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Fishery Bulletin 97(3), 1999 



The net migration results suggest that the west- 

 ward migration of age-2 and older haddock in the 

 winter-spring period is matched by a corresponding 

 eastward migration during the summer-fall period 

 of roughly similar magnitude. The net result is that 

 roughly 20% to 25% of the adult haddock move across 

 the ICJ line during a cycle. There may be a tendency 

 for older haddock to migrate back and forth across 

 the boundary line in greater numbers than for 

 younger haddock because the instantaneous rates of 

 net migration during the winter period for ages 4-8 



1.6 



B 1985 year class . Natural Mortality 



. -, D Fishing Mortality 



"1 Migrating to Canadian side 

 I Migrating to U.S. side 



Figure 11 



History of the (A) 1984 and (Bi 1985 haddock year classes in unit areas 

 5Zj,m. The first bar of each pair represents the population size at the begin- 

 ning of each 6-month period with the numbers gained from migration, if 

 any. The second bar indicates the numbers lost to natural mortality, fishing 

 mortality and migration to the other side of the ICJ line. The number of 

 haddock left over at the end of the time period is represented by the un- 

 shaded portion of the second bar The haddock that migrated across the ICJ 

 line are added to the population or contribute to fishing mortality on the 

 side they are migrating to during the same time period. 



are often greater than for younger ages, i.e. six out 

 of nine times (Fig. 10). No relationship was found 

 between stock abundance and the 1985-93 spring 

 net migration rates, or the 1968-93 spring ratios of 

 relative abundance, when a greater range in stock 

 abundance occurred. The variability seen in the 

 magnitude of movement to the U.S. side in spring 

 from year to year (Figs. 8 and 10) may reflect varia- 

 tion in the timing of migration, variation in the mag- 

 nitude of migration, sampling variation, or immigra- 

 tion from another source. Improved understanding 

 of the source of this variability and 

 better estimates of the magnitude and 

 extent of migration may be possible 

 from repeated surveying during the 

 winter-spring period. 



Distribution and migration show dif- 

 ferences by age. The distribution of 

 age-0 haddock was found to be differ- 

 ent from that of older haddock, as has 

 been previously described (Overholtz, 

 1985; Lough and Boltz, 1989; Pola- 

 check et al., 1992). Haddock eggs and 

 larvae spawned on the northeast peak 

 may be distributed as far south as the 

 Middle Atlantic Bight (Polacheck et. 

 al., 1992). The ratios of relative abun- 

 dance of age-0 haddock during fall are 

 very variable and abundance often fa- 

 vors the U.S. side. There was a pat- 

 tern of strong year classes being more 

 abundant on the U.S. side whereas the 

 weak year classes that followed were 

 more abundant on the Canadian side. 

 Additional research is needed to deter- 

 mine whether there is a mechanistic 

 explanation for this observation. Our 

 results suggest that the distribution 

 and movement of age-1, -2 and -3 had- 

 dock differ from those of older haddock. 

 In spring there was some correlation 

 of ratios of relative abundance such 

 that age-4 and older haddock had simi- 

 lar patterns and age-2 and age-3 had- 

 dock were similar whereas age-1 had- 

 dock did not correlate with any other 

 ages. The differences likely reflect dif- 

 ferent migration patterns of immature 

 and mature haddock. Maturity rates 

 increase from ages 1 to 3 and by age 4 

 all haddock are mature (O'Brien and 

 Brown, 1996; Trippel et al., 1997). 



Haddock biomass (age 2 and older) on 

 all of Georges Bank from 1935 to 1960 

 averaged 153,000 meteric tons (t). In 



