David Knight: Work Out and Work Up: Part II, July 18, 2018

NOAA Teacher at Sea

David Knight

Aboard NOAA Ship Pisces

July 10-23, 2018

Mission: Southeast Fishery-Independent Survey

Geographic Area: Southeastern U.S. coast

Date: July 18, 2018

Weather Data from the Bridge:

Latitude: 29° 45.3′

Longitude: 80° 22.5′

Sea wave height: 1-3 ft

Wind speed: 5 kts

Wind direction: 241

Visibility: 10 nm

Air temperature: 28 °C

Barometric pressure: 1014.9 mb

Sky: Scattered Clouds

Science and Technology Log

Part II. DNA, Gonads, and Diet

DNA Samples.

Certain fish that we collect have samples of their fins collected for DNA testing. For example, if a Spotfin Butterflyfish (Chaetodon ocellatus) is brought up in a trap, a small pair of scissors are used to clip a portion of its anal fin in order to obtain a sample that is then place in a micro-test tube containing a buffer. Back in the on-shore lab, technicians will obtain the DNA, which is then used to determine the genetic make-up of the population in a particular area.

One may assume that the genetic make-up of a population is uniform across the east coast, after all, fish can swim, right? However, that is not necessarily the case. Changes in the frequency of particular alleles create spatial differences in some stocks of fish over a broad area. In other words, there may be slight genetic differences in a population of Gray Triggerfish off of the coast of North Carolina compared to those found in the waters of Florida.

Why does this matter? Currently, the management of most fish occurs over a broad area, often including many states. By understanding the slight differences that may be present in a smaller subset of a population, scientists can create better, more accurate management plans instead of a “one size fits all” model.

Gonads.

As written in an earlier blog, many fish in this region are sequential hermaphrodites and change sex during their life-time, starting off as females, then changing to males.  By taking the gonads of certain species, scientist can determine if the fish is male or female, and taken together with size and age, it is possible to estimate when these fish are transitioning from one sex to another.

By sampling the ovaries of fish, it is possible to estimate the fecundity of the species. Fecundity is the reproductive potential an organism possesses. The number of eggs in an ovary can be estimated and then, taking the age and size data of the specimen, it is possible to predict the potential a population has for growth. Many factors, such as the number of males in a population and the season, can influence the reproductive behaviors of fish, so sampling the gonads provides an additional pieces of data.

Finally, sampling the gonads of fish can help determine the sex ratio in the population. In fish that display sequential hermaphroditism, such as the Black Sea Bass, the number of males in the populations increase with age.

Question: Fisherman will be able to get more money for larger fish, so naturally they will want to “select for” larger fish, potentially decreasing the number of reproductive males in the population. If the number of large, reproductive males in a population decreases, then more females will transition to become male.

What may happen to the average age of sex transition in sequential hermaphrodites?

Diet.

A select few species have their stomach contents sampled. If we know what a particular species is eating, then we are able to understand the trophic interactions within the ecosystem much better. An ecosystem-based management plan will look at the interactions taking place between the many prey and predator species, whom are often competing for the same resources.  Because the diverse species in an ecosystem are inextricably linked, an increase in one species is likely to affect the other. If one species is over-fished or not reproducing at its potential, this may create a ripple effect throughout the ecosystem.

Personal Log

The food on board the NOAA Ship Pisces has been great. The Stewards, Rey and Dana, have kept us well fed with a variety of great meals. We’ve had everything from hot dogs and hamburgers to bacon wrapped filet mignon and shrimp, and a crew favorite, Taco Tuesday! Meal time is very important because not only is the crew refueling for work, but it affords them a chance to sit down, talk, and to catch up on Chip and Joanna Gaines’ newest “Fixer Upper” on the TV that runs continuously. The first day on board, Operations Officer, Lieutenant Jamie Park, told me that any NOAA ship runs on two very important things: 1) diesel fuel, and 2) COFFEE.  The galley is open 24-7 with snacks and drinks always available since crew members are working in shifts, with some getting off at midnight or 4 a.m.. And…., I recently found the freezer that contains Klondike Bars, popsicles, ice cream, and Hot Pockets.

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Did You Know?

The Red Snapper (Lutjanus campechanus) gets its name from its enlarged canine teeth. According to the 2016 stock assessment of South Atlantic red snapper, the stock is overfished and subject to overfishing, but is rebuilding.  Management plans in the South Atlantic and Gulf of Mexico place annual catch limits on both commercial and recreational fisherman to decrease the pressure on the fish, as well as minimum size restrictions to protect young and juvenile snapper. Red Snapper can live over 50 years and are of reproductive age as early as two.

Reference:

NOAA Fisheries. https://www.fisheries.noaa.gov/species/red-snapper