Fishing about and about fishing
OUR GENTLE FISHING PARTNERS
The U.S. National Oceanic and Atmospheric Authority (NOAA) has recently revised its 2006 estimates of dolphin abundance in the eastern tropical Pacific (ETP). NOAA believes that there is a trend of expansion of dolphin populations and that there’re serious indications, which need some more verification, that there were more dolphins than previously estimated, and sees it as a cause for optimism.
Optimism is always a question of the point of view. The dolphin count was about 3 mn heads and growing. Everybody could be happy, wouldn’t it be for the fact that those lovely marine mammals eat fish, and quite a lot of them. In fact, one grown up dolphin can eat on a day as much fish as an average American eats in a year. Those gentle jumpers might be now consuming in the ETP alone 6.5 mn mt, give or take a million.
About a decade ago, Dr. M. de L. Brooke, Curator of Birds at the Department of Zoology, University of Cambridge, published a paper in the “Biology Letters” conservatively estimating the world's seabirds yearly food consumption at
70 mn - an amount approaching the global fisheries landings. If we add to this figure the consumption by marine mammals, this may sum up to 2/3 of what is taken off commercial fish populations. And till the whole issue was properly researched, let’s leave alone those estimates according to which marine mammals are eating 10 times more than the whole world fisheries yield.
I wouldn’t be returning to this issue, if not a recent report from Namibia, which says that seal hunters will be allowed by the Ministry of Fisheries & Marine Resources to kill 6,000 adult males and 80,000 pups, which is the same quota as last year. The seal population estimated at some 850,000 inhabiting offshore southwest Atlantic islands is, as stated by the Namibian Ministry, healthy and not at risk of extinction, while sealing provides revenue from skins, fur, meat, and employment. The seals, says the government, consume 900,000 mt of fish a year - more than a third of Namibia’s fish yield. Nevertheless, according to AP, animal rights activists brace for a showdown with the government over the ”inhumane” practice of sealing, also quoting International Union for Conservation of Nature’s listing seals as endangered.
This brought me back to former estimates of the share of fish taken by those of about 9 mn of various protected marine mammals of which counts were performed. According to Dr. Trites of the University of British Columbia: “consumption of marine organisms, expressed as a percentage of an individual’s body weight per day, ranges from about 4–15% for zooplankton, to 1–4% for cephalopods, 1–2% for fish, 3–5% for marine mammals and 15–20% for sea birds.” My guesstimate is that at least 11 mn mt represent the total consumption by marine mammals around the coasts of the USA alone.
Some super-ardent advocates of protection for all marine mammals have been claiming that “only about 1% of the food eaten by any group of marine mammals was taken in areas home to important fisheries for human consumption”. They can tell it perhaps to the mariners, but not to coastal fishermen. We all know that fishermen, dolphins and pinnipeds are after the same fish in the same areas. That part of the food of marine birds and mammals, which is not made up of commercial fish of all sizes, consists of the latter’s food organisms, be that bonefish or invertebrates.
Even if only a few percent of the prey of the marine mammals is cod, haddock, flounder, and other prime fish, their share in total mortality is most probably, much higher than that of fishing mortality. With their populations continuing to increase, as long as fisheries management is affecting only fishermen, our gentle partners to the fish in the oceans would keep edging into the stocks available to fisheries and reducing the human share of the business.
I hope that my readers won’t mistake me for being indifferent to protecting marine mammals. I fully support the abolishing of the mid-20th century carnage of dolphins by the ETP tuna fleets, because by applying the setting-on-dolphins technique, the California tuna purse-seine fishery reduced their population to 20-30% of original size. But the unsolved question both at that time and nowadays is: does the humanity want to protect populations of these (and other animals), or protect their every single member?
For example, tuna fishermen found a quite efficient way to reduce dolphin by-catch to a small fraction of what it was before, by applying a “back-up” technique and the “Medina-panel”, which could’ve kept the fishery going, while only slightly, if at all, slowing down the dolphin population recovery. But, this hadn’t satisfied the influential “save-the-dolphins” lobby, which pulled off a “zero by-catch” strategy, which apart from saving the dolphins, contributed to the demise of the California tuna fishery.
What I’m asking is not whether or not to cull this or other stock of marine mammals, but when the prevailing fishery-science systems is going to give sufficient consideration to fish mortality caused by marine mammals and birds? How can fish resources be properly managed when main causes of mortality are ignored, and the standard natural mortality factor fed into computer models has little to do with reality? Fisheries management is managing only fishermen, but cannot tell dolphins, seals, sea lions and minke whales what and how much to eat.
So, how about replacing the computer models fed with the standard natural mortality factor of around 20% with something like this:
Total mortality equals:
Natural mortality (of old age, starvation, diseases, etc.) - 10-20%
Predation mortality (by marine mammals, birds and large predatory fish) – 40-60%
Fishing mortality – 20-40%.
These are fuzzy values, and would differ in different cases, but I bet my cap that in many fisheries they’d be far more accurate that those nowadays applied by the official fishery science.