Data Management Plan

This study compares timing of egg extrusion, embryo development, timing and duration of eclosion, and incubation periods of Kodiak, Alaska primiparous and multiparous Tanner crabs (Chionoecetes bairdi) reared in identical conditions to determine if and how these variables differ between reproductive states. Female reproductive state (primiparous or multiparous) and dates of egg extrusion were recorded, eggs were sampled monthly to determine egg stage and area, and larvae were collected daily during eclosion to determine timing and duration of eclosion.

Alaskan waters

Process Steps:

• Female Tanner crabs were captured in the field November 2002 through May 2003 and brought to the Kodiak Fisheries Research Center (KFRC) laboratory. Females were grouped as either primiparous or multiparous. Females that comprised the multiparous group were collected by commercial crab pots fished in Chiniak Bay, Kodiak, Alaska (57°43.25' N, 152°17.5' W,), November, 2002 and delivered to the laboratory. The females collected were ovigerous, hatched their larvae in the laboratory and extruded a new clutch of eggs. Once a female began stripping her pleopods after eclosion, she was paired with a mature male; therefore, the female could either mate or use stored sperm to fertilize a new clutch. It is not know how many previous clutches females in the multiparous group brooded, but they were multiparous because they were collected ovigerous and then extruded a new clutch of eggs in the laboratory. Primiparous females were collected by divers while still pubescent and nearing their terminal molt (as indicated by being in a grasping pair) in Womens Bay, Kodiak, Alaska (57°43.6' N, 152°32.0' W, Fig. 2). Divers searched for pubescent females in mating pairs from November 2002 through May 2003; however, females used in this study were collected between December 2002 and February 2003, except for one female collected in April 2003. The grasping pairs were isolated in underwater cages that were monitored regularly until a female underwent her terminal molt, mated and extruded eggs after which time she was brought into the laboratory. Occasionally, a female underwent her terminal molt in a cage without a male present. When this occurred, the soft shelled female was brought into the laboratory and mated with a male recently collected from the field.
• All females were tagged with an oval 6.5 mm × 20 mm individually numbered plastic Floy tag attached with a cable tie to a fourth walking leg. Data recorded were female reproductive state (primiparous or multiparous), molting and mating dates, dates of egg extrusion and carapace width measured as the greatest straight-line distance across the carapace excluding spines. Mean extrusion dates were calculated as the average date of extrusion within the primiparous and multiparous groups.
• For the duration of the study, crabs were held in a single flow-through tank 0.46 m × 0.46 m × 1.8 m at the KFRC seawater laboratory. Seawater intakes are located at 15 and 26 m depths in Trident Basin approximately 30 m from the laboratory. Both primiparous and multiparous females were held in the same tank to ensure that all crabs in the experiment were exposed to identical conditions. Sand-filtered seawater was used and the tank was chilled from May 2003 through November 2003 to ensure appropriate temperatures. An Onset StowAway TidBiT data logger recorded water temperature in the tank. Crabs were fed ad libitum twice weekly a diet of fish and squid.
• Twenty-four primiparous females and 21 multiparous females were used in this experiment; however, crabs died over the course of the experiment, leaving 14 primiparous and 9 multiparous females at the end. Crabs were sampled on the 15th (± 2) day of every month beginning in January 2003 and ending April 2004, when eclosion occurred. Upon visual examination, all crabs and their eggs appeared healthy when they were sampled. Females died over the course of the experiment, but there was no obvious reason to eliminate the eggs of these females (collected before death) from the study since the eggs appeared to be healthy and developing normally when collected.
• Monthly sampling was a two-step process in which embryo developmental stages were determined and digital images of eggs were captured. A randomly sampled egg clump was removed from each female with forceps and approximately 20 eggs were immersed in Bouin’s solution for 5 minutes to facilitate observation of the external morphology of the embryos (Moriyasu and Lanteigne, 1998). After embryos reached the eyed stage, they were not placed in Bouin’s solution. Embryo developmental stages were determined using a compound microscope at a total magnification of 50x and developmental stages followed those of Moriyasu and Lanteigne (1998) for snow crabs, Chionoecetes opilio (Fabricius, 1788). Additionally, digital images of 10 fresh eggs from each female were taken with a digital camera attached to a compound microscope at a total magnification of 50x; only fresh eggs were used because preserved eggs swell (Moriyasu and Lanteigne, 1998). Image analysis software (Image Pro Plus Version 4.1 for Windows, Media Cybernetics, Inc. 8484 Georgia Avenue, Suite 200, Silver Spring, Maryland 20910) was used to measure egg area rather than diameter to reduce measurement bias due to the imperfect sphericity of the eggs.
• At the end of April 2004, females were placed in individual containers with flow-through seawater at ambient temperature, and nets (101.5 mm with 350 micron mesh) were placed on the seawater outflow to retain all the larvae. Newly hatched larvae were collected daily from each female as in Stevens and Swiney (2007); the amount of larvae released was determined by measuring volume. Larvae from each net were transferred to a graduated cylinder and seawater was added; after the larvae settled, the volume (mL) of larvae in the cylinder was recorded. For the purposes of analysis in this study, eclosion began when 0.1 mL of larvae were collected and ended when females began stripping their pleopods clean which coincided with the last of the larvae hatching. Mean hatch date was the weighted average of larval output over time calculated by multiplying the daily volume of hatched larvae by day-of-the-year, summing the products over time and dividing by the total volume of larvae released. Incubation period was the number of days between when a female extruded eggs and the last day of hatching.

Data were error checked and outliers removed

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