English: A diagram showing a newborn, an average-sized adult, and large adult basking shark (Cetorhinus maximus).

• The maturity and growth of the basking shark are poorly understood.^[1][2]

• Newborn basking sharks are around 1.5 to 1.7 meters (4.9 to 5.6 ft) in length (1.5 m shown in the diagram above).^[1][3]

• The size at maturity for each sex is unclear and varies from source to source. For male basking sharks, stated maturity sizes range from between 4.6 to 7.5 meters (15 to 25 ft) in length.^[4][2][3][5] The size at sexual maturity for female basking sharks in published sources is usually larger than males ranging from 7.7 to 9.8 meters (25 to 32 ft) in length.^[1][2][3][4] Matthews (1950) and Natanson et al. (2008) considered basking sharks over ~7 metres (23 ft) to be mature.^[6][7] Wood (1982) suggested the average adult length of 7.9 metres (26 ft), and Castro (2011) states that specimens 7 to 8.5 meters (23 to 28 ft) are common.^[8][9] Because Wood's average value fits well within Castro's numbers, I have shown it in the diagram above.

• In more modern literature, many large basking sharks have been reported in the region of 9 to 11 meters (30 to 36 ft) in length.^{[2][8][4][10][11][9]} How many of these have been actually measured is less clear. Evidence suggests that females grow slightly larger than males.^[3] There is also evidence of variation in mean size between different oceans and the northern and southern hemispheres.^[12]

• The largest size the basking shark can reach is uncertain. There are historical reports of basking sharks in the region of 12 to 15 meters (39 to 49 ft) in length, but these lack good evidence.^{[13][8][14][9][3]} An individual reported as 40 feet 3 inches (or 12.27 meters) caught in a herring net in Musquash Harbor in 1851 is often cited as the largest.^[8][12] However, Foulis (1852) and Perley (1852), the probable sources of this claim, simply describe it as '40 feet'.^[15][16] A study looking at the growth and longevity of the basking shark concluded that anything larger than ~10 metres (33 ft) was unlikely.^[17]

• Measuring a shark's total length can be challenging due to the natural angle at which the caudal lobes are positioned relative to the rest of the shark's body. Some reports calculate the total length by adding the caudal fin to the pre-caudal length, or by stretching the caudal fin to the maximum possible (sometimes referred to as stretched total length). These methods ignore the angle at which the tail naturally sits, which artificially increases the total length of the shark being measured. The other method is to try and pose the shark's caudal fin as it would be in life. However, this is difficult in large sharks; any inaccuracy in the angle of the caudal fin can affect the reported total length measurement.^[18] Another issue is it is not always clear whether the reported length was measured over the curves of the body or in a straight line parallel to the ground.^[8][11] This possibility of error in measuring or reporting of total length could affect the sizes shown here.

References