Fiddler on the… Net?

Sharks, Skates, and Rays, collectively known a Chondrichthyans, are certainly in class of their own. As the predominant members of the class composed of cartilaginous fish (alongside the chimaeras), they are the stuff of nightmares and wonder, as evidenced by the famous cinematic classic: “Jaws”. But what if we could cause them just as much fear as they often cause us? What would that do to them?

As fishing pressures increase, more and more are caught in nets as by-catch, or accidentally caught organisms that fishermen don’t actively target (Smoker, 2000). For a fish, this can be scary, and cause a lot of stress which as we all know is bad for you in more ways than one. But what really is stress?

Stress is caused by an external stimulus, say a trawling net wrapping around you out of nowhere 100ft below the ocean, and your endocrine system reacting to it. Your endocrine system is the system of hormones your body utilizes to keep itself alive and functioning normally through changes. When the brain picks up on certain stimuli, it forces special organs in the body known as glands to secrete hormones that have effects on other organs. Effects can range from causing organs to secrete their own hormones in a process known as a hormone cascade, to causing the cells of a organ to increase metabolic or other specific functions (Randall et al., 2002). So when you eat a pie or are confronted by a bear (or a member of the opposite sex asking you to prom, often just as scary), your endocrine system causes a response to that.

The latter is the case with stress; when the brain is informed of a negative stimulus (like the aforementioned potential cutie asking you to dance out of nowhere) it sends signals to the hypothalamus (a gland in the center of the brain) to begin secreting hormones that affect the pituitary (another gland in the brain), which secretes hormones that affect the adrenal cortex (located right above your kidneys) that then secrete Cortisol, the stress hormone. This hormone then causes other organs, like the stomach, lungs, liver, adipose tissue (fat cells), immune system, and heart to go into overdrive and empower you to run as fast as you can from that potentially dangerous (or extremely awkward) situation (Randall et al., 2002).

Another aspect of running away from prom dates is the physical one: movement is hard and consumes energy. But all organisms have something called energy budgets; just as you have to draw from a bank account to buy things you need, so do animals, but with energy. The total energy available in an organism divided into the number of actions an animal takes to be successful is the energy budget, and going over budget in one category means detracting from another (Randall et al., 2002).

So what does this have to do with Chondrichthyans? They don’t have prom dates or banks, right? Sure, but they do have an endocrine system and an energy budget, and presumably an innate fear of trawl nets. One recently released study showed that pregnant Southern Fiddler Rays (Trygonorrhina dumerilii) subjected to simulated trawl net capture for 30 minutes in a lab during the pregnancy had pups that were on average 5-3mm shorter and 20-32g smaller than mothers that weren’t subjected to capture-like conditions. Further, the immune response in the mothers rose drastically for a short period after capture-simulation, and stayed higher for the duration of the pregnancy (Guida et al., 2017). This shows that when they were stressed the rays offset their delicate energy budgets for fetal development by consuming too much energy trying to escape the nets, and weren’t as able to give their pups the time they needed to develop. This could have ecological effects for the species as fishing pressures continue to be a threat (Guida et al., 2017; Smoker, 2000).

It’s not all bad news for the rays though. With the continuing research of agencies like the National Oceanic and Atmospheric Administration or NOAA, we’re learning more about where these Chondrichthyans have their pups, and helping fisherman to avoid areas where they could potentially create extra by-catch of these majestic creatures (Smoker, 2000). Remember to always do your part by eating sustainable seafood!

For more information on eating sustainably, check out the National Resources Defense Council’s “Smart Seafood Buying Guide” at https://www.nrdc.org/stories/smart-seafood-buying-guide

Not only do they have some great resources on sustainable seafood, but excellent tips on how to stay healthy eating it! Check it out, and remember: your flappy ray-friends thank you.

 

References:

Guida L, Awruch C, Walker TI, Reina RD (2017) Prenatal stress from trawl capture affects mothers and neonates: a case study using the southern fiddler ray (Trygonorrhina dumerilii). Scientific Reports 7, 46300. doi: 10.1038/srep46300.

Smoker J (2000) Tools For Reducing Inadvertant Take and Bycatch Wastage of Skates and Sharks in Alaskan Hook-and-Line Fisheries. NOAA Fisheries, retrieved 04/13/2017 from: http://www.nmfs.noaa.gov/mb/sk/saltonstallken/skate_final.htm

Randall JD, Burggren W, French K (2002) Eckert Animal Physiology. W. H. Freeman and Company, New York, pp 215–275.

Photo Credits:

Featured Photo: Southern Fiddler ray. Source:Anthony Pearson. Some Rights Reserved. https://www.flickr.com/photos/burna10/5062032282

In text Photo: A Southern Fiddler Ray (Trygonorrhina dumerilii) at the Melbourne Zoo. Source: SuperJew. Creative Commons Attribution-share Alike 4.o International. https://commons.wikimedia.org/wiki/File:Southern_fiddler_ray_02.jpg