Sexing the Catch

NOAA Teacher at Sea: Bruce Taterka

NOAA Ship: Oregon II

Mission: SEAMAP Summer Groundfish Survey

Geographical Area of Cruise: Gulf of Mexico

Date: Thursday, July 8, 2010

Weather Data from the Bridge

Time: 1630 (4:30 pm)

Position: Latitude = 28.20.93 N; Longitude = 095.58.98 W

Present Weather: Could cover 100%

Visibility: 4-6 nautical miles

Wind Speed: 18 knots

Wave Height: 6-8 feet

Sea Water Temp: 28.9 C

Air Temperature: Dry bulb = 27.2 C; Wet bulb = 25.3 C

Barometric Pressure: 1011.56 mb

Science and Technology Log

As you can tell from our previous blogs, we spend a lot of our time on the Oregon II counting, measuring and weighing our catch and loading the data into FSCS. These data are critical to NOAA and the states in managing fish stocks and the Gulf ecosystem. In addition to knowing population size, weights, and lengths of individuals it’s also important to know the sex of the organisms. Information on the male:female ratio helps NOAA and the states assess the ability of the population to reproduce, and to establish sustainable catch levels for commercial fishing.

But how do you determine the sex of marine organisms? For most fish and invertebrates you can only tell the sex by internal anatomy, which almost always requires cutting the animal open. This is time consuming and not always practical when we have a large catch to process and other tasks take priority, such as preparing samples to be analyzed for contamination from the oil spill which is our top priority right now.

For some organisms, however, sex can be determined externally. One of the things we’ve learned in the past week is how to determine the sex of shrimp, flatfish, crabs, sharks, skates and rays. Here’s how:

Shrimp: the males have a pair of claspers (called petasma) on their first set of legs. The petasma are absent in females. The males use the petasma during mating to grasp the female and transfer the sperm sac.

Male - arrows show the petasma


Female - petasma are absent

Crabs: On most crab species females have wide plates curving around the rear of the abdomen, while males have a long narrow plate or plates. On females, the eggs develop under the curved plate.

Male


Female

Female with eggs

Flatfish: When you hold a flatfish up to the light you can see through it, which enables you to do an internal examination without cutting it open. On female flatfish, the gonad extends in a dark red, curved wedge which is absent in the male.

Female showing long curved gonad


Male - long gonad is absent

Sharks, skates and rays. Males have external claspers that they use in mating, while in females the cloaca is smooth and claspers are absent.

Male Angel shark - arrows point to claspers


Female Angel shark - claspers are absent

Personal Log

A tropical depression moved through the Gulf yesterday evening, making it too rough and windy to fish. So instead of counting, measuring and loading data into FSCS, my watchmates and I cleaned the lab, secured our gear, and headed up to the lounge to watch Shutter Island on the large-screen TV. Last night my bunk was like a roller coaster, tossing me from side-to-side and head-to-toe as the ship rolled and pitched in the big swells. Today has been a slow day for the scientists on board, waiting for the storm to pass so we can start trawling again, while the crew and officers remain as busy as ever.