Big Fish Stories
Whale Shark (Rhincodon typus)
At 1:34 AM 16/1/99, Adam P. Summers wrote me as follows:
I am thinking about the limits on size in fishes. In compiling a list of really heavy fish I find that there are very few reliable sources. Quite a few lengths, but few people seem wiling to carry a truck scale around with them. Do you have any references for big sawfishes? What is your best guess for the 4th and 5th heaviest fish in the sea?
We humans have a deep and long-standing fascination with sheer size. Although we may marvel at the intricacy of very small, few things impress us so profoundly as the downright gigantic. In general, length is much easier to measure accurately than weight, as many of our traditional units are based on the dimensions of the human body (foot, pace, hand, yard, etc.). In contrast, most of our measures of weight are based on arbitrary units (probably rooted in commerce, such as the heft of gold or other precious metals).
Big Fish stories are as old as our species' earliest ventures out to sea, but frustratingly difficult for the biologist to verify. Nowhere is this more evident than when trying to verify the rumored weight of a gigantic fish. As I'm sure you realize, weight of a given fish can vary enormously over time with such factors as length, sex, health, maturity state and reproductive condition. The more fierce or bizarre a given large fish is deemed, the more wildly exaggerated estimates of its weight become.
Sawfishes are certainly among the most unusual of fishes. The largest species, in terms of linear dimension, is probably the Green Sawfish (Pristis zijsron) of the Indo-West Pacific, which reportedly grows to a length of 730 cm. No one knows what such a monster sawfish might weigh. Given that a 518-cm specimen (probably of the Smalltooth Sawfish, P. pectinata) caught off Texas weighed 590 kg (McCormack et al. 1963, p 282) and applying the simple-but-useful cube-square law, rough, back-of-the-envelope calculations suggest that a 5-m+ sawfish would weigh about 1 418 kg.
Dubious references to even larger and heavier sawfishes occur. Norman and Fraser 1937 refer to 914-cm-long individuals (p 60) and to a pregnant sawfish estimated to weight more than 2 400 kg (p 63). Mitchell-Hedges 1923 refer to a large male sawfish (possibly P. pectinata) supposedly 884 cm in length, 579 cm in girth, and weighing some 1 955 kg (p 259, upper figure p 260), and to an even larger individual of undisclosed sex supposedly measuring 945 cm in length and weighing a whopping 2 591 kg.
But it is difficult to take stock in such anecdotal records. As you say, few people are willing to haul around a truck scale with them. (And why is it that all the truly gigantic fishes are from so long ago? Is it really that we have fished out the largest individuals, or that verification is so much more readily available nowadays. Few things, it seems, shrink a Big Fish more efficiently than a ruler and a calibrated scale brandished by a qualified scientist!) You might want to contact Madeline Oetinger (according to the most recent AES Membership Directory, she can be contacted at: 1003 Hermitage Dr., Owensboro, KY 42301; E-mail: <103557,firstname.lastname@example.org>), who has done some work on sawfish life history and may know of references to particularly large sawfishes in the primary literature.
As for the 3rd and 4th heaviest fish in the sea, I can only guess. The most likely contenders, it seems to me, are the Tiger Shark (Galeocerdo cuvier), the Manta Ray (Manta birostris), and the Green Sawfish. Reliable weights for the largest of these creatures on record are damnably scarce. The largest Tiger Shark reliably reported in the literature (including Compagno's 1984 FAO Catalogue) are 550 cm long; given that 427-cm specimen weighs about 590 kg, I would estimate that a 5.5-m Tiger Shark would weigh roughly 1,418 kg — about the same as I calculated for a 5-m+ Green Sawfish. Manta Rays are reputed to reach disc widths of up to 670 cm and weights in excess of 1,360 kg.
In short, the contenders for the 3rd and 4th heaviest fish in the sea all max out at roughly 1.4 tonnes. Thus, all I have to go on in making some manner of ranking among them is well-informed, blind guesswork. Never one to shrink from a challenge, I would suggest that a 6.7-m-wide Manta would weigh considerably more than 1.4 tonnes (indeed, weights up to 2.27 tonnes seem reasonable), and — given that roughly 25% of the Green Sawfish's length is taken up by its relatively light-weight saw — and the well-documented variability of the weights of sharks in general, I would speculate that a 5.5-m Tiger Shark would probably seriously outweigh a Green Sawfish of similar length. Thus, I would rank the Manta Ray as the 4th heaviest fish in the sea, and the Tiger Shark as the 5th.
Of course, that's just my opinion.
— R. Aidan Martin
McCormick, H.W., T. Allen, and W.E. Young. 1963. Shadows in the Sea. Weathervane, New York.
Mitchell-Hedges, F.A. 1923. Battles with Giant Fish. Ducksworth, London.
Norman, J.R., and J.C. Fraser. 1937. Giant Fishes, Whales and Dolphins. Putnam, London.