﻿OYSTERS 
  AND 
  METHODS 
  OF 
  OYSTER-CULTURE. 
  281 
  

  

  rapidly 
  in 
  waters 
  between 
  74° 
  and 
  80° 
  F., 
  altbongli 
  tlie 
  mortality 
  is 
  

   greater 
  than 
  at 
  a 
  slightly 
  lower 
  temperature. 
  Under 
  such 
  conditions 
  

   the 
  embryos 
  reach 
  the 
  swimming 
  stage 
  in 
  from 
  3 
  to 
  10 
  hours, 
  a 
  fact 
  

   which 
  is, 
  of 
  course, 
  advantageous 
  to 
  those 
  undertaking 
  artificial 
  propa- 
  

   gation. 
  When 
  the 
  temperature 
  falls 
  to 
  below 
  65° 
  F., 
  development 
  

   almost 
  ceases, 
  and 
  when 
  it 
  rises 
  above 
  80° 
  F. 
  but 
  few 
  of 
  the 
  embryos 
  

   reach 
  the 
  swimming 
  stage. 
  Sudden 
  changes 
  are 
  usually 
  fatal, 
  and 
  cold 
  

   rains 
  kill 
  great 
  numbers 
  of 
  the 
  swimming 
  fry. 
  

  

  Dr. 
  Ryder 
  recommends 
  "that 
  the 
  prevalent 
  temperature 
  of 
  the 
  water 
  

   during 
  the 
  spawning 
  season 
  shall 
  range 
  from 
  08 
  to 
  80° 
  F.'^ 
  It 
  is 
  quite 
  

   possible 
  that 
  in 
  other 
  regions, 
  with 
  oysters 
  native 
  thereto, 
  or 
  even 
  those 
  

   which 
  have 
  been 
  acclimated 
  therein, 
  some 
  other 
  temperature 
  may 
  be 
  

   found 
  more 
  favorable, 
  but 
  no 
  data 
  bearing 
  upon 
  the 
  matter 
  have 
  been 
  

   published. 
  

  

  TEMPERATURE; 
  PLANTED 
  BEDS 
  IN 
  SAN 
  FRANCISCO 
  BAT. 
  

  

  The 
  temperature 
  at 
  San 
  Francisco 
  is 
  usually 
  not 
  much 
  higher 
  in 
  

   summer 
  than 
  in 
  winter, 
  but 
  information 
  upon 
  the 
  subject 
  is 
  limited. 
  

   Upon 
  the 
  oyster-beds 
  at 
  Millbrae 
  it 
  is 
  said 
  to 
  vary 
  from 
  58° 
  to 
  05° 
  F., 
  

   but 
  at 
  the 
  extreme 
  southern 
  end 
  of 
  the 
  bay 
  it 
  ranges 
  from 
  67° 
  to 
  74° 
  F. 
  

   In 
  October, 
  1890, 
  Mr. 
  0. 
  H. 
  Townsend 
  found 
  61° 
  F. 
  at 
  Belmont; 
  at 
  San 
  

   Mateo, 
  nearer 
  the 
  sea, 
  60° 
  F., 
  and 
  at 
  California 
  city, 
  57° 
  F. 
  

  

  In 
  midsummer 
  the 
  temperature 
  was 
  considerably 
  higher; 
  between 
  

   July 
  12, 
  1891, 
  and 
  September 
  7, 
  1891, 
  it 
  ranged 
  from 
  07° 
  to 
  74° 
  F., 
  the 
  

   means 
  for 
  10-day 
  periods 
  during 
  the 
  same 
  time 
  being 
  between 
  69.1° 
  

   and 
  72° 
  F. 
  As 
  Mr. 
  Townsend 
  points 
  out, 
  there 
  is, 
  therefore, 
  a 
  con- 
  

   siderable 
  period 
  during 
  the 
  summer 
  when 
  the 
  temperature, 
  in 
  portions 
  

   of 
  the 
  bay 
  at 
  least, 
  is 
  favorable 
  for 
  spawning 
  of 
  the 
  planted 
  eastern 
  

   oysters. 
  The 
  portions 
  of 
  the 
  bay 
  near 
  the 
  sea 
  appear 
  to 
  have 
  a 
  tem- 
  

   perature 
  several 
  degrees 
  cooler 
  than 
  in 
  the 
  southern 
  portions. 
  

  

  DENSITY 
  OF 
  WATER. 
  

  

  Oysters 
  are 
  found 
  living 
  in 
  water 
  ranging 
  in 
  salinity 
  from 
  1.002* 
  to 
  

   1.025, 
  but 
  the 
  lower 
  densities 
  are 
  always 
  injurious, 
  and 
  prolonged 
  

   exposure 
  to 
  their 
  influence 
  is 
  fatal 
  to 
  oyster 
  life. 
  It 
  is 
  not 
  possible 
  to 
  

   profitably 
  maintain 
  oyster-beds 
  in 
  waters 
  where 
  the 
  density 
  falls 
  below 
  

   1.007 
  for 
  any 
  length 
  of 
  time, 
  the 
  oyster, 
  if 
  not 
  killed, 
  becoming 
  poor 
  in 
  

   quality, 
  pale, 
  watery, 
  and 
  tasteless. 
  Heavy 
  freshets, 
  such 
  as 
  occur 
  in 
  

   the 
  rivers 
  discharging 
  into 
  Chesapeake 
  Bay 
  and 
  at 
  various 
  places 
  on 
  

   the 
  Gulf 
  coast, 
  frequently 
  so 
  lower 
  the 
  density 
  of 
  the 
  water 
  as 
  to 
  prac- 
  

   tically 
  exterminate 
  the 
  oysters 
  on 
  certain 
  beds. 
  Experience 
  apparently 
  

   indicates 
  that 
  the 
  best 
  oysters 
  are 
  grown 
  in 
  densities 
  between 
  about 
  

   1.011 
  and 
  1.022, 
  the 
  former 
  being 
  approximately 
  the 
  specific 
  gravity 
  

   over 
  the 
  Tangier 
  Sound 
  beds, 
  the 
  latter 
  that 
  over 
  the 
  deep-water 
  

   oyster-grounds 
  of 
  Long 
  Island 
  Sound. 
  

  

  * 
  The 
  figures 
  represent 
  the 
  specific 
  gravity 
  aa 
  measured 
  with 
  the 
  salinometer, 
  that 
  

   of 
  pure 
  water 
  being 
  1.000. 
  

  

  