cod end block escape, 3) the fish would not attempt 

 to escape until haulback, and 4) more fish would be gilled in 

 the larger meshes. The study recommended against banning 

 otter trawls or limiting entry. It solely proposed area restric- 

 tions for otter trawlers, but industry did not support this 

 recommendation and thus no action was taken (Herrington 

 1935). 



During the 1920's, a new market for fresh and frozen had- 

 dock fillets was developed. The large demand for this product 

 resulted in the New England otter trawl fleet growing to 323 

 vessels by 1930. The catch of haddock grew from 93.5 million 

 lb in 1924 to 256 million lb by 1929 (Herrington 1936); then 

 came a rapid decline. Industry grew concerned and funds were 

 allotted to the Bureau of Fisheries to study the haddock 

 fishery. 



This study soon identified two major causes of the decline. 

 The first was the failure of annual spawning for several years; 

 the second, a high rate of fishing mortality, this latter factor 

 possibly influencing the spawning failures. A good percentage, 

 as high as 75%, of the haddock being caught were undersized 

 (22-42 cm) and discarded at sea. Herrington (1932) estimated 

 that in 1930, 37 million haddock were landed and as many as 

 90 million were discarded. 



