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  REPOKT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  

  

  haps 
  is 
  not 
  affected 
  by 
  such 
  slight 
  changes. 
  In 
  the 
  case 
  of 
  the 
  latter, 
  

   Dean 
  « 
  says, 
  ' 
  ' 
  The 
  degree 
  of 
  density 
  of 
  the 
  water 
  is 
  one 
  of 
  the 
  most 
  

   important 
  factors 
  influencing 
  spawning," 
  and 
  states 
  that 
  a 
  few 
  thou- 
  

   sandths 
  of 
  a 
  degree 
  (e. 
  g., 
  0.002) 
  makes 
  a 
  decided 
  difference. 
  It 
  is 
  of 
  

   great 
  interest, 
  and 
  of 
  great 
  importance, 
  from 
  an 
  economic 
  point 
  of 
  

   view, 
  that 
  one 
  of 
  the 
  chief 
  difficulties 
  with 
  which 
  the 
  03^ster 
  has 
  to 
  

   contend 
  in 
  perpetuating 
  itself 
  does 
  not 
  affect 
  the 
  soft 
  clam. 
  A 
  good 
  

   "set" 
  seems 
  to 
  occur 
  as 
  readily 
  in 
  brackish 
  as 
  in 
  saltwater. 
  There 
  

   seems 
  to 
  be 
  no 
  definite 
  optimum 
  density 
  controlling 
  either 
  the 
  produc- 
  

   tion 
  or 
  the 
  establishment 
  of 
  the 
  young. 
  

  

  SUMMARY. 
  

  

  Conditions 
  of 
  natural 
  groioth 
  on 
  heaches 
  and 
  flats: 
  

  

  The 
  soil 
  must 
  be 
  tenacious. 
  On 
  a 
  shifting 
  surface 
  sand 
  grains 
  may 
  

   pack 
  into 
  the 
  burrow 
  on 
  the 
  withdrawal 
  of 
  the 
  siphons, 
  preventing 
  

   subsequent 
  extension 
  to 
  the 
  water, 
  and 
  leading 
  to 
  the 
  death 
  of 
  the 
  

   clam. 
  The 
  more 
  rapid 
  the 
  current 
  the 
  more 
  tenacious 
  must 
  be 
  the 
  

   surface 
  to 
  prevent 
  erosion. 
  

  

  Surfaces 
  of 
  clam 
  beds 
  are 
  tenacious 
  from 
  several 
  causes. 
  

  

  {(i) 
  Sand 
  is 
  mixed 
  with 
  cementing 
  substances 
  like 
  tine 
  silt 
  or 
  clay. 
  

   {]>) 
  There 
  is 
  frequently" 
  a 
  growth 
  of 
  an 
  alga 
  on 
  the 
  surface 
  whicli 
  pre- 
  

   vents 
  any 
  erosion, 
  even 
  in 
  swift 
  currents, 
  (c) 
  Clam 
  beaches 
  are 
  some- 
  

   times 
  ston}^ 
  or 
  gravelly, 
  and 
  hence 
  are 
  not 
  shifted, 
  {d) 
  On 
  extensive 
  

   flats 
  thatch 
  vegetation 
  prevents 
  a 
  shifting 
  of 
  the 
  surface, 
  and 
  clams 
  

   frequently 
  are 
  found 
  in 
  great 
  numbers 
  among 
  the 
  plants, 
  (e) 
  Eel 
  

   grass, 
  between 
  tide 
  lines, 
  in 
  the 
  same 
  way, 
  unless 
  growing 
  where 
  the 
  

   soil 
  contains 
  much 
  organic 
  matter, 
  sometimes 
  prevents 
  erosion 
  and 
  

   allows 
  clams 
  to 
  establish 
  themselves. 
  

  

  The 
  food 
  of 
  clams 
  consists 
  of 
  diatoms. 
  They 
  are 
  everywhere 
  pres- 
  

   ent, 
  and 
  this 
  condition 
  may 
  be 
  regarded 
  as 
  constant. 
  The 
  amount 
  of 
  

   food 
  varies 
  in 
  proportion 
  to 
  the 
  rapidity 
  of 
  currents. 
  In 
  large 
  meas- 
  

   ure 
  the 
  rapidit}'^ 
  of 
  the 
  current 
  determines 
  the 
  number 
  of 
  clams 
  that 
  

   ma}' 
  exist 
  on 
  a 
  given 
  area. 
  

  

  Organic 
  matter 
  in 
  the 
  soil 
  sometimes 
  prevents 
  the 
  existence 
  of 
  

   clams. 
  

  

  Overcrowding 
  leads 
  either 
  to 
  the 
  rapid 
  extinction 
  of 
  all, 
  or 
  prevents 
  

   increase 
  in 
  the 
  average 
  size. 
  

  

  Within 
  certain 
  wide 
  limits, 
  the 
  salinity 
  of 
  the 
  water 
  has 
  no 
  apparent 
  

   effect 
  in 
  determining 
  the 
  existence 
  of 
  clams. 
  

  

  The 
  enemies 
  of 
  adults 
  are 
  few. 
  The 
  gastropod 
  mollusk 
  iW?v/v7r/, 
  

   however, 
  has 
  been 
  observed 
  below 
  the 
  surface 
  devouring 
  clams. 
  

  

  The 
  conclusion 
  is 
  that 
  on 
  natural 
  beaches 
  and 
  flats 
  the 
  conditions 
  

   necessary 
  for 
  existence 
  are 
  complex 
  and 
  definite, 
  restricting 
  the 
  dis- 
  

  

  o 
  European 
  Methods 
  of 
  Oyster 
  Culture. 
  U. 
  S. 
  F. 
  C. 
  Bulletin 
  for 
  1891. 
  

  

  