Abstract. -Bluefish (Pomatomus 

 saltatrix) are found along the US At- 

 lantic coast from Maine to Florida, 

 and are the object of a major recre- 

 ational fishery as they migrate 

 northward from the South Atlantic 

 Bight in the spring and return south- 

 ward in the late fall. Acceptance of 

 analytic assessment results for blue- 

 fish has been hindered by the lack 

 of a consistent time series of geo- 

 graphically comprehensive age- 

 length keys for converting bluefish 

 lengths to age. We used bluefish 

 length-age data from North Carolina 

 commercial fisheries during 1986 to 

 1989 to compare the utility of two 

 simple methods for estimating age 

 from length-frequency data with two 

 more rigorous statistical methods. 

 The simple methods were cohort slic- 

 ing using von Bertalanffy growth pa- 

 rameters for bluefish and the appli- 

 cation of a pooled age-length key 

 compiled with data from different 

 times and fishing areas. The two 

 statistical approaches were the iter- 

 ated age-length key method and 

 MULTIFAN. Combined 1986-1989 

 proportions at age estimated by co- 

 hort slicing, pooled age-length key, 

 and iterated age-length key meth- 

 ods were significantly different from 

 those in the test data, based on a 

 quantitative comparison using the 

 Kolmogorov-Smirnov cumulative dis- 

 tribution test. Proportions at age 

 estimated by MULTIFAN were not 

 significantly different from the test 

 data. Our work suggests that 

 MULTIFAN is the best alternative 

 to a time series of fishery-specific 

 age-length keys for the estimation 

 of Atlantic coast bluefish ages from 

 length data. 



A comparison of alternative 

 methods for the estimation of age 

 from length data for Atlantic coast 

 bluefish [Pomatomus sa/tatrix) 



Mark Terceiro 



National Marine Fisheries Service 

 Northeast Fisheries Science Center 

 Woods Hole. MA 02543 



Jeffrey L. Ross 



North Carolina Department of Environment, 

 Health, and Natural Resources 

 Division of Marine Fisheries 

 Morehead City, NC 28557 



Manuscript accepted 16 April 1993. 

 Fishery Bulletin 91:534-549 1 1993). 



Bluefish (Pomatomus saltatrix) are 

 found along the U.S. Atlantic coast 

 from Maine to Florida, migrating 

 northward from the South Atlantic 

 Bight in the spring and returning 

 southward in the late fall. They are 

 the target of a major recreational 

 fishery along the Atlantic coast, with 

 catches averaging 47,000 metric tons 

 (t) per year during 1980 to 1990. For 

 the same period, the commercial 

 catch of bluefish, mainly by otter 

 trawls, averaged 6,400 1 per year. 



Atlantic coast bluefish exhibit fast 

 growth during the first two years of 

 life, attaining fork lengths of over 

 40cm by age 2 (Hamer, 1959; 

 Lassiter, 1962; Richards, 1976; Wilk, 

 1977). They may reach ages of up to 

 12 years and sizes in excess of 100 cm 

 fork length and 14 kg in weight. 

 About fifty percent of bluefish reach 

 sexual maturity by the second year 

 of life (Wilk, 1977). Spawning occurs 

 during two major periods: March and 

 April in the South Atlantic Bight near 

 the inner edge of the Gulf Stream, 

 with a peak about 1 April; and June 

 through September in the Mid- 

 Atlantic Bight, with a peak about 1 

 August (Wilk, 1977; Kendall and 

 Walford, 1979; Nyman and Conover, 

 1988). There is evidence that spring 



and summer spawning fish mix ex- 

 tensively during their lifespan, as 

 summer spawning fish have been ob- 

 served to originate from both cohorts 

 (Chiarella and Conover, 1990). Year 

 classes of bluefish therefore consist 

 of varying proportions of spring- and 

 summer-spawned cohorts. 



In anticipation of a fisheries 

 management plan to regulate com- 

 mercial and recreational catches of 

 Atlantic coast bluefish, the Atlantic 

 States Marine Fisheries Commission 

 (ASMFC) and the Mid-Atlantic 

 Fisheries Management Council 

 (MAFMC), in cooperation with the 

 National Marine Fisheries Service 

 (NMFS), began work on stock assess- 

 ment in 1986. Length-frequency data 

 collected by the Northeast Fisheries 

 Science Center (NEFSC) (bottom 

 trawls, 1976-1986) and by NMFS 

 Marine Recreational Fishery Statis- 

 tics Survey (MRFSS) (1979-1985) 

 were available for analytical assess- 

 ment (i.e., virtual population analy- 

 sis). However, no consistent time se- 

 ries of geographically comprehensive 

 age-length keys were available for es- 

 timating age-frequency from length- 

 frequency data. Therefore, an age- 

 length key (hereafter referred to as 

 the ASMFC pooled key) was devel- 



534 



