﻿200 
  KEPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  

  

  high-tide 
  mark 
  to 
  the 
  usual 
  low-tide 
  mark, 
  very 
  few 
  being 
  found 
  

   below 
  this 
  region. 
  More 
  evidence 
  is 
  needed 
  on 
  this 
  point. 
  If 
  this 
  

   belief 
  is 
  well 
  founded, 
  there 
  is 
  some 
  adverse 
  condition 
  which 
  is 
  more 
  

   or 
  less 
  general 
  and 
  which 
  is 
  not 
  now 
  apparent. 
  

  

  ORGANIC 
  MATTER 
  IN 
  THE 
  SOIL. 
  

  

  There 
  must 
  be 
  a 
  comparatively 
  small 
  amount 
  of 
  decaying 
  organic 
  

   matter 
  in 
  the 
  soil 
  where 
  clam 
  growth 
  is 
  to 
  be 
  maintained. 
  The 
  reason 
  

   is 
  that 
  carbon 
  dioxid 
  and 
  humous 
  acids 
  formed 
  by 
  the 
  decay 
  of 
  organ- 
  

   isms 
  have 
  the 
  effect 
  of 
  removing 
  the 
  lime 
  from 
  the 
  shells 
  of 
  clams 
  and 
  

   lead 
  to 
  their 
  death. 
  

  

  THE 
  EFFECT 
  OF 
  OVERCROWDING. 
  

  

  It 
  is 
  usually 
  easj^ 
  to 
  find 
  between 
  the 
  tide 
  marks 
  on 
  natural 
  clam 
  

   flats 
  certain 
  areas 
  which 
  bear 
  clams 
  so 
  thickly 
  set 
  that 
  growth 
  is 
  

   extremely 
  slow. 
  Such 
  beds 
  may 
  maintain 
  themselves 
  from 
  year 
  to 
  

   year, 
  but 
  evidence 
  will 
  be 
  given 
  to 
  show 
  that 
  their 
  condition 
  is 
  preca- 
  

   rious. 
  If, 
  for 
  any 
  reason, 
  some 
  individuals 
  die, 
  others 
  may 
  be 
  affected 
  

   and 
  the 
  contamination 
  eventually 
  leads 
  to 
  the 
  destruction 
  of 
  all. 
  Much 
  

   depends 
  upon 
  the 
  nature 
  of 
  the 
  water 
  currents. 
  Where 
  they 
  are 
  

   rapid 
  the 
  danger 
  is 
  least. 
  Some 
  areas, 
  therefore, 
  may 
  bear 
  many 
  

   more 
  individuals 
  than 
  others. 
  

  

  THE 
  SALINITY 
  OF 
  THE 
  WATER. 
  

  

  In 
  describing 
  the 
  conditions 
  which 
  are 
  necessary 
  for 
  the 
  existence 
  

   of 
  clams 
  on 
  natural 
  beds 
  it 
  may 
  be 
  well 
  to 
  note 
  the 
  fact 
  that, 
  within 
  

   certain 
  very 
  wide 
  limits, 
  clams 
  appear 
  to 
  do 
  equally 
  well 
  in 
  water 
  

   which 
  is 
  very 
  salt 
  or 
  nearly 
  fresh. 
  Not 
  only 
  is 
  this 
  true, 
  but 
  they 
  

   may 
  be 
  transplanted 
  from 
  one 
  locality 
  to 
  another 
  where 
  the 
  salinity 
  is 
  

   very 
  different 
  without 
  being 
  affected 
  adversely. 
  

  

  The 
  enemies 
  of 
  the 
  adult 
  clam 
  are 
  few. 
  At 
  one 
  point 
  on 
  the 
  shore 
  

   above 
  Cape 
  Cod, 
  the 
  gastropod 
  Neventa 
  was 
  observed 
  digging 
  l)eneath 
  

   the 
  surface 
  and 
  devouring 
  mature 
  clams. 
  That 
  other 
  animals 
  attack 
  

   them 
  in 
  their 
  burrows 
  has 
  not 
  been 
  observed 
  so 
  far 
  as 
  I 
  know. 
  

  

  From 
  what 
  has 
  been 
  said 
  it 
  is 
  perhaps 
  clear 
  that 
  there 
  is 
  much 
  vari- 
  

   ation 
  in 
  the 
  conditions 
  existing 
  on 
  a 
  clam 
  flat, 
  and 
  that 
  the 
  necessary 
  

   combination 
  of 
  circumstances 
  to 
  allow 
  clams 
  to 
  grow 
  and 
  reproduce 
  

   is 
  positive 
  and 
  definite. 
  These 
  conditions 
  restrict 
  the 
  distribution 
  

   to 
  certain 
  more 
  or 
  less 
  clearly 
  defined 
  areas. 
  They 
  are 
  constantly 
  

   changing 
  also, 
  and 
  clam 
  beds 
  appear 
  now 
  in 
  one 
  place 
  and 
  then 
  in 
  

   another. 
  There 
  probably 
  are 
  many 
  other 
  factors 
  in 
  the 
  problem 
  of 
  

   the 
  clam's 
  environment 
  which 
  have 
  not 
  been 
  observed. 
  It 
  may 
  not 
  

  

  