Brodziak and Macy: Growth of Lohgo pealei 



233 



in ML and 1.8% to 3.1% in weight. The exponential 

 growth of L. pealei throughout their life cycle is con- 

 sistent with the fact that squid have high gross- 

 growth efficiency and are metabolic maximizers in 

 comparison with teleosts (O'Dor and Webber, 1986). 



The difference between growth rate in weight of 

 indeterminate-sex squid and adults suggests that 

 there may be a body size above which growth rate 

 increases substantially. This critical size could be 

 related to changes in diet because L. pealei undergo 

 an ontogenetic shift in prey selection from crusta- 

 ceans to fish and other squid as they grow (Vovk, 

 1972; Macy, 1982b; Vovk, 1985; Anderson and 

 Griswold, 1988). Alternatively, this difference could 

 be the result of a shift from somatic to gonadal growth 

 as squid mature ( Macy, 1995 ), although this seems less 

 likely given the substantial variability in size at matu- 

 rity of L. pealei (Macy, 1980). Regardless of the cause, 

 understanding the implications of the rapid growth of 

 adults and its relationship to maturity stage will be 

 important for predicting how the population structure 

 will respond to exploitation. Over the longterm, it is 

 conceivable that intensive exploitation of an annual 

 semelparous species, such as L. pealei, could lead to 

 strong selective pressure for a smaller average size at 

 maturity. Such a reduction in average size at maturity 

 could diminish the reproductive potential of the popu- 

 lation (cf. Murphy et al, 1994), and this could lower 

 resilience to environmental fluctuations by reducing 

 the genetic variation in the population. 



The implications of these estimates of growth for 

 L. pealei in the northwest Atlantic are substantial 

 for the assessment and management of this resource. 

 The short lifespan for this species, combined with 

 the rapid growth of adults and the capacity to spawn 

 year-round, implies that the stock will respond rap- 

 idly to environmental variation and fishing pressure. 

 As a result, monitoring the stock for in-season man- 

 agement would likely require several assessments 

 throughout the year. 



New management measures are being developed 

 for the long-finned squid stock to reflect the improved 

 understanding of its growth and pattern of repro- 

 duction (MAFMC 6 ). At present, management of the 

 stock is based on a level of total allowable catch that 

 cannot be exceeded (MAFMC 7 ) and on an overfish- 



6 Mid-Atlantic Fishery Management Council. 1995. Amend- 

 ment 5 to the fishery management plan and the final environ- 

 mental impact statement for the Atlantic mackerel, squid, and 

 hutterfish fisheries. MAFMC. Dover, DE. 



7 Mid-Atlantic Fishery Management Council. 1992. 1993-1994 

 allowable biological catch, optimum yield, domestic annual har- 

 vest, domestic annual processing, joint venture processing, and total 

 allowable level of foreign fishing recommendations for Atlantic 

 mackerel, Loligo, Illex, and butterfish. MAFMC, Dover, DE. 



ing definition that has been characterized as "risky" 

 (Rosenberg et al. 1994). A preliminary analysis of 

 some of the weight-at-age data presented in this 

 study indicated that the annual level of maximum 

 sustainable yield, based upon average recruitment 

 and an initial estimate of maximum yield per recruit, 

 could be roughly 36,000 t (NEFSC 8 ). This interim 

 estimate was 18%> lower than the estimate of 44,000 

 t, which was based on a presumed two-year lifespan 

 (Sissenwine and Tibbetts, 1977) that has been used 

 as the maximum optimum yield for the stock 

 (MAFMC 7 ). However, this estimate appears overly 

 optimistic because landings above 36,000 t have oc- 

 curred only once, in 1973, when 37,600 1 were landed. 

 Regardless, any revision of the annual level of sus- 

 tainable yield for the stock will need to account for 

 the seasonal patterns of growth and spawning, the 

 potential discarding of juveniles, and variability in 

 stock-recruitment dynamics. Further, it would be 

 more appropriate to estimate sustainable yield and 

 to develop an overfishing definition on a seasonal, 

 rather than an annual, basis for this short-lived spe- 

 cies. In contrast to the current quota-based harvest- 

 ing strategy, a constant harvest-rate strategy that 

 includes a proportional escapement target ( Bedding- 

 ton et al., 1990) on a seasonal basis may be a useful 

 management approach. 



If the long-finned squid stock is managed on a sea- 

 sonal basis, revised stock assessment procedures are 

 likely to require rapid collection of catch and effort 

 data and efficient data analysis during periods of 

 peak fishing activity. Real-time assessment proce- 

 dures have been used to monitor the short-finned 

 squid stock in Falkland Islands waters during the 

 fishing season to achieve proportional escapement 

 goals (Rosenberg et al., 1990), and the use of a con- 

 stant harvest-rate strategy is a potential option for 

 management of the long-finned squid resource. Al- 

 though a constant harvest-rate strategy can be overly 

 restrictive in years of good recruitment and result in 

 a loss of yield, it can also jeopardize the stock when 

 recruitment is poor. Therefore, assessment proce- 

 dures that permit in-season adjustment of the har- 

 vest rate would likely be necessary to maintain an 

 adequate level of spawning biomass if management 

 is conducted on a seasonal basis. 



As with any renewable resource, long-term man- 

 agement of the long-finned squid stock will involve a 

 balance of the risks and benefits of harvesting the 

 resource. Because long-finned squid are semelparous 

 and likely live for less than 1 year, the risk of re- 



Northeast Fisheries Science Center. 1994. Report of the 17th 

 Northeast Regional Stock Assessment Workshop. NEFSC Ref. 

 Doc. 94-06, Woods Hole. Massachusetts, 124 p. 



