Descending Devices Shine Under Pressure
Descending Devices Shine Under Pressure
Under pressure. Normally, those two words would be used when talking about work stress or looming deadlines, but for fish living in deeper waters, it's just a way of life. As the depth of the ocean increases, so does the pressure. Anyone who is SCUBA certified or has taken classes knows that for every 33 feet you descend in the water, the pressure increases by 1 atmospheric unit or 14.69 psi. If you’re learning about this for the first time, this probably just seems like a bunch of numbers and conversions, so let me give you an example of it in action.
If you take an empty plastic water bottle filled with air and swim with it from the surface, down to 33 feet deep, you will notice the air being compressed as the sides of the bottle are pushed in. The deeper it goes, the more pressure it is under, and the smaller it shrinks as the initial volume of air is compressed. When you take the air filled water bottle and swim back to the surface, the air will expand as the pressure decreases.
Want to see another cool example of pressure at depth? The deep sea exploration team from Nautilus Ocean Exploration Trust, has done some cool experiments with styrofoam cups like the one below.
Okay, back to pressure and air pockets. The same thing that happened to the air filled bottle will happen to pockets of air they decrease or increase through the water column. Human lungs are a great example of air filled cavities, but fish have something similar.
Fish are equipped with gas filled organs called swim bladders which they inflate and deflate to move up and down through the water column depths. However, if a fish is caught at depth and is rapidly brought up through the water column without allowing its body to equalize to the change in water pressure, its swim bladder can expand significantly causing features to be distorted, internal body parts to be displaced and distended. This sudden change in pressure is called barotrauma and anglers who frequently catch rockfish have likely seen this first hand. Luckily this isn’t something that happens to all rockfish but is more dependent on where they live and how they are categorized.
There are 4 different categories that Rockfish fall under, each of which is categorized by depth. There are shallow nearshore, deeper nearshore, shelf, and slope dwelling rockfish.
Nearshore rockfish live from the rocky intertidal zone out to the deeper water of 20 feet or more. The deeper nearshore species such as the Black, Blue, Brown, and Calico Rockfish can be found from the edge of the intertidal zone down to 1,000 feet deep! As the name Shelf rockfish suggests, these species like the Freckled, Cowcod, Redstriped, Yelloweye, and Vermilion rockfish spend their lives in the deeper waters along the continental shelf. And the Slope dwelling species like the Rougheye, Blackgill and Splitnose are the deepest of all, and are not usually the targets of anglers.
No matter the speed they are reeled in their swim bladders are unable to handle the significant reduction in pressure. As a result they expand, causing eyes to budge, and displacing stomachs, which are expelled through the rock fish's mouths.
When they get to the surface it is easy to understand how they can be written off as dead or near dead, however a study has been done by researchers at Cal State Long Beach that has a different view.
According to the study, the visual signs of the barotrauma a fish shows is not a reliable prognostic of if it will live. In fact, the largest predictor of survival is the amount of time the fish spends at the surface. 83% of the Southern California Rockfish caught between 217 and 350 feet deep, survived, when returned to depth within 2 minutes of being on the surface. The longer a fish was at the surface, the higher the rates of mortality were.
Regulations
You might not be surprised to learn that the California Department of Fish and Wildlife created a management plan for nearshore fisheries. This Fishery Management Plan is a part of the Marine Life Management Act which aims to prevent overfishing, rebuild depressed stocks, ensure conservation, and promote habitat protection and restoration.
As a part of this they have done studies to determine which species are ones of concern and came up with the following 19 species- Black rockfish, Black-and-yellow rockfish, Blue rockfish, Brown rockfish, Cabezon, Calico rockfish, California scorpionfish, California sheephead, China rockfish, Copper rockfish, Gopher rockfish, Grass rockfish, Kelp greenling, Kelp rockfish, Monkeyface prickleback, Olive rockfish, Quillback rockfish, Rock greenling, and the Treefish.
A part of the protection efforts, is a limited 3 month season from May-August for many of the nearshore species. The Slope and Shelf species have a slightly longer, yet somewhat restricted open season. The rules and regulations can change each year, but you can find the most current ones here: https://wildlife.ca.gov/Fishing/Ocean/Regulations/Groundfish-Summary
Another area they are making conservation efforts is in encouraging people to use descending devices.
As previously stated, the speed at which a rockfish is dropped back to its original depth can vastly improve its chances of survival, but this is no easy task with a fish that is bloated and with air.
There are numerous ways to reduce a fish’s barotrauma and get it back to depth to keep it from becoming prey for birds and sea lions. A simple method is to place the fish underneath a weighted milk crate and lower it back down. I have met seasoned anglers who are accurately able to vent fish - the process of using a needle puncture and release the air- but honestly this method does more harm than good especially if you are untrained. Another simple method is to use one of the many non invasive descending devices such as a SeaQualizer. These are hooked on to the fish’s mouth and allow them to sink and their swim ladder to decompress.
This step of using a descending device might seem like some added work, but it is worth it. Yelloweye Rockfish along with other limited species can take years to regrow their populations so simple steps like using these devices to safely release these rockfish can help to take some of the pressure off of the populations, helping them to make a faster recovery.