FISHERY BULLETIN: VOL. 83. NO. 3 



TABLE 1. — Station information for Atlantic fierrlng samples 

 from tfie Gulf of Maine area for the fall and winter of 1976-77 

 sampling program. (Data from Lough et al. 1982.) 



Vessel 



Cruise 

 No. 



Stn. 



Time 

 Lat. Long. (Night 



N W Date or Day) 



Annandale 76-01 



Researcher 76-01 

 Mt. Mitchell 77-01 



38 43°37' 69°22' 8 Oct. 0300 (N) 



44 43°44' 68°50' 8 Oct. 1415(D) 



59 44°25' 67°35' 9 Oct. 1515(D) 



65 44°36' 67°07' 13 Oct. 0330 (N) 



102 42°58' 70°00' 8 Dec. 1030 (N) 



105 43°30' 69°30' 9 Dec. 1100 (N) 



122 43°14' 70°01' 24 Feb. 1620(D) 



123 43°00' 70°15' 24 Feb. 1933(D) 



1) Hatch date was calculated on the assumption 

 of daily increment deposition, and all data 

 were considered. 



2) Hatch date was calculated on the assumption 

 of daily increment deposition only with larvae 

 which had 60 or fewer increments included for 

 analysis. This was done to determine whether 

 growth differences were present in the earlier 

 months of life. Also, since the range of incre- 

 ment counts for the late-hatched larvae from 

 1976 to 1977 was greater than for early-hatch- 

 ed larvae, use of a truncated data set resulted 

 in more valid comparisons. 



3) Hatch date was calculated on the assumption 

 of nondaily deposition (0.5 increment/d). 



Date of hatching was calculated by subtracting the 

 estimated age of each larva from its date of capture. 

 This calculation, of course, depends on how age was 

 estimated. According to the Lough et al. (1982) cal- 

 culation, a larva with 10 otolith increments would be 

 29 d old: 22 d for the first 3 increments, plus 7 d to 

 lay down the next 7 increments. According to the 

 assumptions used by Townsend and Graham (1981), 

 a larva with 10 otolith increments would be 15 d old, 

 assuming that increment deposition began 5 d after 

 hatch, and was daily thereafter. There is a difference 

 of 14 d between these two estimates of age, and, 

 therefore, estimated day of hatch. This does not af- 

 fect the regression analysis, as long as the indepen- 

 dent variable used is increment count, not age. 



The range of possible hatch dates for each in- 

 dividual was also calculated, based on the considera- 

 tion that deposition rates could vary from 0.5 to 1.0 

 increment/d (after Geffen 1982). Age could be equal 

 to the number of increments plus a constant (5 d) or 

 up to twice the number of increments plus a constant 

 (5d). 



Larvae were classified as either early- or late- 

 hatched within the spawning season. For 1976-77 



the early-late division date was placed at the discon- 

 tinuity in the frequency of hatching plot, which also 

 occurred at the midpoint in the spawning cycle. Divi- 

 sion date for the 1978-79 data set was placed at 

 approximately the division of Townsend and Graham 

 (1981) which they felt represented two different 

 groups of larvae. 



For analysis of nondaily deposition, the data were 

 partitioned to insure that there could be no overlap 

 of early- and late-hatched classification of larvae, 

 assuming deposition ranged from daily deposition to 

 deposition of one increment every 2 d. Any late- 

 hatched larva whose possible range of hatch dates 

 overlapped the division date (for early-hatched vs. 

 late-hatched classification) was eliminated from 

 analysis. This resulted in a loss of data (e.g., the fish 

 whose possible hatch date overlapped the division 

 date) and decreased the ability to detect differences. 



Ordinary least squares linear regressions were fit 

 to each data set. Bartlett's test for homogeneity of 

 variance (Ostle and Mensing 1975) was applied to the 

 data before each analysis. After regressions were fit, 

 the residuals of length were plotted against pre- 

 dicted length and examined for trends (Draper and 

 Smith 1981). F-tests (Ostle and Mensing 1975) were 

 applied to paired linear regressions, early-hatched 

 versus late-hatched, to determine whether the slopes 

 were significantly different. This test showed 

 whether the data were better fit by two lines, one for 

 early-hatched and one for late-hatched larvae, or 

 whether a single regression line was preferable. In 

 the regression plots the change in length is express- 

 ed in millimeters per increment. 



The von Bertalanffy growth equation. 



L, = L^(1 



■k{t-l 



0)) 



was also fitted to the data, using the nonlinear 

 regression procedure (NLIN) within SAS (Statistical 

 Analysis Systems, SAS Institute, Gary, NC). Esti- 

 mates of the parameters {K, L^, ^,) of the von Ber- 

 talanffy equations for early- and late-hatched larvae 

 were compared with a Fisher-Behrens test (Hoenig 

 1982) to determine whether the vector of parameter 

 estimates from the two classifications was signifi- 

 cantly different. 



RESULTS 



Linear regression models fitted to larval length-at- 

 increment count data showed significant differences 

 between larvae hatched early and late in the spawn- 

 ing season. Larvae hatched early had achieved 

 greater length at a given increment count than those 



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