Wright, K. J. 



1968. Feeding habits of immature lake trout (Salvelinus 

 namaycush) in the Michigan waters of Lake Michi- 

 gan. M.S. Thesis, Michigan State Univ., East Lansing, 

 42 p. 



JEFFREY W. FOLTZ 



Department of Zoology 



University of Wisconsin-Milwaukee 



Present address: Environmental, Population and 



Organismic Biology, University of Colorado 



Boulder, CO 80309 



Carroll R. Norden 



Department of Zoology 



University of Wisconsin-Milwaukee 



Milwaukee, WI 53201 



USEABLE MEAT YIELDS IN 

 THE VIRGINIA SURF CLAM FISHERY 1 



The weight of surf clam meat landed in Virginia is 

 estimated by the National Marine Fisheries Ser- 

 vice, Division of Statistics and Market News 

 (DSMN) by multiplying bushels landed by a con- 

 stant of 17 lb (7.71 kg) of total meat per bushel. 

 However, total meat weight includes the viscera, a 

 portion of clam not utilized by the industry. Here- 

 in is an analysis of the yield of useable surf clam 

 meat weight per bushel and seasonal variability 

 in meat weight relative to seawater temperature 

 for Virginia stocks. 



lished by National Oceanic and Atmospheric Ad- 

 ministration (NOAA), Oceanographic Surveys 

 Branch, exhibited seasonal trends which were cor- 

 related to changes in useable meat yield per 

 bushel. Although these temperatures are not in 

 situ measurements, they are a convenient 

 covariate of meat yield. 



The relationship of MMUWB to MMST was es- 

 timated by Model II regression analysis since both 

 variables were subject to sampling error. The 

 choice of a particular Model II analysis relative to 

 the source of the variability (measurement errors, 

 inherent variability, or both) is a somewhat unset- 

 tled subject recently discussed by Moran (1971), 

 Ricker ( 1973, 1975) and Jolicoeur ( 1975). No such 

 theoretical considerations were used in the pre- 

 sent analyses. Four models were employed to de- 

 rive "predictive" equations from the 1974 data: 

 Ricker's (1973) geometric mean analysis (GM re- 

 gression); Wald's (1940) and Bartlett's (1949) 

 arithmetic mean analysis (termed AM regression 

 by Ricker); and principal axis analysis (although 

 it is recognized that variables do not truly have 

 a bivariate normal association). Empirically, the 

 adequacy of the models in predicting the observed 

 1975 annual mean useable meat weight per 

 bushel (AMUWB) from the MMST in 1975 was 

 assessed by a randomized block (two-way) 

 analysis of variance in which the predicted and 

 observed MMUWB were the experimental units 

 replicated by months. MMST was recorded to 

 0.1°C, MMUWB to 0.01 lb. 



Methods 



Results and Discussion 



Monthly mean useable meat weight per bushel 

 ( MMUWB) was estimated from 181 daily landings 

 totaling 167,564 bushels in 1974, and 160 daily 

 landings totaling 270,170 bushels in 1975. The 

 surf clams were harvested from Virginia stocks in 

 the region offshore of Cape Henry and south to 

 about False Cape. 



Meat weight landings reported by DSMN are in 

 pounds, for conformity useable meat weight esti- 

 mates are also cited in pounds. 



Monthly mean seawater temperature (MMST) 

 was estimated from daily surface water tempera- 

 tures recorded at Kiptopeke Beach, Va. (lat. 

 37°10.0'N, long. 75°59.3'W), about 13 n.mi. north 

 of Cape Henry. These data, collected and pub- 



'Contribution No. 801, Virginia Institute of Marine Science, 

 Gloucester Point, Va. 



The MMUWB of surf clams ranged from 10.8 to 

 14.0 lb in 1974, and from 10.6 to 14.5 lb in 1975 

 (Table 1). AMUWB, 12.5 lb in 1974 and 12.6 lb in 

 1975, were nearly identical (P>0.80). There was a 

 cyclical increase in the MMUWB from the minima 

 in winter months to maxima in July and August 

 1974 and in July 1975. The correlation coefficients 

 (r) for MMUWB and MMST were 0.64 and 0.79 in 

 1974 and 1975, respectively; r = 0.71 for the 

 pooled data. 



The sinusoidal trend in MMUWB is probably 

 related to maturation and subsequent spawning. 

 Ropes ( 1968) reported a major spawning period in 

 summer and a minor period in fall in New Jersey 

 waters, but the time and duration of surf clam 

 spawning in Virginia waters has not been re- 

 ported. If increasing MMUWB is indicative of 

 maturation, the data imply that most spawning by 



640 



