440 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



THE NEED FOR AGE DATA 



In 1930, the Bureau of Fisheries (now the 

 Bureau of Commercial Fisheries, U.S. Fish and 

 Wildlife Service) began an investigation to 

 determine (1) what caused the decline of the 

 haddock fishery in waters fished by U.S. vessels, 

 (2) what could be done to increase the abundance 

 of haddock, or at least to prevent further decline 

 in the catch, and (3) what predictions of future 

 catches were possible. 



To carry out the objectives of the investigation, 

 large quantities of data have been and still are 

 collected at important haddock ports (Boston, 

 Gloucester, and New Bedford, Mass.; Rockland 

 and Portland, Maine). Collections have been 

 made routinely at Boston since the early 1930's, 

 and wei-e started later at the other ports. 



The background for the collection of these data 

 is reported by Rounsefell (1948). The data 

 include almost complete records of the poundages 

 landed from the various banks, with records of 

 depths and locations from which the fish were 

 taken, the gear used, and the days spent in fishing. 

 Concurrent with this collection, random samples 

 of the lengths of fish in the landings and selected 

 samples of scales were also collected. For our 

 studies, haddock were measured from the tip of 

 the snout to the fork of the tail. Alxiut 30,000 

 fish were measured in 1959 and 3,500 scale samples 

 were collected from an estimated 24 million had- 

 dock landed. 



The data are analyzed primarily to determine 

 the fluctuations in haddock abundance. Age 

 determinations from scale readings are also used 

 in special studies of the natural and fishing mor- 

 tality rates, growtii rate, and age composition of 

 the catch. 



To process the mass of biostatistics and to main- 

 tain a smooth flow of information relating to the 

 age composition of the fishery, a quick and reliable 

 method of age determination is needed. Scales 

 have been used for 20 or more years at this 

 laboratory. They are easily removed from the 

 fish and it is possible to measure several hundred 

 fish and take scale samples in a relatively short 

 time at the port. The scales are easily processed 

 in the laboratory; scales from 100 fish, for 

 example, can be processed and read in about 1 

 man-day. The purpose of the present paper is 

 to document the techniques originallv used to 



validate the scale-reading method of haddock age 

 determination and to present later studies of the 

 usefulness of the method. 



PREVIOUS STUDIES 



Fisheiy biologists on both sides of the North 

 Atlantic have for many years determined the ages 

 of haddock from interpretation of scale markings. 

 The publications of many of the workers report 

 age compositions and growth rates but do not 

 validate the method by which the scale ages were 

 detennined (cf. Huntsman and Needier, 1927; 

 Schuck and Arnold, 1951; Wise, 1957; Kohler 

 and Clark, 1958). Other workers have reported 

 not only their results but, in addition, have 

 described their methods of interpreting scale age 

 detenninations. These papers are of great inter- 

 est in the present study. 



In a study of haddock in Norwegian waters, 

 Saetersdal (1953) reports that in many investiga- 

 tions haddock ages have been determined from 

 scale examinations without testing the validity of 

 the method. He then proceeds to demonstrate 

 the validity of age determination methods for the 

 Norwegian stocks of haddock, using the Petersen 

 method. He points out that part of the year class 

 of fish under observation failed to form a scale 

 annulus in the second year. He also examined 

 the secular record of the scales, including the time 

 of annulus formation, and concluded, "* * * the 

 zones found in * * * the scales were annual for- 

 mations in the great majority of the cases." 



In North American waters, several workers have 

 used haddock scales for age determination. 

 Among them, Needier (1929) used scale readings 

 to derive growth rates for haddock from Locke- 

 port, the Sable Island banks, and St. Andrews 

 (Canada). He states categorically, "The age of 

 haddock may be determined from the scales." and 

 cites Thompson (1923) for his validation of had- 

 dock scale readings. (Thompson had examined 

 the scales of North Sea haddock and found that 

 95 percent of the scales gave what he believed to 

 be the correct age.) 



Ill a later study Needier (1930) read haddock 

 scales for age determination of fish from the Gulf 

 of Maine and Georges Bank and again cited other 

 workei-s for his proof of the scale method. He 

 concluded, "There can be no doubt of the validity 



