[labrax]

Here is some info from a quick google search

A Population Study of Atlantic Striped Bass - this is page 6 and 7 of the report: http://www.nmfs.noaa.gov/sfa/state_federal/SBpopulations.pdf

Submitted to the:
Committee on Resources of the United States House of Representatives

and

Committee on Commerce, Science, and Transportation of the United States Senate

by
Donald L. Evans
Secretary of Commerce

Gale A. Norton
Secretary of the Interior

Significance of Age Distribution
Following the large 1970 year class produced in Chesapeake Bay, striped bass recruitment remained well below average until 1989 (Richards and Rago 1999). As striped bass recovered during the 1990s, the poor year classes of the previous decades resulted in relatively few older fish in the population. Good recruitment in the 1990s, particularly the 1993, 1997, and 1998 year classes (Figure 2), skewed the age demographics of the population toward younger age groups. However, as these year classes grow older (e.g., striped bass can attain ages in excess of 25 years) and fishing mortality rates on them are controlled, older fish will comprise an increasing proportion of the population. The abundance of older fish (considered in this analysis as ages 10 and older) is expected to sharply increase in 2003 when the large 1993 year class become 10 years old.

The distribution of age classes in a population has important implications for stock productivity and stability. Studies on striped bass have shown that larger fish produce larger eggs and larvae, and larger individuals of these life stages have a greater chance of survival (Zastrow et al. 1989; Monteleone and Houde 1990). Studies on other species such as cod (Marteinsdottir and Steinarsson 1998; Trippel 1998) have demonstrated that first-time spawners are generally less successful in producing offspring than fish that have spawned multiple times. As such, populations that rely heavily on first-time spawners to maintain recruitment levels face a greater risk of recruitment failure than those composed of a number of spawning classes.

The implications of increased fishing mortality on striped bass abundance is well illustrated in Figure 11. A hypothetical cohort of one million striped bass was exposed to four different fishing levels assuming that fish were vulnerable to capture beginning at age five. The hypothetical egg production at age of this cohort under these same fishing levels is depicted in Figure 12. The results indicate that even modest levels of fishing mortality reduce the
proportion of older fish in the stock and shift the bulk of egg production towards younger fish. Shifting the age at which fish are first vulnerable to capture or altering the age groups subject to full exploitation also have major implications on the stock. For example, reducing fishing mortality on ages 8 to 12 (e.g., fish approximately 32 to 40 inches) to one half the full exploitation level results in much greater egg production in the stock and an age distribution in which older fish are much more dominant (Figure 13). Maintaining a diverse number of ages in the population has the biological advantages of increased spawning potential through inclusion of older more fecund fish, and a reduced risk of poor recruitment associated with dependence on younger fish for egg production. In addition, such a strategy provides the opportunity for fishermen to catch trophy-size striped bass.

The migratory nature of striped bass is a complicating factor in fishery management. Striped bass spend their first several years in coastal nursery areas (designated ‘producer areas’ in the Fishery Management Plan) before undertaking long-distance migrations. Once the fish enter the coastal migratory component of the population, their migration route brings them back to the producer areas for a limited time during each spawning season. The challenge to managers is to promote equity among fishermen, recognizing that the availability of different size fish varies by location and season. Historically, fishermen in producer areas have targeted smaller fish while coastal fishermen generally targeted the larger coastal migrants. Regulatory changes in the 1980s amplified these differences as size limits increased in the coastal states (up to 36 inches in some locations) and, together with sharp reductions in fishing mortality, contributed to the restoration of the stocks. Since 1995, when striped bass were declared restored by the ASMFC, fishery regulations have become less restrictive and size limits have been reduced in many states. If one of the objectives of management is to produce a high quality coastal trophy fishery while maintaining the traditional “small fish” fishery in producer areas, one possible approach might be to implement an upper size limit in producer areas and a minimum size limit in the coastal fishery. Such a “slot limit” would potentially afford a sizable portion of the striped bass stock a “length window”of lowered exploitation rates.