National Marine Fisheries Service Data Overview

These data are provided by the Northeast Fisheries Science Center of the U.S. National Marine Fisheries Service in Woods Hole, MA, USA.

Please be aware: a variety of gear types have been used, and these have varying selectivity or sampling efficiency for different organisms. Moreover, a number of different vessels have been involved in sampling, and gear and methods have evolved over time. All of these factors affect sampling and the interpretation of data. NMFS has developed correction factors to adjust for these changes and use other statistical tools for population estimates. The data we present here can be used as an index of abundance (over time or space) within a species or among species with similar vulnerability to the sampling gear. The data refer to a standard tow or sample and are not normalized to a unit area.

National Marine Fisheries Service Field Names and Descriptions

The information listed below is from the National Marine Fisheries Service web site.

Field name Description
cruiseid Cruise id uniquely identifies cruises. The first four digits indicate the year and the last two digits uniquely identifythe cruise within the year.
season The season of the year (summer, fall, winter or spring) during which time the data were collected.
purpose_code The purpose of the cruise as a one or two digit number.
purpose The English "translation" of the purpose_code.
vessel Two or more character vessel code. NMFS calls this SVVESSEL:

AL = R/V Albatross IV
DE = R/V Delaware II
(more to come)

For a complete list of vessel codes and vessel names see the vessel_names table.

cruise_number Cruise number, within the year. NMFS calls this field CRUNUM
gear_type Gear type code. NMFS calls this field SVGEAR.
stratum A predefined area where a net dredge, or other piece of gear was deployed. The code consists of several parts. The stratum group code number (2 bytes) refers to the area fished either inshore or offshore, North or South of Cape Hatteras or the type of cruise (shellfish, State of MA, offshore deepwater). The stratum number (third and fourth digits of the code) refers to the area defined by depth zone. The fifth digit of the code increases the length of the stratum number for revised strata after the Hague Line was established. Stratum group codes are shown in the accompanying table. A change in Bottom Trawl Stratum for the Gulf of Maine-Bay of Fundy has been in effect since Spring 1987, and may be summarized as follows: Previous stratum: 01350 Present strata: 01351, 01352.
tow Sequential number representing order in which station was selected within a stratum
station Unique sequential order in which stations have been completed.Hangups and short tows each receive a consecutive number
lat Beginning latitude of the tow, in decimal degrees. North is a positive number, south is negative.
lon Beginning longitude of the tow, in decimal degrees. East is a positive number, west is negative.
begin_gmt_towdate Beginning tow date in the form DD-MON-YEAR, in GMT, where DD is the two digit day, MON is the three character month abbreviation, and YEAR is the four digit year.
year_gmt Four digit year, GMT.
month_gmt Two digit month, GMT.
day_gmt Two digit day, GMT.
depth_set A four digit number record the depth, to the nearest meter, at the start of the trawl, dredge, or other survey gear deployment.
depth_end Water depth at the end of the tow, in meters.
depth_min Minimum depth at which gear fished, in meters.
depth_avg A four digit number recording the average depth, to the nearest meter, during a survey deployment. The SCS Trawl Event used with FSCS records depth readings every 10 seconds during a typical 30 minute bottom trawl survey tow.
depth_max Maximum depth at which gear fished, in meters.
temp_air Air temperature rounded to the nearest whole degree, in degrees Celsius.
temp_ss Surface temperature of the water, in degrees Celsius.
cloud_code Code to represent percentage of cloud cover. A description of these codes is available in the table below
press_par Barometric pressure, in millibars.
sal_ss Salinity at the surface of the water.
temp_bot Bottom temperature.
sal_bot Bottom salinity.
wind_dir Direction of wind.
wind_speed_kt Speed of wind, in knots
yrday_gmt GMT day and decimal time, as 326.5 for the 326th day of the year, or November 22nd at 1200 hours (noon).
id The NMFS ID field is a combination of the cruiseid, stratum, tow, and station values. (See note 13 below.)
code A three digit alphanumeric field used to code each species caught in a trawl or dredge.
sex A one digit alphanumeric code used to identify species that are sexed at the catch level. This code is used to represent the entire catch of a particular species and not an individual fish or invertebrate. The available catch sex codes are shown below.
catch_numb Expanded number of individuals of a species caught at a given station.
catch_wt Expanded catch weight of a species caught at a given station, to the nearest thousandth of a kilogram, i.e. 3 decimal places.

Stratum Codes
Code Description
01 Trawl, offshore north of Hatteras
03 Trawl, inshore north of Hatteras
04 Shrimp
05 Scotian shelf
06 Shellfish
07 Trawl, inshore south of Hatteras
08 Trawl, offshore south of Hatteras
99 Offshore deepwater (outside of the stratified area)

Cloud Codes
Code Description, in percent sky coverage
0 0
1 10
2 20/30
3 40
4 50
5 60
6 70/80
7 90
8 100
9 n/a

Catch Sex Code Table
Code Description
0 Unsexed
1 Male
2 Female
Lobster Codes (code = 301)
0 Forgot to look
1 Male
2 Female
3 Female with eggs
4 Female V-notch
5 Female V-notch with eggs
Northern Shrimp Codes (code=306)
1 Male
2 Female Stage I for Northern Shrimp
3 Female Stage II for Northern Shrimp
4 Transitional for Northern Shrimp
5 Ovigerous for Northern Shrimp
6 Non-spawning Female for Northern Shrimp
7 Female for Northern Shrimp not staged (stage I or II not determined)

Data Acquisition, Processing and Storage and Retrieval Notes

  1. One must include cruiseid, stratum, tow, and station in order to have a unique key throughout the 40 year time series.
  2. The cruise purpose code is a very important data qualifiersince the NMFS can only attest to the veracity of the data with purpose codes equal to 10, 12, 14, 15, 40, 50, and 60. For a complete list of purpose codes and their meanings click here. By selecting the purpose of the cruise, you can make better assumptions of how the data were collected and who to contact if a question does arise. In addition, gear code, is also very important.
  3. Be careful of cruises where purpose code = 15 (Scotian Shelf revision) also since many of those stations are duplicated in some of the cruises with purpose code = 10 (but they have different strata-tow #s).
  4. Anyone using these data must know what data they have and how the data are going to be used. For example, if you have only cruises with a status code of 10 and a purpose code of 10, then you are dealing with only the seasonal standard bottom trawl surveys. If you do not put a purpose code of 10 in, then you’ll be retrieving data from all of the various cruises that are in the NMFS’ entire database.
  5. The species that are not coded are typically starfish, anemones, debris, etc. All fish species caught are coded and entered into the database.
  6. Only those species that are caught in a given trawl are recorded, but there are some species (e.g., some invertebrates) that may be caught but not coded or included in the database. Therefore, there will not be species records in the database with zero values to represent absence. They just don’t appear in the database.
  7. In order to get a subset of all species caught for the Gulf of Maine (GOM), one can join the station table with the catch table based on a latitude and longitude boundary, or one can use the stratum field to limit records that pertain to the Gulf of Maine (GOM). Available are two PDF files that indicate stratum numbers for the GOM and George’s Bank. One is for offshore stratum the other for inshore stratum. An offshore stratum would include a 01 before the actual stratum number. For example, offshore stratum 37 would be indicated in the field stratum as 01370. Inshore stratum 37 would be indicated with 03370.
  8. The count and weight values need to be corrected for differences in the door, gear and vessel. See the NMFS trawl factors for these corrections and adjustments.
  9. Only those stations of tow type (i.e. NMFS field name STATYPE) "01" are retrieved for 1982 and after. For data collected before 1982, the value for this code is blank, that is, nothing is entered in the NMFS database. Tow types are defined in the the NMFS SVDBS.STATION_VALUE table as follows:
    1 Survey Haul  
    2 Non-random Haul  
    3 Special Random Add-on Station Haul  
    4 Comparison Haul  
    5 No Trawl Haul (e.g. Bongo or XBT)  
    6 Site specific  
    8 Depletion Experiment 23-SEP-1998
    7 Systematic grid  
    9 Systematic parallel transects  
    0 Systematic zig zag transects  
  11. The code for the relative success of the haul is "01". The data presented here is retrieved from the NMFS Oracle database using a value of SHG less than or equal to 136. That is, the status code is 1, the haul code is less than or equal to 3, and the gear code is less than or equal to 6.
  12. Historically, NMFS was only able to capture weight data to the nearest tenth of a kilogram. Therefore, whenever a weight was less than 0.1 kg, the weight was changed to 0. Therefore, there were samples in the catch that were measured and counted, but the weight was less than the scales could accurately measure. This is not the case now.
  13. In some cases, there are entries where the count is zero but the weight for the species is non-zero. This is because there were times when certain species were weighed but not measured. Today, we count those items, but in the past they may not have been.
  14. The fields CRUISE, STRATUM, TOW, STATION are necessary to retrieve a unique station record (UNION_FSCS_SVSTA) The fields CRUISE, STRATUM, TOW, STATION, SVSPP, CATCHSEX are necessary to retrieve a unique catch record (UNION_FSCS_SVCAT)The fields CRUISE, STRATUM, TOW, STATION, SVSPP, CATCHSEX, LENGTH are necessary to retrieve a unique length record (UNION_FSCS_SVLEN)
  15. The NMFS Survey database contains 40 years worth of groundfish data collected using somewhat standard protocols. You can imagine the changes to the database design over time with changing technology. If you are familiar with the stratified random sampling design employed on the Fisheries’ surveys, then the field Cruise identifies a unique groundfish survey. The fields stratum and tow are used together to identify the tows completed within a particular stratum (e.g., stratum 40 contains 5 pre-selected random tows to be surveyed for a particular groundfish survey). The field station is simply the sequential order in which the pre-selected tows were completed. For example, one may decide that the most efficient cruise track would be to complete stratum/tows in the following order:
    Station – Stratum – Tow
    1 – 40 – 4
    2 – 40 – 1
    3 – 39 – 7
    4 – 39 – 6
    5 – 40 – 2

    So, the order of completing a tow within a stratum is based on cruise efficiency and not on completing all tows within a stratum and then moving on. Therefore, the station number is simply used to create a unique key for each record within a cruise (cruise, station). However, during the time series, there were those cases where someone repeated a station number within a cruise, negating the uniqueness of cruise, station. So, we have to use cruise, stratum, tow, station in order to get uniqueness. This is true prior to the 2001 Spring Bottom Trawl Survey. After this point in time, we enforced uniqueness by cruise, station with advent of the Fisheries’ new digital data entry system FSCS. Hence, the need to create a snapshot joining the old with the new.

  16. There were cruises where both the Albatross IV and Delaware II were used to complete all tows within a cruise. The Delaware II was used for inshore tows and the Albatross IV completed offshore tows.
  17. Note that records can be identical except for different strata-tow numbers, and, of course, different purpose codes. One has to be careful about the combination of purpose code and the strata group indicator (1-9, 99). One can see that 05 means Scotian Shelf and if one selects a purpose code of 15, one will not get duplicates.