King crabs are among the largest crabs people eat, and most of their impressive size is in their long legs rather than their body. A crab with a shell about the width of a dinner plate can stretch its legs wider than a person’s arms. A typical red king crab caught in Alaska weighs about 6 pounds, while the giants that make headlines, up to 24 pounds and nearly 5 feet across, are decades old and rare.
Average Size and Weight of a King Crab
Crab size is usually given as the width of the hard shell covering the crab’s back.1Alaska Department of Fish and Game. Red King Crab Species Profile The average male red king crab landed in the Bering Sea weighs about 2.9 kg, or 6.4 pounds.2Wikipedia. Red king crab Red king crabs today rarely grow beyond about 17 cm, or 7 inches, across the shell.3Wikipedia. Red king crab
Most of the edible meat sits in the legs and claws, and a 6-pound crab yields only a few pounds of meat. The frozen legs sold in stores come from crabs of about this size.
Leg span measures from one leg tip to the opposite tip, and it is far larger than shell width.4Wikipedia. Red king crab King crab legs are long and jointed, so a 7-inch shell can carry legs spanning roughly 3 feet or more. Red king crab is the largest commercially fished king crab; golden and blue king crabs are generally smaller.
Fishery rules and buyers measure shell width, not length. Scientists often use length, which runs slightly smaller, and spines on the shell can add about 1 centimeter to a measurement.
Two crabs of the same width can still weigh differently. A crab that has recently shed its shell is often lighter for its size, with watery, less filled-out meat, while one that has gone a long time since its last shed is fuller and heavier. Leg length, claw size, and how well fed the crab was also change the total. So the 6.4-pound average is a middle figure for landed males, and individual crabs scatter above and below it.
In a store, retail king crab legs are sold by the pound, and that weight includes the shell and any ice glaze, so a big share of what you pay for is not meat. Leg sections are often graded by count per pound or by labels like large or jumbo. Those labels differ between sellers and are not an official standard, so compare the actual weight per piece.
How Big the Largest King Crabs Get
The largest recorded male red king crab weighed 24 pounds, about four times an average catch.5Alaska Department of Fish and Game. Red King Crab Species Profile The largest female on record weighed 10.5 pounds.6Alaska Department of Fish and Game. Red King Crab Species Profile The 24-pound male came from Kodiak, Alaska, and was called the world’s largest king crab.7A-Z Animals. Discover the Largest King Crab Ever Caught These record crabs were estimated to be 20 to 30 years old.8Alaska Department of Fish and Game. Red King Crab Species Profile
The record male’s legs spanned nearly 5 feet across.9Alaska Department of Fish and Game. Red King Crab Species Profile Red king crabs can reach a shell width up to 11 inches.10Alaska Department of Fish and Game. Red King Crab Species Profile Some references list a maximum of 28 pounds and a leg span of 5.9 feet, a few inches beyond the official Alaska record.11Wikipedia. Red king crab
Several things keep them rare. Fishing removes many large males before they grow old, and reaching record size takes two to three decades of survival.
Record claims need care. A record needs a measured weight, a known catch location, and a verifier, and many online claims of “giant” crabs have none of these. Weight is the cleaner measure, because leg span depends on how the legs were stretched out and where the tips were measured.
How King Crabs Grow Over Time
Young king crabs that settle onto the seafloor are only about 2 mm across, smaller than a grain of rice.12Elsevier / Journal of Experimental Marine Biology and Ecology. Molting, growth, and energetics of newly-settled blue king crab: Effects of temperature and comparisons with red king crab From there, they grow only when they molt, meaning they shed their hard shell and quickly expand before the new one hardens. A young crab grows about 20% with each early molt.13Elsevier / Journal of Experimental Marine Biology and Ecology. Molting, growth, and energetics of newly-settled blue king crab: Effects of temperature and comparisons with red king crab
In Bristol Bay, red king crabs measure about 9 mm, 23 mm, and 47 mm in shell length at 1, 2, and 3 years.14Fishery Bulletin. Growth of juvenile red king crab (Paralithodes camtschaticus) in Bristol Bay (Alaska) elucidated from field sampling and analysis of trawl-survey data That is roughly a doubling each year early on. In warmer waters near Unalaska, the same ages reach about 16, 38, and 66 mm.15Fishery Bulletin. Growth of juvenile red king crab (Paralithodes camtschaticus) in Bristol Bay (Alaska) elucidated from field sampling and analysis of trawl-survey data Two crabs of the same age can be very different sizes, so age alone does not predict size.
In the eastern Bering Sea, red king crabs take about 7.5 to 9.5 years to reach the size fisheries catch.16Canadian Journal of Fisheries and Aquatic Sciences. Temperature-Dependent Growth of Juvenile Red King Crab (Paralithodes camtschatica) and its Effects on Size-at-Age and Subsequent Recruitment in the Eastern Bering Sea In adult males, each molt can add about 17 mm to shell length.17Fisheries Research. The introduced species red king crab (Paralithodes camtschaticus) in the Barents Sea: II. Growth increments and moulting probability A legal-size crab has therefore shed its shell many times since settling. Young crabs shed several times in their first year, while large adult males may shed only about once a year or less.
Age is hard to know. Shells are discarded, so no growth rings remain, and age is estimated from size and molt history. The 20 to 30 years given for record crabs are estimates.
Why Male King Crabs Are Bigger
Female red king crabs grow about 18% in the molt when they become mature.18Alaska Fishery Research Bulletin. Growth of Female Red King Crabs Paralithodes camtshaticus from Kodiak, Alaska, during Pubertal, Primiparous, and Multiparous Molts After their first eggs, growth drops to about 7% per molt, then near 4% in later years.19Alaska Fishery Research Bulletin. Growth of Female Red King Crabs Paralithodes camtshaticus from Kodiak, Alaska, during Pubertal, Primiparous, and Multiparous Molts Females carry eggs under their abdomen, which redirects energy from growth. A female carries thousands of fertilized eggs for many months until they hatch, and making eggs each year is a steady demand on her body. This is a trade between growth and reproduction, not a sign that females are weaker or unhealthy.
Males do not pay that cost. In golden king crabs, males grow about 10% per molt while egg-carrying females grow about 5%.20Alaska Fishery Research Bulletin. Changes in Chela Heights and Carapace Lengths in Male and Female Golden King Crabs Lithodes aequispinus after Molting in the Laboratory Males end up much larger, which is why the male record is more than twice the female record.
You can tell the sexes apart by the abdominal flap on the underside: males have a narrow triangular one, and females have a broad rounded one for carrying eggs. Most crab sold is male because females must be released.
What Size King Crab Can Be Kept
In Southeast Alaska’s personal-use fishery, only male king crabs at least 7 inches wide may be kept.21Alaska Department of Fish and Game. Regulations – Southeast Alaska Personal Use King Crab Fishery All females and undersized males must be returned to the water unharmed right away.22Alaska Department of Fish and Game. Regulations – Southeast Alaska Personal Use King Crab Fishery Some federal subsistence areas allow males of 6.5 inches or wider.23Legal Information Institute. 36 CFR § 242.28 – Subsistence taking of shellfish Limits can be as low as three crabs per household per year in some areas.24Legal Information Institute. 36 CFR § 242.28 – Subsistence taking of shellfish
For a recreational harvester, the crab must be male and at least as wide as the local minimum. Check the sex first, so you don’t spend time measuring a female you would have to return. Then measure straight across the widest part of the shell, including or excluding spines as the local rules specify. Handle any crab you will release gently and quickly, and never drop or throw it, since injury during release is a known concern in the fishery. Check current local regulations, since emergency orders change seasons.
Bristol Bay’s commercial fishery considered lowering its limit from about 6.5 inches to 6 inches wide.25North American Journal of Fisheries Management. Analysis of Minimum Size Limit for the Red King Crab Fishery in Bristol Bay, Alaska The reason was that handling and releasing smaller crabs was thought to harm the depleted stock.26North American Journal of Fisheries Management. Analysis of Minimum Size Limit for the Red King Crab Fishery in Bristol Bay, Alaska But lowering it would barely raise the share of large spawning males, from about 6% to 8%.27North American Journal of Fisheries Management. Analysis of Minimum Size Limit for the Red King Crab Fishery in Bristol Bay, Alaska
Limits differ because personal-use, subsistence, and commercial rules are set by different agencies for different stocks, so the same crab may be legal in one place and not another. A lower limit lets people keep smaller crabs but can mean more crabs removed before they have had a chance to breed.
What Limits How Big King Crabs Grow
Young red king crabs grow very slowly in near-freezing water, and some kept at 1.5°C never molted.28Journal of Experimental Marine Biology and Ecology. Temperature effects on the molting, growth, and lipid composition of newly-settled red king crab Growth rises quickly in warmer water up to about 8°C, then levels off.29Journal of Experimental Marine Biology and Ecology. Molting, growth, and energetics of newly-settled blue king crab: Effects of temperature and comparisons with red king crab Warming seas cut the time to catchable size from 9.5 to 7.5 years over a decade.30Canadian Journal of Fisheries and Aquatic Sciences. Temperature-Dependent Growth of Juvenile Red King Crab (Paralithodes camtschatica) and its Effects on Size-at-Age and Subsequent Recruitment in the Eastern Bering Sea
Faster growth does not mean a larger maximum size. Very warm water slightly reduced growth per molt, and oxygen limits tighten as water warms.
King crabs also live in cold, deep northern seas, unlike most shore crabs. Cold slows metabolism and extends lifespan, and a long life allows large size despite slow growth.
As a crab’s body grows, its gills cannot keep pace with its oxygen needs.31Journal of Crustacean Biology. The growth, respiration, and reproduction of crustaceans: a synthesis through the Gill-Oxygen Limitation Theory (GOLT) Body mass grows faster than gill surface area, so a bigger crab has relatively less gill to supply each part of its body. Oxygen supply becomes limiting and growth slows in larger crabs.32Journal of Crustacean Biology. The growth, respiration, and reproduction of crustaceans: a synthesis through the Gill-Oxygen Limitation Theory (GOLT) That is one reason sizes level off. King crabs evolved from hermit crab ancestors whose size was capped by available snail shells; dropping the shell let them grow far larger.33PubMed. Evolution of king crabs from hermit crab ancestors