Index of /math/statlib/crab

      Name                    Last modified       Size  Description

[DIR] Parent Directory 01-Jan-1970 01:00 - [TXT] catch 21-Oct-1989 00:00 2k [TXT] celsius 21-Oct-1989 00:00 1k [TXT] datasets 13-Dec-1989 01:00 1k [TXT] dstns 21-Oct-1989 00:00 40k [TXT] eggs 21-Oct-1989 00:00 1k [TXT] fleet 21-Oct-1989 00:00 1k [TXT] fullnes 21-Oct-1989 00:00 37k [TXT] fullness 21-Oct-1989 00:00 37k [TXT] index 13-Jul-2001 13:00 2k [TXT] kodiak 21-Oct-1989 00:00 47k [TXT] notice 21-Oct-1989 00:00 3k [TXT] readme 21-Jan-1990 01:00 22k [TXT] salinity 21-Oct-1989 00:00 1k [TXT] shar 21-Jan-1990 01:00 407k [TXT] sharuuen 21-Jan-1990 01:00 154k [TXT] survey 21-Oct-1989 00:00 239k

                             King Crab Data

This is a description of the Kodiak Island king crab survey data, distributed
for the Data Analysis Exposition being sponsored by the Statistical Graphics
and Statistical Computing Sections at the 1990 American Statistical Society
Joint Statistical meetings in Anaheim.

Here is a quick inventory of the files and their sizes:

  File      Lines  Cols  Bytes  Contents
  -------   -----  ----  ------ ---------------------------------------------
  README      458    -   22672  text: (this file)
  notice       56    -    3355  text: the published notice of the Exposition
  survey     3450   14  244950  the basic survey data
  kodiak     2687    2   48264  map coordinates for the Kodiak Island shoreline
  dstns      1845    5   40590  distributions of crab by size, year, category
  fleet        23    6     946  commercial fleet/catch/price data, by year
  catch        96    4    2112  commercial catch data, by year, district
  eggs         14    2     140  ave number of eggs per female, by year
  salinity     60    3     718  ocean salinity, by month
  celsius      68    3     741  ocean temperature, by month, in degrees celsius
  fullness   1170    7   37440  distributions of females by clutch fullness
  -------   -----  ----  ------ ---------------------------------------------
    total    9920       401584

Data sources:  All the data sets except salinity and temperature were
provided by the Alaska Department of Fish and Game, 211 Mission Road,
Kodiak, AK 99615.  The salinity and temperature data came from Tom
Royer, Institute of Marine Sciences, University of Alaska, Fairbanks,
AK 99775-1080

    |                                                                         |
    |  After scanning through the information below, if you decide you want   |
    |  the entire data set to try your hand at analyzing it, and don't        |
    |  already have it, here are the instructions for getting it:             |
    |                                                                         |
    |    1. If you obtained the data on a PC or Macintosh diskette, you       |
    |       should already have all the data files, and you are done.         |
    |       If not, you may send either one formatted IBM-PC 5.25 inch        |
    |       floppy disk or one 800K double-sided Macintosh diskette to        |
    |       Paul Tukey, Bellcore 2M-391, 445 South Street, Morristown NJ      |
    |       07960.  (Please use this method only as a last resort.)           |
    |                                                                         |
    |    2. If you obtained this README file through anonymous ftp from       |
    | (Internet address, reestablish   |
    |       the ftp connection, cd to pub/crab, and use "get" for each file   |
    |       in that directory. (Use "ls" to list them, or "?" for help.)      |
    |                                                                         |
    |    3. If you obtained this README file by sending an email letter to    |
    | containing the single line            |
    |       "send README from crab", and if you are on a Unix system,         |
    |       you can get the rest of the data files as a self-unbundling       |
    |       shar archive by sending another email letter to                   |
    | containing the single line            |
    |       "send shar from crab".  (It will come in several pieces,          |
    |       with easy instructions for reassembling them.)                    |
    |                                                                         |
    |   3a. If you have the uudecode command you can obtain a uuencoded,      |
    |       compressed version of the shar file by asking the statlib         |
    |       server for "send sharuuen from crab".  The file will come         |
    |       in two pieces with reassemly instructions.  Put the pieces        |
    |       together, uudecode the resulting file, then uncompress the        |
    |       result of that.  (This ends up sending about 140k through         |
    |       the mail, whereas the full shar file is about 430k.               |
    |                                                                         |
    |    4. If you obtained this README as in 3. but you do NOT have          |
    |       access to a Unix system, send another email letter to             |
    | containing the lines                  |
    |                                                                         |
    |         send catch from crab                                            |
    |         send celsius from crab                                          |
    |         send dstns from crab                                            |
    |         send eggs from crab                                             |
    |         send fleet from crab                                            |
    |         send fullness from crab                                         |
    |         send kodiak from crab                                           |
    |         send notice from crab                                           |
    |         send salinity from crab                                         |
    |         send survey from crab                                           |
    |                                                                         |
    |       The data will be sent to you in a number of email letters         |
    |       which you will have to hand-edit to trim away the mail            |
    |       headers and recreate the data files.  The "survey" file           |
    |       will be split into four pieces which you will have to             |
    |       reassemble in the proper order, after trimming them. (You         |
    |       will also receive a "netchop" program that can do the             |
    |       trimming and reassembly but only on a Unix system).               |
    |                                                                         |

=====================  Contents of file "survey" =============================

The main data set consists of king crab pot survey data for the years 1973
through 1986.  The surveys were conducted in the waters around Kodiak Island,
Alaska, using pots similar to the pots used by the commercial fishing fleet.
(A crab pot is a trap that resembles a wooden crate.)  A fixed sampling grid
was used to place strings of pots (stations) consisting usually of 10 pots in
open ocean, or of 2-5 pots in bays.  The pots were left in the water for
periods of 16-24 hours, removed, and the crab counts recorded.  The survey was
conducted each summer, 2-4 weeks prior to start of the commercial fishing
season.  The crab counts are classified by size (roughly representing age) and
sex into six categories.

The basic survey data is a file "survey", containing a 3,450 by 14 matrix
with these columns:

      1. Year (last two digits)
      2. Fishing district (one of four)
      3. Station identifier (alphabetic)
      4. The number of pots fished
    5-6. Latitude and longitude of the location halfway between
             the first and last pot of the station
      7. Number of pre-recruit-4 crab
      8. Number of pre-recruit-3 crab
      9. Number of pre-recruit-2 crab
     10. Number of pre-recruit-1 crab
     11. Number of recruit males
     12. Number of post-recruit males
     13. Number of juvenile females
     14. Number of adult females
A recruit is a male king crab that has reached a certain specified minimum
size that makes him eligible to be caught.  (The precise definition is
somewhat technical, involving "carapace length" and new-shell vs old-shell,
but the details are not important here.)

A pre-recruit-1 is a smaller male, roughly a year too young to be legally
caught.  (The operational definition is again in terms of size.)

A pre-recruit-2 is a still-smaller male crab roughly 2 years away from
reaching legal size.  And so on.

A post-recruit is, roughly, a male crab that was probably already legal a year

A "legal" king crab is any male crab that is either a recruit or
post-recruit.  Since the commercial fleet is only permitted to catch legal
crab, it is the total of recruits and post-recruits each year that is of
primary commercial interest.

Note that for the 1973 through 1979 surveys, "adult female" was defined to be
any female with eggs.  However, starting in 1980, the definition of adult
female was expanded to include large eggless females that exceed a certain
specified size.

*   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   

In addition to the basic survey data, a number of other data sets have been
provided which are thought to have varying degrees of relevance to the primary
analysis and to the graphical presentation of results.

====================  Contents of file "kodiak" ============================

Geographical coordinates of the shoreline of the 17 islands that form the
Kodiak Island group.  The two columns are

      1.  latitude
      2.  longitude

measured in degrees and fractions of a degree.  Each of the 17 groups of
coordinates is terminated by a pair of "NA"s, and the end of each group loops
back to the beginning.  For drawing maps, bear in mind that longitude is
measured East to West, which is right to left.  This suggests plotting
negative longitude instead of longitude.  Also, to draw maps that "look right"
to an Alaskan, you must take into account that in this part of the world the
aspect ratio of one degree latitude (y-axis) to one degree longitude (x-axis)
is 1:1.8 (in terms of actual ground distance).

====================  Contents of file "dstns" ============================
For each of the years in the survey (1973 to 1986), a frequency distribution
of the crab by size (in 1 mm increments) that were surveyed.  Separate
distributions are given for juvenile females, adult females, and all males.
The five columns are:

      1. year
      2. length in mm
      3. count of juvenile females
      4. count of adult females
      5. count of all males

====================  Contents of file "fleet" ============================

Some statistics on the fishing fleet and commercial catch, for each year
between 1960 and 1982.  The six columns are:

      1. year
      2. number of vessels registered for fishing
      3. number of crab caught
      4. total weight in kilograms of crab caught
      5. total number of pot-lifts.
      6. wholesale price of king crab in dollars per pound

=======================  Contents of file "catch" ============================

Commercial catch data for 1960-1982, broken out by district.  The four columns

      1. year
      2. district number (1, 2, 3 or 4)
      3. total catch as a count
      4. total catch in kilograms

========================  Contents of file "eggs" ============================

For each of the 14 years in the survey (1973-86), an estimate of the number of
eggs per female.  Columns are:

      1. year
      2. estimated eggs per adult female

========================  Contents of file "salinity" ========================

For a selection of months in the period 1970 to 1983, a measurement of the
ocean salinity at a depth of 100 meters off the Alaskan coast, given in parts
per thousand.  Columns are:

      1. year
      2. month
      3. salinity

=========================  Contents of file "celsius" ========================

For a selection of months in the period 1970 to 1983, a measurement of the
ocean temperature at a depth of 100 meters off the Alaskan coast, given in
degrees Celsius.  Columns are:

      1. year
      2. month
      3. temperature

=======================  Contents of file "fullness" ==========================

For each year in the survey, a frequency distribution of all females
cross-classified by size (in 1 mm increments) and percent clutch fullness (5
categories).  Clutch fullness is, roughly, the realized egg-bearing potential
of a female crab.  The seven columns are:

      1. year
      2. size, in mm
      3. count of females with 0% fullness
      4. count of females with 1-29% fullness
      5. count of females with 30-59% fullness
      6. count of females with 60-89% fullness
      7. count of females with 90-100% fullness

==========================  General Discussion  ==============================

    The underlying purpose of the survey has been to gather biological
and abundance information to be used in the management of king crab
(opening and closing of fisheries, setting of quotas, etc.)

    The following is a set general questions and issues to stimulate
the analysis.  The list is certainly not exhaustive:

   *  Can trends in crab abundance be characterized?

   *  What can be said about sampling error in this kind of survey?

   *  To the extent that abundance has declined, what factors are linked
      to the decline?  Is there evidence that overfishing is a major
      cause?  Do environmental factors contribute?  Are we seeing
      natural population cycles?

   *  Characterize the dynamics of the crab population

   *  Characterize the changing spatial distribution of the crab

   *  By comparing abundances of recruits, prerecruits and postrecruits
      from year to year, can cohorts be identified and tracked?

   *  Can anything be said about the "social" interaction of crab
      with regard to sexes and age groups?

   *  Although the primary interest is in recruits, clearly having
      a plentiful supply of fecund females to produce new generations
      of crab is essential.  Is the fertility of females in jeopardy,
      as well as their abundance?   Can the supply of recruits in
      a given year be linked to the abundance and fertility of
      females in earlier years?

    We append to this list some questions for discussion contributed
by one of the king crab researchers in Alaska.  While it is not clear
which, if any, of these specific questions could be addressed with
this data, the questions DO give a flavor of the kinds of issues
that are of concern, and the language that is spoken in this industry:

   *  Do the size classifications used provide a realistic view of the
      growth of male crab as portrayed by the change in modes over

   *  If not, what is an improved alogorithm for defining crab age
      classes?  (Keep in mind that crab do not grow continuously, but
      incrementally, and that crab age cannot be measured, other than
      by inference by looking at length frequency information.)

   *  Does the data indicate that M (natural mortality) varies by
      size? by shell age? among years?

   *  What change would M have to have before it would be detectable?

   *  Are F (fishing mortality) and M related?  i.e. does fishing
      mortality affect, in some indirect way (such as through ghost
      fishing by lost pots, illegal catch, mortality from handling
      and sorting crabs) the assumed F values from the catch data?

   *  What affect would increasing or decreasing F have on long term
      average yield and its variance using a 50 year time horizon for
      projections?  What affect would varying size limits have on the

   *  Length frequency data can be obtained from survey data, much
      less costly than Catch Per Unit Effort data.  What information
      is obtained about crab population dynamics from the CPUE data
      that cannot be obtained from the length frequency data when
      coupled with catch data?  without catch data (i.e. when the
      fishery is closed)?

   *  Do crab grow at different rates between years?  Does the
      frequency of skip molting change, based on age of crab, as
      compared to length?  Can these questions be addressed by this
      data set?

    In the course of a preliminary analysis of this data, a person
knowing little about crab (apart from how they taste!) posed several
questions.  Alan Johnson, of the Alaska Department of Fish and Game,
addressed each briefly.  This dialogue may provide some additional

 Q: Although only recruits and postrecruits may be legally fished, some
    number of females and smaller males are probably harvested, either
    by error or deliberate violation.  How extensive it this?

    A: This is tightly controlled, and not regarded as a problem

 Q: How reliable are the figures on commercial catch?  E.g., how
    carefully do vessels measure their catch?

    A: They use a "stick" of the correct size and measure every crab. 
       Of course, if the vessel processes crab onboard instead of
       landing the crab live, they could process illegal crab.  This
       issue has been studied for the Bering sea fishery by comparing
       size distributions.  Onboard observers are now required, but
       historically, in the Kodiak fishery, it is believed that onboard
       processing did not occur.

 Q: How conscientiously do they report?

    A: Counts of crab are guesstimates, pounds are accurate; that's how
       they get paid.   Location of catch could be squirrely because
       the skippers are protective of where they fish.

 Q: How many unregistered vessels (possibly of other nationalities, or
    noncommercial) operate illegally?

    A: None.  This is very tightly controlled.

 Q: I was told that a possibly significant number of crab (of all
    categories) may be injured or destroyed when the pots are lowered
    and land on them.   Once an area is found where there happens to be
    a local concentration of crab, many vessels converge there and
    many pots are dropped.  These pots are LARGE and HEAVY, and the
    ocean floor is literally blanketed with crab.  Also, a certain
    number of pots must have been lost over time, but such "ghost
    pots" may continue to destroy crab.  How serious a factor is this?

    A: No one knows for sure, but the problem has been addressed and is
       thought, at this time, not to be a serious problem.

 Q: Does the area of the survey pretty well cover the area that is
    commercially fished?  A superficial study of this data shows that
    the crab populations tend to be concentrated in smallish
    neighborhoods, and wander around from year to year.  Do they also
    wander significantly from day to day or from week to week?  Do they
    wander on and off the survey grid, so that we might actually miss
    them in a given year's survey?  If they do move from week to week,
    and if it takes several weeks to conduct the survey (how long does
    it take?) is it possible that in a given survey we might actually
    miss an elusive concentration of crab, even if they are on the
    grid?  Or could a given survey accidentally track a concentration
    of crab, erroneously observing the same crab community at several

    A: These issues have been well covered, with the exception that
       minor areas have never been surveyed.  The survey areas changed
       over the years in response to the industry saying "There's crab
       out there".  The catch quotas were based on the survey results,
       so the fishermen wanted the survey to hit the concentrations of

       There is quite a bit of crab movement.  (The fishermen have to
       follow the crab to be really successful).

       Simultaneous movement of the crabs and the survey is a
       potential problem.  The rate of movement of the survey is
       probably higher than that of the crab, day by day.  In the
       survey, up to three strings per day are fished. (There are 39
       pots on a vessel.)  The survey moves faster in the bay

 Q: Getting a handle on sampling error in this survey from the data
    at hand is a staggering task!

    A: Sampling error should probably be handled at the count-per-pot 
       level of resolution, to get within-station and between-station
       variance estimates. [In fact, crab counts within pots are
       available, but we chose to provide only station totals in the
       present data set, in order to keep it down to a manageable size.
       The raw data files from this survey occupy about 80M byte.]

 Q: Even apart from the issues of crab migration on, off, and across
    the grid, and differences in numbers of pots lowered and lengths of
    times they are in the water, there is a serious question about what
    motivates crab to crawl into a pot, and how the presence of crab in
    a pot may encourage or discourage other crabs from entering the
    same pot.  In other words, the crab count from a pot is at best
    only related to the actual crab concentration at that station
    through some unknown (hopefully monotonic) probabilistic function.
    Or does someone somewhere have knowledge of crab behavior at this
    level?  When I asked people questions of this kind at the joint
    meeting of the Alaska Chapters of the ASA and the American
    Fisheries Society in Anchorage, I got the impression that crab
    social behavior is not well understood.

    A: True.  If we redo this set of data at the pot resolution, this
       could be addressed, but not now.  The social behavior is indeed
       not well understood.

 Q: I have the impression that until the mid '70s there was very little
    appreciation of the need to manage the crab population, especially
    to protect the abundance and fertility of females, and that there
    was very little control of commercial crab fishing.

    A: The first surveys were in 1971 and '72 and I think the quotas were
       started about that time.  (The '71 and '72 surveys are not even
       comparable to this data set)

 Q: To what extent has the decline in commercial catch been the result of
    1. increased controls on fishing during this period, and 2. declining
    profitability due to declining crab population?

    A: A declining population causes an INCREASE in profitability.
       Price went up!

 Q: Is crab survey data available for 1987 and 1988?

    A: No pot survey was conducted in those years.  A trawl survey was
       conducted instead, so the '87 and '88 data are not comparable.

==========================  End of README  ==============================