Live Crab Handling

 WHERE THE AMMONIA COMES FROM

DECOMPOSING MORTALITIES

THE METABOLIC PROCESS (OFF THE GILLS)

SILT/MUD

FECES (POOP)

REGURGITATED FOOD

At times it might seem that there is a conspiracy of ammonia producing sources intent on killing your product down to the last crab. However, once the potential sources are identified the conspiracy seems less threatening. The main sources are, in order of potential severity of concentration: 

DECOMPOSING MORTALITIES :

The main thing to remember here is that from virtually the moment a crab dies it starts to decompose and just gets worse from then on. How fast things go to hell depends mainly on the temperature of the water . The colder the water the slower the decomposition. I don't have any hard science to back this up but a rule of thumb I use is that one 2 lb. mortality left in a system for 24 Hrs.can equal the metabolic ammonia output of 50 Lbs.of live crab.

ACTION TO TAKE: PICK THROUGH AND REMOVE DEAD OR WEAK CRAB AT LEAST ONCE A DAY.

2)  THE METABOLIC PROCESS (OFF THE GILLS):

In a clean, well maintained system this is the main source of ammonia and is easily handled by an adequate bio-filtration system. As the crab respires ammonia is released from the gills as a natural part of the metabolic process. The higher the temperature, the higher the metabolic rate, the more ammonia is produced per pound of product.

ACTION TO TAKE: REDUCE THE SYSTEM TEMPERATURE TO 38 DEGREES F. FOR BULK HOLDING AND 40 DEGREES F AND UP TO 50 DEGREES F. FOR DISPLAY TANKS. KEEP A WELL MAINTAINED BIO FILTER OF SUFFICIENT CAPACITY RELATIVE TO THE POUNDS YOU ARE TRYING TO HOLD. WATCH YOUR DISOLVED OXYGEN.

3)  SILT/MUD:

Most first receivers know about what I call 'storm crab'(those crab that have been in the pots through a storm and, as a result, are extremely dirty and, depending on the length and severity of the storm, possibly weak). Storm crab are at the extreme end of the spectrum of the dirty crab syndrome. Much of the silt or mud brought in with the crab is of an organic nature rather than of a silicon nature like sand would be. It decomposes so rapidly that when I tried to have it analyzed one time the lab trying to measure the particles microscopically gave up because it was dissolving as they measured. A certain part of the stuff is, however, stable enough to collect in your bio-filter causing clogging, channeling and therefore reducing the effectiveness of the bio-bed resulting in increased ammonia due to ineffectual bio-filtration.

ACTION TO TAKE: FIRST RECEIVERS: TRY TO SEASON THE CRAB AND SORT ONCE BEFORE SHIPPING. SUBSEQUENT RECEIVERS:RINSE THE INCOMING PRODUCT BEFORE PUTTING IN YOUR TANK EVEN IF YOU HAVE TO USE FRESH WATER FROM A GARDEN HOSE. DO NOT SUBMERGE THE CRAB IN FRESH WATER.

4)  FECES (POOP):

Not many options here is there? The good news is that for other than first receivers there's not much left by the time you get them. It's not a significant source of ammonia anyway.

ACTION TO TAKE: FEED 'EM CHEESE (just kidding)

5)  REGURGITATED FOOD:

Unless you are a first-receiver you probably don't have to worry about this unless it is very early in the season and your supplier is "short stopping" your crab ( just giving them a drink before shipping to you) or direct shipping from the boat. First receivers may have to deal with a fairly significant amount of bait, especially squid, when the gear is getting turned quickly at the beginning of the season.

ACTION TO TAKE: WHEN YOU NOTICE SOMETHING NASTY HANGING OUT OF A CRABS MOUTH OR FLOATING AROUND IN THE WATER, GET RID OF IT.

 MAKING BABIES AND GETTING SOFT

After the long wait you have all endured I hope this segment is not anticlimactic (pun intended).

Most of you have, by now, gotten a taste of the annual bane of Dungeness crab--Soft shell. Unlike blue crab, soft shell Dungeness is somewhat less than desirable. Though the meat is, in my opinion, the tastiest as the crab is filling out after the molt, there isn't very much of it and, worst-of-all, the crab are so weak they ship very poorly. It is all part of the life cycle, however, so it may help to understand some of what is known about why, when and how the cycle happens.

CLUTCHING

Sometime during the spring certain hormones are triggered in the crab signaling the beginning of a reproductive orgy that usually lasts abound 2 or 3 weeks. Males seek out females after being scrupulously segregationists most of the last 12 months. The male wraps his legs around the female, "clutching" her so that he can fertilize the eggs she is carrying. As far as I can tell both genders are fairly indiscriminate about mates. I have regularly seen large males clutching "adolescent" females and small males clutching barren females. For the most part it seems the larger males win out, however, so the integrity of natural selection is maintained in the crab world. Probably the most significant effect you as a crab shipper will see during the clutch is a drop in production. Apparently males think of little else but sex during this period of time. After not eating for a few weeks, however, they can be voracious when the clutch is over. That voraciousness manifests as the traditional "Spring Bite".

(To Be Continued)

WHY CRABS DIE

LACK OF OXYGEN

BLEEDING

MECHANICAL SHOCK

THERMAL SHOCK

DEHYDRATION

AMMONIA POISONING

1) LACK OF OXYGEN 

While in water crabs are able to use about 20% of the oxygen available. That is efficient enough to use up all of the oxygen faster than you would like, were a pump or aerator to fail. In open/flow-through systems of sufficient flow the naturally occurring dissolved oxygen (D.O.) is sufficient to maintain good blood chemistry. In closed/ recirculating systems that are usually operating at lower temperatures it is easier to achieve, through mechanical means, levels of D.O. that are superior to that occurring in nature but if an oxygenation component fails that superiority is relatively quickly used up.

Out of water, the crabs gills are no longer held buoyant. In that situation the gills collapse dramatically reducing their ability to assimilate oxygen from the air. Now add to that, debris in the form of silt or other suspended particulates deposited on the already reduced gill surface further impairing oxygen uptake. Remember the crab is already literally out of its element during shipping. Putting all of these obstacles together might be something like you or I running the Boston Marathon with a bag over our heads. Not a pretty picture in any ones book.

ACTION TO TAKE: IN AN OPEN/FLOW-THROUGH SYSTEM THE BEST WAY TO INCREASE D.O. IS TO DECREASE THE BIO-LOAD OR INCREASE THE FLOW RATE THROUGH THE TANKS. IN A CLOSED SYSTEM DECREASE BIO-LOAD OR INCREASE CASCADING OR OTHER AGITATION AND MIXING SUCH AS WITH VENTURIES OR SKIMMERS WHICH INCORPORATE VENTURIES. IN ALL TYPES OF SYSTEMS ALLOW FOR MECHANICAL FILTRATION AND APPROPRIATE SOAK TIME PRIOR TO SHIPPING TO ALLOW FOR DEBRIS TO CLEAR FROM GILLS.

2)  BLEEDING

Crabs have blood and, yes, they can bleed to death. Crabs are so vulnerable to bleeding that they have evolved a fascinating ability. If a crab is injured in a fight with another crab and is bleeding through a puncture in a leg and the injury is life threatening they can actually voluntarily "throw" the injured leg. There is a muscle attached to a valve sort of apparatus on the joint of each leg closest to the carapace. By contracting that muscle the leg is severed at the joint losing the leg and saving the life. If a crab is in a weakened state or is otherwise stressed it may be incapable of accomplishing this life saving feat and die from loss of blood. That is why proper and gentle handling when loading tanks is so important. Crab handled by fishermen and first receivers are usually handling "hot" crab in warmer (40 degrees and above) water making the crabs especially susceptible to puncture wounds inflicted by other crabs. Crabs are also very territorial, so when they are crowded in a tank they tend to fight. That is when puncture wounds can occur, and cause bleeding or even death. Another puncture danger is from rough handling, like tossing one on top of the other instead of setting the crab in the water. The points on the sides of the shell are capable of actually puncturing the crab it lands on.

ACTION TO TAKE: FIRST RECEIVERS ALWAYS TRANSFER WATER TO WATER OR AT LEAST DRY TO WATER. NEVER TRANSFER WET TO DRY OR DRY TO DRY. A BANDING PROGRAM WOULD BE A GOOD IDEA TOO. WHEN LOADING TANKS TRY TO DISTRIBUTE THE CRAB AROUND THE TANK SO THAT YOU ARE NOT PUTTING CRAB ON TOP OF CRAB ON TOP OF CRAB ETC.. THAT CAN REALLY PISS THEM OFF AND WHEN CRAB ARE PISSED OF SOME ONE IS GOING TO BLEED.

3)  MECHANICAL SHOCK

To my knowledge no definitive research on mechanical shock damage has ever been done. It remains just one of the many areas needing to be studied to further our understanding of why crabs die. We do know, experientially, that Dungeness are far more susceptible to mechanical shock than are East Coast Lobster. Internally Dungeness crab have, proportionally, much larger sinus areas than that of the lobster and I believe that is the principle reason for this lethal vulnerability to mechanical shock.

It has been observed by myself and others that a box of crab packed for air shipping and dropped from waist height can result in excess of 50% mortalities within a few hours. It appears that those large sinuses leave so much space for movement that, when dropped, the internal organs move to such a degree that connective tissue is irreparably damaged. Fishermen have known of this fragile nature for along time. Those in the know have constructed slides or shoots to soften the landing in situations where crabs must be transferred with potentially damaging vertical drops such as from the deck into a hold.

Even small mechanical shocks can have damaging affects. The simple transfer from one container to another and even into water can have serious consequences. The impact of "tossing" crab into a tank can result in mortalities. If not while in your possession then in your customers. Years ago I observed an extreme example of what I'm talking about.

It was in the very early days of live shipping to the east coast markets. I had begun shipping to a new customer who had never bought Dungeness before and who constantly reported excessive next day (after arrival at his facility) mortalities. Even though he seemed to be a nice enough fellow I started to suspect him to be one of those credit junkies who are only satisfied if they are getting their credit fix. It happened that I had an opportunity to fly to his area for a trade show so we timed a shipment to coincide with my arrival. Before the shipment arrived we ran some tests on his system water to rule out problems in that area. Everything looked fine and the crab leftover from the previous shipment looked healthy enough though they were the survivors of a 55% next day mortality. When the shipment arrived at his facility we inspected the outer boxes for evidence of dropping. It all looked good so, scratching my head, I followed him toward his office while the workers prepared to load the crab into the tanks. As we were leaving his warehouse I heard a thump,splash,thump,splash, sound. I turned and watched in horror as the workers were tossing the crab from floor height into the top tank of a triple-stack system using the wall behind as a "backboard" to bounce the crab off! Needless to say we had found the cause of his next day mortality problem.

Later on that same trip I visited a number of large lobster holding facilities and observed similar if not identical practices being used in handling lobster from crate to tank and tank to tank. Obviously I had my work cut out for me as far as education of the new east coast markets were concerned.

ACTION TO TAKE: HANDLE DUNGENESS LIKE YOU ARE DOING YOUR MOTHERS HEIRLOOM DISHES AFTER THANKSGIVING DINNER. SET THE CRAB INTO WATER NEVER THROW THEM OR DROP THEM. WHEN BOXED NEVER DROP THE BOX, SET IT DOWN. CONSPICUOUSLY MARK SHIPPING CONTAINERS AS "FRAGILE" AND SPEND SOME TIME EDUCATING YOUR SHIPPERS TO THE FRAGILE NATURE OF YOUR SHIPMENTS.

4)  THERMAL SHOCK

Have you ever been outside in cold weather then come in and put your hands in what you know to be luke warm water but it feels like it is boiling hot? I liken the effect of thermal shock of crabs, to that. Also, like us, crabs can tolerate lower temperature changes far more readily than higher temperature changes. Like so many areas of shellfish handling there is less known quantitatively than empirically. My own observations have been costly. I think the first time I learned about thermal shock was also the first time I unloaded a tank boat using ice.

We were unloading at our dock where we had a flow through system that pumped raw bay water which was, on that day around 54 degrees F. Knowing of the benefits of chilling to reduce stress during unloading (see  Direct shipping...If you must) we iced the hold down really well getting the core Temp. of the crab down to about 30 degrees F. As soon as a container was full we would weigh it and race it over to the flow through system to get the crab back in water. Bad idea! That 24 degree temperature rise was enough to be, relatively, like cooking the crab. Unfortunately I didn't catch and appreciate that fact until after unloading several thousand pounds. The part I didn't understand then and still don't was the seemingly randomness of the effect...some crab died and others didn't. About 15-20% of the crab throughout the containers died leaving their neighbors apparently unscathed. Your experience may vary as to percentages and temperature ranges but the effect will be similar. We had to learn to let the crab sit and warm slowly for awhile and the slowly introduce the warmer water to the containers when the temperature difference was more than 12 or 15 degrees. I have, however,observed apparent thermal shock mortalities in situations of only a 7 degree temperature rise. Please understand that when I refer to temperature rises relating to thermal shock mortalities I mean abrupt or sudden changes. Dungeness are especially adaptable to slow changes in environmental conditions, thank goodness!

ACTION TO TAKE: ALWAYS BE CONSCIOUS OF DUNGENESS' VULNERABILITY TO THERMAL SHOCK, BOTH UPWARD AND DOWNWARD. WHEN MOVING FROM ONE ENVIRONMENT TO ANOTHER, BE IT SHIPPING CONTAINER TO WATER OR OPEN SYSTEM TO CLOSED REMEMBER THAT ABRUPT CHANGES CAN BE DEADLY. ALLOW FOR TIME TO ACCLIMATE IF POSSIBLE. AIRSHIP RECEIVERS MAY NEED TO OPEN THE BOXES AND LET THEM "BREATH" FOR A BIT BEFORE RETANKING THE CRAB. IF IN DOUBT CHECKING THE CORE TEMPERATURE OF A CRAB, EVEN IF YOU HAVE TO SACRIFICE A LIVE ONE MAY BE THE CHEAPEST ROUTE.

5)  DEHYDRATION

Fortunately dehydration is a fairly simple obstacle to overcome. Unlike the next section to be discussed (Ammonia poisoning) dehydration is a no-brainer. When holding in open or closed systems the fact that they are in water pretty much takes care of things regarding dehydration. During out of water shipping by truck things get a little more critical but still easily manageable. The source of greatest potential for dehydration mortalities is the open or flatbed truck. Uncovered crab going down the road, open to the wind, on a warm fall afternoon are good for about an hour and a half before the top layer are pretty much toast. The next most dangerous scenario is the open container in the refrigerated truck. Here it is like the previous scenario except you are driving on a cold crisp December morning. Two scenarios with the same net effect, namely the wind sucks all of the moisture out of the carapace of the crab, dehydrating the already overworked gills, making them unable to access enough oxygen to maintain life. The result...death. The crab least susceptible to dehydration mortalities are those shipped by air. The reason is that in order to even get close to a plane the crab have to be in a fairly well sealed container which by it's very nature traps the existing moisture in the container and, therefore, in the crabs gills. To further insure a high degree of humidity, especially for the top layer of crab who don't get benefit of the drainage from anyone above them, many shippers will use the infamous wet newspaper. So, unless you let the crab dehydrate before they are packed for shipping there is really little concern for dehydration during air shipping.

ACTION TO TAKE: ALWAYS KEEP THE CRABS PROTECTED FROM WIND OR REFRIGERATION FANS. WET GUNNY SACKS, WET NEWSPAPERS, EVEN A THIN LAYER OF ICE (IN A PINCH) WILL HELP IF THERE IS ANY CHANCE OF WIND REACHING THE CRABS. AIR SHIPPERS CONSIDER USING SOME MEANS OF MAINTAINING HUMIDITY IF THE OUT OF WATER TIME MIGHT EXCEED 15 HRS. NOTE: IF YOU USE GUNNY SACKS BE SURE TO SOAK THEM FOR AT LEAST A DAY AND RINSE THEM AT LEAST ONCE BEFORE PUTTING THEM ON THE CRABS. NOT ONLY WILL THE SACK THEN HOLD MORE MOISTURE BUT SOME SACKS CONTAIN WATER REPELLENTS THAT DO NASTY THINGS TO THE CRAB.

6) AMMONIA POISONING

For the purposes of this discussion, unless otherwise specified, ammonia (NH3), Nitrite (NO2) and Nitrate (NO3) are all referred to as ammonia. A more complete description of the nitrification cycle will be covered in the section regarding Closed Systems under "Bio-Filters".

For those of you with flow through systems ammonia poisoning is not a big worry. If your water flow is slow enough to allow ammonia to accumulate your crabs will die from oxygen deprivation long before the ammonia can poison them. For the rest of us with closed recirculating systems the specter of ammonia looms large.

The ideal level of ammonia (NH3) is, of course, "0". World peace would be nice too. In the real world of over-loaded live systems and overpopulated countries we usually settle for peaks of 2 or 3 ppm in our live systems and the occasional ethnic cleansing in our world. In a well designed and managed system those ammonia peaks should last relatively short periods of time (12 hours or less) brought under control by the bio-filter revving-up or the bio-load decreasing due to your nimble sales efforts. But let's say your bio-filter is less than adequate (read "sucks") and the market is poor (read "sucks" again). What is it that actually happens that causes the crabs to die from ammonia poisoning.

The way crabs get rid of the ammonia which is part of the by-product of metabolizing food, is through a process of diffusion across the gills. In order for diffusion to occur there needs to be a gradient or difference in the concentration of the substance, in this case ammonia, across the surface of the gills which allows for the higher concentration in the crab to go to the lower concentration in the water. All is well until the level of ammonia in the water builds higher than that in the crab. Suddenly the ammonia cannot escape the blood stream. Blood gases balances begin to go awry, the ph of the blood sky rockets...well imagine yourself drinking a pot or two of coffee. Now imagine not being able to go to the bathroom...ever. Things would get pretty uncomfortable for you after awhile. Now imagine being in the same situation with a paper bag tied over your head (your gills unable to efficiently extract oxygen from the water). You could breath a little, but not for long. Same kind of thing with the crabs. (In reality ammonia poisoning is usually a slow and cunning crab killer. If your ammonia levels are high enough to kill crabs quickly you need to go back and re-read "Where the Ammonia Comes From". Apparently you missed something.) One of the quaint little mechanisms crab have developed to try to survive inconveniences such as ammonia poisoning is something you are incapable of, thank goodness, which is to "throw" legs. Any stress can initiate this reaction and our topic is no exception. What the crab is apparently trying to do by throwing legs is to eliminate "extraneous or superfluous" body parts so that more metabolic resources can be spent on increasing the chances that vital organs will survive to grow more legs. Extreme measures but it works if the stress is short lived, i.e. you do a water change or sell a lot of crabs.

The key to avoiding catastrophic ammonia related mortalities is frequent and regular testing. Those of you who use my consulting services have heard this from me before ad naseum, "How will you know what went wrong if you didn't test enough to know what your water quality was before the problem". I have tried to make it easier to track test results by providing a test form in "Forms and Tables".

ACTION TO TAKE: THE FASTEST MOST DEPENDABLE WAY TO REDUCE AMMONIA, NITRITE AND NITRATE IS TO DO A WATER CHANGE, PART OR ALL. SHORT OF THAT THE BIO-LOAD MUST BE REDUCED (GET RID OF CRABS) BUT EVEN THEN IT MAY TAKE TIME FOR YOUR BIO-FILTER TO CATCH UP. IF YOU HAVE TO CONTINUE OPERATING WITH HIGH AMMONIA, MOVE THE CRAB THROUGH AS QUICKLY AS POSSIBLE SINCE SHORT TERM EXPOSURE IS LESS DAMAGING THAN LONG TERM. PREVENTION IS THE BEST MEDICINE. DESIGN RIGHT, MANAGE RIGHT.

FISHIN' BOATS:

The smallest boat I've ever bought crab from was a ten foot long zodiac.

One day we were hanging out waiting for boats to start delivering when a tiny zodiac came around the corner doing about 25 mph. He slowed down as he approached the dock and I thought nothing more about it until I heard a voice from below yell, "do you want these crabs or not! " I looked over the side and sure enough he had about 50 Lbs. of crab that he had caught in rings. He became a regular at Aquatic Resources.

The biggest boat I ever bought crab from was probably around 80 feet. Some Dungeness boats in Alaska are over 100 feet.

Most of the smaller boats are of wood construction, the bigger ones are mostly of steel. I don't ever remember seeing a ferro-cement crabber probably because the abuse would be too much. Occasionally you will see a fiberglass or an aluminum hull.

 BAIT:

If Calamari connoisseurs new how much squid is "wasted" in bait containers by crab fishermen they would be aghast. Squid is a plentiful, relatively inexpensive, bait that works fairly well in most areas and seasons and is a natural feed source for Dungeness. Also used is: clam, mackerel, bonita, rock cod of every persuasion, and some years when they are plentiful and the local supermarkets have over estimated the thanksgiving demand...turkeys.

Did You Know?

The optimum ph level for live Dungeness is 7.5 to 8.5.

Only Sodium Bicarbonate is both safe and practical as a way to increase the alkalinity level of your system water.

One cubic foot of water contains 7.48 gallons.

If forced to continue to move for about 15 minutes (I'm told someone actually chased a crab around with a stick as part of a research project) a Dungeness crab will die of exhaustion.

Most bio-filters can actually produce ammonia.

There are bio-filter systems which are virtually impossible to clog.

Using a "clogless" bio-filter can reduce the footprint required by your existing bio-filter by 80%.

The Ex-Vessel price of Dungeness Crab can increase as much as $.50 in one day.

Because of recent innovations and with the right modifications to your existing system you can throw away your tank bottom bio-filter and hold more crab in your tank.

If you have a protein skimmer/foam fractionator and still have foamy, cloudy water your ph may be too low.

Having the right foam fractionator (protein skimmer) can almost totally eliminate foam from your system and can: reduce ammonia, increase oxygen and virtually eliminate the need for mechanical filtration (given the correct system design).